Haimovici's Vascular Surgery

Haimovici’s

Vascular Surgery 5th edition

As I assume chief editorship with this edition of Haimovici’s Vascular Surgery, I would like to take this opportunity to recognize my parents, Samuel and Emilia, for their guidance and support throughout my life. Enrico Ascher

Haimovici’s

Vascular Surgery FIFTH EDITION

Editor-in-Chief Enrico Ascher Associate Editors L. H. Hollier D. Eugene Strandness Jonathan B. Towne Co-editors Keith Calligaro K. Craig Kent Gregory L. Moneta William H. Pearce John J. Ricotta Founding Editor Henry Haimovici

Blackwell Publishing

© 2004 by Blackwell Science a Blackwell Publishing company Blackwell Publishing, Inc., 350 Main Street, Malden, Massachusetts 02148-5018, USA Blackwell Publishing Ltd, 9600 Garsington Road, Oxford OX4 2DQ, UK Blackwell Publishing Asia Pty Ltd, 550 Swanston Street, Carlton, Victoria 3053, Australia All rights reserved. No part of this publication may be reproduced in any form or by any electronic or mechanical means, including information storage and retrieval systems, without permission in writing from the publisher, except by a reviewer who may quote brief passages in a review. 05 06 07 08 5 4 3 2 ISBN-13: 978-0-632-04458-0 ISBN-10: 0-632-04458-6 Library of Congress Cataloging-in-Publication Data Haimovici’s vascular surgery. — 5th ed. / editor-in-chief, Enrico Ascher ; associate editors, L.H. Hollier, D. Eugene Strandness, Jr., Jonathan B. Towne ; co-editors, Keith Calligaro . . . [et al.] ; founding editor, Henry Haimovici. p. ; cm. Includes index. ISBN 0-632-04458-6 (hardcover) 1. Blood-vessels — Surgery. [DNLM: 1. Vascular Surgical Procedures. WG 170 H151 2004] I. Title: Vascular surgery. II. Ascher, Enrico. III. Haimovici, Henry, 1907– RD598.5.V39 2004 617.4’13 — dc21 2003011854 A catalogue record for this title is available from the British Library Acquisitions: Laura DeYoung Development: Julia Casson Production: Julie Elliott and Debra Lally Cover design: Hannus Design Associates Typesetter: SNP Best-set Typesetter Ltd., Hong Kong Printed and bound by Sheridan Books in Ann Arbor, MI For further information on Blackwell Publishing, visit our website: www.blackwellmedicine.com Notice: The indications and dosages of all drugs in this book have been recommended in the medical literature and conform to the practices of the general community. The medications described do not necessarily have specific approval by the Food and Drug Administration for use in the diseases and dosages for which they are recommended. The package insert for each drug should be consulted for use and dosage as approved by the FDA. Because standards for usage change, it is advisable to keep abreast of revised recommendations, particularly those concerning new drugs. The publisher’s policy is to use permanent paper from mills that operate a sustainable forestry policy, and which has been manufactured from pulp processed using acid-free and elementary chlorine-free practices. Furthermore, the publisher ensures that the text paper and cover board used have met acceptable environmental accreditation standards.

CONTENTS

Preface

x

PART II

Acknowledgments

xi

Basic Cardiovascular Problems

Editors

xii

Contributors

xiii

Hemodynamics of Vascular Disease: Applications to Diagnosis and Treatment,

1

Frank J. Veith and Enrico Ascher

CHAPTER 9 Artherosclerosis: Biological and Surgical Considerations, Bauer E. Sumpio

PART I

CHAPTER 10

Imaging Techniques

Intimal Hyperplasia,

Christopher K. Zarins, Chengpei Xu, Hisham S. Bassiouny, and Seymour Glagov

CHAPTER 2 Ultrasonic Duplex Scanning,

117

David S. Sumner

CHAPTER 1 A Tribute to Henry Haimovici,

CHAPTER 8

7

D. Eugene Strandness, Jr

137

164

CHAPTER 11 Therapeutic Angiogenesis,

K. Craig Kent

176

CHAPTER 3 Duplex Arteriography for Lower Extremity Revascularization, Enrico Ascher and

35

Thrombogenesis and Thrombolysis,

CHAPTER 4

CHAPTER 13 50

Rodney A. White

196

CHAPTER 14 61

Harvey L. Neiman and James Lyons

Cardiopulmonary Assessment for Major Vascular Reconstructive Procedures,

206

John D. Bisognano, Thomas W. Wakefield, and James C. Stanley

CHAPTER 6 Computed Tomography in Vascular Disease, Frederick L. Hoff, Kyle Mueller, and

Etiology of Abdominal Aortic Aneurysm, Ahmad F. Bhatti, Tonya P. Jordan, and M. David Tilson

CHAPTER 5 Fundamentals of Angiography,

183

Donald Silver, Leila Mureebe, and Thomas A. Shuster

Anil Hingorani

Intravascular Ultrasound Imaging,

CHAPTER 12

87

William Pearce

PART III CHAPTER 7 Magnetic Resonance Angiography, Jagajan J. Karmacharya, Omaida C. Velazquez, Richard A. Baum, and Jeffrey P. Carpenter

103

Basic Vascular and Endovascular Techniques CHAPTER 15 Vascular Sutures and Anastomoses,

221

Henry Haimovici

v

vi

Contents

CHAPTER 16

CHAPTER 29

Patch Graft Angioplasty,

Henry Haimovici

231

Retroperitoneal Exposure of the Iliac Arteries, Henry Haimovici

237

CHAPTER 30

348

CHAPTER 17 Endarterectomy,

Henry Haimovici

The Lower Extremity,

CHAPTER 18 Balloon Angioplasty of Peripheral Arteries and Veins, Juan Ayerdi, Maurice M. Solis, and

Henry Haimovici

247

Kim J. Hodgson

PART V

CHAPTER 19

Occlusive Arterial Diseases

Stents for Peripheral Arteries and Veins,

257

Carber C. Huang and Samuel S. Ahn

CHAPTER 31

CHAPTER 20

Pathophysiology of Skeletal Muscle Ischemia–Reperfusion Injury, Walter N. Durán,

Thrombolytic Therapy for Peripheral Arterial and Venous Thrombosis,

354

272

373

Peter J. Pappas, Mauricio P. Boric, and Robert W. Hobson, II

W. Todd Bohannon and Michael B. Silver, Jr.

CHAPTER 32

CHAPTER 21 Role of Angioplasty in Vascular Surgery,

285

Arnold Miller and Charles P. Panisyn

Arterial Embolism of the Extremities and Technique of Embolectomy, Henry Haimovici

388

CHAPTER 33 Fluoroscopically Assisted Thromboembolectomy, Evan C. Lipsitz,

PART IV

409

Frank J. Veith, and Takao Ohki

Surgical Exposure of Vessels

CHAPTER 34 CHAPTER 22 Exposure of the Carotid Artery,

301

Percutaneous Aspiration Thromboembolectomy, Rodney A. White

417

Henry Haimovici

CHAPTER 35

CHAPTER 23 The Vertebrobasilar System: Anatomy and Surgical Exposure, Ronald A. Kline and

304

Ramon Berguer

Asher Hirshberg and

421

Kenneth L. Mattox

CHAPTER 36

CHAPTER 24

Fasciotomy,

Extrathoracic Exposure for Distal Revascularization of Brachiocephalic Branches, Henry Haimovici

308

Calvin B. Ernst, Bruce H. Brennaman, and Henry Haimovici

Ankle and Foot Fasciotomy for Compartment Syndrome of the Foot,

Trans-sternal Exposure of the Great Vessels of the Aortic Arch, Calvin B. Ernst

315

CHAPTER 26 Henry Haimovici

322

CHAPTER 27 Transperitoneal Exposure of the Abdominal Aorta and Iliac Arteries, Henry Haimovici

334

447

Enrico Ascher and Elke Lorensen

PART VI Chronic Arterial Occlusions of the Lower Extremities CHAPTER 38

CHAPTER 28 Retroperitoneal Exposure of the Abdominal Aorta, Calvin B. Ernst

437

CHAPTER 37

CHAPTER 25

The Upper Extremity,

Vascular Trauma,

342

Arteriographic Patterns of Atherosclerotic Occlusive Disease of the Lower Extremity, Henry Haimovici

453

Contents

CHAPTER 50

CHAPTER 39 Nonatherosclerotic Diseases of Small Arteries, Henry Haimovici and Yoshio Mishima

vii

475

Postoperative Surveillance,

Jonathan B. Towne

617

CHAPTER 51 CHAPTER 40 Aortoiliac, Aortofemoral, and Iliofemoral Arteriosclerotic Occlusive Diseases,

Extra-anatomic Bypasses, 499

Enrico Ascher and

David C. Brewster

CHAPTER 52

CHAPTER 41

Popliteal Entrapment and Chronic Compartment Syndrome: Unusual Causes for Claudication in Young Adults,

Percutaneous Interventions for AortoIliac Occlusive Disease, Edward B. Diethrich

522

CHAPTER 53 534

559

Benjamin B. Chang, Paul B. Kreienberg, Philip S.K. Paty, Sean P. Roddy, Kathleen J. Ozsvath, and Manish Mehta

Lumbar Sympathectomy: Conventional Technique, Henry Haimovici

651

CHAPTER 55 Laparoscopic Lumbar Sympathectomy,

CHAPTER 44

657

Armando Sardi and Larry H. Hollier 568

Frank J. Veith, Sushil K. Gupta, Evan C. Lipsitz, and Enrico Ascher

PART VII

CHAPTER 45 Bypasses to the Plantar Arteries and Other Branches of Tibial Arteries, Enrico Ascher and

644

CHAPTER 54

CHAPTER 43

Small-artery Bypasses to the Tibial and Peroneal Arteries for Limb Salvage,

Infected Extracavitary Prosthetic Grafts, Sean V. Ryan, Keith D. Calligaro, and Matthew J. Dougherty

and Henry Haimovici

In Situ Vein Bypass by Standard Surgical Technique, Dhiraj M. Shah, R. Clement Darling, III,

637

William Turnipseed

CHAPTER 42 Femoropopliteal Arteriosclerotic Occlusive Disease: Operative Treatment, Frank J. Veith

625

Frank J. Veith

582

William R. Yorkovich

Aortic and Peripheral Aneurysms CHAPTER 56 Thoracic Aortic Aneurysms,

Joseph S. Coselli

663

CHAPTER 46 Extended Techniques for Limb Salvage Using Free Flaps, David L. Feldman and L.

587

CHAPTER 57 Endovascular Repair of Thoracic Aortic Aneurysms and Dissections, Frank R. Arko

Scott Levin

687

and Christopher K. Zarins

CHAPTER 47 Extended Techniques for Limb Salvage Using Complementary Fistulas, Combined with Deep Vein Interposition, Enrico Ascher

592

Thoracoabdominal Aortic Aneurysms,

695

Nicholas J. Morrissey and Larry H. Hollier

CHAPTER 48 Extended Techniques for Limb Salvage Using Vein Cuffs and Patches, Robyn Macsata,

CHAPTER 58

CHAPTER 59 600

Abdominal Aortic Aneurysm,

Alfio Carroccio

703

and Larry H. Hollier

Richard F. Neville, and Anton N. Sidawy

CHAPTER 60

CHAPTER 49 Intraoperative Assessment of Vascular Reconstruction, Jonathan B. Towne

606

Endovascular Repair of Abdominal Aortic Aneurysms, Juan C. Parodi and Luis M. Ferreira

736

viii

Contents

CHAPTER 61 Endovascular Treatment of Ruptured Infrarenal Aortic and Iliac Aneurysms,

CHAPTER 71 744

Nonatherosclerotic Cerebrovascular Disease, Gary R. Seabrook

843

Frank J. Veith and Takao Ohki

CHAPTER 62 Management of Infected Aortic Grafts,

753

G. Patrick Clagett

Visceral Vessels

CHAPTER 63 Isolated Iliac Artery Aneurysms,

PART IX

763

Henry Haimovici

CHAPTER 72 Surgery of Celiac and Mesenteric Arteries,

861

Stephen P. Murray, Tammy K. Ramos, and Ronald J. Stoney

CHAPTER 64 Endovascular Grafts in the Treatment of Isolated Iliac Aneurysms, Frank J. Veith,

767

Mesenteric Ischemia,

Julie A. Freischlag, Michael M. Farooq, and Jonathan B. Towne

Evan C. Lipsitz,Takao Ohki, William D. Suggs, Jacob Cynamon, and Alla M. Rozenblit

875

CHAPTER 74

CHAPTER 65 Para-anastomotic Aortic Aneurysms: General Considerations and Techniques,

CHAPTER 73

775

Renal Artery Revascularization,

887

Keith D. Calligaro and Matthew J. Dougherty

Daniel J. Char and John J. Ricotta

CHAPTER 75 Visceral Artery Aneurysms,

Matthew J.

902

Dougherty and Keith D. Calligaro

PART VIII Cerebrovascular Insufficiency

PART X CHAPTER 66 Carotid Endarterectomy: Indications and Techniques for Carotid Surgery,

787

Upper Extremity Conditions

Anthony M. Imparato

CHAPTER 76

CHAPTER 67

Vasospastic Diseases of the Upper Extremity, Scott E. Musicant, Gregory L. Moneta,

Eversion Carotid Endarterectomy,

810

R. Clement Darling, III, Manish Mehta, Philip S. K. Paty, Kathleen J. Ozsvath, Sean P. Roddy, Paul B. Kreienberg, Benjamin B. Chang, and Dhiraj M. Shah

James M. Edwards, and Gregory J. Landry

CHAPTER 77 Neurogenic Thoracic Outlet Syndrome,

817

CHAPTER 78 Venous Thoracic Outlet Syndrome or Subclavian Vein Obstruction,

Samuel R. Money

940

Richard J. Sanders and Michael A. Cooper

CHAPTER 69 Carotid Stenting: Current Status and Clinical Update, Robert W. Hobson, II

924

Richard J. Sanders and Michael A. Cooper

CHAPTER 68 Complications and Results in Carotid Surgery, Michael S. Conners, III and

915

827

CHAPTER 79 Arterial Thoracic Outlet Syndrome,

949

Frank J. Veith and Henry Haimovici

CHAPTER 70 Vertebrobasilar Disease: Surgical Management, Ronald A. Kline and Ramon Berguer

835

CHAPTER 80 Arterial Surgery of the Upper Extremity, James S.T. Yao

958

Contents

CHAPTER 81

ix

CHAPTER 91

Upper Thoracic Sympathectomy: Conventional Technique, Henry Haimovici

974

Venous Interruption,

Lazar J. Greenfield and

1097

Contemporary Venous Thrombectomy,

1106

Mary C. Proctor

CHAPTER 92

CHAPTER 82 Thoracoscopic Sympathectomy,

981

Anthony J. Comerota

P. Michael McFadden and Larry H. Hollier

CHAPTER 93

PART XI

Endoscopic Subfascial Ligation of Perforating Veins, Manju Kalra and

Arteriovenous Malformation

Peter Gloviczki

1115

CHAPTER 94

CHAPTER 83 Arteriovenous Fistulas and Vascular Malformations, Peter Gloviczki, Audra A. Noel,

991

Venous Reconstruction in Postthrombotic Syndrome, Seshadri Raju

1131

and Larry H. Hollier

CHAPTER 95 CHAPTER 84 Vascular Access for Dialysis,

Harry Schanzer

1015

and Andres Schanzer

1139

Henry Haimovici

CHAPTER 96

CHAPTER 85 Portal Hypertension,

Ischemic Venous Thrombosis: Phlegmasia Cerulea Dolens and Venous Gangrene,

James D. Eason and

1030

John C. Bowen

1152

Thomas F. O’Donnell, Jr.

PART XII Venous and Lymphatic Surgery CHAPTER 86 Clinical Application of Objective Testing in Venous Insufficiency, John J. Bergan and

Diagnosis and Management of Lymphedema, Mark D. Iafrati and

1047

PART XIII Amputations and Rehabilitations CHAPTER 97 Amputation of the Lower Extremity: General Considerations, Henry Haimovici

Warner P. Bundens

1171

CHAPTER 87 Varicose Veins,

Mark D. Iafrati and Thomas F. O’Donnell, Jr.

1058

CHAPTER 98 Above-the-knee Amputations,

1175

Henry Haimovici

CHAPTER 88 Superficial Thrombophlebitis,

1073

Anil Hingorani and Enrico Ascher

Postoperative and Preprosthetic Management for Lower Extremity Amputations, Yeongchi Wu

CHAPTER 89 Acute Deep Vein Thrombosis,

CHAPTER 99

1078

Anthony J. Comerota

CHAPTER 100 Prosthetics for Lower Limb Amputees,

CHAPTER 90 Acute Upper Extremity Deep Vein Thrombosis, Anil Hingorani and Enrico Ascher

1183

Jan J. Stokosa 1091

Index

1207

1190

PREFACE

It has been nearly three decades since the late Dr Henry Haimovici (1907–2001) first presented to us his landmark publication Vascular Surgery: Principles and Techniques. Even then he observed that, in this historically brief period of time, we had already experienced momentous developments in the magnitude and scope of our specialty. I believe that, unlike any other period of time and unlike any other surgical specialty, we have also maintained the ability to focus and redirect our craft in tandem with, if not in advance of, the changing needs of our patients and the technological advancements available to us. As a great pioneer of vascular surgery, Dr Haimovici was a principal instrument of our success throughout the infancy and maturation of vascular surgery. He was ever committed to its future beyond measure. Henry was also my mentor and a great friend. I am forever indebted to him for the privilege of assuming editorship of this grand textbook. We are also saddened by the loss of yet another great leader in vascular surgery: D. Eugene Strandness, Jr., MD (1928–2002). Dr Strandness fielded numerous contributions throughout the formative years of noninvasive vascular testing and ultimately established what has now become our most effective asset in the diagnosis of vascular disease — the vascular laboratory. His early work focused on physiologic tests, but he was also responsible for the development and application of direct ultrasonic methods for vascular diagnosis. Working with engineers at the University of Washington, he combined a B-mode imaging system and a Doppler flow detector to create the

x

first duplex scanner. These explorers of science were prolific in their contributions to our specialty through their research, publications, and societal leaderships. It is in their footsteps that the current and successive generations of vascular leaders must walk — and they have left great shoes for them to fill. We are proud to have returning Section Editors Larry Hollier (Aortic and Peripheral Aneurysms), Eugene Strandness (Imaging Techniques), and Jonathan B. Towne (Acute Arterial Occlusions of the Lower Extremities). We are also fortunate to have joining us K. Craig Kent (Basic Cardiovascular Problems), John J. Ricotta (Cerebrovascular Insufficiency), Keith D. Calligaro (Visceral Vessels), Gregory L. Moneta (Specific Upper Extremity Occlusions), and William H. Pearce (Venous and Lymphatic Surgery) as Section Editors. This 5th edition of Haimovici’s Vascular Surgery remains true to its heritage of the comprehensive inspection of the practice of vascular surgery. Innovations in operative technique and reflections on noninvasive diagnostic imaging have been examined and each topic has been updated and expanded. This textbook has now included the most current topics regarding endovascular therapy. Extensive changes have been made to this edition — fully 75 chapters have been revised and 25 new chapters have been added. Enrico Ascher, MD New York, New York 2003

ACKNOWLEDGMENTS

It would be impossible for me to express my gratitude to all those who have labored to see this important endeavor come to fruition. There are so many worthy contributors to this edition, including both the prominent leaders of today and the rising stars of tomorrow, that the author’s index reads like the “Who’s Who?” of vascular surgery. Their roles are of great import not only now, but will extend well into the millennium. Within my own practice, I am grateful to my partner and friend, Dr Anil Hingorani, for permitting me the necessary “protected time” away from the operating room and from the clinic when I needed to focus on this project. I also especially wish to recognize my assistant, Ms Anne Ober, for her perseverance, loyalty, and dedication. Her

coordination of activities and gentle massaging of the many personalities involved, when necessary, are unparalleled and much appreciated. Lastly, I must thank Blackwell Publishing for their continued support of this title. Many have contributed their talents, but particular recognitions are due to Julia Casson, Development Editor, and Kate Heinle, Editorial Coordinator. Their professional expertise and roles in the evolution of this complex undertaking are amply evident in the cohesive production that has evolved. Enrico Ascher, MD New York, New York 2003

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EDITORS

ENRICO ASCHER, MD Professor of Surgery Mount Sinai School of Medicine New York, New York Chief, Vascular Surgery Services Maimonides Medical Center Brooklyn, New York L. H. HOLLIER, MD, FACS, FACC, FRCS (ENG) Julius Jacobson Professor of Vascular Surgery Mount Sinai School of Medicine President The Mount Sinai Hospital New York, New York D. EUGENE STRANDNESS, JR., MD, DMED Former Professor of Surgery University of Washington Former Attending Surgeon University of Washington Medical Center Seattle, Washington JONATHAN B. TOWNE, MD Professor of Surgery Chairman of Vascular Surgery Medical College of Wisconsin Milwaukee, Wisconsin KEITH CALLIGARO, MD Associate Clinical Professor University of Pennsylvania School of Medicine Chief, Section of Vascular Surgery Pennsylvania Hospital Philadelphia, Pennsylvania K. CRAIG KENT, MD Chief Columbia Weill Cornell Division of Vascular Surgery Columbia College of Physicians and Surgeons Weill Medical College of Cornell University New York, New York

GREGORY L. MONETA, MD Professor of Surgery Head, Division of Vascular Surgery Oregon Health and Science University Portland, Oregon WILLIAM H. PEARCE, MD Violet R. and Charles A. Baldwin Professor of Vascular Surgery Chief, Division of Vascular Surgery Northwestern University Feinberg School of Medicine Chicago, Illinois JOHN J. RICOTTA, MD, FACS Professor and Chair Department of Surgery State University of New York at Stony Brook Chief of Surgery Stony Brook University Hospital Stony Brook, New York HENRY HAIMOVICI, MD Former Foreign Corresponding Member French National Academy of Medicine Paris, France Former Clinical Professor Emeritus of Surgery Albert Einstein College of Medicine at Yeshiva University Former Senior Consultant and Chief Emeritus of Vascular Surgery Montefiore Medical Center New York, New York

CONTRIBUTORS

SAMUEL S. AHN, MD, FACS Clinical Professor of Surgery UCLA School of Medicine Attending Surgeon UCLA Center for the Health Sciences Division of Vascular Surgery Los Angeles, California FRANK R. ARKO, MD Director, Endovascular Surgery Assistant Professor of Surgery Division of Vascular Surgery Stanford ENRICO ASCHER, MD Professor of Surgery Mount Sinai School of Medicine New York, New York Chief, Vascular Surgery Services Maimonides Medical Center Brooklyn, New York

W. TODD BOHANNON, MD Assistant Professor of Surgery and Radiology Texas Technical University Health Sciences Center University Medical Center Lubbock, Texas MAURICIO P. BORIC, PhD Departomento de Ciencias Fisiológicas P. Universidad Católica de Chile Santiago, Chile JOHN C. BOWEN, MD Chairman Emeritus, Department of Surgery Ochsner Clinic Foundation New Orleans, Louisiana BRUCE H. BRENNAMAN, MD Director, Noninvasive Vascular Laboratory The Medical Center Surgical Associates of Columbus Columbus, Georgia

JUAN AYERDI, MD Division of Peripheral Vascular Surgery Southern Illinois University School of Medicine Springfield, Illinois

DAVID C. BREWSTER, MD Clinical Professor of Surgery Harvard Medical School Surgeon Massachusetts General Hospital Boston, Massachusetts

HISHAN S. BASSIOUNY, MD Associate Professor of Surgery Medical Director of Noninvasive Laboratories Department of Vascular Surgery University of Chicago Chicago, Illinois

WARNER P. BUNDENS, MD Assistant Clinical Professor of Surgery University of California, San Diego San Diego, California

RICHARD A. BAUM, MD Department of Surgery University of Pennsylvania School of Medicine Philadelphia, Pennsylvania

KEITH D. CALLIGARO, MD, FACS Associate Clinical Professor University of Pennsylvania School of Medicine Chief, Section of Vascular Surgery Pennsylvania Hospital Philadelphia, Pennsylvania

JOHN J. BERGAN, MD, FACS Professor of Surgery University of California, San Diego Professor of Surgery Uniformed Services of the Health Sciences Bethesda, Maryland

JEFFREY P. CARPENTER, MD Associate Professor of Surgery Department of Surgery University of Pennsylvania School of Medicine Philadelphia, Pennsylvania

RAMON BERGUER, MD, PhD Professor and Chief Division of Vascular Surgery Wayne State University/Detroit Medical Center Detroit, Michigan AHMAD F. BHATTI, MD Columbia University and St. Luke’s/ Roosevelt Hospital Center New York, New York JOHN D. BISOGNANO, MD, PhD, FACP, FACC Assistant Professor of Medicine University of Rochester Attending Cardiologist Strong Memorial Hospital Rochester, New York

ALFIO CARROCCIO, MD Resident in Vascular Surgery Division of Vascular Surgery Mount Sinai Medical Center New York, New York BENJAMIN B. CHANG, MD Assistant Professor of Surgery Albany Medical College Attending Vascular Surgeon Albany Medical Center Hospital Assistant Professor of Surgery Albany, New York DANIEL J. CHAR, MD Assistant Clinical Instructor of Surgery Division of Vascular Surgery Stony Brook University Hospital Stony Brook, New York

xiii

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Contributors

G. PATRICK CLAGETT, MD Jan and Bob Pickens Distinguished Professorship in Medical Science Professor and Chairman, Division of Vascular Surgery University of Texas Southwestern Medical Center Dallas, Texas ANTHONY J. COMEROTA, MD Professor of Surgery Temple University School of Medicine Chief, Vascular Surgery Temple University Hospital Philadelphia, Pennsylvania MICHAEL S. CONNERS, III, MD Vascular Surgery Fellow Alton Ochsner Clinic Foundation New Orleans, Louisiana MICHAEL A. COOPER Attending Surgeon Rose Medical Center Denver, Colorado JOSEPH S. COSELLI, MD Professor of Surgery Chief, Division of Cardiothoracic Surgery Baylor College of Medicine Houston, Texas JACOB CYNAMON, MD Maimonides Medical Center Brooklyn, New York R. CLEMENT DARLING, III, MD Professor of Surgery Albany Medical College Chief, Division of Vascular Surgery Albany Medical Center Albany, New York EDWARD B. DIETHRICH, MD Medical Director and Chief of Cardiovascular Surgery Arizona Heart Institute Arizona Heart Hospital Director and Chairman Department of Cardiovascular Services Healthwest Regional Medical Center Phoenix, Arizona MATTHEW J. DOUGHERTY, MD, FACS Assistant Clinical Professor University of Pennsylvania Section of Vascular Surgery Pennsylvania Hospital Philadelphia, Pennsylvania WALTER N. DURÁN, PhD Professor of Physiology and Surgery Chief, Division of Microcirculatory Research Department of Physiology University of Medicine and Dentistry of New Jersey New Jersey Medical School Newark, New Jersey JAMES D. EASON, MD, FACS Head, Section of Abdominal Transplantation Ochsner Clinic Foundation New Orleans, Louisiana JAMES M. EDWARDS, MD Associate Professor of Surgery, Division of Vascular Surgery Oregon Health Sciences University

Chief of Surgery, Portland Veterans Affairs Medical Center Portland, Oregon CALVIN B. ERNST, MD Clinical Professor of Surgery University of Michigan Medical School Head, Division of Vascular Surgery Henry Ford Hospital Detroit, Michigan MICHAEL M. FAROOQ, MD Assistant Professor of Surgery University of California, Los Angeles DAVID L. FELDMAN, MD, FACS Assistant Professor of Surgery SUNY Health Science Center at Brooklyn Director, Division of Plastic Surgery Maimonides Medical Center Brooklyn, New York LUIS M. FERREIRA, MD Staff, Vascular Surgery Department Instituto Cardiovascular de Buenos Aires Buenos Aires, Argentina JULIE A. FREISCHLAG, MD Medical College of Wisconsin Milwaukee, Wisconsin SEYMOUR GLAGOV, MD Department of Pathology University of Chicago School of Medicine Chicago, Illinois PETER GLOVICZKI, MD Professor of Surgery Mayo Medical School Chair, Division of Vascular Surgery Director, Gonda Vascular Center Mayo Clinic and Foundation Rochester, Minnesota LAZAR J. GREENFIELD, MD Frederick A. Collier Professor and Chairman of Surgery University of Michigan Medical School Department of Surgery University of Michigan Medical Center Ann Arbor, Michigan SUSHIL K. GUPTA, MD Section Chief Guthrie Clinic Sayre, Pennsylvania HENRY HAIMOVICI, MD Former Foreign Corresponding Member French National Academy of Medicine Paris, France Former Clinical Professor Emeritus of Surgery Albert Einstein College of Medicine at Yeshiva University Former Senior Consultant and Chief Emeritus of Vascular Surgery Montefiore Medical Center New York, New York ASHER HIRSHBERG, MD Associate Professor of Surgery Michael E. DeBakey Department of Surgery Baylor College of Medicine Director of Vascular Surgery Medical Director, Non-invasive Vascular Laboratory Ben Taub General Hospital Houston, Texas

Contributors ANIL HINGORANI, MD Clinical Assistant Professor State University of NY — Brooklyn Attending Surgeon Maimonides Medical Center Brooklyn, New York ROBERT W. HOBSON, II, MD Professor of Surgery and of Physiology Division of Vascular Surgery Department of Surgery University of Medicine and Dentistry of New Jerse New Jersey Medical School Newark, New Jersey FREDERICK L. HOFF, MD Assistant Professor of Radiology Department of Radiology Northwestern University Medical School Chicago, Illinois KIM J. HODGSON, MD Division of Peripheral Vascular Surgery Southern Illinois University School of Medicine Springfield, Illinois L. H. HOLLIER, MD, FACS, FACC, FRCS (Eng) Julius Jacobson Professor of Vascular Surgery Mount Sinai School of Medicine President The Mount Sinai Hospital New York, New York CARBER C. HUANG, MD Endovascular Fellow, Division of Vascular Surgery UCLA School of Medicine Los Angeles, California MARK D. IAFRATI, MD, RVT, FACS Department of Surgery Division of Vascular Surgery New England Medical Center Boston, Massachusetts ANTHONY M. IMPARATO, MD Professor of Surgery New York University School of Medicine New York, New York TONYA P. JORDAN, MD Columbia University and St. Luke’s/Roosevelt Hospital Center New York, New York MANJU KALRA, MBBS FRCSEd Department of Surgery Mayo Clinic Rochester, Minnesota J.J. KARMACHARYA, MD Department of Surgery University of Pennsylvania School of Medicine Philadelphia, Pennsylvania K. CRAIG KENT, MD Professor of Surgery Columbia Weill Cornell Division of Vascular Surgery Columbia College of Physicians and Surgeons Weill Medical College of Cornell University New York, New York SASHI KILARU, MD Vascular Surgery Fellow Weill Cornell Medical College

New York Presbyterian Hospital — Cornell New York, New York PAUL B. KREIENBERG, MD Associate Professor of Surgery Albany Medical College Attending Vascular Surgeon Albany Medical Center Hospital Albany, New York RONALD A. KLINE, MD, FACS Associate Professor of Surgery Wayne State University School of Medicine Program Director, Vascular Surgery Harper University Hospital Detroit, Michigan GREGORY J. LANDRY, MD Assistant Professor of Surgery, Division of Vascular Surgery Oregon Health Sciences University Portland, Oregon L. SCOTT LEVIN, MD Chief, Division of Plastic, Maxillofacial, and Reconstructive Surgery Duke University Medical Center Durham, North Carolina EVAN C. LIPSITZ, MD Assistant Professor, Division of Vascular Surgery Albert Einstein College of Medicine Attending Vascular Surgeon Montefiore Medical Center Bronx, New York ELKE LORENSEN, MD Vascular Fellow Maimonides Medical Center Brooklyn, New York JAMES B. LYONS, MD Interventional Radiologist Desert Samaritan Medical Center Mesa, Arizona P. MICHAEL MCFADDEN, MD Clinical Professor of Surgery Tulane University School of Medicine Surgeon and Surgical Co-Director Lung Transplantation Program Ochsner Clinic New Orleans, Louisiana ROBYN MACSATA, MD Resident, Vascular Surgery Washington Hospital Center Georgetown University Washington, DC KENNETH L. MATTOX, MD Professor and Vice Chair Michael E. DeBakey Department of Surgery Baylor College of Medicine Chief of Staff/Chief of Surgery Ben Taub General Hospital Houston, Texas MANISH MEHTA, MD Assistant Professor of Surgery Albany Medical College Attending Vascular Surgeon Albany Medical Center Hospital Albany, New York

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Contributors

ARNOLD MILLER, MD Associate Clinical Professor of Surgery Harvard Medical School Boston, Massachusetts Chief Department of Surgery Leonard Morse Hospital MetroWest Medical Center Natick, Massachusetts YOSHIO MISHIMA, MD Professor and Chairman of Surgery Tokyo Medical and Dental University Tokyo, Japan GREGORY L. MONETA, MD Professor of Surgery Chief, Division of Vascular Surgery Oregon Health Sciences University Portland, Oregon SAMUEL R. MONEY, MD, FACS, MBA Clinical Associate Professor Tulane School of Medicine Head, Section of Vascular Surgery Ochsner Clinic Foundation New Orleans, Louisiana NICHOLAS J. MORRISSEY, MD Assistant Professor of Surgery Division of Vascular Surgery Mt. Sinai School of Medicine New York, New York KYLE MUELLER, MD Resident, General Surgery Northwestern University Medical School Chicago, Illinois LEILA MUREEBE, MD Assistant Professor, Department of Surgery University of Missouri — Columbia Staff Surgeon, Department of Surgery University of Missouri Health Care Columbia, Missouri STEPHEN P. MURRAY, MD Inland Vascular Institute Spokane, Washington Assistant Clinical Professsor, Surgery Uniformed Services University of the Health Sciences Bethesda, Maryland SCOTT E. MUSICANT, MD Resident in Surgery Oregon Health Sciences University Portland, Oregon HARVEY L. NEIMAN, MD Executive Director, American College of Radiology Reston, Virginia Professor of Radiology Temple University School of Medicine Philadelphia, Pennsylvania RICHARD F. NEVILLE, MD Associate Professor of Surgery Georgetown University Chief Vascular Surgery Georgetown University Medical Center Washington, DC

AUDRA A. NOEL, MD Assistant Professor of surgery Mayo Medical School Consultant Division of Vascular Surgery Mayo Clinic Rochester, Minnesota THOMAS F. O’DONNELL, Jr., MD Andrews Professor and Chairman of Surgery Tufts University School of Medicine Surgeon-in-Chief Chief of Vascular Surgery New England Medical Center Boston, Massachusetts TAKAO OHKI, MD Associate Professor of Surgery Albert Einstein College of Medicine Chief, Vascular and Endovascular Surgery Montefiore Medical Center Bronx, New York KATHLEEN J. OZSVATH, MD Assistant Professor of Surgery Albany Medical College Attending Vascular Surgeon Albany Medical Center Hospital Albany, New York CHARLES P. PANISYN, MD Assistant Clinical Professor of Surgery Tufts Medical School Boston, Massachusetts PETER J. PAPPAS, MD Division of Vascular Surgery Department of Surgery University of Medicine and Dentistry of New Jerse New Jersey Medical School Newark, New Jersey PHILIP S. K. PATY, MD Associate Professor of Surgery Albany Medical College Attending Vascular Surgeon Albany Medical Center Hospital Albany, New York JUAN C. PARODI, MD Vice Director of the Post-Graduate Training Program in Cardiovascular Surgery of the University of Buenos Aires Chief, Vascular Surgery Department Instituto Cardiovascular de Buenos Aires Director, Instituto Cardiovascular de Buenos Aires Buenos Aires, Argentina WILLIAM PEARCE, MD Violet R. and Charles A. Baldwin Professor of Vascular Surgery Department of Surgery Northwestern University Medical School Chicago, Illinois SANJEEV PRADHAN, MD Resident, Department of Surgery Yale University School of Medicine New Haven, Connecticut MARY C. PROCTOR, MS Department of Surgery University of Michigan Medical School Ann Arbor, Michigan

Contributors TAMMY K. RAMOS, MD Creighton University Medical Center Department of Surgery Omaha, Nebraska SESHADRI RAJU, MD, FACS Emeritus Professor of Surgery and Honorary Surgeon University of Mississippi Medical School Jackson, Mississippi JOHN J. RICOTTA, MD Professor and Chairman of Surgery Department of Surgery Stony Brook University Hospital Stony Brook, New York SEAN P. RODDY, MD Assistant Professor of Surgery Albany Medical College Attending Vascular Surgeon Albany Medical Center Hospital Albany, New York ALLA M. ROZENBLIT, MD Maimonides Medical Center Brooklyn, New York SEAN V. RYAN, MD Surgical Resident Pennsylvania Hospital Philadelphia, Pennsylvania RICHARD J. SANDERS, MD Clinical Professor of Surgery University of Colorado School of Medicine Rose Medical Center Denver, Colorado ARMANDO SARDI, MD, FACS Chief Surgical Oncology Medical Director, Clinical Research Center St. Agnes HealthCare Baltimore, Maryland ANDRES SCHANZER, MD Surgical Resident, Department of Surgery University of California at Davis UCD Medical Center Sacramento, California HARRY SCHANZER, MD, FACS Clinical Professor of Surgery Mount Sinai School of Medicine Attending Surgeon Mount Sinai Hospital New York, New York GARY R. SEABROOK, MD Professor of Vascular Surgery Medical College of Wisconsin Milwaukee, Wisconsin DHIRAJ M. SHAH, MD Director, The Vascular Institute Professor of Surgery Associate Professor of Physiology and Cellular Biology Albany Medical College Albany, New York THOMAS A. SHUSTER, DO Vascular Surgery Fellow, Department of Surgery University of Missouri — Columbia Vascular Fellow, Department of Surgery

xvii

University of Missouri Health Care Columbia, Missouri ANTON N. SIDAWY, MD, MPH Professor of Surgery George Washington University Georgetown University Chief, Surgery Service VA Medical Center Washington, DC MICHAEL B. SILVA, Jr., MD Vice-Chairman, Department of Surgery Professor & Chief, Vascular Surgery and Vascular Interventional Radiology Texas Tech University Health Sciences Center Attending Surgeon University Medical Center Lubbock, Texas DONALD SILVER, MD Professor Emeritus, Department of Surgery University of Missouri — Columbia Medical Director, Surgical Services University of Missouri Health Care Columbia, Missouri MAURICE M. SOLIS, MD Chief, Vascular and Endovascular Surgery Macon Cardiovascular Institute and Mercer University School of Medicine Macon, Georgia WILLIAM D. SUGGS, MD Maimonides Medical Center Brooklyn, New York JAN J. STOKOSA, CP Stokosa Prosthetic Clinic East Lansing, Michigan RONALD J. STONEY, MD Professor of Surgery University of California, San Francisco, School of Medicine San Francisco, California D. EUGENE STRANDNESS, Jr., MD, DMed Former Professor of Surgery University of Washington Former Attending Surgeon University of Washington Medical Center Seattle, Washington DAVID S. SUMNER, MD Distinguished Professor of Surgery, Emeritus Chief, Section of Peripheral Vascular Surgery Southern Illinois University School of Medicine Springfield, Illinois BAUER E. SUMPIO, MD, PhD Professor and Vice Chairman of Surgery Chief, Vascular Surgery Yale University School of Medicine Chief, Vascular Service Yale — New Haven Hospital New Haven, Connecticut JAMES C. STANLEY, MD, FACS Professor of Surgery University of Michigan Head, Section of Vascular Surgery University of Michigan Hospital Ann Arbor, Michigan

xviii

Contributors

M. DAVID TILSON, MD Ailsa Mellon Bruce Professor of Surgery (Columbia University) Director Emeritus Department of Surgery St. Luke's/Roosevelt Hospital New York, New York JONATHAN B. TOWNE, MD Chief of Vascular Surgery Froedtert Memorial Lutheran Hospital Professor of Surgery Medical College of Wisconsin Milwaukee, Wisconsin WILLIAM TURNIPSEED, MD Professor of Surgery Section of Vascular Surgery University Hospital Madison, Wisconsin FRANK J VEITH, MD, FACS Professor of Surgery Albert Einstein College of Medicine The William J. von Liebig Chair in Vascular Surgery Montefiore Medical Center New York, New York OMAIDA C. VELAZQUEZ, MD Department of Surgery University of Pennsylvania School of Medicine Philadelphia, Pennsylvania THOMAS W. WAKEFIELD, MD S. Martin Lindenauer Professor of Surgery Section of Vascular Surgery University of Michigan Medical Center Staff Surgeon University of Michigan Hospital and Ann Arbor Veterans Administration Medical Center Ann Arbor, Michigan

RODNEY A. WHITE, MD Associate Chair Department of Surgery Harbor — UCLA Research and Education Institute Chief, Vascular Surgery Division of Vascular Surgery Harbor — UCLA Medical Center Torrance, California YEONGCHI WU, MD Associate Professor of Physical Medicine and Rehabilitation Northwestern University Medical School Director, Amputee Rehabilitation Rehabilitation Institute of Chicago Center for International Rehabilitation Chicago, Illinois CHENGPEI XU, MD Stanford University School of Medicine Division of Vascular Surgery Stanford, California JAMES S.T. YAO, MD, PhD Magerstadt Professor of Surgery Northwestern University Medical School Attending Surgeon Northwestern Memorial Hospital Chicago, Illinois WILLIAM R. YORKOVICH, RPA Physician Assistant Division of Vascular Surgery Maimonides Medical Center Brooklyn, New York CHRISTOPHER K. ZARINS, MD Chidester Professor of Surgery Stanford University School of Medicine Chief, Division of Vascular Surgery Stanford University Medical Center Stanford, California

Haimovici’s Vascular Surgery, 5th Edition Edited by Enrico Ascher Copyright © 2004 by Blackwell Science

CHAPTER 1 A tribute to Henry Haimovici: September 7, 1907, to July 10, 2001 Frank J. Veith and Enrico Ascher

On July 10, 2001, vascular surgery lost one of its founding fathers, Henry Haimovici, whose interesting life was dramatically altered by the upheavals associated with World War II, and who brought scholarly excellence to our specialty. Henry Haimovici was born on the banks of the Danube in Romania on September 7, 1907. After early schooling in Tulcea, Romania, not far from the Black Sea, young Henry, at the age of 20, went to Marseille, France, for his medical education and residency training—first in all specialties and then in general surgery. He was a distinguished student and scholar from the beginning. He developed an early interest in vascular surgery, and the title for his thesis for his medical degree, only awarded upon completion of his training, was “Arterial Emboli to the Limbs.” His thesis was of such high quality that Henry’s chief at the time, Professor Jean Fiolle, suggested that it be published as a monograph. It was, with a preface by another pioneer in vascular surgery, René Leriche, who had become one of Henry’s earliest admirers and supporters. This book was of sufficient quality that it attracted the attention of another vascular surgery pioneer, Geza de Takats, who recommended that it be translated into English so that “this splendid piece of work be available to everyone.” While still in training, Haimovici developed an interest in venous gangrene. He published one of the first case reports on this condition and subsequently a classic monograph on what he termed “ischemic venous thrombosis”, a condition also known under the more popular name, phlegmasia cerula dolens.

Immediately after his residency training, Dr Haimovici was selected by the dean of his medical school to direct a new institute of neurology and neurosurgery which was planned as a joint project by the Rockefeller Foundation. To qualify for this new chief’s position, Dr Haimovici was sent to the United States to study neurophysiology under Dr Walter B. Cannon of Harvard University, regarded as the most prestigious physiologist in America. During his year’s fellowship with Dr Cannon, Henry published key papers on the effects of motor and sympathetic denervation and regeneration. He always considered Dr Cannon to be his most exceptional mentor and his time with him to be his most productive. While in the US, Dr Haimovici also met with all the neurosurgical leaders in North America and had planned further training in neurosurgery before returning to his prestigious appointment in Marseille. However, World War II had broken out, and all of Dr Haimovici’s plans were disrupted. He was drafted into the French Army, but after France surrendered he decided to accept Dr Cannon’s invitation and return to the US. However, his escape from occupied France involved many adventures and lasted two years, by which time Dr Cannon had retired. So Dr Haimovici returned in 1942 to Boston and the Beth Israel Hospital, where he worked with outstanding scientists such as Rene Dubos and Jacob Fine on infections, toxic shock, and the effect of gelatin in preventing thrombosis of injured veins. After two highly productive years in Boston, Dr Haimovici moved to New York, where he married a young PhD biochemist, Nelicia Maier. He and his new

1

2

Introduction

wife combined their interests in studying the metabolism of atherosclerotic arteries, a field to which he would continue to contribute for the rest of his career. In New York City, Dr Haimovici held an appointment in vascular surgery at Mount Sinai Hospital before being

FIGURE 1.1 Henry Haimovici.

appointed chief of vascular surgery at Montefiore Medical Center in 1945. While at these two institutions, he continued to write important articles relating the physiology of the autonomic nervous system, its mediators and its blocking agents, to vascular conditions such as Buerger’s disease and atherosclerosis. His work was published in the leading medical and physiology journals of the time. Dr Haimovici’s scholarly activity extended well beyond his high-quality original investigations. In addition to writing over 200 journal articles and book chapters, Dr Haimovici authored or edited more than 10 books. His monograph on metabolic complications of acute arterial occlusion and related conditions, published in 1988, is now considered a classic. In addition, Haimovici’s Vascular Surgery: Principles and Techniques, first published in 1976, is regarded as one of the finest texts in the vascular surgery field and was also published in a Spanish edition. The first four editions of this important text were edited by Dr Haimovici himself. Despite all these accomplishments, Henry Haimovici’s crowning achievement was his role in founding the International Society of Cardiovascular Surgery (ISCVS). In March 1950, Dr Haimovici, who was editor of the journal Angiology, took the initiative of organizing the International Society of Angiology. He discussed his plans with René Leriche, who became the organization’s first president. A number of the most prominent vascular surgeons from around the world signed on as charter members. Dr Haimovici became the organization’s first secretary-general and drafted its original bylaws, which created regional chapters for this worldwide vascular society. In 1952, the first meeting of the North American chapter of the ISCVS (now the American Association for

FIGURE 1.2 Haimovici at the Harvard Medical School Department of Physiology, 1939 (second row, fifth from left).

Chapter 1 A Tribute to Henry Haimovici

FIGURE 1.3 Haimovici (center) in the French Army, 1940.

3

Vascular Surgery) was held in Chicago. Emile Holman was elected the first president and Henry Haimovici the first secretary-treasurer of the chapter. Meanwhile, he held the post of secretary-general in the international organization from 1950 to 1963. In this position, Dr Haimovici was a major force in organizing the Society’s first four biannual international congresses, in changing the name of the Society in 1957 to the International Society of Cardiovascular Surgery, and in establishing its journal, the Journal of Cardiovascular Surgery. He served as the founding co-editor of this publication from 1960 to 1973 and was a consulting editor until his death. Henry Haimovici was honored with the presidency of the North American chapter of the ISCVS in 1959 and 1960. He served as a visiting professor around the world and was awarded nine honorary degrees. In 1986 he was elected a corresponding member of the French National Academy of Medicine, a truly unique honor for an American surgeon. In his 93 years, Henry Haimovici made his scholarly mark on surgery around the globe. He helped to establish vascular surgery as a true specialty, and he contributed greatly to its scientific underpinnings. He was a leading vascular surgeon in at least two countries and was widely known and well respected everywhere. He was a true surgeon-scholar with an encyclopedic knowledge of the vascular literature. He was a talented editor and writer, and he had organizational skills possessed by few vascular surgeons. Henry Haimovici was a colleague and a friend who will be sorely missed, even though his mark will long remain on vascular surgery.

FIGURE 1.4 Haimovici (second from right) at the French National Academy of Medicine, 1986.

PART I

Haimovici’s Vascular Surgery, 5th Edition Edited by Enrico Ascher Copyright © 2004 by Blackwell Science

Imaging Techniques

Haimovici’s Vascular Surgery, 5th Edition Edited by Enrico Ascher Copyright © 2004 by Blackwell Science

CHAPTER 2 Ultrasonic Duplex Scanning D. Eugene Strandness, Jr

The past decade has seen a dramatic increase in the ability to assess vascular disease wherever it occurs. This has been in large part due to the development of ultrasonic duplex scanning (1,2). This modality, which combines imaging with pulsed Doppler ultrasound, permits access to all major vascular beds, providing information that is relevant to how patients are managed. For some conditions, such as deep venous thrombosis, this method has essentially replaced venography as a diagnostic tool. This method is also beginning to replace arteriography for many areas such as the carotid and peripheral circulation (see Chapter 3). This represents a major advance that, with time, will expand into other areas as well. This chapter addresses the major areas in which ultrasonic duplex scanning can be applied not only for diagnosis, but also for follow-up. The modern duplex scanner combines two basic modalities that can be used in concert to provide the necessary diagnostic information (3). The essential elements of the device are as follows.

Imaging Ultrasound is reflected from tissue interfaces, making it possible to localize and characterize structures of differing acoustic impedance. The transducer consists of piezoelectric crystals that convert an electrical voltage into an ultrasonic vibration. The sound that is reflected back from tissue is again translated into an electrical voltage that is detected by the receiver in the instrument. Those from the more superficial structures return sooner, those from deeper tissues return later. The exact time of return is

determined not only by the distance from the energy source but also by the speed of sound in tissue, which tends to vary somewhat depending on the tissue being interrogated. In medical ultrasound, 154,000 cm/s is used as the average speed of sound in soft tissue. The brightness of the return echo is determined by the strength or amplitude of the sound reflected from the tissues being interrogated. The most common problem that occurs with imaging is refractive distortion (4). The pulsed imaging process assumes that the ultrasound sent into tissue returns along the same line in which the transducer is pointed. However, because of differences in sound speed in tissue, the sound may bend and cause structures to appear in the wrong location, particularly when viewed in the lateral region of the image. If the ultrasound beam is perpendicular to the object, this type of distortion does not occur. It is important to understand this when one examines any images generated by ultrasound. The best resolution will always be seen in those tissues that are perpendicular to the sound beam. For example, as noted in Figure 2.1, the clearest images are seen in the mid-portion rather than the lateral areas of the field scan. The scan format must be understood to appreciate the images that are generated (4). Two of the various possible approaches are shown in Figure 2.2. With the raster scan format, all transmission lines of the beam are parallel, whereas with the sector scan format, all lines emanate from a point source. The scan lines in the raster format are generally generated by a linear array transducer. The potential advantages of the raster format are shown in Figure 2.3. If the blood vessel being imaged is parallel to the skin

7

8

Part I Imaging Techniques

FIGURE 2.3 With the raster scan format and the artery parallel to the skin surface, the double line on the posterior wall of the artery, which represents the combined thickness of the intima and media, can be visualized throughout the length of the scan. FIGURE 2.1 In this ultrasound image of a common carotid artery, the best resolution is in the midportion of the scan. At this point, the tissues of the arterial wall are perpendicular to the sound beam.

(Reproduced by permission from Beach KW, Appendix. In Strandness DE, Jr. Duplex scanning in vascular disorders, 2nd edn. New York: Raven Press, 1993: 285.)

FIGURE 2.2 With the raster scan format (top), all scan lines are parallel and all of the image planes are also parallel. The scan lines originate from a different point along the tranducer’s crystal. With the sector scan format (bottom), the scan lines originate from a small region of the transducer. (Reproduced by permission

sector format, the optimal image area is more limited, as shown in Figure 2.4. Both of these formats have certain advantages that vary depending upon the intended applications. There are also innumerable variations on how the transducers function. These range from electronic beam steering to curved and concave linear array transducers, each of which has specific advantages for some applications. No single transducer design will satisfy all applications. Readers interested in more details are urged to consult the more complete coverage of this subject by Beach (4). Although the scan format used is important, it is also necessary to understand the role of the transmitting frequency, its application, and its effect on the performance of the system (4). Attenuation of the signal is directly related to the transmitting frequency. The goal is to obtain signals (images) with the maximum possible resolution. For superficial structures a high transmitting frequency of 5 MHz is satisfactory, but for deeper structures, such as the renal arteries, a much lower transmitting frequency of 2.0–3.5 MHz may be needed. There is less attenuation of the ultrasound signal with the lower frequencies, making them better for visualizing deeper structures.

from Beach KW, Appendix. In: Strandness DE, Jr. Duplex scanning in vascular disorders, 2nd edn. New York: Raven Press, 1993: 284.)

Doppler

and at right angles to the scan lines, optimal images are obtained. However, if a vessel begins to deviate from this parallel path, image quality may begin to degenerate and some structures such as the double line representing the thickness of the intima–media are no longer seen. With the

The Doppler ultrasound used in nearly all modern systems is pulsed, making it possible to selectively sample flow from any point along the sound beam (5). As with the imaging, knowing the speed of sound in tissue makes it possible to range gate return signals to assess flow velocity at any depth that is reachable by the ultrasound frequency used. The size of the sound packet (the sample volume)

RASTER SCAN

SECTOR SCAN

Chapter 2 Ultrasonic Duplex Scanning

9

FIGURE 2.5 The area in tissue insonated by a continuous wave Doppler is contrasted with that insonated by a pulsed system. As noted, the width of the sample volume can be varied by the degree of focus provided. (Reproduced by permission from Strandness DE, Jr. Duplex scanning in vascular disorders, 2nd edn. New York: Raven Press, 1993: 20.)

FIGURE 2.4 With the sector scan format, the double line that represents the intima and media is seen only in a limited portion of the scan plane as shown. (Reproduced by permission from Beach KW, Appendix. In: Strandness DE, Jr. Duplex scanning in vascular disorders, 2nd edn. New York: Raven Press, 1993: 285.)

for all pulsed systems can be varied considerably depending upon the intended application. The sample volume has both length and width. Its length is determined by the duration of the sound burst and its width is determined by the focusing characteristics of the transducer (Fig. 2.5). The size of the sample volume can be adjusted by the user, so it is important to review how it might be used and the problems that one might encounter with improper use (6). 1.

When examining arteries such as the carotid or femoral, one would like to use as small a sample volume size as possible. If one widens the sample volume to encompass the entire artery, the received signal will be identical to that obtained with continuous wave Doppler ultrasound. Figure 2.6 illustrates the basis for this observation. Near the normal arterial wall, the velocity gradients are very steep, resulting in the recording of a broad range of frequencies. This broadens the velocity spectrum (7,8). As noted, spectral broadening is not seen with a small sample volume placed in the center stream of the common carotid artery. This can be confusing if one attempts to use spectral broadening as a parameter for diagnosing carotid artery stenosis. This will be covered in detail later.

2.

A large sample volume is of benefit when one is examining arteries that experience a great deal of movement with respiration. The best examples of these are the renal, celiac, hepatic, splenic, and mesenteric arteries. With the large sample volume, flow can be monitored during an entire respiratory cycle, avoiding the intermittent loss of the signal due to movement of the sample volume in and out of the artery.

One important difference between pulsed and continuous wave systems is the problem of aliasing (4). Nyquist noted that, in order to faithfully record frequencies, it was necessary to have at least one sample taken for every peak and one for every valley of a waveform. This is the reason that the sample rate [the pulse repetition frequency (PRF)] must be at least twice the transmitting frequency of the pulsed Doppler. Thus, if one needed to record Dopplershifted frequencies of 5 kHz, it would be necessary to use a pulse repetition frequency of 10 kHz. If the Doppler shift were to exceed this limit, the frequencies that exceeded the 5 kHz level would appear beneath the zero frequency line (Fig. 2.7). There are ways to circumvent this problem. One is to simply increase the PRF of the instrument. Another is to reduce the transmitting frequency of the transducer. Finally, it is possible to combat aliasing by baseline shifting, which moves a portion of the reverse flow display to the forward flow location. This method is very commonly used in the currently available systems. The methods used for signal processing of the Doppler data are one of the most important advances in the field. For the velocity data that are recorded to be useful, they must be analyzed in a format that displays all of the pertinent information in the Doppler spectrum. The

10

Part I Imaging Techniques

FIGURE 2.7 Aliasing of a spectral waveform when pulsed Doppler ultrasound is used and the recorded frequencies exceed the pulse repetition frequency (PRF) of the pulsed system. On the left, there is foldover of the peak velocity, which is corrected by doubling the pulse repetition frequency shown on the right. (Reproduced by permission from Strandness DE, Jr. Duplex scanning in vascular disorders, 2nd edn. New York: Raven Press, 1993: 20.)

FIGURE 2.6 These velocity recordings are an ensemble average of 16 heart beats taken as the sample volume is moved from close to the anterior wall of the common carotid artery to the vessel lumen and to the posterior wall region. Near the walls, the spectrum is “filled in” (spectral broadening) owing to the very steep velocity gradients near the wall. (Reproduced by permission from Strandness DE, Jr. Duplex scanning in vascular disorders, 2nd edn. New York: Raven Press, 1993: SG.)

most versatile method in use is fast Fourier transform (FFT) spectrum analysis (4,8). This method has become the standard for displaying all Doppler data with both continuous wave and pulsed systems. The display has frequency (velocity) on the ordinate and time on the abscissa. It also provides information relative to the intensity of the backscattered ultrasound, but for most clinical purposes this information is not used. From a practical standpoint, the most useful clinical data relate to velocity since they are the most sensitive to change in vessel dimensions. As will be shown, velocity criteria are the most commonly used to detect and grade the degree of narrowing of arteries (3,9). The other commonly used parameter is spectral broadening. If blood flow is laminar and the recording is taken from the center stream of the artery, the area beneath the systolic peak will be clear (6–8). On the other hand, if there is turbulence, the red blood cells are no longer moving at a uniform

velocity and the systolic window will be filled (10). However, spectral broadening is being used less because of its qualitative nature. To interpret it properly, it is necessary to know precisely from which regions in the artery the flow is being detected, as well as the size of the sample volume being used (see Fig. 2.6). If one uses continuous wave Doppler ultrasound, all velocity data in the path of the beam will be recorded (6). Since the velocity of flow near the wall of an artery is slower, one will record all velocities up to and including the peak, which is usually in the center stream of the artery. On the other hand, with pulsed Doppler ultrasound, if a large sample volume were employed that encompassed the entire cross-sectional area of the artery, its output would be identical to that of a continuous wave Doppler ultrasound and would provide similar types of FFT displays. It is also clear that, depending upon the intended application, the technologist will vary the sample volume size used. For example, in the case of the carotid artery, it is preferable to use as small a sample volume as possible (10). In contrast, studies of the renal artery often require a larger sample volume for the velocity data to be continuously recorded throughout each respiratory cycle (11). If a small sample volume were used, the artery would move in and out of the sample volume with respiration. In theory, it is possible to record absolute velocities with Doppler methods; therefore, it is important to review briefly some of the concerns and problems that can occur with this method. The major factors that determine the recorded velocity are the transmitting frequency and the angle of the sound beam with the velocity vectors that are encountered (12). The choice of transmitting frequency

Chapter 2 Ultrasonic Duplex Scanning

will depend upon intended application. For superficial vessels, a higher transmitting frequency (5–10 MHz) is used; for deeper vessels, lower frequencies (2.0–3.5 MHz) are used. The angle of incidence is the most difficult variable to control for transcutaneous use. The ideal would be to have the sound beam directed down the center stream of the artery parallel to the velocity vectors. When this is possible, the incident angle of the sound beam is zero, giving a cosine value of 1. Because this is rarely possible in clinical use, one must estimate the angle of incidence of the beam, which can then be used to calculate the angle-adjusted velocity. This is done automatically by the duplex scanners currently in use. However, even with this approach there can be problems that must be appreciated. One of the most difficult is the problem of nonparallel velocity vectors, which are continually changing the angle of the incident sound beam (12). Nonparallel velocity vectors are common in the arterial system and are always found in the vicinity of branch points and bifurcations (7). Also, once the velocity vectors begin to deviate from what one might expect, a finite distance from the source of the velocity disturbance must be traversed before the vectors again assume a laminar flow pattern. A few examples of this problem and the need for its understanding are shown in Tables 2.1 and 2.2. In Table 2.1, velocities were recorded from the common carotid artery using different angles of incidence of the sound beam. In theory, this should make no difference in the recorded velocity, particularly if the velocity vectors were parallel to the wall. However, as noted, there are variations in the calculated velocities that must be related to directional changes in the flow vectors. In Table 2.2, the recordings were made from the superficial femoral artery,

TABLE 2.1 Doppler frequency and angle-adjusted velocity from common carotid artery Incident Angle (%) 40 50 60 70

Doppler Frequency (kHz)

Angle-adjusted Velocity (cm/s)

4.732 4.299 3.726 3.180

97 105 117 145

and an entirely different situation was found. Here, changing the incident angle of the sound beam had very little effect on the angle-adjusted velocity. In this situation, flow is much more stable (laminar), thus permitting a more realistic estimate to be made. This clearly illustrates the differences that can be found depending upon the sampling site within the arterial system. These types of data also emphasize the importance of using a constant Doppler angle for all studies in patients whenever that is possible. We prefer to use 60∞, which is quite easily obtained in most situations (12). However, if this angle of incidence is not obtainable, the technologist must record the angle used. In addition, if follow-up studies are to be performed, the same angle must be used. This will provide consistency among the data obtained. Although most manufacturers refer to the use of anglecorrected velocities, we prefer the term angle-adjusted velocity as representing a more realistic situation for daily clinical practice (4). It is also clear that, because we rarely have the ideal situation for making recordings, the velocity data we obtain is, in general, an estimate. FFT depictions of velocity data have become standard for nearly all instruments, but now “color Doppler” and “power Doppler” have added an entirely new dimension to ultrasound studies (13–15). The color can be obtained with a variety of transducer systems. The Doppler image is formed by analyzing the phase changes between echoes from each scan line. In order to generate one scan line, a series of echoes is required. For each depth, the phase change from echo to echo is measured to determine the frequency shift. A color is assigned to the corresponding depth according to its direction and velocity. In practice, shades of red and blue are used, although this is arbitrary. Color has great appeal because it provides a nearly instantaneous presentation of the velocities, which has the following advantages (14): 1. 2. 3. 4. 5.

1. 2.

Incident Angle (%)

3.

40 50 60 70

Angle-adjusted Velocity (cm/s)

3.561 2.906 2.292 1.524

73 71 72 70

The local vascular anatomy is immediately displayed. The relation of flow to the wall is apparent. Areas of narrowing and turbulence may be detected. The direction of flow is detected. Regional changes in velocity can be seen.

Even given all of the advantages of color, there are problems that need to be faced because they can adversely affect how the data are generated and interpreted. Some of the problems are as follows:

TABLE 2.2 Doppler frequency and angle-adjusted velocity from superficial femoral artery Doppler Frequency (kHz)

11

4.

Aliasing can occur with color. Changes in the direction of the velocity vectors will result in a change in the hue of the color, which may be misinterpreted as an absolute velocity change. The frequency shift information referable to the color bar and velocity should not be construed as representing a true value. The velocity data obtained with color are mean values (4). The temptation to make direct measurements of the degree of stenosis as an index of the degree of narrow-

12

Part I Imaging Techniques

ing must be resisted. Simply changing the gain can drastically alter what one might consider to be the lumen of an artery. Power Doppler does not display the frequency change at the site of interrogation. It reflects the amplitude of the backscattered frequencies—not the Doppler shift. This has certain advantages, particularly when one is interested in the arterial anatomy or the geometry of a stenosis. It is a valuable adjunct to the other aspects of duplex scanning.

Medical Applications of Ultrasonic Duplex Scanning Ultrasonic duplex scanning has reached such a level of maturity that it is now possible to draw some conclusions about its use in cardiovascular medicine (3). There are few technologies currently available as cost-effective or generally as useful as duplex scanning in clinical medicine. As will become evident, no other diagnostic instruments have the versatility found with duplex scanning. Nearly every area of clinical interest and need can be studied with this method.

The Carotid Artery The first area in the circulation to be studied by duplex scanning was the carotid artery (16). This was done for several reasons: first, its proximity to the skin makes it easily accessible to ultrasound; and, second, disease in this location is common and is frequently studied by contrast arteriography. This made it possible to validate the accuracy of duplex scanning in detecting the presence of disease and estimating its severity. It is now clear that arteriography is not a good gold standard for this purpose. Atherosclerosis commonly affects the extracranial circulation but has the highest incidence at the level of the bulb. The carotid bulb is a unique area in the circulation owing to its geometry. It is the only region of the arterial system where a regional dilation is found. The geometry of the bulb creates peculiar flow patterns that can be a source of great confusion if their presence is not recognized (8). It has been theorized that this geometry and the resulting flow patterns explain the localization of the atheroma to this region. As all vascular surgeons recognize, the disease rarely extends beyond the distal limit of the bulb itself, which is one reason that carotid endarterectomy is feasible. The flow changes in the normal bulb that are unique are referred to as boundary layer separation (8). As the flow enters the bulb, that flow near the flow divider will be antegrade at all times in the pulse cycle, while that in the posterolateral region will reverse. The area of reverse flow is the region of boundary layer separation (8). The size of this region varies during the pulse cycle. As flow leaves

the bulb, a helical flow pattern will be generated that is propagated for varying distances into the internal carotid artery. The presence of boundary layer separation can be demonstrated both with FFT displays and with color (Fig. 2.8). The dramatic nature of the flow changes during a single pulse cycle can be seen in the FFT display. The importance of understanding boundary layer separation is that it does not occur when an atheroma fills the posterolateral region of the bulb; that is, it is only seen with a normal bulb. In clinical medicine we must deal with the relation between the extent of disease and the clinical outcome, so it is important to develop criteria that can be used to dictate how the patient should be treated. Over the past several years, we have developed categories of disease involvement detectable by duplex scanning that are of great practical value. These can be summarized as follows (10): 1. 2. 3. 4. 5.

normal; <50% diameter reducing stenosis; 50–79% diameter reduction; 80–99% diameter reduction; total occlusion.

With the publication of the results of the North American Symptomatic Carotid Endarterectomy trial (NASCET) (17,18) and the European Carotid Surgery Trial (ECST) (19), the relationship between the degree of diameter reduction and stroke became clear. The degree of

FIGURE 2.8 In the normal bulb, an area of recirculation is found in the posteriolateral aspect of the bulb. In this area, flow will be both antegrade and retrograde. With the sample volume near the flow divider, all flow is antegrade. However, with the pulsed Doppler sample volume moved to the lateral aspect of the sinus, both forward and reverse flow components are seen. This is referred to as boundary layer separation. (Reproduced by permission from Strandness DE, Jr. Duplex scanning in vascular disorders, 2nd edn. New York: Raven Press, 1993: 113–157.)

Chapter 2 Ultrasonic Duplex Scanning

risk is clearly associated with how much narrowing is present. The highest risk is in the 80% to 99% diameter reduction category. After the early reports that only the 70% diameter reducing lesions were significant, we began to use another velocity-derived parameter to classify this degree of diameter reduction. The algorithm for its detection is easily adapted to the criteria already in common use (19). The diagnostic criteria for determining the degree of diameter reduction are related to two ultrasound features (Fig. 2.9): peak systolic velocity and end-diastolic velocity. We have stopped using spectral broadening except in special circumstances. They are used in the following fashion:

3.

4.

5. 1. 2.

Normal bulb. The major diagnostic finding is boundary layer separation. Diameter reduction <50%. Disease is seen in the bulb on imaging but it does not increase the peak systolic flow velocity across the bifurcation.

13

Diameter reduction >50% but <79%. There is an increase in the peak systolic velocity at the stenosis that exceeds 125 cm/s. Diameter reduction 80% to 99%. The end-diastolic frequency now is greater than 145 cm/s. This is the lesion that is most likely to proceed to total occlusion. Of course, the peak systolic velocity will be much higher. To classify a lesion in the >70% diameter reducing range, it is necessary to divide the peak systolic velocity at the site of the stenosis by the peak recorded from the common carotid artery. If this ratio exceeds 4.0, there is a 90% chance that the lesion exceeds this cutoff value (19). Total occlusion. No flow will be detectable in the internal carotid artery. However, there are other clues that are useful in suspecting this finding. These include the following: 1) end-diastolic flow in the common carotid artery will often go to zero; in 34 cases of total occlusion, end-diastolic flow went to zero in 32;

FIGURE 2.9 The spectral criteria used for detecting varying degrees of stenosis of the carotid artery are shown. The major features, with increasing degrees of narrowing, include the peak systolic velocity, the end-diastolic velocity, and spectral broadening (see text).

14

Part I Imaging Techniques

2) flow in the contralateral carotid artery will be doubled as it now supplies both hemispheres, which results in a marked increase in the end-diastolic velocity; 3) as the sample volume is positioned close to the occlusion, a “thumping” sound may be heard that is very distinctive of total occlusion; and 4) there will be no flow in the internal carotid beyond the bulb—although one might think that color flow would be the best method of detecting a total occlusion, this has not been verified to date. It should be noted that flow in the contralateral carotid will be much higher so it may be necessary to downgrade the degree of narrowing there by one category (3). Because a total occlusion removes the patient from surgical consideration, this diagnosis is of paramount importance. In many cases, it will be necessary to obtain an arteriogram to render the final judgment, but even here there can be problems if the residual flow channel in the stenosis is very narrow and the flow very slow. The accuracy of duplex scanning as a method of detecting and classifying the degree of stenosis has been well established (10). Its sensitivity is in the range of 98% with a specificity that is in the 95% range, which makes it satisfactory for screening populations with either a high or low prevalence of disease (20). Screening Before Intervention The majority of patients with extracranial arterial disease who develop ischemic episodes will do so secondary to disease within the bulb. Although there is no doubt that lesions at the level of the aortic arch can lead to transient ischemic events and strokes, this is very uncommon. However, precise criteria for grading the degree of narrowing of the arteries at the level of the arch have not been worked out with the same precision. It is possible to detect turbulent flow patterns in the proximal common carotid artery that are a clue that problems exist at that level (21). Clearly, for lesions in the innominate and subclavian artery, arm pressures must be measured along with direct insonation of the subclavian arteries. This can be helpful in detecting clinically significant disease. A systolic pressure gradient of more than 15 mmHg between the two arms could be significant. Another area that has been of concern is the carotid siphon (22). It is well known that lesions can develop in this region that might be a cause of ischemic events. This area cannot be studied by duplex scanning. However, the studies that have been performed examining the role of the siphon have not supported the impression that lesions here are a cause of ischemic events. This region can now be evaluated by transcranial Doppler ultrasound, but there is not yet sufficient information to determine if this method is of any value for this purpose. As duplex scanning is an accurate screening test for lesions of the bulb (23,24), could it be used as the sole diagnostic test before carotid endarterectomy? The concern is that the information obtained by duplex scanning alone

might not prove sufficient to proceed safely with the operation. To address this issue, it is necessary to consider the problems that could occur to negate the use of duplex scanning alone: 1.

2.

3.

The key element is a properly performed duplex scan that accurately assesses the location and extent of the involvement In the results of the NASCET and ECST studies, the degree of stenosis was the only factor that determined the need for endarterectomy (17–20). The published results from good laboratories would suggest that a well-done test is as accurate as arteriography in determining the degree of narrowing. This means that vascular surgeons must have confidence in the laboratory doing their testing procedure. This means good quality control and experience (21–23). Does arteriography provide additional information that would preclude operation or suggest a different approach? There are obvious lesions, particularly at the intracranial level, that would, or could possibly, change the approach. These include aneurysms, tumors, and occlusive lesions in the distribution of the middle cerebral artery. Mass lesions would be discovered by the computed tomography (CT) scan, but occlusive lesions would not. Lesions at the level of the aortic arch may dictate a different approach because if undiscovered they may lead to failure of the carotid endarterectomy. This possibility can be avoided by a careful examination of the flow patterns at the level of the aortic arch (24). Interestingly, lesions in the siphon do not appear to contribute to the outcome after endarterectomy. The lesions which occur in the siphon are not generally due to atherosclerosis but are known as intimal cushions, which are smooth and do not appear to ulcerate (25).

We have carried out two prospective studies to assess the role of duplex scanning alone for the selection of patients for endarterectomy (26,27). Over a 29-month period, the vascular surgeons involved in the study had to make decisions relative to the management of 103 patients who were being considered for carotid endarterectomy (111 carotid arteries). For each case, the surgeon recorded his plan before the arteriography. Nine patients were excluded because arteriography was not carried out, or was performed before the surgeon’s evaluation. The duplex scans were diagnostic in 87 (93%) of the 94 cases. The carotid lesion was inadequately evaluated by duplex scan in seven patients because the disease was not limited to the distal common carotid artery or bulb (four cases), anatomic or pathologic features of the carotid artery interfered with imaging or Doppler analysis (one case), or a lesion could not be distinguished with certainty as an occlusion (two cases). When the duplex scan was adequate, the arteriography contributed information that was of additional value in only one case (1%). This patient had a middle cerebral artery stenosis distal to a

Chapter 2 Ultrasonic Duplex Scanning

high-grade stenosis. Operation was withheld because of this intracranial stenosis. Later, he sustained a completed stroke that might well have been secondary to the carotid bifurcation stenosis. We concluded that duplex scanning could be used as the sole preoperative study as long as a satisfactory, complete duplex scan had been performed. Our data suggest that a perfectly satisfactory outcome could be achieved by this approach. In fact, there are clinical trials under way that accept duplex scanning alone as the method used for selecting patients for endarterectomy. Postoperative Studies In the early postoperative period (first week), testing can be done but is generally used to determine the patency of the internal carotid artery. Because of the fresh wound and the patient’s discomfort, it is not always possible to carry out a complete study. However, within 7 to 10 days, a more complete examination can be done if it is deemed necessary. During the follow-up period, the major lesion that develops is myointimal hyperplasia (28,29). This is a smooth lesion that will develop within the first 12 months, and is not a common cause of ischemic events. Some of these lesions can proceed to total occlusion, but this appears to be very uncommon. The progression to internal carotid artery occlusion after operation was found in 4% of the 200 consecutive patients we have followed prospectively (28).

15

Doppler ultrasound, a great deal is known about the normal arterial flow patterns and their use in documenting both the presence and extent of disease. The most important fact to understand is that the velocity patterns are dictated by the vascular resistance offered by the tissue supplied and its metabolic activity at the time of study. There are some generalizations that are useful. The organs and systems that are low-resistance vascular beds are the brain, liver, spleen, and kidney. These organs demand high levels of blood flow at all times during the day. In the supplying arteries, the end-diastolic velocity should always be above the zero baseline (Fig. 2.10). The high-resistance arterial beds are the upper and lower extremities under resting conditions (35,36). At rest, a reverse flow component of the velocity waveform will be prominent until the resistance to flow decreases, such as occurs with and immediately after exercise (Fig. 2.11). The upper limb velocity patterns are more variable because some individuals will not show a reverse flow component even at rest. In the lower leg arteries, reverse flow should always be seen when the patient is at rest. There are arteries supplying tissues of intermediate resistance. The most common and frequently studied by duplex scanning is the superior mesenteric artery. Under fasting circumstances, a small

The Peripheral Arterial System The most widely used noninvasive test for peripheral arterial disease is the measurement of the ankle–arm index (AAI), followed in some instances by exercise testing (30–34). This provides the necessary objective baseline values for both establishing the diagnosis and following the progress of the disease with and without interventional therapy. If the patient is a candidate for intervention, the next diagnostic study performed is arteriography. This study provides the necessary road map for the surgeon in reconstructing the arterial system. Is this approach adequate or can we make significant progress by adding duplex scanning for specific cases (34,35)? The issue of using duplex scanning alone prior to operation will be considered in greater detail in Chapter 3. In order to determine the place for duplex scanning in diagnosis, it is necessary to establish its accuracy compared with arteriography, which is still considered to be the gold standard. Progress in the implementation of duplex scanning for the peripheral arteries had to await the necessary technological improvements that guaranteed access to all arteries of interest. For clinical purposes, it is necessary to scan the arterial system from the level of the abdominal aorta to the ankle arteries and, in the upper extremity, from the level of the subclavian artery to those at the wrist. Based upon previous experience with physiological studies and those conducted with continuous wave

FIGURE 2.10 With a low-resistance type of waveform, the end-diastolic velocity is always above zero. This waveform was taken from the mid-portion of the right renal artery (RRA). Ao, aorta. (Reproduced by permission from Strandness DE, Jr. Duplex scanning in vascular disorders, 2nd edn. New York: Raven Press, 1993: 200.)

16

Part I Imaging Techniques

A

B

FIGURE 2.11 The high-resistance waveform typically has a reverse flow component as shown here from tracings taken from the external iliac artery (EIA), the common femoral artery (CFA), and the proximal superficial femoral artery (SFA-p). (Reproduced by permission from Strandness DE, Jr. Duplex scanning in vascular disorders, 2nd edn. New York: Raven Press, 1993: 166.)

amount of reverse flow is seen in the superior mesenteric artery. Within 20 minutes of eating, this pattern begins to change, with a loss of the reverse flow component and an increase in the end-diastolic velocity as the volume blood flow to the gut increases to meet the metabolic demands of digestion (Fig. 2.12). Interestingly, this same phenomenon is seen with the inferior mesenteric artery, but the flow velocity change occurs only when the material ingested is handled by the colon. The blood flow in the inferior mesenteric artery does not appear to change when foods ingested are handled primarily by the stomach and small bowel. Given these considerations, it is possible to utilize velocity data as diagnostic aids in assessing the status of the arterial system. Documentation of an abnormality depends upon demonstrating flow velocity changes that deviate from this normal pattern. As with other arterial beds, the extent to which the patient becomes symptomatic depends upon both the location and, most importantly, the degree of narrowing that is present. In the

FIGURE 2.12 Changes that occur with vasodilation of the mesenteric vascular bed after food ingestion are shown (top). Taken during fasting and (bottom) after food ingestion. There is a dramatic increase in both the peak and end-diastolic velocities noted. (Reproduced by permission from Strandness DE, Jr. Duplex scanning in vascular disorders, 2nd edn. New York: Raven Press, 1993: 69.)

peripheral arterial circulation, patients will become symptomatic only when the pressure and flow beyond the lesion begin to decrease, making it impossible to maintain adequate nutritional flow either with exercise or at rest. In general, the level of narrowing that is sufficient to do this is a 50% or greater degree of diameter reduction. This is often referred to as a critical stenosis (37). However, some stenoses that narrow the artery by less than this amount can become hemodynamically significant under conditions of increased blood flow (38). In this case the increase in flow across the narrowed segment will induce turbulence that accentuates the normal pressure gradient. When there is a decrease in pressure and flow during exercise, the patient may develop intermittent claudication. Given the above, it is clear that if duplex scanning is to partially or completely replace arteriography, it will have to be able to detect and grade lesions of all levels of severity (39). There are also other considerations that are relevant to this question.

Chapter 2 Ultrasonic Duplex Scanning

1.

2.

3.

4.

5.

6.

The studies have to be done at the sites of disease involvement. This means, of course, that long lengths of the arterial system will have to be scanned. The changes in flow velocity across the stenotic lesions should be a reflection of the degree of narrowing. The information must have clinical relevance for the physician in his or her management of the patients and their problems. The testing will have to be cost-effective and not just another test providing information that is already available from existing and, in some cases, less expensive tests. The testing should provide data that can be used for follow-up comparisons. It has become increasingly clear that accurate, objective follow-up is very useful in making sure that the benefits of therapy can continue. Several examples of this will be covered later in this chapter. Technologists should be capable of performing the tests.

For study purposes, the systems used must be state-ofthe-art, with color Doppler ultrasound and a variety of transducers with different transmitting frequencies. Because the arteries in the abdomen are deeper than those in the leg, lower transmitting frequencies in the range of 2.0 to 3.5 MHz for imaging may be required. For most applications, a 5-MHz system is adequate for Doppler studies. The scanning commences in the upper abdominal aorta, proceeding distally to the arteries at the level of the ankle. The technologist is testing for areas where the peak systolic velocity increases from one segment to another. The criteria that have emerged can be considered in two categories, each of which is very dependent upon the other. The role of color/power alone is reviewed below, but it cannot be divorced from the simultaneous use of the FFT real-time spectral analysis. Color/power Doppler ultrasound provides certain advantages related primarily to rapid identification of the vessels of interest as well as the sites of the lesion(s) and a rough estimate of their severity (13–15). Color Doppler alone must not be used to quantitate the absolute velocity values. It provides data only on the means and not the absolute values for the peaks (4). Power Doppler is based on the amplitude of the backscattered ultrasound and not the velocities. With experience, color has been useful in the following ways: 1.

2.

The normal flow pattern of triphasic flow can be recognized by the transient appearance of blue (reverse flow), which becomes apparent during late systole and early diastole (14,36). With a stenosis there are two changes that suggest that it may be a lesion with more than 50% diameter reduction (15). The first is the appearance of turbulence, which is seen as an admixture of colors just

3.

4.

17

distal to the stenosis. The other indirect sign is the appearance of a bruit. This is recognized as the appearance of spontaneous bursts of color outside the arterial wall. This represents arterial wall vibration. It is only seen at and distal to a stenosis, which is consistent with the clinical observation that bruits are always transmitted downstream of the area of narrowing. An occlusion is recognized by two features (15). One is the lack of color flow at sites where it should be found. The other is the appearance of collateral vessels that take their origin at right angles to the artery. Since this dramatic change in direction of flow, which is now either toward or away from the transducer, the color change at the site of origin of the collaterals will be dramatic. In most cases, the color will be a very light shade of red, or even white, reflecting this dramatic change in the direction of flow. Power Doppler is particularly useful in identifying the anatomy of the segments being examined. For example, the tortuosity seen in the internal carotid artery may be difficult to sort out, but power Doppler makes this much easier.

These color changes are important, but, as mentioned earlier, the best method of determining the actual velocity at suspected sites of narrowing is to make use of the single sample volume of the pulsed Doppler and the FFT to give an accurate measurement of the true velocities at areas of narrowing. Although the color provides the road map, we still must rely on the velocity changes as follows (Fig. 2.13): 䊏

䊏

䊏

䊏

Normally, there should not be a detectable change in peak systolic velocity in short segments of arteries. However, it is well recognized that there is a gradual decrease in peak systolic velocity as one moves down the limb from the level of the abdominal aorta to the tibial arteries at the ankle (36). With roughening of the arterial wall but without a measurable degree of narrowing, the only detectable change will be some spectral broadening (36). For this category we have labeled the disease as being in the 1% to 19% category of diameter reduction. As the lesions progress there will be a progressive increase in the peak systolic velocity (32,33). For stenoses in the 20% to 49% category of diameter reduction, the peak systolic velocity will increase between 30% and 100% over that in the preceding segment. Most importantly, there will be spectral broadening but the reverse flow component is generally preserved. These are not a clinical problems when the patient is at rest. However, in some cases with the increase in flow that accompanies exercise, turbulence can develop which can lead to a pressure drop. For the pressure and flow-reducing lesions (> 50% diameter reduction), the peak systolic velocity within

18

Part I Imaging Techniques

䊏

FIGURE 2.13 The spectral criteria used to separate the varying degrees of involvement of the peripheral arteries are shown. (A) With the normal artery the triphasic waveform without spectral broadening is seen. (B) With 1–19% wall roughening, reverse flow is retained but some spectral broadening can be noted. (C) In the lesions with 20–49% diameter reduction, the peak systolic velocity will increase by 30% to 100% from that of the preceding segment, with spectral broadening noted. Reverse flow may be preserved. (D) In the lesions with 50% to 99% diameter reduction, the peak systolic velocity increases by more than 100% from that of the preceding segment. (Reproduced by permission from Strandness DE, Jr. Duplex scanning in vascular disorders. 2nd edn. New York: Raven Press, 1993: 169.)

the stenotic segment will increase by more than 100% over that in the preceding segment, with a loss of the reverse flow component and the development of marked spectral broadening (35,36). Total occlusion is recognized by the absence of flow.

These criteria have been prospectively tested against arteriography, with the results shown in Table 2.3. When one examines the accuracy of duplex scanning and compares its results against those of arteriography, the ultrasonic method does quite well. The comparison between duplex scanning and the reading of a single arteriographer does not tell the entire story because there is another element of variability in the reading of the arteriograms. To evaluate the interobserver variability, we compared the results when the films were read by two radiologists (see Table 2.3) (36). Because only the stenoses with diameter reductions of less than or more than 50% are clinically relevant, this subset of stenoses was chosen for comparison. In this study, both radiologists used calipers to measure diameter reduction. The senior radiologist was arbitrarily used as the gold standard. The results for this study are summarized in Table 2.4 for the positive and negative predictive values for the segments studied. These types of data reinforce the belief that the gold standard also has limitations, as does duplex scanning. However, this does not negate the potential role for the ultrasonic method. Either method must be used in the context of the clinical presentation. For example, if the patient has intermittent claudication and a superficial femoral occlusion but there is also a suggestion of an iliac artery stenosis, a negative duplex scan of the feeding iliac artery would appear to be sufficient to direct attention to the femoral artery lesion alone. Screening Before Intervention The patients for whom we have reserved duplex scanning are those considered candidates for intervention, be it endovascular or surgical (40). To prospectively test the role of duplex scanning, we conducted a study that included 122 patients who had undergone both duplex scanning and arteriography. There were 110 arteriograms that

TABLE 2.3 Duplex scanning versus arteriography for a stenosis of less than or greater than 50% diameter reduction Arterial Segment Aorta Iliac Common femoral Superficial femoral Profunda femoral Popliteal All segments

Sensitivity (%)

Specificity (%)

Positive Predictive Value (%)

Negative Predictive Value (%)

100 90 67 84 67 75 82

100 90 98 93 81 97 92

100 75 80 90 53 86 80

100 96 96 88 88 93 93

Chapter 2 Ultrasonic Duplex Scanning TABLE 2.4 Comparison of two radiologists in classifying arterial lesions into categories of less than or more than 50% diameter reduction

Arterial Segment Iliac Common femoral Superficial femoral (proximal) Superficial femoral (middle) Superficial femoral (distal) Popliteal All segments

5.

Positive Predictive Value (%)

Negative Predictive Value (%)

94 100 100 100 78 100 88

96 91 88 93 94 95 93

The senior radiologist was arbitrarily used as the “gold standard.”

were preceded by duplex scans. Of this group, 45 were scheduled for angioplasty on the basis of the results of the duplex scan. Angioplasty was performed in 47 of these cases. In one patient, the lesion was felt to be too dangerous to dilate. In a second patient, a significant pressure gradient was not found across the area of stenosis. In a third patient, a stenosis in the superficial femoral artery distal to a total occlusion was missed. Is this approach worthy of the extra effort and time? At present, there are several reasons why these appear to be acceptable. First, if duplex scanning is as accurate as two radiologists reading the same films, why not apply it as a screening test? Second, it is likely that the number of arterial punctures was reduced because the radiologists knew before the procedure where the lesions were to be found. Third, this method is likely to reduce the total number of arteriograms obtained. It appears that many radiologists and surgeons use arteriography as the initial diagnostic procedure, then decide what approach should be used at a later time. Finally, this is a very satisfactory approach in that patients can be made aware of the proposed form of therapy and the likelihood of success. Vein Mapping The saphenous vein is the most satisfactory bypass graft for peripheral arterial occlusive disease, so it is important to determine its adequacy before surgery. The advantages of preoperative ultrasonic assessment are as follows (41). 1. 2.

3.

4.

Anatomic variants are not uncommon, being found in 30% to 70% of patients. Double systems are not uncommon. It is worthwhile to scan patients who have had a vein stripping because a duplicate system that may be usable can occasionally be found. Areas of scarring or occlusion within the vein may be found, which will require the modification of the procedure. The size of the vein may be estimated, providing some confidence as to its suitability as a conduit. In general,

19

a vein with an internal diameter of 2 mm is suitable for bypass purposes. Alternative sources for veins can be determined in those patients in whom the greater saphenous is either absent or inadequate.

In the prospective studies that have been done, the sensitivity of duplex scanning was found to be in the 93% to 96% range. The positive predictive value was also in this range. The specificity is not as high, being in the range of 60% to 70%. In some cases, it is necessary to explore the suspicious venous segments to be certain of their status. In some patients whose lower limbs do not have suitable veins, it may be necessary to screen the arms for a possible conduit. In order to do the study, it is necessary to use a highresolution B-mode system. The linear array transducers (7–10 MHz) have an advantage in that long segments of vein can be seen in the field, which makes the scanning time faster. To facilitate the examination, it is best to do the study with the leg in a dependent position, which can either be the reverse Trendelenburg or the standing position. This provides maximal venous dilation, which is important both for visualizing the vein and for determining its diameter. The scanning procedure takes 20 to 30 minutes, and the technologist can then mark the course of the vein, along with large branches that might be of concern. Follow-up Once the surgical or endovascular procedures is completed and the patient has left the hospital, the long-term outcome is dependent upon two major factors. One is the problem of myointimal hyperplasia (42). This interesting lesion may develop when there has been some injury to the vessel wall. The lesion, in its most simple terms, is an overgrowth of smooth muscle that may significantly narrow the artery or graft at the site of development. If the narrowing becomes sufficiently severe, the procedure may fail. The exact incidence of myointimal hyperplasia is not known, but it has been estimated that up to 30% of those with arterial reconstructions will develop this complication. The lesion will nearly always develop during the first year following the therapy. The other common cause of failure of many reconstructions is disease progression. This can occur either proximal or distal to the site of therapy. Until recently, it was not common practice to follow patients prospectively after surgery, but rather to simply await the appearance of new symptoms. This was not proper, as we now know from the prospective studies that have been done. Regular surveillance of the reconstruction appears to be very important, particularly for vein grafts, to detect new lesions before thrombosis occurs. Surveillance permits early correction of the complication with prolongation of the life of the graft (43,44). For vein grafts, the most suitable method of follow-up has been color Doppler ultrasound with real-time spectral analysis. This permits a complete survey of the graft in-

20

Part I Imaging Techniques

cluding the inflow and outflow arteries as well. The criteria that have been developed relate to the extent of the degree of stenosis and the peak systolic velocity in the graft itself, which can also reflect changes in both the inflow and outflow from the graft. Although the criteria used by different investigators have varied somewhat, the following guidelines would appear to work well for follow-up purposes. Arterial Inflow Most of the grafts being followed have their origin from the common femoral artery, but some will be placed at a lower level, depending on the extent of the occlusive disease. Regardless of the site of origin, there are velocity criteria that can provide information that is useful. These are as follows: a triphasic waveform (forward–reverse–forward flow). This is reassuring that inflow to that point is adequate. The finding of a monophasic waveform at any point proximal to the origin of a vein graft is certain evidence that there is proximal disease that is hemodynamically significant. If one desires to further scan the inflow to localize the site of involvement and estimate its significance, the procedure as described earlier in this chapter should be followed. The Vein Graft Before beginning the scanning procedure, the examiner must be aware of the type of graft used (in situ versus reversed). With the in situ graft, the proximal portion of the graft is larger, and the opposite is found with the reversed graft. With the in situ graft the peak systolic velocities will increase as one approaches the distal anastomosis; the opposite will be seen with the reversed vein graft. There are several points to consider in determining how well a graft is functioning. The areas that are of specific interest are as follows: First is the proximal anastomosis. The geometry of an end–side anastomosis is complex. It is impossible to provide firm guidelines to be used with regard to absolute values for peak systolic and end-diastolic velocities across such unions. However, because follow-up studies permit comparisons from one visit to another, it is possible to document the development of an anastomotic stenosis when changes are found. Second is the vein graft itself. Problems can also develop at sites of valve cusps (4,5). Most myointimal lesions are generally very well localized, as noted in Fig. 2.14. These discrete areas will produce changes in peak systolic velocity, the magnitude of which depends on the degree of diameter reduction. Arteriovenous fistulas may also be present in the in situ graft and are easily recognized by the very high end-diastolic velocities recorded proximal to the fistula. The findings during follow-up that are important can be summarized as follows. The velocities in a graft without any obvious sites of narrowing will be dependent upon several variables including the size of the vein graft and the nature of the outflow. Low velocities (<45 cm/s) can be found in an otherwise normal graft, particularly if the graft is large (6 mm or greater). However, if velocities below 45 cm/s

FIGURE 2.14 This B-mode picture is of a stenotic lesion in a vein graft that developed secondary to myointimal hyperplasia. Arrows indicate site of lesion.

are seen in a vein graft without any obvious sites of stenosis, then it is either secondary to an inflow or outflow problem. For velocities at sites of narrowing within the body of the graft, the problem is not in detecting the site of narrowing, but in estimating its severity and, most importantly, its present and future effect on graft function. If the lesion narrows the graft by more than 50%, it will most likely lead to a fall in distal pressure and flow, which could compromise graft function. The problem is further complicated by trying to predict on the basis of diameter reduction which grafts will thrombose if left alone. This is, of course, the most important issue because vein graft patency, along with preservation of function, is the major goal of a surveillance program. The efforts in this regard have been led by Bandyk (43,44), followed by others who have carried out similar surveillance programs in an attempt to detect those lesions that need prompt intervention in contrast to those that can be safely followed. While there are some differences in the end points used for intervention, the published studies have in general shown an improvement in assisted primary patency of the vein grafts by instituting such a program. Bandyk has proposed that the indications for graft revision be based on the severity of the hemodynamic impairment of the graft rather than the duplex scan findings alone (40,41). He has recommended graft revision for the following situations: 1) a low peak systolic velocity (<45 cm/s) in the distal graft; 2) a decrease in peak systolic velocity of more than 30 cm/s associated with a decrease in the AAI of more than 0.15; and 3) a correctable lesion within the vein graft. Bandyk’s program has achieved an assisted primary patency rate of 85% at 2 years by following this protocol.

Chapter 2 Ultrasonic Duplex Scanning

Idu et al., in a prospective study of 201 vein grafts, reported that for 58 grafts with stenotic graft lesions that were not treated, the following outcome was noted (45): none of the grafts with a 30% to 49% diameter reduction failed; occlusion occurred in 57% of the non-revised grafts with a 50% to 69% diameter reduction, as compared with only 90% of the revised grafts; and grafts with a 70% to 99% stenosis all failed if not treated, as compared with 10% for the revised grafts. By following such a protocol, the primary assisted patency at 48 to 60 months for grafts with lesions not treated at the time of detection was 72%. In contrast, for those in which intervention was performed, the rate during the same time interval was 88%. Mattos et al., over a 39-month period, studied 170 limbs with vein grafts (46). These grafts were studied at 3, 6, and 12 months and then yearly. There were 110 stenoses detected in 62 (36%) of the vein grafts. Of these stenoses, 27% were at anastomoses and 65% were in the graft itself. A total of 77% were detected within the first year. Of this group, 39% of the grafts with lesions were revised. For those grafts with negative scans, the primary patency was 90% at 1 year and 83% at 2 to 4 years. In contrast, the patency rates with grafts that had a stenosis of more than 50% diameter reduction that were not corrected, the patency was 66% at 1 year and 57% for years 2 through 4. Mattos et al. concluded that color duplex scanning was effective in detecting those lesions of more than 50% diameter reduction, which were associated with a high failure rate (46). The criterion for detecting such a stenosis in a vein graft was finding a peak systolic velocity ratio of 2. The ratio is the peak systolic velocity in the stenosis divided by that recorded just proximal to the stenosis. Our studies are quite similar to the above. We have noted that duplex scan velocity measurements are valid predictors of impending graft stenosis. The best predictors of outcome were a velocity ratio of 3.5 or more and a mean graft velocity of <50 cm/s. We recommend repair of correctable graft lesions that fall into this category. Grafts that do not have detectable lesions in the inflow, the graft or outflow regardless of the mean graft velocity may be safely followed (47–50). Most of the changes that require revision will develop within the first few months but the surveillance program must still be followed. The time intervals for study vary somewhat from center to center but are most frequent in the first year. If the graft remains patent without problems at one year, the intervals of study can be every 6 months. If a new problem develops at any time the follow-up interval will have to be shortened to document the stability of the lesion.

important as methods of screening and follow-up after intervention, be it surgical or endovascular. Mesenteric Circulation The two most common events involving the mesenteric circulation are acute mesenteric ischemia and mesenteric angina. In the case of acute ischemia with occlusion of the superior mesenteric artery, the clinical presentation and urgency for a prompt diagnosis are such that duplex scanning has a small role to play. The success of the outcome depends upon the rapidity with which therapy is applied to prevent bowel necrosis, which is associated with a very high mortality rate. Chronic mesenteric ischemia is often difficult to diagnose. Although the clinical presentation of fear of food because it produces abdominal pain and diarrhea accompanied by marked weight loss is typical for the syndrome, the symptoms are often not specific. Often other causes for the symptom complex need to be sorted out. Prior to the availability of duplex scanning, aortography with lateral views of the celiac and superior mesenteric arteries was the only method of establishing with certainty the involvement of these arteries, which is required for the syndrome to develop. It is now well known that all three of the major arteries supplying the small bowel must be involved for this syndrome to develop. This is because the collateral circulation that can develop is normally very extensive. For example, it is possible for the celiac and superior mesenteric arteries to be totally occluded yet the blood supply to the small bowel be entirely normal via the inferior mesenteric artery. Thus, in theory if duplex scanning is to play a diagnostic role, it should be used to investigate all three sources of blood supply to the small bowel. Until recently, most attention has been paid to the celiac and superior mesenteric arteries (51–55). The inferior mesenteric artery, owing to its size and location, has been more difficult to study, but this is now also possible. The guidelines that have been used for the diagnosis of chronic mesenteric ischemia have evolved to include the following (53,54). 1. 2.

3.

The Visceral Arteries With the availability of low-frequency transducers, it has become possible to study flow in the hepatoportal circulation, the mesenteric arteries and the renal arteries. From the standpoint of the vascular surgeon, these have become

21

4.

The criteria used are based on changes in the peak systolic velocity. The normal peak systolic velocities in the abdominal aorta in the region of the origins of the celiac and superior mesenteric arteries are in the range of 100 ± 20 cm/s. As the sample volume of the pulsed Doppler is moved from the aorta to the first portion of the celiac and superior mesenteric arteries, the peak systolic velocity will increase. To establish the normal range for the detected velocities, Moneta et al. studied 100 patients with lateral aortograms as a part of a workup for peripheral arterial disease (54).

22

Part I Imaging Techniques

The peak systolic velocities for celiac and superior mesenteric arteries with a diameter reduction of less than 70% were compared with those noted to have highergrade lesions. Values of less than 275 cm/s for the celiac artery and less than 200 cm/s for the superior mesenteric artery were sufficiently accurate to rule out the highergrade lesions. They considered the higher-grade lesions as potential contributors to the syndrome of chronic mesenteric ischemia as long as both were involved. In practice, the clinical presentation and a finding of high-grade stenoses or occlusions of these two major inputs to the gut are generally sufficient to make the diagnosis and institute therapy. If the inferior mesenteric artery is also studied and found to be normal, it may be necessary to carry out a food challenge to test the ability of the available blood supply to meet normal nutritional needs. Moneta et al. published a case report of a patient whose small bowel was entirely supplied by the inferior mesenteric artery. In this patient, it was shown that the blood flow increase with a food challenge was entirely normal (55). With regard to the response of the blood flow in the superior mesenteric artery to feeding, the normal patterns are now well known. Before detailing the response to a food challenge, it is necessary to review briefly the normal blood flow patterns during fasting. Under fasting conditions, the velocity patterns in the celiac, superior, and inferior mesenteric circulations have been well characterized. The celiac artery supplies the liver and spleen, which are low-resistance organs. This means that the end-diastolic velocity will always be above zero, much as is seen with the internal carotid artery. On the other hand, the mesenteric arteries supplying the gut have a much different pattern. Under fasting conditions, the resistance to flow is high, which results in an enddiastolic velocity that goes to zero and in some cases is associated with a reverse flow component similar to that seen with the arteries supplying the lower limbs. With the ingestion of a mixed meal (Ensure®). there are dramatic changes in the flow in the superior mesenteric artery with little or no change in the flow in the celiac artery. After eating, flow rapidly increases in the first 20 min, reaching a maximal level in 30 to 60 min (56). The changes are in both the peak systolic and end-diastolic velocity, reflecting the increase in volume flow that is required (Fig. 2.15). The response of the inferior mesenteric artery is entirely different. The blood flow to the colon will not change with ingestion of materials destined to be handled by the stomach and small bowel. However, if the material taken by mouth is handled entirely by the colon, flow in the inferior mesenteric artery will increase, but only after the material reaches the colon. One such substance is lactulose, which is handled entirely by the colon. When it is ingested, there is no change in the flow in the superior mesenteric or celiac arteries until 45 minutes later when the material reaches the colon. Then the peak systolic and end-diastolic velocities will increase in the inferior mesen-

FIGURE 2.15 The dramatic changes in the enddiastolic velocities recorded from the superior mesenteric artery after ingesting a variety of meals are shown. (Reproduced by permission from Strandness DE, Jr. Duplex scanning in vascular disorders, 2nd edn. New York: Raven Press, 1993: 69.)

FIGURE 2.16 Example of the changes in the velocity patterns from the inferior mesenteric artery after ingestion of lactulose. Left: fasting; right: after lactulose (see text).

teric artery (Fig. 2.16). These studies clearly show how the small and large bowel respond to different food challenges. However, it has not been possible to use the “food challenge” as a test for mesenteric insufficiency. It has not proven useful for separating cases with marginal disease of the mesenteric arteries from those that truly lead to the full-blown syndrome. Follow-up The success of intervention can easily be monitored using duplex scanning. Because the site and nature of the intervention are known, it is a simple matter to reexamine the area to assess the outcome. Although no group has experience with a large number of these patients, we have had the opportunity of using duplex scanning to detect problems with reconstructions that could be corrected before there was irretrievable loss of the repair. A few examples of how this can be done are in order. Case no. 1 This 49-year-old woman had a classic history of chronic mesenteric angina. A duplex scan revealed a high-grade stenosis of both the celiac and superior mesenteric arteries (Fig. 2.17). This was treated by a saphenous vein graft from the origin of the celiac artery to the superi-

Chapter 2 Ultrasonic Duplex Scanning

or mesentetic artery distal to the pancreas. The graft worked well and the patient was free of symptoms for 9 months, when they returned. A repeat duplex scan showed that there was no flow in the graft. However, it was possible to carry out a transluminal angioplasty of the superior mesenteric artery with complete relief of her symptoms. Case no. 2 This 65-year-old woman experienced marked weight loss associated with the fear of food. Every time she ate she developed abdominal pain and diarrhea. A duplex scan confirmed the presence of a high-grade celiac artery stenosis with occlusion of the superior mesenteric artery near its origin. A reversed saphenous vein graft was placed from the left common iliac artery to the superior mesenteric artery below the level of the pancreas. This worked very well for about 9 months, when the patient returned with recurrence of her symptoms. A repeat duplex scan showed the vein graft to be patent but with a tight stenosis noted at the origin of the vein graft. It was possible to correct this with a transluminal angioplasty at the site of the narrowing, with marked improvement in the velocities across this segment and relief of her symptoms (Fig. 2.18).

Renal Arteries The renal arteries are of great interest for two reasons: hemodynamically significant lesions are a common cause of hypertension, and bilateral lesions can be an important cause of renal failure. One of the problems with regard to this area of the circulation is that the renal arteries are difficult to access by almost any method. Several noninvasive tests have been designed to detect renovascular lesions, but these have been largely ineffective due to the high rate of false-positive and false-negative tests (57,58).

23

While renal artery stenosis has been considered to be uncommon, it appears to be more prevalent then previously thought. Because arteriography was the only available imaging method, it was applied in only very select cases. To give an accurate estimate of the numbers of patients with renal stenosis within the community of patients with hypertension is not possible, but there are some figures that are considered reasonably accurate. For example, within the entire population of patients with hypertension, it is estimated that 1% to 3% will harbor a lesion in the renal artery as the cause. However, if screening is limited to selected subgroups of hypertensive patients, the prevalence of a renal artery problem increases markedly. If screening is limited to patients who have blood pressure that is out of control, have malignant hypertension, or are in renal failure, the diagnostic yield will be in the range of 30% to 45%. Because of the location of the renal arteries, it is necessary to use much lower transmitting frequencies (2.0–3.5 MHz) to reach these arteries. Our own progress in this area has gone through several phases, each of which was important in helping us refine the method. These are as follows: 1.

2.

3. 4. 5.

Determine the feasibility of studying the renal circulation —we found that by studying normal subjects and patients in a fasting state to minimize the presence of bowel gas, complete studies could be done in up to 90% of patients (59,60). Develop diagnostic criteria that could be used to categorize normal renal arteries and those affected by both atherosclerosis and fibromuscular dysplasia. Develop algorithms that would characterize the degrees of narrowing into clinically useful categories. Prospectively test the algorithms against conventional arteriographic methods. Document the potential for using duplex scanning as a method of follow-up for patients who are being treated medically or by some form of intervention. In this regard, we were interested in determining which parameters might be most useful for documenting disease progression.

Diagnostic Algorithms

FIGURE 2.17 This lateral aortogram shows very tight stenoses in the celiac and superior mesenteric arteries of a patient with chronic mesenteric ischemia. (Reproduced by permission from Strandness DE, Jr. Duplex scanning in vascular disorders, 2nd edn. New York: Raven Press, 1993: 96.)

Although it was relatively simple to develop criteria for the documentation of narrowing and estimating the degree of stenosis for arteries that are superficially placed, this is not the case for the renal arteries. By virtue of their location, size and tortuosity, it is often difficult to determine precisely the angle of incidence of the sound beam with the artery. This becomes critical if one is to estimate the degree of narrowing or to utilize these studies for follow-up. From our studies of normal subjects, we found that the normal values for peak systolic velocities for the renal arteries was in the range of 100 ± 20 cm/s (11). If these values were used as absolute cutoff levels for documentation of disease, this might lead to an unacceptably

24

Part I Imaging Techniques FIGURE 2.18 The high-grade stenosis near the origin of the saphenous vein graft from the left iliac artery was treated successfully by balloon angioplasty. (Reproduced by permission from Strandness DE, Jr. Duplex scanning in vascular disorders, 2nd edn. New York: Raven Press, 1993: 224.)

high false-positive level, resulting in unnecessary arteriograms being performed. To avoid this potential problem, we elected to use a cutoff level of 180 cm/s, which is approximately 2.5 standard deviations above the normal range. Any detected peak systolic value below this level would be considered normal. With regard to “significant” stenoses, what level of narrowing is sufficient to activate the renin–angiotensin system and lead to the development of hypertension? The study by Haimovici and Zinicola has provided information in this regard (61). These authors found that, in a dog model, the renal artery had to be narrowed by 60% or more to produce a pressure drop and cessation of urine flow. It was this cutoff level of narrowing that we attempted to estimate by the duplex findings. Kohler et al., in our first retrospective study, found that one of the most useful parameters was the renal/aortic ratio (RAR) (59). This defines the ratio of the peak systolic velocity at the site of narrowing in the renal artery to that recorded from the aorta. If this ratio exceeded 3.5, it appeared to provide a satisfactory cutoff point for the detection of a stenosis of more than 60% diameter reduction (60).

By using the above criteria, the following results were obtained in prospective studies comparing duplex scanning against arteriography (11). 1.

2.

For detection of renal artery stenosis without consideration of the degree of narrowing, the sensitivity of the examination was 95% [95% confidence interval (CI) 90–100%]. The specificity was 90% (95% CI 71–100%). For the detection of a stenosis of more than 60% diameter reduction, the sensitivity was 90% (95% CI 84–99%). The specificity was 62% (95% CI 43–80%). Of the 74 sides with arteriographic confirmation, 10 sides were labeled by duplex scanning as having a stenosis of less than 60% diameter reduction. Only one of these arteries was normal by arteriography. The remaining disagreements were not about the presence or absence of disease but about the precise degree of narrowing. This type of disagreement is not unusual given the uncertainty of interpreting the degree of stenosis by arteriography.

Chapter 2 Ultrasonic Duplex Scanning

3.

4.

For the detection of a total occlusion of the renal artery, the absence of a detectable flow signal combined with a kidney length of less than 9 cm proved to be quite accurate. A total occlusion was detected in 10 of 11 cases. One of the early problems that duplex scanning has largely overcome is the detection of accessory renal arteries. With the availability of color/power Doppler, these are being recognized with increasing frequency. There is no doubt that an accessory renal artery with a pressure and flow-reducing lesion can be the cause of hypertension.

Screening Before Intervention The most important role for screening of patients with hypertension is to detect those cases with renal artery stenosis that might be treatable by endovascular or surgical methods. One additional benefit is to provide referring physicians with a firm diagnosis on which they can base their therapy. Another important and emerging indication is the patient who may be at risk of developing ischemic renal failure. This problem is becoming recognized as increasingly important. It has been estimated that up to 150,000 patients may be on chronic renal dialysis secondary to atherosclerotic involvement of both renal arteries. Our experience to date indicates that up to 25% of patients referred for a screening study will be found to have a stenosis of more than 60% diameter reduction. Two diseases are commonly found as a cause of renal artery stenosis. The most common is atherosclerosis, which commonly affects the origin and first portion of the renal artery. The other is fibromuscular dysplasia, which is primarily a disease found in women and tends to involve the mid and distal renal artery. These are multiple lesions (like a string of beads), which make it difficult to estimate arteriographically the hemodynamic effects of these lesions. The lesions are discovered only when they are the cause of hypertension. If they are successfully treated by either angioplasty or surgery, the blood pressure will either be improved or be cured. We have found that if an RAR of 3.5 or greater is not lowered to below 3.5 by angioplasty, the patient’s hypertension will not be improved. Natural History of Renal Artery Stenosis The relation between renal artery stenosis and hypertension is well known, but the natural history of the atherosclerotic lesions, including-their long-term outcome, is not well understood. This is due to the lack of accurate, safe, and repeatable testing procedures such as duplex scanning. Before considering the long-term outcome, it is necessary to review the types of studies that have been done, the type of information that can be obtained, and its interpretation. Long-term outcome is determined by the rate of progression of atherosclerosis. For our studies we did not include fibromuscular dysplasia since the number of these

25

patients is quite small. Ideally, we would like to document the rate of disease progression by noting the transition from lesser to higher grades of stenosis and total occlusion. This is feasible within rather broad categories, as follows: normal; diseased but less than 60% diameter reduction; greater than 60% diameter reduction; and total occlusion. However, we have documented a method using peak systolic velocity alone to suggest that progression has occurred when the degree of stenosis falls into the 60% to 99% category (62). We have shown conclusively the relationship between the degree of stenosis and loss of renal mass. More about the data shortly (62,63). The patients recruited into the study were from those referred to the Vascular Diagnostic Service at the University of Washington Medical Center. A patient found to have a renal artery stenosis was invited to participate in our long-term surveillance program. In addition to the criteria developed for the grading of disease in the renal artery, we found that renal length (a reflection of mass) is also an important parameter to measure as well as flow patterns and resistance to flow in the cortex of the kidney (8,9,56). There were 170 patients who entered the study, 85 men and 85 women. These patients were discovered by duplex scanning. If the lesions occupied the mid to distal renal artery and the patient was a female, she was excluded from follow-up. There were 295 eligible renal arteries for long-term follow-up. The mean duration of follow-up was 33 months (range 33 months to 7.2 years). In these long-term studies we were interested in several factors: 1) the relationship between the degree of narrowing and kidney length; 2) the relationship between the degree of stenosis and renal failure; 3) the rate of progression of renal artery stenosis; 4) those factors that appeared to be predictive of progression and outcome; and 5) the correspondence between disease of the renal arteries and other sites commonly affected by atherosclerosis. It is important to note that there were no kidneys with loss of length of more than 1 cm in the normal group or the stenosis group with less than 60% diameter reduction. When the loss of renal mass is considered by extent of disease (unilateral vs. bilateral), the patients with bilateral stenoses with more than 60% diameter reduction had three times the risk of developing a smaller kidney (43% vs. 13%, p < 0.02). The progressive loss of renal mass as related to time is shown in Fig. 2.19. With the increasing interest in endovascular therapy of renal artery stenosis and the use of stents, to what extent can ultrasound be used to not only visualize the stent but detect the development of recurrent stenosis and occlusion? Fig. 2.20 illustrates a renal stent that is protruding into the aorta. This will be quite common when the periaortic lesions are being treated. Although the initial evaluation of the long-term outcome focused on the loss of renal mass, a larger number of patients were subsequently included in the follow-up program, permitting a better picture of the problem of disease progression and associated risk factors with the renal

26

Part I Imaging Techniques

FIGURE 2.19 The loss of renal mass (length) as related to baseline degree of disease. (Reproduced by permission from Caps MT, Zierler RE, Polissar NL, et al. Risk of atrophy in kidneys with atherosclerotic renal artery stenosis. Kidney Int 1998; 53: 735–742.)

artery lesions. In our latest follow-up data there were a total of 170 patients each having at least one abnormal renal artery (62–66). The breakdown of these patients is as follows. There were 85 men and 85 women, of mean age 68 years. The follow-up interval was every 6 months. The mean follow-up duration was 33 months (range 3 months to 7.2 years). From the total of 295 eligible arteries, 45 were excluded either for prior intervention or for nondiagnostic studies. From the 295 sides available for follow-up, the renal artery was normal in 56, had a stenosis of less than 60% reduction in 96, a stenosis of more than 60% reduction in 143, and was totally occluded in 21. The loss of renal mass as related to the initial degree of disease is shown in Fig. 2.19. Interestingly, the incidence of progression to occlusion was 10%. As noted, there was a statistically significant relationship between the baseline level of disease and progression. The estimated 3-year cumulative incidence of progression was 18%, 28%, and 49% for renal arteries classified as normal, < 60%, and > 60%. The therapeutic implications of these studies will require more time to evaluate; however, it is clear that atherosclerosis, as in other areas of the circulation, continues to progress in an unpredictable fashion. Of course, if the progression occurs in both renal arteries, the outcome could be renal failure. It is here that earlier intervention by surgical or endovascular means may improve renal function and prevent the patient from going on to dialysis.

The Venous System Acute Deep Vein Thrombosis The most common vascular disorder that develops in the hospital is acute deep vein thrombosis (DVT). The disease

FIGURE 2.20 This color Doppler longitudinal view of the abdominal aorta at the level of the renal arteries clearly shows the presence of a stent which has protruded into the aorta. Stents are readily seen by duplex scanning.

can occur at all levels of the venous system, but its localization must be taken into account when reviewing outcome. For example, the early studies done with 125Ilabeled fibrinogen showed that the earliest sites for the development of venous thrombi were the sinuses in the soleal muscle and the sinuses of the venous valves (67). At this stage the thrombi did not produce symptoms or signs. However, if left untreated, up to 20% of the thrombi progressed to involve the posterior tibial and peroneal veins up to, and often including, the popliteal vein. However, this is not the pattern of involvement that is seen when patients present with symptoms and signs secondary to the development of DVT. More about this later. The term thrombophlebitis is commonly used to describe the involvement of the deep venous system, but it is not appropriate because the process is usually bland and does not lead to a marked inflammatory reaction in the vein or surrounding tissues. This is in sharp contrast to the process seen in the superficial veins, where the inflammatory response is very prominent and is one of its distinguishing features. It is my opinion that these two processes are separate and distinct and should not be considered in the same category. The treatment and potential for future complications is also entirely different for these two components of the venous system. Bedside Diagnosis There is no doubt that acute DVT can lead to the development of pain, swelling, and the appearance of prominent superficial venous collaterals. However, these are not specific enough to make them a reasonable set of guidelines for the diagnosis to be made (68, 69). It is also well known that the process is usually bland without producing any symptoms or signs. One of the most misleading historical factors that has led to confusion in the field is the use of Homans’ sign, which is positive when there is pain in the

Chapter 2 Ultrasonic Duplex Scanning

calf with forceful dorsiflexion of the foot, but is very nonspecific and must not be used at all in the course of an examination. The only situation in which the bedside diagnosis is adequate is with phlegmasia cerulea dolens (massive iliofemoral venous thrombosis). When this develops, the limb is massively swollen from the level of the thigh to the ankle. There is also severe pain, cyanosis, and in rare cases, a marked reduction in arterial inflow to the point where limb viability may be in question. No further diagnostic tests are needed for this syndrome to be recognized. The patients that should be scanned for acute DVT include the following: any patient suspected of having the disease; those with suspected or proven pulmonary emboli; those with unexplained leg swelling after orthopedic, pelvic, or vascular surgery; and patients with chronic leg swelling of uncertain etiology. Four ultrasound criteria are used to establish the diagnosis of DVT (70): 1) thrombus visualization; 2) incompressibility of the vein; 3) absence of spontaneous flow; and 4) loss of flow phasicity. Thrombus visualization is an obvious and certain way of making the diagnosis. However, the method is 92% specific but only 50% sensitive. The low sensitivity is due to the fact that some thrombi are not echogenic enough to be seen. In addition, it is not yet certain during which phases of their development thrombi are most likely to be echogenic. One of the most widely applied diagnostic methods is compression of the venous segment with the head of the transducer (62). This is always done with the vein visualized in a transverse view. If the two walls of the vein cannot be totally coapted with pressure, the test is positive. This maneuver has a sensitivity of 79% and a specificity of 67%. The problems with this method relate to those sites that are not readily compressible and include the inferior vena cava, the common iliac veins, and the superficial femoral vein in the adductor canal. Some investigators suggest that the ultrasound test only involve the common femoral and popliteal vein—use only compression and not include the calf veins or those proximal to the inguinal ligament. This also does not include the use of color/ power Doppler or the flow patterns that can be of use (71). This cannot be accepted as state-of-the-art and is, in fact, dangerous since it ignores key parts of the venous system. Today, with the advances in color/power Doppler combined with spectral analysis, we are able to identify with certainty the tibial/peroneal veins, the gastrocnemial veins and the soleal sinuses. The information obtained with pulsed Doppler ultrasound is very useful in establishing the diagnosis (70). Normally, venous flow is spontaneous in all proximal veins. In the veins below the knee, it may or may not be detected depending upon factors such as the ambient temperature. In a cool environment with vasoconstriction, cutaneous blood flow may be markedly reduced, leading to an overall reduction to the below-knee region. When spontaneous venous flow is not detected particularly from the tibial/peroneal veins, it is necessary

27

to augment flow by foot compression to be certain that the vein being studied is patent. The absence of spontaneous flow is highly specific to venous thrombosis involving the veins from the popliteal vein to the inferior vena cava. Of interest is the fact that the anterior tibial vein is rarely the site of venous thrombosis for reasons that are poorly understood. The anterior tibial vein is not routinely examined for the presence of thrombi. Because flow in the veins of the lower limb is normally dominated by respiratory events, the phasicity of flow is also a very useful parameter. Normally, with inspiration and descent of the diaphragm, intraabdominal pressure increases and venous flow will decrease. The opposite occurs with expiration. The absence of phasic flow is 92% sensitive and is specific for the diagnosis of DVT in the proximal venous segments. As noted above, this may not apply to the veins below the knee where the absence of spontaneous flow is not synonymous with acute DVT. Duplex scanning has largely replaced venography as the diagnostic test of choice. There are some circumstances in which the duplex method cannot be used, for example, when patients are in long leg casts. Another area of some difficulty is the patient with a past history of DVT who is suspected of having another acute episode. If the patient had been previously studied by duplex scanning, the problem would not be difficult, but in most instances this is not the case. As the previous DVT may have led to some chronic changes in the lumen and wall of the vein, it is often difficult to be certain that the findings are specific enough to warrant the diagnosis of recurrent DVT. In this setting it may be necessary to resort to venography, but even here it may be difficult unless dye is seen sleeving around a thrombus—the so-called railroad track sign. However, it is known that a major vein that is the site of an acute DVT will have a larger diameter than its companion in the opposite leg. When the vein has been irreversibly damaged by a previous episode of DVT, its diameter will be smaller than its companion in the opposite leg (72). Chronic Venous Disease Patients who fall into the chronic venous disease group are easily separated into those with primary and those with secondary venous disease. In general, the patients with primary venous disease have varicose veins without associated involvement of the deep venous system. Those patients who have a previous history of DVT and then go on to develop further problems are placed in the secondary category—the post-thrombotic syndrome. The presentation and problems with these two groups of patients are different. However, for both groups of patients, the studies are directed to the assessment of both residual obstruction and valve function. Evaluation of Valve Function The evaluation of valve function is difficult; therefore, it is necessary to review how this is done and the type of information that can be obtained. From a physiologic

28

Part I Imaging Techniques

standpoint, venous valves will close when a reverse transvalvular pressure gradient is produced (73). A small amount of reflux can and will normally occur before valve closure is completed. At present duplex scanning is the only method that can be used to examine specific venous segments in both the superficial and deep venous system. The problems with this and other methods of study relate to the manner in which reflux is induced and how it can be quantified. Most studies in the clinic or at the bedside are with continuous wave Doppler ultrasound. With this simple hand-held device, directional changes in venous blood flow are easily detected when a reverse transvalvular pressure gradient has been created. However, the manner in which the transvalvular gradient is created is a source of some uncertainty. In practice, most physicians have used the Valsalva maneuver and limb compression to induce reverse flow. In addition, most studies are performed with the patient in the supine position, which is not ideal. The veins should be maximally dilated to obtain the optimal results and this can only be realized if the patient is upright or nearly 50 (74). We have conducted a series of studies to develop and document the optimal method of study for the patient with chronic venous disease. It is my view that studies of this type must become standard if we are to make any sense out of many aspects of these difficult and often perplexing problems. First, while the Valsalva maneuver can induce reflux in most cases, there can be problems that greatly limit its application. For example, if there is a competent valve in the iliac or common femoral veins, reflux in the superficial femoral vein cannot be detected. In addition, the farther one moves away from the inguinal area, the less effective the Valsalva maneuver becomes. Limb compression is another method of suddenly increasing the transvalvular pressure gradient but, like the Valsalva maneuver, it has serious problems. It is very ineffective at the thigh level but is fairly good below the knee, where a forceful compression is much easier to perform. To get around many of the problems with Valsalva and limb compression, we developed the cuff inflation–deflation method for documenting reflux at all levels of the venous system, superficial and deep (64). The patients are studied in the upright position to ensure maximal venous filling. The pneumatic cuffs used vary in size from 24 cm for the thigh, to 12 cm for the calf, and 10 cm for the ankle. These cuffs are inflated by an automatic cuff inflator. The pressures used are 80 mmHg for the thigh, 100 mmHg, for the calf and 120 mmHg for the foot. The cuffs are rapidly inflated in 3 seconds, but most importantly, the cuff is completely deflated in less than 0.3 seconds. To determine valve incompetence, the transducer of the duplex scanner is placed less than 5 cm cephalad to the end of the cuff. As the cuff inflates, the vein beneath the cuff is emptied. With rapid cuff deflation, blood will reflux into the emptied venous segment if the valves within that region are incompetent. This method works well for both

the superficial and deep veins from the level of the pelvis to the ankle. It is the only method that provides objective, numerical data that can be referenced to normal values. In our early studies with the cuff method, we were able to determine that normal venous valves will close in less than 0.05 s in 95% of the normal venous segments (Fig. 2.21) (74). If one cannot use the cuff method, it is possible to use a minus 10 degrees Trendelenburg and use the Valsalva maneuver for the proximal veins and limb compression for the distal venous segments. When this is used, normal valve closure time is 2 s or less. With these normal studies as the background, we conduced several prospective studies in patients with acute DVT who were willing to be placed in a follow-up program. From these prospective and long-term studies, we have characterized many of the changes that take place after an episode of DVT. Many of the changes that we have documented explain a good deal about the natural history of patients with DVT. With regard to the problem of the post-thrombotic syndrome, it is not yet possible to predict who will develop the advanced changes that are commonly associated with this problem. Two outcomes are possible after an episode of DVT. One is the development of chronic venous obstruction and the other is the development of venous valve incompetence. Both processes can be present, but venous valvular incompetence is more common.

FIGURE 2.21 Venous valve closure times in normal subjects. The reflux duration was the time to valve closure after cuff deflation. Measurements were from the common femoral vein (cfv), superficial femoral vein (sfv), profunda femoris vein (prf), popliteal vein (pop), posterior tibial at calf level (ptc), and posterior tibial at the ankle (pta). (Reproduced by permission from van Bemmelen PS, Bedford G, Strandness DE, Jr. Ouantitative segmental evaluation of venous valvular reflux with ultrasonic duplex scanning. J Vasc Surg, 1989; 10: 425–431.)

Chapter 2 Ultrasonic Duplex Scanning

The consequences of chronic venous obstruction are different from those associated with valvular incompetence. Venous claudication may develop in patients who have chronic obstruction of the iliofemoral venous segment. They often have patent veins and competent valves distal to this level. With exercise, which has to be quite severe, the marked increase in arterial flow cannot be emptied in a normal manner. This leads to venous congestion of the thigh, which is very painful (75). The patient complains of a bursting pain that can be relieved only by elevation of the limb. Beginning with the studies of Killewich et al., we have been interested in the relation between spontaneous lysis of venous thrombi and venous valvular reflux (76). Several things have been learned from these prospective studies. The major finding can be summarized as follows: lysis starts early after the DVT and is progressive in most patients; recanalization of the occluded venous segments is common (76); and the time of recanalization (lysis) is important in determining which valves will become incompetent. We found that the earlier lysis takes place, the more likely it is that valve function will be preserved (77–80). Valves in veins not involved in the thrombotic process rarely become incompetent during follow-up; and after complete recanalization, the vein diameter will return to a level comparable to that of the noninvolved vein in the other leg. On the other hand, if the thrombus is not completely lysed, the diameter of the vein will be less than that of its partner in the contralateral limb; if recanalization occurs (partial or complete), the ability of the vein to dilate in response to a Valsalva maneuver remains normal (81).

Who Should Be Studied? There are compelling reasons for studying patients with a variety of vascular conditions, but there is little agreement as to which patients with chronic venous disease should be studied and for what purpose. My own approach is as follows.

29

The distinction between the primary and secondary forms of venous disease is important. Because the deep venous system is rarely involved with primary disease, it is very rare for these patients to develop the signs and symptoms of the post-thrombotic syndrome. Post-thrombotic Syndrome While there is little disagreement as to what can lead to the development of the syndrome, there are several unanswered questions that may be answered by the more widespread use of duplex scanning (80). For example, up to one-half of patients with the classic findings of the postthrombotic syndrome provide no historical clues as to why they sustained damage to the deep veins of the leg. There is no history of a previous episode of DVT. This is not surprising because DVT can be bland and produce few or no symptoms. Interestingly, the duplex ultrasound findings in patients with deep vein damage but without a history of DVT are nearly identical to those in patients with a definitive history of the problem (80). The similar findings suggest that extensive venous valvular damage can occur even in patients who have DVT but who never develop symptoms from the process. Which valves are of importance? As duplex scanning can be used to characterize all of the major veins, both superficial and deep, it is possible to relate the extent of the venous damage to patient outcome. The venous valves increase in number as one proceeds toward the foot. In fact, in the inferior vena cava there are no valves. In the iliac veins, valves are not invariably present, but as one moves in a caudal direction to the proximal superficial femoral vein, the greater saphenous, and profunda femoris veins, valves are commonly found. Two to three valves are often found in the superficial femoral vein, but again, this is extremely variable. One or two valves may be found in the popliteal vein. Below the knee there are hundreds of valves, which says a great deal about the importance of this region for continued and useful function of the leg.

Primary Varicose Veins If one accepts the fact that primary varicose veins generally involve only the superficial veins, there would be little need to study them unless some form of intervention were planned. Even then, what might be accomplished by a preoperative duplex scan? If one is contemplating a vein stripping, it is important to determine whether the entire greater saphenous vein will have to be removed. It is possible to restrict the procedure to only the involved veins if one has precise information about the status of the superficial system from the level of the groin to the ankle. Other valuable information that might not be anticipated is the finding of valvular incompetence in the deep system. When this is found, the patient should probably be placed in the secondary category even though there may be no history of a previous episode of DVT.

Transcranial Doppler Ultrasound Aaslid et al., in 1982, first reported the use of transcranial Doppler (TCD) methods for the study of the intracranial circulation (82). This method used a pulsed system of 2 MHz that could successfully penetrate the skull to provide flow information relative to the basal arteries. It was also shown that several anatomic ports could be used to access these arteries. These include the orbit, the transtemporal region, and the foramen magnum. The method as originally developed made use of the hand-held TCD unit, but it is now available with nearly all duplex scanners. The advantage of the use of TCD as a duplex method is clear, but there have been no studies that have shown it to be superior in terms of the information obtained or its use clinically. This will require much more work before its role can be clearly identified. The method

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Part I Imaging Techniques

has been proposed as useful for the following states: the detection of intracranial stenoses and occlusions; estimating the effect of extracranial lesions on flow velocity in the basal arteries; documentation of flow direction in the basal arteries; monitoring flow changes in the basal arteries during carotid endarterectomy; detection of arteriovenous malformations; monitoring flow velocity after subarachnoid hemorrhage to document the course of vasospasm; detection of microemboli; documentation of the ability of the brain to autoregulate in the presence of severe extracranial arterial disease; and documentation of brain death. Examination Method For a complete review of the method employed to interrogate the basal arteries with TCD, the reader is urged to review the work of Otis and Ringelstein (83). The windows chosen will determine which arteries can be detected and the information that is desired. Fig. 2.22 shows the arteries that can be detected along with the nomenclature used. 1.

2.

3. 4.

The transtemporal approach is used to detect flow in the M1 and N2 segments of the middle cerebral arteries (MCA). For the detection of these arteries, the anterior orientation of the sound beam is used. In addition, the C1 segments of the carotid siphon, the A1 segment of the anterior cerebral artery, and often the anterior communicating artery can be detected. With the beam directed in a posterior direction, the P1 and P2 segments of the posterior cerebral and the most anterior portion of the basilar artery may occasionally be detected. The important posterior communicating artery may also be studied in some patients. The transorbital approach is used to study the anterior cerebral circulation. From this site, the ophthalmic artery and the C3 segment of the carotid siphon can be detected. The suboccipital approach is the view used to screen the vertebral and basilar arteries. The submandibular approach is used if one wishes to track the distal internal carotid artery. With this window, it is possible to detect flow in the distal internal carotid artery. This approach is not very commonly used.

Study Parameters A direction-sensing pulsed Doppler is used for transcranial studies, so the parameters include the peak systolic and mean velocity and the direction of blood flow. The dimensions of the basal arteries cannot be measured, so it is not possible to measure volume flow by this approach. To estimate the functional reserve of the brain, the changes in blood flow velocity with hypocapnia and hypercapnia are determined. For the neurosurgeon, this may be the best method to determine which patients are most likely to benefit from extracranial-to-intracranial bypass grafting when the internal carotid arteries are occluded. The values of velocities for the middle cerebral, anterior cerebral,

FIGURE 2.22 The arteries that can be examined by TCD ultrasound and the position of the probe to insonate both tile anterior (A) and posterior (B) aspects of the circle of Willis. In A, the line XX¢ indicates the frontal plane that runs through placement of the probe on either side and perpendicular to the sagittal midline plane of the skull. Z¢ indicates the position of the intracranial carotid bifurcation. The X¢Z¢ distance is generally 63 ± 5 mm. The angle μ is the angle at which the probe is angled anteriorly to obtain signals from the middle and anterior cerebral arteries. The angle is in the range of 6° ± 1.1°. The angle w indicates the angle that is used to insonate the top of the basilar artery (T) and the P1 segments (P¢) on both sides. This angle was found to be in the range of 4.6° ± 1.2°. The basilar artery bifurcation could be detected at depths of 78 ± 5 mm corresponding to the distance XT or X¢T. Y indicates the fictional point at which the sound beam transits the contralateral skull, which is about 2–3 cm posterior to the external acoustic meatus. The P2 segments can also be insonated if the beam is directed even more posteriorly and caudally (X¢P). W lies approximately 5 cm behind the contralateral external acoustic meatus. (C) Basal and cerebral arteries of the circle of Willis. OA, ophthalmic artery; CS, carotid siphon (C1–C3); ICA, internal carotid artery, ACA, anterior cerebral artery (A1¢A2); ACoA, anterior communicating artery; MCA, middle cerebral artery (M1M2); PCA, posterior cerebral artery (P1P2) PCoA, posterior communicating artery; BA, basilar artery, VA, vertebral artery. (Reproduced by permission from Otis SM, Ringelstein EB. Transcranial Doppler sonography. In Zweibel WJ. Introduction to vascular ultrasonography, 3rd edn, Philadelphia: WB Saunders, 1992: 149.)

Chapter 2 Ultrasonic Duplex Scanning

posterior cerebral, and basilar arteries in normal subjects are quite constant and reproducible and tend to decrease with age (85).

Clinical Applications Detection of Intracranial Arterial Stenosis and Occlusion Not surprising, the findings that signify arterial narrowing of intracranial arteries are very similar to those found elsewhere: increased flow velocity at the site of narrowing and spectral broadening (85,86). Although these changes are specific for detection of narrowing, it is not yet possible to estimate the degree of stenosis in these small arteries. It must also be recognized that other lesions can lead to an increase in flow velocity such as arteriovenous malformations. However, in this case the flow changes will not be focal as they will with a stenosis. Occlusions are recognized by the absence of flow. The pitfalls associated with these findings are outlined by Otis and Ringelstein (83).

Assessment of Flow in the Basilar Arteries A potential benefit of TCD is that the effects of varying degrees of extracranial arterial disease on flow velocity in the basilar arteries and the potential contribution of the various components of the circle of Willis. For example, with a very tight internal carotid artery stenosis or occlusion, it is possible to determine by which route and from which arteries the middle cerebral artery receives its flow (83–86). In many cases these findings are quite specific, but it is not yet clear under what circumstances the information can be used from a diagnostic standpoint. For example, if a patient presented with an ischemic event and was found to have no extracranial arterial lesions, but a stenosis was found or suspected in the MCA or siphon, one might assume that this is the responsible vessel. How should TCD be used for patients with suspected extracranial arterial disease? My recommendation is that it be done only if there is no detectable disease in the carotid bulb or the disease found is not sufficient to explain the clinical presentation. There is no justification for doing this examination on all patients having a duplex scan study of the extracranial arterial circulation.

Assessment of Flow in the Posterior Circulation One of the most difficult areas to evaluate clinically is the basilar circulation. Vascular surgeons are often asked to see patients who are suspected of having the subclavian steal syndrome (87,88). These patients are suspected largely because of the nature of the clinical presentation, which varies considerably due to the nonspecific nature of the symptomatology. In general terms, these patients may be dizzy, have drop attacks, and, on very rare occasions,

31

present with exercise-induced dizzy spells (76,78). The patients are initially suspected when by duplex scanning a high-grade stenosis or occlusion of the subclavian artery is found with reversal of flow in the vertebral artery. In our laboratory, we identified 43 patients with reversal of flow in the vertebral artery. Only 7% of this group had symptoms that were compatible with the subclavian steal syndrome. However, the problem is less difficult if the innominate artery becomes involved (89). When this occurs, and there is either a very high-grade stenosis or occlusion, the patients are very likely to become symptomatic with exercise of the ipsilateral arm. Given the above, it is not yet clear what role TCD might play in unraveling this problem. Clearly, duplex scanning can provide the clue as to the site of disease, but this must be combined with a compatible clinical picture (79). We have used TCD to see if it might help sort out some diagnostic dilemmas with the posterior circulation, but unfortunately it has been of little assistance.

Monitoring During Carotid Endarterectomy One area of great potential appeal for TCD is the monitoring of patients undergoing the very common procedure of carotid endarterectomy. It is a relatively simple matter to continuously monitor flow velocity in the MCA during the operation (90–92). There are two areas in which the procedure might have merit. One is with regard to those who need a shunt to avoid a perioperative stroke. Another intriguing area is the detection of emboli during endarterectomy, and their sequelae (91). There is no doubt that TCD can detect emboli and may with more time and experience permit some conclusions as to their size, nature, and potential for causing problems. A study reported by Ackerstaff and Schroeder of 55 patients who were continuously monitored during endarterectomy documented 75 embolic episodes (91). However, in only one case could this be related to the development of a stroke. While it is difficult to prove that one can reduce the stroke rate associated with endarterectomy, there is information combined with intraoperative duplex examination of the endarterectomized segment that can be of assistance.

Vasospasm After Subarachnoid Bleeding Somewhere between 4 and 14 days after an episode of subarachnoid bleeding, cerebral vasospasm can develop. This can have a severe effect on cerebral blood flow and may lead to death if not corrected. It has been noted that TCD is a useful method of monitoring these blood flow changes, permitting intervention before the changes are irreversible (93).

Autoregulation of Cerebral Blood Flow The cerebral circulation can maintain cerebral blood flow within a normal range even with mean blood pressures as

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Part I Imaging Techniques

low as 50 mmHg. One method of testing this response is to use TCD to test the functional reserve of the cerebral arteries. The most convenient stimulus to use is carbon dioxide. In order to do this, it is necessary to monitor the MCA while having the subject breathe increasing concentrations of CO2 (2%, 3%, 4%, and 5%). Since CO2 mainly affects the small cortical vessels and not the MCA itself, any changes in velocity should be a reflection of a change in volume flow (94). If there is no response or a limited increase in blood flow to increasing amounts of CO2, it is presumed that the autoregulatory mechanism has broken down. Study of this response to CO2 may be of importance in selecting patients who could be candidates for the extraintracranial bypass grafting. Although this operation was discarded as being of little value in patients with internal carotid artery occlusion, there was no attempt to separate those patients who were able to autoregulate normally from those who were not. This may well be the only way to select potential candidates for extra-intracranial bypass grafting. The theory is that, if there is no longer any vasomotor reserve, any further reduction in pressure or flow is likely to precipitate an ischemic event.

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89.

90.

91.

92. 93.

94.

velocity in the basal arteries. J Neurosurg 1982; 57: 769–774. Otis SM Ringelstein FB. Transcranial Doppler sonography. In: Zweibel WJ, ed. Introduction to vascular ultrasonography. Philadelphia: WB Saunders 1992: 145–171. Ringelstein EB, Zeumer H, et al. Transkranielle Dopplersonographie der hirnversorgenden arterien: Atraumatische diagnostic von stenosed and verschluessen des carotissiphons und der a cerebri media. Nevenartz 1985; 56: 296. Ringelstein EB. A practical guide to transcranial Doppler sonography. In: Weinberg J, ed. Noninvasive imaging of cerebral vascular disease. New York: Alan R Liss, 1989: 75. Spencer MP, Whisler D. Transorbital diagnosis of intracranial arterial stenosis. Stroke 1986; 17: 916–921. Reivich M, Hollins HE, et al. Reversal of blood flow through the vertebral artery and its effects of cerebral circulation. N Engl J Med 1961; 265: 878–885. Bornstein NM, Norris JW. Subclavian steal syndrome: a harmless hemodynamic phenomenon. Lancet 1986; 2: 303–305. Grosveld WJHM, Lawson JH, et al. Clinical and hemodynamic significance of innominate artery lesions evaluated by ultrasonography and digital angiography. Stroke 1988; 19: 958–962. Ackerstaff RGA, Grosveld WJHM, et al. Ultrasonic duplex scanning of prevertebral segment of the vertebral artery in patients with cerebral atherosclerosis. Eur J Vasc Surg 1988; 2: 387–393. Ackerstaff RGA, Schroeder TV. Intraoperative monitoring with transcranial Doppler sonography. In: Bernstein EF; ed. Vascular diagnosis. St. Louis: CV Mosby, 1993: 361–366. Bernstein EF. Role of transcranial Doppler in carotid surgery. Surg Clin North Am 1990; 70: 225–234. Harders A, Gilsbach JM. Time course of blood velocity changes related to vasospasm in the circle of Willis measured by transcranial Doppler ultrasound. J Neurosurg 1987; 66: 718–728. Markwalder TM, Grolimund P, et al. Dependency of blood flow velocity in the middle cerebral artery on end-tidal carbon dioxide partial pressure—a transcranial Doppler study. J Cereb Blood Flow Metab 1984; 4: 368–372.

Haimovici’s Vascular Surgery, 5th Edition Edited by Enrico Ascher Copyright © 2004 by Blackwell Science

CHAPTER 3 Duplex Arteriography for Lower Extremity Revascularization Enrico Ascher and Anil Hingorani

Contrast arteriography (CA) is still considered the gold standard imaging modality for patients in need of lower extremity revascularization procedures. However, it continues to be associated with local and systemic complications, and patients in general are demanding less invasive alternatives. Encouraged by recent technological advances in duplex ultrasonography, several authors have expressed an increasing interest in the use of duplex arteriography (DA) as a potential replacement of preoperative standard CA for peripheral arterial imaging. Thus, it is not surprising that DA is being investigated for this purpose (1–3). Although some authors have demonstrated an acceptable correlation between arteriography and DA (4–12), others have been less than enthusiastic and continue to advocate preoperative or pre-bypass arteriography (13–16). Some of the factors that may explain these discrepant results include: 1) use of older duplex equipment; 2) inexperience of the vascular technologist(s); 3) lack of formal training and protocols for DA; 4) less commitment in terms of time and effort to perfect the technique; 5) reluctance of the surgeon to give up the visual effect of a complete, uninterrupted study as provided by arteriography; and 6) severe calcification preventing adequate vessel insonation, and other local barriers making DA less feasible in some of these patients. In an effort to explore the use of DA for patients undergoing lower extremity revascularizations, we have used DA during a 4-year period in 466 patients. In addition, some of the techniques that we have used to obtain adequate data from DA for the lower extremity revascularization even in disadvantaged situations are considered.

Material and Methods From January 1, 1998 to May 31, 2001, 466 patients, of whom 262 (56%) were men, underwent 485 lower extremity revascularization procedures at our institution. Preoperative imaging consisted of DA alone in 449 procedures and DA and CA in 36. An attempt to image from the distal aorta to the pedal arteries was made in all the patients. The selection of optimal inflow and outflow anastomotic sites was based on a schematic drawing following DA examination. Inflow disease and the conduit were also assessed by intraoperative pressure gradient (IPG) between the distal anastomosis and radial arteries.

Duplex Scan Examination Two registered vascular technologists performed all duplex scan examinations using either ATL HDI 3000 or 5000 scanners. The protocol included mapping of the arterial system from the mid-abdominal aorta to the pedal vessels. The test starts by placing the patient in the lateral decubitus position opposite to the side of interest, with slight ipsilateral knee and hip flexure for insonation of the distal aorta and the ipsilateral common and external iliac arteries. This position improves the ultrasound field of view by shifting the gas-containing bowel away from the probe (Figs. 3.1–3.3). Next, the patient is placed in the supine position, with mild genuflection and thigh abduction for visualization of the common, superficial, and deep femoral arteries. Still in this position, the aboveknee popliteal artery segment is evaluated from a medial

35

36

Part I Imaging Techniques FIGURES 3.1–3.3 Duplex arteriography of the iliac arteries.

1

2

3

Chapter 3 Duplex Arteriography for Lower Extremity Revascularization

approach and the below-knee segment from a posterior approach. The examination continues by moving the probe medially to insonate the posterior tibial artery and its plantar branches. The patient is then returned to the original position for visualization of the tibioperoneal trunk and peroneal arteries, as well as the origin of the anterior tibial artery. This is accomplished by placing the probe just posteriorly to the lower border of the fibula. The remainder of the anterior tibial artery is visualized by positioning the probe between the tibia and the fibula. Lastly, the dorsalis pedis artery and its metatarsal branches are insonated with the patient in the supine position (Figs 3.4–3.8). During DA, we routinely perform a venous mapping to identify usable veins for harvest, thereby avoiding the additional time and energy needed in pursuit of vein of good quality and caliber. If no usable vein is identified and a bypass to the tibial vessels is required, the diameter and quality of the tibial veins may be measured for a possible prosthetic bypass with a distal fistula. Finally, examination of the subclavian-axillary segment may be performed as a possible inflow source for debilitated patients with severe aorto-iliac disease. This is accomplished without the risk of an additional thoracic aortogram or the time needed for an additional thoracic magnetic resonance angiography (MRA) scan. A variety of scanheads is utilized to obtain highquality B-mode, color, and power Doppler images as well as reliable velocity spectra. Curvilinear 5–2 MHz and phased-array 3–2 MHz probes are used for aorto-iliac scanning. A linear 7–4 MHz probe is used for visualization of the femoral, popliteal, and tibial vessels. High resolution of compact linear 10–5 or 15–5 MHz scanhead allows better visualization of superficial arteries on the ankle and foot. A peak systolic velocity (PSV) ratio ≥2 reflects a lesion ≥50% stenosis, a PSV ratio ≥3 is used to confirm a ≥70% stenosis. Any discrepancies are communicated to the operating surgeon. The arterial segments are classified as normal or mildly diseased (< 50%), significantly stenosed (≥50%), occluded or not visualized. Vessel wall thickness and degree of calcification are reported to aid in the choice of anastomosis sites. A more precise evaluation of arterial size, length, and degree of narrowing, as well as of plaque characteristics, is performed for single focal or sequential lesions suitable for balloon angioplasty and/or stent placement. A color-coded map of the arterial tree is drawn to facilitate reading by the surgeon (8,12). In general, however, color and power Doppler are used primarily, and B-mode and velocity spectra are used to supplement these data, especially in the presence of long lesions or multiple lesions. Since the status of the branches of the arteries can also add valuable data for the surgeon, visualization of as many tibial and pedal branches as possible, including malleolar, plantars, tarsals, deep plantar arteries, and branches of the named vessels, is also performed during DA. We found that the high-frequency probe (10–15 MHz) can be especially useful in this portion of the protocol.

37

Contrast Arteriography In our series, standard percutaneous preoperative CA with digital subtraction arteriography (DSA) was obtained when DA was not able to provide adequate imaging of arterial segments essential for limb revascularization (n = 36). During this time period, these were the only CA images obtained by our service. Patients generally underwent arterial reconstruction the day after CA if there was no worsening of renal function. Patients who underwent mapping but had not undergone revascularization (53 refused, two not needed, six too ill for revascularization) or who were mandated to have a preoperative angiogram by study or training protocols (n = 7) were excluded from this series.

Intraoperative Evaluation Completion arteriography was performed in 210 (43%) cases to evaluate patency of the distal anastomosis and runoff status. All of the infrapopliteal interventions and any bypasses with difficult anastamoses or conduits underwent completion angiography (Figs. 3.9–3.15). The aortoiliac segment was evaluated at the completion of the procedure by measuring the pressure gradient between the distal anastomosis and radial arteries in patients undergoing infrainguinal bypasses. A gradient > 20 mmHg of systolic pressure warranted on-table angiography and repair of the inflow lesions and assessment of the conduit.

Results Indications for surgery were severe claudication in 91 (19%) limbs, tissue loss in 197 (40%), rest pain in 113 (23%), acute ischemia in 46 (10%), popliteal aneurysm in 18 (4%), superficial femoral artery aneurysm in one, abdominal aortic aneurysm in one, and failing graft in 18 (4%). Age ranged from 30 to 97 years [mean 72 ± 12 (SD) years] and risk factors such as diabetes, hypertension, use of tobacco, coronary artery disease, and endstage renal disease were present in 45%, 45%, 44%, 44%, and 13% of the patients respectively. A total of 121 (25%) limbs had at least one previous ipsilateral revascularization. During this time period, the distal anastomosis was to the popliteal artery in 173 cases (100 to the below knee popliteal) and to the tibial and pedal arteries in 255. Inflow procedures to the femoral arteries, embolectomy, thrombectomy, balloon angioplasty, and patch angioplasty accounted for the remaining 57 cases. The specific procedures performed in these patients are shown in Tables 3.1 and 3.2. The mean DA time was 66 ± 20 (SD) min (15–150 min). Owing to difficulties in evaluating some of the arterial segments using DA alone (Table 3.3), additional preoperative imaging (CA) was deemed necessary in 36 cases (7%) as a result of extensive ulcers (4), edema (8), severe arterial wall calcification (4), uncooper-

38

Part I Imaging Techniques FIGURES 3.4–3.8 Duplex arteriography of the infrapopliteal vessels.

4

5

6

Chapter 3 Duplex Arteriography for Lower Extremity Revascularization

39

FIGURES 3.4–3.8 (continued)

7

8

ative patient (4), low flow (4), obesity (8), multiple previous surgeries (13), poor visualization of the origin of anterior tibial artery (1), and very poor runoff (18). Table 3.4 demonstrates differences found between intraoperative findings and preoperative DA. Twelve-month primary patency for femoral above-knee popliteal artery bypass with PTFE was 95%, femoral below-knee popliteal bypass with vein 95%, femoral below-knee with PTFE was 90%, femoral distal with vein was 80% and femoral distal with PTFE was 77%. Overall, 6, 12, and 24 months’ secondary patency rates were 86%, 80%, and 66% respectively. During the entire time period, 34 grafts closed and 21 underwent revision for failure.

The Technology The turn of the millennium has been marked by an accelerated technological progress that stimulated the

development of less invasive treatment and diagnostic procedures. Accordingly, CA has been challenged by the development of MRA and duplex ultrasonography. In the last few years, computer technology improvements related to the ultrasound industry have produced scanners with higher definition B-mode image and more refined color-flow features. Nonetheless, duplex ultrasonography’s most popular feature remains the hemodynamic assessment by velocity spectral waveform PSV ratio, which directly measures the degree of arterial narrowing. However, the presence of collateral branches, tapering or dilation of adjacent arterial segments, arterial bifurcation or tortuosity, presence of close sequential lesions, and inaccuracies in the Doppler angle may affect the velocity-waveform spectra. Therefore, a combined B-mode/color-flow and hemodynamic assessment is desirable. Power Doppler helps to outline the residual lumen and quantify the degree of arterial narrowing, par-

40

Part I Imaging Techniques

10

9

11

FIGURES 3.9–3.15 Arterial mapping and completion angiography.

Chapter 3 Duplex Arteriography for Lower Extremity Revascularization

41

12

14

13

FIGURES 3.9–3.15 (continued)

42

Part I Imaging Techniques FIGURES 3.9–3.15 (continued)

15

TABLE 3.1 Infrainguinal procedures

Femoral popliteal bypass Bypasses to infrapopliteal vessels Superficial femoral, tibioperoneal or popliteal artery balloon angioplasty Thrombectomy Embolectomy

TABLE 3.2 Inflow procedures performed

Vein

PTFE

Total

64 100

109 155

173 255

Iliac angioplasty and stent Axillofemoral bypass Femorofemoral bypass Iliofemoral bypass Aortofemoral

63 11 12 1 2

16 10 7

The other procedures not included on this list include suprainguinal procedures not performed with an infrainguinal procedure or balloon angioplasties.

TABLE 3.3 Areas that were difficult to evaluate with DA (n = 67 patients)

Calcification Iliacs SFA Popliteal Tibials

4 4 1 24

Gas interposition

Pain

Obesity

Uncooperative Patient

12

1

9

8

Low Flow

Open Ulcer

Tortuous

Edema

Total

9

35 5 1 49

1 1

1

2

ticularly in the presence of color bleeding, exacerbated color flashing produced by tight stenosis, or low-flow situations. Inflow and outflow site selection of infrainguinal bypass based on CA involves visualization of an adequate inflow with unobstructed runoff. Thereby, precise estimation of intervening sequential stenoses may be irrelevant for surgical decision-making. Similarly, the information obtained by duplex ultrasonography can be drawn into a diagram to aid surgeons’ visualization of significant lesion and formulation of revascularization strategy.

2

4

6

1

Prior Studies Prior literature examining DA primarily focused on comparing DA with CA (17–20). However, most of these studies attempted to compare the predicted bypass based on DA with that predicted by angiography. Since the variation in the choice of procedure between surgeons given the same angiography data has been well documented, the conclusions that can be drawn from these comparison studies between DA and CA remain questionable (21). In addition, since the vascular technologists performing these examinations in these studies would not

Chapter 3 Duplex Arteriography for Lower Extremity Revascularization

43

TABLE 3.4 Differences between DA and intraoperative findings (completion angiography or graft pressure measurements) Problem

Cause

Change in Outcome

Peroneal, thought to be closed, was open More disease in distal PT More disease in distal PT Not able to see iliac

Heavy calcification Very low flow Very low flow Heavy calcification

No change—had femoral DP bypass None—no other alternative available None—no other alternative available Balloon angioplasty/stent of EIA lesion, stent graft of CIA aneurysm

Distal posterior tibial artery thought to be open

Very low flow distal posterior tibial artery, large distal collateral Did not see (60%) stenosis well in proximal CIA Calcification Did not see stenosis well in proximal CIA Did not see iliacs well Obesity

CIA thought to be open Distal anterior tibial artery thought to be open CIA thought to be open CIA thought to be open EIA thought to be open

be experienced with insonation of the tibial and pedal arteries and have no opportunity to learn from the angiogram or intraoperative findings, the very basis of these comparison studies remains unrealistic and artificial.

Limitations Poor visualization of vessels with extremely calcified vessel walls, skin quality problems such as severe dermatitis, open ulcers, heavy scarring, severe lymphedema, and severe hyperkeratosis are some of the problems associated with DA, as well as rest pain, noncompliant patients, and excessive edema. Additionally, we encountered difficulty visualizing the iliac arteries, owing to colostomy, marked iliac tortuosity, recent abdominal surgery, ascites, morbid obesity, or gas interposition in a few of our patients. To circumvent the problem of severe calcification, we have found increasing the gain, persistence and sensitivity, and using power Doppler and SonoCT technology quite useful. Lack of patient cooperation may be one limitation to accurate DA, particularly for the iliac and infrapopliteal segments. In fact, a small percentage of patients are uncooperative because of altered mental status, inability to position the leg, severe, ischemic pain, or spinal condition. The inclusion of pain medications for severe pain, sedation or having a family member in the laboratory to calm the confused patient was also found very helpful. In certain instances, we re-attempted the examination after a few days of elevation to decrease the edema and attempted overnight fasting prior to the examination to reduce bowel gas. Often, with limited visualization of the iliacs but with normal common femoral waveforms, it was elected to proceed to revascularization, realizing that an intraoperative balloon angioplasty of the iliacs may be needed. Nevertheless, a small number of our patients were not able to have adequate information derived from DA and did require preoperative contrast angiography despite these attempts.

Jump to plantar Stent of CIA Jump to dorsalis pedis Stent of CIA Stent of CIA Stent of EIA

Our evolving experience also demonstrates some of the nuances of the DA examination. We have noted that failure of visualization of all segments of the arterial tree in every patient has not posed a significant issue. Incomplete visualization of the iliac vessels has led to a graft–radial artery pressure gradient that resulted in an intraoperative balloon angioplasty and placement of a stent in the iliac arteries from the proximal anastomosis of the bypass in five instances. In these five patients, no common femoral artery waveform abnormalities were detected, consistent with our prior published data, suggesting that these are not reliable (3). These patients also had SFA disease, making other noninvasive techniques less reliable for detection of these occult iliac lesions. Nevertheless, because of this limitation, the surgeon using DA as a sole preoperative imaging tool needs to be able to perform these endovascular procedures during the revascularization if needed. Since our policy is to perform the inflow angioplasty at the same time as the lower extremity revascularization, and the expertise and tools necessary to perform endovascular procedures are readily available, this has not been an issue at our institution. Furthermore, incomplete visualization of the crural and pedal vessels does not always have a major impact on the course of the procedure. For example, if a surgeon prefers to perform a bypass to the distal anterior tibial artery rather than to the distal peroneal, and the distal peroneal was too calcified to insonate, the lack of data on the distal peroneal may have little impact on the planning of the procedure. In general, our policy to not perform a femoral distal bypass for claudication means that, in the presence of severe SFA disease with at least one vessel runoff and insignificant iliac artery disease, a femoral popliteal bypass will be planned even if the other two tibial arteries could not be completely evaluated. Nevertheless, when difficulties in the evaluation of the crural and pedal vessels are encountered, and the status

44

Part I Imaging Techniques

of these vessels is necessary, additional techniques can be used. In very low flow situations (PSV of < 20 cm/s) such as in the tibial vessels with acute ischemia or cardiogenic shock, setting the pulse repetition frequency at 150 to 350 Hz and using the low wall filter, the highest persistence and highest sensitivity for the color flow imaging can be beneficial. At times, distal compression can augment flow and demonstrate patency of tibial vessels. When the tibial vessels are severely calcified, we have found power Doppler and Sono CT to be useful. In addition, examining the vessels in transverse section, changing the angle, and increasing the gain can at times allow visualization of the vessel. The depth of the tibioperoneal trunk, origin of the proximal peroneal and posterior arteries, and the superificial femoral artery at Hunter’s canal may necessitate the use of a lower frequency probe for visualization. However, this tends to sacrifice details and the resolution, and can make these areas difficult to interpret. In these cases, velocity spectral analysis can also be a useful adjunct. In difficult arterial segments, manipulation of the leg, using a different probe, or utilizing a variety of approaches may be necessary. For example, the medial approach may help to visualize the proximal peroneal, the medial or posterior approach may assist in visualizing the mid-peroneal artery, and the lateral or posterior approach may facilitate the imaging of the distal peroneal and its branches. Thus, the tibial vessels can be adequately evaluated by using a variety of approaches and angles. The most difficult infrapopliteal segments to visualize that we encountered were the first portion of the anterior tibial artery and the bifurcation of the tibioperoneal trunk. We believe this difficulty is due to the depth of the areas. Overall, most of the nonvisualized segments were localized between two occluded segments. Therefore, nonvisualization of these segments was not relevant for surgical decision-making. Contrary to the belief that the peroneal artery is difficult to image, we were able to visualize it using a variety of techniques. Using these techniques, even its continuation from the tibioperoneal trunk can be assessed. The origin of the anterior tibial artery deserves special attention as collaterals in this area may be mistaken for a patent proximal anterior tibial artery. Careful examination of the origin of the vessels and tracing the vessels distally often can solve some of these issues. In addition, identification of the two adjacent veins can help distinguish between a large collateral and the vessel. Despite these techniques, if patency of vessels that were not visualized well is deemed crucial, an angiogram will need to be obtained before the procedure is attempted.

Advantages Invasive contrast angiography remains the gold standard imaging modality in planning these revascularizations even though this modality may not detect outflow vessels

that may be more clearly visualized with duplex or MRA, as occurs in very low flow situations with acute or severe chronic ischemia (10,22). Conversely, DA has the capability to detect these vessels with very low flow (< 20 cm/s). The visualization of these outflow vessels may result in the performance of lower extremity revascularizations that ultimately achieve limb salvage. Moreover, since biplanar arteriography is not the standard for the entire arterial tree, eccentric lesions, especially in the iliacs, may go undetected utilizing contrast angiography. Finally, while MRA does have certain clear advantages over CA, we have noted that as many as 25% of patients are unable to complete their preoperative MRAs due to scheduling difficulties, claustrophobia, metal implants, or pacemakers. The advantages of DA compared with other imaging tools include the identification of the softest portion of the vessel wall that can be marked on the skin before the intended procedure. Skin marking of the most suitable site for outflow anastomosis, particularly for infrapopliteal segments, may limit incision size and eliminate extensive arterial dissection in search of a soft arterial segment. Information of a noncalcified arterial segment is promptly conveyed to the surgeon, important arterial braches may be spared, and long-incision-related complications reduced. While a target vessel may be patent using luminally-based imaging tools, the vessel may be severely calcified in long segments, as in the diabetic and end-stage renal disease population. We have found that preoperative localization of the softest portion of the vessel by DA can accurately identify the most advantageous anastomotic site, thus decreasing the risk of damage to the artery by clamping or incomplete proximal control with a tourniquet due to concomitant severe SFA calcification. Thus, DA can be an invaluable aid to the surgeon in determining the anastomotic site of choice. Since DA is not just a luminal technology, it can be used to assess the actual disease of the vessel. Highresolution duplex imaging can assess the luminal diameter and thickness of the wall down to approximately 1/10th of a millimeter. While a vessel may appear to have a patent lumen with MRA and contrast angiography, the actual thickness of the wall is not evaluated via these techniques. This visualization by DA may change the site for the anastomosis. In addition, DA has the ability to more accurately assess the chronic nature of an occlusion. Therefore, it is possible to differentiate between an isolated chronic SFA occlusion and an acute embolism with little underlying disease, or acute thrombosis with severe underlying atherosclerotic disease. In addition, aneurysmal vessels with partial thrombosis may have little to no luminal dilation and may be undetectable by CA. Similarly, ulcerated and irregular plaques that may be a source of embolization are also poorly assessed with CA. Highresolution DA more clearly visualizes these plaques. Consequently, we have found this imaging modality particularly valuable in determining patient management compared with other technologies.

Chapter 3 Duplex Arteriography for Lower Extremity Revascularization

Furthermore, the hemodynamic information obtained using DA may alter patient management. Volume flow and velocity measurements can help assess whether the visualized lesion is hemodynamically significant, and determine whether repair of the lesion may be beneficial. For example, a poorly visualized iliac plaque with little change in the ratio of peak systolic velocities (< 2) may suggest that the lesion may not be of clinical significance. On the other hand, lesions that are poorly visualized because of severe calcification with elevated ratios distal to the obscured lesion suggest a hemodynamically significant lesion. Other luminal imaging modalities do not readily furnish these details. The portability of the duplex machine should be mentioned. Because the DA can be performed at the bedside, in the operating room, or in the holding area, time spent transporting the patient, and the personnel required, is significantly reduced. Additionally, obtaining the CA or MRA images and their interpretation can entail a delay in the definitive treatment of a severely ischemic limb in a debilitated patient, as well as take a toll on the operative team. With DA, once the patient is identified as needing urgent revascularization, the machine and technician can be brought to any part of the hospital for an abbreviated directed examination.

The DA Team While prior studies have demonstrated the reliability of DA (8,12,13), it is highly operator dependent. We require an experienced technician whose capabilities are well known to the surgical staff. Our DA technicians are MD/RVTs (registered vascular technologists) who each undergo a specialized training protocol including examination of the patient by DA and angiography. The variances encountered between both modalities are then reviewed. In addition, any differences in DA and intraoperative completion angiography are analyzed by all of the surgeons and technologists, resulting in a close relationship. Prior to each procedure, each case is discussed to afford the surgeon a complete picture of the findings, rather than to have the surgeon merely review the mapping. Thus, the intricacies and nuances of the actual quality of the arteries and veins are presented to the surgeon as an adjunct to the mapping and images taken during the examination. For example, the thickness and characteristics of the target vessels can be more effectively communicated by verbal exchange rather than written details or a drawing. This type of data serves to further accentuate the advantages of DA over luminally-based imaging modalities, as this sort of information is not available otherwise. Areas that are not well visualized should be identified as such for the surgeon to decide if this area is crucial. DA demands a high level of technical proficiency, an understanding by the technician of the anatomy and hemodynamics, and appreciation of the intended revascularization. Knowledge and experience of the technolgist play an important role. Details of the exact location of

45

disease with relation to the surgical anatomy are also necessary. For example, identifying disease in the above-, behind-, and below-knee popliteal artery is a concept that must be mastered for DA to be effective. To facilitate these goals, DA technologists at our institution freely visit the operating room to gain insight into the operative procedures. In an attempt to develop a training period at our institution, the first 25 examinations by a new technologist are confirmed with CA or repeated DA examination by an established DA technologist. In the initial stages, a prospective comparative study needs to demonstrate that the DA examinations being performed are as effective as invasive CA in delineating the arterial anatomy (1). In an effort to facilitate the advancement of our DA protocol, every completion angiogram is reviewed with the technologist who performed the examination, as are the iliac angioplasties. The characteristics of the proximal and distal arteries, vein conduit, or tibial vein in the case when an adjunctive arteriovenous fistula is performed, are discussed and any discrepancies are reviewed. DA technologists visit the operating room to witness the intraoperative findings first-hand. In this manner, the constant feedback becomes the cornerstone for the continual improvement in the quality of the DA examinations. This confirms our previous belief that DA can also be used as the only preoperative imaging technique for patients with lower limb ischemia when performed by a well-qualified, experienced registered vascular technologist under the supervision of a vascular surgeon. This is an operator-dependent test that demands the use of different scanners and constant optimization of the image by an operator who has mastered ultrasound technology and hemodynamics.

Shortened Protocol The role of a shortened focused protocol also needs to be explored. Is it necessary to visualize all of the vessels from the aorta to the pedal vessels in every case? For example, the need to scan all the tibial vessels of a patient with claudication and severe iliac disease with no significant femoral disease may be questioned if the surgeon will only perform an inflow procedure for this type of patient. Thus, the DA protocol needs to be tailored for each surgeon, as a complete examination may not be absolutely necessary or additional examinations may need to be performed in certain types of patients, depending on the clinical approach of the operating team. In the presence of a previous patent bypass graft, DA focuses on identifying significant lesions above the proximal anastomosis, evaluating the graft itself for significant lesions, and assessing the best patent artery available for a possible revision. Scanning of the arterial segments between the proximal and distal anastomosis adds very little useful information and may be omitted. Previous occluded bypass grafts are registered, and a complete mapping is performed.

46

Part I Imaging Techniques

Machines DA has further emphasized the need to keep up with rapidly advancing duplex technology, as older machines seem to have decreased resolution, less penetration, increased error on the diameter reduction measurements, lack power imaging, and demonstrate more artifacts. Some earlier investigators attempted to perform DA with less than adequate technology, which may have affected the results (9,11,13–15). As the technology and our knowledge have advanced, so too have our results (5,15,19,23). Therefore, our experience with DA in this patient population continues to evolve as the available technology advances (24).

Renal and Diabetic Patients It has been well documented that patients with diabetes mellitus and/or chronic renal insufficiency are at an increased risk for developing contrast-induced nephropathy when subjected to CA, despite the use of nonionic contrast media (25–28). Although the renal function in most patients with contrast-induced renal failure will return to baseline, a few patients may require hemodialysis and most will have their proposed arterial reconstruction delayed. In modern series, up to 10% of diabetic patients will have contrast-induced renal failure and up to 12% of patients with chronic renal insufficiency will significantly worsen their renal function following CA (3,29,30). In addition, the significant osmotic load associated with dye injection poses a risk for fluid overload for the patients on hemodialysis. Yet, the gold-standard imaging modality for lower limb ischemia continues to be invasive CA even in the presence of diabetes mellitus and chronic renal failure. More recently, several investigators have attempted to validate duplex arterial mapping as a reliable alternative to CA (1,14,16,31). Although some of these studies achieved excellent correlation between DA and CA, few surgeons have actually performed infrainguinal bypasses without preoperative or pre-bypass CA (3). In an effort to examine revascularization without a preoperative dye study, we will focus on our experience with DA in 145 patients who had 180 lower limb arterial bypasses and who were at risk for developing or worsening their renal failure if given nonionic contrast media. From January 1998 to November 2000, lower extremity DA was performed on 145 patients with diabetes mellitus and/or chronic renal failure prior to 180 arterial reconstructions. A total of 121 procedures were performed on 97 patients with diabetes alone, 41 on 33 patients with diabetes and chronic renal insufficiency (CRI), and 18 on 15 patients with CRI alone. Patient ages ranged from 45 years to 98 years (mean 73 ± 10 years). Indications for surgery were severe claudication in 20 (15%), rest pain in 28 (21%), nonhealing ischemic ulcers in 39 (30%) and limb gangrene in 45 (34%). Preoperative CA was performed in 16 procedures, owing to extremely poor runoff based on DA and limited visualization of outflow

vessels. Adequacy of the inflow was confirmed by intraoperative pressure measurements. Post-bypass CA or duplex imaging was obtained to verify the patency of the runoff. The DA procedure time averaged 50 ± 12 min (range 35–90 min). The distal anastomosis was to the popliteal artery in 65 cases (49%) and to the tibial and pedal arteries in 67 (51%). Cumulative patency rates at 1 and 3 months were 94% and 83% respectively. Intraoperative findings confirmed the preoperative DA findings, with the exception of one case in which the distal anastomosis was placed proximal to a significant stenosis, requiring an extension graft. The use of high-quality arterial ultrasonography presents a safe and reliable option to preoperative lower extremity CA for many patients with diabetes or impaired kidney function. The ease of use and favorable patient outcomes achieved by this imaging modality may rival the use of contrast angiography for these patients. This imaging modality can offer results comparable to those achieved with conventional invasive CA while at the same time reducing associated risks. The advantages of avoiding or limiting the use of CA to decrease the incidence of post-procedure renal insufficiency for the diabetic patient and those patients with CRI are self-evident. This complication also results in substantially increased lengths of stay, additional specialty consults and higher costs. In addition, it can also produce suffering for the patient and their family. Moreover, an analysis of natural history studies indicates that 23–63% of patients with diabetes will have progressive renal insufficiency with 10% to 35% winding up on dialysis (32–36). Of the patients with CRI, up to 28% will require eventual dialysis (37,38). It remains unclear whether the administration of intra-arterial dye may result in additional long-term complications in these high-risk patients with peripheral vascular disease.

Acute Ischemia Over the last three decades, the management of acute lower limb ischemia has evolved from simple embolectomies performed with local anesthesia to highly challenging arterial reconstructions. Some of the factors accounting for this dramatic change include a more aggressive approach at limb salvage in the elderly patient by well-trained vascular surgeons, decreased prevalence of rheumatic heart disease, and a substantial increase in the use of warfarin sulfate for cardiac arrhythmias. Accordingly, many of these patients presenting with acutely ischemic limbs will have underlying multisegmental occlusive arterial disease rather than a simple embolus obstructing a healthy vessel. Although the clinical diagnosis of an ischemic leg can often be made without difficulties, the anatomical pattern of the inflow, the outflow, and the occluded arterial segment may at times be impossible to ascertain by standard preoperative imaging modalities. Although invasive CA has been advocated by some authors for patients presenting with acute ischemia (39,40),

Chapter 3 Duplex Arteriography for Lower Extremity Revascularization

it has some limitations, particularly when compared with duplex ultrasound: 1. 2. 3. 4. 5.

It delineates the patent arterial lumen only. It misses thrombosed popliteal aneurysms. It fails to visualize an outflow source in very low-flow situations. It requires potentially nephrotoxic agents. It delays prompt treatment.

Moreover, there are few retrospective reports on the importance of preoperative arteriography in patients with acute ischemia. Conversely, relying solely on a medical history and a physical examination without any preoperative imaging technique may subject patients to unnecessary attempts at embolectomies or thrombectomies and may significantly prolong the operation. This would be quite undesirable in this often high-risk population with multiple cardiovascular risk factors. Furthermore, avoidance of nephrotoxic agents, visualization of low-flow arteries and a more expeditious examination are some of the advantages of DA that are particularly important in these often sick patients presenting with acute lower limb(s) ischemia. The purpose of this section was to focus on whether DA can also be used effectively in the setting of acute ischemia. From January 1998 to February 2001, 68 patients were admitted to our institution with 87 instances of acute lower limb(s) ischemia and underwent 87 operations. There were 34 men and 34 women, whose age ranged from 51 to 95 years (mean 72 ± 12.5 years). There were 44 cases of acute arterial occlusions and 43 cases of bypass graft thromboses. In the former group, the most proximal occluded site was the aorta in one case, common iliac in four cases, external iliac in 15 cases and infrainguinal arteries in 24 cases. In the latter group, there were four suprainguinal grafts, 24 bypasses to the popliteal artery, and 15 bypasses to infrapopliteal arteries. All patients had DA as their initial diagnostic study. The initial duplex protocol varied according to the pulse examination. In patients with a good femoral pulse but absent popliteal pulse, attempts were made to visualize the ipsilateral femoral–popliteal segment and the proximal third of the infrapopliteal arteries. This was extended to the distal tibials vessels and pedal arteries when needed. When the femoral pulse was absent, the protocol started with visualization of the distal aorta, bilateral iliac, and common femoral arteries. This examination was extended into the deep and superficial femoral–popliteal segments in cases of proximal occlusion. None of these cases had preoperative or pre-bypass CA. Intraoperative arterial pressures to confirm the adequacy of the inflow tract and arteriography to assess the runoff were performed in 78% of the cases at the end of the procedure. DA was not completed in 5 of the 87 cases because of severe arterial calcification (3), patient uncooperativeness (1), or obesity (1). DA correctly predicted the extent of the occluded arterial segment in 80 of 82 cases (98%). Of the 44 cases of arterial occlusions, seven were treated by

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thromboembolectomies alone, thromboembolectomies and patch angioplasties in 14 cases, thromboembolectomies and iliac balloon angioplasties with stents in four cases. In the remaining 19 cases a variety of bypasses were required to restore unobstructed flow after an attempted embolectomy. DA correctly identified all seven cases (100%) that required embolectomy alone and 13 of the 14 cases (93%) of thrombectomy and patch angioplasty, two of four cases (50%) of thromboembolectomies with iliac balloon angioplasty and stents. In addition, DA predicted the necessity for bypass operations in 15 of 16 cases (94%) with significant underlying occlusive disease and for three of three (100%) thrombosed popliteal aneurysms. The 1-month arterial patency rate for the 25 embolectomy cases was 65% and 1-month graft patency rates were 59% for 15 femoral–popliteal bypasses and 62% for 24 infrapopliteal bypasses. The time spent to perform DA varied from 20 min to 50 min (mean 30 min). A well-performed DA offers several practical advantages over CA in this subset of patients: 1. 2. 3. 4.

5.

6.

7.

It is noninvasive. It does not require nephrotoxic agents. It is portable and it can be done expeditiously. Color flow and waveform analysis provide a better estimation of the hemodynamic significance of occlusive disease. It allows direct visualization of the entire artery and not only of the lumen, thus enabling plaque characterization. With color flow and power Doppler techniques it is possible to identify patent arteries subjected to very low flow states. It can detect occluded arterial aneurysms, thereby avoiding unnecessary attempts at thromboembolectomies.

Most of the patients in this series had their DA performed during regular hours since it was not possible to have the technologist(s) available at all times. Except for the time of day, there was no other factor differentiating those patients with acute ischemia who underwent DA from those who did not. Regardless of its obvious limitations, this experience demonstrates the advantages of DA in helping the surgeon plan the surgical approach and avert unnecessary thrombectomies and embolectomies that can further contribute to the high mortality and morbidity in patients with acute lower limb ischemia.

Conclusions This experience correlates with our belief that highquality arterial ultrasonography performed by a highly skilled and well-trained vascular technologist may represent an alternative to conventional arteriography for patients in need of primary or secondary lower extremity revascularization. The technologist needs to be trained to

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understand vascular pathology, hemodynamics, and ultrasound technology to perform an accurate DA. Limitations inherent to the technique and very poor runoff observed on ultrasonographic examination may necessitate additional preoperative imaging modalities in certain patients. Despite these techniques, there were two cases in which a jump graft was performed owing to a missed distal lesion. One stenosis in the distal anterior tibial artery was missed, and a large collateral was mistaken for the distal posterior tibial artery in a patient with extremely low flow. Both of these occurred early in the course of our experience, were detected by routine completion angiography, and were remedied with a jump graft. Both patients seemed to have no complications from the procedures. While these cases help illustrate the limitations of DA, the cases seem quite infrequent. These types of limitation need to be weighed against the potential benefits of the DA protocol and the limitations of CA. Nevertheless, further investigation is warranted to resolve the issues that are raised by this experience and to support the use of DA as a viable preoperative imaging tool in place of CA for lower extremity revascularization procedures.

References 1. Mazzariol F, Ascher E, et al. Values and limitations of duplex ultrasonography as the sole imaging method of preoperative evaluation for popliteal and infrapopliteal bypasses. Ann Vasc Surg 1999; 13: 1–10. 2. Ascher E, Mazzariol F, et al. The use of duplex ultrasound arterial mapping as an alternative to conventional arteriography for primary and secondary infrapopliteal bypasses. Am J Surg 1999 Aug; 178(2): 162–5. 3. Mazzariol F, Ascher E, et al. Lower-extremity revascularisation without preoperative contrast arteriography in 185 cases: lessons learned with duplex ultrasound arterial mapping. Eur J Vasc Endovasc Surg 2000; 19: 509–15. 4. Sensier Y, Hartshorne T, et al. A prospective comparison of lower limb colour-coded Duplex scanning with arteriography. Eur J Vasc Endovasc Surg 1996; 11: 170–5. 5. Ligush J Jr, Reavis SW, et al. Duplex ultrasound scanning defines operative strategies for patients with limbthreatening ischemia. J Vasc Surg 1998; 28: 482–90. 6. Sensier Y, Fishwick G, et al. A comparison between colour duplex ultrasonography and arteriography for imaging infrapopliteal arterial lesions. Eur J Vasc Endovasc Surg 1998; 15: 44–50. 7. London NJ, Sensier Y, Hartshorne T. Can lower limb ultrasonography replace arteriography? Vasc Med 1996; 1: 115–19. 8. Polak JF, Karmel MI, et al. Determination of the extent of lower-extremity peripheral arterial disease with colorassisted duplex sonography: comparison with angiography. AJR Am J Roentgenol 1990; 155: 1085–9. 9. Moneta GL, Yeager RA, et al. Accuracy of lower extremity arterial duplex mapping. J Vasc Surg 1992 Feb; 15(2): 275–83.

10. Wilson YG, George JK, et al. Duplex assessment of runoff before femorocrural reconstruction. Br J Surg 1997 Oct; 84(10): 1360–3. 11. Karacagil S, Lofberg AM, et al. Value of duplex scanning in evaluation of crural and foot arteries in limbs with severe lower limb ischaemia—a prospective comparison with angiography. Eur J Vasc Endovasc Surg 1996; 12: 300–3. 12. Koelemay MJ, Legemate DA, et al. Can cruropedal colour duplex scanning and pulse generated run-off replace angiography in candidates for distal bypass surgery. Eur J Vasc Endovasc Surg 1998; 16: 13–18. 13. Cossman DV, Ellison JE, et al. Comparison of contrast arteriography to arterial mapping with color-flow duplex imaging in the lower extremities. J Vasc Surg 1989 Nov; 10(5): 522–8. 14. Larch E, Minar E, et al. Value of color duplex sonography for evaluation of tibioperoneal arteries in patients with femoropopliteal obstruction: a prospective comparison with anterograde intraarterial digital subtraction angiography. J Vasc Surg 1997; 25: 629–36. 15. Lai DT, Huber D, et al. Colour duplex ultrasonography versus angiography in the diagnosis of lower-extremity arterial disease. Cardiovasc Surg 1996; 4: 384–8. 16. Wain RA, Berdejo GL, et al. Can duplex scan arterial mapping replace contrast arteriography as the test of choice before infrainguinal revascularization? J Vasc Surg 1999 Jan; 29(1): 100–7. 17. Proia RR, Walsh DB, et al. Early results of infragenicular revascularization based solely on duplex arteriography. J Vasc Surg 2001; 33: 1165–70. 18. Elsman BH, Legemate DA, et al. Impact of ultrasonographic duplex scanning on therapeutic decision making in lower-limb arterial disease. Br J Surg 1995 May; 82: 630–3. 19. Pemberton M, Nydahl S, et al. Colour-coded duplex imaging can safely replace diagnostic arteriography in patients with lower-limb arterial disease. Br J Surg 1996; 83: 1725–8. 20. Sarkar R, Ro KM, et al. Lower extremity vascular reconstruction and endovascular surgery without preoperative angiography. Am J Surg 1998; 176: 203–7. 21. Kohler TR, Andros G, et al. Can duplex scanning replace arteriography for lower extremity arterial disease? Ann Vasc Surg 1990; 4: 280–7. 22. Carpenter JP, Owen RS, et al. Magnetic resonance angiography of peripheral runoff vessels. J Vasc Surg, 1992; 16: 807–13. 23. Pemberton M Nydahl S, et al. Can lower limb vascular reconstruction be based on colour Duplex imaging alone? Eur J Vasc Endovasc Surg 1996; 12: 452–4. 24. Salles Cunha S, Andros G. Preoperative duplex scanning prior to infrainguinal revascularization. Surg Clin North Am 1990; 70: 41–59. 25. Waugh JR, Sacharias N. Arteriographic complications in the DSA era. Radiology, 1992; 182: 243–6. 26. Lautin EM, Freeman NJ, et al. Radiocontrast-associated renal dysfunction: incidence and risk factors. Am J Roentgenol, 1991 157: 49–58. 27. Gussenhoven MJ, Ravensbergen J, et al. Renal dysfunction after angiography; a risk factor analysis in patients with peripheral vascular disease. J Cardiovasc Surg (Torino), 1991; 32: 81–6.

Chapter 3 Duplex Arteriography for Lower Extremity Revascularization 28. Martin Paredero V, Dixon SM, et al. Risk of renal failure after major angiography. Arch Surg 1983; 118: 1417–20. 29. Rudnick MR, Goldfarb S, et al. Nephrotoxicity of ionic and nonionic contrast media in 1196 patients: a randomized trial. The Iohexol Cooperative Study. Kidney Int 1995; 47: 254–61. 30. Parfrey PS, Griffiths SM, et al. Contrast material-induced renal failure in patients with diabetes mellitus, renal insufficiency, or both. A prospective controlled study. N Engl J Med 1989; 320: 143–9. 31. Wilson YG, George JK, et al. Duplex assessment of runoff before femorocrural reconstruction. Br J Surg 1997; 84: 1360–3. 32. Humphreys P, McCarthy M, et al. Chromosome 4q locus Associated with insulin resistance in Pima Indians. Studies in three European NIDDM populations. Diabetes 1994; 43: 800–4. 33. Nelson RG, Knowler WC, et al. Determinants of endstage renal disease in Pima Indians with type 2 (noninsulin-dependent) diabetes mellitus and proteinuria. Diabetologia 1993; 36: 087–93. 34. Nelson RG, Newman JM, et al. Incidence of endstage renal disease in type 2 (non-insulin-dependent)

35.

36.

37.

38.

39. 40.

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diabetes mellitus in Pima Indians. Diabetologia 1988; 31: 730–6. Perneger TV, Brancati FL, et al. End-stage renal disease attributable to diabetes mellitus. Ann Intern Med 1994; 121: 912–8. Ismail N, Becker B, et al. Renal disease and hypertension in non-insulin-dependent diabetes mellitus. Kidney Int 1999; 55: 1–28. Maschio G, Alberti D, et al. Effect of the angiotensinconverting-enzyme inhibitor benazepril on the progression of chronic renal insufficiency. The Angiotensin-Converting-Enzyme Inhibition in Progressive Renal Insufficiency Study Group. N Engl J Med 1996; 334: 939–45. Kshirsagar AV, Joy MS, et al. Effect of ACE inhibitors in diabetic and nondiabetic chronic renal disease: a systematic overview of randomized placebo-controlled trials. Am J Kidney Dis 2000; 35: 695–707. Dale WA. Differential management of acute peripheral arterial ischemia. J Vasc Surg 1984; 1: 269–78. Cambria RP, Abbott WM. Acute arterial thrombosis of the lower extremity. Its natural history contrasted with arterial embolism. Arch Surg 1984; 119: 784–7.

Haimovici’s Vascular Surgery, 5th Edition Edited by Enrico Ascher Copyright © 2004 by Blackwell Science

CHAPTER 4 Intravascular Ultrasound Imaging Rodney A. White

Intravascular ultrasound (IVUS) has developed rapidly in the last few years. By providing an accurate luminal and transmural image of vascular structures, IVUS displays vascular pathology and illustrates immediate results of interventions. In addition to obvious diagnostic applications, the potential significance of IVUS has become even more apparent owing to the simultaneous development of minimally invasive catheter-based therapeutic techniques, including balloon angioplasty, atherectomy, laser angioplasty, and intravascular stents. The thrust of current development is to incorporate IVUS as an adjunct to peripheral and coronary angioplasty procedures. It is probable that IVUS will become a critical component of future interventional devices, and an understanding of the technique will be essential for those involved in the management of patients with cardiovascular disease.

Device Development and Imaging Configurations A major advantage of diagnostic ultrasound is that it avoids ionizing radiation and intravenous administration of contrast agents. Conventional transcutaneous ultrasound has limited ability to assess structures obscured by bone or air, and to obtain fine resolution of deep-lying tissues. Attaching the ultrasound transducer to an intraluminal catheter and increasing the frequency of the ultrasound energy enhances the interrogation and resolution of organs that are poorly accessible to transcutaneous ultrasound.

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Intravascular Ultrasound Catheter Design The first IVUS catheter prototypes were used to measure intracardiac dimensions and cardiac motion in the 1950s, utilizing A-mode transducers fixed to large intraluminal catheters (1,2). Various devices (A-, B-, and M-mode) were developed for both intravascular and transesophageal imaging of vascular structures, but it was not until the early 1970s that true intraluminal, crosssectional imaging of vessels was reported using a multielement array transducer (3–6). To obtain a 360° cross-sectional image, the ultrasound beam must be scanned through a full circle, and the beam direction and deflection on the display must be synchronized. This can be achieved by mechanically rotating the imaging elements, or by using electronically switched arrays (Fig. 4.1). Current multiple-element IVUS catheters utilize frequencies in the range of 15 to 25 MHz. The plane of imaging is perpendicular to the long axis of the catheter and provides a full 360° image of the blood vessel. A problem of the early phased-array devices was the electronic noise caused by the multiple wires within the catheter itself, as each of the 32 elements was an independent minitransducer needing its own connections. This problem was later overcome by incorporating a miniature integrated circuit at the tip of the catheter, which provided sequenced transmission and reception without the need for numerous electrical circuits traveling the full length of the catheter. As well as reducing the electronic noise, this modification simplified the manufacturing and improved the flexibility of the catheter. A problem of these imaging

Chapter 4 Intravascular Ultrasound Imaging

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FIGURE 4.1 (A) Diagram of a mechanical ultrasound device with rotating (1) and fixed (2) elements. Either the transducer or the mirror may be fixed with the other element in a rotating position. (B) Diagram of a phased-array device with the elements arranged circumferentially around the tip of the catheter. (Reproduced by permission from White RA. Indications for fiberoptic angioscopy and intraluminal ultrasound. Comp Ther 1990;16:23–30.)

catheters, common to all high-frequency ultrasound devices to some extent, is the inability to image structures in the immediate vicinity of the transducer, i.e., in the “near field.” Because the imaging crystals in a phased-array configuration are in almost direct contact with the structure being imaged, a bright circumferential artifact known as the “ring down” surrounds the catheter. The ring-down artifact can be electronically removed, but structures within the masked region will not be seen. Mechanical transducers, the most frequently used type of IVUS catheters, have one of two basic configurations: either the transducer itself or an acoustic mirror is rotated at the tip of the catheter using a flexible, hightorque cable that extends the length of the device. Some catheters use a transducer that is angled slightly forward of perpendicular, which produces a cone-shaped ultrasound beam and results in an image of the vessel slightly forward or in front of the transducer assembly. Devices that utilize a rotating acoustic reflector have the mirror set at a 45° angle to the rotating shaft, producing an image that is perpendicular to the axis of the catheter. In both rotating transducer and rotating mirror devices, ultrasound frequencies between 12.5 and 30 MHz generally are used, although some experimental devices using frequencies up to 45 MHz have produced excellent images of human arteries in vitro (7). In the rotating mirror devices, the ultrasound energy produced by the fixed transducer at the distal tip of the catheter is directed toward an angled mirror placed a short distance proximally. This configuration avoids the necessity for rotating the transducer, and the necessary distance between the transducer and the rotating mirror partially eliminates the ring-down image artifact and the poor resolution near-field of the scan. Both these problems are substantially reduced by allowing the ultrasound energy to travel a short distance in the imaging chamber filled with saline. The scan converter in the image-

FIGURE 4.2 Cross-sectional intravascular ultrasound image of common femoral artery, produced by a rotating mirror mechanical device. a, Artifact caused by the transducer electrical wire; double arrows, fibrous plaque; arrows, arterial media, u, ultrasound catheter void. (Reproduced by permission from Tabbara M, et al. In-vivo human comparison of intravascular ultrasound and angiography. J Vasc Surg 1991;14:496– 504.)

processing unit compensates for this nonimaging portion of the beam and generates images beginning at the surface of the catheter. In the rotating transducer and multiplearray devices, a part of the ring-down region and nearfield zone of the beam occur outside the catheter, so that it is not possible to image clearly in this area. However, both types of mechanical imaging catheters suffer less image loss due to these problems than the phased-array transducers (8). In devices with a distally placed transducer and proximal rotating mirror, it is necessary for an electrical connecting wire to pass along the side of the imaging assembly. This wire produces an artifact that occupies approximately 15° of the image cross-section (Fig. 4.2). A similar artifact is generated in any device in which a wire passes along the side of the imaging element. An interesting modification of the mechanical catheter design involves rotation of both the transducer and the mirror, eliminating any electrical wire artifact. Current disposable mechanical catheters utilize a saline- or water-filled imaging chamber that must be rendered and maintained bubble-free to allow adequate imaging. Miniaturization of the moving parts of the mechanical systems is a major limitation that may ultimately separate these devices from phased-array catheters in their utility in smaller-caliber vessels. On the other hand, as phased-array catheters are used in progressively smaller

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vessels, the problems of ring-down and near-field imaging become more apparent. The smallest currently available mechanical catheters (2.9 Fr. or 0.9 mm in diameter) approximate the size of diseased coronary arteries and, when used with higher-frequency ultrasound, may prove to be superior in most applications.

Computerized Three-dimensional Image Reconstruction Three-dimensional (3-D) intravascular ultrasound imaging has developed as a result of advances in digital computer graphics technology and mass data storage capabilities of personal computers. Algorithms of 3-D image reconstruction can be classified as either surface or volume rendering; currently available 3-D IVUS imaging utilizes surface rendering. Object surfaces are explicitly formed before being depicted on a two-dimensional (2-D) screen using techniques such as hidden-part removal, shading, translucency, dynamic rotation, and stereo projection (9). With this technology, a longitudinally aligned set (up to 300 images per set) of consecutive 2-D images obtained during a “pullback” through a vessel segment is assembled in sequence to produce the 3-D image (Image

Comm, Inc., Santa Clara, CA) (10) (Fig. 4.3). The “pullback” is performed by withdrawing the imaging catheter at a uniform rate using a mechanical device at a rate of 1 cm every 4 seconds. The 2-D IVUS dataset from a 5-cm vessel segment is therefore represented by a 20-s “pullback,” which can be recorded on videotape or reconstructed online. The images are then sampled in digital format following analog-to-digital conversion, at rates of up to 7.5 frames per second (150 frames for a 20-s “pullback”). Currently, most processing is accomplished using datasets recorded on magnetic videotape. Preacquisition of these data allows the user to select the most suitable segments for reconstruction and to adjust screen cropping parameters to electronically eliminate the artifact of the IVUS catheter and other unwanted image data. Approximately 12 seconds of computer processing time is required for the initial reconstruction of a highresolution gray-scale, 2-D longitudinal view of the vessel segment (Fig. 4.4). Before final 3-D reconstruction, the image density threshold is adjusted to optimize differentiation of structures. This step is particularly important when it is necessary to separate tissues of similar echodensity, e.g., soft plaque and thrombus. The 3-D image is then displayed in multiple orientations to allow inspection of

FIGURE 4.3 The 2-D images labeled A, B, and C (center) are “stacked” by the computer, and correspond to the sites labeled with the same letters on the 3-D image (right) and longitudinal section of the 3-D image (left). The longitudinal section of the 3-D image is displayed on the computer monitor to allow optimal adjustments of the image density threshold and viewing orientation. (Reproduced by permission from Cavaye DM, et al. Three-dimensional vascular ultrasound imaging. Am Surg 1991,57:751–756.)

Chapter 4 Intravascular Ultrasound Imaging

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FIGURE 4.4 High-resolution, gray-scale, 2-D longitudinal view of an atherosclerotic human superficial femoral artery. The ultrasound catheter void (u) is seen within the lumen at right and abutting soft plaque (s) at left. C, calcium; single arrows, media. (Reproduced by permission from Cavaye DM, et al. Three-dimensional intravascular ultrasound imaging of normal and diseased, human and canine arteries. J Vasc Surg 1992;16:509–519.)

FIGURE 4.5 Three-dimensional image of the vessel in Figure 4.4. The reconstructed image is viewed in a longitudinal hemi-section to allow complete examination of the luminal surface in this projection. c, Calcium; single arrows, media. (Reproduced by permission from Cavaye DM, et al. Three-dimensional intravascular ultrasound Imaging of normal and diseased, human and canine arteries. J Vasc Surg 1992;16:509–519.)

the arterial segment in all possible projections both from within the lumen and from the adventitial surface (Fig. 4.5). Other parameters such as image sharpness, contrast, and ambient light can be altered to improve the resolution of particular features being examined in the reconstructions. Images of the luminal volume alone can also be produced by removing vessel wall signals. Although it has been shown that 2-D cross-sectional IVUS and gray-scale longitudinal reconstructions provide accurate luminal and transmural dimensions, the accuracy of currently available 3-D imaging has not been established. By viewing all three image formats simultaneously on a screen, however, the location of the 2-D image site along the length of the 3-D image can be identified using a linear cursor, and the dimensions of a site on the 3-D image can be estimated. A continuing problem associated with many 3-D imaging techniques is the near-field effect of the ultrasound imaging catheters at frequencies of 20 to 30 MHz, resulting in bright imaging of the blood immediately surrounding the catheter. As the 3-D imaging software has improved, it has allowed manipulation of the image data to reduce the blood artifact, but this problem still remains in some images because of the inherent features of the imaging catheter.

Forward-looking Intravascular Ultrasound An exciting recent advance is the development of forward-looking IVUS, utilizing acoustic beams that radiate in the shape of a cone from the front of a 7.5-Fr. catheter (Echo Cath, Ltd, Princeton, NJ) (Fig. 4.6). A 27MHz transducer fills a 60° divergent cone with 2000 sequential beams, each comprising 64 axially aligned acoustic measurements. The result is a 3-D image of a volume shaped like a truncated cone, with the near surface located 5 mm from the catheter tip and extending forward 9 mm to the most distant surface. Although this system is experimental, it provides new and unique imaging data that may be critical for guidance of endoluminal devices in treating occlusive vascular lesions.

Intravascular Ultrasound Imaging Techniques Intravascular ultrasound catheters can be introduced percutaneously or through a standard arterial access sheath (7 to 9 Fr.) or through an opening in a vessel during

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A

ization. Image quality is best when the catheter is parallel to the vessel wall—i.e., the ultrasound beam is directed at 90° to the luminal surface—while minor angulations may affect the luminal shape and dimensional accuracy. Eccentric positioning causes the vessel wall nearer the imaging chamber to appear more echogenic than the distant wall, producing an artifactual difference in wall thicknesses. Positioning the catheter in the center of the lumen is especially difficult in tortuous vessels and is often best achieved as the catheter is withdrawn rather than during advancement. Luminal flushing with saline or radiographic contrast agent has been reported to improve delineation of acoustic interfaces in medium and small-sized vessels (11,12).

Clinical Utility of Intravascular Ultrasound Disease Distribution and Characterization

B

FIGURE 4.6 (A) Schematic of forward-looking IVUS catheter. The transducer fills a 60° cone with 200 sequential beams, resulting in an image shaped like a truncated cone, with the near surface located 5 mm from the catheter tip and the far surface extending back a total of 14 mm. (B) Display screen showing the volume image, catheter icon, and cursor (upper left), and representative cross-sections below. (Reproduced by permission from Cavaye DM, White RA, eds. Intravascular ultrasound imaging. New York: Raven Press, 1992.)

a surgical procedure. If large vessels proximal to the arteriotomy are imaged (e.g., iliac artery imaging via a femoral cutdown), a hemostatic access device should be used to reduce blood loss and prevent catheter damage during insertion. Most devices can be passed over a guidewire, which allows more controlled maneuvering of the device within the lumen of the vessel from a remote introduction site, particularly in tortuous or tightly stenotic vessels. It is important to orientate the IVUS catheter within the vessel so that anteroposterior accuracy can be achieved. The best ways to maintain orientation are to use the image artifact produced by the transducer’s connecting wires, and to establish correct initial alignment at the point of catheter insertion. For example, when imaging the aortoiliac segments via a femoral puncture site, rotational alignment can be confirmed by the relative position of anatomical landmarks such as the aortic and iliac bifurcation. Because the catheters are rotationally rigid, there is very little loss of orientation with torquing and manipulation during imaging. Careful positioning of the catheter tip within the vessel and appropriate size matching of the device to the artery caliber are essential to optimize visual-

Several studies have reported that IVUS is accurate in determining the luminal and vessel wall morphology of normal or minimally diseased arteries both in vitro and in vivo (13–18). In muscular arteries, distinct sonographic layers are visible and the media appears as an echolucent layer sandwiched between the more echodense intima and adventitia (see Fig. 4.2). The precise correlation between the ultrasound image and the microscopic anatomy of the muscular artery wall is still uncertain. The internal and external elastic laminae and adventitia are considered to be the backscatter substrates for the inner and outer echodense zones (13,19). The adventitia may be difficult to measure precisely unless the vessel is surrounded by tissues of differing echogenicity such as echolucent fat. Even small intimal lesions such as flaps or intimal tears are well visualized because of their high fibrous tissue content and the difference between the echoic properties of these structures and those of the surrounding blood. The three-layer appearance of muscular arteries is not readily seen in larger vessels such as the aorta, because of the increased elastin content in the media. Intravascular ultrasound devices are sensitive in differentiating calcified and noncalcified vascular lesions. Because the ultrasound energy is strongly reflected by calcific plaque, it appears as a bright image with dense acoustic shadowing behind it (Fig. 4.7; see Figs 4.4 and 4.5). For this reason, the exact location of the media and adventitia cannot be seen in segments of vessels containing heavily calcific disease, and dimensions must be estimated by interpolating adjacent size data. Gussenhoven et al. have described four basic plaque components that can be distinguished using 40-MHz IVUS in vitro (19): echolucent, lipid deposit, or lipid “lake”; soft echoes, fibromuscular tissue, or intimal proliferation including varying amounts of diffusely dispersed lipid; bright echoes, collagen-rich fibrous tissue; and bright echoes with acoustic shadowing, calcified tissue.

Chapter 4 Intravascular Ultrasound Imaging

Numerous investigations have compared angiography and IVUS for determining luminal and transmural dimensions of normal and moderately atherosclerotic human arteries (18,20,21). The cross-sectional areas calculated from biplanar angiograms and measured from IVUS correlate well for normal or minimally diseased

FIGURE 4.7 Intravascular ultrasound image of atherosclerotic human iliac artery. A large calcified plaque (arrows) produces a bright luminal line with acoustic shadowing behind it: u, ultrasound catheter void; a, imaging artifact. (Reproduced by permission from Tabbara M, et al. In-vivo human comparison of intravascular ultrasound and angiography. J Vasc Surg 1991; 14:496–504.)

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peripheral arteries in vivo. Most studies reveal that IVUS and angiography also correlate well when used to image mildly elliptical lumens but, when used to derive dimensions from severely diseased vessels, the angiogram tends to underestimate the severity of disease. By offering a method to define the luminal and transmural morphology and dimensions, IVUS provides a new perspective from which to investigate arterial disease. Recent studies have compared 2-D and 3-D IVUS with angiography and 3-D computed tomography (CT) for imaging abdominal aortic aneurysms (22). Each modality provides unique information regarding the anatomy of the aorta and the distribution of components of the aneurysm (Fig. 4.8). In the case that is illustrated, the aortogram confirmed that the aneurysm was confined to the infrarenal aorta and documented the patency of adjacent branch arteries. The luminal morphology imaged on the angiogram underestimated the size of the aneurysm although displacement of the right ureter suggested a larger dimension. In addition, the angiogram did not provide precise cross-sectional and volumetric data regarding the dimensions of the neck of the aneurysm, quantity of thrombus, aortic wall characteristics, and other findings that were apparent on CT and IVUS. Views of cross-sections of the aneurysm acquired by CT and IVUS enabled accurate sizing of luminal and wall dimensions and correlated closely at various levels along the aorta. Surrounding anatomic structures and characteristics of the vessel wall were highlighted using each method (Fig. 4.9). The IVUS images demonstrated the origin of visceral vessel (superior mesenteric and renal arteries) in relation to the aneurysm and displayed areas of calcification compared with thrombus and fibrous wall components. Calcification was clearly identified by IVUS as hyperechoic areas with shadowing beyond the lesion. Calcification of the wall of the aorta was more readily apparent by IVUS than by angiography or CT. Although

FIGURE 4.8 Left to right: Aortogram, longitudinal gray-scale IVUS, surface-rendered 3-D IVUS, and 3-D CT of the external surface of the aortic aneurysm. The images are of comparable lengths of the aorta with similar magnifications to enable comparison of the methods. (Reproduced by permission from White RA, et al. Innovations in vascular imaging angiography, 3D CT and 2D and 3D intravascular ultrasound of an abdominal aortic aneurysm. Ann Vasc Surg 1994;8:285–289.)

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the 2-D cross-sectional CT and IVUS images corresponded closely for determining the luminal and vessel wall dimensions, the 3-D IVUS reconstructions demonstrated some variation in the shape and topography of the wall surface along the longitudinal axis of the aneurysm compared with the 3-D CT. The 3-D CT outlined the external surface of the aorta, while the IVUS visualized the lumen and transmural wall characteristics. Development of future interventional methods such as intravascular graft deployment will utilize specific applications of each method to enhance precision of endovascular repairs. In particular, IVUS is being used to size and assess the characteristics of the aortic wall and aneurysm before deployment, to precisely place the device during the procedure, and to assess the accuracy of the graft positioning. Conventional angiography has been unable to provide adequately sensitive data regarding the effects of endovascular therapies. For meaningful critical assessment of these new methods, plaque consistency and distribution of residual lesions following intervention must be known. Intravascular ultrasound imaging provides the

ability to accurately measure stenoses produced by comparing luminal dimensions with normal-appearing adjacent reference vessels. This is due in part to the restrictions of single or biplanar arteriography, but also to the fact that an angiogram is a luminal silhouette rather than a transmural image. Three-dimensional IVUS can be used to demonstrate atherosclerotic lesion volume, distribution, and tissue characteristics, and is particularly relevant to investigation of the natural history of atherosclerotic disease and to volumetric plaque studies before and after endovascular interventions. Lesion volume is measurable using 3-D IVUS imaging, but data regarding its accuracy are not currently available. Plaque volume estimation is based on the concept of differing cylindrical volumes, in that the inner (smaller) cylinder is represented by the vessel lumen and the outer (larger) cylinder is confined by the adventitia. By creating a surface-rendered luminal image and a complete cylindrical adventitial reconstruction of a vascular segment, these two volumes can be displayed (Fig. 4.10). The difference between the two cylinders represents the “volume” occupied by the arterial wall elements, either normal or pathologic. If this volume is measured before and after an intervention such as atherectomy, the difference in the volumes represents the amount of actual lesion removed. This information is required to delineate the mechanisms of angioplasty failure, because the roles of residual stenosis and recurrent stenosis have not been adequately defined using currently available angiographically determined data. Intravascular ultrasound provides information essential in the investigation of arterial wall dissections by determining the size, location, and extent of intimal flaps (Fig. 4.11). Because IVUS imaging is a dynamic, real-time imaging modality, the movement of arterial flaps with systolic–diastolic blood flow can be seen. The precise location and orientation of the flap is important as it may determine the need for excision and grafting, stenting, or repair. Intravascular ultrasound has been used to identify the location and severity of dissections and flaps, and may enable endovascular assessment and treatment alone (23–26). Three-dimensional IVUS imaging is especially useful in this role, because aortic dissection commonly results in a spiral or complex-shaped flap that is difficult to appreciate in three dimensions using alternative imaging modalities. Three-dimensional reconstruction allows determination of the dissection entry site, the extent of the flap, and the relation of the false lumen to major visceral branches, and it plays a vital role in experimental endoluminal stenting of aortic dissections.

FIGURE 4.9 Comparison of views by IVUS (top) and CT (bottom) of the aneurysm at the same location. I, Aortic lumen; t, thrombus in the aneurysm; c, calcification; IVC, inferior vena cava; v, vertebral body.

Intravascular Ultrasound as an Adjunct to Endovascular Interventions

(Reproduced by permission from White RA, et al. Innovations in vascular imaging angiography, 3D CT and 2D and 3D intravascular ultrasound of an abdominal aortic aneurysm. Ann Vasc Surg 1994;8:285–289.)

Recent studies have indicated that in percutaneous transluminal angioplasty (PTA), balloon size is often underestimated when selection is made using quantitative angiography, and that optimal balloon size is more accu-

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A

FIGURE 4.11 Intravascular ultrasound image of the distal abdominal aorta in a patient with an acute dissecting aortic aneurysm confirms dissection extending to this level. Dissection flap (double arrows), aortic wall (single arrow), true (T) and false (F) lumens are seen. (Reproduced by permission from Cavaye DM, et al. Intravascular ultrasound imaging of an acute dissecting aortic aneurysm: a case report J Vasc Surg 1991;13:510–512.)

B

FIGURE 4.10 (A) Complete cylindrical vessel reconstruction, with the outer boundary formed by the adventitia. (B) Luminal reconstruction from the same vessel. By subtracting the volume of the luminal cylinder from the volume of the complete vessel cylinder the volume of the vessel wall (pathologic or normal) can be derived. (Reproduced by permission from Cavaye DM, et al. Three-dimensional vascular ultrasound imaging. In Cavaye DM, White RA, eds. A text and atlas of arterial imaging: modern and developing technologies. London: Chapman & Hall, 1993:143–147.)

rately determined by IVUS (27). Other findings suggest that the angiographic success of balloon angioplasty is more likely when hard lesions are disrupted with dissections extending into the media of the vessel, while angiographic failure is seen in lesions that are not displaceable or when circumferential dissections or intimal flaps occur (28). Angiographic success in soft lesions is associated with superficial fissures or fractures of the luminal surface, while vessel recoil and luminal disruption or thrombosis at sites of plaque rupture lead to failure. Intravascular ultrasound is capable of imaging all these features and may be invaluable in providing information that will be used to choose lesions suitable for balloon therapy.

By combining information about plaque and vessel wall consistency with lesion location data such as eccentricity, and by quantitating residual stenosis and dissections, IVUS is ideally suited as a screening and guidance method to improve results of balloon angioplasties (29,30). The balloon ultrasound imaging catheter (BUIC; Boston Scientific, Watertown, MA) has been used clinically with promising results. It has been confirmed that single-plane images can be obtained through the midsection of the angioplasty balloon at all times during the course of the angioplasty procedure, and preinflation, inflation, and postinflation luminal features such as plaque fracture and elastic recoil can be monitored with real-time IVUS (31,32). Peripheral balloon angioplasty has been monitored with IVUS and has been especially useful in identifying and assessing the effect of intimal flaps (9). Preliminary studies have utilized IVUS to localize and treat coarctation of the aorta both experimentally and clinically (33). Intravascular ultrasound clearly shows the coarctation and accurately measures the adjacent normal aortic lumen for balloon sizing. Following dilation, IVUS displays the appearance of the dilation including documentation of dissections. Intravascular ultrasound has been used as a method to study the mechanism of action and function of atherectomy devices, lasers, and stents (34–36). For each type of interventional device, the combination of the guidance

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FIGURE 4.12 Intravascular ultrasound image shows the entire length of a coronary artery segment after rotational atherectomy and balloon dilation. Nine cross-sectional images are shown that are 3 mm apart on center. The most distal images are on the left and show dissection of a circumferentially calcific plaque. There is heavy circumferential and longitudinal calcium, especially at the narrowest residual lumen, which measures 2.3 ¥ 2.7 mm. The largest burr used was 2.15 mm, the adjunct balloon size was 3.0 mm. (Reproduced by permission from Mintz GS, et al. Intravascular ultrasound evaluation of the effect of rotational atherectomy in obstructive atherosclerotic coronary artery disease. Circulation 1992;86:1383–1393.)

FIGURE 4.13 (A) Intravascular ultrasound image of a stent in an artery that appeared fully deployed by fluoroscopic examination, but required further balloon inflation using real-time IVUS before full deployment was achieved; (B) stent struts (single arrow), arterial wall (double arrow).

and lesion assessment capabilities of IVUS with an interventional technique may produce specific benefits for a particular type of approach. Figure 4.12 demonstrates the utility of IVUS imaging in choosing the size of atherectomy and balloon devices for the treatment of coronary lesions (351). Intravascular ultrasound also provides a method to guide deployment and assess the effect of intravascular stents in peripheral vessels. It allows selection of the correct stent size for a particular vessel and is useful in identifying the most appropriate site for stenting. Two- and

three-dimensional IVUS are ideally suited to assessing vascular segments before and after stent deployment. Also, unique information regarding the adequacy of deployment and changes in morphology produced by the stent can be seen (Fig. 4.13).

Developing Applications of Intravascular Ultrasound Intravascular ultrasound is an invasive technique requiring intravascular puncture and catheter insertion. The

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FIGURE 4.14 Fundamentals of tissue characterization. The image on the left is constructed from raw radiofrequency information. One line of this information is shown on the right, with the corresponding tissue elements labeled. The image is created from the amplitude envelope of this signal. More information about specific tissue types, however, is available from computer analysis of the raw signal. The image and signal are from a prototype system (Cardiovascular Imaging Systems, Inc., Sunnyvale, CA) that provides combined imaging and tissue characterization. (Reproduced by permission from Yock PG, et al. Clinical applications of intravascular ultrasound imaging. In: Bernstein EF, ed. Vascular diagnosis, 4th edn. Chicago: Mosby Year Book Medical Publishers, 1993: 994–1000.)

diagnostic applications are useful when combined with invasive studies such as peripheral angiography or cardiac catheterization, or as a guidance method during therapeutic procedures including angioplasty and stent deployment. Developing potentials of the method range from improved localization of vascular tumors before surgery (37) or imaging the long-term function of vena caval filters (38) to possible application as the primary guidance method for laser angioplasty (39). A priority in the development of IVUS technology is the need for further miniaturization and cost-effective manufacturing. Current devices are relatively expensive, and, if the technique is to be of clinical benefit as a component of a disposable catheter system for diagnostic or therapeutic intervention, the price of individual units must be justified by the benefits of IVUS imaging. Future angioplasty guidance devices may combine the benefits of angioscopy and IVUS in a single delivery system suitable for incorporating mechanical or laser ablation devices. Angioscopy would allow visual inspection of the lumen, with ultrasound determining the vessel wall characteristics and dimensions. An added benefit of this type of guidance device would be the ability to select an appropriate ablation method for particular plaque types or volumes. Tissue characterization by analyzing the raw radiofrequency ultrasound signal shows promise for differentiating plaque types (Fig. 4.14). Intravascular ultrasound also provides exciting opportunities for vascular research including investigation of blood vessel compliance, dynamic changes in the vascular wall caused by disease or pharmacologic intervention, and the natural history of atherosclerosis.

References 1. Bom N, ten Hoff H, et al. Early and recent intratuminal ultrasound devices. Int J Card Imaging 1989;4:79–88. 2. Cieszynski T. Intracardiac method for the investigation of structure of the heart with the aid of ultrasonics. Arch Immunol Ther Dow 1960;8:551–557. 3. Kossof G. Diagnostic applications of ultrasound in cardiology. Australas Radiol 1966;10:101–106. 4. Carleton RA, Sessions RW, Graettinger JS. Diameter of heart measured by intracavitary ultrasound. Med Res Eng 1969;May:28–32. 5. Frazin L, Talano JV, et al. Esophageal echocardiography. Circulation 1976;54:168–171. 6. Bom N, Lancee CT, Van Egmond FC. An ultrasonic intracardiac scanner. Ultrasonics 1972;10:72–76. 7. Lockwood CR, Ryan LK, Foster FS. High frequency intravascular ultrasound imaging. In Cavaye DM, White RA, eds. Arterial imaging: modern and developing technologies. London: Chapman & Hall, 1993;125–129. 8. Yock PG, Linker DT, Angelsen BAJ. Two-dimensional intravascular ultrasound: technical development and initial clinical experience. J Am Soc Echocardiogr 1989;2(4): 296–304. 9. Heffernan PB, Robb RA. A new method for shaded surface display of biological and medical images. IEEE Trans Med Imaging 1985; MI-4:26–38. 10. Cavaye DM, Tabbarra MR, et al. Three dimensional vascular ultrasound imaging. Am Surg 1991;57:751–755. 11. van Urk H, Gussenhoven WJ, et al. Assessment of arterial disease and arterial reconstructions by intravascular ultrasound. Int J Card Imaging 1991;6:157–164. 12. Burns PN, Goldberg BB. Ultrasound contrast agents for vascular imaging. In: Cavaye DM, White RA, eds. Arterial imaging: modern and developing technologies. London: Chapman & Hall, 1993:61–67.

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13. Gussenhoven WJ, Essed CE, Lancee CT. Arterial wall characteristics determined by intravascular ultrasound imaging: an in-vitro study. J Am Coll Cardiol 1989; 14:947–952. 14. Kopchok CE, White RA, et al. Intraluminal vascular ultrasound: preliminary report of dimensional and morphologic accuracy. Ann Vasc Surg 1990;4:291–296. 15. Kopchok GE, White RA, White G. Intravascular ultrasound: a new potential modality for angioplasty guidance. Angiology 1990;41:785–792. 16. Mallery JA, Tobis JM, et al. Assessment of normal and atherosclerotic arterial wall thickness with an intravascular ultrasound imaging catheter. Am Heart J 1990;119: 1392–1400. 17. Nissen SE, Grines CL, et al. Application of new phasedarray ultrasound imaging catheter in the assessment of vascular dimensions. Circulation 1990;81:660–666. 18. Nissen SE, Gurley JC, et al. Intravascular ultrasound assessing of lumen size and wall morphology in normal subjects and patients with coronary artery disease. Circulation 1993;88:1087–1099. 19. Gussenhoven WJ, Essed CE, et al. Intravascular echo-graphic assessment of vessel wall characteristics: a correlation with histology. Int J Card Imaging 1989;4: 105–116. 20. Tabbara MR, White RA, et al. In-vivo human comparison of intravascular ultrasound and angiography. J Vasc Surg 1991;14:496–504. 21. Tobis JM, Mahon D, et al. The sensitivity of ultrasound imaging compared to angiography for diagnosing coronary atherosclerosis [abstract]. Circulation 1990;82 (Suppl III):439. 22. White RA, Scoccianti M, et al. Innovations in vascular imaging: angiography, 3D CT and 2D and 3D intravascular ultrasound of an abdominal aourtic aneurysm Ann Vasc Surg 1994;8:285–289. 23. Cavaye DM, French WJ, et al. Intravascular ultrasound imaging of an acute dissecting aortic aneurysm: a case report. J Vasc Surg 1991;13:510–512. 24. Pandian NG, Fries A, et al. Intravascular high frequency two-dimension detection of arterial dissection and intimal flaps. Am J Cardiol 1990;65:1278–1280. 25. Neville RF, Yasuhara H, et al. Endovascular management of arterial intimal defects: an experimental comparison by arteriography, angioscopy and intravascular ultrasonography. J Vasc Surg l991;13:496–502. 26. Cavaye DM, White RA, et al. Usefulness of intravascular ultrasound for detecting experimentally induced

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aortic dissection in dogs and for determining the effectiveness of endoluminal stenting. Am J Cardiol 1992;69: 705–707. Cacchione J, Nair R, Hodson J. Intracoronary ultras ound is better than conventional methods for determining optimal PTCA balloon size [abstract]. J Am Coll Cardiol 1991;17:112A. Leon M, Keren G, et al. Intravascular ultrasound assessment of plaque responses to PTCA helps to explain angiographic findings [abstract]. J Am Coll Cardiol 1991;17:47A. Davidson CJ, Sheikh KR, et al. Intracoronary ultrasound evaluation of interventional procedures [abstract]. Circulation 1990;82(Suppl III):440. Gurley J, Nissen S, et al. Comparison of intravascular ultrasound following percutaneous transluminal coronary angioplasty [abstract]. Circulation 1990;82: 90. Crowley RJ, Hamm MA, et al. Ultrasound guided therapeutic catheters: recent developments and clinical results. Int J Card Imaging 1991;6:145–156. Isner JM, Rosenfield K, et al. Combination balloonultrasound imaging catheter for percutaneous transluminal angioplasty. Circulation 1991;84:739–754. Sanzobrino B, Gillam L, et al. A direct clinical role for intravascular ultrasound: utility in the assessment of coarctation of the aorta [abstract]. J Am Coll Cardiol 1991;17:68A. Smucker ML, Scherb DE, Howard PF. Intra-coronary ultrasound: How much “angioplasty effect” in atherectomy? [abstract]. Circulation 1990;82(Suppl):676. Mintz G, Potkin B, et al. Intravascular ultrasound evaluation of the effect of rotational atherectomy in obstructive athereroscierotic coronary disease. Circulation 1992;86:1383–1393. Cavaye DM, Tabbara MR, et al. Intravascular ultrasound assessment of vascular stent deployment. Ann Vasc Surg 1991;5:241–246. Barone GW, Kahn MB, et al. Recurrent intracaval renal cell carcinoma: the role of intravascular ultrasonography. J Vasc Surg 1990;13:506–509. Greenfield LJ, Tauscher JR, Marx V. Evaluation of a new percutaneous stainless steel Greenfield filter by intravascular ultrasonography. Surgery 1991;109: 722–729. White RA, Kopchok GE, et al. Intravascular ultrasound guided holmium:YAG laser recanalization of occluded arteries. Lasers Surg Med 1992;12:239–245.

Haimovici’s Vascular Surgery, 5th Edition Edited by Enrico Ascher Copyright © 2004 by Blackwell Science

CHAPTER 5 Fundamentals of Angiography Harvey L. Neiman and James Lyons

Angiography has undergone considerable change in the last four decades since Seldinger’s pioneering description of coaxial catheterization technique (1). Numerous technical innovations have introduced a remarkable degree of safety, and diagnostic efficacy and therapeutic breadth. Newer imaging modalities, such as computed tomography (CT), ultrasound (CT), and magnetic resonance imaging (MRI), have refined rather than refuted the crucial role angiography plays in patient management. In fact, these newer imaging tools frequently add impetus for a subsequent, more specialized, arteriographic examination; often a therapeutic intervention. Angiography/interventional radiology is a problemoriented discipline that requires diagnostic acumen, an understanding of pathophysiology of vascular disease, technical skills, and a broad knowledge of management of vascular disease. These skills allow the interventionalist to participate in the diagnosis and treatment of patients with vascular disease and to offer techniques when less invasive therapy is warranted.

History of Angiography The foundations of angiography were developed in the excitement generated by Roentgen with his report of the discovery of x-rays in 1895 (2). The first angiographic examination was performed by Haschek and Lindenthal in the month following Roentgen’s classic description. These authors injected a chalk-containing solution (Teichmann’s mixture) into the blood vessels of an amputat-

ed hand (3). Radiographs of both arteries and veins were first made in live patients by Berberich and Hirsch in 1923 using a 20% solution of strontium bromide (4). The first medical application occurred in 1924 when Brooks proposed angiographic criteria for limb amputation (5). In 1928, Moniz and Diaz reported the first attempt to visualize the cerebral circulation by injecting an intensely radioactive suspension of thorium oxide into a surgically exposed carotid artery (6). McPheeters and Rice, in 1929, used iodized poppy seed oil (Lipiodol) to visualize lower extremity veins (7). The emerging disciplines of arteriography and venography were seldom used, however, until the introduction of organic iodinated contrast materials and the development of rudimentary catheterization techniques. In 1929, Moses reported the use of an organic iodide called Uroselectan for intravenous urography, that was much better tolerated than sodium iodide (8). Uroselectan was subsequently superseded by the improved materials diodrast (Diodone) and neo-iopax (Uroselectan B) (9). During the same year, Forssmann inserted a catheter into his own antecubital vein and obtained a radiograph to confirm his impression that the catheter had reached the right atrium (10). In 1931, Moniz and his colleagues succeeded in visualizing the right heart and pulmonary vessels of a patient using Forssmann’s technique (11). The usefulness of intravenous injection of contrast material for arterial opacification became appreciated when Castellanos et al., in 1937, published results on their experiences (12). Their examinations focused on diagnoses of congenital cardiac anomalies. Studies were limited because of their inability

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to opacify the left heart and because the density of the images after intravenous injection was frequently inadequate. Robb and Steinberg, in 1939, expanded the technical aspects of cardiac imaging when they reported the technique of rapid sequence exposure (13). In 1935, Zeides des Plantes suggested that photographic image subtraction be used to separate contrast material densities from those produced by bone or other normal anatomic structures (14). Application of this concept using computerized digital subtraction techniques has revolutionized the field of arteriography today. Retrograde brachial aortography was described in 1939 by Castellanos and Pereiras (15). In 1941, Farinas reported the retrograde passage of a catheter from the femoral artery into the abdominal aorta for aortography (16). However, the modern era of angiography began with Seldinger’s description, in 1953, of a percutaneous transfemoral method of catheter placement over a guidewire (1). Subsequent major advances include the development of coronary arteriography, pharmacoangiography for the diagnosis and management of gastrointestinal hemorrhage or ischemia, renal, pancreatic and hepatic angiography, as well as other techniques too numerous to describe. Parallel changes of equal importance involve technical advances such as the development of the rapid film changer, biplane imaging, computerized digital subtraction, catheter material technology, low-osmolarity contrast media, balloon catheters, stents, and stent–grafts. Computerized digital subtraction allows the display of isolated vascular anatomy without superimposed anatomic structures. Increased contrast resolution is thus achieved (Fig. 5.1).

Technical Principles Angiographic Equipment The standard angiographic room must contain a high quality fluoroscopic system with video monitoring. Procedures should never be carried out without fluoroscopic guidance. Fluoroscopic monitoring assures increased safety and facilitates procedure efficiency and timeliness. Modern fluoroscopic systems are digitized allowing options such as decreased dose, filmless image acquisition, road mapping and real-time image processing and three-dimensional reconstructions (17). A high capacity three-phase generator of constant load output and a rating of at least 100 kW at 100 kV is also necessary to assure optimum kilovoltage levels at minimum exposure times. Full generator output and voltage stability during the examination require a welldesigned power source free of line interference from other hospital equipment. Automatic line voltage compensation should also be integral to the x-ray generator. Rapid film changers are a further necessity for all types of conventional film-screen angiographic examinations. However, current equipment allows for digital

acquisition and output with display on a high-resolution workstation, negating the need for film. Local and wide area networking are then possible—including the operating room, with image storage on some form of an archive jukebox. Biplane capabilities can be helpful, since image acquisition in a single projection may not accurately demonstrate the abnormality. Sequential filming in a second plane is often required when biplane equipment is unavailable. This, however, increases both the time of the procedure and the amount of contrast media used. For lower extremity arteriography, a programmable stepping tabletop should be available. The stepping tabletop or moving gantry can be used in conjunction with a standard film changer and specialized computer-driven equipment that allows the unit to move at preselected intervals. However, automatic stepping is also available for digital subtraction angiography (18). We have utilized this technique for many years with excellent results. In fact, in our department we are entirely filmless. The angiographic catheterization table should have a floating top to facilitate the carrying out of procedures. If possible, this table should also be able to move up and down for both ease of examination and for proper positioning of the patient. The x-ray tube and image intensifier should operate independently to permit magnification views. The latter two units should be mounted on a “C” or “U” arm for ease of use and optimal filming capabilities. Cine capability is necessary only if cardiac catheterizations are performed in the same room. It is obligatory that every angiographic room have ECG and pulse oxygenation monitoring capability and that all patients be so monitored (19). Intra-arterial pressure monitors are extremely important in evaluating the hemodynamic significance of stenoses, the results of angioplasty, and portal vein pressures. Intravascular pressure determination is also essential in pulmonary angiography before the injection of contrast material. An instrument to measure activated clotting times is also essential. Contrast medium injections are performed with automatic mechanical pressure injectors that provide delivery of a given amount of contrast at a predetermined rate and pressure. Hand injections, however, are utilized for testing the placement of catheters during fluoroscopy and during some digital subtraction applications. The former allows for careful monitoring of the catheter injection site to prevent inadvertent mechanical delivery of contrast into the subintimal space or into an unintended vessel. If film is used instead of digital archival, a laser processor should be in close proximity to the catheterization room for proper management of examinations, since the next “run” often depends on information derived from the previous sequence. Each examination must be tailored to the unique needs of a particular patient. Finally, a well-trained team of angiographic technologists and nurses is invaluable and essential for carrying out high-quality examinations with safety and efficiency. Because of the specialized nature of these procedures, only those staff members most familiar with the examinations

Chapter 5 Fundamentals of Angiography

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B

D

FIGURE 5.1 Digital subtraction arteriogram performed with a stepping table. “Real-time” digital subtraction images are produced. This examination was completed with 85 mL of contrast material to visualize the vascular system from the diaphragm to the feet. (A) Mild atherosclerotic disease of the abdominal aorta with a single renal artery bilaterally (arrows). At least partial patency of the celiac and superior mesenteric arteries. (B) Occlusion of the left superficial femoral artery at its origin (arrow). (C) View of thighs with moderate atherosclerotic disease of the right’s uperficial femoral artery and occluded left superficial femoral artery. (D) Reconstitution of the left popliteal artery at the adductor canal (arrow).

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F

G

FIGURE 5.1 (continued) (E) Image at the knees demonstrating moderate stenosis of the left popliteal artery at the knee joint (arrow). Occlusion of the left tibial peroneal trunk (curved arrow). Occlusion of the right popliteal artery (arrowheads) below the level of the knee joint. (F) Lateral view of the left leg demonstrating two-vessel runoff. The peroneal artery is significantly diseased. (G) Lateral view of the right leg demonstrating single-vessel runoff. (H) View of ankles and feet with slight misregistration because of minimal patient motion.

Chapter 5 Fundamentals of Angiography

should perform them on a regular basis. Routine rotation of all departmental personnel into the angiographic suite should be discouraged.

Catheters and Guidewires Improvement in catheter and guidewire design has been one of the most significant recent advances in angiography. Size 5 Fr. catheters have essentially replaced the 6.5 and 7 Fr. catheters used in previous years. Improvements in catheter surface material have dramatically reduced thrombotic and embolic complications. Wall material has been developed that will allow these smaller-diameter catheters to deliver the high-flow, high-volume injections that are necessary for aortography while maintaining the torquability and trackability needed for selective vessel catheterization. Torquable guidewires are also available which facilitate catheter mobility. Catheterization of previously inaccessible vessels is now possible with the development of 3 Fr. catheters and 0.014- to 0.018-inch guidewire combinations, which are particularly useful in visceral angiography and neuroangiography (63). Specialized catheters have been designed for infusion and pulse-spray delivery of thrombolytic agents over a relatively long segment of vessel. Improvements in guidewire technology have allowed the introduction of hollow guidewires through which infusions can be performed (64). These wires are particularly useful for thrombolytic therapy. Guidewires are also available with balloon tips for remote vessel angioplasty (65).

Contrast Material Low- versus High-osmolarity Agents Virtually all modern angiographic contrast agents are iodinated, monomeric or dimeric substituted benzene derivatives. Iodinated compounds are used primarily because of the ability of the relatively massive iodine atoms to absorb x-rays, producing “positive” contrast without the marked toxic effects seen when other heavier elements are used (9). Carbon dioxide is another angiographic contrast agent that has received some attention because of its economy and low associated morbidity (46,47). Unlike iodinated contrast agents, carbon dioxide facilitates the transmission of x-rays, thereby producing “negative” contrast. Carbon dioxide angiography has become a viable imaging technique with the development of digital subtraction angiography, tilt tables, and closed delivery systems (140,141). Until recently, the most commonly used contrast media were the ionic tri-iodo compounds, diatrizoate and iothalamate. These agents are hyperosmolar and cause localized pain on injection in about 60% of patients. The pain is partly related to the sodium content (23). For these reasons, sodium-free contrast agents such as meglumine diatrizoate or meglumine iothalamate are available. In the last 10 years, there has been explosive growth in the use of

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a new family of relatively low-osmolar iodinated contrast agents. These include the nonionic monomers iopromide, iohexol, ioversol, and iopamidol, and the low-osmolarity ionic dimer, ioxaglate. Universal use of these compounds is limited only by their higher cost. Angiography with these agents is associated with considerably less discomfort than that caused by high osmolarity compounds (23,24). These materials have also been shown to be less nephrotoxic and less injurious to the central nervous system and myocardium (24). However, the nonionic compounds have a lower anticoagulant effect than the ionic agents (24,25), and there have been reports of increased thrombotic complications related to nonionic contrast media usage (26,27). Therefore, many authors recommend adding heparin to nonionic agents, especially for elderly or hypercoagulable patients or for those patients undergoing coronary angiography and/or angioplasty (26,28). Cardiovascular Toxicity Iodinated contrast media produces vasodilation of arteries resulting in increased blood flow. A decrease in systemic pressure is seen with injection of contrast media into the right or left heart, aorta or peripheral arteries (27,28). Other cardiovascular responses to contrast injection are an increase in cardiac output, heart rate, stroke volume, chamber pressure, and circulating blood volume. Contrast media also induces a toxic depressive effect on myocardium. Ventricular fibrillation or other severe arrhythmias occur in up to 0.75% of patients undergoing selective coronary arteriography (29,30). Pulmonary hypertension and systemic hypotension occur with contrast injections into the right heart or pulmonary arteries (31). Low-osmolarity contrast agents are associated with a less pronounced cardiovascular response (22,27). Neurotoxicity Experimentally, injection of contrast media into the carotid artery alters the blood–brain barrier by increasing endothelial permeability, which allows the contrast agent to diffuse into the surrounding tissues (22,32). In humans and animals, meglumine salts have been shown to cause less neurotoxicity than sodium salts (33). CNS side effects of contrast injection include seizures, aphasia, cortical blindness, encephalopathy and amnesia (34,35). Direct injection of contrast media into the artery of Adamkiewicz may result in paraplegia. However, most spinal cord complications are transient and clear within 24 hours (36). The use of low-osmolarity contrast agents appears to be associated with fewer neurological side effects (22,27). Nephrotoxicity Iodinated contrast media is excreted almost entirely by the kidneys. Less than 1% of the administered dose is excreted by the biliary and digestive systems (22). As a result, the kidney is the primary target organ for contrast media toxicity. Contrast-induced nephropathy is thought

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to be due to both the direct chemotoxic effects and the elevated osmolality of contrast media (37). Implicated mechanisms include reduced renal blood flow, glomerular and tubular injury, and complement activation (37). The nephrotoxic effects of contrast media appear to be particularly amplified by azotemia (27). Other less important risk factors include diabetes (especially insulindependent type I), dehydration, blood dyscrasias (including sickle-cell anemia and multiple myeloma), advanced age and generalized infirmity (27,37). Although there is a wealth of experimental and laboratory data which indicate that low-osmolarity contrast media is less nephrotoxic than high osmolarity agents, it is not clear whether this benefit is clinically significant for those patients who are not at increased risk for contrast-induced nephropathy (22,27,38,39). Adverse Experiences Adverse experiences related to contrast media administration can be divided into those that are physiologic, chemotoxic, and anaphylactoid (22). Physiologic reactions commonly include heat and pain located in proximity to contrast agent injection as well as associated nausea and vomiting. Although physiologic reactions are typically mild, these reactions interfere with patient compliance and, therefore may compromise examination quality. Low-osmolarity contrast media has a markedly reduced incidence of these responses (22,27). The chemotoxic effects of contrast media administration have been previously discussed and include direct cardiovascular, renal, and neurological injury. Anaphylactoid reactions are an unusual complication of contrast infusion and a great deal of controversy exists regarding the pathogenesis of this type of response. Implicated mechanisms are thought to be immunologic and include histamine release, complement activation, and antibody–antigen reactions, none of which are mutually exclusive (22,40). These frequently devastating reactions occur unpredictably and are independent of the dose of agent administered (40). Pretesting has not been shown to be a useful predictor of severe reactions (41). The overall incidence of severe, life-threatening reactions is between 0.05% and 0.10% (41) while the risk of death from these reactions ranges from one in 75,000 (42) to one in 169,000 (43). Allergic patients have twice the risk for anaphylactoid reactions, while those patients with asthma or with a history of previous severe reaction may have their risk increased by a factor of five (40). Low-osmolarity contrast media significantly reduces the incidence of severe and potentially life-threatening reactions to contrast administration (22,27,40,43). Pretreatment of high-risk patients with 32 mg of intravenous methylprednisolone 12 hours and 2 hours before administration of contrast media has been shown to reduce the risk of mild, moderate, and severe reactions by 23% to 86% (44). Supplementation with oral H1 or H2 (histamine) blockers and substitution of 50 mg of oral prednisone for methylprednisolone has also been advocated (45).

Preparation of the Patient Ideally, evaluation of the patient should be performed by the angiography staff on the day before a planned angiographic procedure. This will allow ample time for appropriate pre-procedure tests or treatments including additional laboratory evaluation and the initiation of prophylactic steroid therapy for documented contrast allergy. A particular note is made of the patient’s hematologic, renal, cardiac, allergic, and neurologic status. Preangiographic orders include clear liquids after midnight and IV fluid to optimize hydration. Platelets, prothrombin time, partial thromboplastin time and INR should all be in the acceptable range. Coumadin use is a relative contraindication to performing an elective procedure. Heparin infusions should be stopped several hours before the procedure when feasible. Other relative contraindications to angiography are listed in Table 5.1. The popularity of outpatient arteriography places a severe stress on laboratory and other pre-procedure patient studies (138,139). However, the temptation to accept an inadequate preprocedure workup in favor of economy and convenience should be avoided. Informed consent is obtained from all patients at the time of pre-procedure evaluation. Details of the procedure and its risks and benefits, as well as possible alternatives, should be discussed at length. Additionally, the use of conscious sedation must be discussed fully with the patient and informed consent obtained. Almost all catheterizations are performed with both local and intravenous analgesia. Peripheral arterial injections are associated with a varying degree of pain and heat, and these reactions are further exacerbated by patient anxiety. As a result, we are very liberal with the use of intravenous sedation. In our department, we use the narcotic analgesic fentanyl in combination with the sedative midazolam. These agents are administered intravenously immediately prior to the examination and as needed during its course. They have been shown to be both safe and efficacious and their short half-life allows for rapid patient recovery (59). Use of these agents should be limited to those settings where proper monitoring with pulse oximetry and continuous ECG tracing can be perTABLE 5.1 Relative contraindications to arteriography (adapted from reference 61) Recent myocardial infarction or significant arrhythmia History of serious reaction to contrast material Significant hypertension—diastolic pressure greater than 110 mmHg Bleeding diathesis, e.g., prothrombin time greater than twice the control, platelets less than 50,000 Impaired renal function Inability to lie supine on angiography table, e.g., congestive heart failure Retained barium from recent examination

Chapter 5 Fundamentals of Angiography

formed by properly trained and available staff. With the exception of children and for aortic stent–grafting in adults, there is little indication for general anesthesia in angiography. Even a TIPS procedure is performed with conscious sedation. Spinal and epidural anesthesia is rarely indicated. Routine systemic heparinization is not utilized during arteriography unless significant disease is encountered during the passage of the guidewire or catheter or when either of these two instruments results in vessel occlusion when crossing a high-grade stenosis. A bolus of 3,000 to 5,000 units of heparin is administered intra-arterially when these situations are encountered. The routine use of systemic heparinization for angiographic procedures has been advocated in the past (60). However, with the use of standard coaxial guidewire and catheter technique and with frequent flushing of indwelling catheters, routine heparinization is rarely necessary. Following the procedure, patients are sent back to their hospital room or are referred to an area where outpatient monitoring can be performed before discharge. We require at least 6 hours of bedrest in these settings. During this time, a member of the angiography staff should examine the patient and discuss the results of the procedure and possible treatment, if appropriate. If a percutaneous closure device is used, the bedrest time has been reduced to a few hours at our institution. Several closure devices have been developed to close the arteriotomy site. These include collagen plug devices and percutaneous suture closure (142,143). The various devices to achieve rapid hemostasis require proper deployment technique to avoid complications (144,145).

Basic Angiographic Technique A detailed discussion of catheter and guidewire usage is beyond the scope of this chapter. For more information, the reader is referred to basic textbooks on the subject (61,62). Perhaps the most important aspect of angiography is the choice of an appropriate catheterization site. With the close relationship of diagnostic arteriography and interventional radiology, preparation for the former should include contingencies for the latter (83). In a similar fashion, the choice of technique for arteriography should not interfere with the planned surgical approach. In other words, a right retrograde common femoral artery approach should not be used to evaluate an occluded right superficial femoral artery, since this approach may interfere with possible thrombolytic therapy, angioplasty, or surgical treatment of this abnormality. A retrograde left common femoral artery puncture is preferred in this scenario. The most common catheterization site is the common femoral artery. Punctures may be made in the groin crease to assure the shortest penetration of subcutaneous tissue prior to vessel catheterization. This approach allows for

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ease of catheter manipulation and decreases the risk of retroperitoneal hemorrhage associated with external iliac artery puncture (69). Alternatively, punctures may be made over the femoral head, which is typically above the groin crease, thus allowing for more efficient vessel tamponade during post-procedure compression (70). Transbrachial and transaxillary catheterization sites are particularly useful when femoral pulses are weak or absent as seen in patients with severe aortoiliac disease. Both sites have complication rates that are nearly as low as the transfemoral approach (93). Once a catheterization site has been chosen and prepared, a double wall arterial puncture is generally performed using the Seldinger technique (1) which employs a puncture needle with a beveled stylet (Seldinger needle). The stylet is removed and the cannula is withdrawn until pulsatile blood flow is visualized. A guidewire is then advanced through the cannula into the vessel being catheterized and the cannula is removed, leaving the guidewire in place. Manual compression is held over the puncture site, as the guidewire by itself is insufficient for tamponade. Compression is released after a catheter or vascular sheath is successfully advanced over the guidewire into the vessel. Fluoroscopy is used to advance the catheter– guidewire combination. The catheter is never advanced without a leading floppy-tipped guidewire as this may raise an intimal flap. Similarly, mechanical contrast injection is never performed until the location of the catheter is verified fluoroscopically using a hand injection. Catheters can be exchanged over the guidewire as needed. In addition, guidewires can be exchanged as long as an indwelling catheter remains in place. The requirements of the procedure being performed will determine which catheter and guidewire combinations are optimal. Virtually all angiographic procedures require images obtained in at least two projections. This process is frequently time-consuming, as images must be evaluated before subsequent views are chosen. As a result, catheters are frequently left in the same position for minutes at a time. In order to prevent intra- and peri-catheter thrombosis and subsequent embolization, catheters have to be kept flushed with heparinized saline. In single, end hole catheters, a heparinized saline drip is sufficient. However, in those catheters with multiple end holes, a forceful injection by hand is necessary every 1 to 2 minutes. If a sheath is in place, a continuous saline drip is required by using a pressurized bag. Once the procedure is complete, the catheter and/or sheath are removed and the arterial puncture site is compressed by hand for no less than 10 minutes unless a percutaneous device is used. In obese patients, in patients with an abnormal coagulation profile, after particularly long procedures, or after large catheters or sheaths have been used, compression may have to be as held as long as 1 hour. The use of mechanical compression devices or sandbags is strongly discouraged as these prevent direct visualization and palpation of the arteriotomy site.

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Part I Imaging Techniques

Complications of Angiography Nonsystemic complications of arteriography unrelated to contrast administration are usually caused by faulty catheter and guidewire technique. These include: 1.

2. 3.

hematoma, arteriovenous (AV) fistula and/or a pseudoaneurysm (Fig. 5.2) at the arterial puncture site; intimal tear, occasionally resulting in arterial rupture, thrombosis, or pseudoaneurysm formation; distal embolization related to atheroemboli or pericatheter thrombosis.

The most common complications related to arteriography are those that occur at the arterial puncture site. These are much more common during coronary arteriography secondary to the routine use of systemic heparinization during these procedures (107,108). Hematoma and AV fistula formation (Fig. 5.3) typically occur as a result of arterial punctures below the femoral head. These punctures are frequently located in the proximal superficial femoral artery and occur as the result of the inability to compress the arterial puncture site over the femoral head at the end of the procedure. Similarly, retro-

A

peritoneal hemorrhage has been reported following external iliac artery punctures above the femoral head (93,116). Intimal tears (Fig. 5.4) typically occur as a result of forceful catheter and/or guidewire advancement. They may also occur as a result of advancing the catheter without a leading floppy-tipped guidewire. These tears usually progress in a retrograde direction and frequently require no treatment. However, if the injury is severe enough, thrombosis, pseudoaneurysm, or rupture has been known to occur. Distal embolization (Fig. 5.5) usually results secondary to one of two mechanisms. The most common and typically least serious incidents are related to inadequate catheter flushing with resultant intra- and peri-catheter thrombosis and embolization. More serious causes of distal embolization include atheroemboli as a result of mechanical injury to the vessel wall and subsequent distal embolization of vessel wall material. Multiple cholesterol emboli syndrome has also been described, which involves systemic embolization of cholesterol crystals with a subsequent mortality rate greater than 50% (117). Fortunately, this latter complication is extremely rare. If a percutaneous closure device is used, reported complications are hematoma, infection, pseudoaneurysm, embolization, and AV fistula formation (144,145).

B

FIGURE 5.2 Following coronary arteriography, a palpable right groin mass was noted. (A) Digital subtraction arteriogram demonstrates a collection of contrast material (arrow) overlying the right common femoral artery and its bifurcation. (B) Oblique view demonstrates to better advantage the pseudoaneurysm and its neck (curved arrow).

Chapter 5 Fundamentals of Angiography

A

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B

FIGURE 5.3 (A) Advanced atherosclerotic disease is demonstrated on this early arterial phase film from a digital subtraction run. (B) Two seconds later, contrast medium is still seen in the arteries but there is early and intense venous opacification on the right (arrow). Etiology is an arteriovenous fistula from a knife wound.

FIGURE 5.4 Following cardiac catheterization, diminished pulse on the right was noted. Note the intimal flap (arrow) in the right external iliac artery.

FIGURE 5.5 Embolus (arrows) in the distal popliteal artery, proximal anterior tibial and tibial peroneal trunks. Patient underwent cardiac catheterization.

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A widely quoted paper on the complications of angiography published in 1981 (95) reported the overall complication rate for transfemoral arteriography to be 1.7%; the rates for translumbar and transaxillary arteriography were 2.9% and 3.3%, respectively. These complication rates include systemic complications related to contrast administration. For further information regarding contrast-related complications, please refer to the section on Contrast Material. Since the time of that publication, angiographic techniques and the treatment and recognition of complications have improved dramatically. However, these gains have probably been more than offset by the increased use of more invasive interventional, endovascular procedures.

Angiographic Interpretation The fundamental mechanism responsible for angiographic image production is the displacement of blood by contrast media of high atomic weight, thus reducing the transmission of x-ray photons in that region. This results in differential exposure on an x-ray-sensitive film or receptor. Thus, images are obtained reflecting the flow of blood only. Differences in tissue density independent of blood flow are not evaluated. Osseous and air-filled structures visualized on conventional film-screen images are useful only as a reference for anatomic evaluation. Carbon dioxide produces a “negative” filling defect that reflects blood flow but also the effect of gravity. The patient needs to be placed in a head-down position. If improperly injected, CO2 breaks up into individual pockets of contrast. A knowledge of anatomy is crucial for proper angiographic interpretation. Once the vessel is identified, it is important to determine the location of the catheter and at what stage during the injection the image was obtained. For instance, images obtained early during contrast injection will show incomplete arterial opacification while those obtained later may only demonstrate venous filling. The pattern of vessel branching is also important. Vessels typically branch in a progressive and regular manner demonstrating normal arborization. The presence of abrupt and irregular branching, of abnormal narrowing and dilation, and of a prolonged capillary blush or stain are suggestive of neovascularity and may indicate malignancy. Malignancies may also demonstrate early draining veins due to the presence of numerous AV fistulas. After anatomical evaluation, specific vessel wall characteristics should be identified. Normal vessel walls are typically smooth and sharply marginated. The presence of linear defects or smooth undulations may be indicative of intimal tears or vascular spasm, respectively. Less subtle abnormalities such as focal stenoses or occlusions should be searched for as well. These abnormalities are typical of injury and atherosclerotic disease. The presence of large collateral vessels may be the only

indication of a hemodynamically significant stenosis or occlusion which should be searched for if this abnormality is not immediately obvious. Hemodynamic significance is generally assumed to occur when 50% of vessel diameter or 75% of vessel area is compromised (109,110). Vessels need to be observed in multiple views and the clinical and noninvasive findings explained (Fig. 5.6). The presence of hemorrhage or thrombosis should also be determined. Extraluminal, amorphous pools of contrast, which remain unchanged after the majority of contrast media has flowed out of the image, are suggestive of hemorrhage. Nonocclusive vascular filling defects or vascular occlusions with a convex inner surface are suggestive of thrombus and embolus respectively. It is also important to be aware of the numerous artifacts and technical misrepresentations, which may masquerade as real pathology. Artifacts are particularly prevalent when using digital subtraction technology (Fig. 5.6C), especially when the patient moves before mask subtraction. Numerous technical factors such as film fogging or underexposure may also affect image quality. Examples of faulty technique causing spurious findings include poor image timing or inadequate contrast injection resulting in incomplete vessel opacification. In addition, injecting contrast too rapidly, especially in a small vessel, may result in rapid venous opacification resembling an AV fistula. Finally, there should be familiarity with the angiographic appearance of vessel injury resulting from faulty catheter and guidewire technique. These complications include subintimal injection of contrast, AV fistula, pseudoaneurysm, vessel rupture, and thrombosis. These abnormalities as well as others are discussed in the section on Complications of Angiography.

Head and Neck Angiography Indications The role of arteriography in the evaluation of head and neck pathology has become much more focused as a result of the widespread acceptance of ultrasound, CT, and MRI for initial diagnostic evaluation. Magnetic resonance angiography has in particular assumed a dominant role in extracranial artery imaging. Angiography is limited to those patients for whom noninvasive imaging is inconclusive and where the information obtained will influence medical or surgical management, particularly the latter. Specific indications for arteriography include the evaluation of intra- or extracranial trauma, aneurysms, vascular malformations, neoplasms, and hemorrhage. However, the most common indication remains the assessment of cerebrovascular disease (73). Head and neck arteriography includes selective studies of the carotid, cerebral, vertebral, and spinal circulations. Carotid arteriography is performed most com-

Chapter 5 Fundamentals of Angiography

A

C

monly when evaluating extracranial cerebrovascular disease. The indications for carotid arteriography are listed in Table 5.2. Color duplex Doppler ultrasound remains the screening procedure of choice (74). Many patients then receive an MR angiogram or a CT angiogram before surgical intervention, negating the need for contrast angiography (75–77,82).

Risks Head and neck angiography is an invasive procedure and, like all such procedures, is associated with thromboembolic complications related to catheter/guidewire manipulation and contrast administration. Such events may be

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B

FIGURE 5.6 (A) 64-year-old man with bilateral lower extremity ischemic symptoms. Stenosis of right distal common iliac artery and external iliac artery is evident (arrows). No definite lesion on the left to explain symptoms and decreased pulses. Examination is with cut film. (B) Right anterior oblique view with digital subtraction filming again demonstrates the right common iliac artery stenosis (arrow) but foreshortened visualization of the left common iliac artery. (C) Left anterior oblique view demonstrates an ulcerated lesion of the left common iliac artery and a 90% stenosis of the distal left common iliac artery (arrow). Note that there is obliteration of a segment of distal left external iliac artery which appears to represent an area of occlusion. This is a subtraction artifact secondary to overlying bladder contrast media and should not be mistaken for actual pathology.

relatively well tolerated in other circulatory distributions. However, when they occur in the cerebral circulation, stroke or death may result. In order to evaluate arteriographic risks, patients without central nervous system symptoms have to be evaluated separately from those who are symptomatic for central nervous system disease (i.e., transient ischemia attack, amaurosis fugax, nondisabling stroke). In addition, permanent nonfatal central nervous system complications should be classified separately from those that are transient and/or are reversible (i.e., clearing within one week). Risk factors include high-grade stenoses, bilateral stenoses, large volume of contrast, long procedure duration, azotemia, multiple catheter and guidewire exchanges and operator inexperience (78,80–82).

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TABLE 5.2 Indications for diagnostic extracranial carotid arteriography (adapted from reference 73) I. Diagnosis and evaluation of cerebrovascular disease A. Central nervous system symptoms present 1. Angiography is indicated when hemorrhage, tumor, etc. have been excluded by other imaging modalities. Noninvasive testing is not indicated B. Central nervous system symptoms absent 1. Noninvasive testing results positive or inconclusive: angiography is indicated when confirmation is needed for medical or surgical management 2. Noninvasive testing results negative: angiography is not indicated II. Diagnosis and evaluation of head and neck tumors, carotid aneurysms, penetrating vascular trauma and blunt trauma presenting with focal neurological signs after intracranial hemorrhage or contusion has been ruled out

In asymptomatic patients undergoing selective carotid arteriography, the risk of transient/reversible central nervous system complications ranges from 2.2% to 6.0% while the permanent complication rate is about 0.3% (78,79). In symptomatic patients undergoing selective carotid arteriography, the risk of transient or reversible complications ranges from 0.7% to 5.6% while the rate for permanent central nervous system complications ranges from 0.0% to 5.7% (79–81). The generally accepted risk of symptomatic patients for transient or reversible central nervous system complications is about 4% while the risk for permanent central nervous complications in these patients is about 1% (82). The death rate for symptomatic patients undergoing selective carotid arteriography is less than 0.1% (82). For asymptomatic patients, the risks are generally half the rate observed for symptomatic patients.

The common carotid arteries are catheterized individually. Images in at least two obliquities are obtained over both the cervical and intracranial carotid circulations. We prefer the use of the digital subtraction technique as it allows for more rapid image acquisition. Stenoses are the most commonly encountered lesion in patients with cerebrovascular disease (Fig. 5.8). These typically occur at the origin of the internal carotid artery. However, they may also involve the distal common carotid artery. Plaque ulcerations (Figs. 5.9, 5.10) are an ominous finding when associated with stenotic lesions, as they are associated with an increased thromboembolic risk. Stenoses are considered hemodynamically significant when there is compromise of at least 50% of luminal diameter or 75% of luminal area (109,110). When lesions greater than 90% luminal diameter are encountered, immediate systemic heparinization is advised as these patients are at a much higher risk for stroke. Occasionally, complete occlusions of the common or internal carotid artery are encountered. When these occur, careful evaluation of the intracranial circulation is necessary in order to determine collateral flow. The findings for carotid arteriography in patients with blunt or penetrating trauma to the neck are different from those seen in patients with cerebrovascular disease. When penetrating zone II and III neck wounds are associated with focal neurological signs, active bleeding, or expanding hematoma, angiographic evaluation is deferred in favor of surgical exploration (112,113). In patients

Technique and Findings of Carotid Arteriography Carotid arteriography is typically performed following duplex Doppler ultrasound screening and as an outpatient procedure in patients referred for elective evaluation (138,139). In the absence of other significant pathology, patients are admitted for angiography only if they have rapidly progressing cerebrovascular symptoms. Angiography is performed using the femoral approach when it is available. Alternatives include the brachial or the axillary approach. Arch injections may or may not be performed prior to selective carotid artery catheterization (Fig. 5.7). Some workers believe that aortic arch arteriography increases the risk for stroke. However, we find that performing such a procedure before selective carotid artery catheterization allows for proper catheter selection for shorter procedure duration and identifies significant great vessel disease (111).

FIGURE 5.7 Thoracic aortogram performed prior to selective carotid arteriography. Minimal disease of the innominate artery. Moderate stenosis at the origin of the right vertebral artery (arrow). The left common carotid artery is normal as is the visualized portion of the right.

Chapter 5 Fundamentals of Angiography

with zone I injuries, angiography should be performed regardless of findings since vascular injury may be occult (113). In patients with zone II and III injuries but without evidence of active bleeding or focal neurological signs, angiography is performed when the penetrating injury has violated the platysma muscle (113). Angiographic findings include free extravasation of contrast, pseudoaneurysm formation, carotid artery dissection and arteriovenous fistula. In those patients who have received blunt trauma to the neck in the absence of intracranial injury, angiography is performed only when focal neurologic signs are present (115). Angiographic findings are similar to those seen with penetrating trauma but include a larger proportion of patients with isolated intimal disruption.

Pulmonary Angiography Indications

However, in the last five years, the indications have markedly contracted with the concomitant growth of CT pulmonary angiography using multislice, helical CT scanners. In our institution, patients are initially evaluated with ventilation–perfusion scans. If the study is equivocal, CTA is the next most appropriate test. Commonly, however, CTA is becoming the initial procedure of choice (146,147). Pulmonary arteriography is performed almost exclusively for the diagnosis of pulmonary embolism. Rare indications for this study include assessment of congenital heart disease and the diagnosis and possible treatment of congenital pulmonary AV malformations (Osler–Weber– Rendu syndrome). Indications for pulmonary angiography are presented in Table 5.3. In summary, this study should be performed whenever there is uncertainty regarding the diagnosis of pulmonary embolus or when the results of the ventilation–perfusion scan or CTA is at odds with the clinical picture. Pulmonary angiography should also be performed when standard treatment modalities, such as anticoagulation, are relatively contraindicated,

Unlike the other angiographic procedures discussed in this chapter, the technique of pulmonary angiography has undergone little change over the last decade.

FIGURE 5.8 Selective catheterization of the left common carotid artery demonstrates a 98% stenosis of the left internal iliac artery (arrow).

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FIGURE 5.9 Selective catheterization of the right common carotid artery demonstrates no hemodynamically significant stenosis. There is a small ulceration in the proximal internal carotid artery (arrow).

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Part I Imaging Techniques TABLE 5.3 Indications for diagnostic pulmonary arteriography (adapted from reference 73) Suspected pulmonary embolus when ventilation–perfusion scanning cannot be performed High probability ventilation–perfusion scan when there is a contraindication to anticoagulation Indeterminate or low-probability ventilation–perfusion scan in a patient with a high clinical suspicion of pulmonary embolus Diagnosis and evaluation of suspected chronic pulmonary embolus Diagnosis and evaluation of other suspected pulmonary abnormalities, such as vasculitis, congenital and acquired anomalies, tumor encasement, and vascular malformations

FIGURE 5.10 Digital subtraction arteriogram of the right carotid system demonstrating an ulcerated plaque with a hemodynamically significant stenosis at the origin of the internal carotid artery (arrow).

necessitating increased diagnostic accuracy before the institution of potentially harmful therapy.

Risk Historically, the risk of death during pulmonary arteriography was quite high. Earlier studies reported a mortality rate of 2% (84). These events occurred primarily in patients with pulmonary hypertension and a failing right ventricle. It has been hypothesized that both the volume load and the high osmolarity of contrast delivered during main pulmonary arterial injections creates an increase in

right ventricular afterload which is too high for the failing right ventricle to handle. As a result, patients develop immediate systemic hypotension, apnea, and subsequent cardiac arrest in spite of all resuscitative measures. It has been advocated that pulmonary arteriography not be performed with a right ventricular end-diastolic pressure greater than 20 mmHg (85). However, more recent reports have indicated that the death rate following pulmonary arteriography is actually 0.2% and the morbidity is 4.0% (85,86). The reduction in mortality is attributed to the use of both selective catheterization techniques and low-osmolarity contrast media. These changes have resulted in a smaller increase in right ventricular afterload during angiography. Another complication of pulmonary arteriography is perforation of the right ventricle or right ventricular outflow tract, which has been reported to be as frequent as 1% (85) but is now thought to be much more rare. This event occurs during mechanical contrast injection when a pulmonary artery catheter recoils, perforating the ventricle. Perforation may also occur during catheter manipulation in the right heart, especially when an antecubital vein approach is chosen in which a straight-tip catheter is used. This site is no longer in common use and pigtail catheters are most often used. Surprisingly, patients with right ventricular rupture usually recover without sequelae (85). Significant ventricular arrhythmias have also been known to occur during passage of the catheter through the right ventricle. This is thought to be secondary to mechanical irritation of the bundle of His located in the cephalad portion of the intraventricular septum. It is not uncommon for runs of ventricular tachycardia to be noted during this portion of the procedure. Ventricular fibrillation, right bundle branch block, complete heart block, paroxysmal atrial tachycardia, and bradycardia have also been reported. Fortunately, these arrhythmias are usually transient and terminate when the catheter is pulled out of the ventricle or advanced into the pulmonary outflow tract. Relative contraindications of pulmonary arteriography related to catheter-induced arrhythmias include a left

Chapter 5 Fundamentals of Angiography

bundle branch block, as passage of the catheter through the right ventricle may precipitate a right bundle branch block with resultant complete heart block (85). Patients with left bundle branch block should have a prophylactically placed transvenous ventricular pacer wire before pulmonary angiography.

Technique and Findings Patients referred for pulmonary arteriography are typically heparinized before the procedure by the clinical service because of suspected pulmonary embolus. However, heparinization is not a contraindication to the performance of this study. The infusion is simply turned off immediately prior to the venous puncture and restarted following procedure termination if a pulmonary embolus is identified. Bleeding sequelae in fully anticoagulated patients is extremely rare given the low hydrostatic pressure of the venous circulation. Ventilation–perfusion scans are typically ordered prior to pulmonary angiography. However, these studies are limited by their low specificity (86,87). Even patients with lowprobability scans may be referred for pulmonary arteriography, especially if there is a high index of suspicion for pulmonary embolus (73,86,88). The results of the perfusion portion of this study may be used to tailor the pulmonary arteriogram so that unnecessary vessel catheterizations are not performed. Pulmonary arteriography should be obtained within 48 hours of suspected embolization since lysis of pulmonary emboli begins to occur at this time (89). Where available, multislice helical CTA is the procedure of choice prior to routine pulmonary angiography. Pulmonary arteriography is generally performed using a femoral approach. An 8-Fr. pigtail catheter is advanced into the confluence of the inferior vena cava, and an inferior vena cavagram is obtained. This study is performed to rule out inferior vena caval thrombus. A pigtail catheter is used as it has little recoil during mechanical contrast media injection and thus maintains a stable position. The catheter is then advanced into the right atrium where right atrial pressures are obtained. Subsequently, it is passed through the tricuspid valve over the manually curved back end of a guidewire or a deflector wire. The catheter is then advanced with a twisting motion into the pulmonary outflow tract and pulmonary arterial pressures are determined. The latter is mandatory as the rate and volume of contrast administration are decreased in the presence of pulmonary hypertension. With very significant acute pulmonary hypertension, catheter pulmonary angiography may in fact be contraindicated. First- or second-level pulmonary branches are then selected and the pulmonary angiogram is performed. Images are always obtained in at least two and frequently three obliquities (91). Angiographic findings of pulmonary embolus are limited to intraluminal filling defects or pulmonary artery cutoffs or both (89,90)

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(Fig. 5.11). Occasionally contrast will be noted to flow at different rates in vessels adjacent to one another—slowed linear velocity of flow. Regional decreased blood flow (oligemia) and atelectasis may also be seen. These last three findings are suspicious for pulmonary embolus but are not diagnostic as they can be seen with other pathological conditions for which there is a large differential diagnosis (Table 5.4) (90). We film our studies using digital subtraction technique at 4 to 6 frames per second (148).

Thoracic Aortography Indications Perhaps no other area of diagnostic imaging has the immediate impact on patient management as that of angiography for the evaluation of the thoracic aorta. Thoracic aortography has long been held as the gold standard for the evaluation of life-threatening aortic dissection and traumatic injury (118–122). Emergency operative management has traditionally been based entirely on the results of such studies (120,122,123). However, this is changing, with CTA playing an ever-increasing role. Recently, efforts have been made to increase the diagnostic specificity of aortography. Less invasive screening methods have been employed with the hope of avoiding the unnecessary angiographic morbidity and mortality associated with negative studies. It has been reported that the yield of diagnostic aortography for the evaluation of traumatic aortic injury is as low as 10% because of the high true negative rate (120). CT angiography is now widely used for screening patients with suspected aortic pathology. It has both a high sensitivity and specificity (120,124,125). MRI has been found useful in the detection and assessment of aortic aneurysm but its use is strictly reserved for elective evaluation (118,126). The use of MRI for the detection of aortic dissection is currently limited by artifacts which may mimic pathology (129). Although transthoracic and transesophogeal echocardiography have been shown to be reliable diagnostic tools (127,128), their use is limited by the high degree of user dependency required for acceptable diagnostic efficacy (118). The greatest limitation, however, of all these less invasive imaging modalities is the amount of time consumed by their employment, especially in those patients whose chance of survival decreases rapidly with each passing minute. In addition to being expedient, aortography allows for delineation of the great vessel and coronary artery anatomy, which is not possible using the previously described techniques. In addition, the presence or absence of aortic regurgitation and the exact anatomy and location of the intimal tear can be clearly identified. This information is required for proper surgical planning (118). It is for these reasons that the angiographic evaluation of the thoracic aorta is still considered valuable for the evaluation of acutely ill patients.

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A

B

FIGURE 5.11 (A) Anteroposterior view of the chest for pulmonary arteriography. Catheter is placed in the right main pulmonary artery and demonstrates several small emboli. Embolus in the descending ramus is seen en face (arrow). (B) Right posterior oblique view demonstrates to better advantage the large embolus (arrow) occupying much of the descending ramus.

TABLE 5.4 Differential diagnosis for acute pulmonary embolus (adapted from reference 90) Normal Acute pneumonia Atelectasis Bronchiectasis Postinflammatory fibrosis Postsurgical changes Chronic pulmonary embolism Primary pulmonary embolism Pulmonary venous hypertension Emphysema Carcinoma

femoral approach should not be employed as this frequently leads to catheterization of the false lumen, increasing procedure length. This is particularly problematic in acutely ill patients where expediency saves lives. In trying to avoid this occurrence, we choose the right brachial approach. The false lumen is rarely catheterized using this puncture site, even with dissections extending into the innominate artery. Filming with digital subtraction angiography (DSA) is done in left anterior oblique view initially and the anteroposterior (AP) and/or lateral views.

Traumatic Aortic Injury Technique and Risk The technical approach to thoracic aortography is dependent on the pre-angiographic diagnosis. Likewise, the choice of technique is associated with risks unique to each approach. The general risks of angiography are discussed in the section entitled Complications of Angiography.

Aortic Dissection In approaching a patient with an acute aortic dissection, especially those involving the ascending aorta (Stanford type A or DeBakey type 1 and type 2) (135,136), the

For patients presenting with blunt trauma to the chest wall, aortography is performed in our medical center when the supine chest radiograph demonstrates a mediastinal width greater than 8 cm at the level of T4, when there is loss of the aortic knob contour, or upon demonstration of fractures involving any of the first three ribs (121). We do not perform aortography on the basis of injury mechanism alone, although this has been described by others as a sole indication for angiographic evaluation (133,134). If none of these radiographic findings are present, the patient is referred for thoracic CT to rule out the presence of hemomediastinum, abrupt change in aortic arch caliber, and/or abnormal aortic

Chapter 5 Fundamentals of Angiography

arch contour. Frequently, CTA is becoming the initial procedure of choice. The occurrence of any of these findings, or of a nondiagnostic study, is an indication for aortography. The femoral approach is preferred for the evaluation of traumatic aortic injury. These vessel wall disruptions rarely result in dissections so that entering the false lumen is not a consideration in evaluating patients with this pre-procedure diagnosis (121). As aortic injuries are most frequently found at the aortic isthmus, care must be taken in passing catheters and guidewires across this region, as complete disruption, with resultant death, is a possible complication (130).

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abnormalities include pseudoaneurysm formation, also most frequently seen in this region (121). Transmural laceration (rupture) of the aorta is an unusual finding as this is all but incompatible with survival. Rarely, the aorta may be occluded. Injuries to the ascending aorta are extremely rare as they usually result in death at the accident scene (137). Care must be taken to differentiate pseudoaneurysm from a ductus diverticulum, which is a normal variant (121).

Abdominal Angiography Indications

Findings Aortic Dissection The pathognomonic angiographic sign of aortic dissection is the demonstration of a double lumen separated by an intimal flap. Supporting, indirect signs include the appearance of luminal compression, aortic insufficiency and the presence of an isolated intimal flap. Additional, less important angiographic signs include displacement of an angiographic catheter more than 1 cm from the outer aortic wall shadow and the presence of a small ulcer-like collection of contrast projecting beyond the aortic wall (118). The false lumen typically originates along the outside curve of the ascending aorta traveling over the apex of the aortic arch. In DeBakey type I dissections, the lumen spirals inferiorly down the descending aorta to the posterior aspect of the abdominal aorta. The false lumen frequently reenters the true lumen at or near the aortic bifurcation. The true lumen can be differentiated from the false lumen in the ascending aorta upon visualization of the sinus of Valsalva, the coronary arteries, and the aortic valve. These three structures always fill via the true lumen (131). Demonstration of normal aortic arch vessels, and of normal flow characteristics and pressure is also further evidence of true lumen opacification. In the abdominal aorta, vessels may originate from either the true or false lumen (Fig. 5.12). Contrast extravasation into the pericardial sac and/or left pleural space is a sign of rapidly impending demise. False negative angiographic studies occur in approximately 2% of cases and are due predominantly to the presence of a completely thrombosed false lumen (132). Alternatively, both the false and the true lumen may demonstrate equal and simultaneous opacification, thereby obscuring the intimal flap (132).

Traumatic Aortic Injury The findings for traumatic aortic injury are highly variable. Abnormalities as subtle as a small intimal tear may be seen in the vicinity of the aortic isthmus. More severe

Abdominal angiography can be divided into three general areas. The first encompasses selective visceral arteriography. Visceral arteriography no longer plays the diagnostic role that it once did. This is due to the less invasive imaging modalities of ultrasound (US), CT, and MRI. Its use is limited to selected diagnostic procedures and endovascular therapy using pharmacoangiographic and embolization techniques. The most common diagnostic procedure is the evaluation of gastrointestinal (GI) bleeding. Pharmacoangiography employing pitressin to control GI hemorrhage (98) or serotonin to stimulate gastrin secretion from gastrinomas (99) is well described. Embolization techniques combined with delivery of chemotherapy are useful for treating visceral tumors, especially those of hepatic origin (100). Embolization has also been advocated for use in treating primary gastrointestinal hemorrhage or hemorrhage secondary to trauma, especially involving the spleen (101). The role of visceral angiography for the evaluation of portal hypertension is rapidly dissipating as a result of the advent of the transjugular intrahepatic portosystemic shunt (102). Abdominal aortography is used to evaluate both atherosclerotic occlusive disease and aneurysm formation. Abdominal aortic aneurysms may be atherosclerotic, mycotic, congenital, or iatrogenic in origin. US and CT are employed primarily for screening as these modalities are less invasive than aortography (103,104) (Fig. 5.14). MRI has also been employed for aneurysm evaluation (105). In fact, US, CT, and MRI have been advocated as sufficient by themselves for the preoperative workup of abdominal aneurysm (104,106). At our institution, US is used both for screening and for serial aneurysm size determination. CT is used as a screening modality in those patients whose signs and symptoms may be referable to other organ systems and for the evaluation of possible aneurysm rupture. CTA is also invaluable in preprocedure planning for abdominal aortic stent–grafting. However, despite the increasing use of US, CT, and MRI, catheter aortography for preoperative aneurysm evaluation still remains popular throughout the country. Unlike the other less invasive imaging modalities, aortography can clearly identify mesenteric and/or renal artery steno-

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Part I Imaging Techniques

A

B

FIGURE 5.12 Patient presented with severe chest and abdominal pain. Thoracic aortography demonstrated a type 3 dissection. Examination of the abdomen with digital subtraction technique. (A) Early in the run the true lumen is opacified with visualization of the superior mesenteric artery and an aberrant right main renal artery. Only a small segment of the false lumen is seen. (B) Later in the run the false lumen (arrow) is seen to better advantage.

sis, accessory renal arteries, and inferior mesenteric artery occlusion, and can determine the exact relation of the aneurysm to the major aortic branches. This modality is also particularly useful in evaluating distal runoff, especially in those patients with symptoms of claudication. It is not of value, however, in determining aneurysmal size since intramural thrombus may be present, distorting the aortic lumen (104). The third major indication for abdominal arteriography is in the evaluation of renovascular hypertension. Captopril radionuclide renography and possibly duplex color Doppler ultrasound are the imaging procedures of choice as screening techniques. MRA and CTA are also useful in this regard. Arteriography, however, is unmatched in its ability to identify, delineate, and quantify renal artery stenoses. The presence of segmental artery disease and the status of the distal vascular bed can also be assessed. Planning for angioplasty stenting or bypass grafting is also an essential benefit of the procedure.

Technique and Risk The technique and risk of abdominal aortography is discussed in the sections on Peripheral Arteriography and

Complications of Arteriography. A discussion regarding the risk and technique of visceral arteriography is beyond the scope of this chapter.

Findings The angiographic diagnosis of abdominal aneurysm is straightforward. Typically, patients with known abdominal aortic aneurysm are referred for angiographic evaluation before operation or stent–grafting. The size of the aneurysm has usually already been determined by noninvasive imaging modalities. Angiography is necessary to confirm the diagnosis and to determine the extent of aneurysmal involvement of vital structures such as the renal, mesenteric, and iliac arteries (Fig. 5.13B and C). In addition to aneurysmal involvement of these vessels, hemodynamically significant stenoses are searched for since operative ligation of potential collateral vessels may be disastrous. For example, ligation of a hypertrophied inferior mesenteric artery in the setting of superior mesenteric artery stenosis or occlusion will frequently result in bowel ischemia or infarction. Other important considerations include evaluation of the flow to the lower extremities, specifically to the iliac and femoral arteries where graft anastomoses are most commonly performed.

Chapter 5 Fundamentals of Angiography

A

C

Renal artery disease is evaluated with aortography and frequently selective renal artery catheterization (Fig. 5.14). In addition to AP views, multiple oblique views are frequently required to fully evaluate the renal artery. Stenoses can be ostial or proximal and most frequently on an atherosclerotic basis. Mid-renal arterial lesions, often with a classic “string of beads” appearance, are usually of fibromuscular dysplastic origin. The degree of luminal narrowing is assessed for determining hemodynamic significance. Modern digital subtraction angiographic systems can automatically determine degree of stenoses based on pixel densities or area measurements. Poststenotic dilation does not indicate hemodynamic significance. The presence of unopacified flow defects on selective injection may, however, be of

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B

FIGURE 5.13 (A) Computed tomography demonstrates an abdominal aortic aneurysm. The residual lumen is filled with contrast and is surrounded on the left by an eccentric thrombus. (B) Abdominal aortography demonstrates a fusiform aneurysm as manifested by its residual lumen. (C) Lateral view is utilized to better demonstrate the origins of the celiac (arrow) and superior mesenteric (arrowhead) arteries. At times the renal artery origin and, therefore, the length of the infrarenal cuff can be better seen in the lateral view.

value. Selective renal vein renins may also be useful in this regard.

Peripheral Angiography Indications and Basic Concepts Perhaps nowhere else has the role of diagnostic angiography changed so rapidly as it has for the evaluation of patients with suspected peripheral vascular disease. This has occurred primarily as a result of the increasing importance of surgical and interventional therapy for vascular disease below the knee. Refinement in noninvasive vascular testing has also changed the indications by eliminating the need for arteriography to be a screening technique.

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Part I Imaging Techniques

FIGURE 5.14 A 68-year-old woman with uncontrollable hypertension and progressive renal failure. Aortography demonstrates very advanced atherosclerotic disease of the abdominal aorta. Absent right main renal artery. High-grade stenosis of the left main renal artery near its origin (arrow).

Magnetic resonance angiography (MRA) has further redefined the indications. MRA provides excellent depiction of anatomy. Common indications for catheter angiography include incapacitating claudication, rest pain, and tissue compromise. Additional indications include threatened graft thrombosis and vascular injury. The presence of penetrating injury in proximity to a major extremity artery without signs or symptoms of a vascular injury is probably not an indication for arteriography (94,95). However, this issue is controversial and many authors still advocate elective arteriography for the evaluation of “proximity injury” (96,97). Angiographic evaluation should be limited only to those patients for whom the information obtained will have an impact in medical or surgical management. It is imperative that the angiographer possess a thorough knowledge of the patient’s medical history, presenting symptoms, physical findings, and the results of laboratory evaluation prior to angiography. Perhaps just as important is the availability of previous arteriographic studies in order to allow determination of disease progres-

sion. The angiographer is a consultant and should be able to determine the suitability of a patient for the proposed angiographic study. Essentially, two techniques are used to optimize vessel opacification and subsequent visualization (67). The first involves increasing the delivery of contrast agent to the distal vessels while the second involves methods used to increase contrast agent detection. The simplest method of increasing contrast delivery is increasing the volume and rate of contrast injection. Increases in the volume of contrast delivered result in longer injections, which take advantage of the vasodilatory effects of contrast and aid in the coordination of filming sequences (83). However, contrast will not flow faster than blood itself, so that increases in the contrast injection rate result in reflux of excess contrast agent into vessels more proximal than those being studied. Typical injection volumes and rates for programmable lower extremity arteriography are in the range 70 to 100 mL at 8 to 10 mL/s with injection at the bifurcation of the aorta. Selective unilateral catheterization necessitates appropriately lesser amounts and slower rates. Selective vessel catheterization also improves distal vessel opacification by preventing flow of contrast into contralateral vessels or into those vessels more proximal to the ones being evaluated (68). The use of inflow vessel occlusion balloons and of inflated contralateral thigh pressure cuffs has also been reported (67,69). However, we find these last two methods unnecessary for routine utilization. Peripheral vasodilation also allows for greater delivery of contrast material and multiple methods can be used to achieve the same results. The most common modality is pharmacoangiography using agents that relax smooth muscle. Those commonly employed include nitroglycerin, phentolamine, and tolazoline (62). Other methods include producing reactive hyperemia following application of a blood pressure cuff to the distal calf or following the application of local heat (67). We have found the use of nitroglycerin the most efficacious of all the methods described. Increases in contrast detection are generally achieved in two ways (67). The first involves the coordination of film sequences, allowing image acquisition only during maximum contrast opacification. At times this can be rather difficult using conventional film-screen technique since contrast flow cannot be fluoroscopically visualized during image acquisition. This problem can be solved by using stepping intra-arterial digital angiography (“bolus chose”) where direct fluoroscopic assessment of maximal contrast opacification allows for tailoring of the imaging sequence during the study injection itself. The second method employed for increasing contrast detection is the use of intra-arterial digital subtraction angiography. This method provides for a remarkable increase in contrast resolution and is invaluable for evaluating the small, low-flow vessels typically found beyond vascular occlusions. In the past, this method has been limited by the lack of technology allowing stepping

Chapter 5 Fundamentals of Angiography

sequences to be performed during digital subtraction image acquisition. Thus, a separate contrast injection was required for every subtracted image. However, stepping intra-arterial digital subtraction image acquisition is now routine available (18). With some manufacturers the tabletop is moved a precise distance, with others, the gantry is moved. With either technique, precise DSA images are obtained that can delineate vessels as small as the posterior pedal arch. Digital subtraction techniques are required for carbon dioxide studies.

Technique and Risk Peripheral arteriography is typically performed using a femoral artery approach. Alternate approaches include transbrachial/transaxillary catheterization and, rarely, translumbar entry. These approaches are useful if the patient suffers from severe aortic–iliac disease and the femoral pulses are weak or absent. The complication rates associated with these approaches are close to those of femoral catheterization (93). Please refer to the section entitled Complications of Angiography for further information. For peripheral arteriography, we use low-osmolarity contrast media exclusively since the incidence of pain and heat related to contrast injection is much lower and motion artifacts are therefore reduced. In relatively healthy patients with symptoms of aortoiliac and/or distal disease, an abdominal aortogram is obtained prior to evaluating the flow through more distal vessels (the “runoff”). This study is performed in order to evaluate the aorta itself as well as the renal and visceral arteries. Images are typically obtained in one planeunless an aortic aneurysm is present or renovascular disease is noted. In these situations, a lateral image and/or oblique views are obtained. Following evaluation of the aorta, images of the “runoff” are obtained. This study involves acquiring AP images of the pelvis and of the vessels in both lower extremities. We routinely use DSA for the evaluation of aorta and stepping DSA for the runoff. Oblique views of the iliac arteries and common femoral artery bifurcation are obtained, especially if there are symptoms of aortic–iliac disease or if inflow or outflow graft placement is planned at the common femoral artery. Additional oblique views are also frequently necessary to evaluate the below-knee runoff. We prefer lateral images of the trifurcation vessels and the major vessels of the foot in addition to standard AP views of these regions. If the patient has chronic renal failure or has symptoms only of distal disease, or if there is a vascular injury, then arteriography may be limited to the extremity or region affected.

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occlusions is important. A recent embolic occlusion is identified by its convex intravascular appearance as well as the lack of large adjacent collateral vessels (Fig. 5.15). A chronic occlusion is demonstrated by a gradual tapering of the vessel involved as well as the presence of large and numerous collateral vessels (Fig. 5.16). Patients suffering from trauma may demonstrate intimal tears, pseudoaneurysms, extravascular contrast extravasation, and AV fistulas. The hemodynamic significance of a vascular stenosis should be evaluated in patients whose symptoms appear related to decreased blood flow in that vessel. Those obstructions, which compromise greater than 50% of luminal diameter, are (75% area stenosis) considered hemodynamically significant (109,110). Slowed linear velocity of contrast flow is also noted. Hemodynamic significance can also be determined by measuring the pressure gradient across the narrowed lesion. A pressure gradient greater than 15 mm is considered hemodynamically

Findings The findings on peripheral arteriography are mostly related to the evaluation of atherosclerotic disease. Abnormalities such as stenoses and occlusions are commonly searched for. Differentiation between recent and old

FIGURE 5.15 Distal right common femoral and proximal superficial femoral arteries show the presence of several intraluminal filling defects which are emboli (arrows) in this patient with atrial fibrillation.

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Part I Imaging Techniques

B

A

FIGURE 5.16 (A) Axillary arteriography via the left axillary artery and digital subtraction filming demonstrate occlusion of the infrarenal abdominal aorta. Large collateral vessels are demonstrated. The inferior mesenteric artery is very prominent (arrows). Leriche syndrome. (B) Reconstitution of the distal most abdominal aorta just prior to the bifurcation. Small but otherwise normal iliac arteries. (C) Normal superficial femoral arteries.

C

significant. Intraluminal pressure can be determined accurately only when the stenosis is approached in a retrograde manner. When approaching a stenosis in an antegrade fashion, the catheter used to obtain the pressure measurement distal to the diseased segment will spuriously increase the pressure gradient due to the occlusive effects of the catheter within the lesion. The induction of distal vasodilation is occasionally necessary in order to simulate conditions of work or stress. This is typically done using intra-arterial nitroglycerin, although reactive hyperemia may occasionally be used (62,67).

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trauma for vascular injury: results at one year. J Trauma 1991: 31: 502–511. Smith SH, Pond GD, et al. Proximity injuries: correlation with results of extremity arteriography. JVIR 1991: 2: 451–456. Rose SC, Moore EE. Trauma angiography of the extremity: the impact of injury mechanism on triage decisions. CVIR 1988: 11: 136–139. Rosch J, Keller FS, et al. Pharmacoangiography in the diagnosis of recurrent massive lower gastrointestinal bleeding. Radiology 1982: 145: 615–619. Doppman JL, Miller DL, et al. Gastrinomas: localization by means of selective intraarterial injection of secretin. Radiology 1990: 174: 25–29. Cho KJ, Andrews JC, et al. Hepatic arterial chemotherapy: role of angiography. Radiology 1989: 173: 783–791. Sclafani SJA, Weisberg A, et al. Blunt splenic injuries: nonsurgical treatment with CT, arteriography and transcatheter arterial embolization of the splenic artery. Radiology 1991: 181: 189–196. Richtor GM, Noeldge G, et al. The transjugular intrahepatic portosystemic stent shunt (TIPSS): results of a pilot study. Cardiovasc Intervent Radiol 1990: 13: 200–207. Vowden P, Wilkinson D, et al. A comparison of three imaging techniques in the assessment of an abdominal aortic aneurism. J Cardiovasc Surg 1989: 30: 891–896. Todd GJ, Nowygrod R, et al. The accuracy of CT scanning in the diagnosis of abdominal and thoracoabdominal aortic aneurisms. J Vasc Surg 1991: 13: 302–310. Lee JKT, Ling D, et al. Magnetic resonance imaging of abdominal aortic aneurisms. AJR 1984: 143: 1197– 1202. Ruff SJ, Watson MR. Magnetic resonance imaging versus angiography in the preoperative assessment of abdominal aortic aneurisms. Am J Surg 1988: 155: 651–654. McCann RL, Schwartz LB, Pieper KS. Vascular complications of cardiac catheterization. J Vasc Surg 1991: 14: 375–381. Kresowik TF, Khoury MD, et al. A prospective study of the incidence and natural history of femoral vascular complications after percutaneous transluminal coronary angioplasty. J Vasc Surg 1991: 13: 328–333. Mann FC, Herrick JF, et al. The effect on the blood flow of decreasing the lumen of a blood vessel. Surgery 1938: 4: 249. Moore WS, Malone JM. Effect of blood flow and vessel calibre on critical arterial stenosis. J Surg Res 1979: 26: 1. Joyce JW. Occlusive arterial disease of the upper extremity in Spittell JA (ed): Contemporary Issues in Peripheral Vascular Disease 1992: 22: 147–160. Menawat SS, Dennis JW, et al. Are arteriograms necessary in penetrating Zone II neck injuries? J Vasc Surg 1992: 16: 397–401. Hartling RP, McGahan JP, et al. Stab wounds to the neck: role of angiography. Radiology 1989: 172: 79–82. Scalfani SJA, Cavaliere G, et al. The role of angiography in penetrating neck trauma. J Trauma 1991: 31: 557–563. Fakhry SM, Jaques PF, Proctor HJ. Cervical vessel injury after blunt trauma. J Vasc Surgery 1988: 8: 501–508. Rappaport S, Sniderman KW, et al. Pseudoaneurism: a complication of faulty technique in femoral artery puncture. Radiology 1985: 154: 529–530.

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117. Rosansky SJ, Deschamps EG. Multiple cholesterol emboli syndrome after angiography. Am J Med Sci 1984: 288: 45–48. 118. Petasnick JP. Radiologic evaluation of aortic dissection. Radiology 1991: 180: 297–305. 119. DeSanctis RW, Doroghazi RM, et al. Aortic dissection. NEJM 1987: 317: 1060–1067. 120. Madayag MA, Kirshenbaum KJ, et al. Thoracic aortic trauma: role of dynamic CT. Radiology 1991: 179: 853–855. 121. Weiss JP, Feld M, et al. Traumatic rupture of the thoracic aorta. Em Med Clin N Am 1991: 9: 789–803. 122. Richardson JD, Wilson ME, Miller FB. The widened mediastinum: diagnostic and therapeutic priorities. Ann Surg 1990: 211: 731. 123. Blaisdell FW, Trunkey DD, eds. Trauma management cervicothoracic trauma. New York: Thieme, 1986: 3: 223–246. 124. Hamada S, Takamiya M, et al. Type A aortic dissection: evaluation with ultrafast CT. Radiology 1992: 183: 155–158. 125. Caputo GR, Higgins CB. Advances in cardiac imaging modalities: fast computed tomography magnetic resonance imaging and postron emission tomography. Invest Radiol 1990: 25: 838–854. 126. Dinsmore RE, Liberthson RR, et al. Magnetic resonance imaging of thoracic aortic aneurisms: comparison with other imaging modalities. AJR 1986: 146: 309–314. 127. Khandheria BK. Aortic dissection: the last frontier. Circulation 1993: 87: 1765–1768. 128. Erbel R, Oelert H, et al. The European Cooperative Study Group on Echocardiography: Effect of medical and surgical therapy on aortic dissection evaluated by transesophageal echocardiography: implications for prognosis and therapy. Circulation 1993: 87: 1604– 1615. 129. Solomon SL, Brown JJ, et al. Thoracic aortic dissection: pitfalls and artifacts in MR imaging. Radiology 1990: 177: 223–228. 130. LaBerge JM, Jeffrey RB. Aortic lacerations: fatal complications of thoracic aortography. Radiology 1987: 165: 367. 131. Soto B, Harman MA, et al. Angiographic diagnose of dissection aneurysm of the aorta. AJR 1972: 116: 146– 154. 132. Eagle KA, Auertermous T, et al. Spectrum of conditions initially suggesting aortic dissection but with negative aortograms. Am J Cardiol 1986: 57: 322–326. 133. Kirsh MM, Behrendt DM, et al. The treatment of acute traumatic rupture of the aorta: a ten year experience. Ann Surg 1976: 184: 308. 134. Smith RS, Chang FC. Traumatic rupture of the aorta: still a lethal injury. Am J Surg 1986: 152: 660. 135. Daily PO, Trueblood W, et al. Management of aortic dissections. Ann Thorac Surg 1970: 60: 237–247. 136. DeBakey ME, Henly WS, et al. Surgical management of dissecting aneurisms of the aorta. J Thorac Cardiovasc Surg 1965: 49: 130–149. 137. Parmley LF, Mattingly TW, Manion WC. Nonpenetrating traumatic injury of the aorta. Circulation 1958: 17: 1086. 138. Huckman MS. Outpatient brachiocephalic angiography. Radiology 1989: 170: 317–318.

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139. Millward SF, Marsh JJ, Peterson RA. Outpatient transfemoral angiography with a two hour observation period. CVIR 1989: 12: 290–291. 140. Diaz LP, Pabon IP, et al. Assessment of CO2 arteriography in arterial occlusive disease of the lower extremities. J Vasc Interv Radiol 2000: (2Pt1): 163–169. 141. Bees NR, Beese RC, et al. Carbon dioxide angiography of the lower limbs: initial experience with an automated carbon dioxide injector. Clin Radiol. 1999: 54(12): 833–838. 142. Chamberlin JR, Lardi AB, et al. Use of vascular sealing devices (VasoSeal and Perclose) versus assisted manual compression (Femostop) in transcatheter coronary interventions requiring abciximab (ReoPro). Catheter Cardiovasc Interv 1999: 47(2): 143–147: discussion 148. 143. Carere RG, Webb JG, et al. Initial experience using Prostar: a new device for percutaneous suture-mediated closure of arterial puncture sites. Cathet Cardiovasc Diagn 1996: 37(4): 382–391.

144. Cooper CL, Miller A. Infectious complications related to use of the anagio-seal hemostatic puncture closure device. Catheter Cardiovas Interv. 1999: 48(3): 301–303. 145. Carere RG, Webb JG, et al. Groin complications associated with collagen plug closure of femoral arterial puncture sites in anticoagulated patients. Cathet Cardiovascular Diagn 1998: 43(2): 124–129. 146. Raptopoulos V, Boiselle PM. Multi-detector row spiral CT pulmonary angiography: comparison with singledetector row spiral CT. Radiology 2001 Dec: 221(3): 606–613. 147. Remy-Jardin M, Remy J, et al. Diagnosis of pulmonary embolism with spiral CT: comparison with pulmonary angiography and scintigraphy. Radiology. 1996 Sep: 200(3): 699–706. 148. Hagspiel KD, Polak JF, et al. Pulmonary embolism: comparison of cut-film and digital pulmonary angiography. Radiology. 1998 Apr: 207(1): 139–145.

Haimovici’s Vascular Surgery, 5th Edition Edited by Enrico Ascher Copyright © 2004 by Blackwell Science

CHAPTER 6 Computed Tomography in Vascular Disease Frederick L. Hoff, Kyle Mueller, and William Pearce

Significant advances in computed tomography (CT) imaging technology have provided a unique view of the pathology of many vascular diseases. Prior to the 1980s, the diagnosis of many vascular diseases was based primarily on contrast angiography and venography in combination with ultrasound. While contrast arteriography and venography provide the anatomic detail for planning surgical procedures, noninvasive testing is essential to defining the physiologic importance of the anatomic lesion. Ultrasound imaging does provide both anatomic and hemodynamic detail, but its usefulness is limited to superficial structures. In the abdomen, bowel gas and solid organs interfere with the image resolution of ultrasound. In the thorax, ultrasound is limited to intracardiac pathology and the thoracic aorta. Since its advent in the 1960s, and through many advances in the modality over the following three decades, CT has become vital in the preoperative and postoperative management of many vascular diseases. The practice of medicine was transformed by computed tomography (CT). Recognizing this change, in 1979 Cormack and Hounsfield were awarded the Nobel Prize for their development of this technique (1). A key factor in the development of CT was the realization that greater advancement would be obtained not by increasing resolution but by enhancing the contrast between softtissue structures. The development of CT rested on important concepts in multiple fields including mathematics, computer science and physics. The first clinical CT unit was placed at Atkinson Morley’s Hospital in England on October 1, 1971 (1). Each

image took four minutes to acquire and two days were needed to reconstruct the series. The clinical importance of CT was immediately appreciated; by 1976, there were 22 companies manufacturing CT scanners and in 1979, there were over 1,000 scanners in use throughout the world. The procedure was initially termed “computer assisted tomographic” or “CAT” scanning; however, as images are not limited to the anatomic axial plane, this was later shortened to computed tomography (2). There has been continuous and dramatic improvement in both spatial and temporal resolution from that time due to advances in both hardware and software design. CT has had a dramatic impact on the diagnosis and treatment of vascular disease. Before the application of CT, contrast arteriography and venography were the only methods available to evaluate arterial and venous anatomy and disease. CT not only provides more information about the vessel (i.e., thrombus and wall) than these intraluminal techniques, it also provides valuable data about adjacent organs and tissues. Although 30 years old and generally considered a “mature” technology, CT continues to evolve. In the early 1990s helical CT was introduced, with significant impact on vascular applications. The ability to obtain thin, overlapping images rapidly enough to capture contrast within vessels ushered in three-dimensional techniques and “CT angiography.” The late 1990s saw the development of multidetector helical units that went far beyond the advances of helical CT. This chapter reviews both the basic principles of CT and its clinical applications.

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Image Reconstruction

Basic Principles The fundamental concept of CT is to use multiple projections of an object to reconstruct the internal structure of that object (3,4). The creation of a CT image can be divided into three steps: 1) data acquisition involves the actual exposure to radiation and scanning of the patient; 2) image reconstruction; and 3) image display. Data Acquisition A radiographic tube and an array of detectors as well as the associated electronics are mounted on a frame called a gantry (Fig. 6.1). The x-ray tube produces a fan-shaped beam of x-rays that interact with the patient via absorption or scattering; some of the x-rays pass through the patient to interact with the detector array. During data acquisition, the tube and detectors rotate around the patient and the detectors repeatedly measure the number of x-rays transmitted through the patient. The amounts of radiation transmitted to each detector and the gantry angle at the time of the measurement are recorded (Fig. 6.2). Typically, the detector array contains 500 to 1,000 detectors, each of which is sampled approximately 1,000 times per revolution (4). Each line of this information reflects the summation of the attenuation coefficients of all structures in that x-ray path. The entire dataset forms the “raw data” from which an image is reconstructed. Conventional or incremental scanning is obtained by performing a series of individual scans during suspended respiration. Following each scan the patient breathes, the patient table is advanced, and in most machines the tube and detector apparatus rewinds to begin another scan (5). Historically, most scanners operated at a rotation speed of one 360° revolution per second.

From the raw data a digital image is created. A variety of mathematical techniques can be used to accomplish this; these rely on the principles of back projection, iterative formulas, or analytic formulas, either with or without Fourier transformation (6). The result is a matrix of numbers; generally, a 512 by 512 matrix is employed in vascular CT. Each number in this matrix is called a pixel, and each pixel corresponds to a volume of tissue or voxel within the patient (Fig. 6.3). The average density of the tissue within each voxel is represented by the pixel value. The dimensions of the voxel in the scan plane are set by the field of view (FOV) and matrix; the dimensions of the pixel in these axes can be calculated by dividing the FOV by the matrix size. The third dimension, representing the voxel depth, is the image thickness, which is determined by the collimation width of the fan beam. The difference in attenuation of the contents of a voxel relative to water is defined as the CT attenuation number and expressed in Hounsfield units (HU) (7). A 12-bit number scale (212) is used which defines water as zero and air as –1000; therefore each pixel is a number from –1000 to +3095. Image Display This digital image or number matrix is converted to a visual format for interpretation. A gray scale is used, with

Data aquistion and detector assembly

X-ray generator

X-ray tube and collimator

FIGURE 6.1 Diagram demonstrating the radiographic x-ray tube and detector assembly mounted on the gantry. The patient is placed on the table and advanced through the gantry.

FIGURE 6.2 Diagram illustrating three sample positions of data measurement in obtaining a single image. Data is collected from approximately 1000 positions during each revolution. At each position, measurements are obtained from each detector in the array; while the example shows 16 detectors, in actuality between 500 and 1000 are used. The entire group of measurements forms the raw data used to reconstruct the internal structure of the scanned object.

Chapter 6 Computed Tomography in Vascular Disease

the densest materials such as bone (highest Hounsfield units) being assigned lighter shades while the least dense such as air (most negative Hounsfield units) are assigned darker shades. Any color or gray scale format can be chosen; the standard format above follows the conditions found in conventional radiographs. A problem arises in that display devices are limited to demonstrating approximately 60 shades of gray and the human eye may distinguish only 30–100 shades; the 4096 CT numbers cannot be mapped without conversion. Thus, the wide range of numbers is converted for display by window width and level controls. The window level specifies the centering of the gray scale and the choice of width specifies the numbers over which the gray scale is to extend. For example, if the window level is set to zero and the width is set to 500, every pixel a number below –250 will be black and every pixel greater than 250 will be white; if there are 50 shades of gray, each would be assigned a range of 10 numbers

Pixel

Voxel

Slice Width

FIGURE 6.3 Diagram illustrating the concepts of pixel and voxel. The average density of tissues in each volume element or voxel in the patient is represented by a single number in the computer as a pixel or picture element. The dimension of the voxel is equal to FOV/matrix in the x- and y-axes and by the slice width in the z-axis. The matrix of pixels is the digital image.

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with the middle gray used for the numbers adjacent to zero.

Electron Beam Computed Tomography Another approach to obtaining a computed tomography image is significantly different from the conventional and helical machines—electron beam scanning. This was termed “Ultrafast CT,” but now is most commonly called electron beam tomography (EBT) or electron beam computed tomography (EBCT). Developed in the early 1980s, the machine uses an electron beam that is magnetically deflected to hit tungsten targets about the patient to produce x-rays for scanning (8). The advantage is speed: initially designed for cardiac scanning, the EBT unit can obtain eight adjacent images in 50 ms. The unit was later adapted to obtain a single slice for use in body scanning (9). EBCT has not found widespread use in other vascular imaging to date.

Helical and Multidetector Helical Computed Tomography Helical or spiral CT involves a continuous rotation of the gantry as the patient is advanced at a steady rate through it, dispensing with the discrete steps of data acquisition in conventional CT (Fig. 6.4) (10,11). This creates a volume set of raw data which must then be segmented to create planar images. Although it has been argued that the term “helical” more accurately describes the concept of this new technology, both terms are found and used interchangeably in the literature (12). Introduced in 1989, there has been both rapid acceptance and distribution of the technology. The major advantages of helical scanning include rapid acquisition, unlimited ability to obtain overlapping images without increased radiation exposure, high-quality multiplanar reconstruction, and absence of respiratory misregistration (13). The slice profile and noise of images produced from a helical acquisition are frequently slightly worse than a conventionally obtained image; however, the benefits in clinical usage far outweigh these disadvantages (14–16).

FIGURE 6.4 Helical scanning involves the patient transport in a continuous fashion as the tube continuously rotates; the result can be imagined as inscribing a helix about the patient.

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Both hardware and software advances were required to develop helical scanning (17). The major hardware requirements are a slip ring gantry and increased computational power. Most previous CT scanner designs had wires that supplied the electricity to the x-ray tube and transferred the measurement data from the detectors to the computer. Thus, the gantry was only able to travel for a limited distance before it needed to reverse direction and rewind prior to obtaining the next image. The wires connecting the gantry to the base unit were eliminated by use of slip ring connectors, allowing the gantry to circle continuously in one direction. As the patient is continuously moving, the individual radiation measurements collected at each angle of the gantry are obtained at slightly different locations along the longitudinal or z-axis of the patient. Powerful interpolation algorithms are required to estimate the attenuation measurement at each angle if the patient had not been moving and the patient position had been constant. The increased computational power is needed to perform this task. Several unique new concepts that the physician must understand are introduced by helical scanning. Pitch is defined as the table feed per 360° tube revolution divided by the beam collimation. When the patient movement is equal to the beam collimation, the pitch is one. Increasing the pitch allows increased coverage in the z-direction but with some broadening of slice profile and image noise. Use of a pitch greater than one also decreases the radiation dose to the patient. The pitch does not affect the slice thickness or position of obtained images; contiguous images are still obtained with pitches greater than one. A second important concept is that of image increment and overlapping reconstructions. Once the scan has been obtained, the image thickness, which is determined by the beam collimation, cannot be changed in single-detector helical CT. However, as the data is continuous, the location of the image center along the z-axis may be altered. This has two practical applications: it allows overlapping reconstructions for use in post-processing without any increase in radiation dose to the patient and reduces volume averaging effect which may lead to improved detection of small lesions (18). The demand to scan faster continues despite the dramatic improvement provided by helical CT. Two methods are being explored to meet this need: increasing the rotational speed of the gantry and increasing the number of slices obtained with each revolution (19). Scanners have been introduced that can obtain speeds of one revolution in 0.5 seconds. The concept of multidetector CT was introduced in the early 1990s with a dual detector scanner. However, its widespread acceptance did not occur until the late 1990s with the introduction of “quad” or “four slice” machines. The principle and the advantages are easy to comprehend; however, the specifics and applications are more complex (20). Instead of collecting a single thin section or slice of data per revolution, a multidetector CT gathers radiation measurements from two to sixteen adjacent locations along the z-axis of the patient’s body

(Fig. 6.5). This gathering of more data simultaneously can be exploited in two ways (or a combination of both) (21): 1.

2.

The table can be moved faster, covering a greater distance per revolution of the gantry. This enables coverage of greater volumes in the same amount of time. The implication for vascular imaging is great: with multidetector CT the entire aortoiliac system can be scanned while there is still adequate contrast in the vessels. At the most basic, two detectors allow one to go twice as far in the same time—twice the coverage. The multidetector unit can be used to create thinner images of the same volume in the same amount of time. For example, a two-detector machine could obtain 5-mm images of the aorta in the same amount of time as a single-detector unit could do 10-mm images of the same portion of the aorta—twice the resolution.

Once again, as with helical CT technology, several new concepts are introduced. There are several technical approaches to detector design, of little importance to the clinician. However, one should become aware of the concept of detector “row” and “channel.” Most state-of-theart machines available today have between 8 and 32 detector rows. This is the number of detectors in the z-axis along the patient’s body. This does not mean that these can obtain 8 or 32 lines of data or slices per revolution. Most currently are limited to 4 to 8 channels of data per revolution—this is limited by the hard-wired ability of the electronics behind the detector to transfer the data off the gantry and into the computer for image reconstruction. The other technological advance from single to multidetector CT is the ability to change the image thickness (within limitations) after the scan is obtained.

FIGURE 6.5 Diagram illustrating acquisition with a single-detector CT and multidetector CT. The simultaneous acquisition of multiple datasets allows increased coverage in the same amount of time. Multidetector beam profile.

Chapter 6 Computed Tomography in Vascular Disease

Future Technical Innovations The history of CT has been one of obtaining high-quality, progressively thinner images increasingly quickly. The speed of scanning was recently dramatically improved with the implementation of multidetector helical techniques; however, the demand for continued improvement persists. Manufacturers are moving to meet this demand by increasing the rotational speed of the gantry and by increasing the amount of simultaneously obtained data. Increased speed and resolution will entrench time as an important fourth dimension in vascular CT imaging (22). Manufacturers are already at work on “flat panel” CT units. Using detectors used in digital mammography but attached to a CT gantry, the concept of slice thickness may become one of historical interest only. The engineering and computer processing demands posed by such a machine are great. The amount of data that can be obtained during a single revolution is so large that creating the images from the raw data can take hours or days—reminiscent of Hounsfield’s first machine. An ideal in cross-sectional imaging is approaching: the isotropic voxel. An isotropic voxel is one in which the resolution is the same in all three planes. An advantage is the ability to arbitrarily scan the patient in any position and then reconstruct the images in the plane that best demonstrates the pathology (23). Practical questions are numerous. Does the noncontrast abdominopelvic CT become the “KUB” of the twenty-first century? Is the radiation dose to the patient necessary? How are such examinations interpreted—filmed in multiple planes or on workstations? It is clear that as the acquisition capabilities improve, data display techniques will be driven toward change as well. Approaching 30 years of age, CT continues to change the way medicine is practiced.

Vascular Techniques and Protocols Like all CT studies, vascular CT examinations have specific protocols that vary with the clinical indication. In order to provide the maximum diagnostic value, several factors must be specified. For contrast enhanced studies, the most important considerations will relate to contrast delivery and distribution. Examination parameters such as slice thickness, slice interval, and pitch not only affect the resolution of the axial images but the ability to create three-dimensional images. The exact parameters depend on the capability of the specific machine and on the size of the anatomic area to be covered. Due to physical limitations of the scanner, as the area to be included increases, the overall ability to optimize the quality of the scan decreases. Intravenous Contrast Iodine-based intravenous contrast material is routinely used in computed tomography of the vasculature. When properly employed, such contrast material allows ready identification of vessels and improved lesion detection and characterization. All currently used iodine-based

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contrast agents distribute rapidly into the extracellular space. Thus, the enhancement of vessels and organs is dependent on the rate of injection and the length of time from the beginning of the injection to imaging (scan delay), as well as on intrinsic characteristics of the structure such as vascularity. Pre-contrast images are only required in specific situations and are not routinely used in survey studies of the abdomen or vasculature. With regard to the vascular tree, pre-contrast may allow more accurate depiction of wall calcification and differentiation of calcium within thrombus from enhancement (i.e. on postendograft studies). Two general classes of contrast agents are available for use: the older ionic class and the newer nonionic class. The nonionics have a decreased incidence of both minor and major side effects but are more expensive (24,25). Because there is a decreased incidence of nausea and vomiting, there is at least a theoretical advantage in body CT of obtaining fewer suboptimal studies due to the patient moving (26). The amount of contrast material required depends on equipment type and the specific vessel of interest. A 60% iodine concentration (300 mg/mL) is most commonly used; however, lower and higher concentrations are acceptable. Injection of contrast material should always be performed with a power injector. This insures that the desired injection rates and timing are achieved. The terminology used to describe the timing in helical CT has varied in the literature due to local custom and the organ of interest. Early scans (usually using a scan delay of 15 to 30 s) are often called “arterial phase” as most of the contrast remains within the arterial system. Scans through the liver following a 60-s to 70-s delay are termed “portal venous phase;” in fact, with this delay, contrast is seen throughout the parenchyma and in the hepatic veins. This delay is frequently used for routine survey imaging of the abdomen. It is important to realize that the optimal scan delay is dependent on the injection rate; when the rate is changed the delay may require adjustment as well (27,28). It is important to lengthen the scan delay when venous structures are to be examined. A CT optimized to demonstrate the abdominal aorta will provide little information about the inferior vena cava, as it will be unenhanced. As the science of contrast administration has progressed, patient-dependent factors have become more obvious. Most institutions use nearly the same technique for most adult patients. However, differences in cardiac output, weight, time from last meal, and fluid status affect the actual enhancement obtained on the images (29,30). In an effort to tailor the examination to the specific patient, automated systems are available that initiate scanning when the optimal enhancement has been reached (31,32). In general, these use a series of low-dose scans obtained at a single location within the abdomen. A region of interest cursor is placed on the aorta and a threshold density level is set. Following the beginning of the contrast administration, scans are obtained every second or so until the density measured within the region of interest reaches a threshold value. At that time, the diagnostic scan is begun.

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Acquisition Parameters Conventional CT can be used to demonstrate a great deal of vascular pathology, although not as optimally as helical CT. Dedicated vascular studies should be performed on a helical unit if one is available. When using a conventional scanner, 5-mm slice thickness, dynamic table incremention, and the minimum interscan delay should be used. Contrast is typically administered with an initial bolus of 50 mL at 2 to 4 mL/s followed by a maintenance infusion of 0.8 to 1.5 mL/s for an additional 100 to 150 mL volume. Single detector helical CT allows excellent vascular imaging. For the aorta and great vessels, slice thicknesses of 2 to 3 mm are most frequently used. As above, there is a constant trade-off between anatomic coverage and slice thickness. Once the coverage is decided, the smallest possible collimation that will allow the completion of the examination within a single breath hold (20 to 40 s depending on the patient) should be used. Pitches in the 1.5 to 2.0 range are most frequently used. As the pitch is increased the coverage increases, however there is the negative trade-off of increasing slice profile and resultant decreased resolution in the image. Approximately 150 mL of contrast should be administered at a uniphasic rate of 3 to 4 mL/s using either a timing bolus or automated bolus timing software to determine the scan delay. A 50% reconstruction overlap or increment is ideal. Multidetector helical CT allows thinner images or greater anatomic coverage than single-detector CT. For the thoracic or abdominal aorta, slice thicknesses of approximately 1 mm are used. If the scan must include the entire thoracoabdominal aorta, the aortoiliacofemoral system (CT “runoff”), or multiple post-contrast phases (such as in post-endograft studies) are needed, a 2.5-mm to 3-mm slice thickness is used. Pitches on multidetector machines have been defined in various ways by different manufacturers, leading to some confusion. However, using the “beam pitch” definition, which is most analogous to single-detector CT, pitches in the range of 1 to 2 are used. Again, a 50% reconstruction overlap is important to improve the quality of any reconstructed images. The contrast injection techniques for arterial studies using multidetector helical machines are the same as single detector. Post-processing, Three-dimensional Techniques and CT Angiography One of the important advantages of helical acquisition is that a true volume dataset is obtained. This significantly improves the ability to manipulate the data in other than the single scanned orientation. Overlapping reconstructions minimize the “stair-step” appearance in longitudinal planar and three-dimensional applications—with helical technique these can be made without increased radiation exposure. Helical scanning during a single breathhold also eliminates respiratory misregistration that can significantly interfere with these reconstructions. Postprocessing of the dataset can be performed on the scanner

itself or on an offline workstation. The availability of a workstation allows the scanner itself to remain in operation while the image manipulation is being performed. Planar reformations in sagittal, coronal, or oblique planes are the simplest of the post-processing techniques. These can be helpful in localizing masses or disease to a specific space or organ. For example, the origin of a mass located between the liver, adrenal, and right kidney may be more convincingly demonstrated on a longitudinal reformation. Clinicians particularly appreciate coronal images, which they can quickly assimilate. Curved planar reformations may be helpful in placing the entire extent of a single object with a tortuous or curving course on a single image (Fig. 6.6). The term “three-dimensional” is used to describe such techniques as surface rendering, maximum intensity profile, and volume rendering. This is a bit misleading as the images created with all these techniques are not actually three-dimensional but rather two-dimensional projections of a three-dimensional object, similar to a radiograph (33). The three are very different; each has advantages and disadvantages. Surface renderings, also known as shaded surface display (SSD), can be used to visualize selected objects such as vessels or organs from different projections. First, the object of interest is defined by setting cutoff values to define the object by including only pixels of a certain density. A mathematical model is then created of the surface of the object. At this point the size of the dataset is greatly diminished, as each pixel is either positive (defining the object surface) or negative (not on the object surface). This object is then illuminated with a virtual light source; the reflections and shadings on the image give the impression of three-dimensionality. The cutoff values chosen are critical as they can significantly change the size of the object, for example, the degree of a stenosis. This technique removes all gray-scale information: calcified plaques will be indistinguishable from adjacent luminal contrast. Maximum intensity projection (MIP) techniques are simple and particularly suited for angiographic simulation procedures (34). For each imaging direction or view, parallel rays are passed through the imaged volume (the group of axial CT images) and the maximum CT number encountered along each ray is displayed. The remainder of information along that ray is discarded, again greatly reducing the computing power needed to perform this technique. Differentiation between foreground and background is not possible on a single MIP image. To achieve a three-dimensional effect one must view a series of MIP images from different angles. Important advantages over SSD technique include lack of threshold dependency and preservation of attenuation differences (34). Volume rendering techniques add the advantages of shaded surface and MIP techniques with a variety of effects such as semitransparent views, improved surface definition and virtual endoscopic displays (35). In this technique, each voxel is assigned to one of several groups based upon its number. This allows the relationships be-

Chapter 6 Computed Tomography in Vascular Disease

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B

A FIGURE 6.6 Curved planar reformations are used to demonstrate an entire structure that does not lie in a single plane. (A) Axial image with line (arrowheads) demonstrating the path chosen for the reformatted curved coronal image hepatic artery. (B) Curved sagittal image demonstrating the common hepatic (cha) and proper hepatic (pha) arteries as well as the celiac artery (ca), superior mesenteric artery (sma), and gastroduodenal artery (gda).

tween vessels and viscera to be preserved and displayed. A histogram of voxel densities is automatically obtained with each peak representing a specific material. The probability that a single voxel belongs to a specific group is calculated based upon a Gaussian distribution of densities for each material (36,37). Inaccuracies created by the choice of threshold level in SSD and the frequent requirement of editing in MIP are avoided. Volume rendering displays the volume of data in its entirety, unlike both SSD and MIP which discard the majority of data (38). This fact indicates the greatest disadvantage of volume rendering: it requires significantly faster and more sophisticated computer technology. One of the most exciting and clinically used applications of the three-dimensional techniques is CT angiography (CTA) (39,40). Using specially tailored acquisitions and the three dimensional techniques described above, clinical questions which previously required angiography may be answered by CT with decreased cost, decreased invasiveness and decreased inconvenience to the patient. The principles involved are simple: intravenous contrast material is injected and a helix is obtained through the body part of interest while the contrast is predominately in the vessels of interest. Post-processing is then performed to view the vessels in orientations analogous to conventional angiograms (Fig. 6.7). Although all the data is available on the original axial images, the reconstructions and CTA frequently present the information in a more practical, efficient, and useful format. Meticulous technique is required to obtain highquality CTAs. The contrast material must be injected at high rates, usually 4 to 5 mL/s. A timing bolus is helpful to assure that the start of the helix is coordinated with the passage of the bolus. The length of the scan is generally

limited by either the patient’s breath-holding ability or tube heating. Therefore, planning the helix is usually a trade-off between the length of the region to be scanned and slice thickness: a thinner collimation will improve resolution but decrease the volume scanned. Most vascular applications with multidetector scanners use a slice width of 1 to 3 mm. Overlapping reconstructions reduce stair step artifact; a 50% overlap is adequate. Post-processing may use MIP, SSD, or volume-rendering techniques as described above. It is important to interpret these postprocessed images in conjunction with the original axial images, as otherwise basic advantages of CT over conventional angiography such as thrombus, wall, and adjacent organ evaluation are lost (34). Interpretation Principles The conventional approach to CT interpretation is based on “hard-copy” film. In general, a standard 14- to 17-inch film is filled with between 12 and 24 images. Images that are displayed with standard window width and level settings appropriate for differentiation of solid, fluid and aircontaining structures (“body window,” level = 40 to 70, width = 380 to 550) may not be adequate to evaluate vascular structures. With rapid bolus administration, the contrast within the arteries may be so dense that luminal irregularities including intimal flaps may be obscured. Unfortunately, owing to the wide variability of density within the vessels, no standard “vascular” window setting can be set. In general, the level should be raised (80–120) and the width increased (600–1000). A number of forces are conspiring to change interpretation from a film-based environment to “soft-copy” or monitor-based environment. The number of images obtained in multidetector vascular CT studies is frequently

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B

A FIGURE 6.7 CT Angiography. The source images (not shown) were obtained in the axial plane with a 1.25-mm collimation and 1-mm increment during the injection of intravenous contrast at 4 mL/s. (A) Shaded surface display (SSD) of the kidneys and major vessels in a patient with an occluded right common iliac artery. The celiac artery and branches, SMA and IMA are well demonstrated anterior to the aorta. (B) Maximum intensity projection (MIP) created from the same dataset. Only the portions of the SMA, IMA, and celiac branches not lying in projection with the aorta are seen on this projection; one must view MIP images from multiple angles to clarify overlapping structures. However, the calcified plaques not identified on the shaded surface display are visualized.

in the range of 250 to 500. Multiple-phase acquisitions lead to the creation of even more images. This increases both cost and inconvenience as multiple sheets of film are produced. CT interpretation is moving from image analysis to volumetric analysis; this has been defined as the treatment of data not as a stack of images but as a volume of voxels (41). Dosimetry The radiation dose calculation for CT is complex (42). Important principles include: 1. 2.

3.

the dose is administered only to a certain volume of the body, not to the entire patient; the dose can vary considerably from scanner to scanner and from image to image depending on the technical factors set; and the percentage of the dose delivered centrally compared with the skin dose is much greater with CT than with conventional radiography (3,4).

In general, the effective dose in a conventional CT of the abdomen is greater than that of conventional radiographs, generally in the range of 5 to 15 millisieverts (mSv) (43). Because of this, it is important to keep the number of sections obtained as low as possible while filling the diagnostic need (44). Dosimetry considerations are essentially the same with helical and conventional techniques (4). Multidetector CT has inherent inefficiencies, including septa between detector rows, which do not collect data, and loss of use of the radiation penumbra.

Clinical Applications Thoracic Aorta The thoracic aorta can be visualized by a number of modalities including angiography, computed tomography (CT), magnetic resonance imaging (MRI), and transesophageal echocardiography (TEE). Before the 1990s, angiography was considered the gold standard for evaluation of the thoracic aorta for dissections and aneurysms, but advances in technology have led to angiography being replaced by these noninvasive studies as the initial test of choice for evaluating the thoracic aorta. A landmark study in 1993 demonstrated that MRI, TEE, and CT have similar sensitivities for the detection of thoracic aortic dissections, at 98.3%, 97.7%, and 93.8% respectively. MRI was found to have the highest specificity at 97.8%, as compared to CT at 87.1% and TEE at 76.9% (45). A more recent study demonstrated that sensitivity for all three modalities approaches 100%, and CT is superior to both MRI and TEE in the assessment of the supra-aortic branches involved in aortic dissection (46). Despite having somewhat better sensitivity and specificity for thoracic aortic dissections, MRI is limited by its availability and slower image acquisition. The use of TEE has also been limited by its availability, as well as operator variability. It is for these reasons that spiral CT has become the test of choice for the evaluation of thoracic aortic dissection at most medical centers (47,48). The pathognomonic finding for thoracic aortic dissection on CT is two adjacent contrast-filled lumens, which represent a patent true lumen and the false lumen

Chapter 6 Computed Tomography in Vascular Disease

(Fig. 6.8). The two lumens are separated by a thin band termed the intimal flap. The intimal flap can have unusual characteristics which are detected by CT, including partial thrombosis, a circular orientation down the aorta, or multiple false channels. CT is also effective for visualizing more subtle signs of dissection such as internal displacement of intimal calcium, mural thickening, ischemia of end organs supplied by aortic branches, or a left pleural effusion (48). CT also demonstrates the course of the intimal flap in relation to the aortic arch and branch vessel ostia, which is vital for planning surgical repair (49). The major limitations of CT for thoracic aortic dissection are technical factors which can cause a false-positive reading. These include improper timing of contrast injection, aortic wall or cardiac motion, streak artifacts, and periaortic structures. In the future, continual advances in imaging technology, combined with the knowledge of an experienced radiographer, will eliminate many of these factors (50). Thoracic aortic aneurysms can be found in many varieties based on location, shape, and etiology. Approximately 75% of all thoracic aneurysms occur in the descending aorta and are fusiform in shape with an etiology of atherosclerotic disease. Previously, the gold standard for diagnosis and surgical planning of thoracic aortic aneurysms was contrast aortography. Aortography in many studies has been found to underestimate aneurysm size as a result of mural thrombus, and does not provide detail regarding mediastinal hematoma or anatomical relationship of the aneurysm to other mediastinal structures. Spiral CT has now become the primary imaging modality for the evaluation of thoracic aneurysms. The wall of the aneurysm is easily identified by intramural cal-

FIGURE 6.8 Type A or ascending aortic dissection with intimal flap seen in both the ascending and descending thoracic aorta.

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cifications allowing for accurate size measurement. CT also allows for evaluation of the extent of mural thrombus and aneurysm wall for a contained leak, as well as any associated dissection, distal embolization, or pleural effusion (51). Although arteriography remains the gold standard for evaluating traumatic disruption to the thoracic aorta, recent studies demonstrate the expanding role for CT in the diagnosis of such injuries. A prospective 1998 study found that for blunt aortic injury, helical CT had 100% sensitivity compared with 92% for aortography, and specificity for helical CT was 83% compared with 99% for aortography (52). While most centers continue to use aortography for the diagnosis of traumatic aortic injuries, many centers are expanding the role of CT to evaluate for aortic injury in patients with a normal mediastinum on chest roentgenogram but with a suggestive mechanism (53). Overall, CT has become the principal imaging modality for the evaluation of vascular disease of the thoracic aorta. CT has essentially replaced contrast arteriography in the diagnosis of thoracic aortic dissections and aneurysms, and appears to have an emerging role in the evaluation of traumatic thoracic aortic injuries.

Abdominal Aorta The role of CT in abdominal aortic aneurysm (AAA) disease emerged in the 1980s, and CT has been instrumental in the development and clinical application of endovascular repair of AAA in the 1990s. Abdominal ultrasound remains an effective screening modality for AAA disease, but CT has emerged as the primary method of measuring AAA, following rate of aneurysm expansion, and planning for both open and endovascular surgical repair. At the majority of medical centers CT is the sole imaging technique for patients with uncomplicated AAA, and aortography is reserved for the subset of patients with abnormal anatomy, juxtarenal, supraceliac, and complex aneurysms. The characteristic findings of AAA on CT are dilation of the calcified wall of the aortic wall with varying degrees of surrounding thrombus (54). CT is crucial in demonstrating characteristics of AAA requiring more emergent intervention. Evidence of disruption of calcifications with obliteration of surrounding soft tissue may denote aneurysm rupture (55). CT can also demonstrate thickening of the aortic wall and adherence to surrounding structures characteristic of inflammatory AAA (Fig. 6.9). Evidence of eccentric thickening of aortic wall with intramural air is seen in mycotic aneurysms (56). In addition, CT is the imaging method used following open repair to assess graft function as well as complications including perigraft infections and anastomotic aneurysms. The development and rapidly expanding clinical use of endovascular stent–grafts for AAA repair, in the 1990s and present, has been made possible by major advances in CT technology and computer imaging software. The selection of candidates for endograft repair and the subse-

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FIGURE 6.9 Late inflammatory abdominal aortic aneurysm. Contrast enhancement of the aortic wall is easily seen.

length measurements, within the aorta and in tortuous iliac arteries, that are crucial to proper graft sizing and success of the endovascular repair. Another novel technique, coined the “virtual graft” by Fillinger, employs advanced computer imaging to simulate a three-dimensional endograft and display that graft within a three-dimensional reconstruction of the patient’s aorta, to plan the repair and investigate possible complications (Fig. 6.11) (57). Just as CT is vital in the selection of patients and the planning of endovascular AAA repair, it is equally important for the postoperative evaluation of the endograft repair. Despite the precision in the planning of endograft repair, a significant number of life-threatening postoperative complications do occur. These complications include aneurysm enlargement, endoleak, stent deformation, and graft migration. Spiral CT combined with radiographs and Doppler ultrasound are commonly accepted as the gold standard for long-term follow-up after endograft AAA repair for the detection of late complications (58,59).

Iliac Arteries

FIGURE 6.10 With multiplanar reconstruction, accurate measurement of aortic length can be made. The transaxial image is used to determine aortic diameter for endoplacement.

quent selection of endograft sizing requires multiple precise measurements. These measurements include the length and diameter of the proximal neck of the aorta, the length and diameter of the distal cuffs, and distance from the lowest renal artery to the most distal aspect of the graft limbs (Fig. 6.10). These measurements require precision to less than 1 mm, with serious consequences for any error in graft sizing, including endoleak leading to aneurysm rupture as well as migration of the stent (Fig. 6.16). Novel techniques combining spiral CT and multiplanar reformatting have led to the development of CT angiography, allowing for precise three-dimensional reconstructions of the aorta and its branches. In addition, computer software combined with reconstructed images allows for precise

Iliac artery aneurysms are uncommon, and account for approximately 2% of all abdominal aneurysms (60). Iliac artery aneurysms have a wide range of clinical presentation, making diagnosis challenging, but with the prevalence of CT the detection of iliac aneurysms has increased in frequency (61). The high rate of rupture and associated mortality with aneurysms larger than 4 cm necessitates prompt and accurate imaging for diagnosis, as well as follow-up. The traditional approach for the diagnosis of iliac artery aneurysms has been either arteriography or duplex ultrasound. The use of CT in the diagnosis and surgical planning for iliac aneurysms is widely accepted. Studies demonstrate that there is excellent correlation between ultrasound and spiral CT in determining the size of iliac aneurysms, with ultrasound underestimating aneurysm size by 0.03 cm (62). Prior to the development of endovascular grafts, large or symptomatic iliac aneurysms were repaired using an open procedure. There has been significant experience in the treatment of isolated iliac aneurysms using endovascular grafts, and the early results have been excellent with an average decrease in the size of aneurysm of 0.516 cm per year after endograft repair (63). Just as advanced CT imaging is intrumental in the preoperative and postoperative management of endograft repair of AAA, it now has the same role in the diagnosis, operative planning, and postoperative followup for both open and endovascular repair of iliac artery aneurysms.

Peripheral Arteries Vascular pathology of the femoral and popliteal arteries can be accurately visualized by CT. Recent studies have explored the use of CT angiography for evaluating lower extremity peripheral vascular occlusive disease. One

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A

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B

FIGURE 6.11 Virtual reconstruction of the aorta (A) with proposed endograft replacement (B). (Reconstruction provided by Mark Fillinger, M.D. and Medical Media Services.)

study demonstrated CT angiography to be highly accurate in diagnosing occlusion of the femoral artery, popliteal artery, and tibial artery with sensitivities of 100%, 100%, and 94%, respectively. Overall, these studies have shown that CT angiography is not as accurate as conventional angiography in the evaluation of lower extremity vascular disease, but in the future CT angiography may become a reliable noninvasive technique for evaluating for vascular occlusive disease in the lower extremities (64,65). Spiral CT has become widely regarded as a valuable technique for the diagnosis of popliteal artery entrapment syndrome (PAES) and cystic adventitial disease of the femoral and popliteal artery (Fig. 6.12). These are important diagnoses to consider in young healthy patients presenting with claudication. In one study of 45 patients with popliteal arteriopathies, CT diagnosed 98% of the disorders while arteriography diagnosed only 70%. This study also demonstrated that CT detected popliteal artery entrapment in three patients, while arteriography failed to diagnose two of the three patients due to arterial occlusion. In addition, this study found CT effective in diagnosing three cases of adventitial cystic disease of the popliteal artery, while angiography detected disease in only one of these three patients (66). CT findings of PAES vary depending on the anatomic variant, but in the most common variant CT demonstrates that the popliteal artery and vein

FIGURE 6.12 Popliteal artery entrapment. Notice muscle band passing between the artery and vein on the left. Normal artery–vein relationship is on right.

are separated by a muscle band or the displacement of the lateral head of the gastrocnemius muscle medially. Findings of adventitial cystic disease of the femoral or popliteal artery include localized eccentric fluid-filled dilation that does not enhance with contrast. Not only does CT assist in the diagnosis of these unique vascular diseases, it defines the surrounding muscular and fascial planes to assist in planning surgical repair.

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Vena Cava and Mesenteric Venous System

Carotid Arteries

Occlusion of the inferior vena cava (IVC) can be caused by both intrinsic and extrinsic diseases. CT is sensitive for thrombosis of the IVC and tumors, but poorly visualizes the intrahepatic portion of the IVC. It is for this reason that multiple imaging modalities, including vena cavography and MRI, are required for evaluation of disease of the IVC. CT offers the advantage of identifying congenital abnormalities such as duplication of the cava, circumaortic and retroaortic renal veins, and left-sided IVC prior to operative procedures. CT accurately visualizes the portal, splenic, and superior mesenteric veins, and is the diagnostic imaging test of choice of many centers for mesenteric venous thrombosis (Fig. 6.13) (67). Pathognomonic finding of mesenteric venous thrombosis on CT includes marked edema of the mesentery with bowel wall thickening, and an enlarged mesenteric vein with a low-density center surrounded by an enhancing wall.

The imaging modalities of choice for evaluating carotid artery stenosis over the past several decades have been contrast angiography and duplex ultrasound (DU). In fact, many carotid endarterectomies are performed based solely on the results of duplex ultrasound. A recent study from Duke University investigated the accuracy of noninvasive studies of carotid artery stenosis, including MRA, DU, and CT angiography (CTA), versus contrast angiography. Due to the infrequent use of CTA at their institution they compared only DU and MRA to conventional angiography. They found that DU alone misclassified the degree of carotid stenosis in 28% of patients, while MRA alone misclassified the degree of stenosis in 18% of patients (68). Another study comparing CT angiography to conventional angiography found overall agreement between CTA and angiography for carotid stenosis in 89% of patients, and determined that using the twodimensional transverse CT with volume rendering technique provided the highest accuracy (69). A second study, using NASCET > 60% as an indicator for carotid disease, found that, compared to contrast angiography, CTA had a sensitivity of 87%, specificity of 90%, and accuracy of 89% (70). While these studies indicate that cautious decisions to proceed with surgery should be made when based solely on noninvasive imaging of the carotid artery, they also demonstrate that with continued advances in CT technology there may be an emerging role for CT angiography in the evaluation of carotid disease in the future.

Peripheral Veins Duplex ultrasound remains the gold standard for imaging of the deep veins of the leg for deep vein thrombosis, and due to cost there is little role for CT in the evaluation of the deep venous system. CT has a significant role in the identification and characterization of congenital arteriovenous malformations (AVM) of the lower extremities. Owing to the complexity of these malformations, they are best evaluated with multiple imaging modalities such as contrast angiography, CT, and MRI. While arteriography is important for defining the vessels feeding the AVM, CT is important in demonstrating muscle group involvement and fascial planes. One limitation of CT in the evaluation of AVMs is in those that are highly cellular where there is little contrast enhancement, leading to underestimation of the full extent of the malformation.

FIGURE 6.13 Mesenteric venous thrombosis is diagnosed on CT by 1) nonenhancing superior mesenteric vein with enhancing vein (arrow); 2) edema of the mesentery; and 3) bowel wall thickening.

Thoracic Outlet The thoracic outlet is a complex anatomic region. Symptoms may arise for compression of the subclavian artery and vein and brachial plexus. Because of the complex interrelationship between muscles and neurovascular structures, spiral CT is particularly helpful in the diagnosis and perioperative planning. Matsumura and colleagues demonstrated the utility of sagittal and three-dimensional reconstruction in normal individuals and in patients with thoracic outlet symptoms (71). Three-dimensional CT reconstruction provides an accurate detailed picture of cervical and abnormal first ribs. In addition, muscular hypertrophy of the scalene muscle can be seen in thin athletic patients. Sagittal reconstruction was performed before and after abduction and external rotation of the arm (Fig. 6.14). Abduction and external rotation allows the clavicle to pass upward on the first rib, producing occlusion of the subclavian vein, followed by subclavian artery occlusion. Three-dimensional CT reconstruction may also demonstrate abnormalities of the clavicle. Malunion and callous formation of the clavicle compromises the costoclavicular space, producing neurovascular compromise of the thoracic outlet (Fig. 6.15). Unfortunately, this technique is not useful in patients with neurogenic thoracic outlet. For

Chapter 6 Computed Tomography in Vascular Disease

a patient who presents with neurologic thoracic outlet, compromise of the arterial circulation during abduction and external rotation may be demonstrated on the helical CT scan.

FIGURE 6.14 CT scan for TOS is performed with a venous contrast injection with the arm at the side (A) and with the arm abducted and externally rotated (B). Note the occlusion of the subclavian vein (arrows).

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Comments The continued technical advancements made in computed tomography scanners and the computer software used for image acquisition have dramatically changed the way vascular surgeons diagnose and treat a variety of vascular diseases. Vascular surgeons and radiologists now have at their disposal the ability to rapidly and noninvasively obtain and reconstruct CT angiographic and threedimensional images of virtually the entire vascular anatomy. In combination with revolutionary technological advances in endografts, computed tomography has been essential in introducing the discipline of vascular surgery to the era of endovascular surgery. In this era of endovascular surgery, the vascular patient is able to benefit from shortened hospital stays and postoperative recovery time, as well as significant reduction in the comorbidities associated with open operative procedures. Postoperative CT surveillance is important to detect endoleaks (Fig. 6.16).

Future Directions

FIGURE 6.15 Right clavicular fracture with callus formation which compromises the costoclavicular space.

The quality of CT scans will continue to improve with faster software acquisition. However, the most important clinical development is the use of CT scanned images to calculate areas of high wall stress. Concurrent work by Fillinger and Vorpe have used finite element analysis for spiral CT scans to create models to estimate areas of high shear stress and high wall tension. Based on these studies, it is possible that in the future we shall be able to predict which small aneurysms are likely to progress to rupture. Some examples of high wall tension are illustrated in Figure 6.17. The everyday use of such tools will be invaluable. Similarly, findings of high wall tension may be helpful to better design endovascular grafts.

FIGURE 6.16 Late endoleak: notice contrast in aneurysm sac.

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FIGURE 6.17 Finite element (computational stress) analysis may be useful in determining the degree and distribution of mechanical forces or stresses acting on the wall of individual AAA. Shown here are the distributions of wall stresses on the posterior and anterior abdominal aortic walls of six different 3-D reconstructed AAAs and one nonaneurysmal control aorta. Gray-colored regions are those with artificially high stress concentrations due to edge effects. The scale provides stress magnitude. (Figure provided by David Vorp.)

Chapter 6 Computed Tomography in Vascular Disease

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Haimovici’s Vascular Surgery, 5th Edition Edited by Enrico Ascher Copyright © 2004 by Blackwell Science

CHAPTER 7 Magnetic Resonance Angiography Jagajan Karmacharya, Omaida C. Velazquez, Richard A. Baum, and Jeffrey P. Carpenter

Preoperative imaging using contrast angiography is the traditional standard for evaluation of vascular disease. This conventional technique is associated with an overall complication rate of 8% (1,2) including bleeding, hematoma, pseudoaneurysm, pain at the arterial puncture site, temporary or permanent renal insufficiency, contrast allergy, and death. As many as 29% of patients with peripheral vascular disease have coexisting renal insufficiency (3), placing them at increased risk of renal complications with the use of nephrotoxic contrast. Magnetic resonance