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MAKING SENSE OF

VASCULAR

ULTRASOUND

MAKING SENSE OF

VASCULAR

ULTRASOUND

A HANDS-ON GUIDE

Kenneth A Myers MS FRACS FACS DDU(Vasc) Consultant Vascular Surgeon, Epworth Hospital and Monash Medical Centre; Consultant in Vascular Imaging, Melbourne Vascular Ultrasound, Melbourne, Victoria, Australia

Amy Clough BSc DMU(Vasc) Senior Vascular Ultrasonographer, Melbourne Vascular Ultrasound, Epworth Hospital, Melbourne, Victoria, Australia

A member of the Hodder Headline Group LONDON

First published in Great Britain in 2004 by Arnold, a member of the Hodder Headline Group, 338 Euston Road, London NW1 3BH

http://www.arnoldpublishers.com

Distributed in the United States of America by Oxford University Press Inc., 198 Madison Avenue, New York, NY Oxford is a registered trademark of Oxford University Press

© 2004 K. Myers & A. Clough

All rights reserved. Apart from any use permitted under UK copyright law, this publication may only be reproduced, stored or transmitted, in any form, or by any means with prior permission in writing of the publishers or in the case of reprographic production in accordance with the terms of licences issued by the Copyright Licensing Agency. In the United Kingdom such licences are issued by the Copyright Licensing Agency: 90 Tottenham Court Road, London W1T 4LP.

Whilst the advice and information in this book are believed to be true and accurate at the date of going to press, neither the author[s] nor the publisher can accept any legal responsibility or liability for any errors or omissions that may be made. In particular, (but without limiting the generality of the preceding disclaimer) every effort has been made to check drug dosages; however it is still possible that errors have been missed. Furthermore, dosage schedules are constantly being revised and new side-effects recognized. For these reasons the reader is strongly urged to consult the drug companies’ printed instructions before administering any of the drugs recommended in this book.

British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library

Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress

ISBN 0 340 81009 2

1 2 3 4 5 6 7 8 9 10

Commissioning Editor: Joanna Koster Development Editor: Sarah Burrows Project Editor: Naomi Wilkinson Production Controller: Lindsay Smith Cover Design: Sarah Rees

Typeset in 10.5/13 RotisSerif by Charon Tec Pvt. Ltd, Chennai, India Printed and bound in Italy

What do you think about this book? Or any other Arnold title? Please send your comments to [email protected]

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PREFACE

There has been an explosion of new technology for vascular ultrasound throughout the past 30 years. Basic black and white instruments of the mid-1980s have now been replaced by extremely sophisticated units that allow colour display of flow in two or three dimensions. These use both B-mode and Doppler assessment assisted by power and harmonic Doppler imaging with the promise of many new techniques to come. There is hardly a radiological, vascular surgical or vascular medical practice anywhere in the world that does not employ ultrasound scanning to evaluate their patients with arterial or venous disease. General ultrasound practitioners are having to learn the peculiar requirements of vascular ultrasound, its potentials and its limitations. Increasingly, ultrasound is also being used to guide the actual treatment of both arterial and venous disease. The entire balance between diagnosis by conventional arteriography, ultrasound and other imaging modalities is being re- evaluated to obtain the best value from each and allow them to complement each other. The major benefit of ultrasound is that it is non-invasive and relatively inexpensive. However, vascular ultrasound is complex and this can become overwhelming to those who are learning the art, and indeed to established practitioners. The aim of this book is to attempt to get to the heart of how to apply physical and physiological principles to obtain the best results for assessment at various sites. It is designed to be a practical hands-on book for rapid reference in the course of day-to-day practice. However, it is also anticipated that it will be a concise reference book for trainee sonographers learning the techniques and attempting to pass examinations. It is hoped that it will simplify the complex issues so as to make better sense of vascular ultrasound.

ACKNOWLEDGEMENTS

We gratefully acknowledge the assistance provided in producing this book from Cheryl Bass, Andrew Dickenson, Valerie Gregory, Joe Kiss, Greg Lammers, Maurice Molan, Jason Paige, Rhonda Rose, Ian Schroen, Debby Smith, Allen Tabor and Stephen Wood. We particularly acknowledge the advice and support from our colleagues Jane Browne, Jayne Chambers and Penny Koh. We are grateful for the helpful and highly professional support received from Sarah Burrows, Penny Howes and Joanna Koster at the Hodder Headline Group.

Colour artwork sponsored by Philips Ultrasound.

Postscript

We appreciate critical comments regarding improvements, corrections and additions for future editions. Please contact us to make any suggestions that you see fit at: Kenneth Myers, Suite 5.1, 32 Erin Street, Richmond, Melbourne, Victoria, 3121, Australia.

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xii MAKING SENSE OF VASCULAR ULTRASOUND

EDV end diastolic velocity EIA external iliac artery EIV external iliac vein ESP early systolic peak EVAR endovascular aneurysm repair FN false negative FP false positive FV femoral vein GSV great saphenous vein HITS high-intensity transient signals ICA internal carotid artery IIA internal iliac artery IIV internal iliac vein IMA inferior mesenteric artery IMV inferior mesenteric vein IVC inferior vena cava IVUS intravascular ultrasound KE kinetic energy LIMA left internal mammary artery MCA middle cerebral artery MRA magnetic resonance angiography PAS peripheral access system PASV posterior accessory saphenous vein PCA posterior cerebral artery PCoA posterior communicating artery PE potential energy PE pulmonary embolism PFA profunda femoris artery PFV profunda femoris vein PI pulsatility index PICA posterior inferior cerebellar artery PICC peripherally inserted central catheters PPG photoplethysmography PRF pulse repetition frequency PSA persistent sciatic artery PSB pansystolic spectral broadening PSV peak systolic velocity

LIST OF ABBREVIATIONS xiii

PTA posterior tibial artery PTCV posterior thigh circumflex vein PTFE polytetrafluoroethylene PTV posterior tibial veins RAR renal–aortic ratio RI resistance index RIMA right internal mammary artery ROC receiver operating characteristics SFA superficial femoral artery SFj saphenofemoral junction SFV superficial femoral vein SMA superior mesenteric artery SMC smooth muscle cell SMV superior mesenteric vein SPj saphenopopliteal junction SSV small saphenous vein SVC superior vena cava TCCD transcranial colour Doppler TCD transcranial Doppler TE thigh extension of SSV TGC time gain compensation TIA transient ischaemic attack TIPS transjugular intrahepatic portosystemic shunting TN true negative TOS thoracic outlet syndrome TP true positive TSC time sensitivity control UGS ultrasound-guided sclerotherapy

PRINCIPLES OF

VASCULAR

ULTRASOUND

Vascular ultrasound combines various modalities to study blood vessels and blood flow (Fig. 1.1). Modern systems use B-mode and pulsed Doppler combined as the duplex scanner. This book will not attempt to explore all aspects of ultrasound physics as they are covered in dedicated texts listed at the end of the book as ‘Recommended reading’. However, vascular ultrasound cannot be understood without discussing basic principles.

Ultrasound

B-mode (pulsed) M-mode

B-flow

Doppler

Continuous-wave Pulsed-wave

Spectral analysis

Colour Doppler

Contrast imaging

Harmonic imaging

Power Doppler

Fig. 1. Modalities used in vascular ultrasound to study blood vessels and blood flow

2 MAKING SENSE OF VASCULAR ULTRASOUND

BASIC ULTRASOUND PRINCIPLES

Basic characteristics of sound waves are outlined in Box 1.1.

Box 1.1: Characteristics of sound waves ● Frequency : number of cycles per second (1 Hz
1 cycle/s) ● Period : time for one cycle (seconds) ● Wavelength : length of one cycle (mm) ● Velocity : speed of sound wave propagation (cm/s) ● Amplitude : amount of energy in a sound wave. ● Power : rate of energy transfer (W) ● Intensity : power/area (W/m 2 )

Ultrasound has a frequency 20 KHz, outside the range of human hearing. Frequencies used are millions of cycles per second (MHz). Ultrasound is generated and detected by mechanical oscillations from synthetic piezo-electric crystals (piezo-pressure) (Fig. 1.2).

Piezo-crystal

Sound wave

Direction

A B

Fig. 1. Ultrasound signals A: An alternating current applied to a piezo-crystal causes it to expand and contract to generate ultrasound at the same frequency that passes into the body. B: Reflected sound waves strike a crystal and produce alternating electrical signals at the same frequency that are then processed by the ultrasound machine.

4 MAKING SENSE OF VASCULAR ULTRASOUND

Surface

Reflections

Interface

Transducer

Fig. 1. Reflection A ‘strong reflector’ is one where impedances on each side of the interface are considerably different. ● Most soft tissues: only 1–2 per cent reflected. ● Soft tissue and air: 99 per cent reflected so that coupling gel is required between transducer and skin. ● Soft tissue and bone:
40 per cent reflected so that transcranial studies can be difficult. ● Reflections from blood are weak compared with those from solid tissues.

Surface

Refraction Lower impedance

Higher

Interface

Transducer

Fig. 1. Refraction Part of the beam is reflected and the remainder continues to be transmitted but at a different angle depending on the velocity differences for each medium.

PRINCIPLES OF VASCULAR ULTRASOUND 5

(A) (B)

Fig. 1. Scattering This occurs when ultrasound strikes a particle or object which is the same size or smaller than the ultrasound wavelength. A: A particle approximately the same size as the wavelength scatters the wave to a variable degree in different directions. The degree of scattering depends on the ultrasound frequency and angle of insonation. B: A particle smaller than the wavelength such as a red blood cell scatters the wave to an equal degree in all directions (termed Rayleigh scattering ; Baron John William Rayleigh (1842–1919), an English physicist) independent of the angle of insonation.

Intensity (mW/cm

2 )

Depth (cm)

0 0 2

2

1

4 6 8 10

1 – Low frequency 2 – High frequency

Fig. 1. Attenuation ● Exponential decay, mostly from absorption but also from reflection, refraction, scattering and diffraction. ● Less for low-frequency signals, as used for deep abdominal scanning. ● Greater for high-frequency signals, as used for superficial scanning. ● Low for blood, higher for soft tissues, and very high for lung and bone.