Diagnostic Ultrasound

276 Pages·2010·33.83 MB·English

Diagnostic Ultrasound
Physics and Equipment

Second Edition

Diagnostic Ultrasound
Physics and Equipment

Peter Hoskins BA, MSc, PhD, DSc, FIPEM, FInstP
Reader in Medical Physics
Edinburgh University
Edinburgh, UK

Kevin Martin BSc, PhD, FIPEM
Retired Consultant Medical Physicist
Leicester, UK
Abigail Thrush BSc, MSc, MIPEM
Principal Medical Physicist
Barts and the London NHS Trust
London, UK

Second edition

Edited by

cambridge university press
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Cambridge University Press
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Information on this title: www.cambridge.org/9780521757102

© Cambridge University Press 2010

Th is publication is in copyright. Subject to statutory exception
and to the provisions of relevant collective licensing agreements,
no reproduction of any part may take place without the written
permission of Cambridge University Press.

First edition published by Greenwich Medical Media Limited 2003

Th is edition published by Cambridge University Press 2010

Printed in the United Kingdom at the University Press, Cambridge

A catalogue record for this publication is available from the British Library

Library of Congress Catalogung in Publication data
Diagnostic ultrasound : physics and equipment / [edited by] Peter Hoskins, Kevin Martin, Abigail Th rush. – 2nd ed.
p. ; cm.
Includes bibliographical references and index.
ISBN 978-0-521-75710-2 (pbk.)
1. Diagnostic ultrasonic imaging. I. Hoskins, Peter. II. Martin, Kevin, 1948– III. Th rush, Abigail. IV. Title.
[DNLM: 1. Ultrasonography–methods. 2. Physical Phenomena. 3. Ultrasonography–instrumentation.
WN 208 D5367 2010]
RC78.7.U4D516 2010
616.07′543–dc22 2010016391

ISBN 978-0-521-75710-2 Paperback

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accuracy of URLs for external or third-party internet websites referred to
in this publication, and does not guarantee that any content on such
websites is, or will remain, accurate or appropriate.

Every eff ort has been made in preparing this book to provide accurate and up-to-date
information which is in accord with accepted standards and practice at the time of publication.
Although case histories are drawn from actual cases, every eff ort has been made to disguise the
identities of the individuals involved. Nevertheless, the authors, editors and publishers can make no
warranties that the information contained herein is totally free from error, not least because clinical
standards are constantly changing through research and regulation. Th e authors, editors and
publishers therefore disclaim all liability for direct or consequential damages resulting from the use of
material contained in this book. Readers are strongly advised to pay careful attention
to information provided by the manufacturer of any drugs or equipment that they plan to use.

v

1
Introduction to B-mode imaging 1
Kevin Martin

2
Physics 4
Kevin Martin and Kumar Ramnarine

3
Transducers and beam-forming 23
Tony Whittingham and Kevin Martin

4
B-mode instrumentation 47
Kevin Martin

5
Properties, limitations and artefacts of
B-mode images 64
Kevin Martin

6
B-mode measurements 75
Nick Dudley

7
Principles of Doppler ultrasound 84
Peter Hoskins

8
Blood fl ow 96
Abigail Th rush

9
Spectral Doppler ultrasound 105
Abigail Th rush

10 Colour fl ow and tissue imaging 121
Peter Hoskins and Aline Criton

11 Quality assurance 142
Tony Evans and Peter Hoskins

12 Safety of diagnostic ultrasound 155
Francis Duck and Adam Shaw

13 3D ultrasound 171
Peter Hoskins and Tom MacGillivray

14 Contrast agents 181
Carmel Moran and Mairéad Butler

15 Elastography 196
Peter Hoskins

Appendices
A Th e decibel (dB) 215
B Th e binary system 216
C Th e British Medical Ultrasound Society.
Guidelines for the safe use of diagnostic
ultrasound equipment 217
D Useful contacts 226
E Acoustic output parameters and their
measurement 227
Glossary of terms 230
Index 254

Contents

List of Contributors vii
Preface to the second edition ix
Preface to the fi rst edition xi

v

vii

Mairéad Butler MPhys, PhD, MInstP
Research Assistant in Medical Physics
University of Edinburgh, UK

Aline Criton PhD
Ultrasound Director
SuperSonic Imagine, France

Francis Duck PhD, DSc, FIPEM, MBE
Consultant Medical Physicist
Royal United Hospital Bath and
Bath University, UK

Nick Dudley BSc, MSc, PhD, FIPEM
Consultant Medical Physicist
United Lincolnshire Hospitals, UK

Tony Evans BSc, MSc, PhD, CEng
Senior Lecturer in Medical Physics
University of Leeds, UK

Peter Hoskins BA, MSc, PhD, DSc, FIPEM, FInstP
Reader in Medical Physics
University of Edinburgh, UK

Tom MacGillivray BSc, MSc, PhD
Research Fellow in image processing
University of Edinburgh, UK

Kevin Martin BSc, PhD, FIPEM
Retired Consultant Medical Physicist
Leicester, UK

Carmel Moran BSc, MSc, PhD, FIPEM
Reader in Medical Physics
University of Edinburgh, UK

Kumar Ramnarine BSc, MSc, PhD, CSci, MIPEM
Principal Medical Physicist
University Hospitals of Leicester
NHS Trust, UK

Adam Shaw BA, MA(Cantab)
Senior Research Scientist
National Physical Laboratory,
Middlesex, UK

Abigail Thrush BSc, MSc, MIPEM
Principal Medical Physicist
Barts and the London NHS Trust, UK

Tony Whittingham BSc, MSc, PhD, FInstP, CPhys, FIPEM
Retired Consultant Medical Physicist
Newcastle-upon-Tyne, UK

Contributors

vii

Th e aims and intended audience of this second edi-
tion remain unchanged from the fi rst edition. Th e aim
is to provide the underpinning knowledge of physics
and instrumentation needed in order to practise ultra-
sound in a clinical setting. Th e book is primarily aimed
at sonographers and clinical users in general, and will
also serve as a fi rst textbook for physicists and engin-
eers. Th e text concentrates on explanations of prin-
ciples which underpin the clinical use of ultrasound
systems. Th e book contains relatively few equations and
even fewer derivations. In the last 7 years a number of
techniques which existed in embryo form in 2002 have
become available on commercial ultrasound systems,

and are used in a suffi cient number of hospitals to jus-
tify inclusion in this book. Th ere are additional chap-
ters dedicated to 3D ultrasound, contrast agents and
elastography. Th e other chapters have been updated
to include developments in technology, quality assur-
ance and safety. We hope that this second edition of
‘Diagnostic Ultrasound Physics and Equipment’ will
meet the needs of sonographers, physicists and engin-
eers in their training and practice.
Peter Hoskins
Kevin Martin
Abigail Th rush
Autumn 2009

Preface to the second edition

ix

Th is book is an introductory text in the physics and
instrumentation of medical ultrasound imaging. Th e
level is appropriate for sonographers and clinical users
in general. Th is will also serve as a fi rst textbook for
physicists and engineers. Th e text concentrates on
explanations of principles which underpin the clinical
use of ultrasound systems, with explanations following
a ‘need to know’ philosophy. Consequently, complex
techniques, such as Doppler frequency estimation using
FFT and 2D autocorrelation, are described in terms of
their function, but not in terms of their detailed sig-
nal processing. Th e book contains relatively few equa-
tions and even fewer derivations. Th e scope of the book
refl ects ultrasound instrumentation as it is used at the

time of submission to the publishers. Techniques which
are still emerging, such as tissue Doppler imaging
(TDI) and contrast agents, are covered in a single chap-
ter at the end of the book. Techniques which are even
further from commercial implementation, such as vec-
tor Doppler, are not covered. We hope this book fi lls
the gap in the market that we perceive from discussions
with our clinical colleagues, that of a text which is up to
date and at an appropriate level.
Peter Hoskins
Abigail Th rush
Kevin Martin
Tony Whittingham
Summer 2002

Preface to the fi rst edition

xi

Diagnostic Ultrasound: Physics and Equipment, ed. Peter Hoskins, Kevin Martin and Abigail Th rush. Published by Cambridge University
Press. © Cambridge University Press 2010.

principles of its formation. In essence, these principles
are still used in modern B-mode systems, although
they may be used within more complex arrangements
designed to enhance performance.
A B-mode image is a cross-sectional image repre-
senting tissues and organ boundaries within the body
( Figure 1.1 ). It is constructed from echoes, which are
generated by refl ection of ultrasound waves at tissue
boundaries, and scattering from small irregularities
within tissues. Each echo is displayed at a point in the
image, which corresponds to the relative position of
its origin within the body cross section, resulting in a
scaled map of echo-producing features. Th e brightness
of the image at each point is related to the strength or
amplitude of the echo, giving rise to the term B-mode
(brightness mode).
Usually, the B-mode image bears a close resem-
blance to the anatomy, which might be seen by eye, if the
body could be cut through in the same plane. Abnormal

Th e application of ultrasound to medical diagnosis has
seen continuous development and growth over sev-
eral decades. Early, primitive display modes, such as
A-mode and static B-mode , borrowed from metallur-
gical testing and radar technologies of the time, have
given way to high-performance, real-time imaging.
Moving ultrasound images of babies in the womb are
now familiar to most members of the public through
personal experience of antenatal scanning or via televi-
sion. Modern ultrasound systems do much more than
produce images of unborn babies, however. Modern
ultrasound systems are able to make detailed measure-
ments of blood movements in blood vessels and tissues,
visualize moving structures in 3D, and make measure-
ments related to the stiff ness of tissues.
Improvements in technology have been followed
by widespread acceptance and use of ultrasound in
medical diagnosis. Applications have progressed from
simple measurements of anatomical dimensions, such
as biparietal diameter, to detailed screening for fetal
abnormalities, detection of subtle changes in tissue
texture and detailed study of blood fl ow in arteries. In
many areas, ultrasound is now chosen as the fi rst line of
investigation, before alternative imaging techniques.
Th is book describes the physics and technology
of diagnostic ultrasound systems in use at the time of
writing. Th e book may be divided into four sections;
basic physics and B-mode imaging in Chapters 1 – 6 ;
Doppler ultrasound in Chapters 7 – 10 ; quality assur-
ance and safety in Chapters 11 – 12 , and recent tech-
nology in Chapters 13 – 15 . Th is chapter covers the very
basic concepts involved in B-mode imaging.

Basic principles of ultrasound image
formation
We begin the explanation of ultrasound image forma-
tion with a description of a B-mode image and the basic

Introduction to B-mode imaging

Kevin Martin

1

Chapter
1

Fig. 1.1 An example of a B-mode image showing
refl ections from organ and blood vessel boundaries
and scattering from tissues.

2

1 Introduction to B-mode imaging

anatomical boundaries and alterations in the scattering
behaviour of tissues can be used to indicate pathology.
To form a B-mode image, a source of ultrasound,
the transducer, is placed in contact with the skin and
short bursts or pulses of ultrasound are sent into the
patient. Th ese are directed along narrow beam-shaped
paths. As the pulses travel into the tissues of the body,
they are refl ected and scattered, generating echoes,
some of which travel back to the transducer, where they
are detected. Th ese echoes are used to form the image.
To display each echo in a position corresponding
to that of the interface or feature (known as a target)
that caused it, the B-mode system needs two pieces of
information. Th ese are
(1) the range (distance) of the target from the
transducer and
(2) the direction of the target from the active part of the
transducer, i.e. the position and orientation of the
ultrasound beam.

Echo ranging
Th e range of the target from the transducer is measured
using the pulse–echo principle. Th e same principle is
used in echo-sounding equipment in boats to measure
the depth of water. Figure 1.2 illustrates the measurement
of water depth using the pulse–echo principle. Here, the
transducer transmits a short burst or pulse of ultrasound,
which travels through water to the seabed below, where
it is refl ected, i.e. produces an echo. Th e echo travels back
through the water to the transducer, where it is detected.
Th e distance to the seabed can be worked out, if the speed
of sound in water is known and the time between the
pulse leaving the transducer and the echo being detected,
the ‘go and return time’, is measured.
To measure the go and return time, the transducer
transmits a pulse of ultrasound at the same time as a
clock is started ( t = 0). If the speed of sound in water is
c and the depth is d , then the pulse reaches the seabed
at time t = d / c . Th e returning echo also travels at speed
c and takes a further time d / c to reach the transducer,
where it is detected. Hence, the echo arrives back at
the transducer aft er a total go and return time t = 2 d / c .
Rearranging this equation, the depth d can be calcu-
lated from d = ct /2. Th us, the system calculates the tar-
get range d by measuring the arrival time t of an echo,
assuming a fi xed value for the speed of sound c (usually
1540 m s −1 for human tissues).
In the above example, only one refl ecting surface
was considered, i.e. the interface between the water and

the seabed. Th e water contained no other interfaces or
irregularities, which might generate additional echoes.
When a pulse travels through the tissues of the body, it
encounters many interfaces and scatterers, all of which
generate echoes. Aft er transmission of the short pulse,
the transducer operates in receive mode, eff ectively lis-
tening for echoes. Th ese begin to return immediately
from targets close to the transducer, followed by echoes
from greater and greater depths, in a continuous series,
to the maximum depth of interest. Th is is known as the
pulse–echo sequence .

Image formation
Th e 2D B-mode image is formed from a large num-
ber of B-mode lines, where each line in the image is
produced by a pulse–echo sequence. In early B-mode
systems, the brightness display of these echoes was
generated as follows.
As the transducer transmits the pulse, a display spot
begins to travel down the screen from a point corres-
ponding to the position of the transducer, in a direction
corresponding to the path of the pulse (the ultrasound
beam). Echoes from targets near the transducer return
fi rst and increase the brightness of the spot. Further
echoes, from increasing depths, return at increasing
times aft er transmission as the spot travels down the
screen. Hence, the distance down the display at which
each echo is displayed is related to its depth below the
transducer. Th e rate at which the display spot travels
down the screen determines the scale of the image. A
rapidly moving spot produces a magnifi ed image.

Reflection

Reception

t = 0
t = d/c
t = 2d/c

Transmission

Speed of sound c

Depth d

Fig. 1.2 Measurement of water depth using the pulse–
echo principle. The depth is worked out by measuring
the time from transmission of the pulse to reception of
the echo. The speed of sound must be known.