Ultrasound Technology for Clinical Practitioners E-Book

Crispian Oates

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 460

Veröffentlichungsjahr: 2023

Beschreibung

Ultrasound Technology for Clinical Practitioners

A hands-on and practical roadmap to ultrasound technology for clinical practitioners who use it every day

In Ultrasound Technology for Clinical Practitioners, distinguished medical physicist and vascular ultrasound scientist Crispian Oates delivers an accessible and practical resource written for the everyday clinical user of ultrasound. The book offers complete descriptions of the latest techniques in ultrasound, including ultrafast ultrasound and elastography, providing an up-to-date and relevant resource for educators, students, and practitioners alike.

Ultrasound Technology for Clinical Practitioners uses a first-person perspective that walks readers through a relevant and memorable story containing necessary information, simplifying retention and learning. It makes extensive use of bulleted lists, diagrams, and images, and relies on mathematics and equations only where necessary to illustrate the relationship between other factors. Physics examples come from commonly known contexts that readers can relate to their everyday lives, and additional description boxes offer optional, helpful info in some topic areas.

Readers will also find:

• A thorough introduction to the foundational physics of ultrasound, as well as the propagation of the ultrasound pulse through tissue
• Comprehensive discussions of beam shapes, transducers, imaging techniques, and pulse echo instrumentation
• In-depth examination of image quality and artefacts and the principles of Doppler and colour Doppler ultrasound
• Fulsome treatments of measurement taking and safety and quality assurance in ultrasound

Perfect for sonographers, echocardiographers, and vascular scientists, Ultrasound Technology for Clinical Practitioners will also earn a place in the libraries of radiologists, cardiologists, emergency medicine specialists, and all other clinical users of ultrasound.

Leseprobe

Ultrasound Technology for Clinical Practitioners

Crispian Oates

Newcastle University, UK

This edition first published 2023© 2023 John Wiley & Sons Ltd

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The right of Crispian Oates to be identified as the author of this work has been asserted in accordance with law.

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Library of Congress Cataloging‐in‐Publication Data Applied for:ISBN 9781119891550

Cover Image: Courtesy of the AuthorCover Design: Wiley

This book is dedicated to Tony Whittingham who has been my guide and mentor in all things ultrasonic and to Marion my constant companion and encourager.

Acknowledgements

In writing this book, I have been helped by many friends and colleagues. I am very grateful for all their contributions and help, and indebted to them for their advice. It began with interaction with my students over many years and a set of honed lecture notes. More specifically, I have been particularly helped by Gareth Bolton at the University of Cumbria who very kindly let me use his facilities and scanners to get a significant number of the clinical images demonstrating machine settings. He also gave me valuable feedback, reading drafts and looking at the material from the student‐teacher point of view. Stephen Klarich and Jamie Wild gave me invaluable advice on the practicalities of using elastography and Chris Eggett advised me in relation to echocardiography. Barry Ward advised on quality assurance. I am also thankful to Kathia Fiaschi, Carmel Moran, and Heather Venables. Those mentioned and others kindly provided images as indicated throughout the book. Putting together a book like this takes a considerable time and Covid lockdown certainly helped in providing that time. So too did my family and particularly my wife Marion. She has been a great support and encourager and I am deeply thankful to her. However, having acknowledged those who have helped and contributed in various ways, the work is mine as are any errors and mistakes that remain within it.

Crispian OatesApril 2020

List of Abbreviations

ADC

analogue to digital converter

AI

artificial intelligence

A‐mode

amplitude mode

ARFI

acoustic radiation force impulse

B‐flow

B‐mode flow

B‐mode

brightness mode

CA

contrast agent

CAD

computer aided diagnosis

CCA

common carotid artery

CDU

colour Doppler ultrasound (CFM)

CEUS

contrast enhance ultrasound

CFM

colour flow mapping (CDU)

CLA

curvilinear array

CMUT

capacitative micromachined ultrasound transducer

CPU

central processing unit

CT

computerised tomography

CUTE

computed ultrasound tomography in echo mode

CW

continuous wave

DGC

depth gain control (TGC)

ECG

electrocardiogram

FFT

fast Fourier transform

FPS

frames per second

FR

frame rate

FWHM

full width at half maximum (beamwidth)

GPU

graphics processing unit

ICA

internal carotid artery

I

SATA

spatial average temporal average intensity

ISB

intrinsic spectral broadening

I

SPPA

spatial peak, peak average intensity

I

SPTA

spatial peak temporal average intensity

I

SPTP

spatial peak temporal peak intensity

IUCD

intra‐uterine contraceptive device

LA

linear array

MI

mechanical index

M‐mode

motion mode

MRI

magnetic resonance imaging

PA

phased array

PD

power Doppler

PI

pulsatility index

PRF

pulse repetition frequency

PSV

peak systolic velocity

pSWE

point shear wave elastography

PVDF

polyvinylidene flouride

PWD

pulse wave Doppler

PZT

lead zirconate titanate

QA

quality assurance

RBC

red blood cell

RF

radio frequency

RI

resistance index

ROI

region of interest

RSI

repetitive strain injury

Rx

receive (signal)

SA

synthetic aperture

SCA

subclavian artery

SE

strain elastography

SNR

signal to noise ratio

SoS

speed of sound

SR

strain rate

SRT

systolic rise time

SSI

supersonic shear (wave) imaging

STE

speckle tracking echocardiography

SV

sample volume

SWE

shear wave elastography

TDI

tissue Doppler imaging

TGC

time gain control (DGC)

TI

thermal index

TIB

thermal index for bone in view

TIC

thermal index for superficial bone in view

TIS

thermal index for soft tissue

Tx

transmit (signal)

UFCD

ultrafast colour Doppler

UFUS

ultrafast ultrasound

VFI

vector flow imaging

WRRSI

work related repetitive strain injury

Introduction

This book covers the essential physics and technology of diagnostic ultrasound needed by someone practicing ultrasound in the clinical setting, with ultrasound as a primary or significant component of their job. For simplicity, the term ‘sonographer’ has been used throughout for this person but ultrasound is used by a wide range of personnel in clinical practice including doctors, echocardiographers, vascular scientists, midwives, nurse practitioners, and physiotherapists. The book is designed to be accessible to all of these practitioners. Each chapter is liberally illustrated with easily reproducible drawings and clinical images to demonstrate the point being made. The use of equations has been kept to a minimum. Where used, equations are useful in showing the relationship between one factor and another and where changing one thing can have clinical or safety implications. The term ‘scanner’ refers to the ultrasound machine.

Over the years, ultrasound machines have become more user friendly and the machine performs many functions without the user being aware of what is being changed, for example the use of presets for particular patient examinations. It is important to have an understanding of what your equipment, being applied to a patient, is doing. By knowing more about the technology behind the scanner, you will increase in confidence in handling your scanner and be able to be assured that you are obtaining the optimum diagnostic information and are operating in a safe manner for yourself and the patient. The patient may also be reassured that they are being treated by a competent practitioner who knows their equipment and what they are doing.

The emphasis throughout will be on what the user needs to know in order to drive the ultrasound scanner correctly and effectively in order to obtain the best images. We will also look at the technical factors that must be taken into account when interpreting the images to make clinical judgments. In a number of places, it will be necessary or useful to explain a point in greater detail or add additional but less essential information. These will be indicated by using green shaded boxes. Where a point of specific relevance to daily practice is made, green text is used. Key terms are highlighted in bold type.

Ultrasound uses sound waves of a higher pitch than the audible range to form images from within the body. The ultrasound is produced by a transducer probe that is typically placed on the skin, after it has had a liquid gel applied to it. Short pulses of ultrasound are transmitted into the body and are reflected, forming echoes that in turn are picked up by the ultrasound probe. The received signal is then processed to form the image we see. This method of forming images is called the pulse‐echo technique and is similar to that used by sonar on boats or by radar.

In Figure 0.1, we see three typical ultrasound greyscale images. Looking at the three images, the first thing to notice is that there are two basic image formats. A rectilinear format or linear scan (a) and a sector shaped format or sector scan (b,c). Both formats show a cross‐sectional slice through the body as though the body had been cut open, going deep from the transducer probe at the skin surface, and we are looking down onto the cut surface (Figure 0.2).

As shown, the transducer/skin surface is at the top of the linear image and at the narrower point of the two sector images. The orientation of the image may be chosen by the user. The three images are produced by different ultrasound probes and are useful for different clinical examinations. In the first image (a), the linear scan is produced by a linear array probe and is useful for looking at small parts including musculoskeletal examinations and vascular work. The second image (b) is produced by a curvilinear probe and is useful for situations where an extended target is being viewed, for example the abdomen or a foetus. The third image (c) is produced by a phased array probe. This probe has a small footprint on the skin but is able to show an extended field of view in the body, for example viewing the heart from between the ribs.

FIGURE 0.1 Three typical greyscale or B‐mode images from (a) a linear array, (b) a curvilinear array and (c) a phased array. Image (b) shows the greyscale used down the left‐hand side.

FIGURE 0.2 The image plane within the body (a) and the ultrasound image seen (b).

At its most basic, the process of image formation can be thought of as using a narrow beam of ultrasound to sweep through the tissue across the image plane or scan plane, like we might sweep a torch beam across a dark room, to build up a picture of what is there. The image is therefore built up from a series of lines transmitted out from the transducer and going deep into the body, laid side‐by‐side to form the image. Each line uses the pulse‐echo principle to receive echoes from along that line. In the case of the linear scan, it is as though the beam was swept in a straight line along the surface of the skin across the width of the probe. In the case of the phased array, it is as though the probe was rocked at one point on the skin to sweep the beam in a sector.

If we know how fast the pulse travels through the tissue, we can time the echoes coming back and so calibrate the depth of the echo targets in centimetres away from the probe. The marks down the side of each image indicate depth from the transducer probe.

Looking at the images, details of structures producing echoes are shown as bright and dark marks matching a greyscale as seen on the left side of Figure 0.1b. This type of image is known as a B‐mode or greyscale image. Some parts of the image are clearer and more obvious than other parts. In order to interpret these images, the scanner must firstly be set up to produce the optimum quality image and secondly, the person interpreting needs to understand what is really being imaged and what is artefact or misrepresented in the image. As for all imaging modalities, the sonographer needs anatomical knowledge and an understanding of how the images are formed and what limitations the technique has in order to correctly interpret the images.

Whilst modern machines have automated many of the processes involved in ultrasound imaging, there remain a large number of variables under user control that the sonographer must manage effectively to produce optimal images and maximise the diagnostic potential of ultrasound.

We begin our look at ultrasound technology by considering what ultrasound is and how it interacts with tissue. We then move on to look at the production of a B‐mode or greyscale image and its interpretation before going on to consider Doppler ultrasound. We then look at making measurements, safety of ultrasound, and quality assurance before moving on to advanced topics and the latest developments with ultrafast techniques. Finally, we look at elastography. Three appendices cover a check list for performing a scan that covers ‘knobology’, the basic manipulation of equations, and a detailed look at the ultrasound beam.

CHAPTER 1The Basic Physics of Ultrasound

SOUND WAVES

A sound wave is a fluctuating variation in pressure within a medium such as air, water, or solid material. Our ears are sensitive to such pressure changes in air, and we hear sounds all the time. The faster the changes in pressure take place, the higher the pitch or frequency of the sound we hear. Frequency is measured in hertz (Hz) and, for a young person, their hearing goes from 20 Hz to 20 kHz. Middle C on a piano is 261 Hz. A sound above 20 kHz is called ultrasound