Introduction to Medical Electronics Applications

234 Pages·2003·8.83 MB·English

ELECTRONICS
APPLICATIONS
r
D Jennings A Flint BCH Turton LDM Nokes
Introduction to Medical Electronics Applications
Introduction to
Medical Electronics
Applications
D. Jennings, A. Flint, B.C.H. firton and L.D.M. Nokes
School of Engineering
University of Wales, College of Cardiff
Edward Arnold
A member of the Hodder Headline Group
LONDON BOSTON SYDNEY AUCKLAND
First published in Great Britain in 1995 by
Edward Arnold, a division of Hodder Headline PLC,
338 Euston Road, London NWl 3BH
Distributed in the USA by
Little, Brown and Company
34 Beacon Street, Boston, MA 02108
0 1995 D. Jennings, A. Flint, B.C.H. Turton and L.D.M. Nokes
All rights reserved. No part of this publication may be reproduced or
transmitted in any form or by any means, electronically or mechanically,
including photocopying, recording or any information storage or retrieval
system, without either prior permission in writing from the publisher or a
licence permitting restricted copying. In the United Kingdom such licences
are issued by the Copyright Licensing Agency: 90 Tottenham Court Road,
London W l P 9HE.
Whilst the advice and information in this book is believed to be true and
accurate at the date of going to press, neither the author 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
recognised. 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
ISBN 0 340 61457 9
1 2 3 4 5 95 96979899
q p e s e t in Times by GreenGate Publishing Services, Tonbridge, Kent
Printed and bound in Great Britain by J.W. Arrowsmith Ltd., Bristol
Contents
Preface vii
1 Introduction 1
2 Anatomy and Physiology 5
Introduction 5
Anatomical terminology 6
Structural level of the human body 8
Muscular system 12
Skeletal system 19
Nervous system 20
Cardio-vascular system 28
Respiratory system 34
3 Physics 38
The nature of ionising radiation 38
Physics of radiation absorption, types of collision 42
Radiation measurement and dosimetry 43
Outline of the application of radiation in medicine - radiology, radiotherapy 45
Physics of NMR 45
Ultrasound 51
Physics of ultrasound 52
The Doppler effect 60
Generation and detection of ultrasound 66
4 Physiological Instrumentation 75
Introduction 75
Measurement sy st ems 76
Transducers 82
Biopotentials 84
Blood pressure measurement 95
5 Imaging Fundamentals and Mathematics 109
Purpose of imaging 109
Mathematical background 110
Imaging theory 116
Image processing 121
6 Imaging Technology 124
Projection X radiography 124
Computerised tomogaphy 134
Gamma camera 14 0
Nuclear magnetic resonance imaging 143
Ultrasound imaging 148
Doppler ultrasound 162
7 Computing 169
Classification of computers 170
Outline of computer architecture 170
Data acquisition 180
Computer networks 181
Databases 185
Clinical expert systems 196
Privacy, data protection and security 200
Practical considerations 202
8 Hospital Safety 204
Electrical safety 204
Radiation hazards 213
References 215
Index 219
Preface
This book is intended as an introductory text for Engineering and Applied Science Students to
the Medical Applications of Electronics. A course has been offered for many years in Cardiff
in this arena both in this College and its predecessor institution. A new group, the Medical
Systems Engineering Research Unit, was established following the reorganisation of the
College. Restructuring and review of our course material and placing the responsibility for
teaching this course within the new group led to a search for new material. Whilst we found a
number of available texts which were suitable for aspects of our new course, we found a need
for a text which would encompass a wide scope of material which would be of benefit to
students completing their degree programmes and contemplating professional involvement in
Medical Electronics.
Medical Electronics is a broad field. Whilst much of the material which an entrant to medical
applications must acquire is the conventional basis of electronics covered by any student of
electronics, there are areas of special emphasis. Many of these arise from areas which are
increasingly inaccessible to students who necessarily specialise at an early stage in their
education.
The need for diversity is reflected in the educational background and experience of the
authors. Amongst us is a Medical Practitioner who is also a Mechanical Engineer, a Physicist
who now works as a Software Engineer, an Electronics Engineer who made the same move,
and another Electronics Engineer with some experimental experience in Orthopaedics.
The material which this book attempts to cover starts with an Introduction which hopefully
provides some perspective in the subject area. The following chapter provides an introduction
to human anatomy and physiology. The approach taken here is necessarily simplified: it is our
intention to provide an adequate grounding for the material in the following chapters both in
its basic science and the nomenclature which may be unfamiliar to readers with only
elementary biological knowledge.
Chapter Three describes the Physics employed in diagnostic techniques. This encompasses
basic radiation physics, magnetic resonance and the nature and generation of ultrasound.
Chapter 4 discusses the form of some of the basic electronic elements used in Medical
Applications. We describe the specialised techniques which are employed and characterise
the signals which are likely to be encountered. Special emphasis is attached to issues of
patient safety, although these are covered in greater depth in Chapter 8.
The mathematical background for image processing is covered in Chapter 5 . This material has
been separated from our description of representative diagnostic imaging technologies pre-
sented in Chapter 6. This latter Chapter includes material supplied by Toshiba Medical
Systems, whose assistance we gratefully acknowledge.
viii Introduction to Medical Electronics Applications
Chapter 7 contains background material concerning computers, their architecture, application
to data acquisition and connection to networks. It also covers some aspects of the application
of Databases and Expert Systems to Medicine which have long been expected to play central
roles in patient care. The increasing capacity of systems together with their continuing cost
reductions mean that their introduction is now becoming a reality. The introductory parts of
this Chapter will be familiar to many engineers: we have included it to ensure that this book
shall have a wide enough sphere of interest.
Finally, Chapter 8 examines aspects of patient safety which are of concern to engineers. This
area is a particularly difficult one in which to be specific as it is intimately entwined with
changing legislation. We seek to present here principles and what we believe to be good
practice: these must form the basis of any competent engineer’s activity.
This book has been some time in gestation. We wish to acknowledge the patience of our
families, without whom no doubt the task would have been completed more quickly. We have
been assisted too in no small measure by students and researchers in the Medical Systems
Engineering Research Unit who have provided both constructive criticisms and help by
checking manuscripts.
Introduction
This book is concerned with describing the application of technological methods to medical
diagnosis and therapy. It is instructive to review its development through recorded history. It
is apparent that the fastest advances in the application of technology to medicine have
occurred in the 20th Century and with an increasing pace. The following paragraphs touch on
some events in this chain. We should recall that systematic technological assistance has only
recently been widely applied to medicine through engineering. An understanding of the
pathology which technology often helps to identify has largely been developed hand in hand
with its application. In these paragraphs, we identify a number of the technologically based
systems which are described more fully in the succeeding chapters: their descriptions here are
necessarily rather terse.
Medicine arose as a Scientific discipline in ancient times. Bernal(1957) notes that by the time
of the establishment of the Greek civilisation, physicians were a notable professional group
whose activities were essential to the affluent, partly as a result of their unhealthy lifestyle.
They had by the 3rd Century BC distinguished between sensory and motor nervous functions.
In the same era the Hippocratic Oath, or the code of conduct for physicians was written: it
remains today as an ethical basis for much of medical practice.
Spectacles are first described in mid 14th Century Italy. Whilst optical glass had been used for
a long period, the quality of glass used by the ancients was too flawed to be of use for eyesight
correction. The continuing development of spectacle lenses led by about 1600 to the develop-
ment of the first telescopes. By the Renaissance period in the early 15th Century, medicine
was becoming more formalised. Anatomical knowledge progressively improved, and al-
though the topics of pathology and physiology were recognised, they had advanced little from
the time of Galen in Second Century Greece. Modern scientific medicine based on biological
science has largely developed since the mid 19th Century work by Pasteur and others. Bema1
(1957) notes that they provided the theories which led to an understanding of epidemiology
and to rational descriptions of nervous function.
The practical development of a thermometer suitable for measurement of body temperature
dates back to 1625. Whilst internal sounds from the body have been observed by physicians
since the time of the Romans, the stethoscope dates back to the 19th Century, in a form
reasonably similar to the present.
Whilst crafted artificial replacements for severed limbs have been in use for many centuries,
the development of both implanted prosthesis and functional artificial limbs is recent.