Medical X-Ray Techniques in Diagnostic Radiology: A Textbook for Radiographers and Radiological Technicians

470 Pages·1980·50.95 MB·English

MEDICAL X-RAY TECHNIQUES
IN DIAGNOSTIC RADIOLOGY
MEDICAL X-RAY TECHNIQUES
IN DIAGNOSTIC RADIOLOGY
A Textbook for Radiographers and Radiological Technicians
G.J. VAN DER PLAATS
Former Chief Radiologist, St Annada! Hospital, Maastricht
with the assistance of
P. VIJLBRIEF
Radiologist, Research Laboratory,
Radiological Clinic, University of Leiden
M
©G. 1. van der Plaats 1959, 1961, 1969, 1980
Softcover reprint of the hardcover 1st edition 1980 978-0-333-26415-7
All rights reserved, no part of this publication may be reproduced
or transmitted, in any form or by any means, without permission
First edition published by Centrex Publishing Company,
Eindhoven, The Netherlands, 1959
Second edition 1961
Third edition 1969
Fourth edition first published 1980
in Europe (excluding the United Kingdom, Eire,
and Comecon countries), the United States and Canada,
by Martin us Nijhoff Publishers,
The Hague, The Netherlands
Published in the rest of the World by
THE MACMILLAN PRESS LTD
London and Basingstoke
Associated companies in Delhi Dublin
Hong Kong Johannesburg Lagos Melbourne
New York Singapore and Tokyo
ISBN 978-1-349-04632-4 ISBN 978-1-349-04630-0 (eBook)
DOI 10.1007/978-1-349-04630-0
This book is sold subject to the standard conditions of the
Net Book Agreement
Contents
Foreword vii
2 Discovery and production of X-rays; construction and function of the 35
X-ray tube
2 Formation and properties of X-rays 35
3 Dosimetry, radiation hazards and protective measures 58
4 Methods of image formation and laws of projection 85
5 Sharpness and unsharpness 104
6 Contrast 114
7 Perceptibility of detail in the radiographic image; Image quality 131
8 Properties of fluoroscopic screens, radiographic films, intensifying 143
screens and cassettes
9 Image intensification and X-ray television 171
10 Processing technique 192
11 Fluoroscopy and radiographic technique in general 237
12 Special radiographic techniques 260
13 Radiographic examinations using contrast media 329
14 Exposure, exposure tables, automatic density control 337
15 Diagnostic X-ray apparatus 378
16 Diagnostic stands and accessories 412
Index 445
Foreword
by Professor J. H. Middlemiss,
Department of Radiodiagnosis,
The Medical School,
University of Bristol
This book, for so long and so deservedly, has been a favourite and reliable guide
for any person undergoing training in diagnostic radiology whether that person be
doctor or technician. This new, largely re-written edition is even more comprehen
sive. And yet throughout the book simplicity of presentation is maintained.
Professor G. J. van der Plaats has been well known to radiologists in the English
speaking world for more than three decades. He has been, and still is, respected by
them for his vision, his thoroughness, determination and meticulous attention to
detail and for his unremitting enthusiasm. The standard of radiography in the
Netherlands throughout this period has been recognised as being of the highest
quality, and this has, in no small measure, been due to the pattern set by Professor
van der Plaats and his colleagues.
As radiology has developed and grown, as new techniques have been devised, as
apparatus has become more complex and sophisticated, as automation has been
introduced, so has there been a tendency for both radiologist and radiographer,
especially those in training, to become divorced from the fundamental essentials
of their work. The exotic attracts and often there does not seem to be any glamour
in the basic concepts and the basic practices through which radiology has passed
and out of which modern radiology has grown. Yet it is only by having a complete
understanding of the basic practices that modern radiology can exist or can expect
to develop even further. In this book Professor van der Plaats guides the beginner
with great expertise and with consummate interest through all the fundamental
problems step by step, dealing in turn with every aspect of the technical factors
involved in the production of X-ray images. As automation has invaded our dark
rooms there are radiographers qualifying in some industrialised countries who
have never performed and in some cases have never even seen hand processing. The
author has forgotten nothing. He takes the learner through all the fundamental
aspects of processing with a wealth of practical wisdom and experience.
viii Foreword
As radiology continues to grow and as its uses are spreading further and further
into the remote areas of non-industrialised countries, so is simple X-ray apparatus
being designed and manufactured for use in those places. This type of X-ray
service is likely to be termed a primary radiological service. In such a service there
will be no place for image intensifiers, or television chains, probably no place for
fluoroscopy; there certainly will not be automatic processing. It is unlikely that
there will be enough trained radiologists to give constant radiological cover in such
a service. Yet there must be trained radiographers and there must be facilities for
the training of technicians to operate these machines and to provide a service to
the clinician. Professor van der Plaats' book will provide all the knowledge required
by persons undergoing such training, and provide it in such a way that it is under
stood. For this reason alone this book deserves the widest circulation possible in
those parts of the world where a primary radiological service is being developed
and where the training of X-ray operators is being undertaken.
Yet, let it not be thought that this book is only for use where rudimentary use
of radiology is contemplated or where only a primary radiological service is
provided. As mentioned earlier the book is comprehensive. It includes adequate
presentation and discussion on such subjects as contrast media, routine radio
graphic techniques, special techniques, tomography, macro-radiography, stereo
scopic fluoroscopy, cine-radiography and even C .T. scanning; it gives details of
exposures and exposure tables, and density control; it gives details of apparatus
construction. It truly is a compendium.
I recommend it to all training schools where radiographers and radiologists are
trained. And many experienced radiologists will benefit from browsing through its
pages and will wish to keep it on the bookshelf in their departments where they
can refer to it when some technical problem occurs, as inevitably they do occur in
everyday life. This book is about everyday life in a Department of Diagnostic
Radiology.
1
Discovery and Production of X-Rays;
Construction and Function of the
X-Ray Tube
On 8 November, 1895 Professor Wilhelm Conrad Rontgen (1845-1923) discovered
an unknown kind of ray, which he called X-ray. While he was busy with experi
ments on the behaviour of cathode rays (these tests were very much in vogue at
that time) in Hittorf-Geissler-Crookes tubes (glass envelopes in which the air has
been evacuated to a very high degree) he happened to notice that some crystals
lying near the tube had become strongly fluorescent. Rontgen studied this pheno
menon and decided that it was caused by a hitherto unknown radiation.
On 28 December, 1895 in Wiirzburg, he made the first announcement of this
radiation in a paper entitled: 'Uber eine neue Art von Strahlen' (about a new kind
of rays). His presentation of the facts was so convincing as to leave no doubt that
a new kind of radiation had indeed been discovered. Moreover, Rontgen had
already thoroughly investigated-as appeared later-the most important properties
of this new radiation. The discovery of X-rays ranks as one of the greatest dis
coveries of the last century.
In some languages one no longer calls these rays X-rays (in German:
Rontgenstrahlen; Dutch: rontgenstralen; English: X-rays; French: rayons X;
Spanish: rayos X). Rontgen was born in Remscheid-Lennep (near Wuppental),
a town which is worth visiting for its own intrinsic charm. A Rontgen museum
has been founded near the house of his birth and here it is possible to see many
instruments and documents of his time. The museum is constantly kept up to
date and demonstrates the development of X-ray technique throughout the
years. A visit to the place is warmly recommended.
There are several biographies ofW. C. Rontgen, which give particulars of his
great discovery, interspersed with much information about that period and his
1
2 Medical X-ray Techniques
private life. Interesting facts about the pioneers and forerunners of radiology are
also found in other publications. Only a few are mentioned below:
0. Glasser, Dr W. C. R(intgen, Charles C. Thomas, Springfield, Illinois
W. A. H. van Wylick, W. C. Roentgen and the early days of X-rays, Medicamundi,
16 (1), 1-8
D. R. Hill, Principles of Diagnostic X-ray Apparatus, Philips Medical Systems Ltd,
London
1.1 BREMSSTRAHLUNG, CHARACTERISTIC RADIATION, GAMMA
RADIATION
X-rays arise whenever electrons collide at very high speed with matter and are
thus suddenly retarded. The X-rays emitted in this way are known as Bremsstrah
lung (from the German 'bremsen' to brake). The greatest part by far (99 per
cent) of the kinetic energy of the electrons is converted, by means of collisions,
into kinetic energy (heat) of the matter bombarded by these electrons. X-radiation
is produced due to the braking (slowing down) of some electrons in the electric
fields within the material.
When an electron loses all or part of its energy due to the electric fields within
the atom then a photon is created. Its energy (hv, where his Planck's constant
and v frequency) depends on the manner of energy transfer; if this is virtually
complete then a photon with a great deal of energy is created and this represents
short wavelength radiation. Even if all the electrons were to collide with the anode
material with exactly the same speed (for example by means of a constant equal
voltage between the cathode and anode) then the energy transfer of the individual
electrons would still be different and, thus, the photons created would also have
different energies. This is the explanation of the fact that Bremsstrahlung always
consists of X-radiation of many different wavelengths, which together form a
continuous spectrum. In general, the (few) electrons, which give up all their energy,
produce the most 'energetic' photons that can be created at that particular colli
sion velocity; this is also how the shortest wavelength is determined in this radia
tion mixture. Still 'greater' photons (with still shorter wavelengths) can only be
produced by means of high electron speeds (thus higher tube voltage). Apart from
the Bremsstrahlung if the energy of the bombarding electron is great enough
yet another kind of radiation, with certain particular wavelengths that are charac
teristic of the rna terial with which the electrons collide, will also be produced.
This is connected with the characteristic energy of the electrons of the innermost
orbits of the atom of every element. The characteristic radiation is superimposed
upon the continuous Bremsspectrum with one or several spectral lines. The inten
sity of the characteristic radiation of an X-ray tube is usually low in comparison
with the intensity of Bremsstrahlung. However, in specially constructed tubes such
as those for X-ray spectography and mammography use is made of characteristic
radiation in particular.
The maximum energy (or minimum wavelength) of an emitted spectrum is
determined by the maximum speed of the bombarding electrons, in the case of
both Bremsstrahlung and characteristic radiation.
X-rays and the X-ray Tube 3
The emission of electromagnetic radiation in the X-radiation range of wave
lengths also occurs in certain radioactive processes. Radiation emitted by the
nucleus of an atom is called gamma radiation; radiation which originates out
side the nucleus is known as X-radiation. In principle there is really no difference
between this gamma radiation and X-radiation if one disregards their origins.
Formerly, it was impossible to produce X-rays with as great an energy as hard
gamma rays. Today, apparatus such as betatrons, synchrotrons and linear
accelerators can generate X-rays of energy equal to that of even very hard gamma
rays.
1.2 ION TUBES
Before discussing X-ray tubes as used in modern diagnostic techniques, it will be
informative to consider briefly the tubes originally used to generate X-radiation.
These tubes were known as gas (or ion) tubes.
Ion tubes are glass envelopes in which two electrodes are sealed into the glass at
opposite ends. The air is pumped out of these tubes, so that the atmosphere inside
becomes more and more rarefied (approaching a vacuum). At the same time a
great potential difference is applied between the two electrodes making one
positive (anode) and the other negative (cathode). When the air pressure is low
enough, current passes through the tube-which until this point was non-conduc
tive-producing a luminous effect (due to ionisation). With further reduction in
air pressure the electrons and ions are given greater speeds and in their turn cause
further ionisation due to collisions. The electrons travel to the anode, where a
certain amount of X-radiation is then generated; what is more important, how
ever, is that the heavy atomic residues, or gas ions as they are called, are attracted
to the cathode, where the impact of their relatively larger mass releases many
more electrons. When the cathode is shaped like a concave reflector the heavy
concentration of electrons thus released is united into a beam and focused on
to a particular spot on the anode (the focal spot) and there produces intense
X-radiation. Often such ion tubes were provided with a third electrode, the anti
cathode, (connected with the anode), mounted opposite the cathode as a target
for the focused electrons. Figure 1.1 shows such a tube diagrammatically.
In the very beginning of their history these tubes were continuously evacuated
by connecting them to an air pump; later, when it became possible to achieve
the required vacuum, the tubes were 'sealed off'. Almost all later tubes were of the
Figure 1.1 Ion tube. 1. Anode; 2. cathode; 3. anticathode at anode potential; 4. regenerating
device at cathode potential.