Philips Technical Library Principles of Diagnostic X- Ray Apparatus Edited by D.R. Hill MACMILLAN EDUCATION ISBN 978-1-349-02454-4 ISBN 978-1-349-02452-0 (eBook) DOI 10.1007/978-1-349-02452-0 First edition© Philips Medical Systems Ltd. 1973 Revised impression© Philips Technical Library 1975 Reprint of the original edition 1975 All rights reserved. No part of this publication may be reproduced or transmitted in any form, or by any means, without permission. This book is sold subject to the standard conditions of the Net Book Agreement. Published 1975 by THE MACMILLAN PRESS LTD London and Basingstoke Associated companies in New York Dublin Melbourne Johannesburg and Madras SBN 333 17731 2 teJ Philips Trademark of N.V. Philips' Gloeilampenfabrieken Preface This technical publication has been written primarily for students of diag nostic radiography, X-ray engineering and medical electronics. It will also serve as an introduction to the principles of X-ray apparatus and its associated medical electronic equipment for those embarking upon a career in radio logy. The authors are actively involved with the design, service, installation and application of the equipment discussed and have written as a team to ensure a comprehensive treatment of the subject on an up-to-date basis. Acknovvledgements The authors wish to thank Norman Bush for the production of many line drawings, Malcolm Pyke for the graphic artwork and presentation and Ann Horner for the laborious task of typing the complete manuscript. The authors are indebted to various organisations for oermission to publish illustrations of specialised equipment, in particular Sierex Ltd., London for figure 3 in chapter 18 and figures 1,4,5,7 ,11 & 12 in chapter 19, and Medica mundi, Holland for figures 1 and 3 in chapter 1. The writing of the book was encouraged and supported by the Directors of Philips Medical Systems Ltd., London to whom thanks are also due. Contents Chapter Title Author Page 1 History of X-rays. D.R. Hill 1 2 Radiation Physics. D.R. Hill 19 3 Light. D.R. Hill 27 4 X-ray Production. D.R. Hill 33 5 X-ray Interaction with Matter. D.R. Hill 39 6 X-ray Measurements. D.R. Hill 49 7 Electron Emission. B.A. Mansfield, F.S.E.R.T. 63 8 The X-ray Tube. B.R. Douch 113 9 High Voltage Generation. P.R. Hardy 147 10 Exposure Timers. P.R. Hardy 171 11 Interlocks and Safety Devices. P.R. Hardy 183 12 Mobile, Portable and Dental Units. A.H. Pyke 189 13 Beam Centring Devices. J.T.B. Moyle, T.Eng.(CEI),MITE 197 14 Scattered Radiation. W. Thompson, T.Eng.(CEI),MITE205 15 Fluoroscopic Equipment. O.J. Skinner 229 16 Image Intensifier and Television Technique. L.A. Newman, A.H. Pyke & B.A. Mansfield 239 17 Body Section Radiography. B.A. Mansfield 269 18 Skull Tables, Special Trolleys and Chairs. J.T.B. Moyle 291 19 Serial Radiography. J.T.B. Moyle 309 20 Test Equipment and Fault Diagnosis. A.H. Pyke 327 21 Electromedical Equipment in the X-ray Dept. D.R. Heywood B Sc.,M.Inst.P. 347 INDEX 377 Chapter 1 A History of X-Rays 1. 1 The Discovery of a New Kind of Ray Less than 100 years ago an event took place in Germany which was to have a dramatic effect on science and particularly in the field of medicine. On the evening of the 8th November, 1895, a physicist named Wilhelm Ko:1rad Roeatge,1 discovered a radiation which passes thro:1gh matter. Roaatgen's "new kind of ray'' he called X-rays, X for the unknown. With these new rays he made a pj_otograph of his wife's hand showing the bones :md wedding ring. The exposure time required was some 30 minutes. At the first public lecture by Roentgen, 0:1 January 25th 1896, Professor Albert von Ko~liker proposed that "thess new rays not be called X-rays" as Roentgen co:1tinued to name them throughout his life, "b:It should be n1med Roentgen rays in honour of the discoverer". Bo:h forms of nomenclature persist today. HoNever, the accepted interaational unit of X-ray qu1ntity became the Roa,1tgen in 1925. 1 . 2 Catho.Je Rays In 18.37 Mich1el Farad.1y carried o..tt research studies 0.1 the luminoJs effects ;Jroduced by p:1ssing an electric current thro:1gh varioJs gases. In 18.38 ie produced a discharge of electricity thro:1gh space in 1 p.artially evacuated glass tube. S:1ch glass tubes were produced by Heinrich Geissler. The observatio:1s of Faraday led IVilhelm Hittorf, in 1869, to describe ''cathode rays" a.1d the p:1ssage of electricity in 1 vacuum tube. Plucker had 1 1 fig.1 Wilhelm Roentgen 2 already noticed that objects placed between the negative electrode (cathode) and the glass wall would cast shadows on the glass wall. Plucker and Hittorf therefore announced that "cathode rays move straight from the negative electrode," a statement which was soon to be qualified. Shortly afterwards, William Crookes of England became interested in making glass tubes, from which nearly all the air had been pumped, for experiments he was conducting. By 1877 he was able to produce a very low gas pressure in a glass tube, thereafter called a Crookes' tube. Two years later Crookes had greatly clarified the p!J.enomenoa of cJ.thode rays, particularly by his discovery that the rays were deflected by electric and magnetic fields. See 1 Fig. 2. Anode --- --- --- --- --- --- -------- ------ --- --- --- Cathode Rays + 1 fig.2 Crookes' Tube Crookes continued to experiment and came to the conclusion that "cathode rays are a stream of particles cJ.rrying negative electricity ..... and cm be deflected ~Y an electromagnetic field or focussed by a coavex electrode". He also showed that "the particles heat up bodies upon which they fall". Crookes must have been producing X-rays ::tt the same time but they went unnoticed until Roentgen, using the same type of tube, made his discovery at the end of the 19th century. In 1892 Heinrich Hertz conducted experiments from which he concluded that the stream of cathode rays could pass through the glass wall of a vacuum tube. Hertz therefore believed that the cathode rays were a form of electromagnetic waves. He was not happy to refer to them as a stream of parti.cles. 3 It is about this time that Roentgen became interested in the subject. He was at the German University of Wuerzburg when he made his important discovery. Fortunately, he had a deep interest in photography. Thus on November 8th 1895, Roentgen noticed some objects fluorescing in the vicinity of a Crookes' tube which he was supplying with a current from an induction coil connected to a battery. Upon closer examination he found that the photographic plates were affected by this radiation,while the radiation was found to be stopped by extra glass shielding. The objects which fluoresced, he noted, were those coated with a particular chemical. It was obvious that the cathode rays in the tube were the origin of the new phenomenon, so Roentgen made his first report of the discovery on December 28th. 1. 3 The Early Productio:J. of the New Kind of Rays Within a month of Roentgen's discovery, X-rays were being deliberately generated and studied all over the world by those who had a Crookes' tube. The daily newspapers seized on the news and by the end of the month many interested readers were able to produce excellent X-ray photographs of their own. "The Times" ignored the discovery throughout January and "The Morning Post" was lukewarm, having interviewed an official of the Science Museum in London, who said that he did not see very much in it. The Medical Jou.n1als were unimpressed until one interested reader, Campbell-Swinton, convinced them by producingX-rayphotographs, around January 7th, among the first to be taken in England. In March he announced a service in his laboratory in London for X-ray photography of patients sent by doctors. 1. 4 The First Claim to the Discovery of X-rays Crookes' tubes were in use all over the world. Dr. Monell of New York, reported that in 1896 Crookes' tubes were available at the reduced price of ~7 to $15. So much activity was generated as a resultofRoentgen's announcement fuat it is impossible to sort out all the claims for a "first". Strangely enough, however, the pages of history have to be turned back six years for one of these claims. A. W. Goodspeed of Philadelphia, although accidentally, made an X-ray ph<5tograph on February 22nd 1890. Goodspeed demonstrated the effect to his colleague, Jennings, by photographing spark discharges in a Crookes' tube. He displayed his picture after Roentgen's announcement. However, he stated in 1896 "we claim no merit for the discovery for no discovery was made. All we ask is that yo;.t remember that six years ago the first picture in the world by cathodic rays was taken". By 1890 Crookes' tubes had been in use for over 20 years, soX-rays co:lld :1ave been discovered any time between 1870 and 1890. Roentgen's fame is due to the fact that he was aware of a discovery. By 1895 he had been, to use his own words, "interested for a long time in the problem of the cathode rays from a vacuum tube as studied by Hertz and Lenard" However, Helmholtz, who died one year before the discovery of X-rays,had predicted that a radiation would one day be fo;.tnd of such a 4 short wavelength that it would readily pass through matter. 1.5 X-rays, Cathode Rays, and the Physicist Historical events recounted so far have left important questions unanswered. What are cathode rays? Are they streams of particles as postulated by Crookes, or radio waves as proposed by Hertz? What are X-rays and how do they differ from cathode rays? These problems faced the physicists in 1895. Roentgen's interest was not in the gas discharge phenomenon, norwas it to continue after his discovery of X-rays. He was primarily concerned with the physics of solids. It was only the challenge of the problem, apparently, that caused him to deviate temporarily from his main interests. In 1893 the subject was confused and only empirically based. Ten years later it was laid open to mathematical treatment based 0.1 the concept of a charged particle called an electron. In 1893, thirty-four years after Plucker's discovery of cathode rays and after much investigation, there was still no agreement concerningtheir nature. Controversy centred on the nature of cathode rays and X-rays for many years following Roentgen's discovery. 1. 6 The Nature of Cathode Rays It was known that cathode rays were deflected by magnetic fields, produced thermal and mechanical effects on materials in their path and induced phosphorescence in certain materials. However, two rival theories remained open; the ether-wave theory of Goldstein and the corpuscular theory of Crookes. Thomson favoured the corpuscular theory and, from his point of view, the position became confused when Lenard confirmed the observations of Hertz, made in 1892. These showed that to all appearances cathode rays could pass through thin foils and produce effects a few centimetres away in the air oLitsi.de the discharge tube. At first sight the experiments of Lenard and Hertz provided the greatest obstacle to the acceptance of the corpuscular theory. Roentgen, on the other hand, had been aroused by the work of Hertz and his pupil Lenard, and was consequently a cautious advocate of the ether-wave theory. This caused :1im to be initially more concerned with effects observable outside the tube rather than with those taking place in the rarefied gas inside. There is no evidence that he provided himself with a thin-windowed tube, but he must have done, for he soon discovered that some rays outside the tube passed more easily through bodies than cathode rays and they did no~ appear to ':>e deflected by a magnet. Roentgen had certainly discovered a new effect outside the tube as important, fundamentally, as Lenard's observation that cathode rays could 5