The early history of x-ray diagnosis_Mould.pdf

Phys. Med. Biol. 40 (1995) 1741-1787. Printed in the UK

REVIEW

The early history of x-ray diagnosis with emphasis on the contributions of physics 1895-1915 R F Mould 41 Ewhurst Avenue. Sanderstead, South Croydon. Surrey CR2 ODH, UK Received 13 January 1995 Abtract. The contribution of physics to the development of x-ray diagnosis was vital in the early yean of this century following Rontgen’s discovery of x-rays in November 1895. This review records some of the highlights during the period 1895-1915. Much of the information presented has been buried in libraries for more than 50 years and the selection of illustrations and text will be largely unknown to today’s readership of Physics in Medicine and Biology It is also a celebration of what could be achieved in physics before the occurrence of the technological revolution involving not only computer applications but also the disappearance of the small independent x-ray companies into today’s multinational companies. Research and development is nowadays just too expensive for much independent practical high-technology contributions without financial backing. Hence this review takes us to those bygone years of experimental physics in home laboratories, poorly equipped university physics laboratories and of the lecture-demonstrations of the period. The sections are presented in a logical order beginning with the discovery of x-rays, followed by x-ray tube technology to the advent of the hot cathode Coolidge tube. with the third and final section covering diagnostic radiology physics. It has been compiled from personal research over 35 yeam in libraries worldwide, drawing on textbooks, journals. popular magazines, newspapers, x-ray company catalogues and museum exhibits. I have included a certain m o u n t of anecdotal information, because after all, much af the early commentaries were indeed anecdotal-and make very interesting reading. Finally it is commented that although this review is devoted to x-ray diagnosis, x-ray therapy should not be forpotten, and readen are referred to another review by the author on early therapeutic advances.

Contents 1. Introduction 2. Discovery of x-rays 2.1. Wurzburg: November 1895 2.2. Ueber eine neue Art von Strahlen: December 1895 2.3. Rontgen’s communication with Schuster: January 1896 2.4. Lecture-demonstrations: 1896 2.5. Textbooks: 1896 2.6. Experimental physics: 18954 2.7. Work of a hospital physicist: 1895-7 2.8. Advertisements: 1896 3. X-ray tubes 3.1. Electric discharge tubes before 1895 3.2. Rontgen and x-ray tubes: 18954

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3.3. Introduction of a metal target: March 1896 3.4. The focus tube: March 1896 3.5. Funher modifications to x-rays tubes: 1896 3.6. Vacuum regulation 3.7. Target design 3.8. Ancillary equipment 4. Diagnostic radiology physics 4.1. Reference books: 1897-1915 4.2. Hard, medium and soft x-ray quality: 1900 4.3. %sua1 quality control: 1904 4.4. Chiroscopes and Osteoscopes: 1903-4 4.5. Radiochromators, chromoradiometers, quantimeters and pastilles: 1902-5 4.6. Ionization unit of Villard 1908 4.7. Gold leaf and tin foil electroscopes: 1896 and 1904 4.8. Ionization experiments of J J Thomson: 1896 4.9. Free-air ionization chamber: 1896 4.10. Ionization measurements by the 1920s 4.11. Work of a physicist by the 1920s 4.12. Fluoroscopes and photofluoroscopes: 1896-1902 4.13. Densitometer: 1902 4.14. X-ray tube protection: 1902-15 5. T ~ l the y ‘electric egg’ has been hatched

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1. Introduction Rontgen discovered x-rays 100 years ago to the month of publication of this review. The professions in the forefront of technical developments in x-ray apparatus in the late 1890s were mainly physicists and engineers. Although there were also contributions from photographers, because of their interest in images, and ‘medical men’, as they were then called in the scientific literature, who initially wrote mainly on the applications of the new rays in surgery, referring to the location of foreign bodies. Later there were many physics contributions from physicians, not least in the area of proposals for units of measurement, devices to measure beam quality, and equipment accessories such as x-ray tube shields and diaphragms. It is though particularly appropriate that Physics in Medicine und Biology celebrates the centennial with a review which gives emphasis to the contributions of physics and engineering in the early years following the discovery of x-rays. Any journal review must be selective, for reasons of space if nothing else, but in spite of this the following text and illustrations clearly demonstrate the enormous range of applications of physics to early diagnostic radiology, which laid the foundations for the progress which has been achieved in this specialty a century &er Rontgen’s discovery. 2. Discovery of x-rays 2.1. Wiirzburg: November I895 It was on 8 November 1895 in the Physical Institute of the University of Wiirzburg that Wilhelm Conrad Rontgen (figure 1) discovered x-rays. He was experimenting with various

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Figure 1. Ponrait in oils by William Reitr. dated 1895. It is a reasonable likeness but it is impossible for it to havs been painted in 1895, x-rays only having been discovered in the November of that year and the first communication of the discovery in late December. Also. there is no record of Rhnrgen ever sihing far this a i s 1 and indeed it would have k e n out of character (courtesy of Wellcome Trustees).

Lenard and Crookes tubes when an unexpected observation was made. Some platino-barium cyanide fluorescent material smeared on thin cardboard and lying near one of the excited tubes which was covered with black light-tight paper, glowed visibly. It did not take Rontgen long to discover that not only black paper, but other objects such as a wooden plank, a thick hook and metal sheets, were also penetrated by these x-rays. More important though, he found, according to his biographer Glasser (1931, 1933), that ‘Strangest of all, while flesh was very transparent, bones were fairly opaque, and interposing his hand between the source of the rays and his bit of luminescent cardboard, he saw the bones of his living hand in silhouette upon the screen. The great discovery was made’. 2.2. Ueber eine neue Ari von Sirahlen: December 1895

On 1 January 1896 Rontgen wrote to scientific colleagues in several countries enclosing some example radiographs (figures 2, 3 and 4), each marked with the stamp ‘Physik lnstitut der Universitat Wiirzburg’. He published only three papers on the subject of x-rays, none of which included reproduction of any of his radiographs. The first (1895) was entitled ‘Ueber eine neue Art von Strahlen’ was published in the Sitzungsberichie der Physikalischmedizinischen Gesellschafl zu Wiirzburg and was set out in 17 numbered paragraphs. His second (1896) communication was a continuation of the first with additional paragraphs 18-21. These two (1895, 1896) communications by Rontgen which were published in English by Glasser (1933) have been reproduced in 1995 and for the first time ever within

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the pages of a journal (Mould 1995b), they are accompanied by illustrations of the eight original November 1895 radiographs made by Rontgen and mailed to Sir Arthur Schuster (see section 2.3). His third and final paper (1897) was entitled ‘Furthur observations on the properties of X-rays’ and its English translation was published in the 1899 Archives o f f h e Roentgen Ray.

Figure 2. ‘I possess photographs of the shadow of the mouldings of a door separating the rooms in which the discharge apparalus an the one hand and the photographic plate on the other were set up’ (courtesy of Wellcome Trustees).

One of the most recent English translations of the 21 paragraphs of the first two of Rontgen’s papers is by Feather (1958). who describes Rontgen’s attitude to his own work as an extreme example of his general caution and reticence. This translation follows several previous ones, of which the first English version was by Arthur Stanton published in Nature on 23 January 1896 and reprinted in February 1896 in a specially issued pamphlet entitled ‘The new light and the new photography’ for the photographic magazine The Photogram. Selected parts of some of these paragraphs from Rontgen’s first communication are now reproduced after Feather (1958). They clearly show the wide extent of Rontgen’s experiments and his conclusions, which were to gain him in 1901 the award of the first Nobel Prize for Physics (figure 5). [l].. .The fluorescence is still noticeable at a distance of 2 metres from the apparatus. One readily convinces oneself that whatever is causing the fluorescence emanates from the discharge apparatus and from no other point of the circuit. [21 The first striking thing about this phenomenon is that some form of activity capable of exciting vivid fluorescence is passing through the black cardboard envelope, which allows no ultra-violet rays of sunlight or the light of the electric arc to pass through it.. . Glass plates of equal thickness behave differently according as they contain lead (flint glass) or not; the former are much less transparent than the latter. . .

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Figure 3. Photograph of the shadow of a concealed wire winding on a wooden bobbin (Rdntgen 1895). Both figures 2 and 3 were sent by Rdntgen on I J a n u q 1896 Lo Sir Arthur Schuster, Professor of Physics in the University of Manchester (courtesy of Wellcome Trustees).

[3]. . .the transparency of different substances, layers of equal thickness being assumed, is essentially determined by their density.. . [ 5 ] Sheets of platinum, lead, zinc and aluminium were prepared by rolling, of such thickness that all appeared to be approximately transparent. . .

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Thickness

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[6] The fluorescence of barium platinocyanide is not the only recognizable action of the X-rays. . .other bodies also fluoresce: for instance the calcium compounds known as phosphors, as well as uranium glass, ordinary glass, calcspar, rock salt, etc.. .photographic dry plates have proved to be sensitive to the X-rays.. .and where possible I have checked each more important observation made visualy on the fluorescent screen by a photographic exposure.. .

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Figure 4. Hand of Frau Rantgen. This photograph was sent to Professor Ludwig Zender of Frejburg in Breisgau. who had been a former student of Rontgen (counesy of Deutsches Rsntgen-Museum, Remscheid).

[7]. . .Experiments with water and carbon disulphide in mica prisms with a refracting angle of 30" give no recognizable deflection whatever.. . [ 8 ] .. . reflection of X-rays.. .with none of the substances investigated does appreciable regular throwing hack of the rays take place.. . [lo]. , .in comparing the intensities of the fluorescent light of my screen in atmospheric air at two distances, about 100 m m and 200 m m from the discharge apparatus.. .the intensities are related inversely as the squares of the corresponding distances from the discharge apparatus. . . [ l l ] . . .I have not succeeded in obtaining a deflection of the X-rays by a magnet. . . [12]. . .the point of the wall of the discharge tube apparatus which fluoresces most strongly must he regarded as the principal point of origin of the X-rays spreading in all directions. Thus the X-rays originate from the point at which, according to the statement of various workers, the cathode rays strike the wall.. .X-rays are not identical with cathode rays.. .

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Cl31 This generation takes place not only in glass, but also in aluminium., , [171.. .There does appear to be a kind of relationship between the new rays and light rays, at all events the shadow formation, fluorescence and chemical action, which occur with both types of rays, point in that direction. , ..

Figure 5. The 1901 Nobel Prize far Physics ceniiicate awarded to RBnlgen (courtesy of Physical Institute, University of Wurzburg).

2.3. Rontgen’s communication with Schuster: January 1896

An interesting account of the receipt of one of the sets of Rontgen’s photographs and a copy of his first paper which were posted from Wurzburg on 1 January 1896, is recorded by Sir Arthur Schuster (1911) in his memoirs. ‘I opened a flat envelope containing photographs, which without accompanying explanation, were unintelligible. Among them was one showing the outlines of a hand, with its bones clearly marked inside. I looked for a letter which might give the name of the sender and explain the photographs. There was none, but inside an insignificant wrapper I found a thin pamphlet entitled “Ueber eine neue Art von Strahlen” by W C Rontgen. This was the first authentic news that reached England of a discovery made at the end of the year 1895, which both directly and indirectly gave a tremendous impulse to experimental science. Before I left the room I had read and re-read Rontgen’s account, which concisely but convincingly described the experiments, by which he had with remarkable ability, investigated and determined the main properties of the new radiation’. Schuster, then Professor of Physics at Manchester University, goes on to describe the experimental results and then ‘the interest which the discovery roused in the scientific world and the sensation it created generally’ and that ‘there were few laboratories in which attempts were not immediately made to repeat the experiment. This was not all together easy, because few institutions were then provided with the appliances necessary to obtain so perfect a vacuum as that required for the purpose, and also because the English lead glass is much less suitable that the soft German glass to excite and transmit the rays’. He ends with a complaint that the consequence of the discovery was that ‘my laboratory was inundated by medical men bringing patients, who were suspected of having needles

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in various parts of their bodies and during one week I had to give the best part of three mornings locating a needle in the foot of a ballet dancer’. Schuster had even more difficult problems later on 23 April I896 when he sent two assistants to a small town north of Manchester to locate a bullet in the skull of a dying woman who had been shot by her husband. He records that his private assistant completely broke down under the strain and excitement of all this work. His daughter Norah Schuster (1968) has documented this case and states that the probable exposure time for two initial skull radiographs was 60 and 70 minutes when three bullets were located. When Schuster himself visited the patient on 2 May he located a fourth bullet. Figure 6 is a radiograph dated 2 May 1896 captioned ‘a skull, with a bullet placed inside’ and must he one of the earliest examples of a ‘test phantom’ being used by a physicist i n diagnostic radiology.

Figure 6. Skull with B bullet placcd inside, for use es 2 May 1896 (courtesy of Wellcome Trustees).

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test object by Sir Anhur Schuster,

2.4. Lecture-demonstrations: 1896 A A Campbell-Swinton was an electrical engineer and is credited with being the first in the United Kingdom to make a radiograph of any human anatomy when he radiographed

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his own hand on 13 January 1896. Five days earlier he had produced the radiograph shown in figure 7 which is typical of this period and figure 8 shows him during his lecturedemonstration at the Royal Photographic Society, London, on 11 February 1896. This was specifically photographed for a popular journal of the day, The Windsor Magazine, for an article entitled ‘Marvels of the new light’ written by the photographer H Snowden Ward (1896a) and was part of a series including a private x-ray laboratory and an x-ray tube manufacturer’s workshop. The famous pear-shaped x-ray tube design used by Rontgen is clearly visible and in these very early days it seen that wooden chemical retort stands and a pile of hooks formed an essential part of the apparatus for taking an x-ray of the hand.

Figure 7. One of the earliest radiographs in the United Kingdom. This was taken through an aluminium screen on 8 January 1896 (see also figure 20 below, top right) by CampbellSwinton who is s e n at a lecture-demonstration in figure 8 below, and together with other early radiograpms is also reproduced in the 1905 issue of the Journal of the Ronlgen Sociery (courtesy of The Science Museum,London).

Snowden Ward was also a prolific lecturer travelling round England demonstrating the use of x-rays on volunteer patients either introduced by local physicians or members of the audience. Figure 9 is an example of one of his lecture advertisements for 1896. The local newspaper gave the following report. ‘The audience was composed largely of medical

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Figure 8. Photograph in The Windwr Magazine Of April 1896 captioned ‘Mr A A CampbellSwinton surroundcd by his apparatus used in lecturing before The Royal Photographic Society’.

gentlemen, professional and amateur photographers, scientific students and hospital nurses. One of the most successful radiograms was a surgical case of a little boy with a double thumb. The exposure was less than one minute. The hand was moved after 15 seconds and from that fact the image was slightly blurred, Ward conjectured that the vacuum tube was operating for only about one-quarter or one-third the exposure time. The radiograph was taken in the afternoon before the lecture and during the evening he tried to take another radiogram of the hand, but the experiment failed’. Almost a decade later this radiogram was published in the Journal oftbe RBntgen Society (Ward 1905).

2.5. Textbooks: 1896 Snowden Ward (1896b) who was mentioned in the previous section was also one of the earliest authors of a textbook giving practical advice on the use of x-rays. The eight chapters in his May 1896 book were [ I ] A brief history, [2] How to make an accumulator, 131 How to make an induction coil, [4] Apparatus for radiography, [SI Practical radiography+lectricaI, [6] Practical radiography-photographic, [7] Practical radioscopy, [8] Applications and probable advances. This last chapter gives an interesting view of topics considered to be of importance at the end of the first six months following the discovery and is reproduced in summary in table I . There were in fact very few textbooks on x-rays published in 1896, apart from that by Ward, a rather more popular work entitled ‘Something About X-raysfor Everybody’ by Edward Trevert of Lynn, Massachusetts, USA, who appears to have been an electrician, that by Edward P Thompson of New York who described himself as an engineer and inventor, and the much more extensive and academic book by the New York physician Henry Morton and electrical engineer Edwin Hammer (Morton and Hammer 1896). Morton and Hammer divided their text into four parts [l] Definitions, [Z] Apparatus, [3] Operation, [4] Surgical value of the X-ray. They published 91 illustrations which were

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Table 1. Applications, advice and commentary as of May 1896 from the textbaok by Ward (1896b) which went into three editions with Isenthal as co-author in 1898 and 1901.

Surgical applications are by far the most important up to the present. Nervousness of patients is one of the difficulties in surgical work. Clothing need seldom be removed except boots with nails or irons or dresses stiffened with steel or thick whalebones. Splints may remain if they are of wood, Germicidal powen are claimed by three Professon in Chicago, but not from experimental data.

Medicinal value is claimed and Dr Middleton of New York who thinks that the rays which consist of streams of material particies, can be used to convey medicinal matter and deposit it at the actual seat of the disease, thus enabling consumption and cancer to be cured. A plan and elevation are necessary to locate exactly any foreia body, e.g. for a bullet in the thigh, anterior, posterior and lateral radiograms are necessary. A triangulation method may also be adopted by using two tubes at a slight distance apart, so that the two shadows m y be cast upon one screen or dry plate. The object can be located by measuring relative positions of tubes, subject and screen. The fleshy svuctures are now to be differentiated. since radiography has been so far perfected that every p a ~ of I the adult human skeleton has been radiographed. Contents of packets. The Post Office and Customs Offices have found radioscopy very valuable in detecting coins concealed in packets, and watches and other contraband in books. The detective force in Paris and London have found the method useful for revealing the contents of suspected packets which have proved to be infernal machines. Flaws in metal and bad alloying may be detected. False gems may be detected by their x-ray transparency or opacity. The value of cattle food for bone forming purposes is being studied. Radiographing the skull is not difficult, though radiography of the brain will probably long be impossible. The use of the vacuum tube close to the head has been reported to cause the hair to fall out. The arrangements of balteries and induction coils (or Wimshunt and spark gap) are by no means find. The construction of the tube and especially its best extent of exhaustion are still subject to revision. On the best formulae for the dry plates and developer we still want much light.

mainly radiographs but also a photograph of Morton’s laboratory in which simultaneous radiography and fluoroscopy of the hand is seen, figure 10. Morton also published the world’s first whole body radiograph, in the July 1897 issue of The Archives of the Roentgen Ray. His apparatus was described as ‘including a 12” induction coil whose primary was supplied from 117 volt Edison current of the New York street mains and an ordinary Crookes tube with a commencing vacuum corresponding to a spark of 2” which gradually rose to 8”. The distance of the tube to the X-ray plate was 54” and the time taken, including stoppages, was 30 minutes’. spica1 pamphlets of this early period can be found in the historical collection of the British Institute of Radiology and include those of Howgrave-Graham (1896), Dittmar (1896), Niewenglowski (1896), Ward (1896~)and Schurmayer (1899). Popular magazines of 1896 also contained lengthy articles on the discovery, such as The Windsor Magazine (Ward 1896a) and The Strand Magazine (Porter 1896). 2.6. Experimental physics: 18956

The book by Thompson (1896) is not strictly speak a textbook, but more a summary of 210 experiments conducted by various scientists including Faraday, Kelvin, J J Thomson,

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Geissler, Tesla, Crookes, Heris, Lenard, Rontgen, Lodge, Tesla and Edison. It does though contain fascinating descriptions of 19th experimental physics relating to electricity, magnetism and x-rays. Three illustrations, figures 11 to 13, have been selected from this book. Figure 11 is of the Edison sciascope, with Thomas Edison at the right of the photograph. Bottom left is a Sprengel vacuum pump and the x-ray tube is housed in the box. This sciascope formed the centrepiece of the Edison X-Ray Exhibit at the New York Electrical Exposition of the Electric Light Association in June 1896. Figure 12 was first published in the Electrical Engineer, New York on 22 April 1896 and shows the apparatus devised April 1896 by E Wilbur Rice, the Technical Director of the General Electric Company, for obtaining a sciagraph using a Wimshurst machine with 16" diameter glass plates. The principal feature of the arrangement was the introduction of a lead diaphragm containing a central aperture of 7" to 8" diameter opposite the fluorescent spot. This increased the exposure time from 30 minutes to 60 minutes but improved the

Physics contributions in x-ray diagnosis 1895-1915

Figure 10. Henry J Monan's New York x-ray laboratory in 1896.

Figure 11. The Ediaon rkrarcope or 1896.

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Figure 12. The I896 experiment aiRice in which the introduction ofa lead diaphragm improved image sharpness although lengthening the time of exposure.

sharpness of the image. Figure 13 is an experiment by Stine of the Armour Institute of Technology and was first published in the Elecrrical Engineer, New York on 11 April 1896 under the title ‘Source of X-rays determined by skiagraphs of short tubes’. This was to prove that ‘X-rays have their source at the area struck by the cathode rays located directly opposite the disk marked cathode and that the rays did not come from the anode’. Five photographic plates were used as shown in the diagram, with the letter A used for orientation purposes. The object used for imaging purposes were several short sections of tubes with diameters varying from 0.5” to 3”. The skiagraph shown here is for Plate 5 . Figure 14 is the image from an experiment in St Petersburg by Prince Galitzin and Karnojitsky (1896) with the same study aim as Stine, figure 13. They used a board

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Figure 13. Stine's 1896 experiment to determine the source of the x-ray emission.

containing a regular pattern of nails and a photographic plate beneath the board. Some 13 different x-ray tubes were used and in their analysis of the resultant shadow patterns they demonstrated that the x-rays were produced from the target, which in the pear-shaped tube was the glass, marked 0, opposite the cathode which is marked K. The anode is marked A. 2.7. Work of a hospital physicist: 1895-7

Hospital physicists were extremely rare in 1895 and perhaps C E S Phillips of The Royal Cancer Hospital, London (later to be renamed as The Royal Marsden Hospital) was the only one in England immediately prior to the discovery of x-rays. He may well not have been a salaried employee since he was already a millionaire (travelling to the hospital in Chelsea on horseback from Shooters Hill: not a method of transport normally chosen by modern hospital physicists!) and what was later known as a 19th century gentleman scientist who conducted experiments as a hobby rather than as a necessity for earning a living. He

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Figurc 14. 1x96 enpenmcnt o l Galilr,in and Kamojitsky dcvised for the same purpose ac Stine, sec figure 13.

was elected a member of The Royal Institution in 1894 with Lord Kelvin acting as his proposer. He was also a gifted cartoonist as seen from his notebooks and in addition was an accomplished violinist. In 1895 he was experimenting with gas discharge tubes and also with the design of pumps for evacuating the tubes. What is remarkable is that his experimental notebooks together with an album of x-ray pictures, which h e termed Rontographs, starting in February 1896 has survived to the present day. Figure 15 reproduces a page from one of these notebooks of 1899 on the influence of the form of the x-ray tube bulb. His comments following the announcement in The Electrician of 10 January 1896 of Rontgen’s discovery were that he ‘obtained his first result with the new rays on 10 February with an exposure of about one hour’. The Lenard tube used was of the pear-shaped type and Phillips records under the heading of ‘History of the tube’ the following commentary. ‘At first when I excited the tube it glowed with a blueish colour with flickering whiteish flames here and there. This gave no Ronto-effects with a three-quarter hour exposure. The tube then turned greenish after two days pretty continual excitation and Ronto-effects were obtained with one hour exposure. The tube became bathed in green flames internally licking the glass after another day or two and then the best effects were obtained.This best condition lasted about a week and then the resistance of the tube began to increase’.

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Figure 15. Page of an 1899 laboratory notebook of 1899 from London's first hospital physicist: Charles E S Phillips. 'Cossor (a major X-ray tube manufacturer) tells me that the best position of the cathode is just within its tube. If the cathode be placed a litfle beyond the line AB so that it appears somewhat in the wider portion of the bulb, the glass will become covered with green sveaks and patches. The anti-cathode should he placed at mice the focal length of the curved

cathode'.

Later, in 1907, he attended a meeting of the American Rontgen Ray Society and 30 years before the international acceptance of the roentgen as a unit of me&urement for both x-rays and gamma rays, advocated a unit based on ionization either by x-rays or a radioactive element (Philips 1907). This pre-dates Villard's (1908) proposal that a unit be defined as 'that quantity of X-radiation which liberates by ionisation one esu of electricity per cm3 of air under normal conditions of temperature and pressure' which was essentially the same as the first definition in 1928 of the roentgen unit.

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R F Mould Table 2. Selected enuies from the bibliopphy compiled by C E S Phillips for 1896-7. Action of X-rays upon the diamond Buget g: Gas& (France 1896) found that true diamonds are far more transparent CO X-rays than are their imitarions and that the same holds good for jet. Action of Rantgen rays upon electrostatic charges and discharge potentials Borgman & Genhun (France 1896) found that a zinc disc positively charged lost its charge under the influence of X-rays and then acquired a negative charge of a certain fixed value. Arterial system photographed by R h t g e n rays Dutto (Italy 1896) injected sulphate of calcium, which is a salt opaqure to the rays, into the hand of a corpse. The solution was sufficiently dilute to penetrate into the small veins. The result was entirely satisfactoly. Bacteria and Riintgen rays Minck (Germany 1896) found that the rays had no appreciable effect upon typhus bacilli in agar-agar medium. Crookes tube experiments BattWi & Gabbasso (ltaly 1896) described numerous experiments relating to the behaviour of the Crookes tube and investigated the Vansparency of various materials. They pointed out that the curve plotted between density and transparency is roughly a parabola. Thermo-luminescence provoked by Rlintgen rays and Becquerrl rays Borgman (France 1897) used a calcined mixture of M o a 50% of MnSo4 and obtained vigorous thenno-luminous effects with both R6ntgen and Becquerel rays. Solar X-rays on Pike’s Peak Cajori (USA 1896) after careful experiments at a height of 14,147 ft. found no trace of RBntgen rays.

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Ewperiments with spark gap Cave (England 1896) studied the effect of X-rays on spark gap. For a mnstant gap he found that the number of sparks passing per minute was greater under X-rays than when the rays were screened off with a zinc plate. Maximum power of Crookes tubes Chappuis & Nugues (France 1896) found that with a particular induction coil used, the maximum RBntgen radiation was reached with IO breaks per second.

Notes on radiography Hall-Edwards (England 1896) gave an account of radiographs obtained through six. seven and 10 layers of pen-steel, sheet-copper and seven layen of sheet-lead. Tube used required an 11.5” spark and a five minute exposure. Method of estimating intensity of X-rays Branson (England 1896) described a method using an aluminium quadrant in millimetre steps, superposed on a sensitive plate and exposed for a definite time, the number of steps being proportional to the intensity of the X-rays. Reducing q o s u r e in RUntgen photography Basilewsld @rancc 1896) stated thal the use of fluorescent bodies in contact with the sensitive plate could reduce exposure. Photometry of X-rays Roiti (Italy 1896) studied methods of comparing the intensity of X-ray sources. He points out that a spark between the coil and the anode increased the penetrative power of the rays.

However, to return to 1896, Charles Phillips was also producing a bibliography of x-ray literature by subject (rather than by author) which together with the book by Thompson (1896) cannot afford to he ignored by any historian. Most are given only as references, but some of what he considered the more interesting papers are given a short summary and a selection are reproduced in table 2.

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2.8. Advertisements: 1896

Advertisements were often to be found in 19th century scientific books and those by Thompson (1896), Ward (1896a) and Phillips (1897) are no exception. They interestingly describe the equipment commercially available at the time and figures 16 to 18 are some typical examples. 3. X-ray tubes 3.1. Electric discharge tubes before I895

The x-ray tube derives from the cathode ray tubes of Crookes, Hittorf and the 19th century physicists who were investigating electric discharges through gases. These discharge tubes were usually cylindrical in shape but figure 19, which is the first published illustration of tube variants, shows the wide variety available in 1896. This diagam was originally in the French journal Lo Nature and then reproduced in Nature on 28 January 1897. Phillips (1897) reviews the precursors of the x-ray tube and this is summarized in table 3 and it is noted that the early tubes were often referred to as Geissler tubes. Phillips ended his review with the words ‘Truly the “electric egg” has been well hatched!’ after looking back at the 60 years of work on electric discharge and this is also a relevant comment today, 160 years later, with respect to technological advances such as CT scanners, digital subtraction angiography, linear accelerators, etc (Mould 1993). Crookes tubes in figure 19 are numbered 1, 2 and 20, of which 20 is the simple cylindrical discharge tube with two electrodes and a small side tube which would have been connected to a pump, see figure 18, to exhaust the tube. The cathode disc is supported by a small rod normally of platinum, and the disc material would have been aluminium or an alloy of aluminium (R@nneand Nielson 1986). To ensure an airtight seal through the glass wall a metal had to be used with the same coefficient of expansion as the glass. Platinum was used with the tube glass around the rod oRen reinforced by lead glass. The anode of these primitive tubes was an aluminium stick, placed in an arbitrary position usually in a small lateral glass pipe stub: as seen in figure 19 for various tubes. 3.2. Rontgen md x-ray tubes: 1895-6

It was a Crookes tube similar to figure 19 number 1 that was used by Rontgen in 1895 when he discovered x-rays. Others used, and possibly designed, by him are numbered 24 and 32. As already noted, Rontgen only published three papers on the topic of x-rays although his lifetime output was 55 papers and in 1900 he left Wiirzburg to become Professor of Physics at the University of Munich from which time he concentrated on his previous area of interest, solid state physics, until his retirement in 1920 and his death in 1923. Even so, there are a few interesting items of information on record which relate to Rontgen and x-ray tubes. For example in his second communication (Rontgen 1896) he states ‘According to my previous experience, platinum is the best metal for generation of the most efficientX-rays.. ...I use a concave mirror of aluminium as cathode and a piece of platinum foil, which, turned 45” to the mirror axis, constitutes the anode’. This describes a focus x-ray tube, see section 3.4. There is also on record some of Rontgen’s correspondencewith x-ray tube manufacturers such as Reiniger, Gebbert & Schall of Erlangen on 27 November 1896, the original of which has been reproduced by Mould (1980). They are told that their tubes are very good indeed but too expensive and Rontgen asks for a reduction in price from 30 DM to 20 DM. Similar

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3ohn 3. Griffin 8

50n0. Etb.

DEMONSTRATIONS snd dl particulaia, either verbdly 01 by conrapondenoe, given gratis t o intanding purobulan.

22, GARRICK ST., LONDON, W.C. Figure 16. Advertisement from a London company for induction coils. tubes and screens: note the line drawing o f a Cossor x-ray tube on the right, as this is mentioned in the legend to figure 15 (Wad 1896b).

pleas to manufacturers are no doubt still occurring 100 years later although the costs involved will now be somewhat higher than 30 DM! He had also written earlier on 3 November 1897 referring to excellent image quality with their tubes, particularly for a skull radiograph. This

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R O E N T G E N OUTFIT. Photographing Invisible Objects.

PROF. E. THOMSON'S FOCUS TUBES,

NEWTON'S FOCUS TUBES, I>\, li.iC11 l 2 B K I

(1)

Ruhmkorff Coils .AY,>

Electrical Instruments. GENERAL EXPEMMEHTAL WORK.

Figure 17. AdveRisementS fmm New York companies far Roentgen apparatus (Thompson 1896).

forms an illustration in the Reiniger, Gebbert & Schall (1897) catalogue and the exposure is stated to have taken 11 minutes and a chest radiograph in the same catalogue, 12 minutes. In both instances the distance from tube to patient was 15 cm. However, Rontgen did not only use German x-ray tubes but is included in the advertising

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Figure 18. Vacuum pumps were an essential p a of the early equipment required and this advenisement for Geryk pumps were frequent during the penod 1896-9. This advertisement claims it is better than the Sprengel pump which is seen in figure I 1 being used with the Edison skiascope (Phillips 1897).

statements (Kassabian 1907)for the American Queen & Company self-regulating tubes as being of the opinion that these tubes are ‘Especially ingenious’. Finally, a statement attributed to Rontgen from his correspondence (although it seems

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Table 3. Brief selected commentw of work on electric discharge: after Phillips (1897). Other names which would be included in a more extensive review (Eisenberg 1992) include Torricelli, Boyle, Haukesbee, F n W i n , Gdvani, Volta, Ocnted, Amphre, Ohm. Maxwell. Henry, von Helmholtz, Hertz and J J Thomson. Date

Experimenter

Commenhry

1650

Otto von Guericke

Conducted the first vacuum experiment and invented the first air pump.

1140

Abbe Nollet

Guencke’s pump together with facts accumulated by such as Haukesbee, Gilbert and Hooke led him to interest himself i n electricity which he considered to be a highly flammable fluid capable of being set into flame. He used glass egg-shaped globes in his experiments, more or less exhausted of air.

1834

W Snow Harris

No progress o c c m d for a centnry after Nollet until more competent experimenters repeated his work. Snow pointed out that the length of the spark which and elecrric machine will give in air varies in the simple inverse ratio of the gas pressure.

1838

Michael Faraday

Investigated electric glow discharges with a considerably modified ‘electric egg’drawn out into a tube, closed at both ends and more thoroughly exhausted of air.

1838

Heinrich Geissler

Improved methods of making glass tubes for electric discharge studies and showed how to seal little platinum wires into their closed ends. He also invented a special air pump for exhausting these tubes. He observed an unilluminated space surrounding the negafively charged electrode in almost every case This dark space depended on various hctors. including the potential difference between the electrodes. spark length of the coil and degree of rarefaction.

1860

Kelvin, Rhumkorll and others

1860

Gassiot

By 1860 the study of electric discharge had become important Kelvin had introduced the absolute electrometer and the stratified appearance in ceaain cases of the discharge glow had been observed. Set up 3520 water cells, to form the largest battery of its kind ever made, and proved by its means that a vacuum tube placed in circuit with the cells glowed distinctly with a stratified appearance. This began the em when the Rhumkorff coil could be replaced by cells.

1865

H e m “ Sprengel

1869

J o h n Hittarf

1879

Wtlliam Crookes

Invention of the Sprengel mercury air pump which had the power to produce very high rarefactions with rapidity. Conducted experiments under the now improved conditions using the tube named after him. Crookes made known the results of his work at the 1879 British Association meeting.

somewhat out of character), by Wingirdh (1948) and quoted by R0nne and Nielsen (1986) is ‘I do not want to get involved in any thing that has to do with the properties of the tubes, for these things are even more capricious and unpredictable than women’. 3.3. Zntroduction of a metal target: March 1896

The first two major improvements in x-ray tube design were the introduction of a metal target and the focus tube: see section 3.4. In England, Campbell Swinton (see figures 7 and 8) was given credit for this innovation by Gardiner (1909) writing in the Journal of The Rontgen Society on ‘The origin, history and development of the X-ray tube’ and referring

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Forms of tube used for the production of cathode and X rays I. 2

Fiyre 19. Collection of 32 x-ray tubes owned by Gaston S e y y in November 1896, of which three were designed by Crookes,two used (and possibly designed) by R6ntgen and 15 by Seguy himself. They illustrate well the wide variety of designs and include cylindrical, pear-shaped and spherical-shaped x-ray bulbs and bi-cathode tubes.

to the collection of tubes owned by the Society (now the British Institute of Radiology) which in 1909 were handed over to the Victoria and Albert Museum in South Kensington. Gardiner stated that Campbell-Swinton proposed this development in about March 1896 and figure 20 shows this tube in which the cathode rays are incident upon a small sheet of platinum and not on the glass end of the tube.

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Figure 20. The first x-ray tube 10 use a metal target instead of the glass end of the tube. Campbell-Swinton. March 1896 (see top left) (Gardiner 1909). This tube is in the collection of the British Institute of Radiology (Mould 1979). The first anatomical radiograph taken in the United Kingdom is seen top right: also by Campbell-Swinton, t t e n on 13 January 1896. His earlier radiograph of various objects exposed through an aluminium screen is seen in figure 7. The bottom image is of a frog's foot and is the imaging test object used for the first recorded x-ray tube manufacturer's survey: well before the modem interlaboratory comparisons of imaging devices which are organized by medical physicists and clinicians for such as WHO and IAEA (Souchkevitch et al 1988). In 1900 the then President of the Rantgen Society, Dr John Macintyre, decided to offer a gold medal to the m&cr 'of the best practical X-ray tube for both photographic and screen work'. The winning tube is shown centre right. A committee of expens was formed to act as judges and same 28 hlbes were sent in to the Society. It was recorded that 'There was a good deal of grumbling when the award was made to Mr C H F Miiller of Hamburg' and that 'it was a pity that the very elaborate tests through which the tubes were passed were not made public'. The x-ray plate (bottom) of the frog's foot (the hooked nail at the tip of each toe was only one-tenth of a millimetre width) was the final test that decided the award. The tube centre left was not relevant to this Gold Medal survey but is the electfie discharge tube described by Sir William Crookes in 1874 and which has B curved cathode: see figure 21 below.

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3.4. Thefocus tube: March 1896

Gardiner (1909) when commenting upon the Campbell-Swinton tube of figure 20 emphasized that had he also used a curved cathode he would have anticipated the focus tube design of Herbert Jackson, Professor of Physics at Kings College, London, which ‘marked the greatest advance that has been made since Rontgen’s discovery 13 years previously’. Jackson’s communication in the Electrical Review (London) (Jackson 1896) was on 13 March and was preceded by a 7 March announcement in the British Medical Journal, (Thompson 1896, Phillips 1897, Brecher and Brecher 1969) but in America on 7 March, Herbert B Schallenberger working in the Westinghouse laboratory had published in Electrical World a picture of his own focus tube and insisted that he had first used a similar tube as early as 15 February (Schallenberger 1896). The only difference between the Jackson and Schallenberger focus tubes was the angulation of the platinum target-anode. An example of a Jackson focus tube can be seen bottom right in the figure 16 (Ward 1896b) advertisement. The focus tube number 8 in the S6guy (1896) collection of tubes in figure 19 differs from the original Jackson version only in the shape of the glass bulb. However, in spite of the claims and counter claims both in 1896 and later, the real credit for the design of the concave cathode lies not with Schallenberger or with as sometimes stated Rontgen (since he mentioned his focus tube in his second communication) or Jackson, or the American physicist Elihu Thomson whose 1896 focus tube is advertised at the top of figure 17, but as indicated by Isenthal and Ward (1897) with Sir William Crookes, figure 21. Crookes had used this tube in 1879 to demonstrate the heating effect of cathode rays: see also figure 20 (centre left).

3.5.Further mod@catons to x-rays tubes: 18% 1896 and the following years also saw many other modifications to the x-ray tube following the metal target and concave cathode. However, by the mid-1920s the gas tube era was over, because of the advent of the hot cathode or Coolidge tube in 1913, with its much greater stability and the higher x-ray photon energies then possible, (see Coolidge (1913) and Coolidge and Charlton (1933)). For example, tube design was not limited to a single target, bianodal versions were available and the double focus tube was designed to use an alternating discharge such as that derived from Tesla coils (Isenthal and Ward 1898). Sliding cathodes were incorporated in some designs, see bottom right in figure 16. Kathren (1978) in his historical review records that in 1896 the rotating anode tube was introduced by Robert W Wood, a Johns Hopkins University physicist, the Boston physicist John Trowbridge created an oil-immersed x-ray tube, and in Philadelphia Lyman Sayen devised a self-regulating tube. However, the term ‘rotating anode’ used by Kathren (1978) referring to the work of Wood (1896) would be better stated as the first attempt in x-ray tube design to obtain what would later be achieved using a rotating anode. Glasser (1931, 1933) summarizes Wood‘s work as follows ‘A disadvantage of the first tubes was the heating of the glass walls by the cathode rays. This effect made it impossible to increase the load on the tube in order to shorten the exposure time. In an effort-to avoid this heating effect and to distribute it over a larger area of the glass, Wood (1896) suspended in the tube a concave cathode which could be rotated on its axis like a pendulum. By turning the tube continuously during the exposure, the focal point of the cathode rays always fell upon a different part of the glass which was cool and thus the load on the tube could be increased considerably. This tube did not find a ready market on account of its complicated construction but it was the predecessor of modern [i.e. 1931119331 types of tubes which have rotating anodes or cathodes’. This

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Figure 21. Crookes tube of 1879 with a concave cathode which predates the 1896 x-ray focus tube cathodes of Jackson in England and Schallenberger in America.

1896 x-ray tube designed by Wood is illustrated in figure 19 as Number 4: the line drawing on the far left of the second row of this collection of tubes owned by Gaston SBguy.

3.6. Vacuum regularion Vacuum regulation was a problem with the gas tubes, since when the tube was operating the vacuum would in general change, the gas pressure getting either higher or lower, depending on the operating conditions and upon the past history of the tube. Coolidge and Charlton (1933) detail some of the design factors to counteract these and other problems in the best summary review I have encountered: reproduced below. ‘The pressure could usually be reduced by operating the tube intermittently with small currents. However, when the pressure became too low, it could at first be raised by heating the bulb but after a time this would fail and the tube would have to be rebuilt. The most important step being the replacement of the aluminium cathode with a fresh one. To prolong the useful life of the tube, various methods were devised for the introduction,

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when desired, of small amounts of gas. A common method consisted in the application of heat to a suitable chemical placed in a side tube. The Bauer valve was a very successful regulator and consisted of a small piece of unglazed porcelain sealed into the tube envelope. This porcelain was normally covered by liquid mercury which could be displaced at will by squeezing a rubber bulb, thus allowing air from outside to diffuse through the pores of the porcelain into the tube. The osmoregulator of Villard was also used extensively. This consisted of a tiny thinwalled tube of platinum or palladium closed at one end and sealed at the other to the envelope of the tube. Upon heating the regulator with a Bunsen flame, hydrogen diffused through the platinum or palladium into the tube.’ Figure 22 shows three x-ray tubes with vacuum regulation manufactured by C H F Muller of Hamburg before 1905. The small auxiliary bulbs for the regulation are clearly seen, whereas in figure 19 for Sbguy’s collection of 32 tubes in 1896 there are none with vacuum regulation.

3.7. Target design For medical diagnostic work the thin metal target of the early tubes was rapidly replaced by a heavy mass of metal consisting essentially of two parts, a refractory metal face to take the impact of the cathode rays and a heavy back plate consisting of some good-heat-conducting metal which would serve to lead away and temporarily store the heat liberated at the focal spot. The metals were joined together by a brazing process. Platinum and copper came into very general use for the refractory metal face and back plate, respectively. Kaye (1909) had reported that metals of high atomic weight were the most efficient x-ray generators and it was realized relatively soon that the following four principal properties were required for the target material. (1) High atomic number: to give best x-ray efficiency. (2) High melting point and (3) high thermal conductivity: to allow maximum energies for a given focal spot size. (4) Low vapour pressure: to reduce the amount of metal vapourized onto the glass walls. With ductile tungsten it was found that the properties (1) to (4) were combined to the highest degree. However, this was right at the end of the gas tube era and formed the last major advance in tube design. 3.8. Ancillary equipment

Ancillary equipment was required in addition to the x-ray tube and for example the 1896 advertisement in figure 17 shows induction coils and cells. These have been reviewed elsewhere by Mould (1993) including induction coils, influence machines such as the Wimshurst, mercury and electrolytic interrupters and the first interrupterless transformer of Snook (Tyler 1919). For a description of thelapparatus used by Rontgen, including a photograph of his cylindrical ionization chamber with lead cap and aluminium entrance window, see Harder (1987) in the review ‘Rontgen’s discovery-how and why it happened‘. For reviews of the technology of x-ray films, plates and fluorescent screens see Fuchs (1933). Grigg (1965), Ramsey (1970, 1976), and Eisenberg (1992). It is also noted that in most of the early textbooks, see table 4, there are relatively long sections on plates and films, and for example Kassabian (1907) includes advice on the following: Developers: formulas and variety; Modus operandi of development; Improvement of the negative; Printing (positive): toning and mounting. Whereas Knox (1915) emphasizes that ‘when the print has been prepared it is necessary to glaze and mount it on a cardboard. Too great stress cannot be put upon this part of the work‘. At this time, 1915, plate glass was still

Physics contributions in x-ray diagnosis 18954915 Table 4. Reference textbooks of the period 1897-1915. Year

Authors. their profession and place of work

Title of textbook and commenmry

1897

David Walsh, dermatologisrlphysician Lnndon and also Hon. Secretary of the Riintgen Society

The Rontgen Rays in Medical Work. The part of the book an ‘Medical and surgical applications’ was divided into eight sections: Surgery;Dental surgery; Medicine, Obstetrics and gynaecology; Legal medicine; Anatomy; Physiology; Vetinary surgery.

1898

H Snowden Ward, photographer and

Praclicai Radiography (2nd edn). The chapter on ‘Diagnostical applications of radiography’ was divided into ‘Anatomy and pathology of the osseous smctures’ and 'Internal medicine softer tissues’. (See table 1 for the 1896 1st edn of this book.) The Roentgen Rays in Medicine and S u q q (2nd edn) (1st edn was in 1901). Chapter titles include: Pneumonia; Emphysema of the lungs and bronchitis; Pleurisy with effusion and empyema; Hydrothorax and pneumothorax; Heart;Thoracic aneurisms; Oesophagus. abdomen and pelvis; Children; Surgery; Fractures and dislocations; Foreign bodies; Dental surgery; Calculi: Medico-le@ uses.

A W Isenthal. manufacturer of x-ray equipment, London

1902

Francis Williams, physician, Boston, USA

1904

Carl Beck. surgeon, New York. USA

1904

William Pusey, dermatologist, University of Illinois and Eugene Caldwell, x-ray laboratory director. New York, USA

1907

Mihran Kassabian, physician, Philadelphia. USA

1915

Robert Knox,radiologist and radiotherapist, Royal Cancer Hospital. London

Rontgen Roy Diagnosis and Therapy. The part ‘Regionary (Clinical)’ includes: Head: Neck; Chest; Abdomen; Pelvis; Shoulder; Malformations: Diseases of bones and joints; Neoplasms; Fractures; Medico-legal. Rontgen Rays in Therapeutics and Diagnosis. Diagnosis chapters am fluoroscopy and radiography. Mare text for therapy than for diagnosis and these include: Treatment of X-ray b u m ; Diseases of skin appendages; Inflammatory diseases of skin; Treatment of tubemdosis; Skin cancer; Cancer of the breast and in the thorax: Deep-seated cancer; Sarcoma. (See Mould (1993, 199%) for a review of the early years of radiotherapy with illustrations of apparatus.) Rontgen Rays ond Electro-rherapeurics. Chapters include: Fractures and dislocations; Diseases of the osseous system; Localisation of foreign bodies (including Military surgery); Thorax; Abdomen: Genito-urinary; Dentistry; Forensic medicine. Radiography, X-ray 73hempeutics and Radium Therapy. This was one of last major textbooks of the gas X-ray tube era before the Coolidge hot cathode tubes came into routine use worldwide. Chapters include: Injuries of bones and joints; Diseases of bone and joints; Thorax; Alimenmry system; Urinay tract; Congenital malformations.

1169

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Figure 22. (a) Miiller vacuum regulated x-ray tubes advertised in the 1905 Journnl of the R?intzen Sociely. The tube in the centre is also described in detail by Pusey and Caldwell(1904) and Kassabian (1901) and appear to be, with the Queen and Company of Philadelphia selfregulating tube, see also figure 23, devised by Lyman Sayen in 1896. the most papular designs of the early yean of the 2Mh century. The design OD far left incorporates a water-cooled anode.

(b) Schematic diagram of the central Muller x-ray tube (Kassabian 1907). The lever shown hanging vertically in (a), but hon-rontally in (b), from the auxiliary bulb B regulates the interval of the spark-gap (between E and K-). The more distant the lever from the cathode K- of the main tube. the higher the vacuum in that tube and the nearer the cathode K- the lower the vacuum. Should the resistance of the main tube be in excess of that of the spark-gap, the current takes the path of lesser resistance and passes through the auxiliary bulb, and the presence of sparks in the spark-gap shows that the process is proceeding. Should the vacuum of the main tube become too low (soft), the wire (between Ct and the target) is disconnected from the anode of the main tube and attached to the terminal of the electrode (I+) in the auxiliary chamber and the wire E is moved far away. The discharge that pvsres under chis adjustment causes metallic particles from Jc to he driven against thc sides of the tube and the generation of more gas to be occluded on the auxiliary elcctrode. In this way the vacuum of the main tube may be raised. The process required some five minutes and might have to be repeated. To lower the vacuum use is made of electrode C which contains a substance which will give off a certain quantity of gas by the electnc discharge passing through it and hence lower the vacuum. That such complicated procedures were necessary during this period when there wvs still no accurate method of measuring the degree of hardness (penetration) or exposure dose m k e s one realize the great advance that occurred when in 1913 the Coolidge hot-cathode x-ray tube was devised and haw difficult must have been any physicists' life when he attempted any quality control (see figure 23) or radiation dosimetry,

Physics contributions in x-ray diagnosis 1895-1915 J+

B

C

1771

c

Figure 22. (Continued)

in use and for prints the advice was given that they should be previously well hardened in alum or formalin.

4. Diagnostic radiology physics 4.1. Reference books: 1897-1915

The textbooks of 1896 gave very little detail on the applications of x-rays in diagnostic radiology, or rather radiography (or skiagraphy) and radioscopy, and therefore the source books for this review section commence in 1897. Table 4 lists the major references I have used for the period under review which ends in 1915. Also for interest I have listed the professions of the authors of these standard texts of the period. It is noticeable that they include no physicists: I am afraid that the physicist, when involved in a book, was usually only limited to writing a technical chapter and it was some years before books written solely by a physicist, or with a physicist as a co-author (except for Phillips (1897)) were to be published. Some of the earliest were the 1929 book on ‘The Physics of X-ray Therapy’ by Professor Val Mayneord of The Royal Cancer Hospital, London, and in 1915 Professor Sidney Russ of the Middlesex Hospital, London, who with Colwell wrote ‘Radium, X-rays and the Living Cell‘, which was also one of the first books containing a significant amount of radiation biology. Returning to table 4, the massive 704 page and 410 illustrations book of Williams (1902) details very well in its chapter titles the range of medical applications of x-rays in this earlier period. It is also interesting to note the inclusion of chapters on medico-legal matters, the full title of which in Williams (1902) is ‘Usefulness of X-ray examinations to life insurance companies. Medico-legal uses of the X-rays’. In Walsh (1897) the section on legal medicine includes ‘Evidence of injury’ and ‘Evidence in action for malpractice’. In the former he quotes the British Medical Journal of 6 June 1896 where x-ray evidence was presented in a court when a bullet in a hand formed the subject of criminal prosecution. In the malpractice text Walsh (1897) quotes a Dr Richardson in the Boston Medical News of 19 December 1896; ‘Indeed, an early fluoroscopic examination of every fracture may be required of every surgeon for the protection of the patient, and an early photograph for the protection of the surgeon’.

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Many textbooks of this era were subdivided into apparatus and technique, and then followed on with medical applications, concentrating on clinical details. Since this is a review with emphasis on physics contributions, that is on the aspects of technique which were considered of importance in 1896-1915, table 4 provides a summary of the clinical applications. For further reading the following textbooks are recommended: Bruwer (1964), Grigg (1965), British Institute of Radiology (1973). Burrows (1986). Pallardy et af (1989), Eisenberg (1992) and Mould (1993). 4.2. Hard, medium and soji x-ray quality: 1900

The early description of quality was the qualitative scale of hard, medium and soft, which was proposed by Kienbock (1900) and which continued in use in many centres to the end of the gas x-ray tube era. Kienbock actually also included very soft and very hard in a five-point scale but this was almost always used only as a three-point scale. One earlier classification existed, but was not widely used. This was the 1898 proposal by a Dr Porter, referred to by Valenta, who with Eder from the Imperial & Royal Graphical Institute, which was a training school for photographers in Vienna, where the first ever patient was treated therapeutically (Mould 1995a), produced in 1896 the first album of radiographs of small mammals, cameos and other objects. These radiographs are notable for their excellent image quality and one of the few existing albums can be seen in Rontgen’s original laboratory in the former Physical Institute of the University of Wiirzburg, (Eder and Valenta 1896). The Porter definitions, quoted by Kassabian (1907) were as follows. ‘XI-rays penetrate the soft parts easily but the bones with difficulty. Xz-rays those absorbed by the soft tissues. Xs-rays those readily penetrating both soft tissues and bone’. As an aside, logically XI and Xz should be reversed to give a numerical correlation of the X subscript with absorption, but in 1896 I wonder if XI was defined first because it was for the most diagnostically useful x-ray category. Such scales were impossible to use for standardization, particularly as the behaviour of the tubes was so variable. Also, these qualitative assessment were dependent upon the eye, which apart from radiation hazards, not always recognized, led to further variability.

4.3. Visual quality control: 1904 One of the earliest quality control measurements consisted of visually looking at the colour of the glass bulb when the x-rays were being produced. Figures 23(a)-(d) illustrate four conditions of the Queen and Company, Philadelphia, self-regulating x-ray tube previously mentioned in the caption to figure 22(a). These four colour photographs were previously reproduced in both Pusey and Caldwell (1904) and in Kassabian (1907). Figure 23(a) shows the tube operating properly and figure 23(b) what happens if by mistake the tube has been connected ‘with the wrong poles of the exciting apparatus’ and the current is running in the reverse direction. This situation tended to blacken the glass bulb with a fine deposit of metal thrown off from the electrodes and making it subject to very sudden and erratic fluctuations in resistance (and hence degree of hardness). The appearance of a low vacuum is shown in figure 23(c) and in figure 23(d) the appearance is that which occurs a short time after the bulb has been punctured or cracked and hence is partially filled with air. Pusey and Caldwell(l904) remark that after puncturing ‘a series of beautiful effects will be observed until finally the bulb is full of air and sparks pass between the electrodes’.

Physics contributions in x-ray diagnosis 1895-1915

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4.4. Chiroscopes and Osteoscopes: 1903-4

The first radiation physics phantoms to be used consisted basically of skeleton hands and forearms, of which the first was the Chiroscope (Mould 1980) which was exhibited at a meeting of the Rontgen Society in May 1903. It was reported at this meeting that ‘Almost every worker with X-rays has to use the fluorescent screen very frequently in order to test the conditions of his tube by reference to a shadow of his own hand. This process has so often to be gone through that most workers have had to suffer from more or less acute inflammation of the skin of their hands. To obviate this is the function of the Chiroscope. This insInunent consists of an articulated skeleton hand suitably mounted behind a small fluorescent screen, which is to serve as a test object. The fleshy parts of the hand are represented by suitably cut-out tin foil, and the whole is mounted on a holder, the construction of which affords protection to the hand of the operator’. The Osteoscope shown in figures 24(a) and @) is a similar instrument, devised by Beck (1904) using a bony skeleton hand, forearm and elbow joint. Beck hoped that its use would ‘limit the number of wrinkled and shrivelled Rontgen hands of physicians’. However Kassabian (1907) comments that the Osteoscope is ‘injurious to the eye, no matter how well the latter is protected with lead (flint) glasses’. 4.5. Radiochromators, chromoradiometers, quantimeters and pastilles: 1902-5

These quantitative measuring instruments were a great improvement on visual qualitative assessment and were used not only in diagnostic radiology but also in radiotherapy (Mould 1993, 1995a). Only a selection is described here because many designs were produced and sold commercially but intercomparison was virtually impossible because of the plethora of radiation units used which almost covered the entire alphabet, using both lower case and capital letters! However, the most frequently used units of the early years were the pastille or B-unit of Sabouraud and Noir.5 (1904), the X-unit of Kienbock (1905), the H-unit of Holzknecht (1902) and the skin erythema dose, the SED or HED. Eventually these were all rendered obsolete when the roentgen was accepted internationally as a unit of quantity of radiation, but that was not until 1928 at Stockholm at the 2nd International Congress of Radiology. Chemical colour change following irradiation formed the basis of several units. For example, the pastille of 1904 which was used well into the 1930s, was based on the use of a small capsule of platinobarium cyanide and was purchased in small booklets: which were called radiometers. There were two standard tints, A for unexposed and B for the standard epilation dose. The H-unit of 1902 used a fused mixture of potassium chloride and sodium carbonate. The Holzknecht chromoradiometer was equipped with a scale and in a comparison by Schall (1932) it was stated that the epilation dose was 1.ZB which equalled 6H and that the erythema dose was 2.5B which equalled 12H. However, in practice, these units were used by individual physicians and any meaningful comparison was impossible; this was demonstrated by Colwell and Russ (1915) who conducted a dosimetry survey in 1911 of 13 ‘radiologists of repute’. They entitled their report ‘Idiosyncracy and dosage’ to emphasize the then current problems, which were not to be fully overcome until 1937 when the roentgen was accepted as a unit for both x-rays and gamma-rays. Photographic film blackening was another radiation effect upon which a dose unit was based: the X-unit of Kienbock (1905). Small strips of film, known as Kienbock strips, were exposed on the patient’s skin and the density of the developed film was compared to an a r b i t r q scale of blackening using an instrument called a quantimeter. Photographic film

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Figure 24. The Osteoscope is shown in full detail in (a) and in use by Professor of Surgery, New York Past-Graduate Medical School and Hospital, Carl Beck (1904) in (b) which he gave the caption 'Controlling the vacuum by the Osteoscope during exposure'.

blackening had in fact been proposed earlier by William Rollins (1902) the Boston x-ray engineer who worked closely with Francis Williams (1902): but in this case the proposal was for its use as a radiation protection standard. Other radiation effects upon which units of dose were based besides silver bromide film,

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chemical colour change and skin erythema included fluorescence, temperature variation, x-ray tube current, heating (ergs ~ m - ~ change ), in electrical resistance of a layer of selenium and ionization. For a detailed description of more than 50 such units which were proposed for x-rays and gamma-rays prior to 1937 are given by Mould (1980, 1993). Instrumentation was developed not only for the measurement of dose in such as X and H units but also for the measurement of radiation quality in the period before the proposal by the Swiss physicisdphysician Christen (1912) of the concept of half-value-layer, after which many of the earlier methods fell into disuse. One of the earliest of these penetrameters, which was a significant improvement on the qualitative assessment of hard, medium or soft, was by Benoist (1902). It consisted of a thin disc of silver surrounded by 12 aluminium steps of increasing thickness. When the Benoist radiochromometer was placed behind a fluorescent screen the luminosity of the central silver circle was compared with the steps of the aluminium ladder. Soft x-rays were steps 2 or 3 and hard x-rays steps 7 or 8. As a quality control test object it bears a striking similarity to some of the phantoms used today in diagnostic radiology. Many different metals have been used to determine the penetrative power of xrays and for example Pusey and Caldwell (1904) state the following. ‘The platinumaluminium window of Rontgen is the only means which has been suggested for accurately measuring and standardising the penetrating quality of the X-rays’. This ‘window’ was described (but not illustrated) in Rontgen’s third communication (1897): ‘A rectangular piece 4 cm x 6.5 cm of platinum foil of 0.0026 mm thickness, which is cemented to a thin paper screen, and through which are punched 15 round holes arranged in three rows, each hole having a diameter of 0.7 cm. These little windows are covered by panes of aluminium 0.0299 mm thick which fit exactly and are superimposed in such a way that at the 1st window there is one disc and at the 15th window there are 15 discs. If this arrangement is brought in front of the fluorescent screen, it may be observed very plainly, in case the tubes are not too hard, how many aluminium sheets have the same transparency as the platinum foil. The number will be called the window number’. Credit for this particular work of Rontgen (1897) was hardly ever given in the textbooks of 190&15. Figure 25 shows a skiameter based on this principle taken from Kassabian (1907).

Figure 25. Skiameter used to measure the penetrative power of x-rays (Kawbian 1907).

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4.6. Ionization unit of Villard: 1908 A unit based on ionization, the liberation of 1 esu of charge per cc, was proposed by Villard (1908) as the e-unit and although this was later modified by Behnken (1924, 1927) to become the German roentgen (R) unit, it formed the basis of roentgen unit which was revised in 1937 at the 5th International Congress of Radiology, Chicago, for both x and gamma radiation: ‘The quantity of X or gamma radiation such that the associated corpuscular emission per 0.001293 gram of air produces in air ions carrying 1 esu of charge of either sign’.

4.7. Gold leaf and tin foil electroscopes: 1896 and 1904 The earliest measuring device for x-rays which gained widespread use was the gold leaf electroscope which even in the mid-1930s was still being used in some hospitals as a survey meter for the detection of lost radium sources. Based on the same principal, Pusey and Caldwell (1904) described a tin foil electroscope with the two strips 0.75” wide and 5” length for ‘indicating the potential at the terminal of a Crookes tube‘ for the specific reason that although ‘Testing the tube by observing the shadows of the hand is very convenient, hut it is not to be recommended for the reason that the back of the hand is very sensitive to the X-rays and bums are perhaps more liable in this area than any other part of the body’. An enormous number of different designs of ionization measuring instruments have been developed over the years for the measurement of x-rays and gamma-rays and as early as 3 February 1896, Benoist and Hurmuzescu (1896) presented to the Paris Academy of Sciences their observations on the discharge of a gold leaf electroscope by x-rays, figure 26. They noticed that placing a thin aluminium sheet which was connected to earth between the x-ray tube and electroscope did not change the phenomenon and from this they deduced that this method also permitted the measurement of the absorption of various substances to x-rays.

Figure 26. Experimentd arrangement of Benoist and Hurmuzeescu in 1896 to study the ionization in air produced by x-rays. The gold leaf electroscope is seen at the centre of the drawing.

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4.8. Ionization experiments of J J Thomson: 1896

A few days later on 13 February, J J Thomson of the Cavendish Laboratory, Cambridge, UK, spoke before the Royal Society on his studies of the ionizing effect of x-rays. However, his first publication on the subject was in a letter to The Electrician dated 4 February and published 7 February 1896, and reproduced below (Thomson 1896). ‘Those of your readers who are making experiments on Rontgen’s rays may perhaps be interested in a method of testing their presence which is more delicate and expeditious than the photographic plate, and also more easily adapted to quantitative measurements. It is simply a charged insulated metal plate.. . I have found that when this is exposed to Rontgen’s rays it rapidly loses its charge, and the test is so delicate that I have by this means been able to detect the rays after their passage through a zinc plate one-fourth inch thick. The leakage caused by these rays differs materially from that investigated by Elster and Geitel and due to ultra-violet light. In the first place, the Rontgen rays discharge positive as well as negative electricity, and secondly, the leakage goes on even when the electrified plate is embedded in paraffin, ebonite, mica, sulphar, etc. This shows that all substances through which the Rontgen rays are passing become for the time conductors of electricity. This result seems to me very suggestive both as to the nature of the rays and also the conduction through the insulator’. Thomson published further work on this subject for which his most important publication in 1896 was with Ernest Rutherford, entitled ‘On the passage of electricity through gases exposed to Rontgen rays’. 4.9. Free-air ionization chamber: 1896

In November 1896 Jean Pemn’inParis published a drawing of the principal of a free-in-air chamber (figure.27) and listed all the essential elements of an experimental arrangement with the legend ‘Luftkondensator zur Bestimmung des durch Ionisation versursachten Elektrozit2tsverlustes und damit der Intensitat der ionisierenden Rontgenstrahlen’ (Pychlau 1983). It was, though, to be many years before a practical free-air chamber was achieved. 4.10. Ionization measurements by the 1920s

This review ends in 1915 and but because by that time very little had been achieved in the development of ionization chambers I have arbitrarily extend this section to the 1920s because of the importance of ionization measurements. Many useful designs of ionization chambers and electrometers, such as the Wulf electrometer described by Kronig and Freidrich (1922), were eventually available and Peter Pychlau (1983) of the company FTW-Freiburg which still manufactures ionization chamber dosemeters vividly describes the start in Germany of the time when ionization chambers became practical. ‘Measurement of ionising rays using ionisation chambers means measuring small electrical flows or charge quantities. To illustrate the difficulties encountered in making the necessary electrical measuring instruments, one should bear in mind that it was not possible until the first decade of this century to go to a shop and just buy resistors, capacitors, plugs, switches or voltage sources. On 22 December 1920 the main radio station at Konigs Wusterhausen near Berlin, broadcast the first wireless concert. From then on radio sets were manufactured by amateurs and commercially. Broadcasting for the first time created a market demand for radioelectrical components. Up to then these components were manufactured more or less independently in each laboratory and it took a long time before these components were available as standard equipment’.

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au sol

Figure 27. Illustration of the principal of the free-air ionization chamber by Pemn. dated November 1896.

4.11. Work of a physicist by the 1920s

As a follow-on from the previous section on ionization measurements and for comparison with section 2.7 which describes the work of a hospital physicist 1895-97, figure 28 is included because this is probably the earliest existing photograph of a working physicist making ionization measurements. It is not in diagnostic radiology, because it was to be many years before physicists were routinely involved in this area, except for radiation protection work, and many years before quality assurance and quality control in radiodiagnosis formed part of their daily work, (e.g. Souchkevith er a1 1988). The first hospital physicists, which in England were Russ at the Middlesex HospitaI and Hopwood at St Bartholomew's Hospital in the 1910s. followed by such as Mayneord at the Royal Cancer Hospital in the 1920s, started with one-man departments and were almost exclusively working in x-ray therapy, radium therapy and radiation protection. Figure 28 (Union Minsre du Haut Katanga 1929) shows a physicist making 'space measurements' of 'energy distribution within an irradiated region' for a radium bomb unit designed by the Belgians Sluys and Kessler (1925). A spherical aluminium ionization chamber of size 2 cm is being used. For the measurements the ionization chamber was placed in a fixed position and the teleradium unit (which had 13 radium foci) moved relative to the chamber. The seven chapters of the first radiation physics textbook to be actually written by a hospital physicist (Mayneord 1929) shows clearly the work of that time, but also indicates that education and training (of physicians, radiographers and other physicists) was considered of importance from the basic physics included. [I] Discovery and general properties of X-rays. [2] Radiations from an X-ray tube. [3] X-rays and matter. [4] X-ray absorption. [5]X-ray measurements. [6] Important factors affecting choice of therapeutic conditions. [7] X-ray apparatus. 4.12. Fluoroscopes and photofluoroscopes: 1896-1902

The earliest construction for a fluoroscope was a simple cylindrical cardboard tube about 15-20 cm in length, which is closed at one end by a piece of cardboard covered by barium

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Figure 28. Physicist making ionization chamher measurements in the 1920s for a radium bomb machine (Union Minibre du Haut Katanga 1929).

platino-cyanide (Thompson 1896, Glasser 1933) as used by Paul Spiess of the Urania Society, Berlin and reported on 27 February 1896 and by Enrico Salvioni of Perugia, Italy. The first photofluoroscope was also devised in Italy, by J Mount Bleyer of Naples in 1896, figure 29.

Figure 29. The Bieyer photofluoroscope (Thompson 1R96). It was used as early as I April 1896 and reported both in the Elecrricol Ennyinetr and the proceedings of the RoyolAcodemy of Medicine andSuryery ofNop1e.y. The fluoroscope was termed a 'flaring skiascope' 10 differentiate it from the cylindrical tube version. Bleyer eventually moved to New York and worked s a laryngologist (Gngg 1986).

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The fluoroscopes of Spies and Salvioni were essentially only to demonstrate the effects of the x-rays rather than to visualize anatomy such as the hand. It was therefore rapidly modified to the truncated pyramid shape shown being held by Thomas Edison in 1896 in figure 11 and in figure 30 being used by Francis Williams (1902). physician at the Boston City Hospital, for examination of the thorax. 4.13. Densitometer: 1902

Densitometers, either manual or automatic, are most familiar to physicists of today and it is therefore of interest to note figure 31, from Williams (1902), which he describes in the following manner. ‘I designed this instrument, to which I have given the name of densitometer, in order to measnre the density of any part of the thorax, and I chose water as a means of measurement, because this liquid is most akin to the soft tissues of the body, they being chiefly made up of it, as well as to the pathological deposits in the lungs. It consists of an oval box with two bottoms, and is divided into halves, A and B, by a partition that reaches nearly to the false bottom. The sides of this box and the partition are made of copper. The top and both bottoms of thin sheets of aluminium. The half A is closed above and is supplied with a stopcock and a rubber tube: the half B is covered with a lid. Between the two bottoms are placed pieces of two or three ribs, or pieces of ivory corresponding in density to the ribs may be used. The stopcock of A is closed and water poured into B until it is nearly filled. Stopcock in A is then opened and water flows under the partition and rises into this half. This so prepared instrument is then placed close beside the patient’s chest, between it and the arm. While the chest is examined on the fluorescent screen, the water level in B is changed as desired by blowing air into A or sucking air out of A. When the shadows of the ribs in the body and in the densitometer are equally dark, and the light on the portion of the fluorescent screen over B corresponds to the light on the portion of the screen over the thorax, the stopcock is closed, the lid is opened. The depth of water is read off in cm and the density of the lungs in a patient can thus be measured‘. 4.14. X-ray tube protection: 1902-15

X-ray tube protection was non-existent in most centres for many years, and even if some protection procedure was recommended, such as the use of the osteoscope (Beck 1904). figure 24, the x-ray tube was totally unshielded. The use of the protective box by Williams (1902), figure 30, was therefore relatively unusual for the period 1900-5. Later, more sophisticated tube shields and diaphragms became available as seen, figure 32, from the advertisement from a 1909 issue of the Journal of The Rontgen Sociery for equipment manufactured by Alfred Dean of London. By 1915 iris diaphragms were incorporated into the protective tube holder, or tube box as it was then often termed, by several manufacturers and special couches for use with overcouch and undercouch tubes were available, as were vertical screening stands. In figure 33 reproduced from Knox (1915), a plan for a consultins room or ‘hospital outfit’ is shown to conclude this review for the first 20 years of diagnostic radiology. It clearly indicates the tube stand, x-ray couch and upright screening apparatus. The x-ray tube rack indicated at one comer of the room was an essential in the gas tube era since a selection of tubes was essential because of the varying degrees of hardness with time of any single tube and also because they were fragile and easily broken.

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Figure 30. Francis Williams of Roston VAL< one of the foremost pioneers of diagnostic radiology and. for example, used U protective housing for the x-ray tuhe much earlier than many of his colleagues. He also combined this with a diaphragm which was unusual, in that many physicians and surgeons used neither a diaphragm or a tuhe housing. This Williams' photograph (1902) was captioned as follows: 'The patient is seated in a revolving chair which has a leather hack through which the rays can pass. The tube is in the box seen on the kfi. The aluminium screen which belongs in front of the bar: has been removed. The practitioner is so seated that he can control with his "ght hand the length of the spark-gap.the amount of the condenser. and the speed of the commutator and therefore vary the light to suit his needs as the examination proceeds'

Figure 31. The thorax densitometer of Williams (1902).

Physics contributions in x-ray diagnosis 1895-1915

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