1975, British Journal of Radiology, 48, 1036 Correspondence STANTON, L. and LIGHTFOOT, D. A., 1966. Obtaining proper -a— ©-
Trimax
*-
Medichrome
-•—
contrast in mammography. Radiology, 87, 111-115. YOUNG, G. B., 1974. Techniques and radiation in mammography. British Journal of Radiology, 47, 811-815.
Crystallex
Du Pont
Exposure
THE EDITOR—SIR DR. WILLIAM D. COOLIDGE
mAs
Doubtless you will have seen the press notice of the death of Dr. William D. Coolidge at the age of 101. The Editor of our Journal, and also our President, may be interested in the fact that two members of the B.I.R., elected about 1920, Captain Shorten and Captain Barnard, first used a Coolidge Tube some 60 years ago in their X-ray department in Colaba War Hospital, Bombay. They found that due to the high percentage of humidity there was so much leakage of high-tension current along the bare brass leads and over the surface of the coil and tube that it was almost impossible to use the apparatus. Eventually, after many hazardous experiments, this was overcome by earthing the negative terminals of the 20 in. coil then in use and the tube and removing the high-tension wire between these. Three papers on this work were published in the Archives of the Roentgen Society in 1917 and 1919 and aroused world-wide interest. By the end of 1919 over 10,000 radiographs had been produced and several hundreds of treatments given without any • damage to the tube or coil! Shorten died many years ago but Barnard—now in his 91st year—sends you this note. Yours etc.,
60
40
20
T. W. BARNARD. 0
100
200
300
400
500
Particle Size /um FIG. 2. The visibility of the aluminium-oxide particles at different exposures. Any particular point shows the least size of particle visible at that exposure. The lines joining these points separate visible particles on the right from the particles to the left of the line which are too small to be seen.
The Cottage, 7 Carsick Grange, Sheffield S10 3LT. P.S. The Editor may find it of interest to refer to an article I published in Radiography of November 1967, which was illustrated by several radiographs of the 1916-1920 era and photographs of the Colaba War Hospital X-ray Department showing the new method of wiring—and of the first X-ray apparatus at the London Hospital.
THE EDITOR—SIR, RADIOISOTOPE SECTION SCAN VERSUS E.M.I. SCAN
film, visibility of the chest wall is associated with overexposure of the skin region. The Medichrome system also retains its definition over a wide exposure range but is not quite as good as the Du Pont. Mammographic examinations may now be performed using a single-screen vacuum pack (the Du Pont system) without a significant loss in image quality compared with non-screen film. Exposures may be reduced by factors of four or five. Yours, etc., A. L. EVANS, W. B. JAMES, J. MCLELLAN, M. DAVISON.
Department of Radiology, Southern General Hospital, Glasgow, and Department of Clinical Physics and Bio-Engineering, West of Scotland Health Boards, Glasgow. REFERENCES EVANS, A. L., JAMES, W. B., MCLELLAN, J., and DAVISON,
M., 1975. Film and xeroradiographic images in mammography. A comparison of tungsten and molybdenum anode materials. British Journal of Radiology 48, 968-972.
The E.M.I, scanner (Hounsfield, 1973) is a relatively newdevice which will, no doubt, in time be compared with radioisotope brain-section scanning. However, one very approximate but interesting comparison can already be made, on the relative use each method makes of the photons to which the patient is subjected: (1) Radioisotope brain-section scan. Assuming an injected dose of 10 mCi 99Tcm of which, say 27mCi is excreted, the patient is subjected to 8 X 3-7 X 10 X 6 X 60 X 60/0-693 ~ 1013 photons. During the course of a typical brain-section scan, taken on the Aberdeen Section Scanner (Bowley et al., 1973), approximately 30,000 photons are detected,9 representing a fraction of the "incident" photons of 3 X 10 . (2) E.M.I, scan. Assuming an effective linear absorption coefficient of 0-45 cm-1 and an average thickness of 15 cm unit density material, the transmitted fraction is exp (— 0-45x15) ~10- 3 , and we may assume that all the transmitted photons contribute to the image. The5 "physical" E.M.I, scan is therefore approximately 3 X 10 times more efficient than its "biochemical" counterpart—the radioisotope section scan, under the terms of this comparison. During the course of a typical E.M.I, scan approximately 1010 photons are detected (R. A. Shields, private communication). It is difficult to compare the ultimate diagnostic value of the images produced by each method, with such a disparity between the actual number of photons detected.
1036
Trimax
*-
Medichrome
-•—
contrast in mammography. Radiology, 87, 111-115. YOUNG, G. B., 1974. Techniques and radiation in mammography. British Journal of Radiology, 47, 811-815.
Crystallex
Du Pont
Exposure
THE EDITOR—SIR DR. WILLIAM D. COOLIDGE
mAs
Doubtless you will have seen the press notice of the death of Dr. William D. Coolidge at the age of 101. The Editor of our Journal, and also our President, may be interested in the fact that two members of the B.I.R., elected about 1920, Captain Shorten and Captain Barnard, first used a Coolidge Tube some 60 years ago in their X-ray department in Colaba War Hospital, Bombay. They found that due to the high percentage of humidity there was so much leakage of high-tension current along the bare brass leads and over the surface of the coil and tube that it was almost impossible to use the apparatus. Eventually, after many hazardous experiments, this was overcome by earthing the negative terminals of the 20 in. coil then in use and the tube and removing the high-tension wire between these. Three papers on this work were published in the Archives of the Roentgen Society in 1917 and 1919 and aroused world-wide interest. By the end of 1919 over 10,000 radiographs had been produced and several hundreds of treatments given without any • damage to the tube or coil! Shorten died many years ago but Barnard—now in his 91st year—sends you this note. Yours etc.,
60
40
20
T. W. BARNARD. 0
100
200
300
400
500
Particle Size /um FIG. 2. The visibility of the aluminium-oxide particles at different exposures. Any particular point shows the least size of particle visible at that exposure. The lines joining these points separate visible particles on the right from the particles to the left of the line which are too small to be seen.
The Cottage, 7 Carsick Grange, Sheffield S10 3LT. P.S. The Editor may find it of interest to refer to an article I published in Radiography of November 1967, which was illustrated by several radiographs of the 1916-1920 era and photographs of the Colaba War Hospital X-ray Department showing the new method of wiring—and of the first X-ray apparatus at the London Hospital.
THE EDITOR—SIR, RADIOISOTOPE SECTION SCAN VERSUS E.M.I. SCAN
film, visibility of the chest wall is associated with overexposure of the skin region. The Medichrome system also retains its definition over a wide exposure range but is not quite as good as the Du Pont. Mammographic examinations may now be performed using a single-screen vacuum pack (the Du Pont system) without a significant loss in image quality compared with non-screen film. Exposures may be reduced by factors of four or five. Yours, etc., A. L. EVANS, W. B. JAMES, J. MCLELLAN, M. DAVISON.
Department of Radiology, Southern General Hospital, Glasgow, and Department of Clinical Physics and Bio-Engineering, West of Scotland Health Boards, Glasgow. REFERENCES EVANS, A. L., JAMES, W. B., MCLELLAN, J., and DAVISON,
M., 1975. Film and xeroradiographic images in mammography. A comparison of tungsten and molybdenum anode materials. British Journal of Radiology 48, 968-972.
The E.M.I, scanner (Hounsfield, 1973) is a relatively newdevice which will, no doubt, in time be compared with radioisotope brain-section scanning. However, one very approximate but interesting comparison can already be made, on the relative use each method makes of the photons to which the patient is subjected: (1) Radioisotope brain-section scan. Assuming an injected dose of 10 mCi 99Tcm of which, say 27mCi is excreted, the patient is subjected to 8 X 3-7 X 10 X 6 X 60 X 60/0-693 ~ 1013 photons. During the course of a typical brain-section scan, taken on the Aberdeen Section Scanner (Bowley et al., 1973), approximately 30,000 photons are detected,9 representing a fraction of the "incident" photons of 3 X 10 . (2) E.M.I, scan. Assuming an effective linear absorption coefficient of 0-45 cm-1 and an average thickness of 15 cm unit density material, the transmitted fraction is exp (— 0-45x15) ~10- 3 , and we may assume that all the transmitted photons contribute to the image. The5 "physical" E.M.I, scan is therefore approximately 3 X 10 times more efficient than its "biochemical" counterpart—the radioisotope section scan, under the terms of this comparison. During the course of a typical E.M.I, scan approximately 1010 photons are detected (R. A. Shields, private communication). It is difficult to compare the ultimate diagnostic value of the images produced by each method, with such a disparity between the actual number of photons detected.
1036
