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
1975, British Journal of Radiology, 48, 1037
Correspondence The diagnostic value of the E.M.I, scan is clearly established. However, the fact that clinically valuable results are obtained from the radioisotope section scan with currently such low photon utilization would seem to indicate that the radioisotope method should not be abandoned. Ways of improving the photon utilization should be fully explored. Yours, etc., W. I. KEYES.
Medical Physics Department, Aberdeen University, Aberdeen AB9 2ZD. REFERENCES BOWLEY, A. R., TAYLOR, C. G., CAUSER, D. A., BARBER, D. C , KEYES, W. I., UNDRILL, P. E., CORFIELD, J. R., and MALLARD, J. R., 1973. A radioisotope scanner for
rectilinear, arc, transverse section and longitudinal section scanning: (ASS — the Aberdeen Section Scanner). British Journal of Radiology, 46, 262-271.
HOUNSFIELD, G. N., 1973. Computerized transverse axial scanning (tomography): Part 1, Description of system. British Journal of Radiology, 46,1016-1022.
THE EDITOR—SIR, GAIN INSTABILITY OF SCINTILLATION DETECTORS AND CONSEQUENCES FOR DYNAMIC TRACER STUDIES
In measurement systems for regional blood-flow studies, based on the clearance process of an injected radioactive tracer, small scintillation detectors are widely used (Jaffe, McHenry and Goldberg, 1970). In applying commercially available mini-probes, we met serious problems with regard to instability. Our experience may be of interest to other users. Four photomultiplier tubes (Philips XP 1110), were tested and compared with tubes of the same type which were selected by the manufacturer for count-rate stability at our request. Instability of the photomultiplier gain results in shifts of the pulse-height spectrum. Two types of shift can be distinguished: stationary shift, found at a constant countrate, and dynamic shift caused by an alteration of count-rate. The tubes were used in accordance with the recommendaData tions of the manufacturers data handbook (Philips 137 Handbook). The location of the energy peak of Cs was measured with a multi-channel-analyser. The range of the count-rate was 400-3,000 c.p.s. In Fig. 1 an example of the observed shift over four hours is demonstrated. Before these measurements were performed, the tubes were in operation at background radiation level for more than 24 hours. One curve refers to an unselected tube and the other to a tube selected for count-rate stability. It appears that the responses of both
FIG. 2. Relative shift of the energy peak of 137Cs after stepwise alterations of count-rate; dynamic shift of the same tubes as in Fig. 1.
selected and unselected tubes to a count-rate increase from background level was not fully stabilized for at least four hours and that the shift of the energy peak relative to its original location was 10 per cent (unselected) and 4 per cent (selected). The dynamic shift is demonstrated in Fig. 2. This was obtained by stepwise alterations of the intensity of the count-rate as denoted in the figure. Here serious shifts were found (16 per cent especially with the unselected tube). The dynamic shift consists of an almost instantaneous part, followed by a more slowly changing part. It was found that both stationary and dynamic shiftcurves were reproducible. These effects influence dynamic tracer studies. The fast increase, after an injection of tracer, causes a shift with time which may significantly affect clearance functions. The consequences were studied on a clearance process of a well-stirred compartment (clearance decay constant 0-35 min""1), in which a bolus of 133 Xe was injected. The clearance curve was measured simultaneously with a selected and an unselected tube. It turned out that a higher decay constant was always found with the unselected tube. The difference was about 16 per cent, using a symmetrical window with a width of 5/4 of the energy-peak-width at half maximum. The consequences of shift are especially serious if only a discriminator instead of a window is used with the setting point on the rising part of the peak (3). Since we had no other small tubes available, we cannot generalize our conclusion, but it is possible that similar effects may occur also with other types of tubes. Yours, etc., W. A. VAN DUYL. P. J. J. BRENNINKMEJER.
FIG. 1. Relative shift of the energy peak of 137Cs after a stepwise increase of count-rate from background radiation level (stationary shift): lower curve a photcmultiplier tube selected for count-rate stability; upper curve an arbitrary, photomultiplier tube of the same type.
Department of Biological and Medical Physics, Erasmus University of Rotterdam, Medical Faculty, P.O. Box 1738, The Netherlands. REFERENCES JAFFE, M. E., MCHENRY, L. C , and
GOLDBERG, H. J.,
1970. Regional cerebral blood-flow measurement with small probes. Neurology, 20, 225-237. Philips data handbook, part 6 electron tubes. January 1974.
1037
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
1975, British Journal of Radiology, 48, 1037
Correspondence The diagnostic value of the E.M.I, scan is clearly established. However, the fact that clinically valuable results are obtained from the radioisotope section scan with currently such low photon utilization would seem to indicate that the radioisotope method should not be abandoned. Ways of improving the photon utilization should be fully explored. Yours, etc., W. I. KEYES.
Medical Physics Department, Aberdeen University, Aberdeen AB9 2ZD. REFERENCES BOWLEY, A. R., TAYLOR, C. G., CAUSER, D. A., BARBER, D. C , KEYES, W. I., UNDRILL, P. E., CORFIELD, J. R., and MALLARD, J. R., 1973. A radioisotope scanner for
rectilinear, arc, transverse section and longitudinal section scanning: (ASS — the Aberdeen Section Scanner). British Journal of Radiology, 46, 262-271.
HOUNSFIELD, G. N., 1973. Computerized transverse axial scanning (tomography): Part 1, Description of system. British Journal of Radiology, 46,1016-1022.
THE EDITOR—SIR, GAIN INSTABILITY OF SCINTILLATION DETECTORS AND CONSEQUENCES FOR DYNAMIC TRACER STUDIES
In measurement systems for regional blood-flow studies, based on the clearance process of an injected radioactive tracer, small scintillation detectors are widely used (Jaffe, McHenry and Goldberg, 1970). In applying commercially available mini-probes, we met serious problems with regard to instability. Our experience may be of interest to other users. Four photomultiplier tubes (Philips XP 1110), were tested and compared with tubes of the same type which were selected by the manufacturer for count-rate stability at our request. Instability of the photomultiplier gain results in shifts of the pulse-height spectrum. Two types of shift can be distinguished: stationary shift, found at a constant countrate, and dynamic shift caused by an alteration of count-rate. The tubes were used in accordance with the recommendaData tions of the manufacturers data handbook (Philips 137 Handbook). The location of the energy peak of Cs was measured with a multi-channel-analyser. The range of the count-rate was 400-3,000 c.p.s. In Fig. 1 an example of the observed shift over four hours is demonstrated. Before these measurements were performed, the tubes were in operation at background radiation level for more than 24 hours. One curve refers to an unselected tube and the other to a tube selected for count-rate stability. It appears that the responses of both
FIG. 2. Relative shift of the energy peak of 137Cs after stepwise alterations of count-rate; dynamic shift of the same tubes as in Fig. 1.
selected and unselected tubes to a count-rate increase from background level was not fully stabilized for at least four hours and that the shift of the energy peak relative to its original location was 10 per cent (unselected) and 4 per cent (selected). The dynamic shift is demonstrated in Fig. 2. This was obtained by stepwise alterations of the intensity of the count-rate as denoted in the figure. Here serious shifts were found (16 per cent especially with the unselected tube). The dynamic shift consists of an almost instantaneous part, followed by a more slowly changing part. It was found that both stationary and dynamic shiftcurves were reproducible. These effects influence dynamic tracer studies. The fast increase, after an injection of tracer, causes a shift with time which may significantly affect clearance functions. The consequences were studied on a clearance process of a well-stirred compartment (clearance decay constant 0-35 min""1), in which a bolus of 133 Xe was injected. The clearance curve was measured simultaneously with a selected and an unselected tube. It turned out that a higher decay constant was always found with the unselected tube. The difference was about 16 per cent, using a symmetrical window with a width of 5/4 of the energy-peak-width at half maximum. The consequences of shift are especially serious if only a discriminator instead of a window is used with the setting point on the rising part of the peak (3). Since we had no other small tubes available, we cannot generalize our conclusion, but it is possible that similar effects may occur also with other types of tubes. Yours, etc., W. A. VAN DUYL. P. J. J. BRENNINKMEJER.
FIG. 1. Relative shift of the energy peak of 137Cs after a stepwise increase of count-rate from background radiation level (stationary shift): lower curve a photcmultiplier tube selected for count-rate stability; upper curve an arbitrary, photomultiplier tube of the same type.
Department of Biological and Medical Physics, Erasmus University of Rotterdam, Medical Faculty, P.O. Box 1738, The Netherlands. REFERENCES JAFFE, M. E., MCHENRY, L. C , and
GOLDBERG, H. J.,
1970. Regional cerebral blood-flow measurement with small probes. Neurology, 20, 225-237. Philips data handbook, part 6 electron tubes. January 1974.
1037
