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Linear scanning of small animals by an isotope scanner
Technical notes International Journal of Applied Radiation and Isotopes, 1968,Vol. 19, pp. 601-602. Pergamon Press. Printed in Northern Ireland
601 DIVERGENT SLIT VERTICAL
Linear Scanning o£ Small ~tni,,,als by an Isotope Scanner (Received 3 November 1967; accepted 22 January
2o7.
1968) IT Is possible to study the distribution of a radionuclide in the body of an animal at different time intervals by serial profile scanning (1). I t is not possible for m a n y of the small radioisotope laboratories to afford a suitable profile scanner for such studies. I n this communication, we present a method of obtaining serial profile scans in small laboratory animals with a conventional dot scanner, thereby eliminating the expense of additional equipment.
Methods A special slit type lead collimator was fabricated to fit the detector head of our Isotope Scanner* having a I t x 2 in. sodium iodide crystal. T h e slit was 7 cm in length and 2 m m in width at its distal surface and diverged with an angle of 20 ° towards the crystal, so that the entire crystal could view through the slit. W h e n a small animal, such as a mouse, was kept in close apposition to the slit, the crystal viewed only a narrow horizontal segment of the body of the animal. A rapid return switch was utilised for the return of the detector to the starting point after each slow linear traverse. A linear scan was obtained on a rectlinear r e c o r d e r t during each slow traverse of the detector. T h e detector slit was kept at right angles to the long axis of the animal. T h e scanning speed was the same as the chart recorder speed of 0.75 in. per rain so as to have the length of the chart record correspond to the length of the animal. T h e radiation detection characteristics of the slit collimator were studied by plotting an isoresponse curve obtained by moving a point source of radioactivity along the narrow axis of the slit. Comparison was m a d e with an isoresponse curve of a collimator with an uniform non-divergent slit of the same dimensions.
3o7. 507.
Fzo. 1. Isoresponse curve of the sllt collimator with a divergent slit. Figure 2 shows the isoresponse curve of the slit collimator where the slit is uniform and not diverging. Figure 3 shows a serial profile scan of a mouse with a spontaneous malignant t u m o u r after an injection of radioiodinated synkavit. This radiopharmaceutical was reported by us to localise in malignant turnouts after an i.v. injection (z). Figure 3A shows the concentration of the radioactivity only in the region of the t u m o u r immediately after an i.v. injection. Figure 3B shows that after 30 rain there has been a build up of radioactivity in the thyroid and the stomach suggesting deiodination of the c o m p o u n d in vivo. Figure 3C shows the effect of an intraperitoneal injection of potassium perchlorate on the distribution of this compound. T h e stomach and the thyroid discharged the radioiodine but the tumour concentration did not show a significant alteration. Comm~llts
The adaptation of an isotope scanner to operate as a profile scanner requires a suitable slit collimator, so that at any one time the detector sees only a narrow transverse segment of the body during the course of its linear traverse. T h e collimator that we found UNIFORM SLIT VERTICAL
--IOZ
Results Figure 1 shows the isoresponse curve of the slit collimator when the point source was moved along the vertical axis of the slit. T h e efficiency of counting falls off" markedly within a fraction of a eva from the told-line. * Nuclear Chicago Model No. 1700 B. Nuclear Chicago M o d e l No. R 1001 A.
~1
2o7. 3oz
r~
507.
FIo. 2. Isorespons¢ curve of the slit collimator with a uniform non-divergent slit.
Technical notes
602
~ T BOMACH UMOUR
ST~
UMOUR
Flo. 3. Serial profile scanning after an i.v. injection of radioiodinated SynkavJt. (A) Few minutes after i.v. tslI-Synkavit. (B) 30 minutes after (C) 30 minutes after KCIO 4 injection. acceptable had a single slit 7 cm × 2 mm at the outer surface and it diverged with an angle of 20 ° towards the crystal. We had earlier worked with non-diverging slit in which the effective area of the crystal surface utilized for the detection purposes corresponded to the size of the slit at the external surface of the collimator. With the latter type of the slit the resolution was better than the divergent type of the slit but the counting efficiency was reduced by a factor of 5. I n the divergent type of the slit the counting efficiency is high because the entire crystal views through the slit. We preferred to sacrifice the resolution characteristics to some extent to attain better counting efficiency.
Figure 1 shows that the efficiency of the counting diminishes as the source moves away from the surface of the collimator. Since the thickness of an average mouse is about 2 cm there would not be any gross change in the efficiency of counting due to anterior or posterior location of radioisotope concentration. Figure 1 shows that along the narrow axis the count rate falls by 50 per cent when the source is 0.3 cm away from the slit. It is, therefore, possible to separate two areas of concentration which lie within 0.3 cm of each other. Profile scanning for studying distribution of radionuclides in the body does not require a very sharp resolution. It is at best a screening test to find out the optimum time for sacrificing the animals or for scanning. The linear scanning only hints at the possible sites of localisation of radioisotopes but it does not point out the exact organ where it has localised. This information can be obtained only by scanning or by counting of individual organs after sacrificing the animals. Availability of the profile scanning system saves unnecessary waste of large number of animals as serial study is possible in the same animal to study the changing pattern of distribution.
Radiation Medicine Centre Bhaba Atomic Research Centre Tata Memorial Hospital Pard, Bombay-12 India
P. P~MANATHAN
R. D. GANAT~ M. N. M~aTA M. C. PATEL So M. SHARMA
References I. POCHIN E. E. Profile counting, Medical Radioisotopes Scanning. Proceedings of IAEA Symposium, 143 (1959). 2. GANATRAR. D., MANI R. S., RAMANATHANP., MEHTA M. N., DESAI K. B. and DESA! C. N. Radiology 87, 750 (1966).
601 DIVERGENT SLIT VERTICAL
Linear Scanning o£ Small ~tni,,,als by an Isotope Scanner (Received 3 November 1967; accepted 22 January
2o7.
1968) IT Is possible to study the distribution of a radionuclide in the body of an animal at different time intervals by serial profile scanning (1). I t is not possible for m a n y of the small radioisotope laboratories to afford a suitable profile scanner for such studies. I n this communication, we present a method of obtaining serial profile scans in small laboratory animals with a conventional dot scanner, thereby eliminating the expense of additional equipment.
Methods A special slit type lead collimator was fabricated to fit the detector head of our Isotope Scanner* having a I t x 2 in. sodium iodide crystal. T h e slit was 7 cm in length and 2 m m in width at its distal surface and diverged with an angle of 20 ° towards the crystal, so that the entire crystal could view through the slit. W h e n a small animal, such as a mouse, was kept in close apposition to the slit, the crystal viewed only a narrow horizontal segment of the body of the animal. A rapid return switch was utilised for the return of the detector to the starting point after each slow linear traverse. A linear scan was obtained on a rectlinear r e c o r d e r t during each slow traverse of the detector. T h e detector slit was kept at right angles to the long axis of the animal. T h e scanning speed was the same as the chart recorder speed of 0.75 in. per rain so as to have the length of the chart record correspond to the length of the animal. T h e radiation detection characteristics of the slit collimator were studied by plotting an isoresponse curve obtained by moving a point source of radioactivity along the narrow axis of the slit. Comparison was m a d e with an isoresponse curve of a collimator with an uniform non-divergent slit of the same dimensions.
3o7. 507.
Fzo. 1. Isoresponse curve of the sllt collimator with a divergent slit. Figure 2 shows the isoresponse curve of the slit collimator where the slit is uniform and not diverging. Figure 3 shows a serial profile scan of a mouse with a spontaneous malignant t u m o u r after an injection of radioiodinated synkavit. This radiopharmaceutical was reported by us to localise in malignant turnouts after an i.v. injection (z). Figure 3A shows the concentration of the radioactivity only in the region of the t u m o u r immediately after an i.v. injection. Figure 3B shows that after 30 rain there has been a build up of radioactivity in the thyroid and the stomach suggesting deiodination of the c o m p o u n d in vivo. Figure 3C shows the effect of an intraperitoneal injection of potassium perchlorate on the distribution of this compound. T h e stomach and the thyroid discharged the radioiodine but the tumour concentration did not show a significant alteration. Comm~llts
The adaptation of an isotope scanner to operate as a profile scanner requires a suitable slit collimator, so that at any one time the detector sees only a narrow transverse segment of the body during the course of its linear traverse. T h e collimator that we found UNIFORM SLIT VERTICAL
--IOZ
Results Figure 1 shows the isoresponse curve of the slit collimator when the point source was moved along the vertical axis of the slit. T h e efficiency of counting falls off" markedly within a fraction of a eva from the told-line. * Nuclear Chicago Model No. 1700 B. Nuclear Chicago M o d e l No. R 1001 A.
~1
2o7. 3oz
r~
507.
FIo. 2. Isorespons¢ curve of the slit collimator with a uniform non-divergent slit.
Technical notes
602
~ T BOMACH UMOUR
ST~
UMOUR
Flo. 3. Serial profile scanning after an i.v. injection of radioiodinated SynkavJt. (A) Few minutes after i.v. tslI-Synkavit. (B) 30 minutes after (C) 30 minutes after KCIO 4 injection. acceptable had a single slit 7 cm × 2 mm at the outer surface and it diverged with an angle of 20 ° towards the crystal. We had earlier worked with non-diverging slit in which the effective area of the crystal surface utilized for the detection purposes corresponded to the size of the slit at the external surface of the collimator. With the latter type of the slit the resolution was better than the divergent type of the slit but the counting efficiency was reduced by a factor of 5. I n the divergent type of the slit the counting efficiency is high because the entire crystal views through the slit. We preferred to sacrifice the resolution characteristics to some extent to attain better counting efficiency.
Figure 1 shows that the efficiency of the counting diminishes as the source moves away from the surface of the collimator. Since the thickness of an average mouse is about 2 cm there would not be any gross change in the efficiency of counting due to anterior or posterior location of radioisotope concentration. Figure 1 shows that along the narrow axis the count rate falls by 50 per cent when the source is 0.3 cm away from the slit. It is, therefore, possible to separate two areas of concentration which lie within 0.3 cm of each other. Profile scanning for studying distribution of radionuclides in the body does not require a very sharp resolution. It is at best a screening test to find out the optimum time for sacrificing the animals or for scanning. The linear scanning only hints at the possible sites of localisation of radioisotopes but it does not point out the exact organ where it has localised. This information can be obtained only by scanning or by counting of individual organs after sacrificing the animals. Availability of the profile scanning system saves unnecessary waste of large number of animals as serial study is possible in the same animal to study the changing pattern of distribution.
Radiation Medicine Centre Bhaba Atomic Research Centre Tata Memorial Hospital Pard, Bombay-12 India
P. P~MANATHAN
R. D. GANAT~ M. N. M~aTA M. C. PATEL So M. SHARMA
References I. POCHIN E. E. Profile counting, Medical Radioisotopes Scanning. Proceedings of IAEA Symposium, 143 (1959). 2. GANATRAR. D., MANI R. S., RAMANATHANP., MEHTA M. N., DESAI K. B. and DESA! C. N. Radiology 87, 750 (1966).