RADIOISOTOPES

Tritium standard gas for calibrating radioactivity detectors was prepared by the use of tritiated methane synthesized by the reaction of tritiated water with aluminum carbide at ca. 470°C. A long-path proportional counter was used to standardize the radioactivity of the prepared gas. Tritiated gas of less than 10⁴ Bq could be measured by this counter with the overall error of 3.5% (3 σ) . Finally, two types of standard were prepared in a metal cylinder and a glass ampoule. The latter type could be used as a handy calibration source for detectors.

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For the establishment of the experimental system to judge easily the effect of anti-inflammatory drug, ⁶⁷Ga-citrate was used. The weight of granuloma tissues induced by inflammable agent, turpentine oil, gradually increased and reached a maximum at 6 days after the administration of turpentine oil. Gallium-67 accumulation in the inflammatory lesions showed also a maximum at 6 days after that. Both patterns were closely similar each other. These results showed that the processes and/or stages of inflammation could be indicated by the pattern of ⁶⁷Ga uptake.

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New imaging method that was integrated image of radionuclide liver angiogram was proposed. Patients were placed supine beneath gamma cammera, so that the liver, spleen, heart, and lung were included in an anterior image. Integrated image was recorded for 100 s, following injection of 111-222 MBq (3-6 mCi) of ^99mTc tin-colloid. 595 cases were examined, and classified into 3 groups as follows.
Group I: Cases without hepatic dysfunction
Group II: Cases with hepatic dysfunction
Group III: Liver cirrhosis.
Numbers of each group were 208 (35%), 305 (51%), and 82 (14%) respectively. Integrated images were qualitatively determined by macroscopic inspection. Compairing liver intensity and lung intensity, 3 patterns of integrated image were classified.
Pattern I: Liver intensity was greater than lung intensity
Pattern II: Liver intensity was equal to lung intensity
Pattern III: Liver intensity was less than lung intensity
Numbers of each pattern were 412 (69%), 125 (21%), and 58 (10%) respectively. Numbers of group III distributed into each pattern were 8 (10%) in pattern I, 29 (35%) in pattern II, and 45 (55%) in pattern III. The correct diagnosis of liver cirrhosis as follows. In a case of choosing pattern III as diagnostic criterion, sensitivity was 55%, and specificity was 97%. The positive predictive value was 78%, and the negative predictive value was 93%. Total accuracy was 92%. This new method seems useful in evaluating diffuse hepatic disease.

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Before incineration of disposed RIA test tubes, residual ¹²⁵I radioactivity should be measured for the purpose of radiation safety. This confirmation method has been carried out according to the followings:
(1) Residual ¹²⁵I radioactivity of test tubes in the plastic bag was measured from outside with the low-energy γ-ray survey meter (S1371, Ohyo Kohken Co., Ltd.) newly developed by one of the authors.
(2) Gaseous ¹²⁵I released from the residual ¹²⁵I-compounds in test tubes by radiation self decomposition was adsorbed by the activated carbon fiber filter (ACFF), and wasmeasured.
From the above 2 methods, the minimum detectable concentration of residual 1251 in waste tubes would be reached under a level of about 100mBq/ (2.8×10^-6μCi/g) .

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