シールド装着状態のシリンジ製剤を用いたエネルギースペクトル収集法の検討

Abstract

I previously reported on a spectrum sampling method with shielded syringes before use, although the report included only data obtained using technetium-99m. In this study, we sampled the energy spectrum in a similar manner using thallium-201, iodine-123, and gallium-67. In spectrum sampling, a radioisotopic source in a cylindrical shield is located midway between two opposed gamma-camera detectors equipped with collimators. An unshielded syringe before use emits excessive radiation and makes count rates too high to obtain accurate photopeak values. With a shielded syringe, we can sample the spectrum of radiation leaked from the needle side of the syringe and the unshielded part of its plunger side. Consequently, the detectors are exposed to lower-dose gamma rays and probably offer count rates appropriate to measure accurate photopeak values. The study results show the general validity of spectrum sampling and photopeak acquisition in our method. However, a syringe should be located accurately perpendicular to each detector; otherwise, gamma rays did not reach the detectors in some cases, resulting in measurement failures. In addition, when low-energy collimators are used for sampling from (123)I sources, photopeak values depend on penetration. More accurate measurements require the use of high-energy collimators.