Gamma camera with a two-layer diverging-slat collimator for radioisotope monitoring

Abstract

The purpose of this study was to develop and evaluate a gamma camera with a newly designed diverging collimator for monitoring radiation fields in nuclear medicine. Simulations using the Geant4 Application for Tomographic Emission (GATE) were performed to model the gamma camera system designed to monitor Tc-99m radioactive isotopes usually used in nuclear medicine. A gamma camera consists of a diverging collimator, a CsI(Na) scintillation crystal with dimensions of 50.0mm×50.0mm×6.0mm and Hamamatsu H8500 PSPMT. The diverging collimator is composed of two layers of diverging slats stacked directly above each other, and the front layer is rotated by 90° with respect to the back layer. The point source at different positions was simulated, and the optimal slat thickness and slat height were determined by evaluating the spatial resolution and sensitivity. The slat thickness is 1.0mm, the slat height is 40.0mm and the angle of slats ranges from 0 to 22.5°. The front and back layers are composed of 40 and 18 slats, respectively, to achieve equal spatial resolution in the x and y directions. The diverging collimator improves the uniformity of the spatial resolution and sensitivity across the field of view and the count rate better than the pinhole collimator. Experimental measurements were performed, and the results agreed well with simulations in terms of spatial resolution and sensitivity. The results demonstrated that the two-layer diverging-slat collimator is suitable for large area monitoring of the radiation fields.