Optics Optimization for a Solid State Gamma Camera Detector Module

The aim of this study is to optimize optics design parameters for a solid state gamma camera detector module. The design parameter includes surface treatments, crystal size, energy threshold effect, light pipe thickness, and fill factor for sensor packing. The solid state gamma camera detector module proposed in this study was consisted of hexagonally packed 72 silicon drift diodes (SDDs) and a single slap of NaI(Tl) crystal with a light pipe that was optically coupled with SDD sensors. Cramer-Rao (CR) lower bound analysis was conducted to optimize optics parameters. Monte Carlo simulation using DETECT2000 was performed to generate necessary data for the CR bound analysis. The preliminary study showed that white reflector (reflection coefficient = 0.9) on the side surface improved the light collection efficiency (LCE) by 84% compared to that of black paint case (reflection coefficient = 0.1) while the spatial resolution was less sensitive to the side surface treatment. The result also suggested no light pipe for the best spatial resolution performance. However, for the mechanical support and encapsulation of the NaI(Tl) scintillator, 2 mm thick light pipe found to be the candidate for the module. The intrinsic spatial resolution with 2% energy threshold was 0.8 mm in FWHM at the useful field-of-view. The results conclude that the scintillation crystal designed in this study was optimum at 106 mm times 112.6 mm size with white reflector side surface and 2 mm light pipe thickness.