A Monte Carlo study of high resolution PET with granulated dual layer detectors

New arrays of Avalanche Photodiodes (APD) allow the design of novel highly granulated detector modules. Monte Carlo simulations were used to evaluate to what extent this feature can be used for high resolution, high sensitivity PET. Based on a fixed crystal front face of 2 mm² and a fixed number of crystals, sensitivity and scatter fraction for three different geometries were determined: (a) Ring with 143 mm diameter; (b) Ring with only 71 mm diameter but double the axial extent (37 mm); (c) Ring with 71 mm diameter and two radial crystal layers. The sensitivity (a:b:c) was 0.3%:1.1%:1.5% for a line source in air. Studies using a simple mouse-like phantom showed the highest scatter fraction for (b) and comparable sensitivities for (b) and (c). The large diameter of (a) reduced the scatter fraction at the expenses of high sensitivity losses. Line source simulations showed a resolution of about 1.6 mm for (c) at the center for the field of view (FOV). Within a region of 20 mm within the FOV, the resolution of (c) remained close to 2 mm. Geometry (c) is being implemented in the new tomograph MADPET