Sensitivity and Count Rate Performance of Small Bore DOI-PET Scanners Using

Depth-of-Interaction (DOI) detectors, which can improve resolution uniformity in the field-of-view (FOV), enable high sensitivity PET scanners with small bore detector rings. We are developing a small bore PET scanner dedicated for small animals or mammography. We have proposed a DOI detector which consists of a four-layer array of 32x32 crystals (1.44mm x 1.44mm x 4.5mm) and a 256ch flat panel position sensitive photomultiplier tube (FP-PS-PMT). The FP-PS-PMT has a large effective area of 49mmx49mm and multi anodes of 16x16ch, which can be read out in parallel. In this work, we simulated following three geometries based on this detector blocks using GATE (Geant4 Application for Tomographic Emission): two rings of (A) six detector blocks arranged in a hexagonal shape (85mm diameter FOV), (B) four detector blocks arranged in a tetragonal shape (49mm diameter FOV) and (C) in overlapped tetragonal shape (38mm diameter FOV). The axial FOV for two rings of detectors is 99mm. The aim of overlapped detector arrangement in geometry C is to reduce inter-module gaps and achieve higher sensitivity. The absolute sensitivity of geometry A, B and C with non-parallel readout were approximately 19%, 23% and 29%, respectively (400-600keV). Maximum noise equivalent count rate (NECR) of geometry A, B and C at the same condition were also 1250kcps, 920 kcps and 1060kcps, respectively. The decrease of the maximum NECR was caused by dead-time effect. By using an appropriate anode segmentation of the FP-PS-PMT, the maximum NECR was improved by factors of 1.7 for all geometries. Simulation results show that small bore PET geometry improves scanner sensitivity while it affects count rate performance, and parallel readout with appropriate anode segmentation improves count rate performance drastically.World Congress on Medical Physics and Biomedical Engineering 200