A Monte Carlo Simulation Study on Detector Arrangement for a Small Bore DOI-PET Scanner: jPET-RD

We are developing a dedicated small-bore DOI-PET scanner for small animals (jPET-RD). In this paper, we performed Monte Carlo simulations using the GATE (Geant4 Application for Emission Tomography) and investigated the influence of detector arrangement on the imaging and count rate performance. The jPET-RD is based on a large-sized depth-of-interaction (DOI) block detector that consists of a 4-layered array of 32 times 32 LSO crystals (1.4 mm times 1.4 mm times 4.5 mm) and a 256-ch flat panel position-sensitive photomultiplier tube. In this work, three geometries were simulated: two rings of six detector blocks arranged in a hexagonal pattern (FOV 85 mm in diameter), four detector blocks arranged in a tetragonal pattern (FOV 49 mm in diameter) and four detector blocks arranged in an overlapped tetragonal pattern (FOV 38 mm in diameter). Reconstructed images show that the hexagonal scanner has better spatial resolution and resolution uniformity than the other scanners. The resolution performance of the tetragonal scanner declines due to the large inter-detector gaps; however the deterioration of the image quality can be minimized by overlapping each detector. Count rate simulation results show that smaller bore geometry provide higher sensitivity because of its larger solid angle. Although small bore geometry clearly affected the noise equivalent count rate (NECR) due to high detector dead-time, parallel readout with appropriate anode segmentation improved the NECR at 20 MBq by a factor of ~1.4 compared with the non-parallel read out.