Improved Spatial Resolution and Resolution Uniformity of Monolithic PET Detector by Optimization of Photon detector Arrangement

Compared to pixelated detector, monolithic detector has better performance in sensitivity, light collection efficiency and cost. In PET detector, photon detector arrangement is of critical importance, which can influence detector performance significantly. In this study, three monolithic PET detector designs with different photon detector arrangement are proposed to improve spatial resolution and resolution uniformity. The PET detector is based on a $21\times 21\times 21 \mathrm {m}\mathrm {m}^{3}$ LYSO crystal and SiPM (SensL MicroFJ-30035). To improve detector performance with a reasonable number of SiPM, we proposed three different photon detector arrangements: Dual Ended (top and bottom: 5x5 array), Flexible Design A (top and bottom: 4x4 array, lateral: 2x2 array) and Flexible Design B (top and bottom: 3x3 array, lateral: 2x4 array). The Single Ended and Six Ended arrangement were also evaluated as reference. The solid angle criterion (SAC) is designed to evaluate spatial performance with less computation amounts, comparing with Cramer-Rao lower bound (CRLB). The Single Ended, Dual Ended and Flexible Design B detectors were realized to be evaluated in the preliminary experiment. The simulation results show that mean CRLB of Dual Ended, Flexible Design A and Flexible Design B are respectively 0.362, 0.363 and 0.325 mm in x/y direction, and 0.316, 0.331 and 0.325 mm in z direction. The SAC shows a strong correlation with CRLB. The preliminary experiment shows the spatial resolution of Flexible Design Bx/y:2.88 mm,z:5.16mm) is best, comparing with Single Ended (x/y:3.21 mm, z:5.88mm) and Dual Ended (x/y:3.05mm, z: 6.23mm). Flexible Design B has best resolution uniformity in both simulation and experiment. In conclusion, the simulation and experiment results proved that spatial performance of monolithic detector can be improved by optimizing the photon detector arrangement. SAC is a good simple evaluation criterion for spatial performance, which need less computation amounts compared with CLRB.