Crystal surface and reflector optimization for the SiPM-based dual-ended readout TOF-DOI PET detector

Silicon photomultipliers (SiPMs) are now widely used for positron emission tomography (PET) applications because of their high gain and low noise characteristics. The PET image quality has been improved with the advancement of time-of-flight (TOF) and depth-of-interaction (DOI) measurement techniques. For brain-dedicated PET systems, both TOF and DOI information are beneficial for enhancing the reconstructed PET image quality. In a previous study, we proposed SiPM-based dual-ended readout PET detectors that used a mean time method to achieve coincidence timing resolution (CTR) of 349 ps and DOI resolution of 2.9 mm. However, the coincidence timing resolution (CTR) was worse than 300 ps since the crystal surface and the reflector type were not optimized. This study aimed at investigating the optimal crystal surface treatment and the reflector material to achieve a sub-200 ps CTR and sub-3 mm DOI resolution with a dual-ended readout PET detector using an LYSO crystal (2.9 × 2.9 × 20 mm³). The scintillation light inside the LYSO crystal was read out by two SiPMs using the dual-ended readout method. The CTR and DOI resolution were measured with two different crystal surfaces (polished and saw-cut) and three different reflector material scenarios of ESR without grease (i.e., air coupling), ESR with optical grease and Teflon. We digitized the timing and energy signals by using a V775N TDC module (35 ps bit^-1) and V965 QDC module, respectively. The combination of the saw-cut LYSO crystal and the ESR with air coupling resulted in the best CTR (188 ± 32 ps) and DOI resolution (2.9 ± 0.2 mm) with the dual-ended readout configuration. We concluded the dual-ended readout method in combination with the saw-cut crystal and the ESR reflector with air coupling can provide a sub-200 ps CTR and sub-3.0 mm DOI resolution simultaneously.