Optimized Crystal Surface Treatment for Crosshair Light-Sharing TOF-DOI PET Detector

The coincidence resolving time (CRT) and depth-of-interaction (DOI) resolution of PET detectors are affected by the crystal surface treatment and the reflective material, and it is difficult to achieve a balance between their effects. We have developed the crosshair light-sharing (CLS) detector as a high-resolution time-of-flight-DOI detector. The CLS detector uses a three-layered reflective material in a 2-D crystal array to form a loop structure within a pair of crystals, allowing DOI information to be acquired even in the 2-D crystal array. In this study, we investigated the relationship between the crystal surface treatment and the performance of the detector. Three types of LYSO:Ca were used: 1) all crystal surfaces were mechanical polishing (MP); 2) crystals with the one-sided saw-cut surface (1S); and 3) crystals with the two-sided saw-cut surfaces (2Ss). The MP crystals showed the best CRT of 286 ps, but the worst DOI resolution of 7–8 mm. For the 1S crystals, the CRT was slightly degraded to 296 ps, but the DOI resolution of about 5 mm was obtained. For the 2S crystals, the CRT was significantly degraded to 332 ps and the DOI resolution was equivalent to that of the 1S. The crystal array with the 1S showed the best balance.