Silicon photomultiplier-based detector array for TOF PET

Time-of-Flight (ToF) information in PET can contribute to a significant improvement in the reconstructed image signal to noise ratio, enabling image contrast improvement, a reduction in patient radiation dose, and/or shorter scan times. In this study, we propose a multi-element LYSO-SiPM (Silicon photomultiplier) detector architecture with individual readout to enhance time resolution performance. Two 4 × 4 SiPM detector modules were fabricated by tiling individual 3×3 mm² SiPM elements (Hamamatsu MPPC S10931-050P). Each 4×4 array is read out with two edge-on preamplifier boards, each hosting 8 wideband 2 GHz bandwidth RF amplifiers. The temperature of each detector module is regulated by a Peltier cooler and all 32 SiPMs are individually biased through a 32 channel bias supply board. To assess the performance of these modules, 4×4 LYSO scintillator arrays (3.97 × 3.97 × 5 mm³ and 3.97 × 3.97 × 20 mm³) were coupled with optical grease to the detector modules. The detectors were operated in coincidence and their raw signals were digitized by a high speed oscilloscope. Measurements were performed for linearity, energy and coincidence time resolution by irradiating the detectors with a Ge-68 source. A coincidence timing resolution of ~290 ps (FWHM) was obtained with the 5 mm length crystals and ~400 ps (FWHM) with the 20 mm length crystals for a pair of detector pixel in coincidence with a pixel pair. These results are attributed to the scintillator-SiPM active area size mismatch resulting in more than 40% light lost at that interface. A better size match will significantly improve timing performance of the detector modules.