Scintillation crystal side-readout with SiPMs for improved time resolution

Time-of-flight (ToF) capabilities can significantly improve the signal-to-noise performance of clinical PET systems. To realize the full benefits of ToF the timing resolution of PET detectors must be as high as possible. End-readout of long thin scintillation crystals with photodetectors is widely employed, but is not optimal for timing measurements due to significant variations in optical photon transit time and path length as a function of interaction depth. The advent of solid-state detectors enables new scintillation light readout geometries. Reading the crystal out from its side face using very thin semiconductor photodetectors gives light photons a much shorter average path length from interaction location to light sensor and thus lower variance in optical photon transport time, while maintaining the crystal packing fraction and high stopping power. This work presents a study of time resolution on scintillation crystals readout from their side-face. Two 3 × 3 × 20 mm LYSO scintillation crystals were coupled to 3 × 3 mm SiPMs (Hamamatsu MMPC) in end-readout and collimated side-readout configurations. Collimated side-readout acquisition showed a FWHM timing resolution of 232 +/− 1 ps compared to 272 +/− 1 ps timing resolution for end-readout. This significant improvement in time resolution shows that side-readout detector geometries using solid-state sensors may lead to significant improvements in PET detector performance.