Sparse SiPM Pixel Arrangement for a TOF-PET Detector Design that Achieves 100 ps Coincidence Time Resolution

Coupling silicon photomultipliers (SiPMs) to the side of a long and narrow scintillation crystal elements offers near-complete light extraction efficiency, independent of 511 keV photon interaction depth, and reduced scintillation light transit time jitter in its path toward the photodetector. With these advantages, significant improvements in PET detector coincidence time resolution (CTR) can be achieved compared to the traditional scintillation light readout configuration where an SiPM is coupled on the narrow end of crystals. Moreover, the arrangement of photosensors along the crystal's side intrinsically provides a 3-D position sensing detector. One consideration for the side readout approach is the increase in the number of SiPMs required to read each crystal element. In this work, we investigate the achievable CTR when the number of SiPM elements coupled to the side of crystals is parametrically varied, including different crystal lengths and reflector configurations. A simulation model for CTR was validated against measurements with 3–20 mm length crystals employing side readout of scintillation light. The validated simulation model was used to parametrically investigate 27 configurations of SiPMs arranged along the side of crystal elements. Reflector and sensor placement was parametrically varied to find configurations that optimize light collection efficiency (LCE), energy resolution, and CTR. One configuration achieved 101 ± 1 ps FWHM CTR, while maintaining high LCE and good energy performance with a 33% reduction in photosensor area.