Time-of-flight PET detector based on multi-pixel photon counter

Geiger-mode multi-pixel APD is recognized as the best alternative solid-state photo-sensor for vacuum PMTs in various applications. Its magnetic field immunity and high gain have made it popular in MR/PET and high-energy physics detector research. In this paper, we utilized its compactness and high gain in the design of a TOF PET detector. In typical block detectors based on PMT, the full timing capability of both the PMT and scintillator could not be achieved due to the light sharing used in the Anger logic scheme. Since the Geiger-mode APD is a solid-state based technology, we can utilize one-to-one coupling between a scintillator and the photo-sensor to utilize the best timing capability of both. Also, the high photon detection efficiency of MPPC, Geiger mode APD from Hamamatsu, would help improve timing resolution. We made a block detector based on a 4 × 4 array of 3 × 3 mm² MPPC coupled to a 4 × 4 array of 3 × 3 × 25 mm³ LYSO crystals to evaluate its performance. We have achieved an average energy resolution of 9% and 314ps coincidence timing resolution with very good uniformity. This shows that the solid-state based photo-sensor can be used for TOF PET detector. During the development of the detector, we recognized that a compact and low power electronic readout scheme is one of the biggest challenges, including its cost, for MPPC or other Geiger-mode APDs to be realized as products.