Development of a SiPM based MR-compatible DOI-TOF-PET detector

We developed a SiPM based MR-compatible DOI-TOF-PET detector. The detector consists of a scintillator block, a light guide, a 64-channels SiPM array, and front-end electronics (FEE) boards. The scintillator block consists of 2.9 mm × 2.9 mm × 20 mm LGSO crystals in a 16 × 16 array containing light reflectors arranged for four-layer DOI encoding by Anger logic calculation. The FEE including a full-custom mixed-signal ASIC was optimized for SiPM readout and TOF capability. 64-SiPM channels are segmented into four-blocks (16-ch/block) and a trigger signal is generated in each block for reducing degradation of timing resolution caused by dark counts. The ASIC consists of 16-readout channels, 16-DAC channels, an Anger type position encoder, a fast summing amplifier for timing signals, and a slow summing amplifier for energy signals. The readout channel is connected to AC-coupling to the anode of the SiPM and is composed of a fast voltage amplifier (>200 MHz), a slow voltage amplifier (shaper), and an offset controller. A two-dimensional position histogram, which was obtained under uniform irradiation from a 22Na point source, showed that all crystal positions, including DOI direction, were clearly identified and an energy resolution of 13.4 % was achieved. A timing histogram obtained from a quarter block (16-ch) of the developed detector in coincidence with a PMT based detector showed that a timing resolution of 495 ps is expected in the actual system. Based on the developed detectors, we are now developing an MR-compatible DOI-TOF-PET system.