A comprehensive study on the timing limits of the TOFPET2 ASIC and on approaches for improvements

Novel electronic readout schemes of analog SiPMs have shown impressive timing performance of -detectors in positron emission tomography (PET). However, transfering these novel concepts to system level is key to exploit the improved coincidence time resolution (CTR) in (pre-)clinical imaging. In this study, the commercially available TOFPET2 ASIC from PETsys Electronics S.A. is tested in terms of the best achievable CTR. The measurable CTR limits will be obtained by state-of-the-art high-frequency (HF) readout, minimizing the impact of the electronic front-end on the time resolution. We achieved (73 ± 1) ps with the HF readout and (134 ± 10) ps with the TOFPET2 ASIC for a Ce-, and Cadoped lutetium-oxyorthosilcate (LYSO) crystal of 2×2×3mm3 size. We show that SiPM signal amplification and an effectively reduced TOFPET2 input stage impedance boost the CTR of a 20-mm high LYSO:Ce crystal to (187 ± 8) ps. Our studies also lead to the observation of side peaks in the coincidence time difference spectrum. This peaks are studied in depth and a conclusion on the ASIC for 100-ps PET applications is drawn.