Evaluation Of The PETsys TOFPET2 ASIC In Multi-Channel Coincidence Experiments

Aiming to measure the difference in arrival times of two coincident gamma-photons with an accuracy in the order of 200 ps, time-of-flight positron emission tomography (ToF-PET) systems commonly employ silicon-photomultipliers and high-resolution digitization electronics, application specific integrated circuits (ASICs). This work evaluates the performance of the TOFPET2 ASIC released by PETsys Electronics S.A. in 2017 in multi-channel measurements. SiPM arrays fabricated by different vendors (KETEK, SensL, Hamamatsu, Broadcom) were tested in combination with the ASIC. Scintillator arrays featuring different reflector designs, different materials for optical coupling, and different configurations of the ASIC software parameters were evaluated. The benchtop setup used is provided with the TOFPET2 ASIC evaluation kit by PETsys Electronics S.A.. In coincidence experiments, the ASIC shows promising CRTs down to 219.9 ps with two Hamamatsu SiPM arrays (128 channels read out, dE/E 13.08%) and 216.1 ps with two Broadcom SiPM arrays (32 channels read out, dE/E 9.46%). As a side-effect of the dark count suppression scheme, satellite peaks appear in the time difference spectra depending on the configuration of the delay period in the channel trigger circuit. These peaks have been reported by us for prior single-channel experiments and can be reproduced. The length of the trigger delay has an impact on the ASIC performance and can be configured to further improve the CRTs. The integrator gain configuration has been investigated and allows an absolute improvement of the energy resolution by up to 1% at the cost of the linearity of the energy spectrum. Measuring up to the ToF performance of state-of-the-art PET systems while providing a uniform and stable readout for multiple channels at the same time, the TOFPET2 ASIC is treated as promising candidate for the integration in future ToF-PET systems.