Studies of the high rate coincidence timing response of the STiC and TOFPET ASICs for the SAFIR PET scanner

The proposed SAFIR PET detector will measure positron electron annihilations at injected activities up to 500MBq in a mouse or rat. The system is required to have the best possible timing resolution in order to remove accidental coincidences (randoms) and maximise the image quality for short time frames allowing the possibility of 4-D kinetic modelling of simultaneous PET and MRI for the first time. Two different ASICs, TOFPET and STiC, have been investigated with LYSO crystal scintillators coupled to SiPM detectors and using F-18 sources up to 480MBq. Timing responses are very encouraging with a coincidence time resolution of similar to 100 ps measured at low activities, degrading to 130 ps at the foreseen scanner maximum event rate. Sensitivities for single event rates and coincidences are measured and compared with Geant4 Monte Carlo simulations.