Performance Measurements of the SAFIR Prototype Detector With the STiC ASIC Readout

The small animal fast insert for mRi (SAFIR) positron emission tomography insert was proposed for quantitative dynamic acquisition inside a preclinical 7T magnetic resonance imaging scanner to study kinetics of short-lived tracers. For this purpose, the SAFIR readout should be capable of handling high count rates and achieving excellent timing performance. We evaluated one of the available application specific integrated circuits (ASICs) for SiPM readout, namely SiPM timing chip (STiC) version 3.1. In this paper, we show the performances of the SAFIR PET detector with the STiC ASIC readout. The SAFIR PET detector consists of an 8 x 8 array of lutetium yttrium oxyorthosilicate 2.1 mm x 2.1 mm x 12 mm crystals coupled, with optical grease, to an 8 x 8 array of SiPMs with a 2.0 mm x 2.0 mm photo-sensitive area. Signals from the individual SiPM channels were digitized by the STiC ASIC. Hit's arrival time and time-over-threshold (TOT) were recorded into time stamps with 50.2-ps least significant bit. We obtained an average energy resolution of 18.5% full width at half maximum (FWHM) at 511-keV photopeak after TOT nonlinearity correction and an average coincidence resolving time resolution of 244-ps FWHM with time walk correction that satisfy our requirements specification on the detector performance.