Readout electronics and data acquisition of a time of flight detector for positron emission tomography

A multi-element silicon photomultiplier (SiPM) based time-of-flight (ToF) block detector module for Positron Emission Tomography (PET) has been developed. The detector module is based on a 4 × 4 array of LYSO-SiPM elements (Hamamatsu MPPC S10931-050P), with individual bias supply and read out by individual wideband RF amplifier to maximize timing performance. Each output is digitized with a channel of the high speed CAEN V1742 (32 channels, 5 GHz sampling, 12-bit amplitude resolution) to acquire the raw waveform and extract relevant information. As the digitizer is unable to trigger on itself, a trigger board to output a fast pulse that triggers the digitizer whenever any pixel of the detector detects a signal, and process coincident events, has also been fabricated. To assess the performance of one of the modules, a 4 × 4 LYSO scintillator array (3 × 3 × 5 mm³ elements) was coupled to the SiPM photodetectors and energy resolution and timing resolution measurements were performed using a Ge-68 source. At 1.4 V overvoltage, the energy resolution, not corrected for saturation effects of the SiPM, varied from a minimum of 10.1 % to a maximum of 13.3 % with an average energy resolution of 11.4 ± 0.8 % across the 16 channels. With a reference detector (single 3 × 3 × 5 mm³ LYSO and Hamamatsu S10362-33), the average coincidence resolving time (CRT) across the detector module (16 pixels) was 211 ± 6 ps FWHM at 2.2 V overvoltage.