Readout electronics and data acquisition of a positron emission tomography time-of-flight detector module with waveform digitizer

A multi-element silicon photomultiplier (SiPM) based time-of-flight (ToF) detector module for positron emission tomography (PET) has been developed. The detector module is based on a 4 \times 4 array of LYSO-SiPM elements (Hamamatsu MPPC S10931-050P), with individual bias supply for each element. Each element is read out by a wideband, low-noise RF amplifier to maximize timing performance. All 16 outputs are digitized with a high-speed CAEN V1742 digitizer module (32 2 channels, 5 GS/s sampling, 12-bit amplitude resolution, 500 MHz input bandwidth) to acquire raw pulse waveforms for offline timing and energy extraction. As the digitizer has no internal trigger for individual channels, a trigger board has been developed which produces a fast pulse that triggers the digitizer whenever any pixel of the detector detects a signal in coincidence with a reference detector. To assess the performance of the prototype module, a 4 \times 4 LYSO scintillator array (3\times 3\times 5\ {\rm mm}³ elements) was coupled to the SiPM photodetectors and energy/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 \pm 0.8% across the 16 channels. With a reference detector (single 3\times 3\times 5\ {\rm mm}³ LYSO crystal coupled to a Hamamatsu MPPC S10362-33), the average coincidence resolving time (CRT) across the detector module was 206 \pm 7 ps FWHM at 2.4 V overvoltage-the best reported for a PET block (array) detector based on conventional photodetectors to date.