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 × 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 × 4 LYSO scintillator array ( 3×3×5 mm³ 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 ± 0.8% across the 16 channels. With a reference detector (single 3×3×5 mm³ LYSO crystal coupled to a Hamamatsu MPPC S10362-33), the average coincidence resolving time (CRT) across the detector module was 206 ± 7 ps FWHM at 2.4 V overvoltage-the best reported for a PET block (array) detector based on conventional photodetectors to date.