Timing optimization for digital PET detector module based on FPGA-only MVT digitizers

Nowadays, time-of-flight (TOF) PET detectors and systems are becoming increasingly common since scintillators, photodetectors and electronics has made significant progress. It has been well recognized that TOF PET imaging can increase the image signal-to-noise ratio (SNR) and yield other benefits; and the degree of these enhancements is higher as the timing resolution improves. Previously we have developed a digital PET detector module using 48-channel FPGA-only MVT digitizer board and measured a coincidence resolving time (CRT) of 684ps (FWHM) and an energy resolution of 15% @511KeV. In this work, we investigate to replace our currently used SiPM with SiPMs that exhibit better timing characteristics. Specifically, we consider SensL FB30035 and Excelitas C30742-33-50C. We set a pair of single channel LYSO/SiPM detectors, first connect their output to an oscilloscope for both of SiPMs under test and measure their performance in different bias voltage. The results indicate that the CRT obtained for the SensL FM30035, SensL FB30035 and Excelitas C30742-33-50C-X are, respectively, 464ps, 310ps and 247ps FWHM. Based on these data sampled by oscilloscope, we also simulate the MVT sampling process and evaluate two common pulse model's suitability for both of SiPMs. Then we reconnect the signal from these SiPMs to our upgraded 72-channel MVT digitizer board. Timing resolution of 357ps and 278ps are achieved respectively by FB30035 and C30742.