A study on the optimal sampling speed of DRS4-based waveform digitizer for time-of-flight positron emission tomography application

High speed wave-form sampling is becoming a more reliable method for TOF PET detector signal readout; event information including precise time are extracted from the digitized waveform in an unified signal processing chain. In this readout approach, the processing of larger data due to higher sampling rate would be the challenging issue. We conducted a study on the optimal waveform sampling speed using DRS4 evaluation board. The experimental setup consisted of two Hamamastu R9800 PMTs coupled with LSO crystals (6.3×6.3×25mm³). ²²Na was used for positron source, and the two PMTs outputs of coincidence event were digitized varying DRS4 sampling rate in 0.7 - 5 giga-samples per second (GS/s). Initial results show that the coincidence time resolution of ~250 ps was measured in 2 - 5 GS/s, and becomes larger at the lower sampling rate.