Use of the OpenPET data acquisition for a strip-line readout TOF PET detector

We have developed a signal multiplexing method for a SiPM-based time-of-flight (TOF) positron emission tomography (PET). In the method, multiple SiPM signals are connected to a single strip-line, and the position of hit SiPM is decoded from the arrival time difference measured at the two ends of a strip-line. Since the position resolution on strip-line is directly proportional to the accuracy of the measured time, a high speed (≥ 1 GSPS) waveform sampling electronics, e.g., Domino Ring Sampler (DRS4), has been used to determine the time stamp of the strip-line signal as precise as possible: e.g., the electronic time resolution of the DRS4 is measured to be 5 ps. Although the DRS4 waveform sampling provides a good timing accuracy, its large latency time required for digitizing samples could be a limiting factor for high count rate operation. Therefore, in an effort to increase the counting performance, we have come up with a new design of the strip-line board that can work with commonly used time-to-digital converters (TDC) with 50-100 ps electronic time resolution, which provide high counting capability. Hamamatsu MPPC 4×4 arrays (S12642-0404PA-50, 3×3 mm
²
area for each) are employed in the new strip-line board; 32 MPPC signals are routed to 4 strip-lines on the board. For verification purpose, we have conducted experimental tests to readout the current strip-line board by using the OpenPET electronics, which is a general purpose data acquisition developed for nuclear medicine research community. In the test, LYSO scintillator arrays (3×3×20 mm
³
each) are coupled to MPPCs on the strip-line board, and the detector is irradiated by a
²²
Na source with 10 μCi activity. The initial results obtained by using OpenPET are very promising: each MPPC on the strip-line is well identified with 1.2 mm FWHM resolution, and 13.0% FWHM of energy resolution for 511 keV gamma. The results are comparable to the ones by using DRS4 waveform sampler running at 2.5 GSPS.