Performance tests of TOF PET detectors with a strip-line based readout

We are developing a time-of-flight (TOF) positron emission tomography (PET) scanner for brain imaging using SiPMs. In our development, we have adopted a strip-line based signal multiplexing method for efficient channel reduction for SiPMs; the method is using a single strip-line on which multiple SiPMs are connected for sharing readout, and the position of hit SiPM is decoded from the arrival time difference measured at the two ends of the strip-line. We have conducted experimental tests for evaluating the performance of the detectors based on the strip-line signal readout. Hamamatsu MPPC array (S12642-0404PA-50, 3.2 mm pitch) is employed in the detector module; 32 MPPC signals from two MPPCs arrays are routed to 4 strip-lines on the current strip-line board. For the tests, two detectors are used in a coincidence setup, and an array of 4×4 LYSO scintillator (3×3×20 mm
³
, 3.2 mm pitch) is coupled to the MPPC array in each detector. A
²²
Na source with 3 μCi activity is used, and the waveform of the detectors signals are collected by using a Domino Ring Sampler (DRS4) evaluation board running at 2.5 giga sampling rate. The preliminary results show that the position on the strip-line is determined with ~1.0 mm precision from the measured differential time on the strip-line. The average energy and coincidence time resolution are measured to be ~13% FWHM and ~726 ps FWHM, respectively, at 511 keV photo-peak. A systematic investigation of the effects of strip-line on detector performance is carried out in parallel by using a specially designed strip-line board. The test results is presented in the paper.