Highly multiplexed SiPM signal readout for brain-dedicated TOF-DOI PET detectors

Purpose: We investigated the highly multiplexed readout of SiPM signals that are useful in developing braindedicated PET detectors with DOI-capable crystal blocks and large-area SiPM arrays. Methods: The PET detector module used in this study was equipped with a two-layer relative-offset DOI crystal block and a 2 x 2 array of 16-channel SiPMs. The lower crystal-layer consisted of a 14 x 14 array of 1.78 x 1.78 x 8 mm(3) LSO crystals and the upper crystal-layer consisted of a 13 x 13 array of 1.78 x 1.78 x 12 mm(3) LSO crystals. The energy and position information was obtained via signals from the 8 x 8 resistive charge division multiplexing circuit. The timing performance was evaluated with varying multiplexing ratios (i.e. 16:1, 32:1, and 64:1) via first-order analog high-pass filtering. Results: For three different multiplexing schemes, all LSO crystals with two-layer DOI information were clearly resolved and yielded good energy resolutions of 10.5 +/- 1.0% (upper) and 12.1 +/- 1.7% (lower). The 16:1 multiplexing yielded an optimal timing performance with average CRT values of 325 ps FWHM (upper) and 342 ps FWHM (lower); however, the timing performances were maintained almost constant even for 64:1 multiplexing with average CRT values of 336 ps FWHM (upper) and 347 ps FWHM (lower). Conclusions: The highly multiplexed SiPM signal readout via the first-order analog high-pass filtering could be an attractive solution to develop brain-dedicated PET scanners, effectively decreasing the burden of DAQ systems with moderate compromise in terms of TOF and DOI performances.