Comparison of end/side scintillator readout with digital-SiPM for ToF PET

Side-readout of scintillation light from crystal elements in PET is an alternative to conventional end-readout configurations, with the benefit of being able to provide fine depth-of-interaction (DOI) information and good energy resolution while achieving excellent timing resolution required for time-of-flight PET. In this study, the performance of discrete LYSO scintillation elements read out from the end/side with digital silicon photomultipliers (dSiPM) has been assessed. Compared to 3 × 3 × 20 mm³ LYSO crystals read out from their ends that gave a coincidence resolving time (CRT) of 162 ± 7 ps FWHM and saturated energy spectra, a side-readout configuration achieved an excellent CRT of 144 ± 2 ps FWHM after correcting for timing skews within the dSiPM and an energy resolution of 11.8 ± 0.2% without requiring energy saturation correction. On the other hand, with smaller 3 × 3 × 5 mm³ LYSO crystals that can also be tiled/stacked to provide DOI information, a timing resolution of 134 ± 6 ps was attained but produced highly saturated energy spectra.