High-performance dual-ended SiPM readout for TOF-PET with BGO and LYSO:Ce

Detection time performance is a key aspect for time-of-flight positron emission tomography. With recent advancement in SiPM technology and fast readout electronics, one limiting factor on timing performance is light transport in the crystal. For high aspect-ratio crystals with single-ended readout, the time information of approximately half the optical photons is severely degraded as they initially travel in the direction opposed to the photodetector. For promptly-emitted Cherenkov photons, the increase of variance of optical path length limits their intrinsic advantage. Low-noise and high-frequency dual-ended SiPM readout can be employed to mitigate the aforementioned challenges and has the potential to combine ultra-fast timing with highest gamma-ray detection efficiency. We have studied the timing properties of cerium-doped lutetium-yttrium-oxyorthosilicate (LYSO:Ce) and bismuth germanate (BGO) in a symmetric dual-ended SiPM readout configuration. A time-based depth-of-interaction correction and a novel adaptive timestamp weighting was used to optimize the timing performance. Coupling 3×3×20 mm³ polished BGO crystals to Broadcom AFBR-S4N44P014M SiPMs a CTR of 234 ± 4 ps FWHM (harmonic average) was obtained for all photopeak events. For same-sized LYSO:Ce crystals, the measured CTR value is 98 ± 2 ps, which is in excellent agreement with analytic calculations on the timing limits considering scintillation properties and modeling of light transport. The results demonstrate significant timing improvement with dual-ended readout, both for Cherenkov photons in BGO and for standard scintillation for enhanced diagnostic accuracy in PET imaging.