Comparison of simulated and measured coincidence time resolution and energy resolution of scintillation crystals coupled to SiPM device

Abstract Scintillating crystal coupled to a silicon photomultiplier SiPM is a typical detection solution in many modern radionuclide imaging systems such as positron emission tomography (PET). Coincidence time resolution ( CTR ) and energy resolution ( ER ) are two key performance parameters in the field of time-of-flight PET (ToF-PET). Both CTR and ER are system level parameters related to crystal choice dimension, speed and noise of the read-out electronics, calibration and analysis algorithms, and SiPM performance. In this work, the effect of SiPM photon detection efficiency PDE , single photon time resolution SPTR , and correlated and uncorrelated noise on CTR and ER were studied. For this purpose, analytical calculation and Monte Carlo simulation tools for CTR and ER were developed and tested for the onsemi MicroFJ-60035 SiPM device at different operating bias voltages coupled with LYSO and BGO crystals. The obtained analytical and simulation results were compared with experimental measurements performed with a 22 Na source and 3 × 3 × 3 mm 3 LSYO crystal wrapped in Teflon reflector and coupled to SiPMs using optical grease. Good agreement between measurements, simulation, and analytical calculation was found for ER at all device working range, and the best ER of ∼ 9% for 511 keV photopeak was found for the 3 × 3 × 3 mm 3 LYSO crystal. The CTR was simulated for LYSO crystals with different lengths from 3 mm up to 30 mm and varies from 110 ps (3 mm crystal) up to 170 ps (30 mm crystal). It was compared to experimental measurements performed for 3, 5 and 20 mm crystal length, where CTR was measured from 95 ps (3 mm crystal) up to 140 ps (20 mm crystal). A difference from 5 ps up to 20 ps was found between Monte Carlo simulation and CTR measurements depending on the crystal length. The analytical calculation shows on average ∼ 20 ps worse CTR than experimental measurements. The systematic discrepancy between experimental and simulated CTR values might be related to a difference in light collection efficiency and level of electronics noise used in calculations as well as SiPM PDE angular dependency, while the discrepancy between experimental and analytical CTR might be related to read-out electronics noise which seems to have too high effect on analytical calculation.