Scintillation Detector Timing Resolution; A Study by Ray Tracing Software

Abstract

Time-of-flight positron emission tomography requires high timing resolution. In this paper, we determined the influence of scintillation properties on the detector timing resolution for crystals with non-negligible optical transit timespread. In addition to intrinsic scintillation properties, such as the light yield, decay time constant, and scintillation rise time, we also studied the relation between the timing resolution and extrinsic scintillation properties, such as the dimensions of the crystal, the absorption probability of the reflector, the dwell time of photons inside the reflector during the reflection process, and the crystal polish. For this purpose, we developed ray-tracing software. The crystals simulated in this paper are LSO:Ce, LYSO:Ce, LSO:Ce,0.2%Ca, LYSO:0.11%Ce,0.2%Mg, and LYSO:0.2%Ce,0.2%Ca, with dimensions $3 \times 3 \times 5~\hbox{mm}^3$ , $3 \times 3 \times 10~\hbox{mm}^3$ , $3 \times 3 \times 20~\hbox{mm}^3$ , and $4 \times 4 \times 22~\hbox{mm}^3$ . We furthermore studied the optical transit timespread of photons inside polished and etched crystals, which explains the differences in timing resolution.