Simulating the performances of an LSO based position encoding detector for PET

The authors investigated the impact of replacing BGO by lutetium oxyorthosilicate (LSO) in the fabrication of the EXACT HR PLUS position encoding detector for PET. A detailed Monte Carlo simulation was used to track the interactions of energetic photons in the volume of the block as well as to treat the generation and propagation of scintillation light through its geometry. The simulation also accounts for LSO´s non-proportional scintillation response, the bulk attenuation to its own scintillation and the noise contribution from the amplification of photoelectrons in the readout units. The model predicts that the increased photostatistics available in LSO compared to BGO leads to improvements by up to a factor five in the peak-to-valley ratios of the position response of the block to a uniform flood of 511 keV photons. For the crystals located along the diagonal, and considering events in a window of 350 to 650 keV, the position encoding accuracy is found to vary from 69% to 88% representing an absolute gain of at most 8% over its BGO precursor. With peak photoelectron counts of 678 to 2024, the energy resolution of the same crystals is found to vary from 14% to 9%