Influence of crystal material on the performance of the HiRez 3D PET scanner: A Monte-Carlo study

The quest for the ideal inorganic scintillator is still active in PET. The aim of this investigation is to study the imaging performance of a 3D PET system as a function of the crystal when considering the HiRez scanner geometry and its Pico acquisition system. A realistic Monte-Carlo model of the scanner was developed using GATE. The model was tuned to measurements using the NEMA NU2-2001 protocol. Measured energy resolution, time window and energy window were inputs in the simulation, while measured front-end deadtime was introduced externally. Small discrepancies between experiment and simulation were described by relative efficiencies for singles and coincidences. The model was modified by replacing LSO by BGO, GSO, LaBr₃ and CeBr₃, for two different crystal lengths (20 and 30mm). Energy resolution, energy window, time coincidence window and deadtime parameters were adapted in each case. NEC curves were obtained by scaling the experimental HiRez sensitivity for singles and coincidences to the GATE results. The result shows that only the LSO 30 mm case provides superior NEC performance when the axial scanner length is fixed. Considering the HiRez geometry, LSO appears to yield the best imaging performance as measured by peak NEC, due to the combination of high speed and high stopping power.