Assessment of the influence of crystal material and size on the sensitivity of dual head small animal PET scanner

Introduction: Small animal Positron Emission Tomography (PET) is becoming an essential modality for preclinical research in order to develop molecular medicine strategies. However, any developing on this modality is highly appreciated by research communities. It is well known that optimizing current designs in order to improve sensitivity and resolution of these systems is an active research arena. In this study the influence of crystal size and material on the performance of dual-head coincidence imaging system (DHCI) with pixilated crystal has been evaluated. Methods: The GATE Monte Carlo code used in this study for defining the geometry and photon transport into the crystals. The geometry of the systems was well defined in the GATE for each crystal dimension. Scintillation materials which employed as the crystal materials were BGO and LSO with the pixel size of 1.5:0.5:3 millimeters and assessment considered for two crystal thickness of 10 and 15 mm, moreover for accurate simulation 0.2 millimeters Epoxy as their inter crystal material was considered. The FOV for all crystal dimensions and measurements considered 110 mm and an ideal point source with the activity 27 μCi was placed at the center of FOV. The simulation was performed at the 300-650 keV energy window with the assumption of 25% energy resolution. Results: The sensitivity varies for BGO between % 0.34 and % 0.42 and for the LSO between % 0.19 and % 0.31 when the crystal pixel size increase from 1.5 to 3 millimeters and also by increasing the crystal thickness, the sensitivity of the scanners for all the pixel dimension increased. Conclusion: The simulation illustrated that BGO based scanners have higher sensitivity than equivalent size of LSO based one, and also by increasing the crystal thickness, the sensitivity of the scanners increased, Due to its higher stopping power more annihilated of 511 keV photons were stopped in the crystal. The results indicate that the GATE Monte Carlo code is a useful tool for investigation of system performance in order to design detection system in small animal PET imaging system.