Simulation study of sensitivity and resolution for a small animal PET ring based on continuous crystals

Continuous scintillator crystals can offer several advantages over pixellated crystals. Apart from an increase of the active volume, spatial resolution is not limited to the crystal size and Depth of interaction (DoI) can be estimated from the light distribution. Continuous crystals coupled to finely segmented photodetectors can improve simultaneously spatial resolution and sensitivity, the main two factors to maximize in Positron Emission Tomography (PET). The main drawback is the difficulty in the position estimation within the crystal; thus, accurate position estimation algorithms are needed. However, if the standard cuboid crystals are used in the full ring geometry, there will be large wedge-shaped gaps between detector heads. For maximizing the sensitivity and avoiding data truncation, a scanner based on tapered continuous crystals is considered. In this work, a basic comparison between two scanners of the same dimensions based on tapered and cuboid crystals was performed. The study is focused on the quantification of the increase on sensitivity while first preliminary results were obtained in terms of image quality and spatial resolution, An increase of 14.08% on the average sensitivity was obtained for tapered crystals. Image reconstruction was implemented with Filtered Back-Projection (FBP) method using the ideal position interaction of the annihilation photon within the crystal given by the simulations. An improvement on the recovery of homogeneous regions was observed due to less data truncation using tapered crystal.