Preliminary Investigation to Improve Point Spread Function Modeling for a Multi-Pinhole SPECT Camera

Herein we report on the mathematical modeling of the simulated point spread functions (PSFs) of pinhole apertures for clinical I-123 DaTscan imaging on a dual-head SPECT system consisting of fan and multi-pinhole (MPH) collimators on separate heads. The PSFs can be measured sparsely by translating a point source within the volume of interest (VOI). These PSFs were generated using GATE Monte Carlo simulation software and were then modeled using standard 2D Gaussian having 6 parameters, and three other models using higher order polynomial terms as well as cross terms in the exponential. The goal is to efficiently store the parameters of the modeled PSF, measured across the VOI and then interpolate them on the fly during reconstruction. It has been shown that MPH reconstruction can be improved with accurate modeling of the PSF. However, for our application it has been determined that improved accuracy in PSF modeling (reduced NRMSE) can be obtained by incorporating more polynomial terms in the exponential than employed by the standard 2D Gaussian, especially with increased pinhole angulations. In this paper we introduce higher order polynomial terms (degree 3 and 4) as an extension to the Gaussian model and observe that these added terms could significantly reduce the NRMSE.