A voxel-driven system matrix design for multipinhole SPECT with overlapping projection

Single pinhole SPECT can provide high-resolution functional imaging of small animals, while multipinhole SPECT can further increase photon sampling and hence improve system sensitivity. In addition, overlapping projection of a multipinhole system can improve the overall usage of detector area, but such a multiplexing detection inevitably leads to image quality deterioration. Since iterative image reconstruction permits the incorporation of physical factors in the form of system matrix, we propose a voxel-based design which explicitly accounts for multipinhole geometry, aperture diameter, and projection overlapping. The proposed voxel-based system matrix can describe not only the entire process of photon emission from its source and through a pinhole (including voxel depth and aperture size), but also identify the pinhole channel which a photon is passing through. In addition, the projection of the central pinhole is circular, while the projections of an off-centered pinhole consists of two half ellipses. The detection probabilities of each voxel through every pinhole can be then derived from the areas of these composite ellipses. Since the areas also depend on the depth of voxel to pinhole and aperture diameter, the voxel-driven model is also depth-dependent and sensitive. We investigate the performance improvement of the proposed model compared to the traditional ray-tracing model. In terms of spatial resolution, the proposed model can achieve a better resolution uniformity through the field of view.