Approximate Volumetric System Models for MicroSPECT

A microSPECT system has been developed for the purpose of studying murine models of amyloidosis in vivo. The system is equipped with two detector heads, each consisting of a multi-anode photomultiplier tube coupled to a pixellated NaI(Tl) crystal array. Images are reconstructed using an OS-EM algorithm. In this paper, we describe the associated volumetric system models that we have developed in support of both pinhole and parallel hole collimation. These models, which are precomputed and stored to disk prior to reconstruction, are based on simple inner-product computations and a region-growing like search defined by the conic view that each detector pixel has of the image voxels. We provide illustrative experimental results based on phantom and mouse data