Combined fan/parallel beam reconstruction in cardiac SPECT imaging

With three-headed SPECT systems, two heads can aquire truncation-free emission images with parallel-beam (PB) collimators, while the third head acquires transmission images through a fan-beam (FB) collimator. The FB collimator can also be used for emission imaging. Combining FB and PB emission data from the 3 heads, offers the potential for improved sensitivity with the trade-off being truncation artifacts. In this work, the authors investigate 3 methods to combine fan and parallel beam (F&PB) reconstructions. The first approach uses a PB estimate as a prior for the regularized AB-EMML algorithm to reduce truncation in the FB reconstruction. The second approach combines the parallel and re-sorted FB projections and reconstructs a composite image. The third method is based on the work of Jasczak el al. (Phys. Med. Biol., vol. 37, p. 535-48, 1992) where the intermediate F&PB reconstructions are combined to reduce the truncation artifacts inherent In FB imaging. MCAT simulation results indicate that the combined F&PB reconstructions provide decreased image noise while greatly limiting the truncation artifacts inherent in FB imaging.