SPECT reconstruction of combined cone beam and parallel hole collimation with experimental data

Three methods for combining parallel and cone beam (P&CB) SPECT data using modified maximum-likelihood expectation-maximization (ML-EM) algorithms are presented. The first method applies both parallel and cone beam data sets to reconstruct a single intermediate image after each iteration using the ML-EM algorithm. The other two are iterative methods that combine the intermediate parallel beam and cone beam source estimates to enhance the uniformity of images. These two methods are ad hoc methods. These combined collimation methods are qualitatively evaluated using experimental data. Attenuation compensation is performed by including the effects of attenuation in the transition matrix as a multiplicative factor. The results indicate that the combined P&CB approaches suppress artifacts caused by truncated projections and corrects for th distortions of the CB-only images