Experimental evaluation of combined cone beam with parallel hole collimation SPECT data

Three methods of combining parallel and cone beam (P&CB) single photon emission computed tomography (SPECT) data using modified maximum-likelihood-expectation-maximization (ML-EM) algorithms are presented. The first 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 iterative methods combine the intermediate parallel beam (PB) and cone beam (CB) source estimates to enhance the uniformity of images. Earlier studies using computer Monte Carlo simulation indicated that improved images might be obtained by reconstructing combined P&CB SPECT data. In the present work these combined collimation methods are evaluated using experimental data. An attenuation compensation is performed by including the effects of attenuation in the transition matrix as a multiplicative factor. The combined P&CB images are compared with CB-only images, and the results indicate that the combined P&CB approaches suppress artifacts caused by truncated projections and correct for the distortions of the CB-only images.<>