Attenuation and detector response compensations used with Gibbs prior distributions for maximum a posteriori SPECT reconstruction

The relationship between the choice of parameters for a generalized Gibbs prior for the MAP-EM (maximum a posteriori, expectation maximization) algorithm and the model of the projection/backprojection process used in SPECT (single photon emission computed tomography) reconstruction is studied. A realistic phantom, derived from an X-ray CT study and average Tl-201 uptake distributions in patients, was used. Simulated projection data, including nonuniform attenuation, detector response, scatter, and Poisson noise, were generated. From this data set, reconstructions were created using a MAP-EM technique with a generalized Gibbs prior, which is designed to smooth noise with minimal smoothing of edge information. Reconstructions were performed over several different values of the prior parameters for three projector/backprojector models: one with no compensations at all, one incorporating only nonuniform attenuation compensation, and one incorporating both nonuniform attenuation and detector response compensations. Analysis of several measures of image quality in a region of interest surrounding the myocardium shows that, for each projection model, there is an optimal value of the weighting parameter which decreases as the projection process is modeled more accurately.<>