Attenuation Correction for SPECT: An Evaluation of Hybrid Approaches.

Most methods that have been proposed for attenuation compensation in single-photon emission computed tomography (SPECT) either rely on simplifying assumptions, or use slow iteration to achieve accuracy. Recently, hybrid methods which combine iteration with simple multiplicative correction have been proposed by Chang and by Moore et al. In this study we evaluated these methods using both simulated and real phantom data from a rotating gamma camera. Of special concern were the effects of assuming constant attenuation distributions for correction and of using only 180 degrees of projection data in the reconstructions. Results were compared by means of image contrast, %RMS error, and a chi-square error statistic. Simulations showed the hybrid methods to converge after 1-2 iterations when 360 degrees data were used, less rapidly for 180 degrees data. The Moore method was more accurate than our modified Chang method for 180 degrees data. Phantom data indicated the importance of using an accurate attenuation map for both methods. The speed of convergence of the hybrid algorithms compared to traditional iterative techniques, and their accuracy in reconstructing photon activity, even with 180 degrees data, makes them attractive for use in quantitative analysis of SPECT reconstructions.