Iterative methods for correcting attenuation in positron emission tomography

In this paper, two iterative methods for correcting attenuation errors in positron emission tomography (PET) are proposed. The first method is a maximum likelihood (ML) method that simultaneously estimates the emission intensity and attenuation density. The second one is a least squares (LS) reprojection method, where the survival probabilities are estimated by reprojecting a LS estimate of the attenuation density. Both methods are guaranteed to produce nonnegative estimates of the emission intensity and attenuation density, provided that the initial estimates are nonnegative. From simulation studies, it appears that the proposed methods have less noise and provide higher quality images, particularly for short transmission scans (less than 10 minutes), than the EMML algorithm with standard correction