DEVELOPMENTS WITH MAXIMUM-LIKELIHOOD X-RAY COMPUTED-TOMOGRAPHY

An approach to the maximum-likelihood estimation of attenuation coeffi cients in transmission tomography is presented as an extension to earl ier theoretical work by Lange and Carson. The reconstruction algorithm is based on the expectation-maximization (EM) algorithm. Several simp lifying approximations are introduced which makes the maximization ste p of the algorithm solvable. Computer simulations are presented using noise-free and Poisson randomized projections. The images obtained wit h our EM-type method are compared to those reconstructed with the EM m ethod of Lange and Carson and with filtered backprojection. Preliminar y results show that there are potential advantages in using the maximu m likelihood approaches in situations where a high-contrast object, su ch as bone, is embedded in low-contrast soft tissue.