DEVELOPMENTS WITH MAXIMUM-LIKELIHOOD X-RAY COMPUTED-TOMOGRAPHY

An approach to the maximum-likelihood estimation of attenuation coefficients in transmission tomography is presented as an extension to earlier theoretical work by Lange and Carson. The reconstruction algorithm is based on the expectation-maximization (EM) algorithm. Several simplifying approximations are introduced which makes the maximization step of the algorithm solvable. Computer simulations are presented using noise-free and Poisson randomized projections. The images obtained with our EM-type method are compared to those reconstructed with the EM method of Lange and Carson and with filtered backprojection. Preliminary results show that there are potential advantages in using the maximum likelihood approaches in situations where a high-contrast object, such as bone, is embedded in low-contrast soft tissue.