Maximum likelihood reconstruction for pinhole SPECT with a displaced center-of-rotation

The authors describe the implementation of a maximum likelihood (ML) algorithm using expectation maximization (EM) for pinhole SPECT with a displaced center-of-rotation. A ray-tracing technique is used in implementing the ML-EM algorithm. The proposed ML-EM algorithm is able to correct the center of rotation displacement which can be characterized by two orthogonal components. The algorithm is tested using experimentally acquired data, and the results demonstrate that the pinhole ML-EM algorithm is able to correct artifacts associated with the center-of-rotation displacement.