Interior reconstruction using local inverse

Abstract

Truncated projections can arise from a detector with a limited field of view (LFOV). Truncation artifacts can be reduced through extrapolation methods; however the reconstructed images with extrapolation are often over-corrected or under-corrected. Recently, an iterative reconstruction-reprojection algorithm was developed, which incorporated extrapolation with iterative algorithm. It gave the possibility to better reduce truncation artifacts compared to using the extrapolation method alone. This article builds a theoretic foundation for the above iterative reconstruction-reprojection algorithm. The theoretic foundation is suitable to parallel-beam, fan-beam and cone-beam computed tomography(CT). Two assumptions are summarized from the CT system. Then, a truncation-artifact-free solution for the problem of LFOV is derived from these assumptions. The solution contains a "local inverse" of matrix. The local inverse of a matrix is defined using the sub-matrix and its general inverse. The solution can be approximately implemented as the iterative reconstruction-reprojection algorithm which is just the algorithm mentioned above.