Exact local regions-of-interest reconstruction in spiral cone-beam filtered-backprojection CT: theory

Abstract

A recently published local region-of-interest (ROI) technique makes it possible to image a ROI in a long object in cone beam spiral scans without blurring from the overlaying materials; the local ROIs refer to the portions of the object bounded by the parallel projections of the spiral scan path on the (phi) planes in the Radon space. First, the Radon derivative data for the local ROIs are computed from the cone beam data; second, the local ROIs are reconstructed; and finally the ROI is reconstructed from the local ROIs. For any cone beam image detected near the top and the bottom of the spiral path, the integration line segments are limited in different manners depending on whether the local ROI projects onto the corresponding (phi) plane on the uppermost/lowermost complete stage of the projected spiral or not. In this first part in a series of two papers reformulating the local ROI method into a filtered backprojection (FBP)-based algorithm, the theoretical derivation of the FBP-based local ROI method is presented, and the demanding numerical implementation together with the simulation results are reported in the second paper. We have developed a simple procedure to group line segments for the filtering operation according to the manner they are limited. Furthermore, it is found that the filtering operation on the cone beam images is equivalent to a number of 1D Hilbert transforms followed by 1D differentiation in the projected scan path direction.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.