Performance evaluation of local ROI algorithms for exact ROI reconstruction in spiral cone-beam computed tomography

Investigates the performance of exact reconstruction algorithms for spiral cone-beam computed tomography. The authors compare two different approaches of exact algorithms: the first one is the Radon algorithm with explicit calculation of Radon data and subsequent direct inversion, the second approach is a reformulation of the Radon algorithm as a three-dimensional (3-D) filtered backprojection (FBP) method. Both algorithms are able to reconstruct a region of interest (ROI) of a long object by using the local ROI technique. The goal of this study is to identify which algorithm has the better performance with respect to image quality and practicability. The properties of the algorithms are analyzed. Image quality is evaluated regarding artifacts, spatial as well as contrast resolution, and noise properties. The 3-D point spread function (PSF) is examined for violations of isotropy and spatial invariance. In-plane and axial resolutions are derived from the in-plane modulation transfer function (MTF) and the slice sensitivity profile (SSP), respectively. The results show that for the two implementations investigated in this study, the image quality is similar, with a slight advantage of the FBP case. The algorithms yield images almost free of artifacts but with a poor spatial resolution. Regarding practicability, however, the FBP approach seems to be a more convenient and more flexible method because of the sequential processing of the projections and the easy control of image characteristics