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

This paper 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 3D filtered backprojection method. Both algorithms are able to reconstruct a region-of-interest (ROI) of a long object by using the local ROI technique. The filtered backprojection approach seems a convenient method since the projections can be processed sequentially. However, no other justified advantage has been pointed out up to now. 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 3D 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