Abstract: In this paper, variable pitch helical cone-beam CT is studied. We
prove a sufficient condition for the existence of PI-lines inside this variable
pitch helix. Under this condition, we propose a new scanning configuration,
called a spring scan, which can be used to scan a cylindrical object support.
Based on Zou and Pan's BPF algorithm, we develop an exact BPF-type
reconstruction algorithm for helical cone-beam CT in which the pitch of the
helix varies with rotation angles. The algorithm includes four steps and can be
used in region-of-interest (ROI) reconstruction by the PI-line determination
step without a rebinning procedure as other BPF algorithms. Moreover, the
algorithm can exactly reconstruct the object image only using the projection
data within the Tam-Danielsson window, while Katsevich's algorithm requires
more data than it. Furthermore, we test the proposed algorithm using the 3D
Shepp-Logan phantom by a spring scan. The numerical results are described to
support the correctness of the algorithm.
Keywords: Backprojection-filtration, cone-beam, image reconstruction, spring scan, PI-line
