Advanced single-slice rebinning in cone-beam spiral CT: Theoretical considerations and medical applications

The advanced single–slice rebinning algorithm (ASSR) is a highly accurate and efficient approximative algorithm for cone–beam spiral CT that a) yields high image quality even at large cone angles, b) makes use of available 2D backprojection algorithms/hardware and c) allows for sequential data processing. It uses virtual R–planes (reconstruction planes) that are tilted to optimally fit 180 spiral segments. Along these R–planes data of a virtual 2D parallel scanner are synthesized via rebinning from the measured spiral cone–beam data. Reconstruction with 2D filtered backprojection yields the object cross-section in world coordinates (x, y, z(x, y)) which is resampled to Cartesian coordinates (x, y, z) by z–filtering. Geometrical misalignments as well as any arbitrary detector geometry can be easily incorporated in the ASSR algorithm. ASSR, unlike other approximate algorithms, does not show severe cone–beam artifacts when going to larger cone angles. Even for scanners with a high number of detector rows, e.g. 64 rows, a high and isotropic z–resolution is achieved. In–plane resolution is determined by the 2D reconstruction filters which can be chosen as in 2D CT. Even in the case of only M = 4 or M = 8 simultaneously measured slices, ASSR may outperform standard z–interpolation algorithms such as 180MFI. Due to its high efficiency and high image quality ASSR has the potential to be used for medical cone–beam CT.