Truncation Correction for Non-horizontal Filter Lines

State-of-the-art filtered backprojection (FBP) algorithms often define the filtering operation to be performed along non-horizontal filter lines in the detector. For non-horizontal filter lines, a limited scan field of view leads to axially as well as trans-axially truncated projections. In this work, we investigate the influence of axial and trans-axial data truncation on the reconstruction result and present two novel truncation correction methods which effectively handle both types of data truncation. Method 1 is a one-step approach which performs extrapolation along the filter lines to account for axial and trans-axial data truncation simultaneously. Method 2 consists of two steps: the first step handles trans-axial data truncation while axial data truncation is corrected during a modified forward rebinning step. Experiments are presented from simulated data of the FORBILD head phantom. The accurate M-line algorithm is used for reconstruction. Although the discussion is focused on accurate algorithms, the proposed truncation correction methods can be applied to any FBP algorithm.