CT-MAR Reconstruction Using Non-Uniform Fourier Transform

It is well known that metal objects, e.g. hip prostheses or dental fillings, in the field of view of a computer tomography (CT) scanner influence the result of the backprojection. Due to beam hardening and other non-linear effects, star-shaped artifacts appear all over the reconstructed image and may jeopardize a diagnostic interpretation or, at the worst leads to a false diagnosis. By reducing the influence of these objects the quality of the backprojected image can be enhanced and potential misinterpretations can be avoided. The standard CT reconstruction method using filtered backprojection (FBP) is very sensitive to inconsistent Radon data and, therefore, susceptible to metal influenced data. Alternatively to this reconstruction, several direct Fourier methods were proposed, based on the well-known Fourier-slice theorem. By utilizing a nonequispaced Fast Fourier transform (NFFT) applied to arbitrary nodes, a reconstruction can be performed, which delivers comparable results to the FBP. In this paper, a new approach is presented that combines the two image processing steps of a Fourier-based image reconstruction and the reduction of metal-artifacts. Therefor a direct NFFT backprojection method is modified to carry out metal-artifact reduction (MAR) during the reconstruction process in a concurrent step. The results of this novel reconstruction including the artifact reduction are compared to a common artifact-reduction method based on a one dimensional linear interpolation for each column in the Radon space.