A direct sinogram correction method to reduce metal-related beam-hardening in computed tomography

This paper proposes a direct sinogram correction method that does not require metal segmentation and prior knowledge to reduce metal-related artifacts in polychromatic computerized tomography (CT). The metal-related artifacts, being common in dental conebeam CT images, are caused by beam hardening-induced sinogram inconsistency associated with complicated metal-bone-tissue interactions and other factors including scattering. This paper carefully analyzed artifact-causing factors and developed a direct method for sinogram correction to reduce the mismatch between sinogram data and the mathematical model for CT reconstruction. The proposed method attempts to project the beam-hardening affected data to the range space of the Radon transform so that the mathematical model is more consistent with the corrected data, with keeping a part of data where beam hardening effects are small. We tested the performance of the proposed method in numerical simulations and experiments using dental conebeam CT. The results demonstrate that the proposed method successfully reduces beam-hardening artifacts.