Fast and Efficient Artifact Correction for CT Reconstruction

Computed tomography (CT) reconstruction is a highly studied field in image processing that aims to reconstruct 3D images from radiographic projections. In industrial CT in particular, datasets are of substantially higher resolution than in conventional medical applications and the metrological accuracy of computed results is of great importance. This leads to high demands towards the computational performance of reconstruction algorithms. It also imposes a need to compensate for an abundance of artifacts that are introduced when not accounting for physical effects that play a role during the ac- quisition of projections. In this dissertation, we present several techniques that combat such artifacts in CT reconstruction.

Firstly, we devise a method for reducing or eliminating stair artifacts that occur when polygonizing surface meshes from voxel grids that have been reconstructed using CT. We employ the ability of the commonly used filtered backprojection technique to reconstruct infinitesimal voxels at arbitrary positions of the volume, and use it to circumvent the interpolation sub-voxel data that leads to the stair artifacts in the polygonization.

Additionally, we seek to reduce ring artifacts in reconstructed volumes. These artifacts stem from incorrect normalization of detector screen pixels and particularly affects voxels near the axis of rotation in circular scans. We seek to reduce those artifacts by physically correctly modelling the flat-field errors that lead to the emergence of the artifacts. Simultaneously, we demonstrate a computationally efficient way to implement our method in an existing CT reconstruction pipeline.

Finally, the challenge of compensating for geometric calibration errors is addressed. In the case of truncated projections, we develop and evaluate methods for calibration correction with limited or no data redundancy. We consider and examine both methods that operate in projection domain as well as ones operating in image domain.