Streak artifact reduction in helical cone beam CT with redundancy weighting

Redundant data weighting in helical CT affects reconstruction accuracy, susceptibility to motion artifacts and noise. Cone beam weighting (CBW) is used in helical CT with wide cone angle to reduce cone beam artifact and also improve detector utilization and reduce image noise. Earlier proposed approaches usually consider a case when reconstruction view range is less than one rotation (1-PI). However, most practical settings in clinical helical CT use between one and two rotations view range for each reconstructed slice. In this case CBW weighting can be extended to N-PI case. With N ≥ 2 streak artifacts are caused by singularity of the CBW function at Z-positions near the image plane. Note that in this case image plane projects to a small fraction of detector row; and the non-linear form of CBW weight cannot be accurately determined for all image pixels, which causes inaccuracies in CBW weighting that manifests itself in form of streak artifacts. We show that artifacts can be successfully removed by applying upsampling in the segment direction. By making the upsampling adaptive to the view Z-position, numerical performance of the proposed approach can be optimized. Evaluation shows that artifact is completely removed by the proposed approach.