Handling of Long Objects in Iterative Improvement of Non-Exact Reconstruction in Helical Cone-Beam CT
2006 (English)In: IEEE Transactions on Medical Imaging, ISSN 0278-0062, Vol. 25, no 7, 935-940 p.Article in journal (Refereed) Published
In medical helical cone-beam CT, it is common that the region-of-interest (ROI) is contained inside the helix cylinder, while the complete object is long and extends outside the top and the bottom of the cylinder. This is the Long Object Problem. Analytical reconstruction methods for helical cone-beam CT have been designed to handle this problem. It has been shown that a moderate amount of over-scanning is sufficient for reconstruction of a certain ROI. The over-scanning projection rays travel both through the ROI as well as outside the ROI. This is unfortunate for iterative methods since it seems impossible to compute accurate values for the projection rays which travel partly inside and partly outside the ROI. Therefore, it seems that the useful ROI will diminish for every iteration step. We propose the following solution to the problem. Firstly, we reconstruct volume regions also outside the ROI. These volume regions will certainly be incompletely reconstructed, but our experimental results show that they serve well for projection generation. This is rather counter-intuitive and contradictory to our initial assumptions. Secondly, we use careful extrapolation and masking of projection data. This is not a general necessity, but needed for the chosen iterative algorithm, which includes rebinning and iterative filtered backprojection. Our idea here was to use an approximate reconstruction method which gives cone-beam artifacts and then improve the reconstructed result by iterative filtered backprojection. The experimental results seem very encouraging. The cone-beam artifacts can indeed be removed. Even voxels close to the boundary of the ROI are as well enhanced by the iterative loop as those in the middle of the ROI.
Place, publisher, year, edition, pages
2006. Vol. 25, no 7, 935-940 p.
Engineering and Technology
IdentifiersURN: urn:nbn:se:liu:diva-37299DOI: 10.1109/TMI.2006.876156Local ID: 34553OAI: oai:DiVA.org:liu-37299DiVA: diva2:258148