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Proceedings Paper

High-contrast object localization and removal in cone-beam CT
Author(s): D. J. Moseley; J. H. Siewerdsen; D. A. Jaffray
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Paper Abstract

In image-guided procedures high-contrast objects often appear in the imaging field-of-view for the purpose of guiding treatment (e.g., markers intended to localize the target) or delivering treatment (e.g., surgical tools, or in the case of brachytherapy, radioactive seeds). In cone-beam CT reconstructions, these high-contrast objects cause severe streak artifacts, CT number inaccuracy and loss of soft-tissue visibility. We have developed an iterative approach by which high-contrast objects are localized in the 2-D projection set by re-projecting conspicuities from the first-pass 3-D reconstruction. The projection operator, which finds the unique mapping from the world coordinate system to the detector coordinate system for each view angle, is computed from a geometric calibration of the system. In each projection, a two-dimensional 2nd order Taylor series is used to interpolate over the high-contrast objects. The interpolated surface is further modified using a local noise estimate to completely mask the objects. The algorithm has been applied to remove artifacts resulting from a small number of gold fiducial markers in patients being imaged daily with cone-beam CT for guidance of prostate radiotherapy. The algorithm has also been applied to post-operative images of a prostate brachytherapy patient in which the number of seeds can exceed ~100. In each case, the method provides excellent attenuation of image artifact and restoration of soft-tissue visibility. Using a local voxel based metric it was shown that the 2nd order Taylor series with added noise performed best at removing the high-contrast objects from the reconstruction volume.

Paper Details

Date Published: 20 April 2005
PDF: 11 pages
Proc. SPIE 5745, Medical Imaging 2005: Physics of Medical Imaging, (20 April 2005); doi: 10.1117/12.595766
Show Author Affiliations
D. J. Moseley, Princess Margaret Hospital (Canada)
J. H. Siewerdsen, Princess Margaret Hospital (Canada)
Univ. of Toronto (Canada)
D. A. Jaffray, Princess Margaret Hospital (Canada)
Univ. of Toronto (Canada)

Published in SPIE Proceedings Vol. 5745:
Medical Imaging 2005: Physics of Medical Imaging
Michael J. Flynn, Editor(s)

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