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Proceedings Paper

Cone-beam CT image contrast and attenuation-map linearity improvement (CALI) for brain stereotactic radiosurgery procedures
Author(s): Sayed Masoud Hashemi; Young Lee; Markus Eriksson; Håkan Nordström; James Mainprize; Vladimir Grouza; Christopher Huynh; Arjun Sahgal; William Y. Song; Mark Ruschin
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Paper Abstract

A Contrast and Attenuation–map (CT-number) Linearity Improvement (CALI) framework is proposed for cone-beam CT (CBCT) images used for brain stereotactic radiosurgery (SRS). The proposed framework is used together with our high spatial resolution iterative reconstruction algorithm and is tailored for the Leksell Gamma Knife ICON (Elekta, Stockholm, Sweden). The incorporated CBCT system in ICON facilitates frameless SRS planning and treatment delivery. The ICON employs a half-cone geometry to accommodate the existing treatment couch. This geometry increases the amount of artifacts and together with other physical imperfections causes image inhomogeneity and contrast reduction. Our proposed framework includes a preprocessing step, involving a shading and beam-hardening artifact correction, and a post-processing step to correct the dome/capping artifact caused by the spatial variations in x-ray energy generated by bowtie-filter. Our shading correction algorithm relies solely on the acquired projection images (i.e. no prior information required) and utilizes filtered-back-projection (FBP) reconstructed images to generate a segmented bone and soft-tissue map. Ideal projections are estimated from the segmented images and a smoothed version of the difference between the ideal and measured projections is used in correction. The proposed beam-hardening and dome artifact corrections are segmentation free. The CALI was tested on CatPhan, as well as patient images acquired on the ICON system. The resulting clinical brain images show substantial improvements in soft contrast visibility, revealing structures such as ventricles and lesions which were otherwise un-detectable in FBP-reconstructed images. The linearity of the reconstructed attenuation-map was also improved, resulting in more accurate CT#.

Paper Details

Date Published: 9 March 2017
PDF: 7 pages
Proc. SPIE 10132, Medical Imaging 2017: Physics of Medical Imaging, 1013227 (9 March 2017); doi: 10.1117/12.2250371
Show Author Affiliations
Sayed Masoud Hashemi, Sunnybrook Research Institute (Canada)
Young Lee, Sunnybrook Research Institute (Canada)
Univ. of Toronto (Canada)
Ryerson Univ. (Canada)
Markus Eriksson, Elekta AB (Sweden)
Håkan Nordström, Elekta AB (Sweden)
James Mainprize, Sunnybrook Research Institute (Canada)
Vladimir Grouza, Ryerson Univ. (Canada)
Christopher Huynh, Ryerson Univ. (Canada)
Arjun Sahgal, Sunnybrook Research Institute (Canada)
Univ. of Toronto (Canada)
William Y. Song, Sunnybrook Research Institute (Canada)
Univ. of Toronto (Canada)
Ryerson Univ. (Canada)
Mark Ruschin, Sunnybrook Research Institute (Canada)
Univ. of Toronto (Canada)
Ryerson Univ. (Canada)

Published in SPIE Proceedings Vol. 10132:
Medical Imaging 2017: Physics of Medical Imaging
Thomas G. Flohr; Joseph Y. Lo; Taly Gilat Schmidt, Editor(s)

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