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WE‐E‐201B‐04: Parameterization of Scatter Dependent Artifacts in Cone‐Beam CT
Author(s) -
Mail N,
Moseley D,
Jaffray D
Publication year - 2010
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3469450
Subject(s) - image quality , cone beam computed tomography , nuclear medicine , cone beam ct , imaging phantom , optics , image guided radiation therapy , physics , contrast (vision) , medical imaging , artificial intelligence , computer science , image (mathematics) , medicine , computed tomography , radiology
Purpose : X‐ray scatter limits image quality in cone‐beam CT (CBCT), resulting in shading/cupping and skin‐line artifacts, lack of CT number accuracy and reduction in contrast‐to‐noise ratio. In this manuscript, seven metrics of image performance are defined and used to quantify the influence of x‐ray scatter on image quality in a commercial kV CBCT unit used in image‐guided radiation therapy. The dependence on axial FOVz (SI), bowtie compensation, and object shape are examined. The results provide a quantitative framework for assessing physical and computational methods of improving CBCT image quality. Method : Catphan‐600 with and without NEMA‐shaped jacket was imaged at five different FOVz (2–27 cm, SI) to examine the scatter influence on a CBCT equipped radiotherapy unit. CBCT images were acquired with and without the bowtie filter and all scatter corrections were disabled. Seven metrics were examined: (i) m shading , (ii) m skinline , (iii) m lag , (iv) m noise , (v) m CNR , (vi) m CT# , and (vii) m linearity . These were quantitatively analyzed using Matlab‐2008. Results : Increasing the FOVz from 2 to 27 cm significantly reduces image quality in all 7 metrics, m shading exceeded 30%; m skinline (10 mm depth) was increased from 15 to 26% (without bowtie) and was more stable (−5.9% and 6.5%) with the use of the bowtie. m lag was 10.5% and m CNR was reduced by a factor of ∼2 between 2 and 27 cm FOVz. CT numbers (m CT# ) improved in accuracy as FOV was decreased. Conclusion : Quantitative evaluation in phantoms demonstrates significant artifacts with increasing FOV. Bowtie study's led to reduction in shading/cupping and skin‐line, as well as improvement in CNR and CT number accuracy. These improvements will lead to benefits in detection low contrast accuracy, and support initiatives in online and adaptive radiotherapy. Cone‐beam CT can be applied for adaptive planning with improved image quality using proper scatter correction.