title: Investigation of cone-beam CT image quality trade-off for image-guided radiation therapy.
abstract: It is well-known that projections acquired over an angular range slightly over 180° (so-called short scan) are sufficient for fan-beam reconstruction. However, due to practical imaging conditions (projection data and reconstruction image discretization, physical factors, and data noise), the short-scan reconstructions may have different appearances and properties from the full-scan (scans over 360°) reconstructions. Nevertheless, short-scan configurations have been used in applications such as cone-beam CT (CBCT) for head-neck-cancer image-guided radiation therapy (IGRT) that only requires a small field of view due to the potential reduced imaging time and dose. In this work, we studied the image quality trade-off for full, short, and full/short scan configurations with both conventional filtered-backprojection (FBP) reconstruction and iterative reconstruction algorithms based on total-variation (TV) minimization for head-neck-cancer IGRT. Anthropomorphic and Catphan phantoms were scanned at different exposure levels with a clinical scanner used in IGRT. Both visualization- and numerical-metric-based evaluation studies were performed. The results indicate that the optimal exposure level and number of views are in the middle range for both FBP and TV-based iterative algorithms and the optimization is object-dependent and task-dependent. The optimal view numbers decrease with the total exposure levels for both FBP and TV-based algorithms. The results also indicate there are slight differences between FBP and TV-based iterative algorithms for the image quality trade-off: FBP seems to be more in favor of larger number of views while the TV-based algorithm is more robust to different data conditions (number of views and exposure levels) than the FBP algorithm. The studies can provide a general guideline for image-quality optimization for CBCT used in IGRT and other applications.
authors.affiliation: Department of Radiology, Massachusetts General Hospital & Harvard Medical School, Boston, MA 02114, USA.
authors.forename: Junguo
authors.initials: J
authors.lastname: Bian
authors.forename: Gregory C
authors.initials: GC
authors.lastname: Sharp
authors.forename: Yang-Kyun
authors.initials: YK
authors.lastname: Park
authors.forename: Jinsong
authors.initials: J
authors.lastname: Ouyang
authors.forename: Thomas
authors.initials: T
authors.lastname: Bortfeld
authors.forename: Georges
authors.initials: G
authors.lastname: El Fakhri
mesh_terms: D000465:Algorithms; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000592:standards*; D019047:Phantoms, Imaging; D011785:Quality Assurance, Health Care; D061089:Radiotherapy, Image-Guided / Q000379:methods*