Monte Carlo study of the effects of system geometry and antiscatter grids on cone-beam CT scatter distributions

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dc.contributor.author Sisniega, Alejandro
dc.contributor.author Zbijewski, W.
dc.contributor.author Badal, A.
dc.contributor.author Kyprianou, I.S.
dc.contributor.author Stayman, J.W.
dc.contributor.author Vaquero López, Juan José
dc.contributor.author Siewerdsen, J.H.
dc.date.accessioned 2014-05-21T08:08:05Z
dc.date.available 2014-05-21T08:08:05Z
dc.date.issued 2013-04-25
dc.identifier.bibliographicCitation Medical Physics, Vol. 40, nº 5 (2013), pp. 051915-1 - 051915-19
dc.identifier.issn 0094-2405
dc.identifier.uri http://hdl.handle.net/10016/18887
dc.description.abstract Purpose: The proliferation of cone-beam CT (CBCT) has created interest in performance optimization,with x-ray scatter identifie among the main limitations to image quality. CBCT often contends with elevated scatter, but the wide variety of imaging geometry in different CBCT configuration suggests that not all configuration are affected to the same extent. Graphics processing unit (GPU) accelerated Monte Carlo (MC) simulations are employed over a range of imaging geometries to elucidate the factors governing scatter characteristics, effica y of antiscatter grids, guide system design, and augment development of scatter correction. Methods: A MC x-ray simulator implemented on GPU was accelerated by inclusion of variance reduction techniques (interaction splitting, forced scattering, and forced detection) and extended to include x-ray spectra and analytical models of antiscatter grids and flat-pane detectors. The simulator was applied to small animal (SA), musculoskeletal (MSK) extremity, otolaryngology (Head), breast, interventional C-arm, and on-board (kilovoltage) linear accelerator (Linac) imaging, with an axis-todetector distance (ADD) of 5, 12, 22, 32, 60, and 50 cm, respectively. Each configuratio was modeled with and without an antiscatter grid and with (i) an elliptical cylinder varying 70–280 mm in major axis; and (ii) digital murine and anthropomorphic models. The effects of scatter were evaluated in terms of the angular distribution of scatter incident upon the detector, scatter-to-primary ratio (SPR), artifact magnitude, contrast, contrast-to-noise ratio (CNR), and visual assessment. Results: Variance reduction yielded improvements in MC simulation efficien y ranging from ∼17-fold (for SA CBCT) to ∼35-fold (for Head and C-arm), with the most significan acceleration due to interaction splitting (∼6 to ∼10-fold increase in efficien y). The benefi of a more extended geometry was evident by virtue of a larger air gap—e.g., for a 16 cm diameter object, the SPR reduced from 1.5 for ADD = 12 cm (MSK geometry) to 1.1 for ADD = 22 cm (Head) and to 0.5 for ADD = 60 cm (C-arm). Grid efficien y was higher for configuration with shorter air gap due to a broader angular distribution of scattered photons—e.g., scatter rejection factor ∼0.8 for MSK geometry versus ∼0.65 for C-arm. Grids reduced cupping for all configuration but had limited improvement on scatterinduced streaks and resulted in a loss of CNR for the SA, Breast, and C-arm. Relative contribution of forward-directed scatter increased with a grid (e.g., Rayleigh scatter fraction increasing from ∼0.15 without a grid to ∼0.25 with a grid for the MSK configuration) resulting in scatter distributions with greater spatial variation (the form of which depended on grid orientation). Conclusions: A fast MC simulator combining GPU acceleration with variance reduction provided a systematic examination of a range of CBCT configuration in relation to scatter, highlighting the magnitude and spatial uniformity of individual scatter components, illustrating tradeoffs in CNR and artifacts and identifying the system geometries for which grids are more beneficia (e.g., MSK) from those in which an extended geometry is the better defense (e.g., C-arm head imaging). Compact geometries with an antiscatter grid challenge assumptions of slowly varying scatter distributions due to increased contribution of Rayleigh scatter.
dc.description.sponsorship The research was supported by academic-industry partnership with Carestream Health Inc. (Rochester, NY) and National Institutes of Health (NIH) Grant No. 2R01-CA-112163. A. Sisniega is supported by FPU grant (Spanish Ministry of Education), AMIT project, RECAVA-RETIC Network, Project Nos. TEC2010-21619- C04-01, TEC2011-28972-C02-01, and PI11/00616 (Spanish Ministry of Science and Education), ARTEMIS program (Comunidad de Madrid), and PreDiCT-TB partnership.
dc.format.mimetype application/pdf
dc.language.iso eng
dc.publisher American Association of Physicists in Medicine
dc.rights © 2013 American Association of Physicists in Medicine
dc.subject.other Cone-beam CT
dc.subject.other X-ray scatter
dc.subject.other Antiscatter grid
dc.subject.other Image quality
dc.subject.other Monte Carlo
dc.subject.other GPU
dc.subject.other Flat-panel detectors
dc.subject.other Computed-Tomography
dc.subject.other Breast CT
dc.subject.other Micro-CT
dc.subject.other Digital radiography
dc.subject.other Coherent scattering
dc.subject.other Radiation-Therapy
dc.subject.other Photon transport
dc.title Monte Carlo study of the effects of system geometry and antiscatter grids on cone-beam CT scatter distributions
dc.type article
dc.description.status Publicado
dc.relation.publisherversion http://dx.doi.org/10.1118/1.4801895
dc.subject.eciencia Biología y Biomedicina
dc.identifier.doi 10.1118/1.4801895
dc.rights.accessRights openAccess
dc.relation.projectID Comunidad de Madrid. S2009/DPI-1802/ARTEMIS
dc.relation.projectID Gobierno de España. TEC2010-21619-C04-01
dc.relation.projectID Gobierno de España. TEC2011-28972-C02-01
dc.relation.projectID Gobierno de España. PI11/00616
dc.type.version acceptedVersion
dc.identifier.publicationissue 5 (051915)
dc.identifier.publicationtitle Medical physics
dc.identifier.publicationvolume 40
dc.identifier.uxxi AR/0000013298
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