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Monte Carlo study of the effects of system geometry and antiscatter grids on cone-beam CT scatter distributions
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Image of FIG. 1.
FIG. 1.

Geometric configurations illustrated to scale with the common elliptical phantom.

Image of FIG. 2.
FIG. 2.

(a) Illustration of the idealized Common Phantom as used in the simulations of the SA, MSK, Head, C-arm, and Linac CBCT. For the Breast configuration (b), the bone inserts were replaced by glandular tissue.

Image of FIG. 3.
FIG. 3.

Total scatter distributions computed with and without variance reduction techniques for the Linac geometry. (a) MC-GPU with variance reduction (Variance Red. ON) with 5 × 10 photon histories. (b) MC-GPU with no variance reduction (Variance Red. OFF) and 10 photon histories. (c) “Gold standard” MC-GPU without variance reduction and 10 photon histories. (d) The relative difference image computed between the distribution obtained with variance reduction (a) and the “gold standard” distribution (c). In each case, the white bar on the colorbar indicates the mean of the respective distributions.

Image of FIG. 4.
FIG. 4.

(a) Scatter-to-primary ratio at the center of the detector versus SDD and ADD for systems without a grid. (b) Reduction in SPR due to an antiscatter grid (10:1 grid ratio). (c) Histogram of deflection angles of scattered photons reaching the detector plane for a projection perpendicular to the major axis of the Common Phantom.

Image of FIG. 5.
FIG. 5.

(i) Axial reconstructions of primary-only projection data for the Common Phantom. (ii) Reconstructions of projections with scatter included in the simulation (without an antiscatter grid). (iii) Reconstructions of primary + scatter projection data with an antiscatter grid.

Image of FIG. 6.
FIG. 6.

(a) Cupping artifact [Eq. (4) ] in reconstructions of the Common Phantom. (b) Reduction in contrast [from Eq. (5) ] in reconstructions of primary + scatter to that in primary-only. (c) SPR in projections of the Common Phantom with and without a grid. Black bars indicate simulations with primary only. Gray bars show simulations with scatter (and no grid). White bars show simulations with scatter and an antiscatter grid. (d) The ratio of CNR with a grid (CNR) to CNR without a grid (CNR) plotted versus SPR for each CBCT configuration at fixed detector exposure. The horizontal dotted line marks CNR ratio equal to one.

Image of FIG. 7.
FIG. 7.

(a) Distribution (in the plane of the detector) of the fraction of total scatter associated with individual scatter components for MSK CBCT. (b) Fraction of various scatter components versus ADD. (c) Grid rejection factor (i.e., fraction of a given scatter component removed from the total) for each component. (d) Gain-corrected magnitude of total scatter, (left vertical axis) and of all three scatter components , , and (right vertical axis). Solid lines: configuration without a grid; dashed lines: configuration with a grid; black lines: total scatter; gray lines: individual scatter components.

Image of FIG. 8.
FIG. 8.

Axial reconstructions of the anatomical phantoms for the CBCT configurations in Table I . (i) Reconstructions of primary-only projection data. (ii) Reconstructions with scatter included (without an antiscatter grid). (iii) Reconstructions with primary + scatter and an antiscatter grid.

Image of FIG. 9.
FIG. 9.

Distributions of primary, total scatter, and individual scatter components at the detector for various scanner configurations and anatomical sites. Primary and total scatter distributions are shown without and with a grid (both for vertical and horizontal grid orientations). Individual scatter components are shown for the horizontal grid orientation only. The mean total scatter magnitude computed across the detector plane is stated above each distribution. The right column displays the SPR (right vertical axis) and (gain-corrected) intensities of each component (left vertical axis) for gridless configurations.


Generic image for table

Nominal geometry and phantoms for the various CBCT configurations.

Generic image for table

MC simulation efficiency ratio ( ) for various combinations of variance reduction techniques.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Monte Carlo study of the effects of system geometry and antiscatter grids on cone-beam CT scatter distributions