Abstract
Scatter is a significant source of image artifacts in wide-cone CT. Scatter management includes both scatter rejection and
scatter correction. The common scatter rejection approach is to use an anti-scatter grid (ASG). Conventional CT
scanners (with detector coverage not exceeding 40mm along the patient axis) typically employ one-dimensional (1D)
ASGs. Such grids are quite effective for small cone angles. For larger cone angles, however, simply increasing the
aspect ratio of a 1D ASG is not sufficient. In addition, a 1D ASG offers no scatter rejection along the patient axis. To
ensure adequate image quality in wide-cone CT, a two-dimensional (2D) ASG is needed.
In this work, we measured the amount of scatter and the degree of image artifacts typically attributable to scatter for four
prototype 2D ASG designs, and we compared those to a 1D ASG. The scatter was measured in terms of the scatter-toprimary
ratio (SPR). The cupping and ghosting artifacts were assessed through quantitative metrics.
For the 2D ASGs, when compared to the 1D ASG, the SPR decreased by up to 66% and 75% for 35cm water and 48cm
polyethylene, respectively, phantoms, at 80-160mm apertures (referenced to isocenter), as measured by the pinhole
method. As measured by the two-aperture method, the SPR reduction was 59%-68% at isocenter for the 35cm water
phantom at 160mm aperture. The cupping artifact was decreased by up to ~80%. The ghosting artifact was reduced as
well. The results of the evaluation clearly demonstrate the advantage of using a 2D ASG for wide-cone CT.
