title: The effect of x-ray beam alignment on the performance of antiscatter grids.
abstract: While the qualitative effects of grid misalignment are known, we have quantified the effect of different degrees of grid misalignment on image contrast and patient exposure. Radiographs were made of a phantom consisting of five lead disks on top of a 15 cm block of lucite. Four 60 lines/cm grids, having grid ratios of 3:1, 4:1, 6:1, and 8:1 were used. When the tube was angled more than three degrees across the grid lines, the contrast improvement factor decreased substantially for all four grids, as much as 46% for an 8:1 grid with a 12 degrees misalignment. There was a concomitant decrease in film optical density, which if compensated for by an increase in patient exposure, would lead to a higher effective bucky factor. With the exception of the 3:1 grid, if the grid is misaligned by more than 6 degrees, higher signal-to-noise ratios can be attained by removing the grid and using the increased patient exposure to reduce noise.
authors.affiliation: Kurt Rossmann Laboratories for Radiologic Image Research, Department of Radiology, University of Chicago, Illinois 60637, USA.
authors.forename: M D
authors.initials: MD
authors.lastname: Carlin
authors.forename: R M
authors.initials: RM
authors.lastname: Nishikawa
authors.forename: H
authors.initials: H
authors.lastname: MacMahon
authors.forename: K
authors.initials: K
authors.lastname: Doi
mesh_terms: D003102:Colloids; D006801:Humans; D007854:Lead; D020366:Methylmethacrylate; D008768:Methylmethacrylates; D019047:Phantoms, Imaging; D011859:Radiography / Q000295:instrumentation* / Q000379:methods; D012542:Scattering, Radiation; D014965:X-Rays
chemical_list: D003102:Colloids; D008768:Methylmethacrylates; D020366:Methylmethacrylate; D007854:Lead