THE EFFECT OF X-RAY-BEAM ALIGNMENT ON THE PERFORMANCE OF ANTISCATTER GRIDS

While the qualitative effects of grid misalignment are known, we have quantified the effect of different degrees of grid misalignment on ima ge contrast and patient exposure. Radiographs were made of a phantom c onsisting of five lead disks on top of a 15 cm block of lucite. Four 6 0 lines/cm grids, having grid ratios of 3:1, 4:1, 6:1, and 8:1 were us ed. When the tube was angled more than three degrees across the grid l ines, the contrast improvement factor decreased substantially for all four grids, as much as 46% for an 8:1 grid with a 12 degrees misalignm ent. There was a concomitant decrease in film optical density, which i f 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 pa tient exposure to reduce noise. (C) 1996 American Association of Physi cists in Medicine.