(Monday, 7/30/2018) 1:15 PM - 1:45 PM
Room: Exhibit Hall | Forum 1
Purpose: It has been our experience that grid alignment is not routinely evaluated during digital radiography acceptance testing. However, to achieve the best image quality in radiography, for a given patient dose, the anti-scatter grid needs to be properly aligned. Presented is a case when the grid was misaligned. Discussed are how the misalignment was detected during acceptance testing, how the misalignment was evaluated, and the steps taken to align the grid.
Methods: During acceptance testing of a recently installed radiographic and fluoroscopic room equipped with a wall stand, it was found the grid in the wall stand was not properly aligned. The misalignment was found by evaluating un-processed images of a uniform phantom taken at 40-inch and 72-inch SIDs. The wall stand was equipped with a 10:1 ratio, 130-cm focus distance grid. If the grid was properly aligned, at either of the two SIDs initially evaluated, the image pixel values would be greatest in the center and decrease equally on each side with increasing distance from the grid center. To assess if the grid had a manufacturing defect, images were obtained with grid rotated 180°. To evaluate the misalignment, initially images were taken with the grid center shifted to the left and right of the central ray. Subsequently, an alignment assessment jig, consisting of a Lexan™ plate with radiopaque markings and a BB mounted centrally 15 cm above the plate, was constructed.
Results: Grid defects were ruled out by exposing two images with the grid rotated 180°. The alignment evaluation images indicated that the plane of the grid was tilted ≈3° relative to the central-ray. The wall stand was subsequent rotated ≈3° to align the grid orthogonal to the central-ray.
Conclusion: When acceptance testing digital projection radiography systems, grid alignment should be evaluated, particularly for wall stands.
Keywords
Not Applicable / None Entered.
Taxonomy
IM- X-ray: Grids, scatter reduction
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