A method to measure the alignment of the x-ray field, image receptor, and displayed image on fluoroscopic systems
Steiner J, Vanderhoek M, and Vaya M. A method to measure the alignment of the x-ray field, image receptor, and displayed image on fluoroscopic systems. J Med Phys 2019; 46(6):e251.
J Med Phys
Purpose: Fluoroscopy system performance evaluation should assess the xray field, image receptor, and displayed image alignment. Moreover, measurement of alignment is a new annual requirement of The Joint Commission (TJC). We developed a simple, efficient method to measure alignment. Methods: 19 fluoroscopy systems were tested by placing a small radiopaque marker at the image receptor center and laying a 1/16' thick lead sheet over the image receptor. 2 radiopaque rulers were placed on the lead sheet along perpendicular axes. An exposure was acquired and short radiochromic film strips were placed on the rulers at the corresponding 4 edge locations of the displayed image. Then, the film strips were exposed for 30 s until they perceptibly darkened. The darkened film strips, displayed radiopaque marker and displayed rulers were used to determine the alignment of x-ray field, image receptor, and displayed image. Rad/fluoro and C-arm systems (fixed, mobile, and mini) with image intensifier and flat panel image receptors were tested. Results: Alignment of the centers and edges of the x-ray field, image receptor, and displayed image were reported as a percent of the SID (%SID). Maximum and mean distances between the edges of x-ray field and displayed image were 1.2%SID (12 mm) and 0.5 ± 0.3%SID, respectively. Maximum and mean distances between the centers of the x-ray field and displayed image were 0.5%SID (3.5 mm) and 0.2 ± 0.1%SID, respectively. Maximum and mean distances between the centers of the image receptor and displayed image were 0.7%SID (7.6 mm) and 0.3 ± 0.2%SID, respectively. Average testing time was 8.8 ± 2.2 min. Conclusion: X-ray field, image receptor, and displayed image alignment was assessed accurately, simply, and efficiently on a wide variety of fluoroscopy systems. This method satisfies the new TJC requirement for annual assessment of alignment. Future work may expand the method to include simultaneous measurement of the kerma area product.