Purpose: To propose a robust, standardized method for x-ray beam alignment testing between the x-ray field, flat panel image receptor (FPIR), and laser (when applicable) in digital radiography and fluoroscopy devices.
Methods: A small test object (e.g., a metallic washer with inner diameter less than 1 cm) should be placed at the center of the image receptor at a known distance. Test object centering shall be evaluated using the smallest possible field-of-view (FOV). After confirming test object centering with the laser, a computed radiography (CR) plate or radiochromic film shall be placed directly on top of the test object to directly capture the x-ray field. Radiographic exposure should be taken using the largest FOV. The center of the x-ray field shall be determined by the intersection of 2 diagonal lines from the corners of the FOV on the image captured by the CR-plate. Misalignment between the laser and FPIR shall be determined by the difference in position between the center of the test object and the intersection of the drawn diagonal lines on the FPIR image. Similarly, misalignment between the laser and x-ray field shall be determined by the difference in position between the center of the test object and the intersection of the drawn diagonal lines on the CR image. The misalignment between the x-ray field and FPIR can then be determined from these two measurements. An example case is shown using a FujiFilm Persona C mobile C-arm fluoroscopy unit.
Results: The center of the x-ray beam, as well as the center of the FPIR, were both measured to be displaced by 5 mm from the center of the laser.
Conclusion: We’ve demonstrated the efficacy of a beam-centering evaluation technique that can be used for all digital radiography and fluoroscopy systems.
Fluoroscopy, Quality Assurance, Quality Control