Background: Technical failures and incorrect usage of digital X-ray systems may lead to a decreasing image quality,\nartefacts and a higher dose exposure of staff and patients. Although there are no regulations regarding constancy\ntesting in veterinary radiology all operators are required to avoid unnecessary exposure. The aim of this study was to\ndevelop a reasonably inexpensive zoomorphic 3D-printed test specimen for constancy testing that allows the detection\nof changing image quality by visual analysis.\nPrimarily, a calibration curve of the attenuation factor of the 3D-printing material (ZP150) was determined. MATLAB\nconverted every pixel value of a thorax X-ray image of a Beagle dog into an equivalent thickness of printing material.\nThe thickness distribution was printed using a 3D-printer. This printed test specimen was additionally provided with\nfive thin aluminium discs to simulate lung nodules.\nTo evaluate the usability for constancy testing 12 X-ray images of the test specimen were made. Two images (reference\nand control) were taken with the minimum dose in order to obtain images suitable for diagnosis purposes. Eight\nimages were taken with a dose differing 30-140% from the reference dose by varying current-time product (mAs) or\ntube voltage (kVp). Two images were taken with the same parameters as the reference image but edited with different\nimage processing. Six veterinarians (general practitioners) evaluated ten chosen structures in the X-ray images in\na Visual Grading Analysis and scored the image quality of these structures for every image in comparison to the reference\nimage. A Visual Grading Analysis Score was calculated and statistically analysed.\nResults: A higher current-time product led to a negligibly better evaluation of the X-ray image. The lower the current-\ntime product the worse the X-ray images were scored. Likewise, both increasing and decreasing of the tube\nvoltage led to lower scores.\nConclusions: A zoomorphic test specimen can be used for constancy testing of digital X-ray systems in veterinary\nmedicine. Especially a lower dose can be recognised due to deviation in the image quality when compared to the\nreference image. The 3D-printed test specimen is less expensive than test equipment used in human medicine.
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