Effect of oblique ray on image quality of direct digitized radiography system

Objective: To evaluate the effec on image quality of DDR system caused by oblique ray. Methods: (1) Experiment group: A sphere was taken radiographes repeatedly using DDR system, the respective incidence were vertical (0 degree), 15 degree, 30 degree, 45 degree, and all images were printed into laser films. (2) Comparison group: By way of self comparing, conventional films were radio graphed under all conditions as in experiment group with screen-film system instead of flat-panel detector. (3) To evaluate the edge fog of sphere image, micro-density of image edge. Both groups were measured separately. Results: (1) The image edge fog in both experiment group and comparison group increased along with increase of X-ray incidence, the more large angle was, the more amplitude of image fog was. And the amplitude of experiment group was more distinct while with large incidence. When incidence was 45 degree, the edge fog value of experiment group went up to (0.9240±0.0033) mm, while only (0.4840±0.0033) mm of comparison group contrarily. (2) When projecting with 15 degree inclination of tube, the amplitude of variation of image edge fog in both DDR system and screen-film system had no distinct difference (P>0.05); when the lean angle were 30 degree and 45 degree, it had distinct difference (P<0.05). Conclusion: (1) The image edge fog of DDR system has no distinctly difference from screen-film system and better image gotten while the inclination of tube is vertical or small angle. (2) The amplitude of variation of image edge fog have distinctly difference that it of DDR system is visibly over screen-film system, when the inclination of tube is big, the imaging quality will be affected. (authors)