Performance for obtaining maximal gain from a program for digital subtraction radiography

The aim of this study was to evaluate the effect on subtraction image quality of number of a) gray shades sampled during camera recording, and b) reference points positioned in the two images to be subtracted. Intraoral radiographs were obtained in each of 12 patients, one at 0 degrees and one at 15 degrees horizontal angulation in a standardized recording procedure. The radiographs were videorecorded twice sampling 1) 160-180 and 2) 200-220 shades of gray. The 0 degrees radiographic image was digitally copied. Subtractions were performed between the identical (0 degrees/0 degrees) and the non-identical (0 degrees/15 degrees) radiographs from both gray shade samples after positioning 5, 10, 15, and 20 reference points, respectively, in each of the images to be subtracted. The standard deviation in the subtraction image histogram was used as the test parameter for image quality. No differences existed between image quality obtained from the radiographs sampled using 160-180 and 200-220 shades of gray (P greater than 0.05). The standard deviation fell continuously, the more reference points were positioned in the images. For the 0 degrees/0 degrees images the difference was statistically significant between the 5 and 10 point images (P = 0.045) while for the 0 degrees/15 degrees images differences existed between 5 and 10 point images (P = 0.077) and the 10 and 15 point images (P = 0.048). The precision of reference point positioning as evaluated in the two identical images was satisfactory, the divergence being on average 1.4 pixels.(ABSTRACT TRUNCATED AT 250 WORDS)