Assessment of image quality in dental radiography, part 2 - Optimum exposure conditions for detection of small mass changes in 6 intraoral radiography systems

Objective, The purpose of this study was to compare 2 film systems and seve ral digital intraoral systems with regard to visual image quality through u se of a test phantom developed for this purpose. Study design. The detectors used for digital imaging were as follows: Compu ted Dental Radiography (CDR), Digora, Dixel, and Sens-A-Ray without scintil lator layer Two types of digital images were prepared for the observer perf ormance test: one with original gray scales and another with contrast enhan cement. Images with and without enhancement from the 4 systems were display ed to 7 observers. The change in the average number of perceptible holes wa s plotted against exposure, and modified perceptibility curves were created and compared with curves for the film systems. The exposure level at which the maximum number of holes was perceived was defined to be optimum. The o ptimum exposure levels were determined for each digital system and compared with that of the film systems. At the optimum exposure, the average maximu m numbers of perceptible holes in each digital system with and without cont rast enhancement were compared with the maximum numbers for the film system s. The minimum exposure levels were determined to be those at which the num ber of perceptible holes exceeded the number for film, and the possibility of exposure reduction was evaluated. Results. All digital systems except the Digora system showed lower optimum exposures than E-speed film. In all digital images without enhancement, how ever, the maximum number of perceptible holes was significantly lower than that for the film systems at that exposure. With contrast enhancement, all digital systems except the Sens-A-Ray system showed visibility superior to that of the film systems. With the CDR, Digora, and Dixel systems, exposure s could be further reduced by a considerable amount, with greater retention of information than was associated with film. Conclusions. Our results strongly suggest that digital systems, if properly used, can exceed film systems in the detection of smalt mass changes.