The perceptibility curve test applied to direct digital dental radiography

Objective: To compare the effect of an additional scintillator layer on the psychophysical properties of a CCD detector for digital dental radiography. Methods: Radiographs of a test object containing ten holes of increasing depth were obtained throughout the exposure range of two CCD detectors at 70 and 90 kVp. One was the original detector for the Sens-A-Ray system (Regam Medical Systems, Sundsvall, Sweden) and the other the same detector covered by a scintillator layer. Ten viewers evaluated the radiographs for the number of perceptible holes. From these data and the dose response functions for the two detectors, the minimum perceptible exposure difference was found. The reciprocal values of this parameter were plotted against the logarithm of exposure to create Perceptibility Curves (PCs). Results: The four PCs had essentially the same shape and height. There was a shift to lower exposures in the PCs for the detector covered by a scintillator. Conclusions: The two detectors have essentially the same psychophysical properties. Since the detector covered by a scintillator layer is more sensitive, it should be preferred for clinical practice since the dose to the patient is reduced.