Is linear response to x-rays suitable for digital dental x-ray imaging systems? —Theoretical and experimental considerations

Abstract

OBJECTIVES:The purpose of this study was to consider theoretically and experimentally the suitability of linear response to x-rays for digital dental x-ray imaging systems. METHODS:Theoretically, the ability of an imaging system to depict images using linear response to x-rays increases as the exposure increases, within the dynamic range of the system. That is, the highest depiction ability is obtained with the highest incident x-rays to an image sensor, within the dynamic range. Image manipulation, such as density and contrast adjustments, cannot compensate for the lack of image information content yielded at other than optimal exposures. In order to substantiate these theoretical considerations, a visual detection test was performed using an acrylic test object. Images of the test object were obtained at various exposures using Computed Dental Radiography (CDR). All images were observed on a CRT display by six oral radiologists. The observers were allowed to adjust the density and contrast of the images in judging the presence of signals. For each image, the detection rates at the different exposures were statistically compared. RESULTS:As considered theoretically, the detection rate significantly increased as the exposure increased, within the dynamic range of the CDR. Namely, detection rates were lower with images obtained at a low or too high exposure than those obtained at the maximal optimal exposure. CONCLUSIONS:In clinical dental radiography, high depiction ability is necessary for highradiopacity structures. Therefore, linear response to x-rays is not suitable for digital dental x-ray imaging systems.