Psychophysical properties of different imaging systems, such as analogue and digital systems, can be

quantitatively compared with the PCs [11]. Psychophysical properties of the digital intraoral systems have been shown to be superior to those of intraoral films. The main disadvantage of the PC test is that resolution of the imaging system cannot be evaluated with this method. With regard to resolution, digital systems are inferior to analogue films. Simplified version of the PC has also been used to compare different imaging systems [12], [13] and [14] or the effect of different viewing conditions [15]. This approach can be used to evaluate observer performance if the experimental conditions are exactly the same when the comparison is made. Psychophysical property cannot be evaluated with this simplified version since a simple change of the tube potential will easily affect the results [8]. As described above a RG7420 concentration test object used to construct PCs is usually a homogeneous block. An aluminum step phantom with small holes may be used to simulate the clinical radiation contrast range (Fig. 4) [16]. Using this phantom, differences in image quality could be quantitatively evaluated according to the number of visible holes in the radiographs [17]. In contrast to superior psychophysical properties of the digital systems, observer performance

to detect low contrast details in digital systems is inferior to Everolimus that in films in its original displayed image. Such inferior performance was improved by contrast enhancement, since inherent psychophysical properties of the digital systems are superior to those of films [17]. Human perception of all stimuli follows a non-linear relationship between the magnitude stimulus and the perceived Phosphoglycerate kinase one. As the psychophysical phase includes “image store”, “image display”, and “image perception”, displayed images should be presented to the observer in the manner that each change in digital driving level of the display yields a perceptually equal step in perceived brightness by the human observer. This perceptual linearlization plays a significant role in medical image presentation [18]

and a display function standard is proposed to minimize the mismatches between hard and soft copy presentation and to maintain standardized performance [19]. DICOM “grayscale standard display function” (GSDF) is proposed to be used by all imaging systems [20]. By exploiting the GSDF on all parts of the imaging chain, the same contrast impression on every monitor device can be obtained. In addition to perceptual linearlization, compensation for the exponential attenuation function of the X-ray in the object is significant. Fig. 5 shows two radiographs of the step phantom obtained with film and with a digital intraoral system. It is clear that radiographic contrast obtained with the digital system is completely different from that obtained with film.