6 compares the contrast of the two systems in terms of luminance level. The contrast of the thick parts in the digital system is inferior to that of film. As it is known that the logarithmic response of films in conventional radiography approximately compensate for the exponential attenuation function, equal absorber thickness changes will results in approximately equal brightness changes [21]. As a

majority of the digital systems adopt the linear gray-scale response to radiation exposure, CX-5461 solubility dmso some kind of compensation will be needed for the exponential attenuation function of the X-ray to improve human visual perception with the digital systems [21]. A PC test has shown that appropriate correction for attenuation and visual response increases maximum contrast information content of the system [22]. Standard measurement techniques exist to allow the quantification of the physical properties of the radiographic systems which affect image quality (resolution, contrast and noise) [5]. In addition to this, physical model for human contrast sensitivity has been proposed [23]. Using these methods it is possible to theoretically calculate psychophysical

properties of the radiographic systems from their physical properties. De Belder also presented an expression to predict PCs that gives the probability that an average observer will perceive a certain exposure difference [7]. The following expression for digital radiography can be derived from the original definition selleck chemicals for a PC: equation(3) ((Δlog E)min)−1=γ(ΔG)minwhere γ is the gradient of the dose response function of the imaging system. Using this equation, a simplified method to predict PCs of digital intraoral radiographic systems was developed [24]. γ can be simply calculated from the dose response function and (ΔG)min can be calculated using the physical model for human contrast sensitivity including

the effects of internal and external noises. Since contrast and noise properties of the imaging system are included together with human contrast sensitivity function, psychophysical properties of the imaging system can be calculated by this equation. It clearly shows the close relationship selleck chemical between physical and psychophysical properties. Eqs. (2) and (3) imply that contrast information content can be calculated from some physical properties of the system and physical model for human contrast sensitivity [23]. Thus, the numbers of object details that the observers can perceive are calculated with regard to radiographs of the aluminum step phantom. Fig. 7 shows the correlation between calculated numbers of object details from digital radiographs and actual observer data. The correlation coefficient is remarkably high (r = 0.98). In addition, the inclination of the regression line is approximately 45° indicating that the calculated numbers of object details are very close to the actual observer performance [25].