Perceptibility curves for the Digora system

To construct perceptibility curves (PCs) for given calibration settings in order to define psychophysical properties of the Digora storage phosphor system and to evaluate the effects of automatic exposure correction (AEC) on the PCs.

The Digora system was calibrated at two exposures, 80 microC kg(-1) (high calibration) and 40 microC kg(-1) (low calibration). Since the grey levels displayed in the radiographs are adjusted by AEC, dose-response functions at high calibration were obtained using AEC on and off modes. The dose-response function at low calibration was obtained with AEC off. The PC at each experimental setting was calculated using known physical parameters of the system and the performance of the average observer used in a previous study. In addition, PCs were also constructed using transmitted radiation flux behind the test object calculated from the attenuation coefficient in order to study observer and system performance. PCs obtained under these conditions were compared.

The PC using calculated transmitted radiation flux behind the test object showed a wide plateau at the peak owing to AEC, while the PC obtained by a modified approach showed a higher but narrower peak. There were no differences between the two PCs using AEC on and off modes when the PCs were constructed using a modified approach. There were no differences between the two PCs obtained at high and low calibration settings or between the three PCs obtained with AEC on except for the position along the exposure axis.

Psychophysical properties of the Digora system may be determined if we employ registered exposures from a dose-response function with AEC off under a given calibration setting. Under these circumstances the shape and height of the PCs will be unchanged irrespective of the AEC mode.