EXPOSURE DOSE INDEX BASED ON NOISE FACTOR ANALYSIS IN DIGITAL MAMMOGRAPHY: VERIFICATION USING DIRECT-TYPE FLAT-PANEL DETECTOR SYSTEM

In this study, the development of a reasonable index of optimized exposure dose is attempted. Using a direct-type flat-panel system, noise factors contained in the image are analyzed based on the relative standard deviation method, and it is verified that the proposed index conforms with the appropriate standards regarding minimum exposure dose. The findings indicate that Poisson noise is dominant in the general clinical dose range; this noise fraction formed 90% of the total noise in the system considered in this study. Considering the results of previous surveys, it is estimated that the point at which the content rate of the Poisson noise starts to decrease can be considered as the lower limit, below which the dose cannot be reduced further without compromising on image quality. As the 'index' obtained by this method can be easily measured, it is useful as a quantitative indicator for dose determination and optimization.