Contrast-to-Noise Ratio (CNR)
The Contrast-to-Noise Ratio is calculated from the ratio of a contrast value (difference of mean grey values of two regions of interest) and the standard deviation of the noise within a region of interest.
Normalized Contrast-to-Noise Ratio (CNRN):
CNR normalized to a Basic Spatial Resolution (SRb). With magnification CNR is normalized to SRbimage, with no magnification it is normalized to SRbdetector.