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 (CNR_N):
CNR normalized to a Basic Spatial Resolution (SR_b). With magnification CNR is normalized to SR_b^image, with no magnification it is normalized to SR_b^detector.