Contrast to Noise Ratio, written also as CNR, refers to the ability of an imaging modality such as MRI or fluoroscopy to distinguish between various contrasts of an acquired image and the inherent noise in the image. A modern fluoroscope. ...
In MRI, it is defined as: The mri are a fictional alien species in the Faded Sun Trilogy of C.J. Cherryh. ...
CNR = (SA-SB) / noise
where SA and SB are signal intensities for tissues A and B. Noise is usually measured from an ROI (region of interest) in the background, i.e. the measured standard deviation of the ROI. Noise is inherent in the image and arises from the tissue itself. This definition may also apply to other diagnostic imaging modalities in general as well. In probability and statistics, the standard deviation is the most common measure of statistical dispersion. ... Associated with all electronic circuits is noise. ...
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