The signal to noise ratio is a ratio of the signal strength to the noise level (the standard deviation of the signal).

(DQA) This procedure is used by system operators to verify an x-ray system, gamma camera, or CT scanner operation based on relevant image quality parameters like e.g., geometric distortion, x-ray yield, signal to noise ratio. The quality assurance should carry out according to instructions of the manufacturer.

See also Acceptance Checking, Calibration and Calibration Factor.