Signal-to-noise ratio (radiography)
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Signal-to-noise ratio (SNR) is a generic term which, in radiology, is a measure of true signal (i.e. reflecting actual anatomy) to noise (e.g. random quantum mottle). A lower signal-to-noise ratio generally results in a grainy appearance to images.
In radiography, the signal-to-noise ratio, and thus the apparent noisiness of the image, is proportional to the amount of contrast and the square root of the number of photons transmitted. Measures to increase the number of photons, such as increasing the mAs (tube current-exposure time product), therefore increase the signal-to-noise ratio. Contrast can be increased by administering contrast material or lowering the photon energy by reducing the kVp (tube potential).