Exposure Factors and Image Contrast

Receptor Exposure and mAs

Receptor exposure is the amount of radiation that reaches the digital detector. Its primary controlling factor is mAs, the product of tube current (mA) and exposure time in seconds. mAs sets the number of x-ray photons, the beam quantity, and the relationship is directly proportional: doubling the mAs doubles the photons, the receptor exposure and the patient dose. In digital imaging the monitor brightness does not show whether the mAs was right, because processing rescales every image to a standard brightness. The exposure indicator is the radiographer's check on receptor exposure.