Define mAs and its relation to exposure.

• A. mAs = mA × s; controls beam quantity and receptor exposure.
• B. mAs = mA ÷ s; controls beam quality.
• C. mAs = kVp × s; controls receptor sharpness.
• D. mAs = mA × seconds; controls image contrast.

Answer: (A)

The main idea here is that mAs measures the total X-ray tube current over the exposure time and directly sets how many photons reach the image receptor. mAs is defined as milliampere-seconds, calculated by multiplying the tube current (mA) by the exposure time (s). This product controls receptor exposure: higher mAs delivers more photons, giving a darker image with greater receptor exposure; lower mAs reduces photons and lightens the image. The beam’s energy or quality, which affects penetration and contrast, is set by kVp, not by mAs. mAs does not change beam energy or sharpness; it changes how many photons are emitted and thus how much exposure the receptor receives.