The amount of receptor exposure is controlled primarily by:

• A. kVp
• B. Focal spot size
• C. AEC
• D. mAs

Answer: (D)

The quantity of photons reaching the image receptor—the exposure the receptor gets—is determined mainly by mAs, the product of tube current and exposure time. More mA or a longer exposure time produces more x-ray photons, so the receptor is exposed to more radiation and the image appears brighter. kVp governs the energy and penetrability of the photons (beam quality) and thus affects contrast, but it doesn’t set how many photons are produced as directly as mAs does. Focal spot size mainly influences sharpness and heat loading, not the total photon count reaching the receptor. Automatic exposure control can regulate exposures, but the underlying factor that determines receptor exposure is the mAs.