Which factor directly controls receptor exposure and patient dose during an X-ray exposure?

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

Answer: (B)

The amount of radiation that reaches the image receptor—and the dose the patient receives—comes down to how many x-ray photons the tube produces. That quantity is governed by the tube current and exposure time, expressed as mAs. Doubling mAs doubles the photon output, which increases receptor exposure proportionally and raises the patient’s dose accordingly. Other factors influence different aspects: the focal spot size mainly affects sharpness and the tube’s heat load, not the photon count; collimation narrows the beam to the necessary area, reducing both receptor exposure and patient dose by limiting the irradiated field; and kVp changes the energy of the photons, affecting penetration and image contrast and indirectly influencing dose, but not as directly as mAs does for photon quantity. Therefore, the direct lever for receptor exposure and patient dose is the mAs.