How does automatic exposure control (AEC) determine when to stop the exposure?

• A. Automatically terminating the exposure once optimal exposure is achieved.
• B. Continuously adjusting exposure throughout.
• C. Requires manual confirmation.
• D. Ignores patient attenuation.

Answer: (A)

Automatic exposure control stops the exposure by monitoring the radiation reaching the image receptor and terminating the beam once a preset threshold is reached. A detector behind the patient measures the dose, and when the signal reaches the level configured for that technique, the x-ray unit automatically ends the exposure. Thicker or more attenuating patients take longer to reach that threshold, so the exposure duration adjusts implicitly through the detector signal. A safety backup timer is in place to prevent runaway exposure if the detector signal isn’t reached. This approach means there’s no manual confirmation required, and the exposure isn’t continuously adjusted during the shot.