Which component of the AEC system measures the quantity of photons exiting the patient?

The ionization chamber is the component of the Automatic Exposure Control (AEC) system that measures the quantity of photons exiting the patient. When X-rays pass through the patient, they enter the ionization chamber, which is filled with a gas. As photons exit the patient and enter the chamber, they ionize the gas, creating charged particles. This ionization leads to a measurable electrical signal, which is proportional to the number of photons detected.

This signal is then used by the AEC system to determine when the appropriate amount of radiation has been delivered to achieve a diagnostic image. Upon reaching the preset level of exposure, the AEC circuit sends a signal to terminate the X-ray production, preventing overexposure to the patient and ensuring optimal image quality.

The other components mentioned serve different functions within the X-ray system. The rectifier bridge converts alternating current to direct current, while the autotransformer adjusts the voltage supplied to the X-ray tube. The exposure timer, although related to the exposure process, is not responsible for measuring photon quantity but rather for controlling the duration of the exposure. Therefore, understanding the role of each component clarifies why the ionization chamber is the correct choice in this context.