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AEC and Technique Charts
AEC controls exposure time only, so the active chamber must sit directly under the anatomy of interest.
How AEC Works
Automatic exposure control (AEC) ends the exposure once the detector has received the right amount of radiation. Most systems use three ionization chambers placed between the patient and the digital detector, just behind the grid: a center chamber and two outer chambers set higher, to the left and right. Radiation leaving the patient ionizes the gas in the selected chambers, and when the collected charge reaches a preset level calibrated to the target receptor exposure, the exposure stops. The AEC therefore controls exposure time and, through it, mAs; the radiographer still sets the kVp, mA, chambers, density and backup time.