What is the typical role of Automatic Exposure Control (AEC) in DR, and what common errors can degrade image quality?

• A. AEC increases exposure time when signal is reached.
• B. AEC terminates exposure when adequate signal is achieved; errors include misaligned chambers, incorrect chamber selection, and off-center positioning.
• C. AEC reduces patient dose by turning off at start.
• D. AEC calibrates display LUT.

Answer: (B)

Automatic Exposure Control in digital radiography is designed to terminate the exposure once the preset detector signal is reached. This lets the system achieve the desired image density while helping to limit patient dose by avoiding unnecessary exposure.

Problems that commonly degrade image quality arise when the detector chambers aren’t used correctly. If the chambers are misaligned with the beam or anatomy, the system’s signal threshold is based on the wrong area, causing the exposure to end at the wrong moment and producing under- or overexposure. Using the incorrect chamber for a given exam or selecting the wrong chamber can similarly cause inappropriate termination of the exposure, since the chosen detector isn’t representative of the anatomy being imaged. Off-center positioning also yields unrepresentative readings, leading to nonuniform density or mistimed exposure.

These issues are distinct from other functions like adjusting display brightness or lookup tables, which are separate from AEC’s role.