The actual kVp and mA settings used by ABC systems dictate the contrast displayed in fluoroscopic images as well as the dose to the patient. However, images with increased electronic noise generally result. When the power limit is reached, in fluoroscopy of the lateral abdomen or at steep-angled cardiac projections, for instance, further adjustment of exposure factors is no longer possible and the Automatic Gain Control (AGC) circuitry can come into play to maintain image brightness. Such mA adjustment within the kVp range of the ABC is limited by the power rating of the XRT. The tube current (mA) can also be adjusted automatically during this process.
The minimum kVp can be used at the start of an exposure sequence, for instance, to prevent low energy X-rays exposing the patient unnecessary, and is then increased automatically so that a pre-determined image brightness level is reached.
This can be achieved using a small photosensor at the XII output, for instance, which monitors the central portion of intensified images and feeds a signal back to the generator to adjust the kVp, the mA (or both) accordingly.ĪBC systems are generally designed to operate between minimum (e.g. It involves the adjustment of the kV and mA automatically depending on the part of the anatomy being examined. ABC is similar to radiography AEC mode except it is adjusted on the spot film device.ĪBC is used to keep the brightness of the displayed image at a constant level during examinations.
Automatic Brightness Control is the automatic adjustment of the exposure factors such as mA and kVp.