Automatic exposure control: a primer.

AEC is a radiographic density control device that terminates the exposure when a predetermined amount of radiation has been reached. Newer systems control kVp and mA as well as exposure time. The primary goal of AEC is to produce high-quality radiographs consistently with minimal technical factors set by the radiographer. AEC can be a helpful device, but only if the radiographer understands the principles governing its operation, applies them properly, and knows how to compensate for variations. There are certain decisions that must be made by the radiographer, such as proper sensor selection, appropriate kVp and mA selection, density control adjustment, and correct patient positioning both anatomically and relative to the proper sensor. Quality control procedures must be followed to be certain that the entire imaging chain is functioning properly. Although there are similarities among the various systems, there can be wide variations in their design and operation. If the radiographer appreciates the benefits and limitations of the equipment, many problems can be avoided. Understanding the concepts of minimum response and backup time is important because many of the problems that occur when AEC is used can be traced back to them. Although AEC is not a cure-all, in the hands of a skilled radiographer it can aid in the production of high quality radiographs.