Automatic Exposure Control

Abstract

Automatic exposure control systems are now readily available and are widely used in radiography. Their use certainly alleviates many of the problems associated with the choice of exposure factors but unfortunately introduces new problems not apparent with manual exposure selection. Several devices are available but basically only two methods are used, phototiming and ionization timing. Phototiming is used for automatic exposure control for both large and small film formats while ionization timing is used exclusively for the large film format. An automatic exposure system may be sophisticated enough to allow virtually complete automation of exposure selection or, as is more widely available, may control mAs automatically while allowing the operator freedom of choice of kV. The eventual aim, however, is to produce a constant image density independent of patient parameters, and with an automatic exposure system very careful technique is required to achieve this.