Exposure, Exposure Tables, Automatic Density Control

Abstract

In order to obtain a radiograph a certain quantity of energy is necessary which, after penetrating the object, is still able to act upon the emulsion when it reaches the film. This amount of energy is determined by, among other things, the intensity of the radiation (exposure rate) and the exposure time (as has been previously mentioned, exposure equals the exposure rate x time). The exposure rate is highly dependent on the voltage (kV) applied across the tube and is proportional to the current value in the tube (in mA). Since the exposure time is also proportional to the exposure, the current value and the time are combined to form a product, the milliampere-second product (abbreviated to mAs), and is proportional to the exposure. Since a charge of 1 millicoulomb (1 mC) flows per second with a current of 1 mA, then 1 mAs represents a charge of 0.001 C which is carried by the tube current. kV and mAs are the most important electrical factors that determine the exposure of a film.