What feature of the image intensifier ensures that the radiation dose striking the input phosphor is constant?

The feature that ensures a constant radiation dose striking the input phosphor of the image intensifier is the automatic brightness control (ABC). This system automatically adjusts the exposure factors in order to maintain consistent image brightness despite variations in the amount of radiation being emitted by the source or changes in patient anatomy.

When a radiographic procedure is performed, various factors—such as the patient's thickness, density, or position—can alter the amount of radiation that reaches the image intensifier. The automatic brightness control responds to these changes by adjusting the tube current and/or exposure time, thereby keeping the radiation reaching the input phosphor at a near-constant level. This not only helps to optimize image quality but also minimizes the patient’s radiation dose, ensuring greater safety without compromising diagnostic value.

Other options do not serve the same purpose. For instance, a digital dosimeter measures radiation but does not actively control or adjust the radiation dose. Chromatic aberration refers to a lens defect that results in color distortion and is unrelated to radiation dose management. Similarly, collimator accuracy pertains to how well the beam is confined and shaped, influencing exposure but not directly maintaining a constant dose at the input phosphor. Thus, the automatic brightness control is the key feature that ensures the radiation