The New Exposure Indicator for Digital Radiography

This article describes the essential elements of the new standardized exposure indicator (EI) established by the International Electrotechnical Commission for digital radiography systems. First, a review of the limitations of the narrow exposure latitude of film screen radiography is presented followed by the brief description of two digital radiography systems, a computed radiography system and a flat-panel digital radiography system. These systems feature wide exposure latitude, variable speed class, and image processing to produce images that appear with the same density regardless of the exposure used and a characteristic EI displayed on images to provide the technologist with some indication of the exposure level to the digital detector. The third point described focussed on the major elements of the standardized EI of the IEC and described them with respect to standardization efforts, deviation index, and the target EI (EI_T), responsibilities of both the manufacturers and users. This new standardized EI is now proportional to the detector exposure and requires the user to establish EI_T values for all examinations in order to ensure optimization of the dose to the patient without compromising the image quality. The values (EI and EI_T) can now be used to calculate the DI, which provides immediate feedback to the technologist as to whether the correct exposure was used for the examination. Finally, an insight into optimization research will be presented as a means of illustration of a dose-image quality optimization strategy that can be used to determine EI_T values objectively.