With the resultant IEC standard 62494-1 “exposure index of digital X-ray imaging systems,” which provides a unified method to generate an exposure index value, requires users to input a target exposure index (EI_T). This offers the possibility to specify the noise level that is diagnostically appropriate for an examination and indicates a deviation index (DI) value that gives feedback to the user regarding technique and image quality based on signal-to-noise ratio. These are important values in providing feedback in regard to achieving optimal images at a low dose, the EI and DI don’t directly indicate patient dose.
 

“Expected value of the exposure index when exposing the image receptor properly“*

“May depend on the type of detector, the type of examination, on the diagnostic question…“*

*Source: IEC 62492-1 (International Electrotechnical Commission)