1. Detectivity and contrast: Robert F. Wagner's theory

In the 1970s-1980s, the scientific community set out to define a figure of merit that would objectively quantify the performance of an X-ray detector. Universally accepted and used, the EQD was the answer to this problem, but it is not sufficient to qualify a complete radiology "system" comprising the detector, the source, etc., but also the radiologist and the patient, for a given modality (mammography, angiography, etc.). Agreeing on an "extended" merit factor has been the focus of a great deal of energy over the past twenty years. Although it is still the subject of debate, and has not yet been introduced in 2015 to qualify commercial products, an answer is emerging quite clearly. QED and MTF remain the ideal factors of merit when it comes to comparing two detectors of the same kind. And for those wishing to quantify the impact of source, detector and image processing, the notions of...