1. A method of detecting the non-uniformity of radiation detectors participating in a detector inventory test, the method comprising: subjecting each of the detectors in an inventory of detectors to a substantially identical flat field exposure in a series of separate radiation exposures for each of the detectors individually to generate a radiation image in each of the detectors, generating for each of the detectors a number of ROI signals representing the radiation image at a predefined number of regions of interest (ROIs), generating ROI signal ratios by expressing the ROI signals relative to a reference ROI signal detected in one of the regions of interest taken as reference region of interest for each of the detectors, averaging the corresponding ROI signal ratios over the detectors in the inventory of detectors participating in the inventory test to extract the non-uniform characteristics of the radiation exposure, calculating the local deviations of the ROI signal ratios expressed relative to the corresponding inventory average ROI signal ratios for the detectors participating in the detector inventory test, and calculating the absolute value of the largest of the deviations from the average ROI signal ratios for each individual detector in the inventory of detectors.