Comparison of low-contrast detail detectability with five different conventional and digital radiographic imaging systems

Five different X-ray imaging systems were evaluated comparatively with respect to few-contrast detail detectability. The systems included in this study were two screen-film systems (speed classes 200 and 400), a computed radiography system, a digital selenium-based system with electrometer scanning and an indirect-type flat-panel detector system. Images of a contrast-detail phantom were acquired with all systems at a set of exactly matched exposures, The digital images were processed in a way to approximate the density and contrast appearance of the conventional Afm images when printed on laser film. Six observers evaluated a total number of 46 films with respect to the threshold contrast for each detail size. Correct observation ratios and threshold contrasts were determined for all sizes and conditions. The overall results show that the low-contrast detectability with all digital imaging systems is equal to or better than that with the conventional film-screen systems. The advantage is more evident for the newer digital systems (selenium detector and flat-panel detector) where as the CR images are more on a par with the conventional films. The results can be understood assuming that low-contrast detection is limited mainly by quantum noise in the images and taking into account the different levels of detective quantum efficiency of these imaging systems.