[Image quality parameters of film-screen systems]

The image quality in radiology is to a large extent determined by three measurable parameters of screen-film systems: the H-D curve, the modulation transfer function and the Wiener spectrum. Measuring methods of the three parameters are described and results are presented. It turns out that the modulation transfer function is correlated to the visual sharpness and the Wiener spectrum is correlated to the visual impression of graininess. The combination of the three parameters to a single image quality criterion in the form of the detective quantum efficiency (DQE) demonstrates that the DQE is not a generally valid quality criterion for high sharpness and low graininess.