[Sharpness of detail and density in film-screen systems]

A study of detail perceptibility and of screens based on rare earths, using different types of films, shows that the intensifying action of these screens has a voltage gradient; however even the lowest intensifications are still above those of CaWO4 special screens. Sharpness of definition is very great at low kV values. There is a rapid drop as the density increases, this drop being due to a "saturation" effect. This effect becomes less and less noticeable at medium and high kV levels. Medichrome film shows a satisfactory visualisation of details even at very high densities. Screens with maximum intensifying effect with films of great sharpness of detail but less sensitivity do not offer any advantage over medium-intensifying screens with medium-sensitive films; this also applies to the required dose.