[Application of intensigying screens on the basis of rare earths (author's transl)].

Investigations on intensifying screens with rare earths are presented with special regard to clinical application. Speed, gradation (gamma), resolution as well as contrast transfer factor (ctf) are examined and compared with corresponding results of CaWO4 Special Screens. The examined screens on Lanthan and Gadolinium base show a marked kV dependence especially at lower voltage (for instance 40 kV) which is unfavourable. The speed of these screens is lower than that of CaWO4 Special screens. Lanthan screens (MR 400/SE 4 LG 17) intensify twice to three times (MR 600/SE 6) compared with CaWO4 Special Screens. Intensification of the Gadolinium screens is lower except the screen/film combination alpha 8/XM which is only due to the higher speed of the XM film. Resolution and contrast transfer factor are in the range of CaWO4 Special Screens with the exception of the highest intensifying systems MR 600/SE 6 respectively alpha 8/XM with lower resolution and contrast transfer factor. Gradation is nearly the same with CaWO4 Secial Screens. The mottle caused by rare earth screens is due to a.) its own structure and b.) to quantum noise disturbing the image quality. Clinical application is demonstrated with a phantom and further discussed.