Radiographic screen with improved resolution

Abstract

A conventional x-ray screen-film system includes a phosphor intensifying screen 'sandwich', including a backing layer facing the x-rays, the phosphor layer itself, and a so-called 'overlayer' adjacent the photographic film. X-rays passing through the backing cause scintillations within the phosphor, emitting light photons which, in turn, pass through the overlayer, a small air gap (caused by lack of perfect optical contact of the overlayer and the adjacent surface of the film) and into the film so as to form a latent image on the photographic film. The present change involves making the overlayer partially light absorbing so that those light photons which, for example, have been totally internally reflected at the overlayer to air gap surface, returned into the phosphor and then scattered out again through the overlayer, will be absorbed to a much larger extent than those light photons which travel more or less directly from their point of origin through the overlayer into the film, since the indirectly transmitted photons will travel through the overlayer at least three half-trips (at least two of which will be at a substantial angle and therefore through a relatively long path). This selective absorption of the long-path light photons substantially increases the resolution of the screen-film system without adversely affecting the signal-to-noise ratio (in particular, the quantum mottle).