Utilization of Monoenergetic X-Ray Beams to Examine the Properties of Radiographic Intensifying Screens

Monoenergetic x-ray beams, produced by the direct electron excitation of characteristic K x rays in elemental targets, are important for measuring the response of different components of radiologic imaging systems. Previous studies have investigated the energy dependence of the scatter produced as an x-ray beam traverses the object to be radiographed and the efficacy of antiscatter grids in reducing this unwanted component of the image signal. Presently, these beams are being. utilized to examine the image information transfer properties of x-ray intensifying screens conventionally used in screen-film imaging systems. The technique of single photon counting is being employed to determine the relative probability. distribution of the number of optical photons emitted from the screen after absorption of an incident x ray. These data can be, used to determine the average number of light quanta emitted per absorbed x ray. In addition, the shape of these distributions can be used to determine the image information transfer properties of a particular screen. Results of these measurements for a typical calcium tungstate screen and one of the new rare-earth phosphor screens are presented.