Screen optics effects on DQE in digital radiography: Spatial frequency effects

摘要

The effect of screen optics on the spatial-frequency-dependent DQE of digital radiographic systems, expressed as the Lubberts factor L(f), is studied for both isotropic granular and structured columnar (CsI) x-ray screens. Analytical models for L(f) are derived from diffusion theory for isotropic screens, and optical ray tracing methods are also used to obtain depth-dependent line spread functions, MTF's, and Lubberts factors for both isotropic and columnar screens. The theoretical methods are used to investigate the dependence of L(f) on backing reflectance, thickness, x-ray absorption coefficient, and screen type. An experimental method to estimate L(f), in which an electron multiplying charge coupled device (EMCCD) is used to image individual x-ray bursts, is described. Preliminary results are obtained from data on sample screens, and are compared with the theory.