Computation of detective quantum efficiency of medical x-ray radiographic screen-films

Abstract

Detective quantum efficiency (DQE) is one of the important measures in the assessment of image quality and detector performance. Detective quantum efficiency of radiographic screen-film depends on noise power spectrum (NPS), modulation transfer function (MTF), gamma of the film and photon fluence. DQE of two types of screenfilms namely Lanex Regular/T-Mat G/RA and Lanex Regular/T-Mat L/RA were determined using MTF and NPS data, separately. For calculation of gamma of the film, characteristic curves of each screen-film were used to find slope of straight part of the curves. Photon fluence was estimated using published literature. DQE of the screenfilms were computed by MATLAB program for three optical densities 0.7, 1.0 and 1.4. The X-ray source was at 81 kVP. MTF of Lanex Regular/T-Mat G/RA was found to be slightly better than Lanex Regular/T-Mat L/RA for spatial frequencies between 0.5 and 3.0, but it was found to be slightly better MTF for Lanex Regular/T-Mat L/RA for spatial frequencies between 5.2 and 7.0. NPS of Lanex Regular/TMat G/RA was found one and a half times bigger than Lanex Regular/T-Mat L/RA. DQE comparison of these two types of screen-films was made. The results show Lanex Regular/T-Mat G/RA has better DQE than Lanex Regular/T-Mat L/RA, at low frequencies.