LAUSR

Abstract The aim of this study was to characterize SNR transfer ability of a digital radiographic system for patient equivalent thicknesses that cover a wide range of clinical examinations Detector MTF, NNPS and DQE measured for different beam qualities using IEC methodology. These measurements were repeated with the grid but aluminum filters of the RQA beam quality were replaced with PMMA slabs of 5, 10, 15, 20 and 25 cm thicknesses. The effects of focus unsharpness were investigated by repeating these measurements with these slabs and positioning the edge phantom at the patient input plane, without the presence of scattering material. eDQE was evaluated for different thicknesses of PMMA slabs using standard and different MTF measurement method. A large region of interest was used to form the edge spread function (ESF), thus including the influence of scattered radiation on the MTF curve; this was termed MTFsys. The system DQE was calculated using MTFsys and abbreviated as modified eDQE (eDQEmod) and compared to the standard method of eDQE. The effect of scatter on the system SNR characteristics is a low spatial frequency effect, while focus unsharpness becomes the main degrading signal transfer factor at higher spatial frequencies. Reasonable agreement was found between modified eDQE (eDQEmod) and eDQE that calculated with standard method for all beam qualities. Inclusion of scattered radiation in the MTF measurement, rather than explicit measurement of scatter fraction (SF) is a quick and reasonably accurate means of estimating the eDQE.