The modulation transfer function (MTF) of a radiographic system is often evaluated by measuring the system's edge spread function (ESF) using edge device. However, the numerical differentiation procedure of the traditional slanted edge method amplifies noises in the line spread function (LSF) and limits the accuracy of the MTF measurement at low frequencies. The purpose of this study is to improve the accuracy of low-frequency MTF measurement for digital x-ray imaging systems. An edge spread function (ESF) deconvolution technique was developed for MTF measurement based on the degradation model of slanted edge images. Specifically, symmetric oversampled ESFs were constructed by subtracting a shifted version of the ESF from the original one. For validation, the proposed MTF technique was compared with conventional slanted edge method through computer simulations as well as experiments on two digital radiography systems. The simulation results show that the average errors of the proposed ESF deconvolution technique were 0.11% ± 0.09% and 0.23% ± 0.14%, and they outperformed the conventional edge method (0.64% ± 0.57% and 1.04% ± 0.82% respectively) at low-frequencies. On the experimental edge images, the proposed technique achieved better uncertainty performance than the conventional method. As a result, both computer simulation and experiments have demonstrated that the accuracy of MTF measurement at low frequencies can be improved by using the proposed ESF deconvolution technique.
Keywords: Digital x-ray imaging; deconvolution; edge spread function; modulation transfer function.