Affiliations: [a] School of Precision Instrument and Optoelectronics Engineering, Tianjin University, Tianjin, China | [b] Center for Bioengineering and School of Electrical and Computer Engineering, University of Oklahoma, Norman, OK, USA | [c] Tianjin Key Laboratory of Biomedical Detecting Techniques and Instruments, Tianjin, China
Correspondence:
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Corresponding author: Hong Liu, Center for Bioengineering and School of Electrical and Computer Engineering, University of Oklahoma, Norman, OK 73019, USA. E-mail:liu@ou.edu
Abstract: 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, edge spread function, modulation transfer function, deconvolution
