Slope detector for determination of the ringing artifact in filtering x-ray images

In order to reduce the grid artifacts, which are caused by using the antiscatter grid in obtaining x-ray digital images, we analyze the effect of applying band-rejection filters (BRFs) in the frequency domain. The property of the grid artifacts is quite different depending on the shape of the object to be recovered in the spatial domain. Furthermore, if the frequency component of the grid artifact is relatively close to that of the object, then simply applying a BRF may seriously distort the object and cause the ringing artifact. In this paper, we propose a hybrid filtering scheme, which can cooperate such different properties in the spatial domain. In order to perform a robust detection of the position of the ringing artifact, we propose the frequency-modulation (FM) model for the extracted signal, which corresponds to a specific grid artifact. An estimation of the position image for the ringing artifact is then conducted based on the slope detection algorithm, which is commonly used as an FM discriminator in the communication area. Numerical result for real x-ray images shows that applying BRFs in the frequency domain in conjunction with the spatial property of the ringing artifact can successfully remove the grid artifact, distorting the object less.