Department of Electronics Engineering, Hankuk University of Foreign Studies, Gyeonggi-do 449-791, South Korea.
Med Phys. 2013 Jun;40(6):061905. doi: 10.1118/1.4807085.
Grid artifacts are caused when using the antiscatter grid in obtaining digital x-ray images. In this paper, research on grid artifact reduction techniques is conducted especially for the direct detectors, which are based on amorphous selenium.
In order to analyze and reduce the grid artifacts, the authors consider a multiplicative grid image model and propose a homomorphic filtering technique. For minimal damage due to filters, which are used to suppress the grid artifacts, rotated grids with respect to the sampling direction are employed, and min-max optimization problems for searching optimal grid frequencies and angles for given sampling frequencies are established. The authors then propose algorithms for the grid artifact reduction based on the band-stop filters as well as low-pass filters.
The proposed algorithms are experimentally tested for digital x-ray images, which are obtained from direct detectors with the rotated grids, and are compared with other algorithms. It is shown that the proposed algorithms can successfully reduce the grid artifacts for direct detectors.
By employing the homomorphic filtering technique, the authors can considerably suppress the strong grid artifacts with relatively narrow-bandwidth filters compared to the normal filtering case. Using rotated grids also significantly reduces the ringing artifact. Furthermore, for specific grid frequencies and angles, the authors can use simple homomorphic low-pass filters in the spatial domain, and thus alleviate the grid artifacts with very low implementation complexity.
在获取数字 X 射线图像时使用散射消除栅格会产生栅格伪影。本文针对基于非晶硒的直接探测器，研究了栅格伪影减少技术。
为了分析和减少栅格伪影，作者考虑了一种乘法栅格图像模型，并提出了一种同态滤波技术。为了使用于抑制栅格伪影的滤波器造成的损伤最小，使用相对于采样方向旋转的栅格，并建立了用于搜索给定采样频率的最优栅格频率和角度的最小-最大优化问题。然后，作者提出了基于带阻滤波器和低通滤波器的栅格伪影减少算法。
针对具有旋转栅格的直接探测器获得的数字 X 射线图像，对提出的算法进行了实验测试，并与其他算法进行了比较。结果表明，提出的算法可以成功减少直接探测器的栅格伪影。
通过使用同态滤波技术，与常规滤波情况相比，作者可以使用相对较窄带宽的滤波器来显著抑制强栅格伪影。使用旋转栅格还可以显著减少振铃伪影。此外，对于特定的栅格频率和角度，作者可以在空间域中使用简单的同态低通滤波器，从而以非常低的实现复杂度减轻栅格伪影。
