Removal of Gridline Artifacts in Cone-beam CT Based on Wavelet Transform
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摘要: 采用平板探测器的X射线锥束成像系统中，由于散射会带来图像伪影从而劣化图像质量，通常采用在平板探测器前安装滤线栅来去除散射，但滤线栅会在获取的图像上形成周期性的条状伪影，如何去除条状伪影是X射线锥束成像系统中的一个关键技术问题。本文对已有的滤线栅条纹去除方法进行概述，创新性地提出基于频谱拼接的小波变换方法，既能在损失物体细节信息少的前提下很好地去除滤线栅条纹，又不会引入小波变换谐波。通过实际实验，检验该方法的有效性。Abstract: In cone-beam computed tomography with flat-panel imagers, scattered X-ray photons lead to reduced image quality. Insertion of an anti-scatter grid between the patient or object and the flat-panel imagers is one of the most used techniques for reducing scattered radiation. However, while the scatter is reduced, gridline artifacts can be visible. Suppressing gridline artifacts in cone-beam computed tomography is significant. In this paper, the existing methods of removing gridline artifacts are summarized. Moreover, the wavelet transform method based on spectrum coalescence is innovatively proposed for removing gridline artifacts. Wavelet transform can remove gridline artifacts effectively and without introducing wavelet transform harmonics thus reducing the loss of object details. The effectiveness of this method is verified by experiments.
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Key words:
- gridline artifacts /
- wavelet transform /
- spectrum coalescence
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图 1 水平放置的防散射滤线栅的主视图和俯视图
Figure 1. Front view and top view of the anti-scattering grid placed horizontally
图 2 小波变换方法去除滤线栅条纹的整体思路
Figure 2. Schematic representation of the idea to remove gridline artifacts by wavelet transform
图 3 第10层多贝西小波的低通和高通滤波器响应函数的幅度谱
Figure 3. Amplitude spectrum of low-pass and high-pass filter response functions of layer 10 Daubechies wavelet
图 8 检验小波变换方法有效性的对照实验
Figure 8. A comparative experiment to test the effectiveness of the wavelet transform method
图 9 小波变换法处理前后的“水”
Figure 9. “Water” before and after processing by the wavelet transform method
图 10 小波变换法处理前后的“老鼠”
Figure 10. “Mouse” before and after processing by the wavelet transform method
图 12 “水”在小波变换法处理前后的差异的一维离散傅里叶变换幅度谱
Figure 12. One dimensional discrete Fourier transform amplitude spectrum of the difference of “water” before and after processing by the wavelet transform method
图 13 “水”在高斯带阻滤波或小波变换法处理前后的差异的二维离散傅里叶变换幅度谱的局部
Figure 13. The local region of the amplitude spectrum of two-dimensional discrete Fourier transform of the difference in “water” before and after the processing with the Gaussian band stop filter or wavelet transform method
图 14 经对照组1、实验组1、实验组2处理后的“水”的一维离散傅里叶变换幅度谱
Figure 14. One dimensional discrete Fourier transform amplitude spectrum of “water” treated with control group 1, experimental group 1, and experimental group 2
图 15 经对照组1、实验组1、实验组2处理的“水”CT重建的中心截面局部图
Figure 15. Local central section of “water” CT reconstruction treated with control group 1, experimental group 1 and experimental group 2
图 16 经对照组1、实验组1、实验组2处理的“老鼠”CT重建的中心截面局部图
Figure 16. Local central section of “mouse” CT reconstruction treated with control group 1, experimental group 1, and experimental group 2
表 1 频谱拼接的定量效果
Table 1. Quantitative effect of spectrum coalescence
统计参数 加条纹图像 不做频谱拼接图像 做频谱拼接图像 峰值信噪比 29.719 34.475 37.758 结构相似性 0.984 0.995 0.998 与原图差异的标准差 9.122 5.085 3.458 
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