Cupping artifact correction for low-energy X-ray industrial CT images
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摘要: 为了去除X射线工业CT图像中的杯状伪影,提高CT图像的识别能力和量化分析精度,提出一种基于分度投影和权函数的射束硬化校正方法。首先分析得出杯状伪影主要是由X射线连续谱穿过被测物体过程中出现的射束硬化所导致。然后扫描阶梯模型,采集不同厚度下的投影数据并求出线衰减系数,通过拟合曲线,得到硬化模型函数和权函数校正模型函数,并确定权函数。接着,扫描被测圆柱形工件,采集不同分度下的投影数据。最后,针对每一个分度投影数据,采用权函数与当前分度投影数据乘积的方法进行硬化校正。对含有杯状伪影的实际CT图像进行了校正实验,结果表明,与多项式拟合法相比,该方法校正后的灰度图像没有放大噪声,且信噪比提高3.29%,有效地消除了杯状伪影,同时较好地保留了图像边界细节。Abstract: A beam hardening correction method based on indexing projection and weight function is proposed to remove the cupping artifacts of low-energy X-ray industrial CT images and to improve the identification capability and quantitative analysis. Firstly, it is concluded from theoretical analysis that cupping artifacts is dominated by beam hardening occurring when X-ray continuous spectrum passes through the object to be measured. Then, projection data and line attenuation coefficient of different thickness are acquired through scanning ladder model. The hardening model function and weight function correction model function which determines the power function are obtained by fitting curve. Furthermore, we scan the measured round workpiece to get the projection data under different indexing. Finally, for each index projection data, the projection data of cupping artifacts are corrected by combining the weight function and current indexing projection data. A correction experiment is carried out in the actual CT images including cupping artifacts. The result indicates that the SNR of gray image using the proposed method has increased by 3.29% with no amplification of noise, which shows that the proposed method more effectively eliminates the cupping artifacts and keeps better image edges as compared with the polynomial fitting method.
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