Zhu Lei, Wang Jing, Xing Lei
Department of Radiation Oncology, Stanford University, Stanford, California 94305, USA.
Med Phys. 2009 Mar;36(3):741-52. doi: 10.1118/1.3063001.
Scatter correction is crucial to the quality of reconstructed images in x-ray cone-beam computed tomography (CBCT). Most of existing scatter correction methods assume smooth scatter distributions. The high-frequency scatter noise remains in the projection images even after a perfect scatter correction. In this paper, using a clinical CBCT system and a measurement-based scatter correction, the authors show that a scatter correction alone does not provide satisfactory image quality and the loss of the contrast-to-noise ratio (CNR) of the scatter corrected image may overwrite the benefit of scatter removal. To circumvent the problem and truly gain from scatter correction, an effective scatter noise suppression method must be in place. They analyze the noise properties in the projections after scatter correction and propose to use a penalized weighted least-squares (PWLS) algorithm to reduce the noise in the reconstructed images. Experimental results on an evaluation phantom (Catphan600) show that the proposed algorithm further reduces the reconstruction error in a scatter corrected image from 10.6% to 1.7% and increases the CNR by a factor of 3.6. Significant image quality improvement is also shown in the results on an anthropomorphic phantom, in which the global noise level is reduced and the local streaking artifacts around bones are suppressed.
在X射线锥束计算机断层扫描（CBCT）中，散射校正对于重建图像的质量至关重要。现有的大多数散射校正方法都假定散射分布是平滑的。即使经过完美的散射校正，投影图像中仍会残留高频散射噪声。在本文中，作者使用临床CBCT系统和基于测量的散射校正方法表明，仅进行散射校正并不能提供令人满意的图像质量，并且散射校正图像的对比度噪声比（CNR）的损失可能会抵消去除散射的益处。为了规避这个问题并真正从散射校正中获益，必须有有效的散射噪声抑制方法。他们分析了散射校正后投影中的噪声特性，并提出使用惩罚加权最小二乘（PWLS）算法来降低重建图像中的噪声。在评估体模（Catphan600）上的实验结果表明，所提出的算法将散射校正图像中的重建误差从10.6%进一步降低到1.7%，并将CNR提高了3.6倍。在人体模型的结果中也显示出显著的图像质量改善，其中全局噪声水平降低，骨骼周围的局部条纹伪影得到抑制。
