Evaluation of scatter radiation and restoration of reconstructed images of 3D X-ray cone-beam CT scanner

与螺旋CT相比，锥束CT具有在较短的时间内获得三维图像和较高的身体纵向分辨率的优点。然而，由于二维投影数据中包含了大量的散射辐射，使得重建图像的质量较差，在CT图像中会出现火罐伪影。在本研究中，我们试图提高重建图像的质量，并获得了以下结果：1。利用蒙特卡罗模拟，定量分析了二维投影数据上散射辐射的强度分布。根据这些模拟数据，我们评估了散射辐射对三维重建图像的依赖性。仿真结果表明，入射x射线的强度分布被控制在探测器上的主辐射是均匀的，投影数据中包含的散射辐射减少了。然后，我们使用领结滤波器重建了三维CT图像，控制了入射x射线的分布，证实了CT图像质量的提高。利用小波变换的多分辨率分析、反扩散方程模型和离散分布的软件校正等图像处理技术，提高了CT图像的质量。这些技术对于提高散射辐射退化的重建图像的质量是非常有用的。特别是利用多分辨率分析得到的加权因子，可以在不增加计算时间的情况下重建CT图像，提高图像质量。我们的研究结果对锥形束CT扫描仪的实际应用是有效的。

Cone-beam computed tomography (CT) has some advantages that it can make a three-dimensional (3D) image in shorter time and with higher resolution in longitudinal direction of body than the helical CT scanner. However, because large amount of scatter radiation is included in 2D projection data, the quality of reconstructed image is worse and cupping artifacts appear in CT images. In this study, we have tried to improve the quality of reconstructed images and obtained the following results :1.Using Monte Carlo simulation, we analyzed quantitatively the intensity distribution of scatter radiation on 2D projection data. From these simulation data, we have evaluated the dependence of scatter radiation on 3D reconstructed images.2.Simulation results showed that intensity distribution of incident x-ray were controlled primary radiation on detector to be uniform, the scattered radiation included in projection data were decrease. Then, we reconstructed 3D CT images using a bow-tie flitter, which controlled the incident x-ray distribution and confirmed that the image quality of CT images improved.3.We have improved the quality of CT images using image processing techniques, such as multiresolution analysis of wavelet transform, antidiffusion equation model and software correction with scattered distribution. These techniques were very useful to improve the quality of reconstructed image degraded by scatter radiation. Especially, usage of the weighting factors which were obtained from multiresolution analysis, we could reconstruct the CT images without any extra computing time and improve the image quality.We Confirm our results are effective to make the cone-beam CT scanner in practical use.