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

锥形束计算机断层扫描（CT）具有一些优点，它可以在更短的时间内获得三维（3D）图像，并且在身体纵向方向上具有比螺旋CT扫描仪更高的分辨率。然而，由于二维投影数据中包含大量的散射辐射，重建图像质量较差，并且在CT图像中出现杯状伪影。本研究从提高重建图像质量的角度出发，取得了以下成果：1.利用Monte Carlo模拟方法，定量分析了散射辐射在二维投影数据上的强度分布。从这些模拟数据中，我们评估了散射辐射对三维重建图像的依赖性。2.模拟结果表明，通过控制探测器上的初级辐射，入射X射线的强度分布均匀，投影数据中包含的散射辐射减少。然后，利用蝴蝶结滤波器对入射X射线分布进行控制，重建三维CT图像，证实了CT图像质量的提高。3.利用小波变换的多分辨率分析、反扩散方程模型和散射分布的软件校正等图像处理技术，提高了CT图像的质量。这些技术对于改善散射辐射引起的重建图像质量具有重要意义。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图像，提高图像质量，为锥束CT的实用化提供了有效的方法。

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.