锥束CT重建及环形伪影校正算法研究

发布时间：2018-04-12 22:02

本文选题：锥束CT + 周期性　；参考：《中北大学》2017年硕士论文

【摘要】：计算机断层成像技术(Computed Tomography, CT),是目前最为重要的医学诊断和工业无损探伤的工具之一。锥束CT以其分辨率高,成像成本低,成像速度快的特点,已经被广泛应用到航空、航天、医疗、机械等领域。本文主要针对圆轨迹下FDK重建算法和环形伪影的校正两个方面进行了研究。1.本文介绍了 X射线的产生与特性,进而介绍了 Beer定律、Radon的正逆变换以及投影定理等CT重建的基础理论。然后对反投影、滤波反投影以及扇束等距FBP等重建算法进行了分析和推导,并阐述了滤波反投影类型重建算法的原理和一般重建步骤,为后序的研究奠定了基础。2.对FDK重建算法进行了理论的推导,并分析了其离散化实现的过程。根据FDK重建过程的特点,利用正余弦函数在某种程度上体现出来的周期性特点对极坐标下的FDK重建算法做了优化改进。经过本文改进的算法可以一次反投影重建144幅投影数据,并且将正余弦函数的运算量大大降低;接着利用正余切函数的对称性,一次性将多个重建后图像的像素点转化到笛卡尔坐标系下;最后通过实验验证了本文优化算法的可行性,与传统的FDK重建算法相比,经过本文优化的算法在重建速度上提高了近10倍。3.针对探测器响应不一致而产生环形伪影的问题,首先对环形伪影的产生原因以及其具有的特征进行了分析;其次在研究了一种单向自适应平滑处理算法的基础上,研究了一种基于Otsu多阈值分割的改进算法。实验结果证明,这种改进方法能够在保证图像细节信息的情况下有效地去除环形伪影。
[Abstract]:Computed Tomography (CTT) is one of the most important tools for medical diagnosis and industrial NDT.Cone-beam CT has been widely used in aviation, aerospace, medical, mechanical and other fields because of its high resolution, low imaging cost and fast imaging speed.In this paper, FDK reconstruction algorithm and annular artifact correction under circular locus are studied.This paper introduces the generation and characteristics of X-ray, and then introduces the basic theory of CT reconstruction, such as Beer's law, Radon's forward and inverse transformation, projection theorem and so on.Then, the reconstruction algorithms such as backprojection, filter backprojection and fan beam equidistant FBP are analyzed and deduced, and the principle and general reconstruction steps of filter back-projection reconstruction algorithm are expounded, which lays a foundation for the research of the back order. 2.The theory of FDK reconstruction algorithm is deduced, and the realization process of its discretization is analyzed.According to the characteristics of FDK reconstruction process, the FDK reconstruction algorithm under polar coordinates is optimized and improved by using the periodicity of sine cosine function to some extent.The improved algorithm can reconstruct 144 projection data at one time, and reduce the computation of sine cosine function greatly, and then utilize the symmetry of normal cosine function.The pixel points of the reconstructed image are transformed into Cartesian coordinate system at one time. Finally, the feasibility of the optimization algorithm is verified by experiments, which is compared with the traditional FDK reconstruction algorithm.The proposed algorithm improves the reconstruction speed by nearly 10 times. 3.In order to solve the problem that the detector response is inconsistent, the reasons and characteristics of annular artifact are analyzed firstly, and then a one-way adaptive smoothing algorithm is studied.An improved multi-threshold segmentation algorithm based on Otsu is studied.The experimental results show that the improved method can effectively remove the annular artifacts under the condition of guaranteeing the details of the images.
【学位授予单位】：中北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：R814.42;TP391.41

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