角度受限下纳米CT图像处理及三维重构算法研究

发布时间：2017-12-28 07:00

本文关键词：角度受限下纳米CT图像处理及三维重构算法研究　出处：《中国科学技术大学》2016年博士论文　论文类型：学位论文

【摘要】：近些年,随着X射线光源性能的不断进步,高灵敏度、高稳定性的X射线探测器的开发,微纳米级X射线光学元件加工技术的提升,精密机械平台及控制系统的使用,基于波带片的X射线显微成像结合传统CT方法得到的纳米CT成像技术得到显著地发展。其中,硬X射线纳米CT具有强穿透能力、大焦深、高分辨、无需真空环境、包含多种材料吸收边、三维成像等优势,已经在材料科学、微电子产业、环境工程、能源科学等众多领域得到广泛应用。软X射线纳米CT对于生物样品具有天然的高衬度、能够保持样品“鲜活”时的结构和形态等特性,已经应用于药物研发、细胞机理、纳米颗粒等诸多领域。因此纳米CT成像技术具有其独特优势,能够弥补电镜、光学显微镜等其它显微成像手段的一些不足。纳米CT系统采集的投影数据需要经过数据预处理、三维重构、图像分割、后处理分析计算等一系列的处理步骤,最终才能得到准确、清晰、有意义的信息。投影图像的预处理是后续系列处理步骤的前期准备,需要校正采集的数据中存在的坏点、亮度不均匀、投影间光强不相等、噪声、转轴偏差等。而三维重构是纳米CT应用过程的最关键步骤,是把叠加的信息分离的过程,良好的图像重构质量能真实反映样品三维结构信息,也是进行后处理计算的前提。然而,三维重建常常面临投影数据不完备的难题,在纳米CT数据重建中,经常遇到投影角度受限的情况,因此迫切需要发展合适的重构算法加以解决。国家同步辐射实验室于2007年左右建成了一台硬X射线纳米CT设备,随后又建设了软X射线纳米CT设备,本论文结合我们平台的数据特点,开展了以下几方面的工作：1.总结了X射线纳米显微成像技术的优势和特性,并分别综述了硬X射线纳米CT和软X射线纳米CT的工作原理及主要光学元件的原理与参数。我们选择了几个典型例子来说明硬X射线纳米CT具有的独特优势：对硅酸锌纳米棒自组装催化剂颗粒成像,内部结构与缺陷能够清晰呈现,这是电镜等其它成像手段所不能的：对锂离子电池中的氧化铜电极进行锂化-反锂化过程原位动态成像,氧化铜颗粒等随电池充放电过程的变化被清晰记录：对有丝分裂的酵母细胞成像,体现了相衬成像模式下,硬X射线纳米CT对生物大样品能成高衬度像的能力。为了展示软X射线纳米CT的应用价值,我们分别选取了牛痘病毒感染细胞、疟原虫感染红细胞、药物对细胞的作用、免疫金标记的干细胞、微凝胶颗粒与油滴颗粒相互作用等进行成像的例子,同时还列举了其与荧光显微镜联合成像,以及应用于近边X射线吸收光谱成像等来体现软X射线纳米CT目前的应用领域。2. 发展了多种纳米CT图像预处理算法。对投影数据进行一系列的预处理,提出了基于金颗粒点轨迹追踪、中心骨架提取,并进行中心骨架的正弦曲线预估与位移校正,来达到转轴自动校正的目标：根据投影数据特点,在单幅投影光强均衡化的基础上,提出了不同投影间光强均衡的方法,使得所有投影更加均匀：针对投影中空白部分(背景)进行阈值滤波,减少误差,达到背景“干净”的目标,为三维重构、后期分析处理等打下良好基础。3.研究CT成像的基本原理,分析比较了传统滤波反投影算法和迭代重构算法的特点及不足；并分析了纳米CT成像数据特点,研究了能突破奈奎斯特采样定理的压缩感知理论。在此基础上,我们改进并发展了适用于纳米CT数据的基于全变分的纳米CT重构算法。并通过一系列模拟数据来对比在投影中含有噪声,以及投影角度稀疏、投影角度受限等数据不完备情况下,算法与传统重构算法的重构效果好坏；还对硬X射线纳米CT上采集的投影角度受限的酵母细胞数据,及从软X射线纳米CT上采集的投影角度受限的碳纳米管数据分别采用基于全变分的纳米CT重构算法与传统重构算法进行了重构并对比分析,发现前者优势明显。4.针对纳米CT、工业CT、电镜等断层成像中经常遇到的离散样品重构问题,本文在充分研究分析了现有的离散断层重构算法的基础上,着力于解决现有算法对样品灰度先验知识的过分依赖,以及当图像灰度数量增多时,重构质量下降明显的问题。本文提出了一种以每个单独区域作为一个研究对象的多灰度图像离散断层重构算法,算法继承了离散断层重构算法对投影角度受限强耐受力等优点的同时,还避免了对图像灰度先验知识的依赖等劣势。通过一系列实验验证了算法的稳定性、收敛性、重构精度、灰度极限数量等各项性能指标,从而证明了此算法能够突破多组分离散样品在投影角度受限情况下定量重构分析这一瓶颈,为有效提升离散断层成像方法在纳米CT等断层成像中的广泛应用提供了更广大空间。
[Abstract]:In recent years, with the continuous progress of X ray source performance, the development of X ray detector with high sensitivity and high stability, the micro nano X X-ray optics processing technology, precision mechanical platform and control system, nano CT imaging imaging system X ray microscope combined with traditional CT methods were statistically significant based on the development of. Among them, the hard X - ray CT nanoparticles have strong penetrating ability, large focal depth and high resolution, no vacuum environment, including edge, three-dimensional imaging and other advantages of various materials absorption, has been widely used in many fields of material science, microelectronics industry, environmental engineering and energy science. Soft X ray nano CT has been applied to many fields such as drug discovery, cell mechanism, nanoparticle and so on. Therefore, the nano CT imaging technology has its unique advantages, which can make up for some shortcomings of other microscopic imaging methods, such as electron microscope and optical microscope. The projection data collected by nano CT system need a series of processing steps, such as data preprocessing, 3D reconstruction, image segmentation, post-processing, analysis and calculation, so as to get accurate, clear and meaningful information. Preprocessing of projection image is prepare for the later series of processing steps, need to point, brightness correction data are not uniform, not equal intensity projection, noise, axis deviation. Three dimensional reconstruction is the most critical step in the application process of nano CT. It is the process of separating the superimposed information. The quality of good image reconstruction can truly reflect the three-dimensional structure information of the sample, and it is also the premise for post processing calculation. However, 3D reconstruction often faces the problem of incomplete projection data. In the reconstruction of nano CT data, projection angle is often limited. Therefore, it is urgent to develop appropriate reconstruction algorithm to solve it. In 2007, built around a hard X ray nano CT equipment in National Synchrotron Radiation Laboratory, then the construction of the soft X ray nano CT devices, this paper combined with the characteristics of our data platform, to carry out the work in the following aspects: 1. summarizes the advantages and characteristics of nano X ray imaging technology, and the principle and the parameters of the working principle of hard X ray nano CT and nano CT soft X ray and the main optical elements were reviewed. We chose some typical examples to illustrate the advantages of hard X ray nano CT: zinc silicate nanorods self-assembled catalyst particle imaging, the internal structure and defects can be clearly presented, this is the electron microscope and other imaging method can not do: lithium lithium - process in situ dynamic imaging of copper oxide lithium electrode ion batteries, copper oxide particles change with the battery charge and discharge process is clearly recorded: on yeast cell mitosis of imaging, phase contrast imaging mode, the hard X - ray CT nanoparticles on biological samples into a high degree as the ability of lining. In order to show the application value of soft X ray nano CT, we selected the vaccinia virus infected cells and Plasmodium falciparum infected red blood cells and drugs on cell function, immunogold labeling of stem cells, the microgel particles and oil droplets interactions such as imaging examples, and also lists the combined imaging and fluorescence microscope, and applied to the near edge X-ray absorption spectroscopy X imaging to reflect the application of soft X ray nano CT current. 2. a variety of nano CT image preprocessing algorithms have been developed. The projection data preprocessing is proposed to extract a series of gold particles trajectory point tracking and framework based on the sine curve and central frame prediction and displacement correction, to achieve the goal: shaft automatic correction according to the characteristics of the projection data, based on a single projection intensity equalization, and puts forward the method of intensity balance different projection, the more uniform for all projection projection blank part (background) threshold filtering, reduce errors, achieve the background of "clean" target, and lay a good foundation for the later analysis, 3D reconstruction. 3., we studied the basic principles of CT imaging, analyzed and compared the characteristics and shortcomings of traditional filtered back projection algorithm and iterative reconstruction algorithm, analyzed the characteristics of nano CT imaging data, and studied the compressive sensing theory that could break through the Nyquist sampling theorem. On this basis, we have improved and developed a fully variational based nano CT reconstruction algorithm for nanoscale CT data. And through a series of simulation data to compare the noise in the projection, and the projection angle, sparse projection angle limited data in case of incomplete, or reconstruction algorithm and traditional reconstruction algorithm; yeast cell data of hard X ray projection angle acquisition on nano CT limited, the data collected from the soft and carbon nanotubes X ray nano CT projection of the limited angle respectively by nano CT total variation reconstruction algorithm and traditional reconstruction algorithm for the reconstruction and comparative analysis based on the former found obvious advantages. 4. aiming at the problem of discrete sample reconstruction often encountered in nano CT, industrial CT, electron microscope tomography, this paper analyzes on the basic of research on discrete tomography reconstruction algorithm on the current focus on solving the existing algorithms over reliance on sample gray prior knowledge, as well as the increase in the number of gray image, the obvious problem of reconstruction quality drop. This paper puts forward a method to separate each region as a research object of the discrete fault reconstruction algorithm of grayscale image, the algorithm inherits the discrete fault reconstruction algorithm of limited projection angle strong tolerance advantages but also avoids the disadvantage of image prior knowledge dependence. Through a series of experiments, the stability, convergence, precision of reconfiguration, the number of gray limit and so on are verified.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TP391.41

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