衍射层析成像及双聚焦与三维成像系统的研究

发布时间：2018-05-03 03:13

本文选题：衍射层析成像 + 雷达成像　；参考：《太原理工大学》2017年硕士论文

【摘要】：基于傅里叶的衍射投影定理的衍射层析成像系统在成像与目标识别方面具有突出的优势,因此被广泛的应用于各种不同领域,尤其是医学检测,因其无创伤性,高精度的优点,被人视为是能够替代传统的计算机断层扫描(Computed Tomography,CT)的一个新技术,是国内外研究热点。与传统雷达成像相比,衍射层析成像是一种重建目标函数的新技术。成像依照重建后所携带的目标信息可分为两类:一类是获取目标的大小、位置、形状以及内部结构等信息的成像可被称为几何成像或视觉成像;另一类旨在反映目标的物理或电学性质变化,如折射率、介电常数、磁导率等信息,这类成像可被称为物理成像。传统雷达成像通常是对目标进行视觉成像,而基于衍射层析成像的雷达则是关注于目标电特性的变化。现今已被成熟运用的物理成像的工业成品有计算机断层扫描,因当时计算机技术的不足,成像算法都是以物理光学近似为前提将问题简单化,因此,信号源只能采用X高频射线等高频信号,对人体辐射性强,无法适用于常规检测。当目标尺寸与电磁波波长为同一量级时,此时衍射现象明显,电磁波传播路径不能简单的看作直线传播,因此傅里叶衍射投影定理被提出,该定理以波动方程为基础,通过计算包含衍射信息的散射场还原目标函数,本质上属于逆散射问题。本文利用惠更斯原理,引入了原生源和次生源概念,通过公式推导,研究了源和场的关系,以及在射线理论或弱散射的条件下,场和源能互相线性表示。接着本文推导衍射层析成像原理的基本公式,讨论了限制成像质量的理论因素和实际因素。论文的主要工作即创新点如下述两点所示。(1)分析了限制成像的因素,首次提出了双聚焦成像系统,同时采用视觉成像和物理成像的双聚焦模式,达到高质量的目标重建。视觉成像弥补了投影模式下衍射层析成像频谱域的缺陷,还原目标轮廓信息,结合衍射层析成像提供的目标电特性变化,重建完备的目标图像。论文通过理论分析与数据仿真,验证该双聚焦成像系统的可行性。(2)建立了基于双聚焦的三维成像系统,给出了完整的系统模型,论文通过仿真建模,分析了成像质量与旋转角度的关系。验证了三维成像系统的可行性。本文提出了双聚焦成像及三维成像系统,论文对系统的成像性能进行了初步的探索,通过仿真对理论进行验证。该研究对衍射层析成像的应用有重要意义和潜在价值。
[Abstract]:The diffraction tomography system based on Fourier diffraction projection theorem has outstanding advantages in imaging and target recognition, so it has been widely used in various fields, especially in medical detection, because of its advantages of non-traumatic and high accuracy. It is regarded as a new technology which can replace the traditional computed tomography (CTT), and it is a research hotspot at home and abroad. Compared with traditional radar imaging, diffraction tomography is a new technique to reconstruct objective function. Imaging can be divided into two categories according to the target information carried after reconstruction: one is the imaging of the size, position, shape and internal structure of the target, which can be called geometric imaging or visual imaging; The other is to reflect the changes of physical or electrical properties of the target, such as refractive index, permittivity, permeability and so on. This kind of imaging can be called physical imaging. Traditional radar imaging is usually used to visualize the target, while the radar based on diffraction tomography focuses on the change of the target's electrical characteristics. The industrial products of physical imaging that have been used now are computer tomography. Because of the insufficiency of computer technology at that time, imaging algorithms simplify the problem on the premise of physical and optical approximation. The signal source can only use X-ray and other high-frequency signals, which can not be used for routine detection because of its strong radiance to human body. When the size of the target is the same as the wavelength of the electromagnetic wave, the diffraction phenomenon is obvious, and the propagation path of the electromagnetic wave can not be simply regarded as the straight line propagation. Therefore, the Fourier diffraction projection theorem is proposed, which is based on the wave equation. By calculating the objective function of scattering field which contains diffraction information, it is essentially an inverse scattering problem. In this paper, the concepts of primary and secondary source are introduced by using Huygens principle. The relationship between source and field is studied by formula derivation, and the field and source energy are expressed linearly under the condition of ray theory or weak scattering. Then the basic formula of diffraction tomography principle is deduced, and the theoretical and practical factors that limit the imaging quality are discussed. The main work of this paper is innovation as shown in the following two points. (1) the factors limiting imaging are analyzed and a double focus imaging system is proposed for the first time. The dual focusing mode of visual imaging and physical imaging is used to achieve high quality target reconstruction. Visual imaging makes up for the defects in the spectral domain of diffraction tomography in projection mode, and restores the contour information of the target, and reconstructs the complete target image by combining the changes of the electrical characteristics of the target provided by the diffraction tomography. Through theoretical analysis and data simulation, the feasibility of the double focus imaging system is verified. (2) the 3D imaging system based on double focus is established, and the complete system model is given. The relationship between imaging quality and rotation angle is analyzed. The feasibility of 3D imaging system is verified. In this paper, double focus imaging and three dimensional imaging system are proposed. The imaging performance of the system is preliminarily explored, and the theory is verified by simulation. This study is of great significance and potential value for the application of diffraction tomography.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TP391.41

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