血管的三维重建

对血管的三维重建问题,我们假定血管为等径管道,通过分析其几何特性,给出了确定其管道中轴线和半径的数学模型--搜索每个切片截面,求最大内切圆,该内切圆圆心即为切片截面与管道中轴线的交点,该内切圆半径即为管道半径,再通过拟合各个交点求出轴心线. 本模型中,我们确立了两种有效的误差分析方法;并由此发现由于中轴线与切片交角过小会使结果产生较大偏差.为解决此问题,我们从其它方向重新对血管进行切割,再进行处理求解,得到更加精确的结果.     

全自动测量轴对称目标三维姿态的新方法

针对靶场试验中目标三维姿态测量的问题,研究了一种全自动测量轴对称目标三维姿态的新方法.首先对靶场目标成像模型进行分析,其次采用几何主动轮廓模型(GAC)和改进的Hough 变换算法高精度提取图像上目标的中轴线,在此基础上利用目标成像的共线方程对传统中轴线法求出的俯仰角和偏航角进行自动修正,消除了传统中轴线法求取目标姿态结果的二义性,得到了符合实际情况的目标三维姿态参数.实验证明,该算法能高精度地提取目标中轴线,并可快速求解真实的三维姿态角.     

一种改进的血管三维数字仿真方法

为了克服目前血管三维仿真方法中普遍存在的计算量大、精确度不高、缺乏合理的理论证明等问题,更好地实现血管的三维数字仿真、提高仿真精度,本文提出了一种改进的仿真方法。将血管的平行切片图像进行二值化处理,叠加,建立数学模型,得到三维血管的半径,利用求得的半径和Bresenham算法得到每张平行切片图像的最大内切圆圆心,利用多项式拟合建立中轴线空间曲线。     

血管切片的三维重建

本文讨论血管的三维重建问题.我们通过研究,证明了以下的定理.定理设C(i)是中轴线和平面Z=i的交点,那么存在以C(i)为中点且端点P1(i),P2(i)在ω(i)上的线段,并且在P1(i),P2(i)处ω(i)的切线相互平行.根据定理,我们找到利用求截面图象边界曲线的平行切线方法找到中轴线和100个截面的交点及管道的直径59.1238pixel.并用这100个交点的数据拟合出中轴线的方程:x(t)=-0.207806-0.610303t+0.206455t2-0.0144935t3+0.000517774t4-8.394241977754047×10-6t5+6.133353112035975×10-8t6-1.6673218267444805×10-10t7y(t)=158.211+1.86595t-0.266798t2+0.0141407t3-0.000325412t4+3.043275597680807×10-6t5-9.899171274615063×10-9t6z(t)=t然后我们用中轴线的方程重建了三维血管,并求出了重建血管在40个平面上的截面ω′(i)(30≤i≤69),并与原始截面ω(i)(30≤i≤69)进行比较,截面平均符合率高达96.8024%.     

激光三维雕刻中实时切片算法研究

如何对三维模型进行快速切片一直是分层制造的关键技术,分析对比两类切片方式,基于格式通用性、操纵灵活性及数据处理快速性方面考虑,选择STL文件作为该系统与三维造型软件的接口规范.从实时切片角度出发,在充分分析STL文件格式的基础上,提出STL模型拓扑快速重建的算法思想.通过预先为模型建立点表及邻接边表,实现模型的实时切片.该切片算法已经应用于激光三维雕刻系统,结果表明,算法快速稳定.最后给出了一个三维雕刻实例.     

金属材料断口的计算机三维重构及分析

利用分层切片重构物体的原理,通过图像处理和三维数据场可视化的技术手段,自主开发出一套金属断裂面三维重构的软件-JHX_FSR.该软件自动处理由光学显微镜拍摄的一系列断口宏观侧面的切片照片,得到重构的三维断口形貌,经检验该软件可以较精确地重构断口.此外,通过空间几何的角度对断口的局部区域进行定量分析,结果证实,在断口三维数据场准确的情况下,从空间几何的角度对断口进行定量分析可以作为计算机分析断口的判据之一.     

Jacobi-Bernstein基变换矩阵的一些性质

在计算机辅助设计中,经常需要不同形式的曲线、曲面之间的变换,以完成曲线、曲面的降阶以及不同几何造型系统之间数据交换的操作,而这些变换的误差将依赖于相应变换矩阵的条件数.由于这个原因,我们研究了Jacobi-Bernstein矩阵的与其条件数相关的若干性质,而且通过计算变换矩阵与逆变换矩阵的无穷范数我们以显形式给出了这些条件数的上界.我们还给出了这些条件数在CAGD中的应用实例.     

基于三维点云螺纹中轴线的拟合方法研究

螺纹中轴线的精确测定是决定螺纹三维测量结果是否准确的重要因素之一。中轴线的倾斜、偏移会对工件坐标系的建立、螺纹的三维重构、参数检验等测量操作引入误差。基于三维点云的最小二乘拟合算法,开展了螺纹中轴线的拟合方法研究。根据螺纹表面点云数据,利用螺纹表面与中轴线的特征关系建立最小二乘数学模型,通过计算点云数据的三维凸包滤除螺纹自身三维结构带来的拟合误差,使螺纹中轴线的测定更精准。通过仿真实验,基于三维点云的最小二乘拟合算法拟合的直线与三维点云的距离方差为0.34,在旋合长度范围内与投影法确定的直线两端最大距离为0.15μm,符合三维测量高精度标准,基于三维点云的最小二乘拟合算法可以快速、准确地拟合螺纹中轴线。     

基于形态自相关和时频切片分析的轴承故障诊断方法

频率切片小波变换(Frequency Slice Wavelet Transform,FSWT)是一种新的时频分析方法,信号中的噪声会降低FSWT分析的频率分辨率。为了提高分析精度,提出了基于形态滤波和时延自相关的时频切片分析方法,并成功应用到轴承故障诊断中。该方法首先采用多结构元素差值形态滤波和时延自相关方法对信号进行降噪,采用FSWT分解降噪后的轴承振动信号,然后根据轴承故障特征频率选择时间频率切片区间,进行细化分析来提取故障特征。仿真信号与轴承故障诊断实例的分析验证了该方法的有效性。     

三维CAD环境下任意曲线的生成方法研究

利用三维CAD软件提供的API工具,对给定的任意曲线方程进行读取和分析,然后采用离散和拟合算法,在指定的草图平面中绘制出光滑的曲线,为进一步在三维CAD环境中精确地完成复杂曲面的三维造型,提供一种草图绘制工具。这有利于实现复杂机械零部件的造型和设计。     

Vessel wall detection and blood noise reduction in intravascularultrasound imaging

Scattering from blood limits the contrast between the vessel wall and the lumen in intravascular ultrasound imaging. This makes it difficult to localize the vessel wall, especially on still images. This paper presents a method for automatic detection of vessel walls and reduction of blood noise based on correlation of the RF-signal between adjacent frames. The ultrasound RF-signal is quadrature demodulated, digitized, stored in memory, and transferred to a computer for processing and analysis. The absolute value of the cross-correlation coefficient between two adjacent frames is used to differentiate between stationary and fluctuating signals. Models and numerical calculations presented in this work indicate that the cross-correlation coefficient obtained from a radially dilating vessel wall will be larger than 0.8 under standard 20 MHz imaging conditions. The corresponding value from blood is less than 0.2 for blood velocities exceeding 0.5 cm s^-1 . The blood-noise filter is based on detecting this difference in correlation and displays vessel wall regions with no modifications, while regions detected as blood are rejected. A simplified vessel-wall detector that is suitable for real-time implementation is proposed. The performance of this detector and the blood noise filter are demonstrated by in vitro experiments     

变形模型技术在冠状动脉造影图像序列后处理中的应用

以冠状动脉血管轴线的三维运动跟踪和心脏的形状建模为例,论述了变形模型在X射线心血管造影图像序列后处理中的应用.首先采用3D snake模型,表示血管轴线的曲线在三维空间中的变形,完成对血管骨架的序列重建.然后以各时刻的血管骨架点作为采样点,采用基于扩展超二次曲面的变形模型,建立心脏形状模型,通过分析不同时刻模型参数的变化,获得心脏变形参数的估计.     

血管管道的三维重建

文章对血管管道的三维重建进行了讨论.根据题目所给信息,首先读取100张血管切面图,把它们转换成数据矩阵,然后分三步进行处理:第一步,通过搜索切面最大内切圆求出管道的半径,提出两种方案,分别是切线法和最大覆盖法;第二步,轨迹的搜索,本文提出了三种方法,分别为网格法、蒙特卡罗法和非线性规划法;第三步,中轴线在三平面上投影的精确定位,分别用最小二乘和分段最小二乘进行了曲线的拟合.最后又对三维重建的血管管道进行了检验和误差分析.利用以上算法较好地进行了管道的重建,从而得出所求半径为29.529,中轴线上100点的坐标见表1,其在XY,YZ和XZ平面上的投影分别为图8到图15.     

Analyzing Raman maps of pharmaceutical products by sample-sample two-dimensional correlation

Sample-sample (SS) two-dimensional (2D) correlation spectroscopy is applied in this study as a spectral selection tool to produce chemical images of real-world pharmaceutical samples consisting of two, three, and four components. The most unique spectra in a Raman mapping spectral matrix are found after analysis of the covariance matrix. (This is obtained by multiplying the original mapping data matrix by itself.) These spectra are identified by analyzing the slices of the covariance matrix at the positions where covariance values are at maxima. Chemical images are subsequently produced in a univariate fashion by visually selecting the wavenumbers in the extracted spectra that are least overlapped. The performance of SS 2D correlation is compared with principal component analysis in terms of highlighting the most prominent spectral differences across the whole data set (which typically comprises several thousand spectra) and determining the total number of species present. In addition, the selection of the unique spectra by SS 2D correlation is compared with the selection obtained by the orthogonal projection approach (OPA). Both comparisons are found to be satisfactory and demonstrate that a quite simple SS 2D correlation routine can be used for producing reliable images of unknown samples. The main benefit of using SS 2D correlation is that it is based on a few data processing commands that can be executed separately and produce results that are closely related to the chemical features of the system.     

Absorbing boundary conditions for a 3D non-Newtonian fluid-structure interaction model for blood flow in arteries

Blood flow in arteries is characterized by pulse pressure waves due to the interaction with the vessel walls. A 3D fluid-structure interaction (FSI) model in a compliant vessel is used to represent the pressure wave propagation. The 3D fluid is described through a shear-thinning generalized Newtonian model and the structure by a nonlinear hyperelastic model. In order to cope with the spurious reflections due to the truncation of the computational domain, several absorbing boundary conditions are analyzed. First, a 1D hyperbolic model that effectively captures the wave propagation nature of blood flow in arteries is coupled with the 3D FSI model. Extending previous results, an energy estimate is derived for the 3D FSI-1D coupling in the case of generalized Newtonian models. Secondly, absorbing boundary conditions obtained from the 1D model are imposed directly on the outflow sections of the 3D FSI model, and numerical results comparing the different absorbing conditions in an idealized vessel are presented. Results in a human carotid bifurcation reconstructed from medical images are also provided in order to show that the proposed methodology can be applied to anatomically realistic geometries.     

From medical images to anatomically accurate finite element grids

The successful application of computational modelling of blood flow for the planning of surgical and interventional procedures to treat cardiovascular diseases strongly depends on the rapid construction of anatomical models. The large individual variability of the human vasculature and the strong dependence of blood flow characteristics on the vessel geometry require modelling on a patient‐specific basis. Various image processing and geometrical modelling techniques are integrated for the rapid construction of geometrical surface models of arteries starting from medical images. These discretely defined surfaces are then used to generate anatomically accurate finite element grids for hemodynamic simulations. The proposed methodology operates directly in 3D and consists of three stages. In the first stage, the images are filtered to reduce noise and segmented using a region‐growing algorithm in order to obtain a properly defined boundary of the arterial lumen walls. In the second stage, a surface triangulation representing the vessel walls is generated using a direct tessellation of the boundary voxels. This surface is then smoothed and the quality of the resulting triangulation is improved. Finally, in the third stage, the triangulation is subdivided into so‐called discrete surface patches for surface gridding, the desired element size distribution is defined and the finite element grid generated. Copyright © 2001 John Wiley & Sons, Ltd.     

Theoretical design of vascular imaging based on hall effect

The conceptual technique of vascular imaging and blood flow functional imaging based on Hall Effect is presented in this article. With this non‐invasive approach, both 3D anatomical imaging of the vasculature and functional imaging of blood flow in the deep structure of the human body can be obtained without radiation risk. The technique is based on the fact that the induced charges can be generated when the blood flows through the magnetic field. The induced electric field strength is measured by two groups of detector arrays, which captures not only the position of vasculature in each section, but also the velocity of blood flow and vessel size. The captured images can also be used for 3D reconstruction of the anatomical models. The designed system architecture including both hardware and software is described. © 2013 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 23, 85–96, 2013     

Flexural behavior of three-axis woven carbon/carbon composites

This work examines the processing characteristics and flexural behavior of 3D woven carbon/carbon composites. Two types of the composites have been made, both having 3-axis orthogonal structures. The first combines solid rods along the axial direction. The rod, 1 mm in diameter, is composed of unidirectional carbon fibers and a phenolic resin. The second is a conventional type composed of carbon yarns in all axes. Both preforms were then impregnated by the phenolic resin. Matched molds were used to enhance fiber packing and to cure the resin under a hot press. The green composites were then heat-treated at various temperatures ranging from 200° through 1000° C. The second set of specimens was made by applying multi-cycle impregnation and carbonization. Flexural tests were carried out for these two sets of specimens. Their responses to the load and the induced damage behavior have been examined. The use of rods enhances fiber packing and reduces fiber crimp, leading to higher material performance. Decomposition of the resin due to the heat-treatment results in weak interfacial bonding and compressive failure in axial yarns. The efficiency of densification has been examined. The induced damage configurations vary significantly in these specimens, as a result of the processing. Some unique modes associated with the 3D structure are discussed.