Automatic construction of multiple-object three-dimensional statistical shape models: application to cardiac modeling

A novel method is introduced for the generation of landmarks for three-dimensional (3-D) shapes and the construction of the corresponding 3-D statistical shape models. Automatic landmarking of a set of manual segmentations from a class of shapes is achieved by 1) construction of an atlas of the class, 2) automatic extraction of the landmarks from the atlas, and 3) subsequent propagation of these landmarks to each example shape via a volumetric nonrigid registration technique using multiresolution B-spline deformations. This approach presents some advantages over previously published methods: it can treat multiple-part structures and requires less restrictive assumptions on the structure's topology. In this paper, we address the problem of building a 3-D statistical shape model of the left and right ventricle of the heart from 3-D magnetic resonance images. The average accuracy in landmark propagation is shown to be below 2.2 mm. This application demonstrates the robustness and accuracy of the method in the presence of large shape variability and multiple objects.     

Coupled nonparametric shape and moment-based intershape pose priors for multiple basal ganglia structure segmentation

This paper presents a new active contour-based, statistical method for simultaneous volumetric segmentation of multiple subcortical structures in the brain. In biological tissues, such as the human brain, neighboring structures exhibit co-dependencies which can aid in segmentation, if properly analyzed and modeled. Motivated by this observation, we formulate the segmentation problem as a maximum a posteriori estimation problem, in which we incorporate statistical prior models on the shapes and intershape (relative) poses of the structures of interest. This provides a principled mechanism to bring high level information about the shapes and the relationships of anatomical structures into the segmentation problem. For learning the prior densities we use a nonparametric multivariate kernel density estimation framework. We combine these priors with data in a variational framework and develop an active contour-based iterative segmentation algorithm. We test our method on the problem of volumetric segmentation of basal ganglia structures in magnetic resonance images. We present a set of 2-D and 3-D experiments as well as a quantitative performance analysis. In addition, we perform a comparison to several existent segmentation methods and demonstrate the improvements provided by our approach in terms of segmentation accuracy.     

Morphological iterative closest point algorithm

This work presents a method for the registration of three-dimensional (3-D) shapes. The method is based on the iterative closest point (ICP) algorithm and improves it through the use of a 3-D volume containing the shapes to be registered. The Voronoi diagram of the "model" shape points is first constructed in the volume. Then this is used for the calculation of the closest point operator. This way a dramatic decrease of the computational cost is achieved.     

Neighbor-constrained segmentation with level set based 3-D deformable models

A novel method for the segmentation of multiple objects from three-dimensional (3-D) medical images using interobject constraints is presented. Our method is motivated by the observation that neighboring structures have consistent locations and shapes that provide configurations and context that aid in segmentation. We define a maximum a posteriori (MAP) estimation framework using the constraining information provided by neighboring objects to segment several objects simultaneously. We introduce a representation for the joint density function of the neighbor objects, and define joint probability distributions over the variations of the neighboring shape and position relationships of a set of training images. In order to estimate the MAP shapes of the objects, we formulate the model in terms of level set functions, and compute the associated Euler-Lagrange equations. The contours evolve both according to the neighbor prior information and the image gray level information. This method is useful in situations where there is limited interobject information as opposed to robust global atlases. In addition, we compare our level set representation of the object shape to the point distribution model. Results and validation from experiments on synthetic data and medical imagery in two-dimensional and 3-D are demonstrated.     

Efficient electromagnetic modeling of three-dimensional multilayermicrostrip antennas and circuits

An efficient method-of-moments (MoM) solution is presented for analysis of multilayer microstrip antennas and circuits. The required multilayer Green's functions are evaluated by the discrete complex image method (DCIM), with the guided-mode contribution extracted recursively using a multilevel contour integral in the complex _ρ-plane. An interpolation scheme is employed to further reduce the computer time for calculating the Green's functions in the three-dimensional (3-D) space. Higher order interpolatory basis functions defined on curvilinear triangular patches are used to provide necessary flexibility and accuracy for the discretization of arbitrary shapes and to offer a better convergence than lower order basis functions. The combination of the improved DCIM and the higher order basis functions results in an efficient and accurate MoM analysis for 3-D multilayer microstrip structures     

Three-Dimensional Wave Optical Simulation for Image Sensors by Localized Boundary Element Method

A novel wave optical simulation method [a localized boundary element method (BEM)] has been developed. This method enables us to execute 3-D wave optical simulation with much smaller memory space and much shorter calculation time than conventional BEMs or finite-difference time domain methods. The light gathering power dependence on cell size and microlens height and distance, the color shading characteristics of inner lens structures, and the light gathering power and cross talk of light waveguide were analyzed by this method. A smaller cell needs a shorter focal length microlens, which can be realized by inner lens structures in CCD or the waveguide structures in CMOS image sensors. It is shown that this method can optimize these structures by calculating the color shading dependence on the microlens shape and the cross talk dependence on the waveguide materials. This method was found to be powerful and useful for the 3-D wave optical analysis of image sensors.     

元胞自动机方法模拟硅的各向异性腐蚀研究

随着计算机运算速度的提高及M EM S结构变得日渐复杂,元胞自动机(CA)方法逐渐在M EM S CAD方面显出优势。针对硅的各向异性腐蚀模拟,首先建立硅衬底表面元胞的腐蚀过程二维CA模型,然后推广为三维CA模型,从而建立了硅的各向异性腐蚀的连续CA模型。已有实验结果和理论分析证明了模型的效果。     

Parameterization-invariant shape comparisons of anatomical surfaces

We consider 3-D brain structures as continuous parameterized surfaces and present a metric for their comparisons that is invariant to the way they are parameterized. Past comparisons of such surfaces involve either volume deformations or nonrigid matching under fixed parameterizations of surfaces. We propose a new mathematical representation of surfaces, called q-maps, such that L2 distances between such maps are invariant to re-parameterizations. This property allows for removing the parameterization variability by optimizing over the re-parameterization group, resulting in a proper parameterization-invariant distance between shapes of surfaces. We demonstrate this method in shape analysis of multiple brain structures, for 34 subjects in the Detroit Fetal Alcohol and Drug Exposure Cohort study, which results in a 91% classification rate for attention deficit hyperactivity disorder cases and controls. This method outperforms some existing techniques such as spherical harmonic point distribution model (SPHARM-PDM) or iterative closest point (ICP).     

Study and design of step-index channel waveguide bends withlarge-angle and low-loss characteristics

By using micro-prisms, improved three-dimensional (3-D) bends of the embedded and buried waveguides of step-index profile are proposed. A simple phase compensation rule for the optimal design of the micro-prism is also presented. Through the simulation of 3-D semivectorial finite-difference beam propagation method, the transmission characteristics of the improved bends are shown to have been enhanced dramatically as compared with those of the conventional ones. Even for a bend angle of as large as 10°, the normalized transmitted power can still be greater than 95%. These results of 3-D bends are then compared with those of the two-dimensional (2-D) ones which are simplified from 3-D structures by the effective index method, and physical explanation of the discrepancy between the 3-D and 2-D results is introduced. The influences of waveguide structures and prism parameters on the transmission characteristics are discussed in detail. Some criteria for the design of large-angle low-loss 3-D improved bends are also accessed     

Quasi-static effective permittivity of periodic compositescontaining complex shaped dielectric particles

A methodology is described for computing the quasi-static effective permittivity of a two-dimensional (2-D) or three-dimensional (3-D) lattice of dielectric particles. The particles in this composite material may have complicated shapes. This methodology uses a moment method based technique to determine the electric dipole moments of the particles immersed in a uniform electric field. The effective permittivity is then obtained using an appropriate macroscopic model. With this methodology, the mutual interaction between particles can be accounted for accurately. The computed effective permittivity for round cylinders and spheres suspended in a host are compared with our previous T-matrix method results as well as the Maxwell Garnett (MG) formula predictions. Three additional examples involving square (2-D), rounded square (2-D), and spherical (3-D) dielectric inclusions are also given, illustrating the shape effects on the computation of the quasi-static effective permittivity. While the square- and cubic-shaped particles can possess great mutual interaction, surprisingly their effective permittivity is well predicted for all volume fractions by the simple MG formula in both 2-D and 3-D problems     

基于非均匀采样的多模型红外三维目标跟踪

针对红外三维目标跟踪过程中目标姿态变化导致跟踪器失效的问题,提出了一种基于非均匀采样的多模型方法.首先用若干个原型视图表征三维目标,将这些原型视图对应的原型形状作为目标的多模型形状表示,并建立了这些原型形状之间的转移概率矩阵.在粒子滤波框架下,以对数极坐标变换下的原型视图中目标的灰度分布特征作为参考目标模型.通过对形状转移概率采样,实现了样本形状的转移与传播.此方法提高了跟踪器对于姿态变化的鲁棒性,同时具有非均匀采样特性的对数极坐标变换可以抑制图像尺度、旋转造成的畸变,并起到压缩周边的计算量的作用.仿真结果表明,这种算法对三维目标有较好的跟踪效果.     

A 3-D reconstruction algorithm for interpolation and extrapolation of planar cross sectional data

A three dimensional (3-D) reconstruction algorithm utilizing both linear interpolation and linear extrapolation was developed for the study of human prostatic cancer. The algorithm was validated by comparing the volumes and shapes of original to reconstructed objects. Synthetic objects of known geometry and wax models with shapes characteristic of prostatic carcinomas were assessed with standard planimetry and by the digital interpolation-extrapolation method. Volume and multifocality measurements obtained by reconstructing excised prostate glands using histologic maps obtained from whole-mount sections were tested. The new algorithm provided greater accuracy in determining tumor volumes than conventional methods. This model provides a basis for mathematical analysis of prostate cancer lesions.     

A hybrid BEM/WTM approach for analysis of the EM scattering fromlarge open-ended cavities

An effective hybrid boundary-element method (BEM) and wavelet-transform method (WTM) is proposed to analyze electromagnetic scattering from three-dimensional (3-D) open-ended cavities with arbitrary shapes. This hybrid technique formulates the original cavity problems by a magnetic field integral equation. The BEM is employed to establish the mapping between the original complex integral surface and the unit square. The WTM is used to reduce the density of the moment matrix. Since a surface integral equation has to be solved, the WTM requires a two-dimensional (2-D) wavelet basis to implement the numerical computation. The previous fast iterative algorithm for 2-D wavelets has been extended for efficiently constructing various 2-D wavelet basis functions by a tensorial product from two one-dimensional (1-D) regular multiresolution analyses. Unlike the conventional method of moments, the proposed hybrid technique can always obtain sparse moment matrix equations, which can be efficiently solved by sparse solvers. As the level scales for numerical discretization of cavities increase, larger compression rates can be obtained, which makes it possible for the hybrid BEM/WTM technique to efficiently solve scattering from large open-ended cavities with complex terminations. Numerical results are presented to demonstrate the merits of the proposed method     

Experiments for 3-D structuring of thick resists by gray tone lithography

With the conventional micromachining technologies: isotropic and anisotropic dry and wet etching, a few shapes can be done. To overcome this limitation binary multi-masking technique, laser micro-stereolithography, or direct electron-beam-writing were used, but an inexpensive one-step UV-lithographic method, using the so-called “gray-tone lithography”, seems to be the best choice to produce local intensity modulation during exposure process. The paper reports on the study of arbitrary three-dimensional (3-D) shaping of negative and positive thick resists, using this method, and common technologies in standard ICs fabrication. Particular emphasis is placed on the design, manufacturing and use of half-tone transmission masks, required for UV-lithographic step in the fabrication process of mechanical, optical or electronics components. The original design and fabrication method, for the gray-tone reticles, were supported by experiments showing the main advantage of this new technology: the 3-D structuring of thick resists in a single exposure step, and also a high aspect ratio obtained over 9:1. Experimental results are presented in SEM micrographs, only for positive thick resists, showing different 3-D shapes in positive and negative polarity, and also the results obtained by using the wall-type test structure for aspect ratio evaluation. Finally, by optimization of the lithographic process, interesting applications are shown.     

Development of a Rat Computational Phantom Using Boundary Representation Method for Monte Carlo Simulation in Radiological Imaging

Computational models for small experimental animals are important in medical imaging and radiation dosimetry researches. The boundary representation method by use of nonuniform rational B-splines (NURBS) is adopted in this paper to develop a rat computational phantom based on the previously obtained segmentation data for cryosectional color photographic images of an adult male Sprague–Dawley rat. Continuous two-dimensional contours for a total of 14 major structures were outlined from the downscaled anatomical atlas, corresponding to a voxel size of ${hbox{0.2}}times {hbox{0.2}} times {hbox{0.2}} { hbox{mm}}^{3}$ and stacked to reconstruct the three-dimensional (3-D) shapes. The NURBS model was then appropriately fitted through the surface of each organ. Monte Carlo simulation of cone beam X-ray computed tomography was performed focusing on the thorax region to demonstrate the usefulness of the computational phantom in radiological imaging. The integrated whole-body geometry is presented with smooth internal and exterior boundaries. Organ centroid coordinates and volume information are tabulated for future comparison purposes. The rat phantom can be used in 3-D dose calculation and other computational applications as well.      

UAV-Borne 3-D Mapping System by Multisensor Integration

To represent 3-D space in detail, it is necessary to acquire 3-D shapes and textures simultaneously and efficiently through the use of precise trajectories of sensors. However, there is no reliable, quick, cheap, and handy method for acquiring accurate high-resolution 3-D data on objects in outdoor and moving environments. In this paper, we propose a combination of charge-coupled device cameras, a small and inexpensive laser scanner, an inexpensive inertial measurement unit, and Global Positioning System for a UAV-borne 3-D mapping system. Direct georeferencing is achieved automatically using all of the sensors without any ground control points. A new method of direct georeferencing by the combination of bundle block adjustment and Kalman filtering is proposed. This allows objects to be rendered richly in shape and detailed texture automatically via a UAV from low altitude. This mapping system has been experimentally used in recovery efforts after natural disasters such as landslides, as well as in applications such as river monitoring.      

3-D IIR filtering using decimated DFT-polyphase filter bank structures

Two three-dimensional (3-D) under-decimated uniform discrete Fourier transform polyphase filter bank structures are proposed along with two applications: first, the sub-pixel motion discrimination of two-dimensional spatial objects moving with approximately constant local velocity in a noisy 3-D spatio-temporal image sequence and, second, the selective filtering of 3-D spatio-temporal broad-band plane waves based on their directions of arrival. The desired 3-D filter passband shapes are realized utilizing combinations of highly selective first-order 3-D infinite-impulse response frequency-planar filters in each band between the analysis and synthesis sections. Measured spatio-temporal performance confirms the high-quality broad-band transmission of passband signals, high directional selectivity and low computational complexity.     

任意行波管慢波结构中导体和介质损耗的三维有限元分析

该文给出一种用于精确计算任意行波管慢波结构中介质和导体损耗的3维有限元分析方法。给出一种新型的慢波结构指定频率本征分析方法。不像传统的指定相移本征分析方法在慢波结构有耗有限元仿真中必须求解一个非线性的广义本征问题,指定频率本征分析方法仅仅需要求解一个线性的广义本征问题,而且慢波结构的导体和介质损耗可以不需要任何的后处理而精确地得出。通过仿真实际的慢波结构,验证了指定频率本征分析方法可以精确地计算出慢波结构的导体和介质损耗。