CT系列图像的三维层次化子块生长分割

准确地从CT系列图像提取感兴趣的组织是手术规划的基础,针对肝脏轮廓分割存在分割不全的问题,提出了基于三维区域生长算法的腹部CT图像分割方法。算法首先由用户选择若干个生长点,然后充分利用CT系列图像层间的相似性,提出基于子块的改进区域生长算法,实现三维的层次化子块区域生长,以更准确提取肝脏区域,其中生长准则由系统分析用户选择的生长点的邻域子块属性获得,以减少用户的干预。实验结果表明,算法能在较少的干预下快速分割出来CT系列图像中的肝脏轮廓。     

基于体平滑的体绘制纹理伪边界消除算法

直接体绘制能够清楚的显示三维数据场的内部信息,是科学可视化中非常重要的一类方法。其中,基于二维纹理映射的三维数据直接体绘制方法具有绘制速度快、可交互性强的优点。其基本思路是将三维数据体在时间或深度方向形成一组水平纹理切片,通过这些切片的纹理贴图,实现三维数据体的体绘制,在交互性和资源消耗之间取得了较好的平衡。本文针对基于二维纹理映射的直接体绘制方法中在透明与不透明边界产生阶梯状条纹的伪边界问题,提出了一种基于体平滑的算法。该算法通过在透明数据与不透明数据的边界进行体平滑,使采样过程中缺失的数据表现到抽样的切片上,从而在最终图像生成阶段淡化甚至消除阶梯状条纹伪边界。实验结果表明,相对于传统二维纹理映射方法,本算法实现体绘制效果平滑,提高了绘制效果。     

医学图像三维可视化中任意平面切片的研究与实现

对医学图像的三维重建技术进行研究,利用介于面绘制和体绘制之间的切片法来实现三维体数据可视化,并针对断层图像序列所生成三维体数据的切片方法进行了深入讨论。提出一种可操作性很强的切片方法,能较好地实现三维体数据中冠状面、矢状面、特别是任意平面的切片。同时,该方法已经用VC6．0结合VTK（Visualization Toolkit）编程进行实现,效果符合医学诊断要求,并得到了有关应用。     

Augmented reality simulator for training in two-dimensional echocardiography.

In two-dimensional echocardiography the sonographer must synthesize multiple tomographic slices into a mental three-dimensional (3D) model of the heart. Computer graphics and virtual reality environments are ideal to visualize complex 3D spatial relationships. In augmented reality (AR) applications, real and virtual image data are linked, to increase the information content. In the presented AR simulator a 3D surface model of the human heart is linked with echocardiographic volume data sets. The 3D echocardiographic data sets are registered with the heart model to establish spatial and temporal congruence. The heart model, together with an animated ultrasound sector represents a reference scenario, which displays the currently selected two-dimensional echocardiographic cutting plane calculated from the volume data set. Modifications of the cutting plane within the echocardiographic data are transferred and visualized simultaneously and in real time within the reference scenario. The trainee can interactively explore the 3D heart model and the registered 3D echocardiographic data sets by an animated ultrasound probe, whose position is controlled by an electromagnetic tracking system. The tracking system is attached to a dummy transducer and placed on a plastic puppet to give a realistic impression of a two-dimensional echocardiographic examination.     

Measurement protocol of women's nude breasts using a 3D scanning technique

It has been difficult to obtain accurate surface data for women's breasts, since the borderline of the breast is ambiguous at the skin surface. In this paper, we scanned 37 women's nude breasts using 3D phase shifting moiré and explored a measurement protocol to get a reliable boundary of the breast and thereby provided new shape parameters for breasts. The folding line method was useful for finding a continuous and natural boundary for the breasts, so that the breasts base and volume could be measured more accurately. The global average radius of the curvature of the bottom breast line was suggested as a useful shape parameter for the design of a comfortable and form-fitting brassiere, especially for those who have a skewed bottom breast curve. It is also expected that data on breast volume based on natural anatomy would be a useful reference for surgical operation on the breast.     

Three-dimensional surface reconstruction of tree canopy from lidar point clouds using a region-based level set method

In this article, a novel method is proposed for three-dimensional (3D) canopy surface reconstruction of trees using a region-based level set method. Both individual tree crowns and clusters of trees are first marked for further exploration. Multiple horizontal slices corresponding to different heights are obtained. The 3D structure of tree canopy is built using raw data from lidar point clouds. Also, new applications are proposed based on the new method for 3D forest reconstruction. The biomass parameters of the forest, including tree intersection area, tree equivalent crown radius, and canopy volume, can be calculated from stacking 2D slices of trees. Tree types are also identified and classified. The results indicate that this approach is effective for 3D surface reconstruction of forests including individual trees and clusters of trees, and that critical forest parameters (such as tree intersection area, tree position, and canopy volume) can be derived for the evaluation and measurement of biophysical parameters of forests.     

Interactive Construction and Animation of Layered Elastically Deformable Characters

An interactive system is described for creating and animating deformable 3D characters. By using a hybrid layered model of kinematic and physics-based components together with an immersive 3D direct manipulation interface, it is possible to quickly construct characters that deform naturally when animated and whose behavior can be controlled interactively using intuitive parameters. In this layered construction technique, called the elastic surface layer model, a simulated elastically deformable skin surface is wrapped around a kinematic articulated figure. Unlike previous layered models, the skin is free to slide along the underlying surface layers constrained by geometric constraints which push the surface out and spring forces which pull the surface in to the underlying layers. By tuning the parameters of the physics-based model, a variety of surface shapes and behaviors can be obtained such as more realistic-looking skin deformation at the joints, skin sliding over muscles, and dynamic effects such as squash-and-stretch and follow-through. Since the elastic model derives all of its input forces from the underlying articulated figure, the animator may specify all of the physical properties of the character once, during the initial character design process, after which a complete animation sequence can be created using a traditional skeleton animation technique. Character construction and animation are done using a 3D user interface based on two-handed manipulation registered with head-tracked stereo viewing. In our configuration, a six degree-of-freedom head-tracker and CrystalEyes shutter glasses are used to display stereo images on a workstation monitor that dynamically follow the user head motion. 3D virtual objects can be made to appear at a fixed location in physical space which the user may view from different angles by moving his head. To construct 3D animated characters, the user interacts with the simulated environment using both hands simultaneously: the left hand, controlling a Spaceball, is used for 3D navigation and object movement, while the right hand, holding a 3D mouse, is used to manipulate through a virtual tool metaphor the objects appearing in front of the screen. Hand-eye coordination is made possible by registering virtual space to physical space, allowing a variety of complex 3D tasks necessary for constructing 3D animated characters to be performed more easily and more rapidly than is possible using traditional interactive techniques.     

Efficient computation of cross-sections from human brain model by geometric processing

In this paper, an efficient method for computing the cross-sections of the internal structure from a 3D human brain model has been proposed. It can extract image slices from the brain model in sagittal, coronal, and axial views used for computed tomography and ultrasonography. A doubly connected edge list (DCEL) has been used for speeding up the computation during geometric processing, since the DCEL captures the topological relationship among vertices, edges, and faces of the triangulated surface. For a sectional plane, image slices are computed quite efficiently using the information of geometric coherence from the previous sectional plane with the help of DCEL. The optimal distance between two successive sectional planes is determined from the frequency distribution (Poisson distribution) of the edge lengths in the model. It reduces computational overhead without compromising on the quality of output, as demonstrated by experimental results.     

Design and implementation of software for assembly and browsing of 3D brain atlases

Visualization software for three dimensional digital brain atlases present many challenges in design and implementation. These challenges include the design of an effective human interface, management of large data sets, display speed when slicing the data set for viewing/browsing, and the display of delineated volumes of interest (VOI). We present a software design, implementation and storage architecture that addresses these issues, allowing the user to navigate through a reconstructed volume quickly and smoothly, with an easy-to-use human interface. The software (macostat, for use with Macintosh OS) allows the user to rapidly display slices of the digital atlas at any arbitrary slicing angle, complete with delineated VOIs. The VOIs can be assigned colors of the user's choosing. The entire atlas, or selected portions, may be resliced with slices stored as individual image files, complete with delineations. These delineations may be transferred to corresponding sections of experimental materials using our analysis program (brain). The software may be obtained from the laboratory's web site: http://www.neuroterrain.org     

"智能剪刀"在体数据切割中的应用

在二维图像分割中，“智能剪刀”是一种非常用的交互方法。     

Isthmus based parallel and symmetric 3D thinning algorithms

We propose a 3D symmetric homotopic thinning method based on the critical kernels framework. It may produce either curvilinear or surface skeletons, depending on the criterion that is used to prevent salient features of the object from deletion. In our new method, rather than detecting curve or surface extremities, we detect isthmuses, that is, parts of an object that are “locally like a curve or a surface”. This allows us to propose a natural extension of our new method that copes with the robustness to noise issue, this extension is based on a notion of “isthmus persistence”. As far as we know, this is the first method that permits to obtain 3D symmetric and robust curvilinear/surface skeletons of objects made of voxels.     

A software system for evaluation and training of spatial reasoning and neuroanatomical knowledge in a virtual environment

This paper describes the design and development of a software tool for the evaluation and training of surgical residents using an interactive, immersive, virtual environment. Our objective was to develop a tool to evaluate user spatial reasoning skills and knowledge in a neuroanatomical context, as well as to augment their performance through interactivity. In the visualization, manually segmented anatomical surface images of MRI scans of the brain were rendered using a stereo display to improve depth cues. A magnetically tracked wand was used as a 3D input device for localization tasks within the brain. The movement of the wand was made to correspond to movement of a spherical cursor within the rendered scene, providing a reference for localization. Users can be tested on their ability to localize structures within the 3D scene, and their ability to place anatomical features at the appropriate locations within the rendering.     

逆向工程中基于精确截面信息的曲面拟合*

针对带有精确截面信息的有序离散点的三维曲面重构问题,提出了一种NURBS曲面快速重构方法。该方法有效地减少了运算数据量,提高了运算效率,同时改进了传统曲面拟合在处理非均匀截面数据点时曲线曲面形状的失真和运算的不稳定现象,最后应用三维图形标准以及图形函数库在实际系统中验证了该方法的有效性。     

A denoising method for pavement 3d data based on breakpoint interpolation and reference plane filtering

In order to meet the current pavement intelligent detection and feature parameter extraction requirements, a 3D pavement surface data denoising method based on breakpoint interpolation and reference plane filtering (BI-RPF) is proposed and demonstrated using 3D pavement data acquired by a laser-based 3D imaging system. First, the principal structure and major characteristics of 3D pavement data were analyzed. Next, the breakpoint interpolation method considering the relationship between ordinate and slope was proposed to complete the missing values from the original pavement data. Then, reference plane filtering based on the horizontal and longitudinal reference plane was realized so as to overcome the unevenness of the pavement. Finally, the filtering effectiveness of the proposed method was compared with that of the standard deviation filtering and median filtering methods. The results show that the proposed filtering method takes breakpoints and uneven road surface into account, which can provide more accurate 3D road surface data under more complex conditions. The algorithm provided a good denoising effect while retaining valid data describing the road surface morphology, which establishes a foundation of BI-RPF to 3D pavement reconstruction.

     

Photogrammetric reconstruction of free-form objects with curvilinear structures

The shapes of many natural or man-made objects have curve features. The images of such curves usually do not have sufficient distinctive features to apply conventional feature-based reconstruction algorithms. In this paper, we introduce a photogrammetric method for recovering free-form objects with curvilinear structures. Our method chooses to obtain the topology and geometry of a sparse 3D wireframe of the object first instead of directly recovering a surface or volume model. Surface patches covering the object are then constructed to interpolate the curves in this wireframe while satisfying certain heuristics such as minimal bending energy. The result is an object surface model with curvilinear structures from a sparse set of images. We can produce realistic texture-mapped renderings of the object model from arbitrary viewpoints. Reconstruction results on multiple real objects are presented to demonstrate the effectiveness of our approach.     

Dynamic picking system for 3D seismic data: Design and evaluation

In the framework of data interpretation for petroleum exploration, this paper contributes two contributions for visual exploration aiming to manually segment surfaces embedded in volumetric data. Resulting from a user-centered design approach, the first contribution, dynamic picking, is a new method of viewing slices dedicated to surface tracking, i.e. fault-picking, from 3D large seismic data sets. The proposed method establishes a new paradigm of interaction breaking with the conventional 2D slices method usually used by geoscientists. Based on the 2D+time visualization method, dynamic picking facilitates localizing of faults by taking advantage of the intrinsic ability of the human visual system to detect dynamic changes in textured data. The second, projective slice, is a focus+context visualization technique that offers the advantage of facilitating the anticipation of upcoming slices over the sloping 3D surface. From the reported experimental results, dynamic picking leads to a good compromise between fitting precision and completeness of picking while the projective slice significantly reduces the amount of workload for an equivalent level of precision.     

基于面绘制技术的医学影像立体显示

医学影像立体显示技术利用二维医学图像序列重建出三维模型,为医生提供了直观、全面、准确的病灶和正常组织信息,给临床诊断和治疗带来了巨大进步,是当今医学领域研究的热点。三维重建有体绘制和面绘制两种方法,本文主要介绍了面绘制方法的原理和实现,选择基于体素的表面重建方法,利用国际上广泛应用的可视化工具包VTK提供的MC算法实现面绘制,并对轴、冠、矢三个方向的任意切面进行显示。     

ISDMS—a scientific data management system

This paper describes the design and development of the Idaho National Engineering Laboratory Scientific Data Mangement System (ISDMS). The ISDMS is an integrated system providing organization, processing, control and retrieval of scientific time series data in a large laboratory environment using Control Data Corporation (CDC) computers. Data reformatting, graphics, data manipulation, data management, engineering analysis and general utility functions are offered to engineers, scientists, and other end users. The ISDMS usage has grown steadily since its first release into production status in early 1979. The current configuration is well received by the user community and meets most requirements for studying and analysing data in a scientific environment.     

Surface extraction from multi-field particle volume data using multi-dimensional cluster visualization

Data sets resulting from physical simulations typically contain a multitude of physical variables. It is, therefore, desirable that visualization methods take into account the entire multi-field volume data rather than concentrating on one variable. We present a visualization approach based on surface extraction from multi-field particle volume data. The surfaces segment the data with respect to the underlying multi-variate function. Decisions on segmentation properties are based on the analysis of the multi-dimensional feature space. The feature space exploration is performed by an automated multi-dimensional hierarchical clustering method, whose resulting density clusters are shown in the form of density level sets in a 3D star coordinate layout. In the star coordinate layout, the user can select clusters of interest. A selected cluster in feature space corresponds to a segmenting surface in object space. Based on the segmentation property induced by the cluster membership, we extract a surface from the volume data. Our driving applications are Smoothed Particle Hydrodynamics (SPH) simulations, where each particle carries multiple properties. The data sets are given in the form of unstructured point-based volume data. We directly extract our surfaces from such data without prior resampling or grid generation. The surface extraction computes individual points on the surface, which is supported by an efficient neighborhood computation. The extracted surface points are rendered using point-based rendering operations. Our approach combines methods in scientific visualization for object-space operations with methods in information visualization for feature-space operations.