【作者】 袁清伟；

【导师】 刘伯强；

【作者基本信息】 山东大学 ， 生物医学工程， 2009， 硕士

【摘要】 随着CT、MRI等医学影像设备的出现,传统的医学诊断方式发生了革命性的变化,利用医学影像设备,医生可以直接从二维面方向对人体内部组织进行观察,从一定的程度上提高了诊断效率和诊断的准确性。医生通过观察一组CT,MRI的二维切片去发现病变体,这主要依赖与医生的读片经验和对图像的定性分析,如何获取病变体更直观准确的信息,因此二维图像的三维可视化技术就被提上了研究日程。由于计算机技术的迅速发展,对于海量的体数据进行三维可视化已成为可能。医学图像的三维可视化是一个多学科交叉研究领域,是计算机图形学和图像处理在生物医学工程中的重要应用。本文首先介绍了三维数据场的结构,对本文将用到的可视化工具包VTK(Visualization Toolkit)的可视化流程和可视化模型作了系统全面的分析,同时对DICOM格式的CT图像相关知识进行了介绍。本文的研究重点是三维可视化技术,文中对可视化中的面绘制技术,体绘制技术和虚拟切割技术进行了重点研究和探讨。面绘制技术中主要介绍了轮廓线连接法,Marching Cubes法和DividingCubes法的原理,并在重点研究MC算法原理的基础上,针对经典的MC算法中产生海量的中间三角面片,极大的耗费了绘制时间,提出了减少三角面片的改进的MC算法。改进的MC算法通过减少满足约束条件的顶点,以达到减少中间过程中生成的三角面片的数目,并通过实验证明改进的MC算法在不明显降低绘制效果的前提下减了少构造的中间三角面片,明显的提高了绘制速度。体绘制技术中介绍了错切—形变法,抛雪球法和光线投射法。光线投射算法是体绘制技术中的典型算法,也是被广泛应用的一种算法,文中对光线投射算法的原理和实现以及绘制结果伪色彩的添加进行了重点探讨。同时本文利用DICOM格式的CT序列图像(512×512×118),借助可视化工具包VTK,结合C++编程在普通计算机上实现了上述的面绘制和体绘制的相关算法。为更充分的利用已有的图像信息,更好的辅助诊断,很多情况下仅仅重建出三维模型是远远不能满足诊断的需求的,因此本文在实现了面绘制和体绘制的基础上又对虚拟切割技术进行了探讨,包括规则面的虚拟切割,任意面的虚拟切割和盒状切割。规则面的切割是指从解剖学上三个重要的解剖方向进行虚拟切割。任意面的切割更加灵活,可以从不同角度不同方向对绘制结果进行切割,以便更好的满足医生观察的需要。盒状切割是一种更为复杂的虚拟切割技术,立方盒的六个面都具有切割功能。在对上述各种切割技术的原理进行了详细研究的基础上,结合VTK对虚拟切割进行模拟,得到了较为满意的结果。本文不仅从理论上论述了可视化算法的原理,更重要的是利用可视化工具包VTK在普通计算机上实现了相关可视化算法,为辅助诊断奠定了基础,有着重要的实践意义。更多还原

【Abstract】 The way of traditional medical diagnosis has made a revolutionary change since the mergence of the devices of medical images such as CT and MRI. With the help of these devices, the doctors can observe the inner tissue of a human body by using 2D images. It improves the diagnost efficiency and diagnost accuracy at certain extent. Nowdays, the doctors tends to diagnose by observing a series of slices of CT, MRI images. It mainly depends on the doctors’ experience. How to get more intuitionistic and accurate information about conditions of patient? The technology of three-dimensional visualization was put on the research agenda.This paper first introduces the structure of the three-dimensional data, the visualizaion process and visualization models of VTK (Visualization Toolkit) and the related knowledge of CT image.The three-dimensional visualization of the volume data has become possible because of the rapid development of computer technology. The visualization of medical images is a cross-cutting reaserch areas of different disciplines. It is the important application of the computer graphics and imge processing in bioledical engineering. The study focuses on the three-dimensional vlisualiztion technology. In this paper, the technology of surface rendering, volume rendering and virtual cutting are reasearched and discussed.Surface rendering technology includes many methods, this article introduces the principles of the algorithm of outline connection, Marching Cubes and Dividing Cubes. At the basis of studying the methods, we presented an improved MC algorithm against the classic MC which produces lots of triangular patches and uses lots of time during the rendering process. the improvede MC algorithm reduce the vertexes which meet the constrain condition to reduce the number of triangular patches, and the experiment proves that the improved MC can reduce the rendering time by reducing the trianglar patches at the premise of not obvous reducing the effect of rendering result. This article also disscusses several algorithms of volume redering, such as Shearp-warp, splating and Ray-casting. Ray-casting used widely is the typical algorithm. Its theoy and implementation, as well as the pseudo-color mapping to the result are the foucus of the paper. In the article, the CT images (512×512×118) are used to implement the algorithms of surface rendering and volume rendering in personal computer with VTK (Visualization Toolkit) and C++.In many cases, the reconstruction of a three-dimensional model is far from enough to meet the needs of the diagosis. In order to obtain more image information in to diagnosis, the article continues to study the virtual cutting technology after the successful implementation of the surface rendering and volume rendering. It includes the virtual cutting of orthogonal palnes, virtual cutting of arbitrary palne and box-shaped cutting. The virtual cutting of orthogonal palnes means cutting the rendering results along the important anatomical direction, while the virtual cutting of arbitrary plane is more flexible. It can cut the results from different angles and different direction to obtain more information to meet doctors’ need. Box-shaped cutting is a more complex virtual cutting technology. The six planes of the cubic box have the function of virtual cutting. Then VTK is used to simulate the virtual cutting after the detailed study of the principle of the above-mentioned virtual cutting technology, and we get the satisfactory experiment results.This papper theoretically discusses the principles of visualization algorithm. More importantly, the algorithms are implemented on the computer with VTK. It laid the founfation for assisted diagnosis, has important practical significance.更多还原