摘要
虚拟手术是虚拟现实技术在现代医学领域中的应用。虚拟手术仿真系统的开发应用不但可以为医生提供内窥镜手术的训练平台,还可以辅助真实的手术治疗。它的出现大大方便了内窥镜手术的推广和应用。因此,虚拟手术具有很好的研究价值和应用前景。
实用的虚拟手术系统必须绘制出逼真的手术场景。要展现人体皮肤、各种组织器官和骨骼表面丰富的纹理细节,就需要综合运用纹理合成技术来进行纹理绘制。考虑到人体器官表面纹理的生理特殊性和几何形状复杂性,进行简单的纹理映射不能够满足系统需求。因此,对纹理合成技术进行改进和综合应用也是虚拟手术系统研发的重点内容之一。本文着眼提高虚拟手术系统中的纹理合成速度和合成质量两方面内容,分别对二维纹理合成技术和三维曲面纹理合成技术进行了研究和部分改进。主要内容如下:
对二维纹理合成技术的理论基础进行了研究,提出了一种基于样图的逐点纹理合成算法。该算法能够计算识别样本的基本纹元,并自动选择最佳邻域进行二维纹理合成。在此基础上,作者设计了一个通用的图像处理和纹理合成软件Dipper,能够实现对医学纹理样本的快速、有效合成。
对一种基于块的三维曲面纹理合成过程进行了改进,在这种算法的基础上,增加了网格简化和矢量场计算两个步骤,从而实现了快速有效的三维曲面纹理合成。采用这种方法不但能够有效消除曲面纹理合成中常见的纹理变形和接缝等问题,并且大大加快了曲面纹理的合成速度。
最后,本文结合“虚拟膝关节镜手术系统”实例,设计了虚拟手术中的纹理贴图框架模型,并建立了纹理样本数据库。在系统开发过程中,使用这个纹理贴图框架,能够根据不同场景的不同需求,自由选择二维映射或三维曲面直接合成两种方法来绘制物体的纹理细节。这种混合的纹理贴图框架技术,不但为系统提供了更加逼真、一致的虚拟手术场景,而且加快了系统场景的更新速度,达到了虚拟手术系统的开发要求。
Virtual Surgery is the application of Virtual Reality technology in the field of modern medicine. The development and application of the Virtual Surgery system can not only provide the endoscopic surgery training platform for doctors, but also support real surgery. Its emergence promotes the popularity and application of endoscopic surgery greatly. Therefore, the Virtual Surgery is of great research value and prospect.
Practical Virtual Surgery system must draw a realistic surgical scene. In order to show the rich texture details of surface skin, all kinds of soft tissues and bone surface, it is necessary to make comprehensive use of Texture Synthesis Technology. Because of the human organs' complexity of texture and geometrical features, a simple Texture Mapping system can not meet the need of Virtual Surgery system. Thus, the improvement and comprehensive application of the Texture Synthesis Technology is one of the key technologies of the research and development of Virtual Surgery system. This thesis focuses on the improvement of the texture synthesis in the perspective of speed and quality, and does some research on 2D texture synthesis and 3D texture synthesis technology. This research can be described as follows.
In 2D texture synthesis technology, this thesis adopts a method based on the sample point by point, presents a best neighborhood algorithms and develops a practical software named "Dipper" which can process image and texture synthesis. The software "Dipper" realize fast and effective of synthesis the medical samples texture
This thesis proposes a new method of 3D texture synthesis algorithm. Firstly, the triangle mesh is simplified and segmented. Then, a growth direction of the vector field is calculated on the triangle mesh. Base on the vector field, the texture is synthesized on the surface patch by patch. This algorithm not only avoids the phenomena of seaming and distortion in 3D surface texture synthesis, but also accelerates the process of texture synthesis.
Finally, as shown in the example of "Virtual Arthroscopy Surgery System", we design the texture mapping framework and establishes the texture sample database. In the system development process, the use of the texture mapping framework can meet different scenes by choosing 2D texture mapping or 3D surface texture synthesis in rendering texture details for virtual objects. The proposed framework can provide more realistic and consistent virtual surgery scenes. Besides, it significantly speeds up the updating rate of the virtual scenes and therefore satisfies the demands of Virtual Surgery system.
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