虚拟手术中软组织形变与切割技术研究

发布时间：2018-06-20 20:00

本文选题：局部模型 + 无网格伽辽金法　；参考：《哈尔滨工程大学》2012年博士论文

【摘要】：传统手术训练使用人类的尸体、动物或橡胶人体模型作为训练对象，存在着尸源短缺、成本昂贵、与真实人体组织特性差别较大及迫害动物等诸多局限和问题，计算机技术的迅速发展使得数值模拟技术逐渐成为解决此类问题的重要手段，研究人员开始探索将虚拟现实技术应用于医护人员的外科手术培训中，通过建立集成有视觉显示、力觉再现、听觉、嗅觉等多感知的虚拟手术环境，给予医生逼真的手术场景，实现手术培训教学、术前规划、术中辅助支持、术后分析、复杂手术的反复演练等全面训练医护人员的目的。虚拟现实技术与现代医学的结合为高科技医学技术的发展提供了广阔的空间，也使得虚拟现实技术面临一个崭新而艰巨的挑战。在实际手术中，医生主要依靠视觉与触觉反馈信息进行手术操作，因此虚拟手术系统大都是针对视觉与触觉两大方面的仿真研究，通过视觉反馈直观地呈现出逼真的虚拟手术场景及操作对象，利用触觉反馈感受虚拟环境中力的作用并对操作作出及时、正确的判断。本文也是从视觉与触觉反馈两方面出发，选择典型的且难度较大的人体软组织器官作为研究对象，紧紧围绕虚拟手术中具有代表性的形变与切割两项关键技术展开深入的研究，主要工作如下：首先，针对图像的手动分割工作量大及自动分割精度不高的问题，提出了将手动分割与自动分割相结合的医学图像分割方式，重建了具有人体解剖结构特征的胃组织及肝脏组织的几何模型，并对其进行视觉渲染与纹理映射，从而得到了真实度较高的人体软组织模型；对力反馈技术及反馈力的计算与测试方法进行了研究，提出了基于PVDF（Polyvinylidene Fluoride，聚偏二氟乙烯）压电薄膜传感器的反馈力测试方法，并应用于软组织形变与切割模拟中反馈力的测试上。其次，针对医学触诊的特点及现有形变仿真建模方法的不足，提出了可变区域的局部质点-弹簧/阻尼器（ALMSDM）模型，该模型具有位置可变及区域可扩展的优点，改善了以往文献中局部建模方法区域限定及全局的面模型形变恢复能力差的问题，并在虚拟软组织面模型与体模型中得到了较好的应用。从系统实时性的角度，针对ALMSDM在面模型与体模型中的应用，分别提出了顶点法向量的局部更新思想与预计算策略，使系统的实时性得到了较大的改善。从形变恢复能力、反馈力分析及实时性评测三方面对面模型与体模型的ALMSDM进行了评价，进而验证所提算法的可行性与通用性。再次，创新性地将无网格法理论应用于虚拟手术的形变建模中，在对质点积分无网格伽辽金法进行深入研究的基础上，针对虚拟软组织形变多为大变形的特点，提出了一种改进的质点积分无网格伽辽金法，并采用二维梁理论对所建模型进行了理论验证；然后基于改进算法建立了虚拟软组织形变仿真的静态模型与动态模型，在静态模型仿真中采用静态位移累加的方式实现了动态形变过程的模拟，与动态模型相比，其速度很快，但由于缺少中间连续变化的过程使得该模型计算精度不高；动态模型的形变仿真计算量相对较大，，本文综合考虑了动态模型的特点及虚拟手术实时性能的要求对模型进行了近似求解。仿真实验与对比分析表明，无网格法在软组织形变仿真中表现出良好的稳定性和可靠性，避免了基于网格建模方法在模拟大形变时容易出现网格扭曲、锁死等问题，解决了虚拟软组织大变形时误差大的问题；最后采用PVDF传感器对动态模型的实际反馈力进行测试，并与反馈力模型计算得到的数据进行对比分析。本文最后对虚拟手术切割算法进行了研究，针对现有切割算法存在的问题，提出了切口边界独立绘制的方案，即切口边界的绘制不再依赖于网格破裂后的拓扑重组；结合切口的特点及样条方法的优越性质，提出新颖的基于Bézier曲线的切口再现算法，解决了切口绘制不光滑的问题；通过在区域边界点与Bézier曲线之间直接添加弹簧约束的方式，使模型能够灵活、真实地控制切口的张裂度，实现了切口弹性张开的逼真效果；对切割操作中含摩擦力与不含摩擦力的计算模型进行了理论与实测的对比分析，并设计了手术切割后摘除异物的仿真实验。
[Abstract]:The traditional surgical training uses human body, animal or rubber body model as the training object. There is a shortage of corpse sources, high cost, large difference with the real human tissue characteristics and the persecution of animals and other limitations and problems. The rapid development of computer technology makes the numerical simulation technology gradually become an important means to solve such problems. The researchers began to explore the application of virtual reality to the training of medical and nursing personnel. By establishing a virtual operating environment integrated with visual display, reappearance of force, hearing, smell and so on, a realistic operation scene was given to the doctor, the training teaching, pre operation planning, auxiliary support, postoperative analysis, and complex hands were carried out. With repeated drills and other comprehensive training medical personnel. Combined with virtual reality technology and modern medicine has provided a broad space for the development of high-tech medical technology, virtual reality technology has faced a new challenge.
In the actual operation, the doctor mainly relies on the visual and tactile feedback information to operate the operation, so the virtual operation system is mostly aimed at the two aspects of the visual and tactile simulation. The virtual operation scene and the operating object are presented intuitively through the visual feedback, and the effect of the force in the virtual environment is felt by the tactile feedback. From the two aspects of visual and tactile feedback, this paper also selects typical and difficult human soft tissue organs as the research object, and focuses on two key technologies of representative deformation and cutting in virtual surgery. The main work is as follows:
First, in view of the problem of manual segmentation and low automatic segmentation accuracy, a medical image segmentation method, which combines manual segmentation and automatic segmentation, is proposed. The geometric model of gastric tissue and liver tissue with human anatomical features is reconstructed, and the visual rendering and texture mapping are carried out. The human soft tissue model with high authenticity is studied and the calculation and test method of force feedback technology and feedback force are studied. The feedback force testing method based on PVDF (Polyvinylidene Fluoride, polyvinylidene fluoride) piezoelectric thin film sensor is put forward and applied to the test of feedback force in soft tissue shape change and cutting simulation.
Secondly, in view of the characteristics of medical palpation and the shortage of existing deformation simulation modeling methods, a local particle spring / damper (ALMSDM) model with variable regions has been proposed. The model has the advantages of variable location and region extensibility, which improves the poor recovery ability of regional model and the global surface model in the previous literature. The problem is better applied in the virtual soft tissue surface model and the body model. From the point of view of the real time of the system, in view of the application of ALMSDM in the surface model and the body model, the local updating idea and the Precalculation strategy of the vertex normal vector are put forward respectively, so that the real-time performance of the system has been greatly improved. From the deformation recovery ability and feedback, the feedback of the system is greatly improved. The three aspects of force analysis and real-time evaluation are evaluated on the ALMSDM of the face model and the body model, and the feasibility and versatility of the algorithm are verified.
Thirdly, the theory of meshless method is applied to the deformation modeling of virtual surgery. On the basis of the deep study of the meshless Galerkin method, a modified particle integral meshless Galerkin method is proposed in view of the characteristics of the large deformation of virtual soft tissue, and the two dimensional beam theory is used to build the model. The static model and dynamic model of the virtual soft tissue deformation simulation are established based on the improved algorithm, and the dynamic deformation process is simulated by the static displacement accumulation in the static model simulation. Compared with the dynamic model, the speed is very fast, but the process of lack of continuous change in the middle is very fast. The accuracy of the model calculation is not high, and the calculation of the dynamic model is relatively large. In this paper, the characteristics of the dynamic model and the requirements of the real time performance of the virtual operation are considered. The simulation experiment and the comparison analysis show that the meshless method shows good stability and reliability in the soft tissue deformation simulation. It avoids the problem of grid distortion and locking, which can solve the problem of large error in the large deformation of virtual soft tissue. Finally, the PVDF sensor is used to test the actual feedback force of the dynamic model, and the data obtained by the feedback force model are compared and analyzed.
At the end of this paper, the virtual surgical cutting algorithm is studied. In view of the existing problems of the existing cutting algorithms, a scheme for the independent rendering of the incision boundary is proposed. That is, the drawing of the incision boundary is no longer dependent on the topology reorganization after the mesh breaking, and a novel B e zier curve based on the characteristics of the incision and the superiority of the spline method is proposed. The algorithm of incision reappearance solves the problem of unsmoothness in cutting the cut. By adding a spring constraint directly between the boundary point of the region and the B e zier curve, the model can be flexibly and truly control the crack extension of the incision, and the realistic effect of the elastic opening of the incision is realized, and the calculation of the friction and non friction force in the cutting operation is made. The model is compared with theoretical analysis and field measurement, and the simulation experiment of removing foreign body after surgical incision is designed.
【学位授予单位】：哈尔滨工程大学
【学位级别】：博士
【学位授予年份】：2012
【分类号】：R318.6;TP391.9

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