面向虚拟手术的人体肝脏物理建模方法研究

The physical modeling of human soft tissue plays a crucial role in medical simulation. It is a key research issue to improve the modeling efficiency while keeping the modeling accuracy.In this project, we will use liver, a typical human soft tissue, as our research subject.We will investigate a physical modeling method that is suitable for the modeling of complex soft tissues for real-time virtual surgery. The main research work of this project includes: (1) For modeling efficiency, a novel volume spring will be introduced to the traditional mass spring system. A surface mash topology and proper force representation will be investigated to simulate volume behavior. (2) A novel volume discretisation method will be investigated. The mass distribution of the surface node will then be obtained based on the relation between the surface nodes and internal volume of the tisse. (3) Through biomechanics experiments on real soft tissue and parameter analysis, the relation between the physical properties of soft tissue and the model parameters will be established. The physical meaning of the model paprameters will then be specified. (4) A novel dynamic grid modification algorithm will also be investigated to further enhance the performance of dynamic modeling..This project will provide an important research reference for the physical modeling of other biomechanics soft tissues. The research results can also be directly applied to the field of medical image processing and medecal simulation,such as surgical navigation and virtual surgery systems.

人体软组织物理建模对虚拟手术系统具有举足轻重的作用，如何在保证建模精确性的前提下提高建模效率是当前急需解决的关键问题。本项目以具有典型特征的人体软组织-肝脏为对象，拟建立满足虚拟手术交互实时性的复杂软组织物理建模方法。主要研究工作包括：（1）在表面模型的质点-弹簧系统基础上，引入体弹簧，扩充表面网格拓扑结构，建立力表达策略，满足模型的体行为模拟；（2）研究基于平面法线修正的体离散化方法，将表面元素的属性设置与其所对应的内部体积产生联系，完成属性动态分配；（3）通过真实软组织生物力学实验和参数分析，建立生物软组织材料特性与模型参数之间的关系，明确各个参数设定的物理意义；（4）研究动态网格密度修正算法进一步提高动态建模的效果，最终实现人体软组织系统的高效精确建模。本项目的研究为其它生物软组织的物理建模方法的研究提供了有益的借鉴，其成果还可直接应用于手术导航、手术规划等医学图像处理和仿真领域。

本研究以腹部CT图像为基础，通过肝脏轮廓自动提取，轮廓离散化和网格点的自动生成和优化算法建立了肝脏软组织的表面几何模型。在保证模型真实性的同时，减少了模型网格点数，为后面实时渲染软组织的变形奠定了基础。并在传统质点弹簧模型的基础上，加入了体弹簧控制，通过基于重心修正的体离散化方法解决了模型质点质量分配的问题。同时，在软组织物理建模当中考虑了软组织的阻尼特性和粘弹特性对软组织形变的影响，使其在受力形变过程中更接近实际变化。通过设计真实肝脏的拉压实验和针穿刺实验，建立了肝脏组织在此过程中的力与位移变化关系模型，通过模型推导和实际测量数据的分析，得到了真实肝脏组织的阻尼系数和粘弹系数，为物理建模中组织特性参数的设定提供了参考。并在ANSYS仿真环境下，建立了肝脏穿刺实验的虚拟实验模型，通过ANSYS固有模型分析和应力应变曲线测量，进一步验证了真实肝脏穿刺实验的可靠性。并基于AABB包围盒算法实现了软组织模型之间的快速碰撞检测，通过改进三角形间相交测试算法、优化包围盒树更新策略和设计GPU加速算法，极大提升了碰撞检测效率，缩短了碰撞检测时间，实现碰撞实时渲染。