面向精准肝脏切除手术的软组织切割模拟 关键技术研究

Precise liver resection is designed to completely remove target lesions and ensure the integrity of the anatomical structure、maximization of functional liver volume, and minimizing the hemorrhage. It is a more sophisticated and complex surgery. Therefore, virtual precise liver resection surgery simulation has raised new challenges in accuracy, reality and real-time interaction. On the basis of the liver surface model, by performing a series of operations on simulated liver model, the fractal method based on the self-similarity of organisms was used to repair the pipeline of liver model after refinement and denoising, to achieve the reconstruction of accurate three-dimensional model of liver. In order to accurately simulate and locate the region to be incised in the stained liver, permeation and adsorption interaction terms were added to the basic N-S equation, and the diffusion coefficient was improved. Aiming at the mutual restriction between precision and real-time interaction in the cutting computation model, a separate strategy is proposed to represent the surface incision and the internal cutting deformation simulation. Used with the seepage mechanics of biological porous media and fractal theory, the blood flow model during cutting process was established, which was related to the physiological characteristics of the liver, such as the porosity, specific surface, pore size and permeability of the liver, as well as the pipe type, vessel shape and size. Finally, in order to improve the simulation effect, we plan to invite different clinical staff to evaluate after actual surgery. The achievements and conclusions obtained are important for improving the efficiency and quality of surgical training on liver.

精准肝脏切除手术旨在彻底清除目标病灶的同时，确保剩余肝脏解剖结构的完整和功能性体积最大化，并最大限度控制手术出血，是一类更为精细、复杂的外科手术。因此，对其进行模拟在精度、逼真度、实时性上都提出了新的挑战。本项目在肝脏表面模型上，经过管道提取、细化、去噪，运用基于生物体自相似性的分形方法对管道进行修补，重构出精细的三维模型。为了精确模拟肝脏待切割区域的染色定位，在N-S方程上添加渗透、吸附交互作用项，并对扩散系数进行改进。针对肝脏组织切割计算模型中逼真度与实时性相互制约的问题，提出一种表面切口绘制和内部切割形变仿真分开描述的策略。运用生物多孔介质渗流力学和分形理论，建立肝脏的孔隙度、比面、孔径和渗流的渗透率与管道类型、血管形状、大小等生理特征有关的流血模型。最后，邀请合作医院的不同医护人员进行现场实际手术操作评价，改进模拟效果。本项目的研究成果对于提高肝外科医生训练效率和质量具有重要意义。

与传统的外科医生培训方法相比，在虚拟现实（Virtual Reality, VR）基础上发展起来的虚拟手术仿真系统（Virtual Surgery Simulating System, VSSS）具有成本低、效率高、可重复练习、不受时空和伦理道德约束等优点，正成为医疗领域的研究热点和前沿课题。切割作为实际手术中使用频率最高、最普遍的手术操作，对其进行“无失真”模拟是虚拟手术仿真系统不可缺少的重要组成部分。.本项目以医学上常用的二维CT图像为数据源，运用Morphing连续形变技术对三维表面模型进行体素化，从而得到包含内部点云的人体软组织体模型。Morphing的建模方法在插值时采用的是Hermite插值，这种插值方法是一种非线性的插值方法，在肝脏模型的左右两侧会根据曲率的不同进行插值，不同的曲率插值的点云数量不同，重构的模型可以更好地拟合软组织的几何外形，精度更高。为了提高虚拟手术中软组织切割过程中反馈力模拟的准确性，本项目提出了一种基于粒子滤波（Partical Filter）算法的切割力模拟仿真的新方法。由于概率密度函数用粒子来表示，因此能够在切割过程中精确地预测手术刀具与软组织之间的相互作用力。基于PF方法的均方根误差（RMSE）的范围为0.0014至0.0034，平均绝对误差（MAE）小于0.0399。为了提高血液模拟的真实性，本文提出了一种改进的SPH出血模拟方法。该算法采用改进的WCSPH方法改进了传统算法中压强的求解，使其更符合血液自身的特性。此外，本文提出一种基于密度的自适应光滑长度算法，使粒子系统可以根据邻居粒子的密度自适应的调节粒子的光滑长度，提高了插值精度，降低了计算误差，提高了模拟的稳定性。在此基础上，构建了由三维体模型重构模块、视觉渲染模块、触觉渲染模块、切割仿真模块和其他模块等五大模块组成的逼真度高、沉浸感强、可实时交互的虚拟肝脏切除模拟仿真训练系统。经过南昌大学附属医院外科医护人员的实际操作和评价，所研制的虚拟仿真与实际手术一致性较高，沉浸感较强，交互性较好，切割模拟操作已能满足临床培训目的。