医学超声穿刺导航的实时定位及软组织建模研究

发布时间：2019-05-14 04:40

【摘要】：超声穿刺导航可以实时显示穿刺针在组织内的运动情况,为穿刺路径选择提供依据,是超声辅助治疗的重要手段,具有广阔的发展空间。然而,现有超声穿刺导航系统存在着操作复杂、定位不精确、穿刺角度固定麻烦等问题,所以穿刺手术对医生手法的依赖程度高,而且经常需要进行多次穿刺。针对上述情况,本文提出基于电磁定位方式的超声自由穿刺导航方法；并针对影响穿刺精度的关键因素——软组织变形,采用有限元方法进行详细的分析；最后基于便携式超声成像系统,提出自由穿刺导航的软硬件设计方案。具体研究内容如下： 1)超声穿刺导航算法研究。本文根据超声穿刺导航系统的临床应用,分析现有系统的不足和各种定位方式的优缺点,得出电磁定位系统具有定位准确、体积小、重量轻、受环境因素影响小等特性,适合用于超声穿刺系统实时定位的结论。故本文将电磁定位应用于现有的超声成像系统中,进而设计了基于电磁定位方式的实时导航算法——建立坐标变换的数学模型,研究将磁场坐标与声场坐标进行精确配准的手段,以便实时标示穿刺针相对于超声图像的位置,从而为提高穿刺准确性,缩短穿刺时间提供有效方法。 2)穿刺过程软组织形变的有限元仿真。软组织形变是影响穿刺精度最主要的因素,研究软组织变形对提高穿刺的准确性具有重要的临床意义。本文基于有限元方法,将软组织离散化为有限个单元,并对各个离散单元进行弹性力学分析,建立软组织的线性弹性模型。根据该理论模型,采用ANSYS有限元分析软件进行软组织变形仿真,根据软组织的材料属性、单元参数、应用边界条件和初值条件对网格化的模型施加载荷,仿真得出穿刺过程中软组织的形变数据。该形变模型可为穿刺导航系统实现穿刺前的路径规划和避障预警提供一种有效的手段。 3)软硬件方案设计。针对现有数字化便携式超声成像系统,本文设计了超声穿刺导航系统软硬件方案。硬件设计采用ARM+FPGA双核处理器外加电磁定位器的方案,系统中ARM除负责系统的实时控制,如按键响应、字符界面的显示、应用软件的选择、FPGA的信号控制等任务外,还进行定位系统位置信号的采集工作；而FPGA主要负责超声图像信息的采集和处理、探头控制、图像存储、定位信息的合成显示。系统软件体系结构的设计采用消息驱动的方式,以保证代码的运行效率。
[Abstract]:Ultrasonic puncture navigation can show the movement of puncture needle in tissue in real time, and provide the basis for puncture path selection. It is an important means of ultrasound assisted therapy and has a broad space for development. However, there are some problems in the existing ultrasonic puncture navigation system, such as complex operation, inaccurate positioning, trouble in fixing puncture angle, so puncture surgery has a high degree of dependence on doctor's manipulation, and often needs to be punctured many times. In view of the above situation, this paper proposes an ultrasonic free puncture navigation method based on electromagnetic positioning mode, and analyzes the soft tissue deformation, which is the key factor affecting the puncture accuracy, in detail by finite element method. Finally, based on the portable ultrasonic imaging system, the hardware and software design of free puncture navigation is proposed. The specific research contents are as follows: 1) the research of ultrasonic puncture navigation algorithm. According to the clinical application of ultrasonic puncture navigation system, this paper analyzes the shortcomings of the existing system and the advantages and disadvantages of various positioning methods, and concludes that the electromagnetic positioning system has the characteristics of accurate positioning, small volume, light weight and little influence by environmental factors. It is suitable for real-time positioning of ultrasound puncture system. Therefore, this paper applies electromagnetic positioning to the existing ultrasonic imaging system, and then designs a real-time navigation algorithm based on electromagnetic positioning, which is to establish the mathematical model of coordinate transformation. The method of accurate registration between magnetic field coordinates and sound field coordinates is studied in order to mark the position of puncture needle relative to ultrasonic image in real time, so as to provide an effective method for improving puncture accuracy and shortening puncture time. 2) finite element simulation of soft tissue deformation during puncture. Soft tissue deformation is the most important factor affecting puncture accuracy. It is of great clinical significance to study soft tissue deformation to improve the accuracy of puncture. In this paper, based on the finite element method, the soft tissue is discretized into finite elements, and the elastic mechanics of each discrete element is analyzed, and the linear elastic model of soft tissue is established. According to the theoretical model, the soft tissue deformation is simulated by ANSYS finite element analysis software. According to the material properties and element parameters of soft tissue, the boundary condition and initial value condition are used to apply the load to the gridded model. The deformation data of soft tissue during puncture were obtained by simulation. The deformation model can provide an effective means for puncture navigation system to realize path planning and obstacle avoidance early warning before puncture. 3) Software and hardware scheme design. Aiming at the existing digital portable ultrasonic imaging system, the software and hardware scheme of ultrasonic puncture navigation system is designed in this paper. The hardware design adopts the scheme of ARM FPGA dual-core processor plus electromagnetic locator. In the system, ARM is not only responsible for the real-time control of the system, such as keystroke response, character interface display, application software selection, FPGA signal control and so on. The position signal acquisition of the positioning system is also carried out. FPGA is mainly responsible for ultrasonic image information acquisition and processing, probe control, image storage, positioning information synthesis and display. The design of the system software architecture adopts the message-driven way to ensure the running efficiency of the code.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：R318.6

【参考文献】