基于有限元的螺旋电极刺激视神经的电场特性分析

发布时间：2018-06-28 13:55

本文选题：视神经假体 + 新型螺旋电极　；参考：《天津医科大学》2012年硕士论文

【摘要】：研究目的：视觉假体是一种旨在恢复部分或完全失明患者视觉功能的电子设备。电刺激视神经能够产生视觉感知。刺激电极几何形状对神经损伤和刺激选择性有很重要的影响。有限元方法是一种可用于求解复杂容积导体模型电场分布的数值方法。本论文应用有限元软件COMSOL Multiphysics设计出一种形状自适应的新型螺旋电极,其目的是使其尽可能减小神经损伤,实现选择刺激视神经纤维束,为神经电刺激提供计算支持。研究方法： 1.应用有限元软件COMSOL Multiphysics建立视神经和螺旋袖套电极的几何模型：选用不同的电极刺激模式(单级、双极和三极)刺激视神经。应用有限元方法,选择合适的网格剖分和边界条件,通过计算电势、电场和电流密度分布来分析不同的电极刺激模式对刺激的影响。 2.建立视神经容积导体模型,模型包含五个半径相同的纤维束。在三极刺激模式下,通过COMSOL Multiphysics计算不同神经纤维束处的电势和电流密度,并应用激活函数来分析电极——神经间距离对刺激的影响。 3.研究视神经周围组织电特性对刺激效果的影响。选取不同厚度的脑脊液层(cerebrospinal fluid, CSF),通过参数扫描的方法分析CSF厚度变化对刺激效果的影响。 4.设计出一种新型螺旋电极。它由起支撑和绝缘隔离作用的硅橡胶螺旋支架和嵌入支架内的铂金触点组成。引入激活函数来表征刺激效果,应用COMSOL Multiphysics仿真分析新型螺旋电极对视神经纤维选择性刺激的能力,并考虑电极触点位置的变化对选择性的影响。研究结果： 1.单级模式下,沿着电极表面的电流密度分布是非均匀的。在电极和神经髓鞘接触处局部最大,远离电极迅速减小。仿真结果表明,双极刺激模式下,分别位于神经干对侧位置的两个电极间的电流存在一定的纵向分量有可能使神经干兴奋。同样刺激条件下,三极刺激模式的电流密度最大值、电场强度最大值都要比双极模式高。 2.在三极螺旋触点电极刺激下,电极——神经距离对神经轴向的电势变化影响不明显。距离电极近的神经纤维束电流密度值大,激活函数幅度变化最明显。 3.CSF厚度的增加对电势的影响不明显。应用参数扫描的方法仿真表明,由于脑脊液层的电导率比其他组织大,随着脑脊液层厚度增加,电极电场分布范围更大,但对电流的散射阻碍使神经刺激效果变差。 4.假定激活函数的归一化阈值为0.1V/m2,新型螺旋电极激活函数大于阈值的比例比传统袖套电极大1.2410%。当新型螺旋电极两端的电极触点靠近中间触点时,可以优先激活细视神经纤维束,后激活粗纤维束。研究结论： 1.电流密度最大值集中分布在电极——神经髓鞘接触处。双极刺激模式所需引线少,植入简单,易于临床应用。三级模式触点多,更有利于实现选择性刺激。根据结果需求选择最适宜的刺激模式,获得最佳刺激结果,从而为视神经假体的研究提供一定的帮助。 2.通过分析不同纤维束的刺激结果,可以在一定程度上表明电极——神经间的距离关系对刺激的影响。仿真结果表明位于神经中心的纤维束激活函数值相对较小,最不容易兴奋。 3.CSF层厚度变化对刺激结果的分析可以为临床中螺旋袖套电极植入视神经提供一定的计算支持。 4.新型螺旋电极减小了电极与神经的接触面积,选择性比传统袖套电极好。改变新型螺旋电极的触点位置可以实现选择性激活视神经纤维束。
[Abstract]:Purpose of study :

The visual prosthesis is an electronic device designed to restore the visual function of a partial or completely blind patient . The electrical stimulation optic nerve can produce visual perception . The stimulation electrode geometry has an important influence on neural injury and stimulation selectivity . The finite element method is a numerical method which can be used to solve the electric field distribution of complex volume conductor models . The purpose of this paper is to design a novel spiral electrode with adaptive shape by using the finite element software COMSOL Multiphysics .

Study method :

1 . The geometric model of optic nerve and spiral cuff electrode was established by using the finite element software COMSOL Multiphysics : different electrode stimulation modes ( single stage , bipolar and tripolar ) were used to stimulate optic nerve . The finite element method was applied to select the appropriate meshing and boundary conditions , and the effects of different electrode stimulation patterns on stimulation were analyzed by calculating potential , electric field and current density distribution .

2 . The optic nerve volume conductor model was established , and the model consisted of five fiber bundles with the same radius . In the three - pole stimulation mode , the potential and current density at different nerve fiber bundles were calculated by COMSOL Multiphysics , and the effect of electrode _ nerve distance on stimulation was analyzed by using the activation function .

3 . The effects of electrical characteristics of optic nerves around optic nerve on stimulation effect were studied . Different thicknesses of cerebrospinal fluid ( CSF ) were selected , and the effects of CSF thickness changes on stimulation effect were analyzed by parameter scanning .

4 . A new kind of spiral electrode is designed . It is composed of silicone rubber spiral support and platinum contact embedded in the support . The activation function is introduced to characterize the stimulation effect . The stimulation effect is analyzed by COMSOL Multiphysics simulation , and the influence of the change of electrode contact position on selectivity is taken into account .

Results of the study :

1 . In single mode , the current density distribution along the surface of the electrode is non - uniform . The local maximum at the contact of the electrode and the nerve myelin sheath decreases rapidly away from the electrode . The simulation results show that there is a certain longitudinal component of the current between the two electrodes in the lateral position of the nerve trunk in the bipolar stimulation mode . The maximum value of the current density and the maximum electric field intensity in the three - pole stimulation mode are higher than that of the bipolar mode .

2 . Under the stimulation of the three - pole spiral contact electrode , the electric potential change of the electrode _ nerve distance to the axial direction of the nerve is not obvious . The current density value of the nerve fiber bundle near the electrode is large , and the amplitude change of the activation function is most obvious .

3 . The effect of the increase of CSF thickness on electric potential is not obvious . The simulation results show that because the electrical conductivity of the cerebrospinal fluid layer is larger than that of other tissues , the distribution range of the electric field of the electrode increases with the increase of the thickness of the cerebrospinal fluid layer , but the scattering of the current impedes the effect of neural stimulation .

4 . Assuming that the normalized threshold of the activation function is 0.1V / m2 , the proportion of the new spiral electrode activation function greater than the threshold is 1.2410 % larger than that of the conventional sleeve electrode . When the electrode contact on both ends of the new spiral electrode is close to the middle contact , the fine optic nerve fiber bundle can be preferentially activated , and then the coarse fiber bundle is activated .

Conclusions of the study :

1 . The maximum concentration of the current density is distributed in the contact of the electrode _ nerve myelin sheath . The bipolar stimulation mode has few lead wires , simple implantation and easy clinical application . The three - stage mode contact is more and more advantageous to realize selective stimulation . According to the result demand , the most appropriate stimulation mode is selected , and the best stimulation result is obtained , so as to provide certain help for the research of optic nerve prosthesis .

2 . By analyzing the stimulation results of different fiber bundles , the influence of the distance relation between the electrodes and nerves can be indicated to some extent . The simulation results show that the value of the fiber bundle activation function is relatively small in the center of the nerve and is not easily excited .

3 . The analysis of CSF layer thickness changes to stimulation results can provide some calculation support for the implanted optic nerve of spiral cuff electrode in clinic .

4 . The new spiral electrode reduces the contact area between the electrode and the nerve , which is better than the traditional cuff electrode . The selective activation of the optic nerve fiber bundle can be realized by changing the contact position of the novel spiral electrode .
【学位授予单位】：天津医科大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：R318.6

【相似文献】