Effect of numerical simulation of vascular wall thickness on fluid-structure interaction analysis of complex intracranial aneurysms

doi:10.3969/j.issn.2095-4344.2014.11.021

Abstract

Abstract:

BACKGROUND: Intracranial aneurysms have a high mortality, and finite element analysis to predict fracture risk has become a hot topic at present. Finite element analysis requires reliable fluid-structure interaction model, blood model of aneurysm is very easy to obtain, but the vascular wall model can not be obtained directly, only by artificial settings, which may have an impact on calculation results.

OBJECTIVE: To investigate the effects of vascular wall thickness on fluid-structure interaction analysis in finite element modeling of complex intracranial aneurysms, and provide a more reliable method of finite element modeling for the numerical simulation study of intracranial aneurysms.

METHODS: A three-dimensional numerical model of tandem left intracranial internal carotid artery aneurysms of a 67-year-old man was obtained by three-dimensional angiography. Four fluid-structure models were got postoperatively by thickening vascular wall, which were artificially set for 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm. According to intraoperative measured data, dynamic characteristics of fluid-structure interaction of tandem internal carotid artery aneurysms were simulated by the finite element method, comparing four models to calculate the difference between the results.

RESULTS AND CONCLUSION: Among the four models, there were no difference in blood flow chart, blood pressure drop chart and wall shear stress chart (P > 0.05). The deformation of the vascular wall was the most obvious in C₂ segment of the internal carotid artery, and the thicker vessel wall was accompanied by the more apparent deformation (P < 0.01). Von Mises stress in the vessel wall of the four models reached a local maximum in the I and J points, the thinner vessel wall was accompanied by the larger local maximum (P < 0.01). The settings of vascular well may affect the fluid-structure interaction analysis of complex intracranial aneurysms and appropriate thickness settings will obtain accurate calculation.

中国组织工程研究杂志出版内容重点：组织构建；骨细胞；软骨细胞；细胞培养；成纤维细胞；血管内皮细胞；骨质疏松；组织工程

全文链接：

Key words: blood vessels, aneurysm, hemodynamics, finite element analysis

CLC Number:

R318

Liu Bo, Li Zhi-wei . Effect of numerical simulation of vascular wall thickness on fluid-structure interaction analysis of complex intracranial aneurysms[J]. Chinese Journal of Tissue Engineering Research, 2014, 18(11): 1765-1773.

Figures/Tables 7

2.2 颈内动脉串联动脉瘤构建不同厚度血管壁的流固耦合模型的计算结果总体情况观察4个模型流固耦合分析得到的血液流线图、血液压力降图、血管内壁壁面切应力图、血管壁变形情况分布图、血管壁Von Mises 应力分布图(图3-5)发现：在心动周期每个时刻血液流线图、血液压力降图、血管内壁壁面切应力图、血管壁变形情况分布图和血管壁Von Mises 应力分布图的ANSYS染色均无明显变化，只是色彩代表的值随时在变。上述几种分布图中4个模型之间ANSYS染色差别也不大，只是色彩代表的值存在差异。 2.3 颈内动脉串联动脉瘤构建不同厚度血管壁的流固耦合模型的血液流动情况为了便于分析，如图3所示，选取心动周期几个典型时刻血管腔内流线图进行观察，取入口压力达到某最小值的时刻设为0 s，观察0，0.1，0.19，0.3，0.4，0.6 s血液流动情况，这几个时刻的左侧颈内动脉C2段压力、左侧眼动脉、左侧大脑中动脉、左侧大脑前动脉血流速度的对应值如表2。其中在0 s时入口压力和出口速度达到最小值，在0.19 s时入口压力和出口速度达到最大值。0.1，0.3 s位于入口压力和出口速度快速上升和快速下降阶段，0.4 s位于降中峡，0.6 s位于缓慢下降阶段。观察0.4 mm模型心动周期不同时刻流线图发现，各时刻流线图的流速不停地在变化，在0.19 s时整个模型流速达到最大值，但每个时刻血液流动的总体样式基本一致，即在动脉瘤A，B，C，D，E血管腔内均形成明显漩涡，每个动脉瘤的漩涡类型在整个心动周期基本不变。整个心动周期在颈内动脉C7段流速均达到最大值，分别是 0 s(114.1 cm/s)，0.1 s(213.2 cm/s)，0.19 s(236.1 cm/s)，0.3 s(214.2 cm/s)，0.4 s(175.9 cm/s)，0.6 s(146.0 cm/s)。整个心动周期血流速度在动脉瘤A，B，C，D瘤腔边缘均较低，在几个典型时刻瘤腔内血流速度最低值分别达到：0 s(0.2 cm/s)，0.1 s(0.8 cm/s)，0.19 s(0.9 cm/s)，0.3 s (0.8 cm/s)，0.4 s(0.2 cm/s)，0.6 s(0.2 cm/s)。动脉瘤E瘤腔内流线呈螺旋状，部分区域流速快，部分较慢，且其速度分布在心动周期各时刻存在差异。 0.3，0.4，0.5，0.6 mm模型心动周期不同时刻流线图均有相同表现。由于每个模型计算了10个周期，每个周期0.19 s时C7段均是流速最大值，对10个周期流速最大值取均值，单因素方差分析结果显示4个模型差别无显著性意义(P > 0.05，表3)。"

2.5 颈内动脉串联动脉瘤构建不同厚度血管壁的流固耦合模型的壁面切应力分布如图5所示，该图是颈内动脉串联动脉瘤0.4 mm模型不同时刻壁面切应力分布图。动脉瘤A，B，C，D，E瘤腔内壁面切应力均不高，但在颈内动脉C7段靠近E动脉瘤处存在G和H点，此处壁面切应力在整个心动周期均明显高于其他区域，G和H点值大小相当。G和H点在心动周期各时刻壁面切应力的值是：0 s(8.28 Pa)，0.1 s(3.89 Pa)，0.19 s(28.57 Pa)，0.3 s(24.00 Pa)，0.4 s (17.11 Pa)，0.6 s(12.61 Pa)。在每个心动周期0.19 s时G，H点壁面切应力达最大值。由于每个模型计算了10个周期，每个周期0.19 s时G，H点均是最大值，计算10个周期G，H点最大值的均值，单因素方差分析显示4个模型的差异无显著性意义(P > 0.05，表3)。 2.6 颈内动脉串联动脉瘤构建不同厚度血管壁的流固耦合模型的血管壁变形情况观察每个模型整个心动周期管壁变形图，发现每个时刻管壁变形图ANSYS渲染的色彩基本一致，说明整个模型管壁变形的区域分布情况固定不变。但由于整个心动周期模型内的血流速度和压力不停地在变化，故每个血管段的管壁变形量也在不停地变化。以0.4 mm模型为例，其中0.23 s时刻管壁变形量最大，如图4B所示，该图显示0.23 s时的管壁变形情况，变形最明显的是左侧颈内动脉C2段，颈内动脉颅内段变形较小。颈内动脉C2段管壁变形量最大可达2.78 mm，约占血管直径的30%，如果该段血管不在颅骨内走行，管壁移位震动将会很大。由于每个模型计算了10个周期，每个周期均在0.23 s时C2段变形量最大，计算10个周期C2段变形量最大值的均值，比较4个模型均值之间差异，经过单因素方差分析提示差异有显著性意义(P < 0.01，表3)，变形量大小排序依次是：0.3 mm模型(3.93 mm)>0.4 mm模型(2.83 mm) > 0.5 mm模型(2.15 mm)>0.6 mm模型(1.30 mm)。 2.7 颈内动脉串联动脉瘤构建不同厚度血管壁的流固耦合模型的血管壁内壁面Von Mises 应力分布观察每个模型不同时刻内壁面Von Mises 应力分布图，发现不同时刻的Von Mises 应力的分布特性是一致的，即每个时刻ANSYS渲染的图形和图4C一样。如图4C所示，在A，B，C，D，E动脉瘤的根部附近出现Von Mises 应力增大，其中在I，J两点处达到局部最大值，I和J两点的值相差不大，J点略大于I点。由于血流速度和压力随时在变，血管壁内壁面同一点在不同时刻Von Mises 应力大小是不同的，其中在0.19 s时刻整个模型Von Mises 应力值达到最大值。观察 0.4 mm模型整个心动周期，绘制I，J两点Von Mises 应力值随时间变化曲线如图6。发现I，J两点Von Mises 应力值随时间变化的节奏和入口压力变化节奏一致，该曲线和左侧颈内动脉C2段灌注压曲线总体形态类似，即在整个心动周期里，Von Mises 应力值先快速升高，后减慢上升，在0.19 s时达到最大，之后快速下降，0.4 s后缓慢下降直至最低值。 4个模型Von Mises应力分布图类似，由于每个模型计算了10个周期，每个周期均在0.19 s时I，J两点Von Mises 应力达最大值，J点均略大于I点，计算10个周期J点Von Mises 应力达最大值的均值，比较4个模型均值之间差异，经过单因素方差分析提示差异有显著性意义(P < 0.01)，见表3，大小排序依次是：0.3 mm模型(784.3 kPa) >0.4 mm模型(708.1 kPa)>0.5 mm模型(612.6 kPa)>0.6 mm模型(528.0 kPa)。"

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