热力学有限元方法研究骨组织热传导的三维空间分布

Three-dimensional space distribution of thermal conductivity in bone tissue: A thermodynamics finite element analysis

参考生物力学有限元模型方法建立牛胫骨近端三维热力学有限元模型。选取新鲜牛胫骨上段15cm,以层厚2mmCT扫描胫骨近端,运用同济大学生物医学工程研究所实验室编写的数字图像处理程序处理CT图像,点云采集文件输入逆向工程软件Geomagic进行实体模型构建。将生成的实体模型IGES文件导入到有限元分析软件Ansys9.0中去,构建热力学有限元模型,进行三维热力学有限元模型的传热计算。模型骨结构表面温度设定37℃,骨内指定部位假设有15mm直径球形区域热源,温度为90℃,在该条件下执行稳态计算。结果显示距离热源不同距离的横截面温度分布等值线密度不同,越接近电极,等值线越密集,且呈不规则椭圆形。在模型矢状面上,距离热源越近,温度分布等值线越密集,越远越稀疏,亦呈不规则椭圆形分布。提示牛胫骨组织消融范围的大小与电极针暴露长度和空间布针位置密切相关。在骨组织中,整个热力场围绕消融电极呈不规则椭圆球形分布。

Biomechanics finite element method was used to establish a three-dimensional thermodynamic model of bovine proximal tibia. A 15-cm-long fresh bovine proximal tibia bone was selected, and the CT scan was 2 mm. CT images were prepared through the digital image processing procedures compiled by Institute of Biomedical Engineering Laboratory of Tongji University. Acquired point cloud file was input into Geomagic software to construct solid model. The IGES file of solid model was input into the finite element analysis software Ansys 9.0 to construct thermodynamic finite element model. Heat transfer calculation of thermodynamic 3D finite element model was done. Surface temperature of the bone model was set to be 37 ℃. A 15-mm spherical source of heat was assumed to locate in the designated area of the model at 90 ℃ and steady-state calculation was implemented. Contour density of the temperature distribution in cross-section was different according to distance of the beater. The closer the distance from the electrode, the more intensive the density of isogram was. All isograms exhibited irregular oval shape. In the sagittal plane of the model, contour density of the temperature distribution was more intensive near to the beater, while was more sparse far from the heater. Isograms were also irregular oval. The results of the study indicate that ablation size and scope in bovine proximal tibia tissue are closely related to the exposed length and space location of the needle electrode. In bone tissue, the entire thermodynamic field around the thermal ablation electrode presents irregular oval ball.