A new material mapping procedure for quantitative computed tomography-based, continuum finite element analyses of the vertebra.
A new material mapping procedure for quantitative computed tomography-based, continuum finite element analyses of the vertebra.
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DOI：
10.1115/1.4004190
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发表时间：
2011-07
期刊：
影响因子：
--
通讯作者：
Morgan EF
中科院分区：
文献类型：
--
作者：
Unnikrishnan GU;Morgan EF
材料特性估计的不准确性和将这些特性分配到有限元模型中的误差限制了基于定量计算机断层扫描(QCT)的椎体有限元分析的可靠性、准确性和精确度。在这项工作中，开发了一种新的网格无关的材料映射程序，以提高基于QCT的有限元模型预测椎体力学行为的质量。在这个过程中，引入了一个中间步骤，称为材料块模型，以确定基于骨密度的材料属性的分布，然后将这些属性映射到有限元网格上。首先对校准体模进行了敏感性研究，以了解材料块的大小对计算的骨矿密度的影响。人们观察到，改变材料块的大小只会对矿物密度的预测产生微小的变化。然后对椎体的方形柱状区域和整个椎体进行有限元(FE)分析，以研究材料块大小对FE结果的影响。脊柱和椎体的刚度预测值随着块大小的减小而减小。当将这些结果与网格收敛分析的结果进行比较时，发现单元大小对椎体刚度的影响小于材料块大小。该映射过程允许基于准确表示材料场所需的块大小来确定有限元研究中的材料属性，而有限元的大小可以独立地并且基于有限元解所需的数值精度来选择。这项研究中开发的不依赖网格的材料映射程序可能特别有助于提高椎体成形术和脊柱转移的有限元分析的准确性，因为这些分析通常需要在不同材料之间的交界处进行网格细化。此外，标测程序并不是特定于椎骨的，因此可以应用于许多其他解剖部位。
Inaccuracies in the estimation of material properties and errors in the assignment of these properties into finite element models limit the reliability, accuracy, and precision of quantitative computed tomography (QCT)-based finite element analyses of the vertebra. In this work, a new mesh-independent, material mapping procedure was developed to improve the quality of predictions of vertebral mechanical behavior from QCT-based finite element models. In this procedure, an intermediate step, called the material block model, was introduced to determine the distribution of material properties based on bone mineral density, and these properties were then mapped onto the finite element mesh. A sensitivity study was first conducted on a calibration phantom to understand the influence of the size of the material blocks on the computed bone mineral density. It was observed that varying the material block size produced only marginal changes in the predictions of mineral density. Finite element (FE) analyses were then conducted on a square column-shaped region of the vertebra and also on the entire vertebra in order to study the effect of material block size on the FE-derived outcomes. The predicted values of stiffness for the column and the vertebra decreased with decreasing block size. When these results were compared to those of a mesh convergence analysis, it was found that the influence of element size on vertebral stiffness was less than that of the material block size. This mapping procedure allows the material properties in a finite element study to be determined based on the block size required for an accurate representation of the material field, while the size of the finite elements can be selected independently and based on the required numerical accuracy of the finite element solution. The mesh-independent, material mapping procedure developed in this study could be particularly helpful in improving the accuracy of finite element analyses of vertebroplasty and spine metastases, as these analyses typically require mesh refinement at the interfaces between distinct materials. Moreover, the mapping procedure is not specific to the vertebra and could thus be applied to many other anatomic sites.
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