Institute of Solid Mechanics, Mechatronics and Biomechanics, Faculty of Mechanical Engineering, Brno University of Technology, Brno, Czech Republic.
Institute of Solid Mechanics, Mechatronics and Biomechanics, Faculty of Mechanical Engineering, Brno University of Technology, Brno, Czech Republic.
J Mech Behav Biomed Mater. 2021 May;117:104393. doi: 10.1016/j.jmbbm.2021.104393. Epub 2021 Feb 18.
Patient-specific approach is gaining a wide popularity in computational simulations of biomechanical systems. Simulations (most often based on the finite element method) are to date routinely created using data from imaging devices such as computed tomography which makes the models seemingly very complex and sophisticated. However, using a computed tomography in finite element calculations does not necessarily enhance the quality or even credibility of the models as these depend on the quality of the input images. Low-resolution (medical-)CT datasets do not always offer detailed representation of trabecular bone in FE models and thus might lead to incorrect calculation of mechanical response to external loading. The effect of image resolution on mechanical simulations of bone-implant interaction has not been thoroughly studied yet. In this study, the effect of image resolution on the modeling procedure and resulting mechanical strains in bone was analyzed on the example of cranial implant. For this purpose, several finite element models of bone interacting with fixation-screws were generated using seven computed tomography datasets of a bone specimen but with different image resolutions (ranging from micro-CT resolution of 25 μm to medical-CT resolution of 1250 μm). The comparative analysis revealed that FE models created from images of low resolution (obtained from medical computed tomography) can produce biased results. There are two main reasons: 1. Medical computed tomography images do not allow generating models with complex trabecular architecture which leads to substituting of the intertrabecular pores with a fictitious mass; 2. Image gray value distribution can be distorted resulting in incorrect mechanical properties of the bone and thus in unrealistic or even completely fictitious mechanical strains. The biased results of calculated mechanical strains can lead to incorrect conclusion, especially when bone-implant interaction is investigated. The image resolution was observed not to significantly affect stresses in the fixation screw itself; however, selection of bone material representation might result in significantly different stresses in the screw.
基于患者个体的方法在生物力学系统的计算模拟中正日益受到广泛关注。目前，这些模拟（通常基于有限元法）都是基于诸如计算机断层扫描（CT）等成像设备的数据来进行常规创建的，这使得模型看似非常复杂和先进。然而，在有限元计算中使用 CT 并不能必然提高模型的质量，甚至不能增强其可信度，因为这些都取决于输入图像的质量。低分辨率（医疗）CT 数据集并不总是能够为 FE 模型提供详细的小梁骨表示，因此可能导致对外载机械响应的错误计算。图像分辨率对骨-植入物相互作用的机械模拟的影响尚未得到充分研究。在这项研究中，以颅骨植入物为例，分析了图像分辨率对建模过程和骨中机械应变的影响。为此，使用骨标本的七个 CT 数据集（分辨率范围从 25μm 的微 CT 分辨率到 1250μm 的医疗 CT 分辨率）生成了几个与固定螺钉相互作用的骨的有限元模型。比较分析表明，使用低分辨率（从医疗 CT 获得）的图像创建的 FE 模型可能会产生有偏差的结果。主要有两个原因：1. 医疗 CT 图像不允许生成具有复杂小梁结构的模型，这导致将骨小梁之间的孔隙用虚构质量替代；2. 图像灰度值分布可能会失真，从而导致骨的机械性能不正确，从而导致不现实甚至完全虚构的机械应变。计算出的机械应变的有偏差的结果可能会导致错误的结论，尤其是在研究骨-植入物相互作用时。观察到图像分辨率不会显著影响固定螺钉本身的应力；然而，选择骨材料表示形式可能会导致螺钉中的应力有很大差异。
