Pistoia W, van Rietbergen B, Laib A, Rüegsegger P
Institute for Biomedical Engineering, University of Zürich and Swiss Federal Institute of Technology (ETH), Moussonstrasse 18, CH-8044 Zürich, Switzerland.
J Biomech Eng. 2001 Apr;123(2):176-83. doi: 10.1115/1.1352734.
Micro-finite element (microFE) models based on high-resolution images have enabled the calculation of elastic properties of trabecular bone in vitro. Recently, techniques have been developed to image trabecular bone structure in vivo, albeit at a lesser resolution. The present work studies the usefulness of such in-vivo images for microFE analyses, by comparing their microFE results to those of models based on high-resolution micro-CT (microCT) images. Fifteen specimens obtained from human femoral heads were imaged first with a 3D-pQCT scanner at 165 microns resolution and a second time with a microCT scanner at 56 microns resolution. A third set of images with a resolution of 165 microns was created by downscaling the microCT measurements. The microFE models were created directly from these images. Orthotropic elastic properties and the average tissue von Mises stress of the specimens were calculated from six FE-analyses per specimen. The results of the 165 microns models were compared to those of the 56 microns model, which was taken as the reference model. The results calculated from the pQCT-based models, correlated excellent with those calculated from the reference model for both moduli (R2 > 0.95) and for the average tissue von Mises stress (R2 > 0.83). Results calculated from the downscaled micro-CT models correlated even better with those of the reference models (R2 > 0.99 for the moduli and R2 > 0.96 for the average von Mises stress). In the case of the 3D-pQCT based models, however, the slopes of the regression lines were less than one and had to be corrected. The prediction of the Poisson's ratios was less accurate (R2 > 0.45 and R2 > 0.67) for the models based on 3D-pQCT and downscaled microCT images respectively). The fact that the results from the downscaled and original microCT images were nearly identical indicates that the need for a correction in the case of the 3D-pQCT measurements was not due to the voxel size of the images but due to a higher noise level and a lower contrast in these images, in combination with the application of a filtering procedure at 165 micron images. In summary: the results of microFE models based on in-vivo images of the 3D-pQCT can closely resemble those obtained from microFE models based on higher resolution microCT system.
基于高分辨率图像的微观有限元（microFE）模型已能够在体外计算松质骨的弹性特性。最近，已开发出在体内对松质骨结构进行成像的技术，尽管分辨率较低。本研究通过将基于体内图像的微观有限元分析结果与基于高分辨率微观计算机断层扫描（microCT）图像的模型结果进行比较，研究了此类体内图像在微观有限元分析中的实用性。从人类股骨头获取的15个标本，首先用分辨率为165微米的3D-pQCT扫描仪成像，然后用分辨率为56微米的microCT扫描仪再次成像。通过对microCT测量结果进行降尺度处理，创建了第三组分辨率为165微米的图像。直接从这些图像创建微观有限元模型。每个标本通过六次有限元分析计算出其正交各向异性弹性特性和平均组织冯·米塞斯应力。将165微米模型的结果与56微米模型（作为参考模型）的结果进行比较。基于pQCT的模型计算出的结果，在模量（R2 > 0.95）和平均组织冯·米塞斯应力（R2 > 0.83）方面，与参考模型计算出的结果具有极好的相关性。从降尺度微观CT模型计算出的结果与参考模型的结果相关性更好（模量的R2 > 0.99，平均冯·米塞斯应力的R2 > 0.96）。然而，对于基于3D-pQCT的模型，回归线的斜率小于1，必须进行校正。对于分别基于3D-pQCT和降尺度微观CT图像的模型，泊松比的预测准确性较低（R2 > 0.45和R2 > 0.67）。降尺度后的微观CT图像与原始微观CT图像的结果几乎相同，这一事实表明，3D-pQCT测量需要校正并非由于图像的体素大小，而是由于这些图像中较高的噪声水平和较低的对比度，以及在165微米图像上应用了滤波程序。总之：基于3D-pQCT体内图像的微观有限元模型结果可以与基于更高分辨率微观CT系统的微观有限元模型结果非常相似。
