High-resolution three-dimensional-pQCT images can be an adequate basis forin-vivo mu FE analysis of bone

Micro-finite element (mu FE) models based on high-resolution images have en abled the calculation of elastic properties of trabecular bone in vitro. Re cently, techniques have been developed to image trabecular bone structure i n vivo, albeit at a lesser resolution. The present work studies the usefuln ess of such in-vivo images for mu FE analyses, by comparing their mu FE res ults to those of models based on high-resolution micro-CT (mu CT) images. F ifteen specimens obtained from human femoral heads were imaged first with a 3D-pQCT scanner at 165 mum resolution and a second time with a mu CT scann er at 56 mum resolution. A third set of images with a resolution of 165 mum was created by downscaling the mu CT measurements. The mu FE models were c reated directly from these images. Orthotropic elastic properties and the a verage tissue von Mises stress of the specimens were calculated from six FE =analyses per specimen. The results of the 165 mum models were compared to those of the 56 mum model, which was taken as the reference model. The resu lts calculated from the pQCT-based models, correlated excellent with those calculated from the reference model for both moduli (R-2 > 0.95) and for th e average tissue von Mises stress (R-2 > 0.83). Results calculated from the downscaled micro-CT models correlated even better with those of the refere nce models (R-2 > 0.99 for the moduli and R-2 > 0.96 for the average von Mi ses stress). In the case of the 3D-pQCT based models, however, the slopes o f the regression lines were less than one and had to be corrected. The pred iction of the Poisson's ratios was less accurate (R-2 > 0.45 and R-2 > 0.67 ) for the models based on 3D-pQCT adn downscaled mu CT images respectively) . The fact that the results from the downscaled and original mu CT images w ere nearly identical indicates that the need for a correction in the case o f 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 combin ation with the application of a filtering procedure at 165 micron images. I n summary: the results of mu FE models based on in-vivo images of the 3D-pQ CT can closely resemble those obtained from mu FE models based on higher re solution mu CT system.