Accuracy of High-Resolution In Vivo Micro Magnetic Resonance Imaging for Measurements of Microstructural and Mechanical Properties of Human Distal Tibial Bone

摘要

Micro magnetic resonance imaging (µMRI) is an in vivo imaging method which permits three dimensional (3D) quantification of cortical and trabecular bone microstructure. µMR images can also be used for building microstructural finite element (µFE) models to assess bone stiffness, which highly correlates with bone’s resistance to fractures. In order for µMR image-based microstructural and µFE analyses to become standard clinical tools for assessing bone quality, validation with a current gold standard, namely the high-resolution micro computed tomography (µCT) is required. Microstructural measurements of 25 human cadaveric distal tibiae were performed for the registered µMR and µCT images, respectively. Next, whole bone stiffness, trabecular bone stiffness, and elastic moduli of cubic sub-volumes of trabecular bone in both µMR and µCT images were determined by voxel-based µFE analysis. The bone volume fraction (BV/TV), trabecular number (Tb.N^*), trabecular spacing (Tb.Sp^*), cortical thickness (Ct.Th), and structure model index (SMI) of µMRI showed strong correlations with µCT measurements (r²=0.67~0.97), and bone surface to volume ratio (BS/BV), connectivity density (Conn.D), and degree of anisotropy (DA) had significant but moderate correlations (r²=0.33~0.51). Each of these measurements also contributed to one or many of the µFE-predicted mechanical properties. However, model-independent trabecular thickness (Tb.Th^*) of µMRI had no correlation with the µCT measurement and did not contribute to any mechanical measurement. Furthermore, the whole bone and trabecular bone stiffness of µMR images were highly correlated to those of µCT images (r²=0.86 and 0.96), suggesting that µMRI-based µFE analyses can directly and accurately quantify whole bone mechanical competence. In contrast, the elastic moduli of the µMRI trabecular bone sub-volume had significant but only moderate correlations with their gold standards (r²=0.40~0.58). We conclude that most microstructural and mechanical properties of the distal tibia can be efficiently derived from µMR images and can provide additional information regarding bone quality.