Image-based Assessment of Cortical Bone

Recent advances in solid-state MRI now allow detection and quantification of key constituents of cortical bone in situ and in vivo. These comprise water in the various compartments, as well as matrix and mineral components. The importance of the new capabilities is that they permit probing the chemical composition and ultrastructure of cortical bone, both of which are known to be predictive of the bone's mechanical properties and of fracture incidence in patients with metabolic and degenerative bone disease. This brief article reviews the ultrashort echo time (UTE) methods and soft-tissue suppression techniques used for quantitative imaging of cortical bone. Of particular interest is the measurement of cortical bone water content and the separation of the two major fractions assignable to pore and collagen-bound water. Pore water fraction yields cortical porosity without the need to spatially resolve the pores, thereby providing a means to assess a parameter that affects the bone's mechanical competence. A similar methodology enables quantification of matrix density, whereas solid-state P-31 MRI allows measurement of mineral content. While the methods reviewed are still in their infancy, translation to the clinic appears feasible.