Advancements of MRI Measurements of Bound and Pore Water Concentration of Cortical Bone for Evaluation of Fracture Risk
Manhard, Mary Katherine
The current standard for diagnosing fracture risk comprises measurements of bone mineral density (BMD), primarily by dual-energy X-ray absorptiometry (DXA). However, bone strength is affected by many factors other than BMD, such as architecture, collagen content, and porosity. Nuclear magnetic resonance (NMR) measures of the water bound to the collagen matrix (bound water) and free water occupying pore space (pore water) have shown promise in further assessing fracture risk. This dissertation work translated NMR based techniques into Magnetic Resonance Imaging (MRI) methods; the Double Adiabatic Full Passage (DAFP) sequence for measuring pore water concentration and the Adiabatic Inversion Recovery (AIR) sequence to measure bound water concentration. These imaging methods can be used to obtain maps of bound and pore water content throughout the cortical bone volume. MRI methods were first validated against NMR methods and shown to have good repeatability in vivo, and then were compared to whole bone material properties and found to show significant correlations with strength and toughness. The AIR and DAFP methods, initially carried out with 3D data acquisition, were further improved by implementing 2D quantitative imaging sequences which significantly reduced scan time. The sequences are being applied in populations of healthy and osteoporotic patients for longitudinal evaluation. In short, measures of bound and pore water concentration have the potential to give a new and more thorough evaluation of bone characteristics and health that is not obtainable with currently used methods.