Magnetic resonance studies of architecture and composition of bone
The mechanical competence of bone depends upon a combination of its mass, structural arrangement and chemical composition. Assessment of these parameters allows evaluation of bone health and appropriate timely action to be taken to restore its integrity. Magnetic resonance imaging (MRI), which is non-invasive and non-ionizing, shows its potential as an alternative technique to measure bone architecture and composition. The objective of this dissertation research was to further develop in-vivo MR techniques that can yield accurate and meaningful measurements for diagnostic purposes. Advances in high-resolution MRI now permit in-vivo imaging at a resolution of ∼100-200 μm, which is sufficient for individual trabeculae to be partially resolved. Here, various pulse sequences were evaluated based on the accuracy of their image-derived structural parameters, which depends on both the signal-to-noise ratio (SNR) and image quality. Within the current hardware and safety limit constraints, the specially developed 3D fast spin echo sequence was identified as the most suitable sequence for the application because it produces superior SNR efficiency and is insensitive to artifactual trabecular thickening effect experienced by the gradient echo sequences. To study bone composition, novel techniques for in-vivo bone-water (BW) quantification based on an extremely short echo time pulse sequence were developed and validated. Initial works showed significant negative correlations between BW and bone mineral density (BMD) while BW being a stronger group discriminator than BMD. The data suggests that, upon further investigation, BW can potentially be used as a new measure of bone strength. The work accomplished in this dissertation represents another step toward improved noninvasive diagnostic tools to quantify bone structural parameters and bone composition, which together with the clinical measurement of bone density can provide a more complete picture of bone integrity.