Characterization of material microstructure using intermolecular multiple-quantum coherences.

摘要

This dissertation concerns the development of novel NMR methodologies based on intermolecular multiple-quantum coherence to the study of materials microstructure. First I provide an outline of the two main theoretical frameworks: classical and quantum mechanical---which model is best depends on the application. The quantum model can be useful for devising phase cycling strategies to isolate specific quantum coherence transfer pathways, while the classical Bloch equations are well suited for numerical calculations of the NMR signal and its time evolution. Several techniques to obtain numerical solutions are discussed, as they are essential steps in bridging the gap between theory and experiment, or for optimizing pulse sequence parameters in specialized applications.; The core of the dissertation presents an MRI image contrast for detecting material heterogeneities in the local spin density, a numerical algorithm to extract sub-voxel resolution in MRI or NMR, a method to drastically improve the speed of numerical simulations based on the classical Bloch equations, a study of structural anisotropy and internal magnetic fields in trabecular bone, an MRI image contrast for detecting fiber orientation in a material, and preliminary in vivo results demonstrating image contrast in mouse tumors and investigating the contribution of flow and oxygenation effects in pig brain and human brain. Finally, I propose several possible directions for future research in this exciting new field.