Development of Advanced MRI Methods for Improving Signal and Contrast in Biomedical Imaging Applications

This dissertation reports advances in magnetic resonance imaging (MRI), with the ultimate goal of improving signal and contrast in biomedical applications. More specifically, novel MRI pulse sequences have been designed to characterize microstructure, enhance signal and contrast in tissue, and image functional processes. Using these pulse sequences, intermolecular multiple quantum coherence (iMQC) signals that arise from the dipolar field over well-defined distances can be observed; these signals were used here to probe material microstructure. Using iMQCs, the restricted diffusion in uni- and multi-lamellar vesicles such as liposomes and polymersomes was characterized, with potential applications for monitoring drug transport and release; moreover, mesoscopic anisotropy in developing rat brains was studied, which required significant pulse sequence optimizations and corrections to the original dipolar field framework. We have also developed and applied modified multipulse echo sequences with optimized interpulse delays for tissue imaging. These sequences have enhanced the signal and may provide new contrast in various tissues, including normal, tumor, and fatty tissues. Finally, the use of MRI to study functional processes, including temperature and perfusion, is described.