  This thesis 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. In this thesis, rat brain and red bone marrow images are acquired
using iMQCs (intermolecular multiple quantum coherences) between intermediate
separated spins. As an important application, iMQCs images in different
directions can be used for anisotropy mapping and tissue microstructure
analysis. At the same time, the simulations prove that the dipolar field from
the overall shape only has small contributions to the experimental iMQC signal.
Besides magnitude of iMQCs, phase of iMQCs should be studied as well. The phase
anisotropy maps built by our method can clearly show susceptibility information
in rat brain. It may provide meaningful diagnostic information. To deeply study
susceptibility, the modified-crazed sequence is developed. Combining phase data
of modified-crazed images and phase data of iMQCs images is very promising to
construct microstructure maps. Obviously, the phase image in all above
techniques needs to be highly-contrasted and clear. To achieve the goal,
algorithm tools from Susceptibility-Weighted Imaging (SWI) and Susceptibility
Tensor Imaging (STI) stands out superb useful and creative in our system.
