MRI is a powerful technique that is commonly used in clinical settings. It is non-invasive, does not employ ionizing radiation, and is capable of high spatial and temporal resolution, making it ideal for a wide variety of imaging applications, both for active diagnostic applications and preventative medicine. The strategies described in this thesis further increase the diagnostic ability of MRI by selectively delivering contrast enhancing nanoparticles to areas of interest, either through changes in cellular, organ, and systemic behavior as a result of disease states, or through biospecificity conferred by surface-bound targeting ligands. In doing so, this allows MRI to accurately probe systemic processes or cellular targets previously not available as diagnostic indicators, and has the potential to dramatically expand the spectrum of biological characteristics that can be visualized and quantified using MRI. The work in this study represents a step towards the creation of specialized, use-specific diagnostic agents that have the potential to improve the accuracy and speed of clinical diagnoses. iii