The effects of polymer coatings on the proton transverse relaxivities of superaramagnetic nanoparticle MRI contrast agents

Magnetic resonance imaging (MRI) is a widely used diagnostic tool for imaging soft tissue. The use of magnetic contrast agents has provided the opportunity to ex- tend the versatility of MRI by enhancing the contrast between di erent tissue types. One type of MRI contrast agent is based upon nanoparticles of iron oxide coated with a functional polymeric material that provides stability and biocompatibility. However, little is known about the e ects that these polymer coatings have on the proton transverse relaxation. The purpose of this thesis was to explore the e ects of these polymer coatings. To achieve this goal, the theoretical models of magnetic particle induced proton transverse relaxation reported in the literature were experimentally tested to de- termine their validity and accuracy. In addition, examinations were conducted to further understanding of the basic properties of polymer coated magnetic nanoparticles, including their stability in suspension and functionality. Furthermore, small angle neutron scattering was used to examine the structures of the polymer coatings by studying micelles and polymer coated nanoparticles. Finally, proton relaxometry was carried out on series of aqueous suspensions of magnetic nanoparticles with polymer coatings that were systematically varied. It was found that the theoretical models used to predict magnetic nanoparticle induced proton transverse relaxivities were very good estimators of actual relaxivities, provided that an accurate measurement of the particle size distribution in aqueous suspension was obtained. In addition, the number of polymer chains per unit surface area on a magnetic nanoparticle was found to be a function of the particle size, which in turn, could a ect the structure of the polymer around the nanoparticle. Furthermore, it was found that the polymer coatings investigated in this thesis were highly solvated and, contrary to other studies, had no direct a ect on the proton transverse