Study of MRI Contrast Effect of Dispersible Ferrimagnetic Iron Oxide Nanocubes

Abstract

Iron oxide nanoparticles have received lots of attention as magnetic resonance image (MRI) contrast agents. Iron oxide nanoparticles are used for various purposes because size of the nanoparticles changes their magnetic properties from paramagnetic to superpara, ferrimagnetic. Extremely small iron oxide nanoparticles (<4nm) were used as contrast agents for T1-weighted MR images since it has paramagnetic property. Clusters of superparamagnetic iron oxide nanoparticles(~10nm) were used as intravenously injectable T2 MRI contrast agents. Some of this kind has been used in clinics. Magnetosome-like ferrimagnetic iron oxide nanocubes (FIONs >40nm) labeled single cells and pancreatic islet grafts and detected in vivo by 9.4 T and 1.5T MR respectively. In this thesis, relatively small ferromagnetic iron oxide nanoparticles were used to fabricate intravenously injectable T2 MRI contrast agents. Around 20 nm sized iron oxide nanoparticles have high saturated magnetization, but small remanent magnetization. PEG-phospholipid encapsulation enables spacing to prevent the aggregation and induces aqueous-dispersible property. The dispersible ferromagnetic iron oxide nanocubes (DFIONs) showed high r2 relaxivity and exhibited high colloidal stability in aqueous media. Dispersible ferrimagnetic iron oxide nanoparticles (DFIONs) were designed to maximize its saturated magnetization and to minimize its remanent magnetization. In the end, DFIONs entered static dephasing regime and achieved the optimum relaxivity for iron oxide nanoparticles. In addition, DFIONs are biocompatible and did not affect cell viability at concentrations up to 0.75 mg Fe/ml. As a result, DFIONs could be examined as in vivo MRI contrast agents. With the high r2 value, it was possible for DFIONs to perform in vivo MR imaging of tumors by intravenous injection, with a clinical 3T MRI.