Doctoral Defense: Studies of magnetic nanoparticle shape and size effects on T2 relaxation in magnetic resonance imaging, and power absorption in an alternating magnetic field

Wednesday, August 15, 2012 – 10:30am
Reiss 261A
Joseph York
Department of Physics, Georgetown University

Magnetic nanoparticles have been shown to influence contrast in magnetic resonance imaging (MRI). The magnetic fields of particles vary depending on the shape of the particle. The effects of ferromagnetic nanoparticles with various shapes and sizes on the transverse relaxation rate of water protons were analyzed using T2-weighted MRI. Oblate particles were shown to have a stronger effect on the transverse relaxivity than smaller spherical or prolate particles. A linear relationship between the transverse relaxivity and the ratio of particle surface area to volume was observed. It indicates decreasing the surface area to volume ratio of magnetic nanoparticles enhances the relaxivity.

Magnetic particle hyperthermia is the use of ferromagnetic nanoparticles to heat a cancer tumor to destroy it. This phenomenon is possible because these particles absorb power from an alternating magnetic field. Heating trials were performed on aqueous suspensions of ferromagnetic nanoparticles having various shapes and sizes. The results show power absorption of the samples diminishes over time regardless of particle shape or size, and the initial absorption rates of the samples depend on the sample type and preparation conditions. Power absorption was observed in all particles tested, including prolate and oblate particles with anisotropy fields greater than the strength of the applied alternating field. Additionally, large levels of aggregation were observed in all samples tested indicating particle interactions may affect the ability of the samples to absorb energy from the applied field.