Enhanced Detection of Magnetic Nanoparticles Using a Novel Microwave Ferromagnetic Resonance Imaging System

Objective: An aluminium faceted chamber designed for 3D microwave imaging (MWI) of the breast has been integrated into an electromagnet in order to carry out signal acquisition experiments for an inverse scattering-based ferromagnetic resonance imaging (FRI) system, or magnetic contrast-enhanced MWI system. Methods: For this proof of concept, the chamber has been equipped with four wire monopole antennas, and low-contrast oil-based targets have been tested with varying concentrations of iron oxide magnetic nanoparticles (MNP) to serve as ferromagnetic contrast agents. The electromagnet is capable of sustaining a static polarizing magnetic field (PMF) greater than 0.2 Tesla (2000 Gauss) across the imaging chamber to modulate the MNPs' ferromagnetic response, effectively changing the targets' magnetic permeability. Differential scattered field data are then collected through the application and withdrawal of this PMF. Results: This study has successfully characterized a particular narrow band of frequencies within the asymmetric faceted chamber that demonstrate significant differential responses corresponding to the weak magnetic signal physically isolated from the MNPs, tested on different sizes and positions of targets containing various concentrations of MNPs. Conclusion: Similar to ferromagnetic resonance (FMR) spectroscopy, in which detection of FMR phenomena is best achieved at probing frequencies coinciding with the structural resonant frequency of a metallic cavity, these resonant frequencies of interest yield a high level of sensitivity to MNP permeability changes and are suitable for imaging within the chamber. Significance: These represent the first experimental results of a full-scale FRI system capable of detecting and eventually imaging MNPs at biologically relevant concentrations.