A New Technique for Magnetic Nanoparticle Imaging Using Magnetoencephalography Frequency Data

Abstract

Nanoparticles are objects of nanometer dimensions. Magnetic nanoparticles consist of an inorganic core of iron oxide. An outer coating of bioactive molecules such as peptides or antibodies surrounds this core, which can be chemically functionalized to conjugate with specific molecules in cells. There is potential to utilize the magnetic properties of these particles for internal imaging of living organisms using magnetoencephalography (MEG). While it is clear that bulk movement of a collection of particles should be detectable by MEG either as a flow or via rigid mechanical motion, it would be far more useful to detect the particles in situ. We have taken the first step towards this goal by demonstrating that MEG can detect these particles at fixed locations by focusing on the magnetic noise generated from random rotations of the particles’ magnetic moments. Using a 151-channel MEG device, a glass vial of Fe3O4 in a colloidal suspension was measured at stationary locations within the MEG helmet region. The data was collected at 300, 1200 and 12000 Hz with up to 4000 Hz bandwidth. Between 10 and 50 ten-second trials were collected. Fast Fourier transforms for each MEG channel was generated. The net effect of these fluctuations was not detectable in the time domain. However, these fluctuations appeared as an increase in noise in the frequency domain. The character of the noise had a 1/f^n slope where 0<n<1 with n approaching 0 (= white noise) as the concentration of the sample was reduced. Spatial contour maps of the frequency data showed a distinct peak near the location of the sample. These results suggest that MEG is sensitive enough to detect and potentially localize a stationary vial of magnetic nanoparticles in a colloidal suspension.