Harmonic Signal Analysis for Magnetic Nanoparticle Imaging

Abstract

A harmonic signal analysis of magnetic nanoparticles (MNPs) used as tracers in magnetic particle imaging (MPI) was conducted. The harmonic spectrum from three types of immobilized MNPs namely, Resovist, fluidMAG, and SupraBead, were measured at excitation fields of 1.4 mT and 28 mT with a frequency of 10 kHz. Resovist showed the richest spectrum, followed by fluidMAG and SupraBead.These different harmonic properties among samples were analyzed on the basis of the magnetic moment m and anisotropy energy E B of the MNPs. We show the conditions of m and E B required for harmonic signal generation. As m and E B are widely distributed within As MPI generally utilizes harmonic signals, it is important to select MNPs that can generate strong harmonic signals. However, MNPs show a wide variety of magnetic properties, depending on their magnetic moment m and anisotropy energy E B [7]. Therefore, it is important to establish a clear quantitative relationship between these parameters and harmonic signals in order to determine suitable MNPs for MPI applications.In this study, we investigate the properties of the harmonic signals generated by MNPs. First, we measure the harmonic signals from three types of commercial MNPs, namely, Resovist®, fluidMAG, and SupraBead. Then, samples with different harmonic properties are analyzed using the m and E B of MNPs. We also perform a numerical simulation for harmonic spectrum based on the Landau-Lifshitz-Gilbert (LLG) equation. A good agreement is obtained between the measured spectrum and the numerical simulation.