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 EB of the MNPs. We show the conditions of m and EB required for harmonic signal generation. As m and EB are widely distributed within MNPs, a fraction of MNPs satisfies the m and EB conditions and contributes to the harmonic signals. Resovist shows the largest such fraction satisfying these conditions. This is reflected in the experimentally obtained rich harmonic spectrum of Resovist. The experimental data was found to agree well with the numerical simulation results based on the Landau–Lifshitz–Gilbert equation when the distributions of m and EB within the MNPs were taken into account. These findings may serve as an important basis in the optimization of MNPs for MPI.
