A Phenomenological Description of the MPS Signal Using a Model for the Field Dependence of the Effective Relaxation Time

In this paper, we present a new approach to describe the magnetic particle spectroscopy (MPS) signal, which is based on Shliomis´ effective field method. Contrary to other approaches, we do not model single particle dynamics via the Landau-Lifshitz-Gilbert equation, but use measurable quantities to minimize the influence of unknown model parameters. The necessary material values are gained from static magnetization and magnetorelaxometry measurements. The model contains two free parameters to describe the field-dependent relaxation time. To obtain these parameters, we currently still need measured MPS data to find the relaxation parameters that match the experimental results, but we are looking into methods to avoid this matching. We present the equations to calculate the harmonic spectrum of an magnetic particle imaging tracer. We also present first results of this method obtained on FeraSpin R and other tracer formulations and compare the calculated spectrum to the measured harmonics. For all formulations, we found a coefficient of determination R²>0.99 between our model and the measured spectra.