Estimating the hysteresis loss in magnetic nanoparticles by magnetic particle spectroscopy

<i>Objective<u>.</u></i>Magnetic fluid hyperthermia is a promising adjuvant cancer therapy presently approaching clinical application. The therapeutic effect stems from the heat produced by magnetic nanoparticles (MNPs) administered to the tumor site and exposed to an AC magnetic field applied from outside the body. The objective of our study is to improve the integration of magnetic particle imaging (MPI) and hyperthermia as a theranostic application by allowing a real-time monitoring of local heat generation.<i>Approach.</i>The area of the dynamic hysteresis loop of the MNP is a measure of the heat produced by the MNP. However, depending on the specifics of the measurements, an accurate determination of the dynamic hysteresis loop of MNPs by conventional magnetic particle spectroscopy (MPS) can be hindered due to missing information of the first harmonic. The method presented in this work provides a solution to this problem by extracting the area of the hysteresis loop from measured MPS spectra through the reconstruction of the first harmonic.<i>Main results.</i>The method was tested on three distinct commercial MNP systems and found to be in good agreement with hysteresis loops directly obtained through AC magnetometry, confirming the method's reliability.<i>Significance.</i>This advancement enables accurate real-time monitoring of the energy dissipated as heat by the particles during MPS measurements and thus directly contributes to the development of MPI-guided hyperthermia.