Multi-frequency hyperthermia characterisation via calorimetry and AC magnetometry measurements

Abstract

Hyperthermia characterisation of magnetic nanoparticles (MNP) is challenging, with highly variable results reported by different laboratories and large uncertainties associated with the measured values. Here, two experimental methods for probing the heating power of MNP for magnetic field hyperthermia (MFH) therapy are compared. The first technique is calorimetry using a bespoke non-adiabatic system capable of measurements at varying frequencies and intensities of magnetic drive-field. Heat losses during calorimetry were compensated for by incorporating a loss-parameter and fitting process during analysis of the raw measurement data to calculate the sample’s specific loss power (SLP). The second technique was AC magnetometry to measure the sample hysteresis when exposed to drive-fields with variable frequencies and amplitudes. The area of the measured hysteresis loop is used to calculate the SLP. Two distinct commercial magnetic nanoparticle systems (Ferucarbotran and RCL-01) were studied using both measurement techniques at varying drive-field frequencies and intensities. Estimates of the intrinsic loss power (ILP) parameter were made based on detailed analysis of the SLP values for multiple frequencies and intensities for each nanoparticle system and experimental approach. For both nanoparticle systems, the calorimetry technique produced higher estimates of the ILP than the AC magnetometry technique. Despite these variations, the results were encouragingly similar, with all values falling within the calculated uncertainty envelopes and relative differences in the results for the two nanoparticles systems being consistent between the measurement techniques (suggesting systematic errors). Furthermore, the experimentally determined values showed strong agreement with literature. The presented study highlights the potential value of carrying out hyperthermia characterisations with differing drive-field types and measurement methods. This approach can reduce inaccuracies by assisting in identifying outliers and aiding the identification of measurements which fall within the Linear-Response Regime for the given nanoparticle. Thus, the presented approach offers additional security when characterising the ILP of MNP.