Pulsed magnetomotive ultrasound for viscoelastic characterization of soft tissues during magnetic hyperthermia

<i>Objective.</i>Magnetic hyperthermia (MH) has proven effective as an ablative therapy in oncology through the use of magnetic nanoparticles (MNPs), whereas magnetomotive ultrasound (MMUS) has emerged as a promising technique for detecting MNPs and conducting elastographic assessments. However, integrated strategies that leverage MNPs both for localized heating via MH and for quantification of treatment-induced viscoelastic changes using MMUS remain largely unexplored. This study proposes a theranostic approach that combines thermal ablation via MH with the simultaneous quantification of viscoelastic properties through MMUS.<i>Approach.</i>A pulsed magnetic field was applied to induce displacements and assess viscoelasticity using MMUS, while an alternating radiofrequency magnetic field was used to generate MH. A force-independent formulation based on the Kelvin-Voigt model was used to estimate viscoelastic parameters, first in tissue-mimicking phantoms for validation using benchmark methods, and subsequently in<i>ex-vivo</i>bovine liver to evaluate the effects of MH.<i>Main results.</i>Notably, no<i>a priori</i>knowledge of MNPs distribution was required to quantify MH-induced changes. The elastic and viscous components, along with the damping ratio, were identified as suitable MMUS-derived markers to characterize tissue alterations due to MH. The elastic parameter increased by at least 35% after MH, indicating that higher thermal doses correlate with greater elastic stiffening. Moreover, even in the case where tissue elasticity remained unchanged, the viscous property and damping ratio still exhibited increases of at least 100% relative to pre MH values, underscoring the sensitivity of these parameters to thermally induced changes in tissue viscosity.<i>Significance.</i>The findings demonstrate the potential of integrating MH and MMUS for real-time monitoring and quantification of treatment effects in oncology. Furthermore, this approach may enhance our understanding of the interplay between tissue viscoelasticity and water diffusion following MH, supporting the full use of viscoelastic parameters as clinical biomarkers.