Theoretical predictions for spatially-focused heating of magnetic nanoparticles guided by magnetic particle imaging field gradients

Abstract

Magnetic nanoparticles in alternating magnetic fields (AMFs) transfer some of the field’s energy to their surroundings in the form of heat, a property that has attracted significant attention for use in cancer treatment through hyperthermia and in developing magnetic drug carriers that can be actuated to release their cargo externally using magnetic fields. To date, most work in this field has focused on the use of AMFs that actuate heat release by nanoparticles over large regions, without the ability to select specific nanoparticle-loaded regions for heating while leaving other nanoparticle-loaded regions unaffected. In parallel, magnetic particle imaging (MPI) has emerged as a promising approach to image the distribution of magnetic nanoparticle tracers in vivo, with sub-millimeter spatial resolution. The underlying principle in MPI is the application of a selection magnetic field gradient, which defines a small region of low bias field, superimposed with an AMF (of lower frequency and amplitude than those normally used to actuate heating by the nanoparticles) to obtain a signal which is proportional to the concentration of particles in the region of low bias field. Here we extend previous models for estimating the energy dissipation rates of magnetic nanoparticles in uniform AMFs to provide theoretical predictions of how the selection magnetic field gradient used in MPI can be used to selectively actuate heating by magnetic nanoparticles in the low bias field region of the selection magnetic field gradient. Theoretical predictions are given for the spatial decay in energy dissipation rate under magnetic field gradients representative of those that can be achieved with current MPI technology. These results underscore the potential of combining MPI and higher amplitude/frequency actuation AMFs to achieve selective magnetic fluid hyperthermia (MFH) guided by MPI.

Combining magnetic particle imaging and magnetic fluid hyperthermia in a theranostic platform

“…The simulations were based on the theoretical model developed by Dhavalikar and Rinaldi (Dhavalikar and Rinaldi 2016) which was constructed using the magnetization relaxation equation described by Martsenyuk et al (Martsenyuk, Raikher, and Shliomis 1974) to calculate heat dissipation as specific absorption rate (SAR). SAR values are calculated directly from a thermodynamic model wherein the work done by an applied magnetic field on the particles is dissipated as heat.…”

Design and validation of magnetic particle spectrometer for characterization of magnetic nanoparticle relaxation dynamics

“…the magnetic nanoparticles, with theoretically higher resolution in a short process time. MPI detects nanoparticle density spatially by probing locally their dynamic magnetization in a spatial selection gradient field and finds application in real-time cardiovascular imaging, 3 stem cell tracking 4,5 and hyperthermia 6 . The MPS described herein has no spatial scanning capability, but can assess both particle suspension relaxation and saturation, related to their performance for MPI 7 …”

Specific Loss Power in Magnetic Hyperthermia: Comparison of Monodispersion and Polydispersion

“…(1) without any assumptions or another magnetization equation derived microscopically from the Fokker-Planck equation [15] for more detailed analysis. Dhavalikar et al [23] used the phenomenological magnetization equation derived by Martsenyuk et al [24] instead of the Shliomis' equation [12] used in this study. The comparative studies between the present results with those obtained by the equation of Martsenyuk et al [24] are currently in progress.…”