Magnetic nanoparticle hyperthermia therapy is a promising technology for cancer treatment. The technique involves delivering magnetic nanoparticles (MNPs) into tumors, then activating the MNPs using an alternating magnetic field (AMF). The AMF generating system produces not only a magnetic field, but also an electric field. The electric field penetrates normal tissue and induces eddy currents, which result in unwanted heating of normal tissues. The magnitude of the eddy current depends, in part, on the AMF source and the size of the tissue exposed to the field. The majority of in vivo MNP hyperthermia therapy studies have been performed in small animals, which, due to the spatial distribution of the AMF relative to the size of the animals, do not reveal the potential toxicity of eddy current heating in larger tissues. This limitation has posed a nontrivial challenge for researchers who have attempted to scale up from a small animal model to clinically relevant volumes of tissue. For example, the efficacy limiting nature of eddy current heating has been observed in a recent clinical trial, where patient discomfort was reported. Until now, much of the literature regarding increasing the efficacy of MNP hyperthermia therapy has focused on increasing MNP specific absorption rate or increasing the concentration of MNPs in the tumor; i.e. - improving efficacy at what is thought to be the maximum safe field strength and frequency. There has been a relative dearth of studies focused on decreasing the maximum temperature resulting from eddy current heating, to increase therapeutic ratio. This paper presents two simple and clinically applicable techniques for decreasing maximum temperature induced by eddy currents. Computational and experimental results are presented to understand the underlying physics of eddy currents induced in conducting, biological tissues and to leverage these insights for the mitigation of eddy current heating during MNP hyperthermia therapy. Phantom studies show that these techniques, termed the displacement and motion techniques, reduce maximum temperature due to eddy currents by 74% and 19% in simulation, and by 77% and 33% experimentally. Further study is required to optimize these methods for particular scenarios; however, these results suggest larger volumes of tissue could be treated, and/or higher field strengths and frequencies could be used to attain increased MNP heating, when these eddy current mitigation techniques are employed.
The influence of specific absorption rate averaging schemes on the spatial correlation between mass-averaged specific absorption rate and radio-frequencyinduced steady-state temperature-rise distributions in the "Visible Human" body model exposed to plane waves in the 30-800 MHz frequency range is investigated through finite-difference time-domain modeling. The averaged specific absorption rate is computed on the basis of the IEEE Std. C95.3-2002 specific absorption rate massaveraging algorithm, employing 1-g and 10-g averaging tissue masses and several air-inclusion factors. The analysis reveals that the 10-g average specific absorption rate yields larger global correlation with the corresponding radio-frequencyinduced temperature-rise distribution for the considered plane-wave exposures, while the dependence on the air-inclusion factor features a distinctive threshold behavior.
During exposure to the cell phone electromagnetic field (EMF), some neurons in the brain at areas of peak specific absorption rate (SAR) absorb more electromagnetic energy than is permitted by existing guidelines. The goal of the present work was to investigate the influence of cell phone-like EMF signal on excitability and memory processes in single neurons. A Transverse Electromagnetic Cell (TEM Cell) was used to expose single neurons of mollusk to the EMF. Finite-Difference Time-Domain (FDTD) method was used for modeling the TEM Cell and the EMF interactions with living nerve ganglion and neurons. Neuron electrophysiology was investigated using standard microelectrode technique. SAR deposited into the single neuron was calculated to be 8.2 W/kg with a temperature increment of 1.21°C. After acute exposure, the threshold of firing of action potentials (AP) was significantly decreased (p ≈ 0.001). Time of habituation to stimulation with the intracellular current injection was increased (p ≈ 0.003). These results indicate that acute exposure to EMF at high SARs impairs the ability of neurons to store information.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.