Abstract
Purpose We describe a modified Helmholtz induction coil, or Maxwell coil, that generates alternating magnetic fields (AMF) having field uniformity (≤10%) within a = 3000 cm3 volume of interest for magnetic hyperthermia research. Materials and methods Two-dimensional finite element analysis (2D-FEA) was used for electromagnetic design of the induction coil set and to develop specifications for the required matching network. The matching network and induction coil set were fabricated using best available practices and connected to a 120 kW industrial induction heating power supply. System performance was evaluated by magnetic field mapping with a magnetic field probe, and tests were performed using gel phantoms. Results Tests verified that the system generated a target peak AMF amplitude along the coil axis of ∼35 kA/m (peak) at a frequency of 150 ± 10 kHz while maintaining field uniformity to >90% of peak for a volume of ∼3000 cm3. Conclusions The induction coil apparatus comprising three independent loops, i.e., Maxwell-type improves upon the performance of simple solenoid and Helmholtz coils by providing homogeneous flux density fields within a large volume while minimizing demands on power and stray fields. Experiments with gel phantoms and analytical calculations show that future translational research efforts should be devoted to developing strategies to reduce the impact of nonspecific tissue heating from eddy currents; and, that an inductor producing a homogeneous field has significant clinical potential for deep-tissue magnetic fluid hyperthermia.
Highlights
Combining magnetic materials or magnetic fluids with low frequency (50–400 kHz) alternating magnetic fields (AMFs) to treat deep-seated tumors by focal heating has generated interest for several decades [1,2,3,4,5,6,7,8,9]
Tests verified that the system generated a target peak AMF amplitude along the coil axis of ~35 kA/m at a frequency of 150 ± 10 kHz while maintaining field uniformity to >90% of peak for a volume of ~3,000 cm3
The induction coil apparatus comprising three independent loops, i.e. Maxwelltype improves upon the performance of simple solenoid and Helmholtz coils by providing homogeneous flux density fields within a large volume while minimizing demands on power and stray fields
Summary
Combining magnetic materials or magnetic fluids with low frequency (50–400 kHz) alternating magnetic fields (AMFs) to treat deep-seated tumors by focal heating has generated interest for several decades [1,2,3,4,5,6,7,8,9]. Design of devices for biomedical applications employing low-frequency AMFs reduces to well-established engineering considerations for applicator or coil geometries to produce magnetic fields having desired flux density in a specified volume [10, 12, 13,14,15]. Preclinical and clinical experience with MFH using low-frequency AMFs have established its viability as a treatment for cancer [1,2,3,4,5,6,7,8, 16, 17]
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