Design and Control of Field-Free Region Using Two Permanent Magnets for Selective Magnetic Hyperthermia

Abstract

Magnetic hyperthermia using magnetic nano particles (MNPs) is a very innovative method for application in cancer therapy. However, the heat generated by MNPs can destroy normal cells, which necessitates localized heat treatment methods to minimize the damage inflicted by magnetic hyperthermia. One such method involves the use of a field-free region (FFR). In this paper, the conditions for controlling the FFR based on the magnetic properties of the MNPs were theoretically calculated and verified through experiments. The strength of the gradient magnetic field for controlling the FFR was determined by the relationship between the nanoparticle size, the magnetizing condition, and the temperature change depending on the strength of the AMF. Based on this, a new method for the quantitative generation and control of FFR for selective heat treatment was proposed. We tested the selective heating and temperature control by controlling the FFR. We observed the changing dimension of FFR and heat distribution of MNPs according to changes in the gradient field. When we used 9.56 nm sized MNPs and controlled the distance between two magnets, the area of FFR varied from a minimum of 7.41 cm2 to a maximum of 26.24 cm2. In addition, the temperature increase varied from approximately 5 to 45 K when the FFR was controlled using an AMF operating at 12 kA/m and 207 kHz. We hope our findings will be a crucial consideration in system design and potentially in effective cancer therapy.

Keywords

• Selective hyperthermia
• field-free region (FFR)
• Fe₃O₄MNPs
• superparamagnetic theory