Power absorption of milliscaled implants in alternating magnetic field for magnetically induced hyperthermia

The magnetically induced hyperthermia (MIH) system, based on the principle that milliscaled ferromagnetic alloy thermoseeds produce heat in a radio frequency (RF) alternating magnetic field due to eddy current and hysteresis, has been used in tumor clinical trials for decades. To provide guidance for implant distribution in tumors and temperature field simulation of MIH planning system, the theoretical formula for power absorption of an implant is deduced investigating geometry and orientation using the electromagnetic field constraint equation, including cylindrical and spherical implants. Then, the electromagnetic parameters that affect the power absorption have been analyzed using Matlab to simplify the formula. This simplified formula serves as a calculation model that can be easily programmed for temperature field simulation in a MIH system. Finally, the performance of several implants used for MIH is compared by power absorption per unit volume. The results show that the power absorption of the cylindrical implant per unit volume is maximized when the axis is parallel to the external magnetic field. The absorbed power of the spherical implant is slightly less than that of the cylindrical implant, and the formula is independent of the magnetic field direction. As a result, the use of a spherical implant will lead to a simplified calculation of the temperature field in a MIH system.