Control of the temperature rise in magnetic hyperthermia with use of an external static magnetic field

Abstract

Our purpose in this study was to investigate the usefulness of a method for controlling the temperature rise in magnetic hyperthermia (MH) using an external static magnetic field (SMF), and to derive an empirical equation for describing the energy dissipation of magnetic nanoparticles (MNPs) in the presence of both the alternating magnetic field (AMF) and SMF through phantom experiments. We made a device that allows for MH in the presence of an SMF with a field-free point (FFP) using a Maxwell coil pair. We measured the temperature rise of MNPs under various conditions of AMF and SMF and various distances from the FFP (d), and calculated the specific absorption rate (SAR) from the initial slope of the temperature curve. The SAR values decreased with increasing strength of SMF (Hs) and d. The extent of their decrease with d increased with an increase of the gradient of SMF (Gs). The relationships between SAR and Hs and between SAR and d could be well approximated by Rosensweig's equation in which the amplitude of AMF (Hac) is replaced by √[Hac(2)]/√[Hac(2)+Hs(2)], except for the case when Gs was small. In conclusion, the use of an external SMF with an FFP will be effective for controlling the temperature rise in MH in order to reduce the risk of heating surrounding healthy tissues, and our empirical equation will be useful for estimating SAR in the presence of both the AMF and SMF and for designing an effective local heating system for MH.

A Simulation Study on the Specific Loss Power in Magnetic Hyperthermia in the Presence of a Static Magnetic Field

“…We investigated the effect of SMF on the temperature rise in magnetic hyperthermia using this device and then evaluated the feasibility of controlling the temperature rise using an SMF with an FFP under various conditions of the AMF and SMF. Our experimental results demonstrated that the SLP value (referred to as "SAR" in our previous paper [16]) decreased with increasing H s [16]. Thus, the present results shown in Figure 4 to Figure 6 appear to support our experimental results [16].…”

“…This device can also generate an FFP and move it by varying the DC electric currents applied to the individual Maxwell coils [16]. We investigated the effect of SMF on the temperature rise in magnetic hyperthermia using this device and then evaluated the feasibility of controlling the temperature rise using an SMF with an FFP under various conditions of the AMF and SMF.…”

“…We previously made an experimental device that allows for magnetic hyperthermia in the presence of the SMF that was generated using a Maxwell coil pair [16]. This device can also generate an FFP and move it by varying the DC electric currents applied to the individual Maxwell coils [16].…”

“…In 2009, Tasci et al [15] proposed and designed a system that focuses the heat into very small regions using a static magnetic field (SMF) with a fieldfree point (FFP) generated by two solenoid coils, and reported that this method will be useful for making magnetic hyperthermia a more effective approach to cancer therapy with a decreased risk of heating surrounding healthy tissues. We have also investigated the usefulness of this method using phantom experiments and reported that it is useful for controlling the temperature rise in magnetic hyperthermia [16]. Although this approach appears to be useful for focusing the heat deposition into the targeted tissue or organ, it would be necessary to investigate the effectiveness of this approach under various conditions of MNPs, AMF, and SMF.…”

Long‐Term Stability and Reproducibility of Magnetic Colloids Are Key Issues for Steady Values of Specific Power Absorption over Time

“…For fitting this behaviour, a linear function is usually used [30] but also a Box-Lucas function has been proposed to extract the SPA values. [35,37] The initial increase of temperature can be extracted from (dT/dt)max so that a standardized protocol for calculating the SPA can be given.…”