@phdthesis{oai:air.repo.nii.ac.jp:00003444,
 author = {Ton, That Loi and トン, タット ロイ},
 month = {Mar},
 note = {Cancer is the second leading cause of death globally behind ischemic heart disease and stroke, accounting for an estimated 9.6 million deaths in 2018 according to World Health Organization. Magnetic hyperthermia is a promising cancer therapy which has been gaining more attention in recent years owing to fewer side effects compared to chemotherapy and less invasive than surgical therapy. This therapy utilizes the fact that the antitumor effect occurs when the tumor is heated continuously within the therapeutic temperature range of 40‒45℃. Heat generation in magnetic hyperthermia mainly ascribes to hysteresis and/or relaxation loss from magnetic particles subjected to a high-frequency magnetic field.
To date, magnetic hyperthermia applications capable of heating the affected part at a constant temperature while being minimally invasive in detecting the temperature and position of heating element are not established, thus the development of such systems are needed. So far, we are aiming to develop an induction heating system while monitoring the temperature and position of heating element. In previous studies, Mitobe et al. succeeded in developing a microsize thermosensitive ferromagnetic implant with low Curie temperature (FILCT) as a self-controlled heating element. FILCT was then coated with gold to improve its heating efficiency (Au Au-FILCT). Furthermore, a wireless temperature measurement method has been proposed to monitor the temperature of the tumor during treatment by using the implant as a thermal probe.
The results obtained in this study are listed below.

(1) Development of hyperthermia implant with high heating efficiency and high permeability
The previously developed Au-FILCT improved significantly the heating efficiency of FILCT (8 times), but part of the applied magnetic field was shielded ascribed to the conductive coating around FILCT. As a result, the change in the detected voltage induced in pickup coil (hereafter pickup voltage) was reduced by half, thereby the accuracy of our wireless thermometry was significantly lowered compared to that of FILCT. As an alternative approach to the gold coating, we proposed to mix FILCT with a high heating-efficient magnetic nanofluid. In the case of using a commercial nanofluid named Resovist® (MRI contrast agent), the heating efficiency of the proposed mixture of micro/nano-magnetic particles was improved 4.3 times, and the accuracy of the thermometry was improved 1.3 times compared to that of FILCT under a m agnetic field of 500 kHz, 4.95 kA/m. A similar tendency was obtained when using a lab-made nanofluid.

(2) Development of localization technique of hyperthermia implant
The implant in the tumor cannot be seen from the body surface. When the implant deviates from the central axis of the magnetic field supply and detection unit composed of drive coil and pickup coil (MFSD unit), the magnetic flux density applied on the implant decreases, resulting in a decrease in its heating efficiency and the thermometry accuracy. To solve this problem, we devised a position adjustment method in which the central axis is aligned directly above the implant by referring to three voltages induced in three pickup coils symmetrically installed inside drive coil. Using the constructed position adjustment system, it was possible to automatically locate the position of the implant with accuracy below 1 mm by operating MFSD unit in two modes of coarse adjustment (rotary scanning) and fine adjustment (linear scanning).

(3) Development of rotary scanning technique of body motion artifact reduction method
It is considered that the relative position between MFSD unit and the implant is fluctuated due to the periodic physiological motions such as respiration and heartbeat induced artifact during treatment. Therefore, we cannot distinguish whether the change in pickup voltage is caused by the change in temperature of the implant around the therapeutic temperature, or by the change in distance between MFSD unit and the implant by the artifact. To overcome this problem, we proposed a body motion artifact reduction method by using rotary scanning technique on MFSD unit in a different period cycle from the periodic respiration and heartbeat. Using the difference in the frequency domain of spectral component of rotary scanning (signal) and that of the artifact (noise), only the target signal is extracted. Using the constructed verification system, we confirmed that regardless of the presence of the artifact, the change of the extracted power around the Curie point is sufficiently large to detect whether the temperature of the implant has reached the therapeutic temperature. In particular, in the case with the artifact the SN ratio for temperature measurement was ‒3.1 dB, whereas the SN ratio after reducing the artifact using the proposed method was enhanced significantly 38.7 dB.

The thesis is composed of six chapters. In Chapter 1, we introduced the background and purpose of the research. Chapter 2 introduced the principle of hyperthermia such as its biological effects with respect to temperature, and heating methods used in hyperthermia. We then introduced the heating method used in this study named magnetic hyperthermia, and summarized the previous studies such as development of self-controlled heating mediator, wireless temperature measurement technique, and heating system for clinical application using the proposed wireless temperature measurement technique. In Chapter 3 to Chapter 5, we introduced the development and the obtained results from the evaluation experiments of (1) development of the implant of micro/nanomagnetic particles, (2) development of the automatic implant localization technique, and (3) development of the rotary scanning technique, respectively. Finally, we concluded the important results in this study and outlined future work in Chapter 6.},
 school = {秋田大学},
 title = {Study on Wireless Detection Techniques of Temperature and Position for Hyperthermia Using Magnetic Particles with Low Curie Temperature},
 year = {2019}
}