A STUDY ON RF/MICROWAVE APPLICATIONS: MAGNETIC FLUID HYPERTHERMIA AND BRAIN STIMULATION

Abstract

In this dissertation, studies on magnetic fluid hyperthermia and brain stimulation as an application field of RF/microwave are presented.<br/> In the first chapter, a magnetic fluid hyperthermia (MFH) has been studied. Magnetic, iron oxide, nanoclusters (MNCs) with regular size distribution and high stability were successfully prepared. In order to enhance the therapeutic effect of MNC, the process of finding optimal conditions was performed according to various factors, such as particle size distribution, external magnetic field frequency, and intensity. The correlation between heat generation ability and the various factors was evaluated by measuring the specific loss power (SLP). The 60 nm MNC showed the highest heat capacity ability in the various field conditions. Breast cancer stem cells (bCSCs) with chemo/radio-resistance were exposed to the optimized alternating magnetic field after treating with the MNC. The MNC promoted an appropriate temperature increase within 10 min. Thus, the treated CSCs were progressed to the thermal-mediated apoptotic cell death. <br/> When MNCs are injected into a biological tissue for MFH therapy, cell and in vivo experiments cannot guarantee the same effects because of metabolic, blood volume, or rate. The synthesized MNCs suitable for MFH were injected directly into the middle of tumor tissue of nude mice. Since the micro-environment of the MNC has changed, the magnetic field conditions have changed to achieve a therapeutic effect. The intensity of magnetic field has changed with the temperature change of the biological tissue. It has been shown that tumor volume decreases after MFH treatment. However, total tumor tissue was not treated. To increase the therapeutic effect, the same amount of the MNC was injected into various sites of cancer tissues of the other mouse. As a result, it was visually confirmed that the tumor tissue was destroyed without damage to healthy tissues.<br/> As a second study, the results of neuronal stimulation using electromagnetic fields are presented. A conventional transcranial magnetic stimulation (TMS) system was improved by using a full-bridge inverter circuit. The proposed TMS system can control the pulse width and generate a complex brain stimulation protocol. We then tested if TMS modulate nociceptive behaviors. A new TMS protocol mimicking thalamic burst firing patterns was tested for endogenous thalamocortical (TC) activity. The experimental results showed that nociceptive behaviors decreased after applying the TMS. <br/> The proposed TMS system modulates the envelope of continuous signal to produce thalamic burst firing patterns. The study continues to investigate whether the envelope modulated microwave signal affects the firing rate of neurons. Microwaves were used to narrow the electromagnetic field distribution and modulate brain activity with less power than conventional brain stimulation methods such as a TMS. Microwave circuits for the brain stimulation system were developed by MMIC technology and semiconductor manufacturing process. in-vivo experiments confirmed that microwave signals with repetitive pulse envelopes successfully changed the activity of individual neurons. <br/> In this dissertation, it was shown that RF/microwave can increase the temperature of biological tissue through energy conversion agent, MNCs. Through this, cancer treatment can be expected. This dissertation has also demonstrated the possibility that modulation of the signal can be practically applied to control brain activities.<br/>