2Department of Surgery, School of Medicine, Akita University, Akita, Japan. 3Department of Electrical and Electronic Engineering, Akita University, Akita Japan.
Accuracy Improvement of Wireless Temperature Technique by Rotary Scan for Hyperthermia using Ferromagnetic Implant Loi Tonthat1, Hajime Saito2, Ryuhei Miyamoto3, Masafumi Suzuki3, Noboru Yoshimura3, Kazutaka Mitobe1 1
Department of Computer Science and Engineering, Akita University, Akita, Japan 2 Department of Surgery, School of Medicine, Akita University, Akita, Japan 3 Department of Electrical and Electronic Engineering, Akita University, Akita Japan Abstract: Soft-heating method is one type of hyperthermia that necrotizes malignant tumors in cancer treatment by means of heat generated by a ferromagnetic material. The magnetic permeability of ferromagnetic particle decreases immediately when its temperature increases over the Curie point (43℃). Therefore, we can concurrently use the ferromagnetic particles as a thermal probe for wireless temperature measurement during hyperthermia treatment. A challenge remains when dealing with body movement artifact as the relative position between the detection coil and the material is fluctuated by breathing or beating of the heart. As a result, the accuracy of temperature detection decreases. In this report we suggest and verify the validity of the new inspection system for the body movement artifact removal by regularly circling a unit of the magnetic field supply coil and the detection coil around the upper surface of the tumor region. Keywords: Hyperthermia, wireless temperature measurement, body movement artifact, ferromagnetic implant, rotary scan.
1. Introduction In Japan the largest cause of death is from malignant neoplasm [1]. Common types of cancer, including lung, stomach and colon are certain to continue to increase and thus it is necessary to pursue effective cancer therapy. Hyperthermia has been used for many years to treat various types of malignant tumor cells that are more sensitive than normal tissue cells to thermal deposition in the range of 40-45̊℃. This approach has garnered much attention recently as a possible new method for cancer treatment that is minimally invasive, has fewer side effects and results in a better quality of life for advanced-cancer patients. We previously described a system in which hyperthermia was induced using a Ferromagnetic Implant with a Low Curie Temperature (FILCT) based on the soft-heating method. This was able to mediate automatic temperature control and had antitumor effects in a mouse melanoma [2,3]. At the sample time, we use the FILCT as a thermometer probe for wireless temperature measurement via the magnetic permeability of ferromagnetic particle decreases immediately when its temperature increases over the Curie point [4, 5]. Before using our system in clinical settings, a challenge remains when dealing with body movement artifacts such as breathing or beating. It is expected that, when the ferromagnetic material has been injected into tumor region, the relative position between the pickup coil and the material fluctuates per body movement. As a result, it cannot distinguish that the ferromagnetic material has reached the target temperature (Curie point) or that there is a change of the relative position between the pickup coil and the ferromagnetic material. In this report, we propose a newly rotary scan method to solve body movement artifacts. In this method, a Magnetic Field Supply and Detection unit (MFSD unit), the magnetic field detection coil was integrated with the magnetic field supply drive coil, is circled in a period different to the period of body movement, and as such it can separate the spectral component specific to the rotary scan with the spectral component specific to body movement by using a Fourier transform. As a result, it can concurrently reduce the body movement artifacts and extract only the component
specific to the rotary scan to measure temperature target tumor. As a basic experiment we only experiment in a condition where the sample tube is placed while fixed on a tube holder and then assess the appropriateness of the wireless temperature measurement with a rotary scan method.
2. Method A new experiment system was developed to verify the validity of the rotary scan method. The experiment setup is shown in Fig. 1. In this system, an alternating current was applied from a function generator (WF1994A, NF Corp., Yokohama, Japan) and was amplified by a bipolar amplifier (BP4610, NF Corp., Yokohama, Japan). The amplifier signal was applied to the drive coil, and then a magnetic field was produced around it. The pickup voltage was measured by a lock-in amplifier (7265 DSP, AMETEK Co., Tokyo, Japan) which performs a synchronous detection that required a reference signal. The pickup voltage can be confirmed in real
Fig. 1 Block diagram of the experiment setup.
Table 1 Drive coil and pickup coil specifications. Drive coil Pickup coil External diameter[mm] 118 125 External diameter[mm] 76 10 Thickness[mm] 9 5 The number of turns 20 10 time by LabVIEW on a PC. To evaluate the appropriateness of this wireless temperature measurement method with a rotary scan, temperature of the Au-coated FILCT was measured by a fiber optic thermometer (FL-2000, Anritsu-meter, Tokyo, Japan). We used a robot arm (Motoman-SIA10F, Yaskawa, Kitakyushu, Japan) to produce an accurate constant-period rotary scan in this system. To examine a shift in the vector magnetic flux due to temperature of the Au-coated FILCT around the Curie point, the sample (1.0 g of Au-coated FILCT with 1.0 g of deionized water) was heated to about 70℃ and measured the pickup voltage until temperature of the sample cooled naturally past the Curie point at about 37℃. As a basic experiment, a low magnetic field was generated by alternating current (4A, 2560Hz) in the drive coil. In a state where there was no ferromagnetic material, the pickup voltage was set offset to 0V by using the auto-offset of the lock-in amplifier. The distance between the pickup coil and the sample was set at 1cm. After heating the sample to 70℃, the tube was installed in tube holder. We then used a robot arm to circle the MFSD unit (period 14.8s, radius 15mm) around and under the sample and started to measure the pickup voltage. The specifications of the drive coil and pickup coil are shown in Table 1.
Fig. 2 Relationship between pickup voltage and temperature of the Au-coated FILCT. immediately when the FILCT decreases near 43 ℃ and becomes stable below 43℃. As such, the FILCT attracts a stronger magnetic flux when temperature of the FILCT decreases near 43℃. In summary, this means that we can use the FILCT as probe for to measure temperature during hyperthermia treatment.
5. Conclusion In this report, we described a rotary scan method to solve body movement artifacts for hyperthermia using ferromagnetic implants. As a basic experiment we assessed the appropriateness of wireless temperature measurement with a rotary scan method in a condition where the sample tube was placed fixedly in a tube holder. However, we will verify in the future studies the validity of this method by simulating body movement by randomly moving the Au-coated FILCT while circling the MFSD unit.
3. Results
Reference
From the experimental results, the relationship of the induced voltage of pickup coil (pickup voltage) and temperature of the Au-coated FILCT is shown in Fig. 2. The first vertical axis shows the pickup voltage, the second vertical shows temperature of the Au-coated FILCT and the horizontal axis shows the time of measurement. Each maximum pickup voltage occurred when the distance between the pickup coil and the Au-coated FILCT was nearest, and each minimum pickup voltage occurred when the distance was farthest. Accordingly, one period of the pickup voltage showed one period of rotation of the MFSD unit. This meant that the period of the pickup voltage is synchronized with the period of rotation of the MFSD unit. Moreover, it is apparent that when temperature of the Au-coated FILCT, which was heated to about 70℃, decreases near the Curie point, the maximum pickup voltage increases immediately and then when temperature of the Au-coated FILCT decreases below the Curie point, the maximum pickup voltage is for the most part stable.
1. Ministry of Health, Labour and Welfare (Japan): [accessed on De-cember 10, 2013] 2. Saito H, Mitobe K, Ito A, Sugawara Y, Maruyama K, Minamiya Y, Motoyama S, Yoshimura N and Ogawa J: Self-regulating hyperthermia induced using thermosensitive ferromagnetic material having a low Curie temperature. Cancer Science. 99, pp. 805‒809, 2008. 3. Ito A, Saito H, Mitobe K, Minamiya Y, Takahashi N, Maruyama K, Motoyama S, Katayose Y and Ogawa J: Inhibition of heat shock protein 90 sensitizes melanoma cells to thermosensitive ferromagnetic particle-mediated hyperthermia with low curie temperature. Cancer Science. 100, pp. 558‒564, 2009. 4. Mitobe K and Yoshimura N: Noninvasive Tem-perature Measurement Method for Hyperthermia Treatment using Ferromagnetic Implant with Low Curie Temperature. IEEE EMBS. pp. 4384‒4386, 2008. 5. Mitobe K and Yoshimura N: Low-invasive Heating and Temperature Measurement Method for Hyperthermia Treatment using The Metal Coated Ferromagnetic Implant with Low Curie Temperature. BIODEVICES International Conference on Biomedical Electronics and Devices Proceedings. pp. 341-344, 2011.
4. Discussion We confirmed that the pickup voltage clearly changes around the Curie point as shown in Fig. 2. This comes about because the permeability of external gold is almost stable at around 43℃ while the magnetic permeability of internal FILCT increases
