IntroductionRecently, early cancer detection is made possible with latest technologies such as CT, MRI, and so on. In the case of bile duct cancers, however, it is often advanced stage when cancers are detected because the symptom does not often appear at the early stage and projecting the cancer is difficult by the latest imaging technology. To treat cases like this, metallic stents have come to be used to support the lumens. So far stents have been used for life extension rather than for radical treatment. We propose the stents that function as thermotherapy for cancer besides its original efficacy. Thermotherapy is the method of treating cancer by the use of heat, and it is generally well known that at the temperature of 42.5 °C or more, the survival rate of tumor tissue decreases rapidly, while normal cells can survive up to 44 °C. If we take advantage of this 1.5 degree temperature difference, the necrosing of the tumor tissue is expected to be much more effective. We explicated that the stents can potentially be used as a heat source of thermotherapy by the external excitation. It is confirmed that eddy current loss causes heat of stents, We. It is shown in following equation. We = σe ( B * f ) σe : The constant decide according to material f : frequency [Hz] Bm: The maximum magnetic flux density [Wb/m2] Actually, the stent is heated in the intestine of rats. But, attainments of intestine's temperature after 2000 seconds by excited magnetic field are difference. So, it is necessary that examination to ensure the heat control. Methods Stents must be themosensitive magnetic materials and have lower Curie point to control heating and necrose tumor tissue alone, because stents are heated by eddy current loss. In this paper, we adopted magnetic shunt steel consisting of Fe, Ni and Cr. First, we measured effective permeability of the magnetic shunt steel. Subsequently, the magnetic shunt steel stent with the size of clinical use was compared with a clinical stent (Fig.1). We measured temperature of the stents as a function of magnetic flux density and compared the temperature characteristics with that of a clinical stent. Results and conclusion As Fig.2 shows, effective permeability of the magnetic shunt steel decreases rapidly between 70 and 80 °C The temperature profile of the magnetic shunt steel stent depended on magnetic flux density is quite different from that of clinical stent. While the clinical stent shows temperature dependency on magnetic flux density (Fig.3), the temperature of magnetic shunt steel stent keeps 78 °C irrespective of magnetic flux density (Fig.4). We confirmed the heating of the stent at Curie point. Stents with relatively high Curie point between 70 and 80 °C are useful for widespread tumor tissue because higher heat causes necrosis in wider area.
An optical isolator is fabricated for silicon-on-insulator circuits. The isolator, which employs a nonreciprocal phase shift in a Mach-Zehnder interferometer, is fabricated by directly bonding a magneto-optic garnet on a Si waveguide. A maximum isolation of 21 dB is obtained at 1559 nm. Extended AbstractAn optical isolator plays an essential role in protecting optical active devices from unwanted reflections. The optical isolator compatible to silicon-on-insulator (SOI) circuits has never been realized. We fabricated the isolator on an SOI wafer for the application to silicon photonic circuits. The isolator employs a nonreciprocal phase shift in a Mach-Zehnder interferometer. The device is fabricated in a 300-nm-thick Si guiding layer with a rib waveguide structure. To provide the nonreciprocal function, a magneto-optic garnet, Ce:YIG, is directly bonded on the Si rib waveguide using a surface activated direct binding technique. It is important to conduct the process in a temperature as low as 250 oC for circumventing the problems associated with mismatch in thermal expansion between silicon and garnet. A maximum isolation of 21 dB is obtained for TM mode at 1559 nm.
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