JP2005028084A - Coil and heating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air core coil for efficiently heating a living body and to provide a heating apparatus including the coil, concerning a treatment method for allowing an implant to indwell in the living body, impressing an AC magnetic field, so as to heat a tumor, and causing necrosis. <P>SOLUTION: Distance between a conductor and the living body is made to be substantially uniform about the air core coil, so that the cross-sectional shape of a coil air core part is allowed to have a shape close to the cross section of an object. Then efficiency is raised by reducing the impression of the AC magnetic field on an unnecessary part. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention provides means and apparatus for efficiently heating an implant placed in a living body for thermotherapy such as cancer.

Recently, a treatment method for heating and necrosis of a tumor by placing an implant in a living body and applying an alternating magnetic field has been attempted. In this case, a system that surrounds the treatment target with a circular air-core coil and applies an alternating magnetic field is often employed. For example, in Nagoya Journal of Medical Science 59 (1996) 49-54, a human head is surrounded by a circular air-core coil against a tongue cancer, and an alternating magnetic field is applied.
Nagoya Journal of Medical Science 59 (1996) 49-54

  In the conventional coil described above, the shape of the target living body is not taken into consideration, and an AC magnetic field is applied to a portion that does not need to be used, so that it is an inefficient structure that wastes applied power. .

  The present invention is intended to solve the problem of such a conventional coil. It reduces the application of an alternating magnetic field to unnecessary portions, and efficiently reduces living body heating and thus high-frequency power output. It is intended to be realized.

Means to solve the problem

In order to achieve the above object, the present invention makes the cross-sectional shape of the air core part of the coil a shape close to a non-circular object cross-section. For example, the human torso is flat, and if it is surrounded by a circular coil, an unnecessary space is created in the front-rear direction of the human body, but an unnecessary space can be kept small with a coil having an elliptical or rectangular cross section. Realize efficient living body heating.

Action

The average magnetic field strength <H> in the air-core coil is given by <H> = Φ / (μ ₀ · S), where S is the area of the coil air-core. Here, μ ₀ is the vacuum permeability (constant), and Φ is the number of magnetic fluxes penetrating the coil. In general, Φ is given by the inductance L of the coil and the current I flowing through the coil, and Φ = LI. When the area of the coil is reduced, the inductance L decreases with the same number of turns, but the current I increases when the same power is applied. Therefore, the number of magnetic fluxes Φ does not change greatly with respect to changes in the coil area. Therefore, when the area S is reduced, the magnetic field strength <H> can be increased for the same power application.

Even if the area S is reduced, the inductance L can be made substantially the same by increasing the number of turns. In this case, the current amount 1 can be increased depending on the resistance value of the coil. Accordingly, since the number of magnetic fluxes Φ increases, when the area S is reduced, it is possible to obtain an effect of increasing the magnetic field strength <H> more than the area reduction for the same power application.

The invention's effect

  An increase in magnetic field strength was observed due to a decrease in the area of the air core of the coil.

  First, an implant that generates heat by application of an alternating magnetic field is placed at a target position in a living body. In this case, as the implant, a fluid in which metal powder or metal oxide powder is dispersed or a solid obtained by solidifying this fluid is often used, and a conductor solid may be used. Next, as shown in FIG. 1, the target site is passed through an air-core coil, and an AC magnetic field is applied to locally heat the target site.

  The frequency of the applied AC magnetic field is usually 100 kHz to 2000 kHz, preferably 300 kHz to 750 kHz.

  Since the shape of the torso of the animal including the human body is almost symmetrical, the shape of the air core of the air core coil that treats the torso is usually symmetrical in the direction corresponding to the left and right.

  The shape of the air core part of the air core coil that treats the human torso can be an ellipse or a rectangle. FIG. 2 shows an example suitable for the cross-sectional shape of the human torso, and the air core is oval. However, in many cases, including the human torso, symmetry is not necessary in the direction corresponding to the front and rear. For the human torso, the ratio h / w with respect to the width w and height h is preferably 0.4 to 0.9, particularly preferably 0.5 to 0.7. When the human body includes a shoulder, h / w is preferably from 0.3 to 0.7, particularly preferably from 0.4 to 0.6.

  It is desirable that the shape of the air-core coil and the cross-sectional shape of the target living body are close to each other, but the magnetic field strength is extremely large near the coil as compared with the central portion. It is appropriate to provide a gap of 2 cm or more between the coil and the living body.

  When the living body is heated, the cross-sectional shape varies depending on the individual. In order to bring the air core cross section close to the cross section of each living body, it is desirable to prepare several types of coils having different cross-sectional shapes and cross-sectional areas in advance, and select the optimum coil according to the shape of the target living body.

  One means for bringing the air core cross section close to the cross section of each living body is the use of a coil conductor having means for changing the cross sectional shape and cross sectional area. In this case, a flexible metal plate, a metal wire, a flexible hose or the like is used for part or all of the conductor.

  When the shape of the air core of the coil is optimized for the part to be heated, the other part of the living body may be an obstacle, making it difficult to insert the air core. For example, when the human torso is to be heated, this is the case when the optimum coil cannot pass through the buttocks. As a means for avoiding this, for example, use of a coil having means for changing the above-described cross-sectional shape and cross-sectional area can be mentioned. When inserting the living body, the coil air core part is expanded or deformed to insert the living body, and then the shape is restored to the optimum state when an alternating magnetic field is applied.

  It is also possible to install a coil at the target position without passing through the part that becomes an obstacle. One method is to use a coil composed of a plurality of conductors and connected by detachable contacts. In this case, after removing the contact and directly surrounding the target site with a coil, the contact is closed and an alternating magnetic field is applied. Another method is to use a coil in which the entire conductor is flexible. In this case, it is possible to directly wind the target site with a coil.

  As shown in FIG. 3, a matching device is usually connected to the air-core coil, and a high-frequency power source is connected to the matching device. A high-frequency power source usually consists of an oscillator and a plurality of amplifiers. The matching unit plays a role of adjusting the impedance and preventing the incident wave from being reflected. When the shape or cross-sectional area of the coil is changed, the impedance is also changed. Therefore, a matching device having the ability to cope with the change is required. Use a matching unit that can handle the frequency range of the AC magnetic field used and the impedance range of the coil. When the range of impedance and frequency covers a wide range, a plurality of matching devices are prepared and the optimum one is selected.

  It is desirable to reduce the resistance value and reduce the loss due to Joule heat in the matching unit, the air-core coil, or the connection portion thereof. For that purpose, it is effective to prevent copper from increasing the resistance due to oxidation by silver plating and to reduce the resistance value of the metal by cooling. Further, since an alternating current of 100 kHz or more flows on the surface of the conductor, it is effective to increase the surface area of the conductor forming the coil.

  A cooling medium such as gas or cooling water is used to cool the matching unit and the coil. When a lower temperature is required, a liquefied gas such as liquid nitrogen is used. For this reason, a metal pipe is usually used for the coil conductor. When using a metal wire as the coil conductor, an insulating coating is applied to the outside of the wire and a coolant is injected.

  As described above, compared with a circular coil, a coil that is flat and has a reduced air core area has a smaller inductance. To obtain the same inductance L, the number of turns may be increased. An increase in the number of turns leads to an increase in the length d of the coil, and the range of treatment can be expanded.

  Even with the same cross-sectional shape, the inductance L and the resistance value R vary depending on the number of turns of the coil and the density of the turns. As a result, even when the same power is input, the number of magnetic fluxes Φ or the magnetic field strength increases or decreases depending on the difference in the values of L and R. It is necessary to select the optimum number of turns and the density of the windings in consideration of the matching circuit connected to the coils and the like, and further considering the necessary coil length d.

  A copper pipe having a diameter of 4 mm was wound around an elliptical mold 6 times, 7 times and 8 times to produce three types of coils of the present invention. The width and height of the elliptical coil air core are w = 20 cm and h = 12 cm. The coil No. 6 was wound six times. 1 and the coil No. 7 was wound 7 times and 8 times. 2 and no. 3. For comparison with these, we also created a conventional circular coil. It is wound six times around a circular mold having a diameter of 20 cm. This circular coil is referred to as coil No. 4 The characteristics of these coils are summarized in Table 1. No. 1 and No. No. 4 has the same number of turns. 2 and No. 4 has substantially the same inductance. No. 3 and no. 4 has almost the same resistance value.

  No. The coils 1 to 4 were sequentially connected to a matching unit and a high-frequency power source, and the magnetic field strength generated at the center position of the coil and the temperature rise when the implant was placed at that position were measured. For measurement of the magnetic field strength, a high frequency of 200 kHz is applied at 100 W. Moreover, in the measurement of a temperature rise, what suspended magnesium powder in the carboxymethylcellulose sodium salt aqueous solution is used as an implant. The temperature rise is a change from room temperature when a 200 kHz high frequency 200 W is applied for 3 minutes.

Three types of elliptical coils and circular coils were compared, and Table 1 summarizes the magnetic field strength and the temperature rise of the implants. No. Compared with the circular coil No. 4, the magnetic field strength produced by the elliptical coils (No. 1 to No. 3) is large. The temperature rise of the implant also qualitatively agrees with the measurement result of the magnetic field strength. From these things, the effect of reducing the area of the air-core part of a coil was confirmed.

  By generating an alternating magnetic field using an air-core coil with a shape close to that of a living body, it is possible to efficiently heat an implant placed in the living body for thermotherapy such as cancer. Applicable to equipment. .

It is an external view of the non-circular air core coil which inserted the human body into the air core part which shows one Example of this invention. It is sectional drawing which shows an example of the coil of this invention. It is an example of the block diagram of the heating apparatus of this invention.

Explanation of symbols

1. Human body 2. 2. Air core coil 3. Indwelled part of the implant 4. Human body torso cross section Coil air core

Claims (7)

  A coil intended to insert a living object such as a human body or an animal into an air core and generate heat by generating an alternating magnetic field in an implant placed in the living body. A non-circular coil that is uniform.   It is a flat coil whose air core cross section is close to the shape of the human torso, with the aim of inserting the human torso into the air core and heating the implant placed in the human torso by generating an alternating magnetic field, A coil in which the ratio h / w of the width w to the height h of the air-core cross section is 0.3 to 0.9.   The coil according to claim 1 or 2, further comprising means for changing the length d of the coil, the area of the air core, or the shape of the air core.   The coil according to claim 1, 2 or 3, wherein a conductor constituting the coil is composed of a plurality of parts, and these are connected by a detachable contact.   A heating apparatus for heating a living body by an alternating magnetic field, comprising the coil according to claim 3 or 4 and having means for matching in accordance with a change in impedance of the coil.   A device with a plurality of coils according to claim 1, 2, 3 or 4 having different cross-sectional shapes and cross-sectional areas, and having a function of selecting and replacing an optimum coil according to a target living body, A heating apparatus for heating a living body by an alternating magnetic field, having means for matching in accordance with a difference in coil impedance.   The apparatus which has a coil of Claim 1, 2, 3 or 4, or the apparatus of 5 or 6, Comprising: The heating apparatus which heats a biological body with the alternating current magnetic field of 100-2000 kHz.

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