WO2016159371A1 - 経頭蓋磁気刺激装置用コイル装置 - Google Patents
経頭蓋磁気刺激装置用コイル装置 Download PDFInfo
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- WO2016159371A1 WO2016159371A1 PCT/JP2016/060965 JP2016060965W WO2016159371A1 WO 2016159371 A1 WO2016159371 A1 WO 2016159371A1 JP 2016060965 W JP2016060965 W JP 2016060965W WO 2016159371 A1 WO2016159371 A1 WO 2016159371A1
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N2/00—Magnetotherapy
- A61N2/02—Magnetotherapy using magnetic fields produced by coils, including single turn loops or electromagnets
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N1/00—Electrotherapy; Circuits therefor
- A61N1/40—Applying electric fields by inductive or capacitive coupling ; Applying radio-frequency signals
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N2/00—Magnetotherapy
- A61N2/004—Magnetotherapy specially adapted for a specific therapy
- A61N2/006—Magnetotherapy specially adapted for a specific therapy for magnetic stimulation of nerve tissue
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N2/00—Magnetotherapy
- A61N2/004—Magnetotherapy specially adapted for a specific therapy
- A61N2/008—Magnetotherapy specially adapted for a specific therapy for pain treatment or analgesia
Definitions
- the present invention relates to a coil device for a transcranial magnetic stimulation device and a transcranial magnetic stimulation device provided with the coil device.
- the first treatment performed for neuropathic pain is drug treatment.
- drug treatment is not effective for all patients because of the narrow scope of treatment.
- a method of directly stimulating the primary cerebral motor cortex using electrodes embedded in the head has been proposed.
- the electrical stimulation treatment using an implanted electrode has a problem that the burden on the patient is very large because craniotomy is required.
- transcranial magnetic stimulation that stimulates the primary cerebral motor area non-invasively without using an embedded electrode.
- the method of stimulating the brain with a pulsed magnetic field was proposed, and it was clarified that this transcranial magnetic stimulation method can improve neuropathic pain after stroke.
- transcranial magnetic stimulation is superior in that it does not require craniotomy, its therapeutic effect lasts only for about one day, so it is necessary to receive magnetic stimulation treatment every day.
- Transcranial magnetic stimulation generates a pulsed magnetic field from a coil built in a coil device placed on the head surface, and magnetically stimulates the brain with an electric field induced in the brain by this pulsed magnetic field. It is a technique to do.
- the coil is connected to a drive circuit.
- this drive circuit in order to generate an instantaneous current in the coil, electric charges are accumulated from the power supply device (including an AC power supply, a power supply circuit, and a booster circuit) to the capacitor. Thereafter, a current is passed through the stimulation coil by turning on the thyristor. The thyristor is turned off after a current flows through the diode through the resonance circuit of the stimulation coil and capacitor.
- a current for one cycle of the sine wave flows through the stimulation coil.
- a constant period of alternating current is applied to the coil to form a variable magnetic field, and an eddy current in the opposite direction to the coil current is induced in the brain under the influence of the variable magnetic field.
- the action potential is generated by stimulating the neuron with its eddy current.
- the body part corresponding to the stimulation site is affected. For example, if the primary motor area connected to the nerve of the hand or foot is magnetically stimulated, the nerve of the hand or foot is stimulated and the corresponding part moves. This is because the current flowing in the coil induces the opposite current in the brain, which stimulates interneurons and even cortical spinal neurons, and the part of the body corresponding to the stimulated brain part moves It is considered a thing.
- the advantage of magnetic stimulation is that it is very invasive. Specifically, the magnetic field reaches the brain without being affected by the living tissue. Therefore, it hardly stimulates the scalp with pain receptors and there is almost no pain caused by the stimulation.
- magnetic stimulation for humans was first reported in 1985, and has since been clinically applied in the diagnosis of neurological diseases. In addition, it has been reported that repetitive transcranial magnetic stimulation to patients with various neurological and psychiatric disorders improves their symptoms. In recent years, the application to treatment has progressed. Yes. For example, for the treatment of depression, stimulation to the prefrontal cortex was found to be effective, and in 2008, the US Food and Drug Administration (US Food and Drug Administration) magnetic stimulation for drug-resistant depression Approved treatment. Many clinical studies have been conducted on the treatment of Parkinson's syndrome, and knowledge indicating the effectiveness of magnetic stimulation has been accumulated. As already mentioned, magnetic stimulation treatment has an analgesic effect on neuropathic pain. Therefore, in Japan, magnetic stimulation treatment is currently being performed for patients with various neurological diseases in a well-equipped hospital.
- the conventional magnetic stimulation device has a weight of about 70 kg and requires electric work for installation, so it can be used only in a well-equipped medical institution.
- treatment by a skilled medical worker is necessary. Therefore, it is the actual situation that only treatment by medical institution specialists is performed, and it is necessary to go to the medical institution every day in order to continuously obtain the pain-relieving effect. Therefore, in order to reduce the burden on the patient, there is a need for the development of a home magnetic stimulation treatment device that can be used only by operations by non-medical workers.
- Transcranial Magnetic Stimulators At present, various transcranial magnetic stimulators have been introduced and used in the medical field. These magnetic stimulation apparatuses are made on the assumption that a medical worker such as a doctor operates, and the site to be stimulated is determined by the doctor.
- stimulation of the vicinity of the primary motor cortex of the patient's brain confirms the convulsion phenomenon called toitch (twitch), and the position of the brain where Toitch was confirmed. Is set as the stimulation point, and 90% of the stimulation intensity that can be confirmed by Toitch is applied to the coil during treatment. If the stimulation position within the brain is shifted by several millimeters, a region different from the intended stimulation region is stimulated. For this reason, it is important that the coil is accurately placed on the target site so that the stimulus of the appropriate intensity is applied to the target site.
- Circular Coil There is a circular coil commercially available from Magventure, USA. This circular coil has a merit that it can be stimulated in a wide range, for example, with a single spiral coil in which a single conductor (conductor) is spirally bent along the Archimedes spiral. There is a demerit that stimulation efficiency is bad. The stimulation intensity in the central part of the coil is almost zero. Therefore, it is considered that the circular coil is inappropriate for use in a test or treatment for locally stimulating a narrow portion.
- (B) 8-shaped coil There is an 8-shaped coil developed by Magstim of the United States. This 8-shaped coil is obtained by bending a single conducting wire (conductor) and incorporating an 8-shaped spiral coil having two spiral coil portions in a casing.
- one circular coil is energized in a clockwise direction and the other circular coil is energized counterclockwise, thereby strongly stimulating the part corresponding to the central part of both circular coils.
- high stimulation efficiency can be obtained because local stimulation can be performed.
- the robustness which means that eddy currents can be generated in a wider range and that magnetic stimulation can be effectively applied even if there is a slight deviation
- the 8-shaped coil has an advantage that the brain can be stimulated with high resolution because its spatial resolution is within 5 mm.
- (C) H-coil In 2005, an H coil was proposed by Zangen et al.
- the H coil has an advantage that the deep part of the brain can be stimulated by a current flowing in a part having a direction component perpendicular to the brain. For example, it can stimulate up to about 2.5 times the depth of an 8-shaped coil.
- the H coil has a problem that the stimulation efficiency is poor. Therefore, it is considered that the H coil is effective for treating depression and the like that are required to stimulate the deep dorsolateral prefrontal cortex.
- Another feature is that there is little attenuation of the induced electric field when stimulating deep areas. Therefore, there is an advantage that the patient does not feel instantaneous pain during magnetic stimulation.
- the data set here is a combination of the strength of the magnetic field generated by the permanent magnet attached to the stimulation coil and the three-dimensional position of the stimulation coil.
- the strength of the magnetic field is measured by a plurality of magnetic sensors. In this method, first of all, in the hospital, the patient wears a glass-type fixture for attaching a magnetic sensor.
- the magnetic force generated from a plurality of permanent magnets attached to the coil is detected by a magnetic sensor.
- the doctor specifies the optimal stimulation position and acquires the optimal stimulation position and the corresponding three-dimensional position of the coil in advance.
- a data set obtained in advance is used to determine how to move the coil to the optimal stimulation position while observing the monitor.
- the positional deviation error was about 5 mm.
- Modified 8-shaped coils Various modified 8-shaped coils are currently used [Refs. 4 to 15]. These deformed 8-shaped coils are obtained by overlapping two spiral coil parts partially (superposition type: see FIG. 11) and arranging two spiral coil parts in parallel without overlapping (non-overlapping). Matching type: see FIG. 3).
- the 8-coil coil is also divided into the Archimedes type (non-eccentric type) in which two spiral coil parts are bent along the Archimedes spiral, and the center of each of the two spiral coil parts developed by Mr. Sekino et al. Is eccentric toward the other spiral coil portion (eccentric type).
- the eccentric type 8-shaped spiral coil has a structure in which the center of the circular coil is close to the other circular coil, and the conductive wires are densely arranged at the center of the 8-shaped coil. For this reason, eddy currents can be concentrated directly below the center by flowing current in the opposite direction to the coil part where the two spiral coil parts are close to each other or the overlapping coil parts. It is a feature that efficient local stimulation can be obtained. However, it is considered that there is room for improvement in the robustness of the modified 8-character coil.
- Magsim 70 mm (P / N 9790) developed by Magstim in UK SA34 0HR, Car Mama Zenger, Whitland, Spring Garden (Spring Gardens, Whitland, Carmarthenshire SA34 0HR) is a general 8-character type. It is a coil.
- the Medtronic Dantec MCB70-Double Coil (the Medtronic-Dantec-Dante) developed by Magpro, located in Falm DK-3520, Denmark, Lucernemarken 15, DK-3520, Farum, Denmark.
- MCB70 double coils are bent so that the patient facing surfaces of the circular coil portions on both sides fit the brain.
- the object of the present invention is to generate a higher induced electric field strength than the conventional technique for the magnetic stimulation target area of the brain (referred to as an area to be magnetically stimulated), and to have a robustness compared to the conventional technique.
- An object of the present invention is to provide a coil device that can be used for a home magnetic stimulation device and a transcranial magnetic stimulation device including the coil device.
- a coil device for a transcranial magnetic stimulation device is provided so that a coil faces a human head surface, and generates an electric current by an induced electric field in a magnetic stimulation target region in a brain by electromagnetic induction.
- a coil device for a transcranial magnetic stimulation device for stimulating neurons A coil formed by winding a conductive wire along a predetermined reference plane; The head is provided opposite to the coil at a position on the opposite side of the coil.
- the coil is driven, a current due to an induced electric field flows, and the brain is driven by the current due to the induced electric field.
- a magnetic body that increases an electric current generated by an induced electric field that flows in the magnetic stimulation target area of the magnetic stimulation area as compared with the case where there is no magnetic body.
- the present invention it is possible to generate a higher induced electric field strength for the magnetic stimulation target region of the brain compared to the conventional technique, and it is more robust than the conventional technique. Can be used.
- FIG. 1 is a perspective view showing a schematic configuration of a transcranial magnetic stimulation device according to an embodiment of the present invention. It is a circuit diagram which shows the coil drive circuit integrated in the system of FIG. It is sectional drawing of the coil apparatus integrated in the system shown in FIG. It is a perspective view which shows the relationship between a coil and a magnetic body in the coil apparatus shown in FIG. It is a perspective view which shows the relationship between a coil and a magnetic body in the coil apparatus shown in FIG. It is a perspective view of the cube-shaped non-shaped magnetic body which laminated
- FIG. 5 is a perspective view of a rectangular parallelepiped non-shaped magnetic body in which electromagnetic steel plates are laminated in the Y direction.
- This embodiment provides a new transcranial magnetic stimulation device coil device and a transcranial magnetic stimulation device including the coil device based on the knowledge based on the analysis results described later in detail.
- a coil device for a transcranial magnetic stimulation device includes a coil in which a conductive wire is wound in a spiral shape along a reference plane, and a magnetic element disposed along the coil above the coil.
- the reference surface may be a flat surface, a curved surface, or a spherical surface. That is, the coil device for the transcranial magnetic stimulation device according to the embodiment is provided so that the winding coil faces the human head surface, and generates an electric current by an induced electric field in the magnetic stimulation target region in the brain by electromagnetic induction.
- a coil device for a transcranial magnetic stimulation device that stimulates neurons by winding a conductive wire along a predetermined reference plane, and the head is on the opposite side across the coil
- a magnetic stimulation target region in the brain is provided at a position above the coil so as to face the coil, and when the coil is driven, a current caused by an induced electric field flows.
- a magnetic body that increases an electric current generated by an induction electric field flowing through the base plate as compared with the case where there is no magnetic body.
- the coil may be any of a non-eccentric spiral coil, an eccentric spiral coil, or a dome type coil.
- the coil may be either a non-eccentric 8-character coil or an eccentric 8-character coil having two spiral coil portions.
- the magnetic body when the direction of the line connecting the centers of the two spiral coil portions along the reference plane is the X direction, and the direction perpendicular to the X direction along the reference plane is the Y direction, the magnetic body includes a plurality of magnetic bodies.
- the electromagnetic steel plates may be laminated in the X direction.
- the magnetic body includes a plurality of magnetic bodies.
- the electromagnetic steel sheets may be laminated in the Y direction.
- the magnetic body includes a plurality of magnetic bodies.
- the magnetic body may be laminated in the winding direction of the coil. That is, you may comprise by laminating
- the second laminated magnetic body portion may be disposed at the center of the coil device, and the first laminated magnetic body portion may be disposed on both sides of the second laminated magnetic body portion. Good.
- the magnetic body may be a quadrangle, a polygon, a circle, an egg, or an ellipse when viewed from the Z direction orthogonal to the X direction and the Y direction.
- the magnetic body may have an opening at the center when viewed from the Z direction orthogonal to the X direction and the Y direction.
- the coil device for the transcranial magnetic stimulation device is: An 8-shaped coil having two spiral coil portions wound in a spiral shape; A magnetic body disposed along the coil above the coil; The magnetic body is configured by laminating a plurality of electromagnetic steel plates in the arrangement direction of the conducting wire in the central portion of the coil.
- a coil device for a transcranial magnetic stimulation device is provided: An 8-shaped coil having two spiral coil portions wound in a spiral shape; A magnetic body disposed along the coil above the coil; The magnetic body is configured by laminating a plurality of electromagnetic steel plates in a direction perpendicular to a direction connecting the centers of the two spiral coil portions.
- the transcranial magnetic stimulation device includes any one of the coil devices described above.
- a transcranial magnetic stimulation device 1 is a magnetic stimulation device 4 that applies magnetic stimulation to a magnetic stimulation target region of a brain of a patient 3, for example, supported by a support mechanism (not shown) (for example, a chair 2 or a bed).
- the magnetic stimulation device 4 includes a coil device 5 and a control unit 6 in order to form a dynamic magnetic field that applies magnetic stimulation to the brain of the patient 3.
- the coil device 5 is preferably supported by an appropriate positioning unit 7 so that it can move freely along the head surface of the patient 3 and can be positioned at an arbitrary position.
- the coil device 5 includes a coil 8 and a casing 9 made of an electrically insulating material surrounding the coil 8.
- the casing 9 includes a holder 10 formed integrally with the casing 9, and is held by the positioning unit 7 via the holder 10.
- the coil 8 is an 8-shaped coil.
- the 8-shaped coil may be either an overlapping type in which two spiral coil portions are partially overlapped or a non-overlapping type in which two spiral coil portions are arranged in parallel without overlapping.
- the 8-shaped coil includes an eccentric type in which two spiral coil portions are bent along Archimedes' spiral, and an eccentric type in which the center of each of the two spiral coil portions is moved toward the other spiral coil portion. Any of these may be used.
- the casing 9 is integrally provided with three or more observation objects (for example, a target such as a mark 11 or a protrusion). These observation objects are used to determine the relative position and direction of the coil 8 with respect to the patient's head.
- observation objects for example, a target such as a mark 11 or a protrusion.
- the transcranial magnetic stimulation apparatus 1 may be configured as follows, for example.
- the control unit 6 includes a box-shaped housing 12.
- the housing 12 includes an input unit 13 and an output unit 14.
- the input unit 13 includes a driving condition setting unit 15 that sets driving conditions (for example, voltage, current, and frequency applied to the coil 8) of the transcranial magnetic stimulation apparatus 1; a tomographic imaging apparatus (for example, MRI, CT, and PET).
- a data receiving unit 17 that receives the tomographic image data generated by the human body (particularly the head) 16; a mark 11 provided on the casing 9 of the coil device 5 and a wearing product such as glasses worn by the patient 3 (for example, glasses) Alternatively, from a stereo imaging optical three-dimensional position sensing camera (hereinafter simply referred to as “camera”) 19 that simultaneously photographs three or more observation objects (for example, the mark 18 or the protrusion) provided on the skin of the patient 3.
- a data receiving unit 20 for receiving the image data is provided.
- the camera 19 is attached to a fixed portion of a living room in which the positioning unit 7 or the transcranial magnetic stimulation apparatus 1 is accommodated.
- the above-described tomographic imaging device 16, data receiving unit 17, stereo imaging optical three-dimensional position sensing camera 19, data receiving unit 20, and the like are used to position the coil device 5 with respect to the head irradiation site. It is good also as other modes.
- the current applied to the coil is not only a current (AC) whose flow direction changes periodically with time, but also a current whose flow direction is constant and whose magnitude varies periodically (so-called “pulse”). It should be understood to include “flow”).
- the output unit 14 is connected to a display 21 such as a liquid crystal display device or a computer (not shown) having a display, and outputs data (for example, image data) output from the control unit 6 to the display 21 to output the data. It is comprised so that the image corresponding to can be displayed.
- a display 21 such as a liquid crystal display device or a computer (not shown) having a display, and outputs data (for example, image data) output from the control unit 6 to the display 21 to output the data. It is comprised so that the image corresponding to can be displayed.
- a coil drive circuit 25 shown in FIG. 2 is accommodated in the housing 12, and this coil drive circuit 25 is electrically connected to the coil 8 via a cable 26.
- the position of the coil 8 with respect to the patient's head is obtained based on the image taken by the camera 19.
- the relative position of the coil 8 with respect to the patient's head is displayed on the display 21.
- the coil 8 can be installed in the target location (for example, optimal stimulation position) of a patient's head.
- the coil drive circuit 25 is driven based on the coil drive condition input through the input unit 15 to give magnetic stimulation to the brain of the patient 3. As shown in FIG.
- the coil drive circuit 25 uses the output from the power supply circuit 62 that converts the output voltage of the power supply 61 to a desired voltage, the booster circuit 63 that boosts the output of the power supply circuit 62, and the output from the booster circuit 63.
- a capacitor 64 that stores current
- a resistor 65 that adjusts the current flowing through the capacitor 64
- a semiconductor switch 66 that operates the output from the capacitor 64 at a predetermined timing to form an alternating current.
- the semiconductor switch 66 is turned on by a control circuit 67.
- a current obtained by driving the semiconductor switch 66 is applied to the coil 8 and includes a thyristor 31 that is controlled to be turned off and / or a diode 31D that is connected in parallel in the opposite direction.
- FIG. 3 shows a schematic configuration of the coil device 5.
- the coil device 5 has a casing 9 made of a nonmagnetic and nonconductive material.
- the bottom surface 21 of the casing 9 that faces the patient's head is on a plane (XY plane) that includes the left-right direction (X direction) of FIG. 3 and the front and back directions (Y direction) of the figure orthogonal thereto. It is a flat surface that is parallel or nearly parallel. In the present embodiment, this plane is the reference plane.
- the coil 8 is accommodated in the casing 9.
- the coil 8 is arranged such that two spiral coil portions 81 and 82 formed by bending one conductive wire 80 in a spiral shape are not overlapped along the reference plane, and the two spiral coil portions 81 and 82 are arranged.
- This is an eccentric and non-overlapping 8-character spiral coil in which each center is eccentric toward the other spiral coil portion.
- the direction connecting the centers 83 and 84 of the two spiral coil portions 81 and 82 constituting the 8-shaped spiral coil 8 (corresponding to the eccentric direction) is the X direction and the reference.
- a direction parallel to the surface and perpendicular to the X direction is defined as a Y direction
- a direction perpendicular to the reference surface is defined as a Z direction.
- the winding 80 extends in the Y direction at and around the central portion 85 located in the middle of the centers 83 and 84 of the coil portions 81 and 82.
- a cubic shaped magnetic body 22 having a predetermined volume is accommodated in the casing 9 on the coil 8 with a predetermined space between the coil 8 and the coil 8.
- the magnetic body 22 may be a single plate made of an electromagnetic steel plate (a magnetic material of the above-described comparative model), or a laminate in which thin electromagnetic steel plates whose surfaces are covered with an insulating film are stacked.
- the lower surface of the coil 8 is configured to face the brain surface
- the upper surface of the coil 8 is configured to face the magnetic body 22.
- the induction electric field strength in the magnetic stimulation target region of the brain is greatly increased and the induction electric field is concerned. Can be generated over a wider area.
- the magnetic body 22 includes laminated bodies 22A and 22C (see FIGS. 5 and 7) in which electromagnetic steel plates are laminated in the X direction, laminated bodies 22B and 22D (see FIGS. 6 and 8) in which electromagnetic steel plates are laminated in the Y direction, electromagnetic Any of laminates 22E to 22H (FIGS. 9 to 12) in which steel plates are laminated in the XY direction may be used.
- the magnetic body 22 may be provided with an opening 23 penetrating the upper surface and the lower surface at the center thereof (see FIGS. 7, 8, 11, and 12).
- the form shown in FIGS. 9 and 11 is obtained by laminating the electromagnetic steel plates in the regions on both sides in the X direction and laminating the electromagnetic steel plates in the region between them in the Y direction.
- the form shown in FIG. 10 and FIG. 12 is obtained by laminating the electromagnetic steel plates in the regions on both sides in the Y direction and laminating the electromagnetic steel plates in the region between them in the X direction.
- model names are assigned to the models shown in FIGS. 5 to 12 as follows.
- Model of FIG. 5 Model MX
- Model of FIG. 6 Model MY
- Model of FIG. 7 Model MXa
- Model of FIG. 8 Model MYa
- Model of FIG. 9 Model MZY
- Model of FIG. 10 Model MZX
- Model of FIG. 11 Model MZYa
- Model in FIG. 12 Model MZXa.
- the planar shape (the shape viewed from the Z direction) of the magnetic body 22 may be any of a quadrangle and a non-rectangle (for example, a circle, an egg, or an ellipse).
- the coil 8 in FIGS. 3 and 4 is an eccentric and non-overlapping 8-character spiral coil.
- the type of the coil 8 is not limited, and is an eccentric and superposition type 8-shaped spiral coil, a non-eccentric and superposition-type 8-shaped spiral coil, a non-eccentric type and a non-overlapping type 8 Any of the spiral coils can be used.
- the bottom surface 21 of the casing 9 is a flat surface, but may be a curved surface as shown in FIGS.
- the coil 8 does not need to be parallel to the curved surface but is a curved surface.
- it may be arranged in parallel to a flat surface including the X direction and the Y direction, or may be arranged in parallel to the curved surface.
- the magnetic body 22 does not need to be parallel to the curved surface but is a curved surface.
- it may be arranged in parallel to a flat surface including the X direction and the Y direction, or may be arranged in parallel to the curved surface.
- the spherical coil can be formed by arranging the conductive wire along the spherical surface.
- the spherical laminated magnetic body can be formed, for example, by pressing a flat laminated magnetic body into a spherical shape.
- the bottom surface of the casing 9 may be a bent surface obtained by intersecting two flat surfaces at a predetermined angle.
- the coil 8 may be any of an eccentric type, a non-eccentric type, a superposition type, or a non-superposition type.
- the coil 8 and the magnetic body 22 are bent surfaces. It may be arranged “along” with the reference plane. For example, it may be arranged in parallel with a flat surface including the X direction and the Y direction, or may be arranged in parallel with the bent surface.
- the bottom surface 21 of the casing 9 may be a spherical surface.
- the coil 8 is spherical and does not have to be parallel to the spherical surface. It only needs to be arranged “along” with the reference plane. For example, it may be arranged in parallel to a flat surface including the X direction and the Y direction, or may be arranged in parallel to the spherical surface.
- the magnetic body 22 is also a spherical surface and does not have to be parallel to the spherical surface. It only needs to be arranged “along” with the reference plane. For example, it may be arranged in parallel to a flat surface including the X direction and the Y direction, or may be arranged in parallel to the spherical surface.
- the size of the magnetic body 22 is preferably set to a size that can cover the coil 8 as a whole. However, when the coil 8 is an 8-shaped coil, it is preferable that the coil 8 has a size covering at least the minimum inner diameter region of the two spiral coil portions.
- the coil is an 8-character spiral coil including two spiral coil portions.
- the present invention is also applicable to a spiral coil including three or four spiral coil portions.
- the coil device 5 configured in this way, as described in the above-described analysis, by arranging the magnetic body along the coil, a larger induction electric field strength can be obtained compared with the coil device without the magnetic body. It can form on the brain surface.
- a magnetic material is formed by laminating electromagnetic steel sheets in a direction perpendicular to the direction connecting the centers of two spiral coil portions, while minimizing leakage magnetic flux and A higher induced electric field strength can be formed at a target treatment site, which is a magnetic stimulation target region, with high robustness in a predetermined direction.
- the inventors of the present invention have created two analysis models for the magnetic stimulation coil device in order to improve the magnetic stimulation efficiency, reduce the leakage magnetic field, improve the stimulation robustness, and downsize the finite element method.
- one analysis model is a model (hereinafter referred to as a “comparison model”) in which a rectangular parallelepiped brain model and a superposition type eccentric 8-shaped spiral coil are arranged inside a rectangular parallelepiped space (air region). ).
- a comparison model in which a rectangular parallelepiped brain model and a superposition type eccentric 8-shaped spiral coil are arranged inside a rectangular parallelepiped space (air region).
- cuboid a model in which a cubic magnetic body is arranged (hereinafter referred to as “cuboid”). , Called “modified model”).
- the size of the rectangular parallelepiped space is 1000 ⁇ 1000 ⁇ 1600 mm (“size in the X direction ⁇ size in the Y direction ⁇ size in the Z direction”. Displayed similarly.)
- the size of the brain model was 140 ⁇ 140 ⁇ 40 mm.
- the eccentric 8-character spiral coil is formed by spirally winding a conductor (conductor) having a width of 2 mm and a height of 6 mm along one plane to form two spiral coil portions 81 and 82.
- Each of the two spiral coil portions 81 and 82 has two eccentric spiral coil portions 81 and 82 in which the respective centers 83 and 84 are eccentric toward the other center.
- Each of the eccentric spiral coil portions 81 and 82 has a minimum inner diameter of 18 mm, a maximum outer diameter of 122 mm, an eccentric amount (distance between the outer diameter center of the eccentric spiral coil portion and the inner diameter center) of 27.5 mm, and left and right eccentric spiral coils.
- the distance between the inner diameter centers of the coil portions 81 and 82 is 42.5 mm, and the minimum coil gap on the eccentric side (in FIG. 18, the left side region is the eccentric spiral coil portion 81 shown on the right side and the right side region is the eccentric spiral coil portion 82 shown on the left side).
- the minimum coil gap on the eccentric side in FIG. 18, the left side region is the eccentric spiral coil portion 81 shown on the right side and the right side region is the eccentric spiral coil portion 82 shown on the left side.
- the eccentric 8-shaped spiral coil 8 having the above configuration has a line 8L connecting the centers of the two eccentric spiral coils (hereinafter, this line is referred to as "center axis of the eccentric 8-shaped spiral coil") in the X direction. Arranged.
- the brain model and the eccentric 8-shaped spiral coil are positioned at the center of the eccentric 8-shaped spiral coil on the center of the brain model 90.
- a 30 mm gap was formed between the brain model 90 and the eccentric 8-shaped spiral coil 8.
- the eccentric 8-shaped spiral coil 8 has a line connecting the centers 83, 84 of the two eccentric spiral coil portions 81, 82 (hereinafter, this line is referred to as "center axis of the eccentric 8-shaped spiral coil”) in the X direction.
- the direction perpendicular to the central axis 8L of the eccentric 8-character spiral coil 8 on the plane of the coil was arranged in the Y direction.
- a rectangular parallelepiped magnetic body 22 is arranged on the eccentric 8-shaped spiral coil with a gap of 0.5 mm.
- the rectangular parallelepiped magnetic body 33 four types of magnetic bodies 100A to 100D shown in FIGS. 21 to 24 were prepared.
- the magnetic body 100A in FIG. 21 is a rectangular parallelepiped magnetic body (non-R-shaped) formed by laminating electromagnetic steel plates in the Y direction in FIG.
- the magnetic body 100B of FIG. 22 is a rectangular magnetic body (b-shaped) in which a square opening (45 mm ⁇ 80 mm) is formed at the center of the magnetic body 100A.
- a magnetic body 100D of FIG. 24 is a rectangular parallelepiped magnetic body (non-R-shaped) formed by laminating electromagnetic steel plates in the X direction in FIG.
- a magnetic body 100D of FIG. 24 is a rectangular magnetic body (b-shaped) in which a square opening (45 mm ⁇ 80 mm) is formed in the center of the magnetic body C.
- Each of the magnetic bodies 100A to 100D has a sufficient area to cover the entire upper surface of the eccentric coil 8. In the calculation, the thickness of the electrical steel sheet was ignored.
- the electrical conductivity of the brain model 90 was 0.11 (S / m) (this is equal to that of the gray matter of the brain), and the relative permeability was 1.
- the electric conductivity in the air region was 0 (S / m), and the relative permeability was 0.
- the magnetic substance had an electric conductivity of 10 7 (S / m) and a relative permeability of 5000.
- the number of elements in both analysis models was about 1,000,000.
- the modified models including the magnetic bodies 100A, 100B, 100C, and 100D are referred to as “modified model MY”, “modified model MYa”, “modified model MX”, and “modified model MXa”, respectively.
- Je is the eddy current.
- the vector potential of the coil current is given by the following equation (5) from the well-known Bio-Savart law.
- Equation (7) is obtained from Equations (2) to (4) and Equation (6).
- equation (9) the equation to be satisfied by the complex field is given by equation (9) below.
- (B) Analysis of induced electric field strength the induced electric field strength on the upper surface of the brain model 90 (hereinafter referred to as “brain surface induced electric field strength”) for each of the comparative model and the four modified models.
- the distribution and the induced electric field at the center point on the upper surface of the brain model 90 (hereinafter referred to as “target point”) were analyzed.
- FIG. 26 shows the distribution of the induced electric field strength on the brain surface in the comparative model MF (FIG. 18), and the modified models MY, MYa, MX, MXa (FIG. 19, FIG. 21). (See FIG. 24)
- FIG. 27 to FIG. 30 show the distribution of brain surface induced electric field strength in FIG.
- the effective brain surface induced electric field strength of the comparative model without a magnetic substance was 118 (V / m).
- the effective brain surface induced electric field strengths of the four modified models MX, MXa, MY, and MYa are 120 (V / m), 129 (V / m), 297 (V / m), and 207 (V / m), respectively.
- each of the modified models obtained a larger effective brain surface induced electric field strength than the comparative model.
- MY a model having a rectangular magnetic material in which electromagnetic steel plates are laminated in the Y direction
- an effective brain surface induced electric field strength about 2.5 times that of the comparative model was obtained.
- any of the modified models MX, MXa, MY, MYa in which the magnetic body 22 is disposed on the eccentric 8-character spiral coil 8 generates more induced electric fields on the surface of the brain model 90 and the comparison model MF. It can be seen that it can be formed inside.
- the central axis of the eccentric 8-shaped spiral coil is parallel to the direction. It can be seen that an induction electric field much larger than the models MX and MXa in which electromagnetic steel sheets are laminated in the (X direction) can be formed on the surface of the brain model 90 and in the inside thereof.
- (C) Inductive electric field in magnetic body With respect to the modified models MX and MY including the rectangular magnetic body 22 in which electromagnetic steel plates are laminated in the X direction and the Y direction, the induction electric fields generated in the Y direction cross section and the X direction cross section at the center of the magnetic body. The intensity distribution of was analyzed. The analysis results are shown in FIGS. As shown in FIGS. 31 and 32, in the case of the modified model MX, a result that a high-intensity induction electric field appears on the lower surface side of the magnetic body 22 and a low-intensity induction electric field appears on the upper surface side of the magnetic body 22 is obtained. It was.
- a high-intensity induction electric field appears on the upper surface side of the magnetic body 22 and a low-intensity induction electric field appears on the lower surface side of the magnetic body 22 in the left region, but a high-strength induction electric field appears in the right region.
- a low strength induction electric field appeared on the upper surface side of the magnetic body 22 while appearing on the lower surface side of the body 22.
- an induced current flows in one ring along the Y-direction cross section, and in the modified model MY, along the X-direction cross section in each of the left and right regions. It is thought that the induced current flows in the opposite direction in a ring shape. Therefore, in any of the modified models, it is considered that the magnetic permeability of the magnetic material reduces the magnetic resistance around the coil, enhances the magnetic field on the brain surface, and strengthens the electric field in the brain. In the rectangular magnetic body 22 of the modified model MX in which electromagnetic steel plates are laminated in the X direction, an induced current as shown in FIG.
- the induced current weakens the induced current generated on the surface of the brain. It is thought that current flows.
- the induced current does not decrease in the brain because the induced current does not flow in the central portion.
- the induced current as shown in FIG. 34 flows in the rectangular magnetic body 22 of the modified model MY in which electromagnetic steel plates are laminated in the Y direction
- the current flowing in the coil portions 81 and 82 is orthogonal to the induced current generated on the brain surface.
- the permeability decreases, but the induced electric field generated on the brain surface by the current flowing through the coil portions 81 and 82 It is thought that there is no weakening. Therefore, as shown in Table 1, it is considered that the modified model MY of the rectangular magnetic body 22 in which the electromagnetic steel plates are laminated in the Y direction can obtain the most efficient stimulation.
- modified models MY, MYa, MX excluding the modified model MXa (the model having the X-shaped laminated B-shaped magnetic body), all satisfy the safety standards set by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). Obtained.
- ICNIRP International Commission on Non-Ionizing Radiation Protection
- the leakage magnetic field of the comparative model without the magnetic body 22 was the smallest, and it was found that the leakage magnetic field increased in the order of the non-R-shaped rectangular magnetic body and the R-shaped rectangular magnetic body. . This is because the magnetic field escapes upward in the Z-axis through the central opening in the letter-shaped magnetic body, whereas the leakage magnetic field is blocked by the induced current in the magnetic body in the non-square-shaped rectangular magnetic substance. It is thought that the magnetic field decreases.
- the modified models MY and MYa in which the electromagnetic steel plates are laminated in the Y direction have higher robustness than the modified models MX and MXa in which the electromagnetic steel plates are laminated in the X direction.
- the magnetic permeability of the magnetic body 22 causes the magnetic flux lines above and to the side of the coil 8 to be attracted to the magnetic body 22 and the effect of reducing the leakage flux above and to the side is exhibited. It was confirmed. Therefore, in particular, in a magnetic stimulation apparatus for home treatment, it is considered that the use of the magnetic body 22 is effective because a reduction in leakage magnetic flux is required to avoid interference with peripheral devices.
- the distribution of the induced current in the brain can be adjusted by changing the method of laminating the magnetic steel sheets in the magnetic body 22. Furthermore, it was confirmed that by expanding the distribution range of the induced current, the stimulation effect at the target point is not affected even if the coil is displaced, that is, the robustness against the displacement can be improved. This is also useful for home treatment magnetic stimulation devices because the positioning mechanism can be simplified.
- the magnetic body 22 is disposed above the coil 8. This is to exclude an invasive model in which the magnetic body 22 is embedded in the brain.
- the analysis model was created using “Femap with NX Nastran v10.3.1” commercially available from SIMENS Co., Ltd. In creating each element of the analysis model, the resolution was set to 1-5 mm.
- FIG. 37 An eccentric 8-character coil shown in FIG. 37 was used for the analysis. This coil was developed by Mr. Sekino in 2012, and has the advantage that a higher stimulation efficiency can be obtained compared to a non-eccentric 8-character coil.
- a pulse current of 3.15 kHz and 3 kA was applied to the left coil in FIG. 36 in the counterclockwise direction.
- a pulse current of 3.15 kHz and 3 kA was applied to the right coil in FIG. 36 in the clockwise direction.
- the magnetic material (iron core) used in the analysis was iron, a ferromagnetic material that was easily available.
- the relative permeability of iron was set to 5,000, and the electrical conductivity of iron was set to 10,000,000 (S / m).
- the iron shape was a rectangular parallelepiped in consideration of ease of processing. In the model assuming a magnetic body made of a laminate of thin iron plates, the electric conductivity in the direction perpendicular to the laminating direction is zero when analyzing the electromagnetic field in order to give directionality to the electric conductivity of the magnetic body. S / m).
- the analysis method is as described above.
- the stimulation efficiency is evaluated by the average value of the induced electric field intensity at the center of the brain model surface. Specifically, the average value of the induced electric field strength of elements in a sphere having a radius of 10 mm from the central portion of the surface of the brain model shown in FIGS. 37A and 37B was defined as the average induced electric field strength.
- the area having 70% of the maximum value of the induced electric field at the central part of the brain model surface is set as the effective stimulus intensity, and the maximum half value of each area in the X-axis direction and Y-axis direction is robust.
- the effective stimulation distance was used as an evaluation index. This effective stimulation distance is on the straight line in the X-axis direction and the straight line in the Y-axis direction that passes through the central part of the upper surface of the brain model, and is 70% of the induced electric field intensity at the central part of the upper surface of the brain model.
- the distance between the coordinates and the center of the upper surface of the brain model was set as the “effective stimulation distance”.
- model 3 Analytical model A model without the magnetic body 22 (model 1), a model having a rectangular parallelepiped magnetic body (model 2), and a rectangular frame type magnetic body having a rectangular opening formed at the center of the rectangular parallelepiped magnetic body.
- a model (Model 3) was created. The arrangement 22 of the coil and the magnetic body is as described above. In each analysis, a model number is assigned from 1. The dimensions of model 2 and model 3 are as shown in FIGS. 37A and 37B. In the case of the square frame type magnetic body in FIG. 37B, it is considered that the portion where the induced current flows is most preferable for the opening range.
- the size of the opening 22a is determined so that the centers of the outermost conductor portions of the left and right circular coil portions 81 and 82 coincide with the opening edge.
- the relative permeability of the magnetic body 22 was 5,000.
- the electric conductivity of the magnetic material is isotropic and was set to 10,000,000 S / m.
- the distance between the lower surface of the coil 8 and the upper surface of the brain model 90 was 30 mm.
- the induced current flowing in the magnetic body 22 is considered to be greatest at the central portion of the magnetic body 22. This is because, as is clear from Faraday's law of electromagnetic induction, the central portion of the magnetic body 22 has the largest rate of change in magnetic flux density, and therefore the induced electric field in the central portion is large. In addition, since the electrical conductivity is isotropic, the induced current is also increased. In the case of model 3 (FIG. 37B) in which the central portion of the magnetic body 22 is cut, it is considered that the magnetic flux extends in the Y-axis direction at the upper and lower portions of the rectangular frame type magnetic body having a low magnetic resistance.
- the leakage of the magnetic field is small
- the induced current in the central portion of the magnetic body 22 induces an electric field in the central portion of the surface of the brain model 90. Since the square frame type magnetic body does not induce such an electric field, it is considered that the model 3 having the square frame type magnetic body has the highest stimulation efficiency.
- FIGS. 38A to 38C show the analysis results of the induced electric field strength on the surface of the brain models 90 of the above models 1 to 3. From the analysis results, the brain surface average induced electric field strength of model 1 without magnetic body 22 (FIG. 38A) is 69.3 V / m, and the surface average induced electric field strength of model 2 having rectangular solid magnetic body 22 (FIG. 38B) is 49. The surface average induced electric field strength of model 3 (FIG. 38C) having the frame type magnetic body 22 of .5 V / m was 120 V / m.
- FIG. 39 shows the evaluation results of the stimulus robustness of each of the models 1 to 3.
- the effective stimulation distance in the X-axis direction was 0.041 m, and the effective stimulation distance in the Y-axis direction was 0.0678 m.
- the effective stimulation distance in the X-axis direction is 0.0304m, and the effective stimulation distance in the Y-axis direction is 0.0735m.
- the effective stimulation distance in the X-axis direction is 0.303 m
- the effective stimulation distance in the Y-axis direction is 0.0689 m. It was.
- the stimulation efficiency of Model 3 was greatly improved. Specifically, the stimulation efficiency of model 3 was 173% of the stimulation efficiency of model 1. However, the stimulation efficiency of model 2 was about 71% of the stimulation efficiency of model 1. There was no significant difference between the models in terms of stimulus robustness.
- the model 3 having the rectangular frame type magnetic body 22 has a higher stimulation efficiency than the model 1 without the magnetic body 22 because the magnetic field of the coil 8 is collected on the magnetic body 22 due to the presence of the ferromagnetic body (iron). It is thought that Also, the higher stimulation efficiency was obtained in the model 3 having the rectangular frame type magnetic body 22 than in the model 2 having the rectangular parallelepiped type magnetic body 22. This is because the induced current forms an electric field in the opposite direction to the electric field of the coil 8 on the surface of the brain model 90, whereas the square frame type magnetic body 22 does not form such an opposite electric field. Conceivable.
- Model 3 has a high stimulation efficiency, since the magnetic resistance of the portion where the magnetic material exists is significantly reduced, the magnetic flux almost passes through the magnetic material, and the brain is more efficiently transmitted. This is because a magnetic field can be sent to the surface.
- FIG. 40A is a contour diagram showing the induced current density (X direction component) on the surface of the rectangular parallelepiped magnetic body
- FIG. 40B is a contour diagram showing the induced current density (Y direction component) on the surface of the rectangular parallelepiped magnetic body.
- the Y-axis direction component of the current density has a stronger intensity in the Y + direction, which is opposite to the induction electric field created by the coil 8 on the surface of the brain model 90 (ie, Y direction) induction electric field is induced.
- FIG. 40B in the square frame type magnetic body, the induced current in the Y + direction is not induced in the excised central portion, so the coil 8 induces in the central portion of the brain model 90. The induced electric field is not attenuated.
- FIG. 41 shows an approximate graph of the magnetic field strength portion on the line extending in the Z-direction from the magnetic body toward the brain model at the coil central portion of the coil having the square frame type magnetic body.
- 0 of the Z coordinate is the brain surface
- FIG. 41 represents the magnetic field density on the Z direction line passing through the center of the coil. From FIG. 41, it can be seen that a stronger magnetic field is formed in the Z-direction in the model having the square frame type magnetic body 22 than in the model without the magnetic body 22.
- the magnetic body 22 was formed by laminating a plurality of magnetic plates, and the direction in which the induced current flows was limited by changing the laminating direction. As is apparent from the above analysis results, when the magnetic plates are laminated in the Y-axis direction, the induced current does not flow in the same direction. Therefore, in the model having the square frame type magnetic body 22, it is formed at the central portion of the brain surface by the coil. It is considered that the induced electric field is not affected. In addition, if both end portions of the magnetic body in the X-axis direction are stacked in the X-axis direction, it is considered that the induced current that the coil forms in the direction of the induced eddy current on the surface of the brain model can flow in the magnetic body.
- the examination was conducted only for the rectangular parallelepiped magnetic body. The reason is that the induced current flowing in the central part of the magnetic material can be controlled roughly by adjusting the stacking direction of the magnetic plates.
- the magnetic resistance of the rectangular parallelepiped type magnetic material is a square frame type magnetic material. Because it is smaller than that of the body.
- Analytical model Four analytical models having a rectangular parallelepiped magnetic body, that is, an X laminate model 1 in which magnetic plates are laminated in the X-axis direction (a model in which induced current flows along the YZ plane), and a magnetic plate in the Y-axis direction Y-stacked model 2 (model in which induced current flows along the XZ plane), XY-stacked model 3 in which magnetic plates are stacked in the X-axis direction and the Y-axis direction, and non-magnetic model 4 without magnetic material were prepared. .
- the XY stacking model 3 is configured such that the magnetic plates are stacked in the X-axis direction in the regions on both ends in the X-axis direction, and the magnetic plates are aligned in the Y-axis direction in the intermediate region between the regions on both ends. Laminated.
- this XY laminated model 3 an induced current in the direction opposite to the induced current generated in the brain by the eccentric 8-shaped coil 8 alone flows in the magnetic body. It is considered that the electric field is generated in the same direction as the induction electric field generated by the letter-shaped coil 8 and the stimulation efficiency is improved.
- the distance between the surface of the brain model 90 and the lower surface of the coil 8 was set to 13 mm, which is substantially the same as the actual stimulation environment.
- FIGS. 43A to 43D show the analysis results of the average induced electric field strength at the target site on the surface of the brain model 90 for each of the four analysis models 1 to 4.
- FIG. From the analysis results the average induced electric field strength of the X laminated model 1 is 120 V / m, the average induced electric field strength of the Y laminated model 2 is 415 V / m, the average induced electric field strength of the XY laminated model 3 is 502 V / m, and a non-magnetic model.
- the average induction electric field strength of 4 was 139 V / m.
- the X-axis direction effective stimulation distance and the Y-axis direction effective stimulation distance of the X-axis stacked model 1 are 0.0242 m and 0.0644 m, respectively, and FIG. , (D), the X-axis direction effective stimulation distance and the Y-axis direction effective stimulation distance of the Y-axis stacked model 2 are 0.0346 m and 0.0649 m, respectively, and are shown in FIGS.
- the X-axis direction effective stimulation distance and the Y-axis direction effective stimulation distance of the XY-axis stacked model 3 are 0.0607 m and 0.0697 m, respectively, as shown in FIGS. 44 (g) and (h).
- the X-axis direction effective stimulation distance and the Y-axis direction effective stimulation distance of the magnetic body model 4 were 0.0327 m and 0.0598 m, respectively.
- the XY laminate model 3 shows the highest stimulation efficiency.
- the Y-stacked model 2 shows a stimulation efficiency that is two to three times higher than the stimulation efficiency of the non-magnetic material model 4, but a downward induced electric field acts on both end regions of the brain model.
- the induced current shown in FIG. 45 flows in the magnetic body, and thereby an induced electric field is created in the same direction as the direction of the induced electric field formed by the eccentric 8-shaped coil in the central part of the brain surface. For this reason, it is considered that a high induction electric field strength was obtained in the central portion, which is the target portion.
- FIG. 46 shows a photographic image of the analysis result of the induced current density in the magnetic body. As is clear from FIG. 46, it can be confirmed that the induced current shown in FIG. 45 flows in the magnetic body.
- the robustness of the Y stacked model 2 and the XY stacked model 3 is improved by about 10% compared to that of the non-magnetic model 4.
- the effective stimulation distance spreads about twice in the X-axis direction. This is because the induced electric field produced by the eccentric 8-shaped coil is extremely high in locality, but by providing a Y-axis laminated magnetic material, an induced electric field in the X-axis direction is induced on the surface of the brain. It is considered that the electric field has spread in the X-axis direction as a whole.
- the induction electric field is spread in the X-axis direction as a whole due to the strong induction electric fields formed at both ends of the brain surface.
- the results of evaluating the robustness of Models 1 to 3 are shown in FIG.
- the effective stimulation distance in the X-axis direction and the effective stimulation distance in the Y-axis direction of model 1 in FIG. 47B are 0.0607 m and 0.0697 m, respectively.
- the effective stimulation distance in the X-axis direction and effective stimulation distance in the Y-axis direction of model 2 in FIG. Were 0.0529 m and 0.0666 m, respectively, and the effective stimulation distance in the X-axis direction and the effective stimulation distance in the Y-axis direction of Model 3 were 0.0526 m and 0.0669 m, respectively.
- model 1 showed similar values regarding the stimulation efficiency. This indicates that even with model 2 having a length of 100 mm in the Y-axis direction, stimulation efficiency comparable to that of models 1 and 3 having a longer length in the Y-axis direction can be obtained. There was no significant difference between models 1, 2 and 3 in terms of stimulus robustness in the Y-axis direction. Regarding the stimulus robustness in the X-axis direction, Model 1 had the largest stimulus range, and the other models 1 and 3 had a stimulus range of about 13% smaller than that.
- the magnetic material of the smallest model 2 with a Y-axis direction length of 100 mm has optimal stimulation efficiency. I can say that.
- Optimum thickness of laminated magnetic material used for home coil From the viewpoint of obtaining a stimulation coil 8 having a weight suitable for home treatment, the magnetic flux generated by the coil can be sufficiently collected. In addition, the thickness of the magnetic material that provides the required stimulation efficiency was examined.
- the magnetic flux ⁇ obtained by the equivalent circuit of FIG. 49 is given by the equation (10).
- r 1 ,..., R 10 (in the case of a 10-turn coil) are the average radii of the respective conductive wire loops of the eccentric 8-shaped coil.
- the magnetic field H is expressed by the following equation.
- N is the number of turns of the coil 8
- NI is the magnetomotive force.
- S 2.93 7.
- the model 1 X-axis direction effective stimulation distance and the Y-axis direction effective stimulation distance are 0.0490 m and 0.0606 m, respectively.
- the model 2 X-axis direction effective stimulation distance and the Y-axis direction effective stimulation distance are 0.0485 m, 0.
- the X-axis direction effective stimulation distance in the X direction and the Y-axis direction effective stimulation distance of Model 3 were 0.0461 m and 0.0613 m, respectively.
- dome-shaped coil Stimulus robustness optimal for home-use transcranial magnetic stimulation device Helmet-type alignment system that enables adjustment of coil position by patient himself has been studied. However, such a self-adjusting system is desired to have a robust performance that can tolerate an alignment error of about 20 to 30 mm. It is also important to know in advance the relationship between the properties of magnetic materials and their robustness. Therefore, various magnetic models were prepared, and the stimulus robust performance was evaluated for each model.
- FIGS. 51A and 51B Analytical model With respect to a model (FIGS. 51A and 51B) in which a laminated magnetic body in the X-axis direction is disposed in the hollow portion of the dome-shaped coil shown in FIGS. 50A and 50B, the brain surface induction electric field, the X-axis direction, and the Y-axis Directional stimulus robustness was evaluated.
- a dome-shaped coil model (model 1) having a magnetic body having a thickness of 4 mm and a dome-shaped coil model having a thickness of 12 mm (model 3) were prepared.
- the part that appears below the coil model is the brain model 90.
- the reason why the magnetic body 22 in which the magnetic plates are laminated in the X direction is employed is to prevent the disturbance of the distribution of the induction electric field created in the brain model by the dome-shaped coil. This model can increase the stimulation efficiency without excessively changing the stimulation robustness.
- FIGS. 52A to 52C show the analysis results of the brain surface induced electric field for the coil models 1 to 3, respectively. From the analysis results, the average induction electric field strength of the coil model 1 (non-magnetic material, FIG. 52A) is 71.8 V / m, and the average induction electric field strength of the coil model 2 (magnetic material thickness is 4 mm, FIG. 52B) is 453 V / m. m, the average induction electric field strength of the coil model 3 (the thickness of the magnetic material was 12 mm, FIG. 52C) was 501 V / m.
- the magnetic field created by the dome-shaped coil is collected in the magnetic material, and the stimulation efficiency of the brain is dramatically improved.
- the thickness of the magnetic body 22 is increased, the distance between the lower surface and the upper surface of the magnetic body 22 is increased, thereby reducing the action of the brain surface induced electric field being weakened by the induced current on the upper surface.
- the brain surface induced electric field is further increased.
- the effective stimulation distance in the X-axis direction and the Y-axis direction of the coil model 1 without the magnetic body 22 is 0.0821 m and 0.0450 m, and the X-axis direction and the Y-axis of the coil model 2 having the magnetic body 22 having a thickness of 4 mm.
- the effective stimulation distance in the direction was 0.0755 m, 0.0555 m, and the effective stimulation distance in the X-axis direction and the Y-axis direction of the coil model 3 having the magnetic body of 12 mm was 0.0745 m, 0.0560 m.
- the effective stimulation distance in the X-axis direction is reduced by providing the laminated magnetic body 22 in the X-axis direction.
- the shape of the stimulation range becomes closer to a circle by arranging the magnetic body 22.
- the inductance of the coil model 2 having the magnetic body 22 having a thickness of 4 mm was 85.9 ⁇ H.
- the winding density and cross-sectional area of the coil 8 are large, and the magnetic material is disposed inside the coil 8, so that the inductance is considered to be large.
- FIG. 54 Comparison of Stimulus Robustness Stimulus robustness (effective stimulus distance) evaluated for the above-described plurality of analysis models is summarized in FIG.
- the coil models with numbers in FIG. 54 (hereinafter referred to as CM1 to CM14) are as follows.
- CM1 a coil model having an X laminated rectangular parallelepiped magnetic body (220 ⁇ 122 ⁇ 10 mm);
- CM2 a coil model having a Y-stacked rectangular parallelepiped magnetic body (220 ⁇ 122 ⁇ 10 mm);
- CM3 Coil model having an XY laminated rectangular parallelepiped magnetic body (220 ⁇ 122 ⁇ 10 mm);
- CM4 non-magnetic coil model;
- CM5 Coil model having an XY laminated rectangular parallelepiped magnetic body (220 ⁇ 100 ⁇ 10 mm);
- CM6 a coil model having an XY laminated rectangular parallelepiped magnetic body (220 ⁇ 140 ⁇ 10 mm);
- CM7 Coil model having a Y-stacked rectangular parallelepiped magnetic body (220 ⁇ 122 ⁇ 2 mm);
- CM8 Coil model having a Y-stacked rectangular parallelepiped magnetic body (220 ⁇ 122 ⁇ 5 mm);
- CM9
- Fig. 54 shows the following.
- the only model whose effective stimulation distance in the X-axis direction is smaller than that of the non-magnetic model CM4 is the coil model CM1 having the X-stacked rectangular parallelepiped magnetic body (220 ⁇ 122 ⁇ 10 mm). The reason is that the induced current in the X direction laminated magnetic body acts to reduce the brain surface induced electric field generated by the coil.
- the effective stimulation distance in the Y-axis direction does not change greatly.
- the Y-axis direction component of the induction electric field created by the eccentric 8-shaped coil in the central part of the brain surface is sufficiently strong, so that it still maintains a large value even under the influence of the induction electric field created by the magnetic body 22. It is believed that there is.
- XY laminated magnetic coil models CM3, CM5 and CM6 have the same stimulation range, although the stimulation direction is different from that of a highly robust dome-shaped coil.
- the induced current in the X-direction laminated magnetic portion acts in the direction of increasing the induced electric field created by the eccentric 8-character coil in both end regions of the brain model. This is because the induced current in the part creates an electric field in the direction orthogonal to the induced electric field created by the eccentric 8-shaped coil in the center of the brain model. That is, the induced current in the magnetic body acts so as to extend the brain-induced electric field created by the 8-shaped coil in the X-axis direction.
- the induction electric field generated by the coil on the brain surface can be offset by adjusting the lamination direction.
- the induction electric field formed in the part directly below the central part is not affected, and therefore effective stimulation in the X-axis direction and the Y-axis direction is achieved. It is considered that the distance has increased as shown in FIGS. 55A and 55B.
- the non-medical worker When a non-medical worker other than the patient operates the system, the non-medical worker is considered to approach 60 to 100 cm from the stimulation coil 8. Accordingly, in order to ensure safety for non-medical workers, it is desirable to set the magnetic field level at a location 60 to 100 cm away from the stimulation coil 8 to a safe value or less.
- FIG. 56 shows an equivalent magnetic model used for the analysis. Equation (12) shows the magnetic circuit equation of the equivalent circuit of FIG.
- Equation (14) Since it can be assumed that the magnetic flux flowing through the magnetic circuit does not decrease, Equation (14) is established.
- Equation (16) the magnitude of the magnetic flux that does not enter the magnetic body and leaks into the air region is given by Equation (16).
- the magnetic flux leaking from the magnetic body 22 is large, so that it can be expected that a strong leakage magnetic field is generated around the coil 8.
- the magnetic flux leaking in the Z-axis direction is considered to be the strongest, the leakage magnetic flux in the X-axis direction and the Y-axis direction is also expected. Therefore, a magnetic shield covering the magnetic body 22 and the coil 8 is assumed and reduction of the leakage magnetic field is considered.
- the current I flowing on the surface of the magnetic body 22 is considered to be about 1 kA at maximum if the coil current is 3 kA. Therefore, the strength of the magnetic field generated at a location about 1 m away from the center of the coil in the Z-axis direction by the induced current in the magnetic body 22 is obtained as shown in Expression (17) based on the Bio-Savart equation.
- the magnetic shield is preferably made of a material such as ferrite that not only prevents leakage magnetic fields but also prevents induced currents from flowing therethrough as much as possible.
- the analysis model of FIG. 57 is similar to the analysis model shown in FIG. 35, but differs in the size of the air region and the presence of the magnetic shield.
- the size of the air region was set to 2 m ⁇ 2 m ⁇ 2 m in order to study the influence of the leakage magnetic field over a wide range.
- the magnetic body 22 is a rectangular parallelepiped magnetic body of 220 mm ⁇ 120 mm ⁇ 10 mm in which magnetic plates are laminated in the Y-axis direction.
- the electric conductivity of the magnetic body 22 was 10 7 S / m and the relative permeability was 1,500.
- the magnetic shield 91 that surrounds the upper side and the four sides of the magnetic body 22 is made of Ni—Zn ferrite, and has an electric conductivity of 10 ⁇ 5 S / m and a relative permeability of 1,500.
- the distance between the magnetic body 22 and the magnetic shield 91 in the Z direction was set to 20 mm, and the distance between the lower surface of the magnetic body 22 and the ceiling surface (inner surface) of the magnetic shield 91 was set to 46 mm.
- Three models with different distances in the XY direction between the magnetic body 22 and the magnetic shield 91-5 mm Model 1
- 10 mm Model 2
- 20 mm Model 3
- Model 4 Three models with different distances in the XY direction between the magnetic body 22 and the magnetic shield 91-5 mm
- 10 mm Model 2
- 20 mm Model 3
- Model 4 the leakage magnetic field strength of each was calculated.
- the safety standard 21 A / m of the leakage magnetic field is a relatively small value, it is considered important to consider the influence of a relatively small induced current generated inside the ferromagnetic material. Therefore, it is preferable to surround not only the magnetic field generated from the coil 8 but also the magnetic field generated from the magnetic body 22 by surrounding the laminated magnetic body 22 with a material having a low electrical conductivity such as ferrite. . From the viewpoint of miniaturization of the coil device, it is preferable that the distance between the ferrite and the laminated magnetic body 22 is as small as possible. However, if both of them are too close, the ferrite instead of the laminated magnetic body 22 becomes a magnetic path having a smaller magnetic resistance. The stimulation efficiency to the brain is reduced.
- Table 4 shows the leakage magnetic field strengths calculated for the models 1 to 4. In the analysis where the magnetic field strength did not converge to 21 A / m (in the table, the numerical value is enclosed in parentheses), the magnetic field strength at the position of 1 m from the center of the coil 8 located at the end of the air region is described. did.
- the Z + direction leakage magnetic field of the models having the magnetic shield was smaller than that of the model without the magnetic shield 91 (model 4).
- the leakage magnetic field decreased as the distance between the magnetic shield 91 and the magnetic body 22 decreased.
- the leakage magnetic field is reduced by providing the magnetic shield 91 in the X-axis direction and the Y-axis direction.
- the leakage magnetic field increases as the distance between the magnetic body 22 and the magnetic shield 91 decreases. This is considered to be because the radius of curvature of the magnetic lines of force increases as the distance between the magnetic body 22 and the magnetic shield 91 increases. For example, when the distance between the magnetic shield 91 and the magnetic body 22 is 5 mm, the incident angle of the magnetic force lines with respect to the magnetic shield 91 becomes small. As a result, the magnetic force lines are easily absorbed by the magnetic shield 91 and the leakage magnetic field in the Z-axis direction is small. It is considered to be.
- the horizontal distance between the magnetic shield 91 and the magnetic body 22 is 5 mm (magnetic shield 91A) with respect to the magnetic shield 91.
- the incident angle of the magnetic force line is larger than the incident angle when the horizontal distance between the magnetic shield 91 and the magnetic body 22 is 20 mm (magnetic shield 91B), and therefore, the magnetic force line reaches farther in the Z + direction.
- the magnetic shields 91A and 91B are alternatives.
- a solid line 93 is a line of magnetic force when the distance between the magnetic body and the ferrite is 5 mm
- a dotted line 94 is a line of magnetic force when the distance between the magnetic body and the ferrite is 20 mm.
- the magnetic field strength along the upper surface of the magnetic shield 91 in the X-axis direction is evaluated, but when the distance between the ferrite magnetic shield 91 and the magnetic body 22 is 5 mm, The peak of the magnetic field strength is at a portion close to the portion 93m, and in the case of 20 mm, the peak of the magnetic field strength is at a portion slightly away from the portion 94m in the negative Z-axis direction. In the model with the distance between the magnetic substance and the ferrite of 20 mm, the magnetic field strength was small.
- the inductance of model 4 without the magnetic shield 91 was 16.7 ⁇ H, and the inductances of models 1 to 3 in which the distance between the magnetic shield 91 and the magnetic body 22 was set to 5 mm were 17.0 ⁇ H, 16.8 ⁇ H, and 16.7 ⁇ H, respectively. .
- the distance between the magnetic shield 91 and the magnetic body 22 becomes smaller, the magnetic flux from the coil 8 passes through the magnetic shield 91, so that the inductance is considered to have increased.
- the average values of the induced electric field strength in the central part of the brain surface in Models 1 to 4 were 287 V / m, 307 V / m, 304 V / m, and 300 V / m, respectively. From this result, it is considered that when the distance between the magnetic body 22 and the magnetic shield 91 is 10 mm or less, the magnetic resistance of the magnetic shield 91 becomes smaller than the magnetic resistance of the magnetic body 22, and as a result, the brain surface induced electric field becomes weak. Therefore, it is considered appropriate to set the distance between the magnetic body 22 and the magnetic shield 91 to about 10 mm.
- (A) Analytical Model As shown in FIG. 59, three analytical models (models M1 to M3) in which the width of the flange 91F is 5 mm, 10 mm, and 15 mm were created.
- the material of the flange 91F is Ni—Zn ferrite.
- Table 5 shows the leakage magnetic field analyzed for each analysis model in FIG. In the analysis in which the magnetic field strength did not converge to 21 A / m (analysis in which the numerical values are enclosed in parentheses in the table), the magnetic field strength at a position 1 m in the horizontal direction from the center of the coil, which is the end of the air region, was described.
- the return of the ferrite is the flange 91F.
- the average values of the brain surface induced electric fields at the target points of the models M1 to M3 were 309, 309, and 309 V / m, respectively. Therefore, the optimal length of the flange 91F is 15 mm.
- the reason why the longest flange 91F is effective is that, as shown in FIG. 60, a part of the magnetic flux leaking from the bottom opening of the magnetic shield 91 is trapped by the flange 91F.
- the leakage magnetic field of the model in which the distance between the magnetic body 22 and the magnetic shield 91 is set to 10 mm and the flange 91F having a length of 15 mm is provided is 56 with respect to the X + direction of the model without the magnetic shield 91 and the flange 91F. 8%, 51.2% in the X direction, 67.0% in the Y + direction, 70.0% in the Y direction, and 51.2% in the Z direction.
- the leakage magnetic field in the X direction is not a problem. Further, when assuming that the medical worker holds the stimulation coil with his / her hand, the distance in the Y direction and the Z direction can be increased by the length of the arm.
- the coil inductance of the model having the flange 91F of 5 mm was 16.9 ⁇ H
- the coil inductance of the model having the flange 91F of 10 mm was 17.1 ⁇ H
- the coil inductance of the model having the flange 91F of 15 mm was 17.4 ⁇ H. It can be considered that as the length of the flange 91F increases, the magnetic flux passing through the magnetic shield 91 increases and the inductance increases.
- the effective stimulation distance in the X-axis direction and the effective stimulation distance in the Y-axis direction are 0.0455m and 0.0604m, respectively, and the magnetic shield 91 with the flange 91F (the horizontal distance between the magnetic body 22 and the magnetic shield 91 is
- the model having 10 mm and the length of the flange 91F (5 mm) has an effective stimulation distance in the X-axis direction and an effective stimulation distance in the Y-axis direction of 0.0459 m and 0.0605 m, respectively.
- the distance 91 is 10 mm and the length of the flange 91F is 10 mm.
- the effective stimulation distance in the X-axis direction and the effective stimulation distance in the Y-axis direction are 0.0461 m and 0.0608 m, respectively.
- the horizontal distance between the body 22 and the magnetic shield 91 is 10 mm, and the flange 91
- the length 15 mm) X-axis direction effective stimulation distance and Y-axis directions the effective stimulation distance model with were each 0.0464m, 0.0629m.
- the magnetic body 22 disposed inside the coil can also function as the magnetic shield 91.
- the frequency is about 3 kHz
- the induced current inside the magnetic body 22 is substantially canceled and only slightly exists on the surface of the magnetic body 22.
- the electromagnetic wave generated by it may reduce the therapeutic effect, so that the magnetic body is not sufficiently effective as the magnetic shield 91.
- Ni—Zn ferrite has a relative permeability of 1,500 and an electric conductivity of about 0.00001 S / m, and can be regarded as an insulator.
- Ni—Zn ferrite also has a relative temperature coefficient of about 1 to 3, and the magnetic permeability is not easily affected by temperature. Further, ferrite takes a certain value until the magnetic permeability reaches a certain frequency, but if the frequency is exceeded, the magnetic flux density cannot follow the change of the magnetic field, and the phase of the magnetic flux density may be delayed with respect to the magnetic field.
- Ni-Zn ferrite (HF70) has a certain permeability-frequency characteristic and does not adversely affect transcranial magnetic stimulation treatment with a stimulation frequency of about 3 kHz. Therefore, Ni—Zn ferrite is considered appropriate for the material used for the magnetic shield 91.
- the total weight of the optimally shaped magnetic body 22 and magnetic shield 91 obtained from the above analysis is about 2.1 kg.
- the weight of the eccentric 8-shaped coil itself is about 1 kg.
- the entire coil device including the magnetic body 22 and the magnetic shield 91 is about 3 kg, which is a weight that can be stably supported even in a home system.
- Inductance of the stimulating coil device The inductance of the magnetic ferrite model, which seems to be most appropriate, was about 17.4 ⁇ H.
- the inductance of the coil was analyzed based only on the air region, and calculated based on Equation (18) using the sum of the magnetic field energy in the air region.
- the induced current flowing through the magnetic body 22 is determined by the rate of change of magnetic flux based on Faraday's law. In this case, the induced current is considered to be affected by the speed at which the magnetic material is magnetized by the magnetic field and the speed at which the magnetic field generated from the coil changes, but the former is sufficiently larger than the latter, so The induced current flowing is considered to be almost equal to the induced current obtained by the analysis.
- Magnetic saturation of iron Iron has a magnetic property of hysteresis.
- the magnetic flux passing through the magnetic body 22 was calculated to be 0.328 ⁇ (see Equation (13)).
- the relative magnetic permeability is low at high magnetic fields.
- the induced electric field density in the magnetic body is considered to be about 10 to 50 ⁇ . Since the saturation magnetic flux density of iron is 2.15 ⁇ , it may be necessary to improve the magnetic flux by increasing the thickness of the iron in order to obtain desired characteristics with iron.
- the laminated magnetic body 22 is formed by sandwiching an insulator between a plurality of magnetic plates.
- Mn—Zn ferrite can be suitably used as the insulator.
- Mn—Zn ferrite has a relative permeability of 5,000, which is the same as iron, a volume resistivity of 0.3 ⁇ ⁇ m, and an adaptive frequency up to 1 MHz.
- the intensity of the induced electric field in the brain necessary for obtaining an effective therapeutic effect is 200 V / m. Therefore, in the case of the laminated magnetic coil model, it is considered that an effective therapeutic effect can be exhibited by applying a pulse current having a peak value of 1.18 kA to the coil. If the peak current can be reduced, the capacitor and booster circuit of the magnetic field generator can be greatly reduced, and the system cost can be significantly reduced accordingly.
- This embodiment relates to the development of a stimulation coil for the purpose of home treatment of patients with neuropathic pain by transcranial magnetic stimulation. Therefore, the coil model with the best stimulation efficiency was obtained by numerical analysis. Next, a lightweight coil model was obtained by numerical analysis while maintaining good stimulation efficiency. We also obtained a magnetic shielded coil model that reduces the effects on the human body by numerical analysis. From the above numerical analysis, the following conclusions were obtained.
- the effective stimulus distance in the X-axis direction is expanded by using ferrite for the shape of the magnetic material and the magnetic shield. Specifically, when the Y-axis laminated magnetic material is inserted, the effective stimulation distance in the X-axis direction can be increased by about twice.
- Ni-Zn ferrite cuboid top plate with a size of 250 x 150 x 5 mm, two cuboids (front and back plates) with a size of 240 x 5 x 46 mm, and a size of 5 x 150 x 46 mm
- a coil model in which a magnetic body is covered with a box-shaped magnetic shield consisting of two rectangular parallelepipeds (side plates) (the distance from the magnetic body is 10 mm), and a flange with a width of 15 mm is attached along the lower opening edge of the box-shaped magnetic shield
- the magnetic field strength at a location 1 m away in the X + direction is 51.4 A / m
- the magnetic field strength at a location 1 m away in the X direction is 42.1 A / m
- the magnetic field strength at a location 1 m away in the Y + direction is 21.84 A / m.
- the magnetic field strength at a location 0.965 m away in the m and Y directions is 21 A / m
- the magnetic field strength at a location 0.329 m away in the Z + direction is 21 A / m. Therefore, even if the coil model provided with the magnetic shield approaches from the center of the coil to 33 cm in the Z + direction and 97 cm in the Y direction, the human body is not affected.
- the simulation was performed assuming that the coil dimensions were as follows. The outermost diameter was 100 mm, the inner diameter was 20 mm, and the number of turns was 10.
- the conducting wire had a cross section of 6 mm long ⁇ 2 mm wide. The gap between the closest conductors was 0.5 mm.
- the current applied to the coil was 3 kA and the frequency was 3.15 kHz.
- about the dimension of the steel plate it was set as 220 mm in width, 122 mm in height, and 10 mm in thickness as follows.
- the weight of the steel sheet is approximately 2.1 kg, assuming that the specific gravity of iron is 7.85 t / m3.
- the relative permeability was 5000, the conductivity was 1.0 ⁇ 10 7 S / m, and the direction perpendicular to the stack was 1.0 ⁇ 10 ⁇ 7 S / m.
- the steel sheet was positioned 3.5 mm above the upper surface of the central eccentric 8-shaped coil.
- a conductor simulating the brain had a conductivity of 0.11 S / m, a length of 140 mm, a width of 140 mm, and a height of 40 mm. This conductor was set to be located 10 mm below the coil lower surface.
- the model of the entire experiment is as shown in FIG.
- the stimulus intensity was evaluated by averaging the magnitude of the electric field vector in the element within a radius of 10 mm from the stimulus center.
- the width of the vertically laminated portion of the side portion was changed from 6 mm to 36 mm, respectively, and the relationship between the width of the side portion and the average electric field strength achieved was plotted.
- 22X is an X-direction laminated magnetic body
- 22Y is a Y-direction laminated magnetic body
- the Y-direction laminated magnetic body 22Y is sandwiched between a pair of X-direction laminated magnetic bodies 22X in the X direction.
- the stimulation strength (induction electric field strength) was greatly improved by the laminated steel sheet.
- the average electric field strength at the center was 218 V / m and 335 V / m, respectively (FIGS. 63B and 63C). This is 1.5 times and 2.1 times the electric field strength (160 V / m, FIG. 63A) when there is no steel plate, respectively.
- the stimulation intensity due to the longitudinal lamination is 111 V / m (FIG. 63D), which is reduced compared to the case where there is no steel plate.
- FIGS. 64 (a1) and 64 (a2) an eddy current is generated by an 8-shaped coil in the longitudinally laminated steel sheet, and this induced current has a great suppression effect on the stimulation intensity. .
- a large loss current is generated due to the fact that the cross-sectional area of the steel sheet with respect to the interlinkage magnetic flux group becomes very large.
- FIGS. 64 (b1) and 64 (b2) it can be seen that there is a region where a loss current is generated in the steel sheet even in the case of the lateral lamination. Accordingly, it is assumed that the stimulation intensity when using the steel sheets laminated in the transverse direction is higher than that without the steel sheet, but the stimulation intensity is slightly attenuated.
- FIG. 65 shows the relationship between the width of the side portion that is a vertical stack and the stimulation intensity.
- the stimulation intensity was 456 V / m when the width was 30 mm.
- the inductance was 11.7 ⁇ H in the model without the iron core, whereas it was 17.2 ⁇ H when the 30 mm wide combined laminated steel sheet was used.
- the disconnection between the laterally laminated portion and the longitudinally laminated portion has successfully hindered the loss induced current generated in the steel sheet, as compared with the case where a unidirectional laminated core is used laterally. It can be seen that in the combined steel sheet, the induced current is considerably reduced.
- the model with the combined eccentric steel sheet combined with the central eccentric 8-shaped coil is 2.8 times the stimulation strength compared to the case without the steel sheet, and therefore compared to the normal 8-shaped coil without the iron core. A stimulation intensity of 3.4 times was achieved.
- the inductance value has become slightly larger than when the steel plate is not used, so it is expected that there will be a slight change in the frequency of the stimulation pulse in TMS.
- the inductance of the TMS coil typically has a value of 10 ⁇ H to 35 ⁇ H, and it is considered that this change in inductance can be dealt with by appropriately selecting a circuit having an appropriate value capacitor.
- a study has been made on a circuit that can generate a pulse having a free shape regardless of an inductance value. By using such a circuit, it is considered that a change in inductance is not considered.
- the coil in which the eccentric 8-character coil 8 is combined with the magnetic body 22 and the magnetic shield 91 can be sufficiently used as a coil for a home magnetic stimulation apparatus.
- the present invention it is possible to generate a higher induced electric field strength than the conventional technique for the magnetic stimulation target area of the brain (referred to as an area to which the magnetic stimulation is applied).
- an area to which the magnetic stimulation is applied it is possible to provide a coil device that has robustness and can be used for, for example, a home magnetic stimulation device, and a transcranial magnetic stimulation device including the coil device.
- the coil device for a transcranial magnetic stimulation device is provided so that a winding coil faces a human head surface, and generates a current by an induced electric field in a magnetic stimulation target region in a brain by electromagnetic induction to generate a neuron.
- a coil device for a transcranial magnetic stimulation device for stimulating a coil wherein the coil is formed by winding a conducting wire along a predetermined reference plane, and the head is on the opposite side across the coil, An induction provided at a position above the coil so as to be opposed to the coil, and when the coil is driven, a current caused by an induced electric field flows, and the current caused by the induced electric field flows to the magnetic stimulation target region in the brain.
- It is characterized by comprising a magnetic body that increases the electric current generated by the electric field as compared to when there is no magnetic body. Therefore, according to the present invention, it is possible to generate a higher induced electric field strength for the magnetic stimulation target region of the brain compared to the conventional technique, and it is more robust than the conventional technique. Can be used. Furthermore, when the magnetic body is configured by being laminated in the winding direction of the coil, it is possible to further increase the current due to the induced electric field flowing in the magnetic stimulation target region in the brain.
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Abstract
Description
近年,脳卒中などの生活習慣病の患者数が増加している。生活習慣病の後遺症の1つが,神経障害性疼痛である。神経障害性疼痛とは,何らかの理由によって神経が障害され,それによって生じる手足の痛みである。
経頭蓋磁気刺激は,頭部表面に置いたコイル装置に内蔵されたコイルからパルス磁場を発生させ,このパルス磁場によって脳内に誘導された電場で脳を磁気刺激する手法である。そのために、コイルには駆動回路に接続される。この駆動回路によれば、瞬間的な電流をコイルに発生させるために、電源装置(交流電源,電源回路,昇圧回路を含む。)からコンデンサへ電荷を蓄積する。その後,サイリスタをターンオンすることにより刺激コイルに電流を流す。刺激コイルとコンデンサの共振回路にダイオードを通して電流が流れたのち,サイリスタがオフになる。これにより,正弦波1周期分の電流が刺激コイルに流れる。以上の動作を繰り返すことにより、コイルには一定周期の交流が印加されて変動磁場が形成されるとともに、その変動磁場の影響を受けて脳内にはコイル電流とは逆向きの渦電流が誘導され、その渦電流でニューロンを刺激することによって活動電位を発生される。
現在,医療現場では,種々の経頭蓋磁気刺激装置が導入され利用されている。これらの磁気刺激装置は,医師等の医療従事者が操作することを想定して作られており,刺激する部位は医師によって決められている。具体的な治療の一例として神経障害性疼痛の治療では,患者の脳の一次運動野付近を刺激してトイッチ(twitch)と呼ばれる指が動くけいれん現象を確認し,トイッチが確認出来た脳の位置を刺激ポイントに設定し,トイッチが確認できる刺激強度の90%の電流を治療時にコイルに印加する。脳内部の刺激位置が数ミリでもずれると,目的の刺激部位とは違った部位が刺激されてしまう。そのため,目的の刺激部位に適正強度の刺激が与えられるように,コイルは目的の部位に正確に設置されることが重要である。
上述のとおり,経頭蓋磁気刺激では目的の脳部位を正確に刺激することが重要である。それを行うために,様々な位置合わせシステムが開発されてきた。例えば,赤外線カメラを用いた位置合わせシステムが提案されている。このシステムによれば,頭(脳)と刺激コイルにつけた複数の目印が付属の光学式カメラで撮影され,頭(脳)とコイルの位置関係がモニター画面に表示される。また,患者のMRI画像データとカメラの画像を組み合わせることで,コイルと脳の相対的な位置を正確に把握し,より正確な位置合わせが可能である。実際,位置ずれ誤差は多少異なるが,概ね数ミリ程度である。しかし,システムのサイズが大きい,また医療従事者でないと扱えない,さらに価格が高い,といった問題がある。
上述のとおり,在宅用の磁気刺激装置はコンパクトであることが望ましい。一方,電力供給部の大きさはコイルの刺激効率に反比例する。従って,高刺激効率であればあるほど電力供給量が少なくてすみ,回路素子の数が少なくなり,装置は小型で且つ安価になる。そのため,より効率良く刺激を与えることができる,様々な刺激コイルが開発されてきた。また,経頭蓋磁気刺激は,その刺激特性に応じて治療効果が異なるため,多様な刺激特性をもつ様々なコイルが開発されてきた。
米国のマグベンチャー社(Magventure)から商業的に提供されている円形コイルがある。この円形コイルは,例えば,一本の導線(導体)をアルキメデスの螺旋に沿って渦巻き状に曲げた一つの渦巻きコイルをケーシングに内蔵したもので,広範囲に刺激が出来るというメリットがある一方で,刺激効率が悪いというデメリットがある。コイル中央部分の刺激強度はほぼゼロに近い。従って,円形コイルは,狭い部分を局所的に刺激する検査や治療に利用するのは不適切であると考えられる。
米国のマグスティム社(Magstim)によって開発された8字型コイルがある。この8字型コイルは,一本の導線(導体)を曲げて2つの渦巻きコイル部分を有する8字渦巻きコイルをケーシングに内蔵したものである。
2005年,Zangen氏らによって,Hコイルが提案された。Hコイルは,脳に垂直な方向成分をもつ部分に流れる電流によって脳の深部を刺激することができるという利点がある。例えば,8字型コイルに比べて約2.5倍の深さまで刺激できる。しかし,Hコイルは,刺激効率が悪いという問題がある。そのため,深部の背外側前頭前野を刺激することが求められるうつ病等の治療には,Hコイルが有効であると考えられる。また,深部を刺激する際に誘導電場の減衰が少ない,ことが特徴として挙げられる。そのため,磁気刺激の際に患者が瞬間的な痛みを感じにくいという利点がある。
上述のように,従来の位置合わせシステムは高価な機器を用いており,かつ医師による操作が必要であったため,在宅用装置としては適していなかった。この問題を解消する目的から,大阪大学の西川氏らはより操作しやすいデータセット型磁場ナビゲーションシステムを開発した[参考文献3]。ここでいうデータセットとは刺激コイルに取り付けた永久磁石が発する磁場の強度と刺激コイルの3次元位置の組み合わせである。磁場の強度は,複数の磁気センサで計測される。本手法では,まず病院において患者に磁気センサの付いためがね型固定具を装着する。めがね型固定具を同じ位置に装着させるために,コイルに取り付けた複数の永久磁石から発する磁力を磁気センサで検出する。また,医師が最適刺激位置を特定し,最適刺激位置とそれに対応するコイルの三次元位置を予め取得する。患者自身がコイルを位置合わせする場合,予め得られたデータセットを利用し,最適刺激位置に移動させるためにはどのように動かせばいいかをモニターを見ながら判断し,操作する。本システムを20代男性の健常者が利用した際の位置ズレ誤差は5mm程度であった。
上述のように,在宅用の磁気刺激装置はコンパクトであることが重要である。そのために,高効率な刺激コイルが求められている。しかし,これまで開発されてきたコイルは多様な刺激特性を有するものの,在宅用として用いるためには,効率性を改善すべきである。また,医師が操作することなどを前提としており,広範囲に刺激できるロバスト性の高いコイルはまだ開発されていなかった。
現在,種々の変形8字型コイルが利用されている[参考文献4~15]。これらの変形8字型コイルは、2つの渦巻きコイル部分を部分的に重ね合わせたもの(重ね合わせ型:図11参照)と,2つの渦巻きコイル部分を重ね合わせることなく並列に配置した(非重ね合わせ型:図3参照)に分類される。8字渦巻きコイルはまた,2つの渦巻きコイル部分をアルキメデスの螺旋に沿って曲げたアルキメデス型(非偏心型)と,2000年に関野氏らによって開発された、2つの渦巻きコイル部分のそれぞれの中心を他方の渦巻きコイル部分に向けて偏心させた(偏心型)に分類される。これらのうち,偏心型の8字渦巻きコイルは,円形コイルの中心を他方の円形コイルに近づけた構造で,8字型コイルの中央部分に導線が密に配置されている。そのため,2つの渦巻きコイル部分が接近したコイル部分又は重ね合わされたコイル部分に逆向きに電流を流すことで,渦電流を中心部直下に集中させることができるため,非偏心8字型コイルよりも効率のよい局所的な刺激が得られるという特徴である。ただし、変形8字型コイルについても、ロバスト性については改善の余地があると考えられる。
刺激特性を向上するために,コイルの形状等を変える手法以外にも,多くの手法が提案されている。例えば,2003年には,円形コイルに強磁性体の鉄心を添えることで刺激効率を改善することがビー・エイチ・ハン(B.H.Han)氏らによって提案された[参考文献19~21]。例えば,円形コイルの上にそれと同じほぼ大きさの積層鉄心を配置したモデルでは,鉄心を挿入しないモデルに比べて,その刺激強度が最大で50~60%向上することが確認された。本手法によれば,先ほどの手法に比べて,刺激効率改善が約3倍まで改善された。しかし、8字渦巻きコイルについては,治験器として実用化されることが検討されつつも,その刺激特性を向上させるための鉄心の形状・配置に関する研究はこれまで行われていない。
磁気刺激システムの位置合わせを簡易にするために,より刺激ロバスト性の高いコイルが特許文献3で提案されている。この特許文献で提案されたコイルの解析モデルは,導線の巻数を20回,導線の上側球面半径を56mm,導線の下側球面半径が100mmである。このモデルに5.28kA,パルス幅298μsの電流(脈流)を印加し,半球形脳モデル(電気伝導率0.1065S/m)の表面における誘導電流密度を解析した。その結果,従来の8字型コイルに比べて,刺激ロバスト性の改善が確認された。ただし,刺激効率については更なる改善が望まれる。
所定の基準面に沿って導線を巻回して構成されたコイルと,
上記頭部とは上記コイルを挟み反対側である位置において、前記コイルに対向するように設けられ、前記コイルが駆動されたときに誘導電場による電流が流れ、かつ当該誘導電場による電流により上記脳内の磁気刺激対象領域に流れる誘導電場による電流を、磁性体がないときに比較して増大させる磁性体とを備えることを特徴とする。
以下、本発明に係る種々の実施形態について図面を参照して説明する。なお、以下の各実施形態において、同様の構成要素については同一の符号を付している。
(2)それぞれの組み合わせについて,数値解析の結果をもとに刺激ロバスト性を評価し,磁性体の形状と刺激ロバスト性の相関関係をまとめた。
(3)漏れ磁場を抑えるために偏心8字型コイルにフェライト部材を設けたモデルであって,国際非電離放射線防護協会(ICNIRP)の磁場安全性基準(21A/m)を満足する距離(コイルからの距離)を最小化するモデルを数値解析によって決定した。
導線を渦巻き状に巻いた2つの渦巻きコイル部分を有する8字状のコイルと,
前記コイルの上方に前記コイルに沿って配置された磁性体とを有し,
前記磁性体は,前記コイルの中央部における導線の配置方向に複数の電磁鋼板を積層して構成されている。
導線を渦巻き状に巻いた2つの渦巻きコイル部分を有する8字状のコイルと,
前記コイルの上方に前記コイルに沿って配置された磁性体とを有し,
前記磁性体は,前記2つの渦巻きコイル部分の中心を結ぶ方向と直交する方向に複数の電磁鋼板を積層して構成されている。
図1を参照すると,経頭蓋磁気刺激装置1は,図示しない支持機構(例えば,椅子2又はベッド)に支持された、例えば患者3の脳の磁気刺激対象領域に磁気刺激を与える磁気刺激装置4を有する。磁気刺激装置4は,患者3の脳に磁気刺激を加える動磁場を形成するために,コイル装置5と制御ユニット6を有する。
図5のモデル:モデルMX;
図6のモデル:モデルMY;
図7のモデル:モデルMXa;
図8のモデル:モデルMYa;
図9のモデル:モデルMZY;
図10のモデル:モデルMZX;
図11のモデル:モデルMZYa;
図12のモデル:モデルMZXa。
本願発明の発明者らは,磁気刺激コイル装置について,磁気刺激効率の向上,漏れ磁場の削減,刺激ロバスト性の向上,及び小型化を図るために,2つの解析モデルを作成し,有限要素法を用いて誘導磁場の強度,漏れ磁場,局所性を評価した。図18に示すように,1つの解析モデルは,直方体の空間(空気領域)の内側に直方体の脳モデルと重ね合わせ型の偏心8字渦巻きコイルを配置したモデル(以下,「比較モデル」という。)である。別の解析モデルは,図19に示すように,直方体の空間(空気領域)の内側に,上述の直方体の脳モデルと偏心8字渦巻きコイルに加えて,立方体の磁性体を配置したモデル(以下,「改変モデル」という。)である。
比較モデルと改変モデルにおいて,直方体空間の大きさは1000×1000×1600mm(「X方向のサイズ×Y方向のサイズ×Z方向のサイズ」を示す。以下,同様に表示する。),脳モデルの大きさは140×140×40mmとした。図20に示すように,偏心8字渦巻きコイルは,幅2mm,高さ6mmの導線(導体)を一つの平面に沿って渦巻き状に巻回して2つの渦巻きコイル部分81,82を形成するとともにそれら2つの渦巻きコイル部分81,82のそれぞれの中心83,84を互いに他方の中心に向けて偏心した,2つの偏心渦巻きコイル部分81,82を有するものである。各偏心渦巻きコイル部分81,82は,最小内径を18mm,最大外径を122mm,偏心量(偏心渦巻きコイル部分の外径中心と内径中心との間の距離)を27.5mm,左右の偏心渦巻きコイル部分81,82の内径中心間距離を42.5mm,偏心側の最小コイルギャップ(図18において,右側に示す偏心渦巻きコイル部分81では左側領域,左側に示す偏心渦巻きコイル部分82では右側領域)を0.5mmとした。以上の構成を有する偏心8字渦巻きコイル8は,2つの偏心渦巻きコイル部分の中心を結ぶ線8L(以下,この線を「偏心8字渦巻きコイルの中心軸」という。)をX方向に向けて配置した。
(a)誘導電場の計算式
電流密度の解析は有限要素法に基づき,EDDY-jω法で行った。電磁場の満たす方程式は磁場をB,コイル電流のベクトルポテンシャルをAc,渦電流のベクトルポテンシャルをAe,電場をE,電流をJ,スカラーポテンシャルをφ,時間をtとすると、磁場Bは式(1)、電場Eは式(2)で与えられる。
磁気刺激効率を評価するため,比較モデルと4つの改変モデルのそれぞれについて,脳モデル90の上面における誘導電場強度(以下,「脳表面誘導電場強度」という。)の分布と,脳モデル90の上面の中央点(以下,「ターゲット点」という。)における誘導電場を解析した。ターゲット点における誘導電場を評価するために,図36に示すように、ターゲット点90Cから半径10mmの半球90Sの内側にある脳エレメント(解析にあたって定義された脳モデル90の要素)における誘導電場の平均値を有効刺激脳表面誘導電場強度とした。
図18の比較モデルと,図21~図24に示す4つの磁性体100A~100Dを含む図19の改変モデルについて,図25に示すように,ターゲット点から上方(Z軸方向)に60cm離れた評価地点の磁場強度を計算した。
刺激コイル8が所定の位置からずれた場合でも目的の刺激位置に所望の刺激強度を与えることができる領域の大きさ(ロバスト性)を評価するため,脳表面における最大誘導電場の70%を有効刺激強度とし,有効刺激強度と同じ又はそれ以上の電場を有する領域を有効刺激領域とした。有効刺激領域のX方向幅とY方向をそれぞれ求め,それらの半分の値を最大許容ずれ誤差とした。
(a)脳表面の誘導電場強度
比較モデルMF(図18)における脳表面誘導電場強度の分布を図26,改変モデルMY,MYa,MX,MXa(図19,図21~図24を参照)における脳表面誘導電場強度の分布を図27~図30に示す。
ターゲット点における有効刺激脳表面誘導電場強度を表1に示す。
X方向、Y方向にそれぞれ電磁鋼板を積層した直方磁性体22を備えた改変モデルMX,MYについて,磁性体中央部のY方向断面とX方向断面に生じた誘導電場の強度分布を解析した。解析結果を図31及び図32に示す。図31及び図32に示すように,改変モデルMXの場合,高強度の誘導電場が磁性体22の下面側に表れ,低強度の誘導電場が磁性体22の上面側に表れるという結果が得られた。改変モデルMYの場合,左側領域では高強度の誘導電場が磁性体22の上面側に表れるとともに低強度の誘導電場が磁性体22の下面側に表れるが,右側領域では高強度の誘導電場が磁性体22の下面側に表れるとともに低強度の誘導電場が磁性体22の上面側に表れる,という結果が得られた。
比較モデルと4種の改変モデルについて,偏心8字渦巻きコイル8の上表面の中心点から上方(Z軸方向)に60cm離れた位置(「評価地点」という。)の漏れ磁場強度を計算した結果を得たが,評価地点における漏れ磁場の強度は,比較モデルでは8(A/m),4種の改変モデルではそれぞれ9(A/m),24(A/m),9(A/m),20(A/m)であった。また,改変モデルMXa(X方向積層のロ字型磁性体を有するモデル)を除く改変モデルMY,MYa,MXはいずれも,国際非電離放射線防護委員会(ICNIRP)が定める安全基準を満たす結果が得られた。
誘導電場のピーク(最大)値の70%以上の誘導電場強度を有する範囲のX方向とY方向の幅を計算し,その幅の半分の値を最大許容ずれ範囲(コイル中心の位置ずれが許容される範囲)を比較モデルと4種の改変モデルについて求めた,最大許容ずれ範囲を表2に示す。
2.2.1 解析モデル
シミュレーションによって最適な刺激効率の磁性体の形状モデルを求めるために,実際の治療環境に近い有限要素解析モデルを作成した。磁性体の形状や空気領域の設定等の点で解析条件ごとに多少の差異はあるが,概略図35に示す構成の基本解析モデルについて解析を行った。各解析モデルにおいて,実際の人の頭の皮膚から脳の灰白質までの平均距離が約13mm[参考文献23]であることから,コイル8と脳モデル90の表面との距離は13mmに設定した。また,脳や磁性体22よりも大きな空気領域を設定した。脳や磁性体22に比べて空気領域が小さ過ぎると,空気領域の端領域における解析磁場が変形し,実際に形成される磁場と相違する可能性があると考えられるからである。さらに,磁性体22はコイル8の上方に配置した。脳内に磁性体22を埋め込む侵襲性モデルを除外するためである。
解析には,図37に示す偏心8字型コイルを用いた。このコイルは,2012年関野氏によって開発されたコイルで,非偏心8字型コイルに比べてより高い刺激効率が得られるという利点がある。図36の左側のコイルには,反時計回り方向に,3.15kHz,3kAのパルス電流を印加した。図36の右側のコイルには,時計回り方向に,3.15kHz,3kAのパルス電流を印加した。
解析に用いた磁性体(鉄心)は,入手が容易な強磁性体の鉄とした。鉄の比透磁率を5,000,鉄の電気伝導率を10,000,000(S/m)に設定した。鉄の形状は,加工の容易性を考慮して直方体とした。薄い鉄板の積層体からなる磁性体を想定したモデルについては,磁性体の電気伝導性に方向性を持たせるために,電磁場を解析する際に積層方向と直交する方向の電気伝導率を0(S/m)に設定した。
有限要素法の解析は,株式会社フォトンから商業的に入手可能な電気伝導率ソフトウェアPhotoSeries[参考文献28]を用いて行った。その際,過電流解析は,動磁場の周波数応答解析ソフトPHOTO-EDDYjw[参考文献27]を用いて行った。このプログラムは,形状データ,物性値,境界条件,コイル電流の入力条件に基づいて磁場分布を有限要素法により計算するものである[参考文献24~26]。
誘導電場の計算式は「2.1.2 解析方法(a)誘導電場の計算式」で説明した通りである。有限要素法を用いた解析の計算は,分解能を約1mmに設定した場合,約20時間要した。解析結果の表示には,Femapを用いた。
2.2.6.1 磁性体の形状による刺激効率とロバスト性の変化
偏心8字型コイルに強磁性体である鉄の部材を設けることで,コイルから上方向に広がる磁場を磁性体に集めることにより脳モデル表面に向けて強い磁場を形成すること,また,磁性体内の誘導電流が新たに脳表面に誘導電場をつくることで刺激効率を向上すること,を確認すべく解析を行った。また,種々の形態の磁性体を付設したコイルのロバスト性を評価した。
解析方法は上述のとおりである。刺激効率は,脳モデル表面の中央部分における誘導電場強度の平均値で評価する。具体的には,図37A及び図37Bに示す脳モデルの表面中央部分から半径10mmの球内にある要素が有する誘導電場強度の平均値を平均誘導電場強度とした。
磁性体22の無いモデル(モデル1)と,直方体型磁性体を有するモデル(モデル2),直方体型磁性体の中央部分に四角形の開口を形成した四角枠型磁性体を有するモデル(モデル3)を作成した。コイルと磁性体の配置22は前述のとおりである。なお、各解析において、モデル番号を1から付すものとする。モデル2とモデル3の寸法は図37A及び図37Bに示すとおりである。図37Bの四角枠型磁性体の場合,開口の範囲は最も誘導電流が流れる部分が好ましいと考えられる。従って,開口22aの大きさは,左右円形コイル部分81,82の最外周導線部分の中心が開口縁に一致するように決めた。磁性体22の比透磁率は5,000とした。磁性体の電気伝導率は,等方的であり,10,000,000S/mとした。コイル8の下面と脳モデル90の上面との距離は30mmにした。
上記モデル1~3の脳モデル90の表面における誘導電場強度の解析結果を図38A~図38Cに示す。解析結果から、磁性体22の無いモデル1(図38A)の脳表面平均誘導電場強度は69.3V/m,直方体型磁性体22を有するモデル2(図38B)の表面平均誘導電場強度は49.5V/m,枠型磁性体22を有するモデル3(図38C)の表面平均誘導電場強度は120V/mであった。
磁性体の電気特性,すなわち,誘導電流の方向,が刺激効率に及ぼす影響を検討した。
直方体型磁性体を有する4つの解析モデル,すなわち,磁性板をX軸方向に積層したX積層モデル1(誘導電流がYZ面に沿って流れるモデル),磁性板をY軸方向に積層したY積層モデル2(誘導電流がXZ平面に沿って流れるモデル),磁性板をX軸方向とY軸方向に積層したXY積層モデル3,磁性体の無い無磁性体モデル4を用意した。
4つの解析モデル1~4についてそれぞれ,脳モデル90の表面のターゲット部位における平均誘導電場強度の解析結果を図43A~図43Dに示す。解析結果から、X積層モデル1の平均誘導電場強度は120V/m,Y積層モデル2の平均誘導電場強度は415V/m,XY積層モデル3の平均誘導電場強度は502V/m,無磁性体モデル4の平均誘導電場強度は139V/mであった。
上述した,磁性体形状による刺激効率の変化と磁性体の電気的特性による刺激効率の変化の検討をもとに,最適な刺激効率を有する磁性体の構成を検討した。上述のように,磁性体は,その形状により,Z+方向の磁場を集めて脳表面に向かう大きな磁場を作ることが確認できた。しかし,偏心8字型コイルの最外周導線部分の近くでは,コイルによって誘導される誘導電流が小さく,コイルから発生する磁場も弱いため,磁性体のY軸方向長さがコイルの同方向長さより短くても,刺激効率に影響はないと考えられる。
解析のために,磁性体の大きさが異なる3つのXY積層モデル-220×122×10mm(モデル1(図47B)),220×100×10mm(モデル2(図47A)),220×140×10mm(モデル3)―を作成した。このようなモデルを用意したのは,偏心8字型コイル8の全体を覆う大きさの直方体型磁性体22はコイル8が形成するほぼ全ての磁場を集めることから最も刺激効率が良いと考えられる。また,上述のとおりXY積層モデルが最も刺激効率が良いと考えられる。さらに,そのような磁性体と比較することによって最適な磁性体形状が得られると考えられるからである。
3つの解析モデル1,2,3について,脳モデル表面のターゲット部位における平均誘導電場強度を解析した結果から、モデル1の平均誘導電場強度は502V/m,モデル2の平均誘導電場強度は507V/m,モデル3の平均誘導電場強度は506V/mであった。従って,X方向の長さは最も小さい(100mm)モデル2が最適であることが確認された。
在宅治療用に適した重さの刺激コイル8を得るという観点から,コイルが発生する磁束を十分に集めることができ且つ必要な刺激効率が得られる磁性体の厚さを検討した。
コイル8の取り扱いの点から,磁性体は軽ければ軽いほど好ましい。しかし,磁性体を薄くしすぎると,コイル8から発生する磁力線を磁性体22内に集めることができなくなる。そこで,コイル8から発生する磁束線をほぼすべて集めることができる磁性体の厚さを,3つのY軸積層モデル(磁性体の厚さが2mm,5mm,10mmのモデル1,2,3)について近似的に計算した。計算上,各モデルを図49の等価磁気回路に置き換えた。図49において、Sは磁性体22のYZ断面の面積である。
3つのY積層モデル(磁性体の厚さがそれぞれ2mm,5mm,10mmのモデル1,2,3)を作成し,それぞれのモデルについて脳表面誘導電場強度を計算し比較した。
この解析結果から、モデル1,2,3における脳表面中央部分の平均誘導電場強度はそれぞれ390V/m,380V/m,415V/mであった。この解析結果が示すように,磁性体の厚さは脳表面誘導電場の平均値に大きな影響を与えることがなく,磁性体22の厚さが2mmの場合でも,コイル8から発生する磁束をすべて集めることができることが分かった。厚さが2mmの磁性体22の重量は40グラムで,実際の使用において重量が問題となることはないと考えられる。
(a)在宅用経頭蓋磁気刺激装置に最適な刺激ロバスト性
患者自身によるコイル位置の調整を可能にするヘルメット型の位置合わせシステムが検討されているが,このような自己調整型システムは約20~30mmの位置合わせ誤差を許容できるロバスト性能が望まれる。また,磁性体の特性とロバスト性の関係を予め知見しておくことが大切である。そこで,種々の磁性体モデルを用意し,それぞれについて刺激ロバスト性能を評価した。
特許文献3で提案されたドーム型コイル(図50A及び図50B参照)に磁性体を設けたモデル(図51A及び図51B)のロバスト性を評価した。
図50A及び図50Bに示すドーム型コイルの中空部にX軸方向積層磁性体を配置したモデル(図51A及び図51B)について,脳表面誘導電場と,X軸方向とY軸方向の刺激ロバスト性を評価した。磁性体の無いドーム型コイルモデル(モデル1),厚さ4mmの磁性体を有するドーム型コイルモデル(モデル2),厚さ12mmの磁性体を有するドーム型コイルモデル(モデル3)を用意した。図51A及び図51Bにおいてコイルモデルの下に表れる部分は脳モデル90である。
コイルモデル1~3に対する脳表面誘導電場の解析結果をそれぞれ図52A~図52Cに示す。解析結果から,コイルモデル1(無磁性体、図52A)の平均誘導電場強度は71.8V/m,コイルモデル2(磁性体の厚さが4mm、図52B)の平均誘導電場強度は453V/m,コイルモデル3(磁性体の厚さが12mm、図52C)の平均誘導電場強度は501V/mであった。この結果が示すように,X方向積層磁性体を設けることにより,ドーム型コイルの作る磁場を磁性体に集め,脳の刺激効率が飛躍的に向上することが分かる。また,磁性体22の厚さが大きくなると,磁性体22の下表面と上表面との距離が大きくなり,それにより上表面の誘導電流によって脳表面誘導電場が弱まる作用が小さくなることから,磁性体22の厚さが12mmのコイルモデル3では脳表面誘導電場が更に増加したと考えられる。
上述した複数の解析モデルについて評価した刺激ロバスト性(有効刺激距離)を図54にまとめた。図54の番号のコイルモデル(以下、CM1~CM14とする。)は以下の通りである。
CM2:Y積層直方体型磁性体(220×122×10mm)を有するコイルモデル;
CM3:XY積層直方体型磁性体(220×122×10mm)を有するコイルモデル;
CM4:無磁性体コイルモデル;
CM5:XY積層直方体型磁性体(220×100×10mm)を有するコイルモデル;
CM6:XY積層直方体型磁性体(220×140×10mm)を有するコイルモデル;
CM7:Y積層直方体型磁性体(220×122×2mm)を有するコイルモデル;
CM8:Y積層直方体型磁性体(220×122×5mm)を有するコイルモデル;
CM9:無磁性体ドーム型コイルモデル;
CM10:X積層直方体型磁性体(厚さ4mm)を有するドーム型コイルモデル;
CM11:X積層直方体型磁性体(厚さ12mm)を有するドーム型コイルモデル;
CM12:磁性体から距離10mmの位置にフェライト(返しが15mm)を挿入したコイルモデル;
CM13:X積層四角枠型磁性体を有するコイルモデル;
CM14:Y積層四角枠型磁性体を有するコイルモデル。
(a)漏れ磁場
放射線を利用した在宅システムは,国際非電離放射線防護協会(ICNIRP)が定める,人間が被曝しても安全とされる電磁波レベルの安全基準(表3参照)を満たす必要がある。経頭蓋磁気刺激装置では,そこで想定されている刺激条件が約3kHzであるため,許容磁場レベルは21A/mである。
I=3.03,
μ0=4π×10-7,
lair-below=0.04π,
liron=0.22,
μr=5000,
Siron=0.122×0.01
図57の解析モデルは,図35に示す解析モデルと似ているが,空気領域の大きさと磁気シールドの存在の点で相違する。空気領域の大きさは,広い範囲に亘って漏れ磁場の影響を検討するために,2m×2m×2mに設定した。図57に示すように,磁性体22は,Y軸方向に磁性板を積層した,220mm×120mm×10mmの直方体型磁性体である。磁性体22の電気伝導率は107S/m,比透磁率は1,500とした。磁性体22の上方と4つの側方を囲む磁気シールド91は,Ni-Znフェライトで作られており,その電気伝導率は10-5S/m,比透磁率は1,500とした。磁性体22と磁気シールド91のZ方向の間隔は20mm,磁性体22の下面と磁気シールド91の天井面(内面)との距離は46mmに設定した。磁性体22と磁気シールド91のXY方向の間隔が異なる3つのモデル-間隔5mm(モデル1),間隔10mm(モデル2),間隔20mm(モデル3)-と,磁気シールドの無いモデル(モデル4)を作成し,それぞれの漏れ磁場強度を計算した。
モデル1~4について計算した漏れ磁場強度を表4に示す。磁場強度が21A/mに収束しなかった解析(表中,数値を()で囲った解析)では,空気領域の端に位置する,コイル8の中央部から1mの位置での磁場強度を記載した。
表4から分かるように,国際非電離放射線防護協会(ICNIRP)が定める安全基準21A/mをすべての方向について満足するモデルは無かった。従って,磁性体22と磁気シールド91の距離を10mmに設定したモデルを改良し,図59に示すように,箱型磁気シールド91のコイルに対向する下端開口に該下端から内方に向かって水平方向に突出する環状のフランジ(返し)91Fを設けた解析モデルを作成した。
図59に示すように,フランジ91Fの幅が5mm,10mm,15mmの3つの解析モデル(モデルM1~M3)を作成した。フランジ91Fの材料はNi-Znフェライトである。
図59の各解析モデルについて解析した漏れ磁場を表5に示す。磁場強度が21A/mに収束しなかった解析(表中,数値を()で囲った解析)では,空気領域の端であるコイル中央から水平方向に1mの位置での磁場強度を記載した。
3.1 磁性体を8字型コイルの上に配置する理由
磁束を誘導するために,例えば,ソレノイドではコイル8の内側に磁性体を配置することが行われている。しかし,経頭蓋磁気刺激装置で利用される偏心8字型コイルの両円形コイル部分81,82は導線を例えば10回程度らせん状(スパイラル)に巻いたものであるため,該円形コイル部分81,82の中央に形成された小さな空間に鉄心等の磁性体22を効果的に配置するのは難しく且つ費用もかかることから,在宅用コイル8には不向きである。代わりに,患者の頭部に磁性体を埋め込み,そこに磁束を集める方法も提案されている。しかし,この方法は開頭手術を要し,非侵襲性を利点とする経頭蓋磁気刺激治療の特徴を生かすことができないことになる。これに対し,コイル8の上に磁性体22を配置する構成は,上述したすべての問題を解消するものであり,かつ,コイルから発生する磁束を治療に必要な程度まで集めることができる,という利点がある。
コイルの内側に配置した磁性体22も磁気シールド91として機能し得る。例えば,3kHz程度の周波数であれば,磁性体22内部の誘導電流は実質的に打ち消され,磁性体22の表面に僅かに存在するだけである。しかし,経頭蓋磁気刺激装置にあっては,微小な電流であってもそれによって発生する電磁波が治療効果を減じかねないため,磁性体は磁気シールド91として十分に有効とは言い難い。
在宅治療用の経頭蓋磁気刺激装置を神経障害性疼痛患者が自ら操作して治療を行う状況を想定した場合,患者自身が刺激コイル8を毎回同じ場所に位置決めできることが好ましい。そのため,患者にヘルメットを装着させるとともに,そのヘルメットに刺激コイル8を固定する技術が提案されている。このような形態にあっては,ヘルメットに対して刺激コイル8を簡単に装着できることが望まれる。
上述の解析から求められた最適な形状の磁性体22と磁気シールド91の合計重量は約2.1kgである。偏心8字型コイル自体の重量は約1kgである。従って,磁性体22と磁気シールド91を含むコイル装置全体は約3kgで,それは在宅用システムでも安定して支持できる重量である。
最も適当との思われる磁性体フェライトモデルのインダクタンスは約17.4μHであった。コイルのインダクタンスは,空気領域のみで解析を行い,空気領域中の磁場エネルギーの総和を用いて式(18)に基づいて計算した。
磁性体22を流れる誘導電流は,ファラデーの法則に基づいて,磁束の変化率によって決定される。この場合,誘導電流は,磁性体が磁場によって磁化される速度とコイルから発生する磁場が変化する速度の影響を受けると考えられるが,前者は後者よりも十分に大きいため,実際に磁性体内に流れる誘導電流は解析で得られる誘導電流にほぼ等しいと考えられる。
鉄は,ヒステリシスの磁気特性を持つ。一方,磁性体22を通過する磁束は0.328τと算出した(式(13)参照)が,ヒステリシスを考慮すると,高磁場では比透磁率は低くなる。この点を考慮すると,磁性体内の誘導電場密度は約10~50τと考えられる。鉄の飽和磁束密度は2.15τであることから,鉄で所望の特性を得るためには,鉄の厚さを厚くすることで磁束を増やすなどの改善が必要になる可能性がある。
積層磁性体22は,複数の磁性板の間に絶縁体を挟んで形成される。この場合,絶縁体には,Mn-Zn系フェライトが好適に利用できると考えられる。Mn-Zn系フェライトは,その比透磁率が鉄と同じ5,000,体積抵抗率が0.3Ω・mで,適応周波数が1MHzまでである。
無磁性体コイルモデルの3.93倍の刺激効率が得られる有磁性体コイルモデルが作成できた。有効な治療効果を得るために必要な一次運動野の誘導電流強度は一定であるが,脳内誘導電流の大きさはコイル電流に比例する。上述した解析では,コイル電流を3kAに設定した。このとき,XY積層磁性体を含むコイルモデルによって脳内に誘導される電場は507V/mであった。有効な治療効果を得るために一次運動野に必要な誘導電流密度は180A/m2であることが過去の臨床実験結果で報告されている。刺激部位の電気伝導率を灰白質のそれと同じ0.11S/mと仮定すると,有効な治療効果を得るために必要な脳内誘導電場強度は200V/mである。従って,積層磁性体コイルモデルの場合,1.18kAにピーク値を持つパルス電流をコイルに印加すれば,有効な治療効果を発揮できると考えられる。ピーク電流を下げることができれば,磁場発生装置のコンデンサや昇圧回路を大幅に縮小でき,それに伴って,システムのコストも大幅に下げることができる。
本実施形態は,経頭蓋磁気刺激による神経障害性疼痛患者の在宅治療を目的とした刺激コイルの開発に関する。そのために,数値解析により,最も刺激効率の良いコイルモデルを求めた。次に,数値解析により,良好な刺激効率を維持しつつ,軽量なコイルモデルを求めた。また,数値解析により,人体への影響を減らす磁気シールド付きコイルモデルを求めた。以上の数値解析から,以下の結論が得られた。
本実施形態において、コイルの寸法は以下のものとしてシミュレーションを行った。最外径は100mm、内径は20mm、ターン数は10とした。導線は、縦6mm×横2mmの断面とした。導線同士で最も接近する部分の間隙は0.5mmとした。コイルに印加される電流は3kA、周波数は3.15kHzとした。また、鉄鋼板の寸法については以下の通り、幅220mm、高さ122mm、厚み10mmとした。鉄鋼板の重量は鉄の比重を7.85t/m3として、およそ2.1kgとなる。比透磁率は5000、導電率については1.0×107S/m、また積層に垂直な方向には1.0×10-7S/mとした。鉄鋼板は中央偏心8字型コイルの上部表面から3.5mm上部に位置するとした。脳を模擬した導電体は導電率を0.11S/mとし、縦140mm、横140mm、高さ40mmとした。この導電体は、コイル下部表面から10mm下に位置するように設定した。実験全体のモデルは図61に示した通りである。刺激強度は、刺激中心より半径10mm以内のエレメントにおける電場ベクトルの大きさを平均したものにより評価した。
鉄鋼板の最適な積層方向について検討するため、実験全体の外観を変えずに鉄鋼板の種類を変更したモデルを用意した。まず、3種類の鉄鋼板について、積層のない鉄鋼板、縦方向積層の鉄鋼板、横方向積層の鉄鋼板をモデル化した。これらの3モデルは、鉄鋼板を併用しないモデルにおける刺激強度との比較を行った。次に、中央部が横積層となり、側部が縦積層となるような、異方向の積層を組み合わせた鉄鋼板のモデルを用意した。同モデルの外形は図62に示す通りである。側部の縦積層部分の幅をそれぞれ6mmから36mmで変化させ、側部の幅と達成される平均電場強度の関係をプロットした。図62において、22XはX方向積層磁性体であり、22YはY方向積層磁性体であり、Y方向積層磁性体22YはX方向で1対のX方向積層磁性体22Xで挟設される。
図63A~図63Eに示すように、刺激強度(誘導電場強度)は積層鉄鋼板によって大きく向上した。積層のない鉄鋼板と横方向積層の鉄鋼板については、中央における平均電場強度がそれぞれ218V/m、335V/mとなった(図63B及び図63C)。これは、鉄鋼板のない場合の電場強度(160V/m、図63A)に対しそれぞれ1.5倍、2.1倍である。一方で、縦方向積層による刺激強度は111V/m(図63D)となり、鉄鋼板のない場合に対し減少している。
図63Eに示すように、異方向の積層鉄鋼を組み合わせたモデルは、単方向の積層鉄鋼としたものに比較してより強い刺激強度を達成できることがわかった。図65には、縦方向積層となっている側部の幅と刺激強度の関係を示している。側部幅を最適化すると、幅30mmの場合に刺激強度が456V/mとなった。また、インダクタンスについては、鉄心のないモデルで11.7μHであったのに対し、30mm幅の組み合わせ積層鉄鋼板を利用した場合17.2μHとなった。
4…磁気刺激装置、
5…コイル装置、
6…制御ユニット、
8…コイル、
8L…中心軸、
9…ケーシング、
22,22A~22H…磁性体、
25…コイル駆動回路、
26…ケーブル、
31…サイリスタ、
31D…ダイオード、
61…交流電源、
62…電源回路、
63…昇圧回路、
64…コンデンサ、
65…抵抗、
66…半導体スイッチ、
67…制御回路、
80…導線、
81,82…コイル部分、
83,84…コイル部分の中心、
85…コイルの中央部、
90…脳モデル、
91,91A,91B…磁気シールド、
91F…フランジ、
100A~100D…磁性体。
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Claims (12)
- コイルが人間の頭部表面に対向するように設けられ、電磁誘導によって脳内の磁気刺激対象領域に誘導電場による電流を発生させてニューロンを刺激する経頭蓋磁気刺激装置のためのコイル装置であって、
所定の基準面に沿って導線を巻回して構成されたコイルと、
上記頭部とは上記コイルを挟み反対側である位置において、前記コイルに対向するように設けられ、前記コイルが駆動されたときに誘導電場による電流が流れ、かつ当該誘導電場による電流により上記脳内の磁気刺激対象領域に流れる誘導電場による電流を、磁性体がないときに比較して増大させる磁性体とを備えることを特徴とする経頭蓋磁気刺激装置用コイル装置。 - 前記基準面は平面、曲面又は球面であることを特徴とする請求項1の経頭蓋磁気刺激装置用コイル装置。
- 前記コイルは、非偏心渦巻きコイル、又は偏心渦巻きコイルであることを特徴とする請求項1又は2記載の経頭蓋磁気刺激装置用コイル装置。
- 前記コイルは、2つのコイル部分を有する非偏心8字渦巻きコイル、又は2つのコイル部分を有する偏心8字渦巻きコイルであることを特徴とする請求項1又は2記載の経頭蓋磁気刺激装置用コイル装置。
- 前記コイルは、ドーム型コイルであることを特徴とする請求項1又は2記載の経頭蓋磁気刺激装置用コイル装置。
- 前記磁性体は、前記コイルの各ターン巻線が積み重なる方向へ、当該磁性体を構成する個々の積層板を積み重ねて構成されたことを特徴とする請求項1~4のうちのいずれか1つに記載の経頭蓋磁気刺激装置用コイル装置。
- 前記基準面に沿って前記2つのコイル部分の中心を結ぶ線の方向を第1の方向とし、前記基準面に沿って前記第1の方向と直交する方向を第2の方向とするとき、前記磁性体は、複数の電磁鋼板を前記第1の方向又は前記第2の方向に積層して構成されたことを特徴とする請求項4記載の経頭蓋磁気刺激装置用コイル装置。
- 前記基準面に沿って前記2つのコイル部分の中心を結ぶ線の方向を第1の方向とし、前記基準面に沿って前記第1の方向と直交する方向を第2の方向とするとき、前記磁性体は、複数の電磁鋼板を前記第1の方向に積層して構成された第1の積層磁性体部分と、複数の電磁鋼板を前記第2の方向に積層して構成された第2の積層磁性体部分とを備えたことを特徴とする請求項4記載の経頭蓋磁気刺激装置用コイル装置。
- 1個の前記第2の積層磁性体部分と1対の前記第1の積層磁性体部分とを備え、
前記第1の方向で、前記第2の積層磁性体部分を上記1対の第1の積層磁性体部分で挟設するように設けられたことを特徴とする請求項8記載の経頭蓋磁気刺激装置用コイル装置。 - 前記磁性体は、前記第1の方向と前記第2の方向に直交する第3の方向から見たとき、四角形、多角形、円形、卵型、又は楕円型の形状を有することを特徴とする請求項1~9のうちのいずれか1つに記載の経頭蓋磁気刺激装置用コイル装置。
- 前記磁性体は、前記第1の方向と前記第2の方向に直交する第3の方向から見たときの中央に開口を有することを特徴とする請求項1~10のうちのいずれか1つに記載の経頭蓋磁気刺激装置用コイル装置。
- 請求項1~11のいずれかの経頭蓋磁気刺激装置用コイル装置を備えたことを特徴とする経頭蓋磁気刺激装置。
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WO2017150490A1 (ja) * | 2016-03-04 | 2017-09-08 | 国立大学法人東京大学 | コイル及びそれを用いた磁気刺激装置 |
JP2019024987A (ja) * | 2017-07-31 | 2019-02-21 | 株式会社Ifg | 磁気刺激装置 |
WO2019078582A1 (ko) * | 2017-10-16 | 2019-04-25 | 서울대학교 산학협력단 | 금속판과 숏스텁을 이용한 뇌 자극용 어플리케이터 |
JP7458507B2 (ja) | 2020-12-16 | 2024-03-29 | 帝人ファーマ株式会社 | 経頭蓋磁気刺激装置 |
WO2023248580A1 (ja) * | 2022-06-23 | 2023-12-28 | スミダコーポレーション株式会社 | ベクトルポテンシャル発生装置、ベクトルポテンシャルコイル配置方法、ベクトルポテンシャルトランス、および非接触給電システム |
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ES2895748T3 (es) | 2022-02-22 |
US20180071545A1 (en) | 2018-03-15 |
AU2016241024A1 (en) | 2017-10-26 |
AU2016241024B2 (en) | 2020-05-21 |
CN107530549A (zh) | 2018-01-02 |
JPWO2016159371A1 (ja) | 2018-02-15 |
EP3278838B1 (en) | 2021-10-20 |
KR102610369B1 (ko) | 2023-12-05 |
EP3278838A1 (en) | 2018-02-07 |
US10603506B2 (en) | 2020-03-31 |
CA2981424A1 (en) | 2016-10-06 |
CN107530549B (zh) | 2021-05-18 |
JP6448009B2 (ja) | 2019-01-09 |
EP3278838A4 (en) | 2018-12-05 |
KR20170134496A (ko) | 2017-12-06 |
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