JP2012187149A - Magnetic stimulation coil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic stimulation coil having high penetrance to a brainpan and suitable for TMS (Transcranial Magnetic Stimulation).SOLUTION: A coil surrounding the outer side face of a conductor core is held with a yoke from outside the coil. Thus, leakage magnetic fluxes are substantially reduced. Also, by forming a slit on the conductor core, an eddy current is concentrated on the slit, and a magnetic flux penetrates deep in the brain through the brainpan in TMS. Further, by forming the yoke into a cylindrical body with the U-shaped cross section, the brain can be stimulated to a position several times deeper compared to a magnetic simulation coil in the shape of a figure 8.

Description

  The present invention relates to a magnetic stimulation coil, and more particularly to a magnetic stimulation coil used in a transcranial magnetic stimulation method.

Transcranial magnetic stimulation, also abbreviated as TMS, excites neurons in the brain by inducing weak currents in tissues (according to Faraday's law of electromagnetic induction) by rapid magnetic field changes. It is a non-invasive method. By this method, brain activity is caused with minimal discomfort, and the function of the circuit connection of the brain is examined.
The repetitive transcranial magnetic stimulation method is also abbreviated as rTMS (Repetitive transcranial magnetic stimulation) and gives long-term changes to the brain. Many small previous studies have shown that this method has many neurological symptoms (eg refractory central pain, voluntary movement disorders, spastic paralysis after spinal injury, Parkinson's disease) and psychiatric symptoms (eg depression) It has been shown to be an effective treatment for panic disorder.
In simple terms, the coil used in TMS is a device that applies Faraday's law of electromagnetic induction and passes current through insulating tissues such as the scalp and skull without causing discomfort. The coil is placed in a plastic body and applied to the head. When a voltage is applied to a coil from a huge capacitor, a rapid current change occurs in the winding. This creates a magnetic field that is perpendicular to the plane of the coil. The magnetic field passes through the scalp and skull without being obstructed, and induces a current in the brain opposite to the coil current in the tangential direction to the skull. The induced current generated in the brain activates nearby neurons as well as electrical stimulation to the cortical surface. Because the brain is not a uniform electrical conductor but has an irregular shape, this current path is complex to model. Due to stereotaxic control based on MRI, the error from the target of TMS stimulation is estimated to be several millimeters (Hannula et al., Human Brain Mapping 2005).
For example, an eddy current type AC magnetic field generator disclosed in Patent Document 1 is known as a prior art having a possibility of being used for such TMS.
In this apparatus, the outer periphery of a cylindrical conductive material block is surrounded by a coil constituting an electromagnet, and an eddy current in a direction perpendicular to the central axis is generated in the block by energizing the coil. In the cylindrical block, a minute hole is formed at the central axis position, and a slit at a radial position where one end communicates with the minute hole and the other end opens on the outer surface is provided. Thereby, the uniformly distributed magnetic flux by the coil is effectively converged in the minute hole, and the magnetic flux density in the minute hole is increased.

JP 63-84103 A

  However, in the magnetic field generator disclosed in Patent Document 1, when this is adopted for transcranial magnetic stimulation, it is predicted that the permeability of magnetic flux from the scalp to the brain inside the skull is still insufficient. I was able to.

  Therefore, as a result of intensive research, the inventor provided slits extending substantially in the diametrical direction in the conductor core, and by enclosing the coil surrounding the conductor core with the yoke, the magnetic flux density was highly concentrated. The present invention was completed by knowing that it was possible.

  An object of the present invention is to provide a magnetic stimulation coil having a high degree of penetration into the skull and suitable for TMS.

  In the first aspect of the present invention, the cross section perpendicular to the axis is circular, elliptical, or polygonal, and is formed of a columnar body having a predetermined axial length, and surrounds the outer surface of the conductor core. A coil that is wound around the conductor core to form an electromagnet together with the conductor core, and a yoke that holds the coil from the outside thereof, and one end of the conductor core is electrically conductive when viewed from the end surface. A slit opened on the outer surface of the body core and closed at the position near the outer surface on the opposite side of the opening position along the plane including the central axis of the conductor core or an axis parallel to the central axis. And a magnetic stimulation coil formed to have a predetermined width, a predetermined axial length, and a predetermined transverse direction length.

According to the first aspect of the present invention, for example, the conductor generated on the end face of the conductor core by passing a pulse current through the coil that is wound around the conductor core and formed into a cylindrical shape. Eddy currents in the outer circumferential direction of the core can be concentrated along the wall of the slit. Therefore, when this magnetic stimulation coil is used for the TMS method, the permeability of the magnetic flux can be further increased, and effective magnetic stimulation can be performed.
At this time, since the coil is held by the yoke, magnetic flux leakage does not occur from the held portion. Therefore, the concentration of the magnetic flux can be greatly increased as compared with the case where the coil is not held by the yoke.
The heat generated when a large current is passed through the exciting coil can be efficiently dissipated by configuring the conductor core with, for example, copper or silver.

Further, the conductor core is formed of a columnar body having a predetermined axial length with a cross section perpendicular to the axis thereof being circular, elliptical or polygonal. For example, it can be configured as a cylindrical body, elliptical cylindrical body, or polygonal cylindrical body having a constant cross-sectional area in the axial direction. The top and bottom surfaces can be flat. The conductor core can be made of a conductive material such as gold, silver, copper, and alloys thereof.
The coil is wound around the outer surface of the conductor core, for example, a plurality of times to form a cylindrical shape, and surrounds the outer surface of the conductor core over its entire length.
The yoke has a cylindrical shape, for example, and holds the cylindrical coil so as to wrap inside the yoke. That is, for example, a cylindrical yoke made of an electromagnetic steel plate is configured to embrace the inside of the conductor core and a cylindrical coil wound around the outer peripheral surface thereof. The diameter of the yoke is larger than that of the coil, the diameter of the coil is larger than that of the conductor core, and the axial length of the yoke is designed to be approximately the same as or slightly longer than that of the coil and core.
The slit is provided, for example, in a straight line at a position of a transverse line (for example, a diameter when the upper surface is circular) including the center of the end surface (upper surface) when the conductor core as a columnar body is viewed from the end surface (upper surface). It is done. That is, one end of the slit extending linearly when viewed from the end face opens at the outer surface of the conductor core, and the other end is closed at a position near the outer surface on the opposite side. Therefore, the slit extends over the entire axial length so as to be along a plane including the central axis of the conductor core. The slit has a width of about 1 mm, for example, is formed over the entire axial length of the cylindrical body at the diameter position and substantially the same length (depth) as the diameter, thereby dividing the conductor core that is the cylindrical body into two. . In other words, the conductor core has a configuration in which the columnar body is roughly divided into two by the slit including a plane including the axis (or a plane parallel to the axis). In addition, in the case of a conductor core made of a true cylinder having a circular cross section, the slit is not limited to the diameter position, but is parallel to the diameter when viewed from the end face, for example, at a position slightly displaced from the diameter position. It can also be formed at various positions.

  A second aspect of the present invention is the magnetic stimulation coil according to the first aspect, wherein the yoke is formed of a cylindrical body having a U-shaped cross section so as to hold both ends of the coil in the axial direction.

  According to the second aspect of the present invention, the leakage of the magnetic flux that is about to leak outward in the axial direction of the coil is indicated by the bottom of the yoke that forms the magnetic path. End), and the concentration of magnetic flux can be further increased.

  According to the first and second aspects of the invention, since the outer surface of the coil is covered with the yoke, the leakage magnetic flux can be greatly reduced, and the eddy current can be concentrated on the slit of the conductor core, When used for transcranial magnetic stimulation, magnetic flux concentrated deeper into the brain can be penetrated through the skull.

  In addition, the magnetic stimulation coil according to the present invention can stimulate the brain up to several times deeper than a conventionally known magnetic stimulation coil configured in, for example, an 8-shape.

It is a perspective view which fractures | ruptures and shows the one part of the magnetic stimulation coil which concerns on Example 1 of this invention. It is a perspective view which shows the whole structure of the magnetic stimulation coil which concerns on Example 1 of this invention. It is a top view of the magnetic stimulation coil which concerns on Example 1 of this invention. It is sectional drawing by the AA line of FIG. 3 of the magnetic stimulation coil which concerns on Example 1 of this invention. It is a graph which shows the relationship between the transcranial depth position at the time of performing transcranial magnetic stimulation using the magnetic stimulation coil which concerns on Example 1 of this invention, and the brain current density.

  Embodiments of the present invention will be specifically described below with reference to the drawings.

1 to 4, a magnetic stimulation coil 100 includes a conductor core 110 formed of a cylindrical body having a predetermined length (height) (a cross section of which is formed in a circle having the same area in the length direction). The conductor core 110 is spirally wound, for example, about 10 turns around the entire outer peripheral surface of the conductor core 110, and encloses the cylindrical excitation coil 120 as a whole (cylindrical shape). And a yoke 200 that holds the exciting coil 120 so as to be wrapped inward. The yoke 200 has a cylindrical shape having an outer diameter that is slightly larger than the outer diameter of the exciting coil 120, and has a U-shaped cross section with its axis including the axis opened inward in the radial direction. Yes. The conductor core 110 around which the exciting coil 120 is wound is accommodated in the concave portion 210 opened inward of the yoke 200. Specifically, the inner circumferential surface of the yoke 200, which is a cylindrical body having a predetermined thickness as a whole, is bored by a predetermined depth (a depth that can accommodate the coil) in the radial direction, and a cross section (single cross section) on a plane including the axis thereof ) Is a U-shape. The exciting coil 120 is accommodated in the recess 210. The thickness of the yoke 200 is arbitrary.
That is, the yoke 200 is formed of a cylindrical body having a predetermined height and a predetermined radius so as to surround the conductor core 110. The material of the yoke 200 is, for example, permendur or an electromagnetic steel plate, and a thin plate can be wound around the exciting coil 120 to form a wound iron core. Alternatively, the yoke 200 can be configured by stacking a number of thin plates formed in a concave shape on the outer peripheral surface of the exciting coil 120 to form a cylindrical shape as a whole.
The magnetic stimulation coil 100 is composed of the conductor core 110, the exciting coil 120 surrounding the conductor core 110, and the yoke 200 that holds the exciting coil 120.
The conductor core 110 is a cylindrical body (for example, a diameter of 70 mm and a height of 40 mm) made of copper (may be iron, nickel, etc.) and having a circular cross section having the same area and shape in the axial direction. Is formed with a slit 130 having a predetermined width that substantially halves this in the vertical direction (axial direction). That is, the conductor core 110 has a shape that is substantially equally divided into two half-cylindrical portions (half blocks) having a semicircular cross section by the slit 130.
The conductor core 110 may be an elliptic cylinder or a prism. In this case, the yoke 200 that holds the exciting coil 120 is also an elliptical cylinder or a rectangular cylinder according to the shape of the conductor core 110.

Specifically, when the conductor core 110 is viewed in an end view (plan view), the slit 130 has one end at a position of a transverse line (diameter) including the circle center of the upper end surface as shown in FIG. 130B opens to the outer peripheral surface of the conductor core 110, and the other end 130A is closed at a position near the outer peripheral surface (leaving a wall having a thickness of about 1 mm). As described above, the slit 130 having a length substantially equal to the diameter of the cylindrical body (conductor core 110) extends along a plane including the central axis of the conductor core 110, and its width (for example, 1 mm width) is constant. It is.
In this case, the slit 130 is processed by, for example, wire cut electric discharge machining.

In the magnetic stimulation coil 100 configured as described above, when a pulse current is applied to the exciting coil 120 by means not shown, the circumferential direction of the conductor core 110 is caused by the magnetic flux generated by the exciting coil 120. An eddy current is generated.
In this case, since the conductor core 110 is separated and insulated from each other by the slit 130, a part of the eddy current circuit is formed along the direction in which the slit 130 extends. That is, the current flows along the circumferential direction of the conductor core 110, then flows in the diameter direction along the slit 130, and flows through the bridge portion (the portion connecting the two semi-cylindrical portions) that is the slit terminal portion, The flow again flows along the slit 130 in the diametrical direction opposite to the flow on the opposite bank, and further flows along the circumferential direction.
In other words, the current density is increased because the current flow direction is reversed on the opposite bank of the slit. As a result, when this magnetic stimulation coil 100 is applied to a magnetic stimulation device, the current density of eddy current in the slit portion becomes large, and the penetration degree of magnetic flux through the cranium increases dramatically.
Further, at this time, since the entire back surface (outer surface) of the cylindrical excitation coil 120 is held in the concave portion of the yoke 200, the leakage magnetic flux can be minimized and the entire magnetic stimulation coil 100 is also provided. As a result, the mechanical strength can be increased. This is because when an electric current is passed through the exciting coil 120, an external force acts in the direction in which the semicylindrical portions open with the slit 130 as a boundary, and this is supported by the yoke 200 which is a cylindrical body that holds the exciting coil 120. This means that mechanical deterioration and breakage of the exciting coil 120 and the conductor core 110 are prevented.

Here, when magnetic stimulation was performed using the magnetic stimulation coil 100 with an yoke (EC coil) according to Example 1 of the present invention and a conventionally known 8-shaped coil, the heads of the central portions of the respective coils were used. The relationship between head depth and brain current density was determined. The relationship between the head depth at the center of the coil and the current density in the brain was obtained by numerical analysis. The result of this numerical analysis is shown in FIG. Note that the outer diameter of the 8-shaped coil and the outer diameter of the magnetic stimulation coil 100 are matched.
From this result, it was found that the magnetic stimulation coil (EC coil) according to the present invention can stimulate the brain to a site several times deeper than the conventional 8-shaped magnetic stimulation coil.

  The magnetic stimulation coil according to the present invention is extremely useful for a magnetic stimulation apparatus used in, for example, the TMS method.

100 magnetic stimulation coil,
110 conductor core,
120 exciting coil,
130 slits,
200 York.

Claims (2)

A conductor core made of a columnar body having a predetermined axial length and having a circular, elliptical or polygonal cross section perpendicular to the axis;
A coil that is wound around the conductor core to form an electromagnet together with the conductor core so as to surround the outer surface of the conductor core;
A yoke for holding the coil from the outside thereof,
When the conductor core is viewed from the end surface, a slit whose one end opens on the outer surface of the conductor core and the other end closes at a position near the outer surface opposite to the opening position is formed on the conductor core. A magnetic stimulation coil extending along a plane including a central axis or an axis parallel to the central axis and having a predetermined width, a predetermined axial length, and a predetermined transverse line length.   The magnetic stimulation coil according to claim 1, wherein the yoke is formed of a cylindrical body having a U-shaped cross section so as to hold both ends of the coil in the axial direction.

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