JP3027086B2 - Z-axis gradient magnetic field coil - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

This invention relates to a Z-axis gradient field coil used in a magnetic resonance (MR) system.

[0002]

2. Description of the Related Art In an MR system, it is necessary to provide a gradient magnetic field along each of three orthogonal axes (XYZ) of an orthogonal coordinate system. In a system in which a static magnetic field is formed in the Z-axis direction, a coil for generating a Z-axis gradient magnetic field includes:
Conventionally, it has been formed by winding a wire around a bobbin.

In this prior art, in order to generate a predetermined gradient magnetic field, a ring-shaped groove (plurality) is formed at a predetermined position (plurality) of a bobbin, and a wire is wound around the groove a predetermined number of times. I was However, in this method, the production requires skill and the processing is troublesome.

On the other hand, Japanese Patent Laid-Open No. 3-48402 proposes forming a Z-axis gradient magnetic field coil by winding a flexible insulating substrate having a desired coil pattern on a bobbin and attaching the flexible insulating substrate to a bobbin. According to the proposed coil, the conventional bobbin processing and wire winding steps are not required. Further, since it is only necessary to wind and attach the flexible insulating substrate to the bobbin, the Z-axis gradient magnetic field coil can be easily formed.

[0005]

The problem to be solved by the present invention is disclosed in Japanese Patent Application Laid-Open No. 3-48.
In the case of generating a strong gradient magnetic field in the Z-axis gradient magnetic field coil shown in No. 402, by reducing the width of one conductor strip included in the coil pattern, the conductor included per unit length of the coil is reduced. It is necessary to increase the number of strips. Reducing the width of the conductor strips in this way increases the electrical resistance of each conductor strip and thus of the entire coil. In general, a large-capacity power supply is required to supply a current to a coil having a large electric resistance, and there is a problem in heat generation of the coil. Therefore, a coil having a small electric resistance is desirable.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and provides a Z-axis gradient magnetic field coil capable of generating a strong gradient magnetic field without increasing the electric resistance of a conductor forming a coil pattern. The purpose is to do so.

[0007]

In order to achieve the above-mentioned object, a Z-axis gradient magnetic field coil according to the present invention is characterized in that a flexible printed board on which a predetermined coil pattern is formed is wound a plurality of times. And

Further, the second Z-axis gradient magnetic field coil of the present invention comprises a plurality of pairs of elongated conductor strips, and a current I flowing into the first of the plurality of strips, and thereafter, the plurality of pairs of elongated conductor strips. Let the strip flow sequentially,
One flexible insulating substrate on which a coil pattern including an interconnect means for flowing the current from the last strip of the plurality of strips is formed such that one end is the lowermost layer and the other end is the uppermost layer. A coil that is wound in a substantially cylindrical shape over a plurality of layers, and generates a Z-axis gradient magnetic field in accordance with the flow of the current I. A coil structure formed as a result of the winding includes a cylinder. A plurality of pairs of conductor strips having a length around the circumference and arranged substantially parallel and symmetrically with respect to a central cutting plane perpendicular to the central axis of the cylinder and through which current flows in directions opposite to each other are included. Characterized in that a gradient magnetic field in the Z-axis direction is generated by the conductor strip of (1).

[0009]

The flexible insulating substrate has a length capable of being wound around the bobbin a plurality of times. When the substrate is wound a plurality of times in a cylindrical shape and a current is supplied, a predetermined gradient magnetic field is generated. Such a predetermined coil pattern is formed.

The coil pattern comprises a plurality of pairs of elongated conductor strips and a current I flowing into a first one of the plurality of strips and then sequentially flowing through each pair of the plurality of strips. Interconnect means for causing the current to flow out of the last of the plurality of strips. When the substrate is wound a plurality of times into a cylindrical shape, the coil structure formed as a result of the winding has a length that makes a round around the cylinder, and is substantially formed with respect to a central cutting plane orthogonal to the central axis of the cylinder. At least one pair of conductor strips that are arranged parallel and symmetrically with each other and carry current in opposite directions.

As described above, in the Z-axis gradient magnetic field coil of the present invention, the flexible insulating substrate is wound a plurality of times,
Since conductor strips may overlap in the radial direction,
The number of conductor strips included per unit length of the coil can be increased without reducing the width of the conductor strip. Therefore, a Z-axis gradient magnetic field coil that has a small electric resistance and can generate a strong gradient magnetic field is provided.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a view showing a configuration of an embodiment of a Z-axis gradient magnetic field coil according to the present invention. In the drawing, reference numeral 30 denotes a flexible insulating substrate. The substrate 30 has a length four times or more the circumference L of the cylindrical bobbin on which the coil is to be wound and held. On the surface of this substrate, conductor strips S1 to S15, S1 'to S1
5 'and connecting conductors C0 to C18, C1' to C9 'and C
A coil pattern composed of 12 'to C17' is formed by an etching process. This coil pattern is connected to a power supply circuit (not shown) via terminals 31 and 32.

As shown in FIG. 1, each conductor strip pair S1-S1 ', S2-S2',..., S15-S1
5 'is symmetric with respect to the center line OA of the pattern. The connection conductors connect the conductor strips sequentially so that a current flows in the opposite direction in each conductor strip pair.

FIG. 2 is a sectional view of a coil structure formed by winding the substrate 30 around a bobbin 51. The board 30 is bent around a bobbin with the area 37 as the lowermost layer after the area 38 in which the end connection conductor is present is bent toward the area 37 in which the conductor strip is present, and the areas 36, 35, 34 and 4 Wound in layers.

FIG. 3 is a sectional view taken along the line DD 'in FIG. As a result of the substrate 30 being wound around the bobbin 51 over four layers, the substrate 30 passes through the origin O (center of the coil) O of the central axis Z of the cylindrical bobbin and intersects a plane XY perpendicular to the central axis Z by 1
Five sets of conductor strip pairs S1-S1 ', S2-S2',
.., S15-S15 'are arranged symmetrically. Each conductor strip forms a one-turn coil wound around the Z axis. When a power supply line from a power supply is connected to the terminals 31 and 32, a current flows through each conductor strip. The current flowing through the conductor strips S1 to S15 and the current flowing through the conductor strips S1 'to S15' are opposite in direction. As a result, a gradient magnetic field in the Z-axis direction is formed in the bobbin.

As shown in FIG. 3, the conductor strip pairs S1-S1 ', S2-S2',..., S7-S7 'are arranged so that their distances from the plane XY are sequentially increased. Of the conductor strips form a narrow pitch distributed winding coil. On the other hand, the conductor strip pairs S8-S8 ', S9-S9',
, S11-S11 'and conductor strip pair S12-S
12 ', S13-S13',..., S15-S15 'are arranged at equal distances from the plane XY, and a group consisting of these conductor strips is densely wound in a plurality of turns at the same position. Forming a coil.

FIG. 4A is a diagram showing the arrangement of conductor strips in a Z-axis gradient magnetic field coil proposed in Japanese Patent Laid-Open No. 3-48402, and FIG. 4B is a diagram showing the arrangement of conductor strips of a coil in the present invention. It is a figure which shows schematically.
In the coil shown in FIG. 4A, the substrate is wound only once around the bobbin. Therefore, if the coil needs to be wound many times, the width of each conductor strip P must be reduced, and therefore, In addition, the electrical resistance of the conductor strip increases. In the present invention, since the substrate is wound a plurality of times, as shown in FIG. 4B, the width of each conductor strip can be made wider than before. Therefore, a Z-axis gradient magnetic field coil having a small electric resistance is provided.

As shown in FIG. 1, the connecting conductors include a first group C12-C18 and C12'-C17 'extending in the same direction as the conductor strip, and a second group extending in a direction orthogonal thereto. C0 to C11, C1 '
To C9 '. The magnetic field generated by the current flowing through the connection conductor belonging to the second group is
Since it has a direction orthogonal to the Z-axis direction, there is no need to consider cancellation. However, since the magnetic field generated by the current flowing through the connection conductor belonging to the first group has the Z-axis direction, it is necessary to consider the cancellation.

FIG. 5 is an enlarged view of a part at the end of winding of the coil structure. FIG. 5 shows a region 33 at the end of the substrate 30.
A first group of connection conductors C12 to C18,
The first group of connection conductors C12 'to
C17 'basically overlaps the same position of the coil except for the connection conductor C18. This is because the region 38 is bent toward the region 37 where the conductor strip exists. Since the directions of the currents flowing in each of the overlapping connection conductors are opposite, the magnetic fields having the Z-axis direction generated by the respective currents cancel each other. Connection conductors C12 to C1
7 and the length of the connecting conductors C12 'to C17' are optimally selected such that both magnetic fields are substantially canceled out. For example, the lengths of the overlapping connecting conductors C12 and C12 'are equal, and the lengths of the connecting conductors C13 and C13', the connecting conductors C14 and C14 ', and the connecting conductors C17 and C17' are also set equal. .

However, as for the connection conductor C18, there is no connection conductor to be overlapped on the region 38 side. Also,
Although a portion C15-1 of the connection conductor C15 overlaps with the connection conductor C15 ', the remaining portion C15-2 is a connection conductor C15.
15 'does not overlap. Further, a portion C16-1 of the connection conductor C16 overlaps with the connection conductor C16 ', but the remaining portion C16-2 does not overlap with the connection conductor C16'. Therefore, in strict consideration, these connection conductors C1
It is considered that the magnetic field having the Z-axis direction generated by the current flowing through 8, C15-2, and C16-2 is not canceled by the connection conductor existing in the region 38.

If it is necessary to eliminate these unresolved magnetic fields, the following measures are effective.
That is, when the power supply lines 91 and 92 are connected to the terminals 31 and 32, the power supply line 91 is connected to the connection conductors C18 and C as shown in FIG.
15-2 and C16-2. With this configuration, the current flowing through the power supply line 91 and the current flowing through the connection conductors C18, C15-2, and C16-2 have opposite directions.
The magnetic field having the Z-axis direction generated by the current flowing through 16-2 can be canceled by the magnetic field generated at the portion where the magnetic field having the Z-axis direction is overlapped and laid on each connection conductor of the feeder line 91.

In the above embodiment, the region 38 is turned back. However, even if the region 33 is turned back, the magnetic field having the Z-axis direction generated by the current flowing through the connection conductor existing in the region 38 can be obtained. Are canceled by a magnetic field having a Z-axis direction generated by a current flowing through the connection conductor existing in the region 33.

Further, in the above embodiment, since the coil pattern which is symmetrical with respect to the center line OA of the pattern is used, there is a pair of conductor strips in each layer of the coil structure. However, the symmetry of the coil pattern is not always an essential requirement. FIG. 6 shows an example of a coil pattern which is equivalent to the coil pattern shown in FIG. 1 but has no symmetry. In the coil structure obtained by winding using the coil pattern shown in FIG. 6, the pair of conductor strips are present on different layers. However, the generated Z-axis gradient magnetic field is shown in FIG.
Needless to say, this is exactly the same as the case where the coil pattern is used.

FIG. 7 shows another embodiment of the present invention.
In the present embodiment, a case is considered in which a gradient magnetic field having a required strength cannot be obtained only by a coil formed on a flexible insulating substrate. Specifically, the present embodiment is characterized in that a wire can be additionally wound.

In this embodiment, a notch is provided at a position where the wire of the substrate is wound, in the direction in which the conductor strip extends. In FIG. 7, the positions on the substrate 30 where the wires are wound are cut out as indicated by 61 and 62. Therefore,
In this case, the substrate 30 is formed in an E-shape as a whole, and a desired coil pattern P is formed thereon by an etching technique. At both ends of the coil pattern P, terminals 31 and 32 are provided for allowing current to flow in and out of an external circuit.

The substrate 30 is wound around a bobbin starting from the end A of the substrate. In this embodiment, the substrate 30 is wound around a bobbin in three layers. In the coil pattern P shown in FIG. 7, the connection conductor does not include a conductor extending in the same direction as the conductor strip. Therefore, it is considered that one of the ends of the substrate is folded to cancel an unnecessary magnetic field. do not have to.

FIG. 8 shows a case where the substrate 30 shown in FIG.
FIG. 7 is a view showing a state where the notches are wound, and notches 61 and 62 form grooves 71 and 72, respectively. next,
As shown in FIG. 9, wires 8 are inserted into these grooves 71, 72.
1 is wound. Since the grooves 71 and 72 function as guides, the wire 81 can be wound at a predetermined position with a predetermined width.

Although the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications can be made. For example, the coil pattern shown in the above embodiment is merely an example, and a coil pattern that generates a desired gradient magnetic field can be appropriately adopted. The number of layers around which the substrate is wound may be further increased. However, since the thickness of the substrate cannot be ignored, it is inevitable that the outer diameter of the coil will increase when the number of layers is large. Therefore, it is required that the length of the conductor strip existing in the outer layer be increased in one round.

[0029]

As is apparent from the above description, in the present invention, since the flexible insulating substrate on which the predetermined coil pattern is formed is wound a plurality of times, the conductor strips may overlap in the radial direction. Therefore, the number of conductor strips included per unit length of the coil can be increased without reducing the width of the conductor strip.
Therefore, a Z-axis gradient magnetic field coil that has a small electric resistance and can generate a strong gradient magnetic field is provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a flexible insulating substrate constituting a Z-axis gradient magnetic field coil of the present invention.

FIG. 2 is a sectional view showing a state where the flexible insulating substrate shown in FIG. 1 is wound.

FIG. 3 is a sectional view taken along the line DD ′ in FIG. 2;

FIG. 4 shows Z proposed in JP-A-3-48402.
It is a figure which shows schematically arrangement | positioning of the conductor strip in an axial gradient magnetic field coil, and arrangement | positioning of the conductor strip of the coil in this invention.

FIG. 5 is an enlarged view of the end of winding of the coil structure.

FIG. 6 is a diagram showing an example of a coil pattern which is equivalent to the coil pattern shown in FIG. 1 but has no symmetry.

FIG. 7 is a view showing another example of the flexible insulating substrate constituting the Z-axis gradient magnetic field coil of the present invention.

8 is a diagram showing a coil structure obtained as a result of winding the substrate shown in FIG. 7 around a bobbin.

FIG. 9 is a view showing a state in which a wire is further wound around the coil structure shown in FIG. 8;

[Explanation of symbols]

30 flexible printed circuit board 31, 32 terminal 51 bobbin S1-S15, S1'-S15 'conductor strip C0-C18, C1'-C9', C12'-C17 '
Connection conductor

Claims (9)

(57) [Claims] 1. A Z-axis gradient magnetic field coil wherein a flexible printed circuit board on which a predetermined coil pattern is formed is wound a plurality of times. 2. A plurality of pairs of elongated conductor strips and a current I flowing into a first one of said plurality of strips and then sequentially flowing through said plurality of strips to allow said current to flow through said plurality of strips. A single flexible insulating substrate on which a coil pattern including an interconnecting means for flowing out from the last strip of the strips is substantially formed over a plurality of layers such that one end is a lowermost layer and the other end is an uppermost layer. A coil that is wound in a cylindrical shape and generates a Z-axis gradient magnetic field in accordance with the flow of the current I. The coil structure formed as a result of the winding has a length that goes around the cylinder. And a plurality of pairs of conductor strips which are arranged substantially parallel and symmetrically with respect to a central cutting plane perpendicular to the central axis of the cylinder, and in which current flows in directions opposite to each other. A Z-axis gradient magnetic field coil, wherein a gradient magnetic field in the Z-axis direction is generated by the strip. 3. The Z-axis gradient magnetic field coil according to claim 2, wherein the conductor strip pairs included in the coil structure are arranged at different distances from the center cut plane. 4. The Z-axis gradient magnetic field coil according to claim 2, wherein the conductor strip pairs included in the coil structure are arranged at an equal distance from the center cut plane. 5. The conductor strip pair included in the coil structure includes a group arranged at an equal distance from the center cutting plane and a group arranged at a different distance from the center cutting plane. The Z-axis gradient magnetic field coil according to claim 2, wherein: 6. The coil according to claim 2, wherein the coil pattern formed on the flexible insulating substrate has symmetry. 7. The Z-axis gradient magnetic field coil according to claim 2, wherein the coil pattern formed on the flexible insulating substrate has no symmetry. 8. Among the interconnecting means included in the coil pattern, interconnecting means located at the start end and the end of winding of the substrate extend in the same direction as the conductor strip extends. A first group and a second group extending in a direction orthogonal to the direction in which the conductor strip extends, wherein the beginning of the winding or the end of the winding is creased at the boundary between the interconnecting means and the conductor strip. The first group of interconnecting means located at the start end and the end end of the winding overlap, whereby the magnetic field generated by the current flowing through the interconnecting means included in each group The Z-axis gradient magnetic field coil according to claim 2, wherein the coils cancel each other. 9. A notch extending in the same direction as the conductor strip is formed in the substrate, and a wire is additionally wound in a groove portion of a coil structure formed as a result of winding the substrate. The Z-axis gradient magnetic field coil according to claim 2, wherein: