JPH05308017A - Gradient magnetic field generating equipment - Google Patents

Abstract

PURPOSE:To obtain a gradient magnetic field generating equipment which generates magnetic fields excellent in linearity and has miniaturization potential by overlapping a normal conduction coil in the odd number layers and that in the even number layers with the twisted parts between their turns crossed. CONSTITUTION:A cylindrical unit 10 consists of a distributed winding coil 12. The distributed winding coil 12 is so constituted that a normal conduction coil 121 is reversed and laid over another normal conduction coil 122. A plurality of twisted parts 121B and 122B between turns of the coils 121 and 122 are crossed each other. When power is applied to the normal conduction coil 121 of the distributed winding coil 12 through its lead connection 121A, the current flows to the lead connection 122A of the normal conduction coil 122 via the interlayer connection 121C of the coil 121 and that 122C of the coil 122. During the travel of the current an irregular magnetic field at the twisted part 121B between turns is compensated by that in the opposite direction at the twisted part 122B between turns. Thus the normal conduction coils 121 and 122 are connected to each other through the respective interlayer connections 121C and 122C, which enables the miniaturization of the equipment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gradient magnetic field generator for use in, for example, an image forming apparatus using nuclear magnetic resonance (NMR) and for generating a gradient magnetic field inclined along a certain axial direction. It is a thing.

[0002]

2. Description of the Related Art A conventional gradient magnetic field generator of this type is shown in FIGS. 3 to 6 disclosed in Japanese Patent Laid-Open No. 62-194842.
It will be explained based on.

FIG. 3 is a sectional view of a nuclear magnetic resonance imaging apparatus using a gradient magnetic field generator. In FIG. 3, 40 is a main magnet that generates a static magnetic field that is spatially uniform and temporally stable, and 41 is an imaging element. A conventional gradient magnetic field generator that determines the slice plane at the time and adds position information to the nuclear magnetic resonance signal, 42 is an RF coil that transmits a high-frequency electromagnetic wave that causes the magnetic resonance of the subject 43, and 44 is the nucleus of the subject 43 An antenna for receiving magnetic resonance signals.

Further, the gradient magnetic field generator 41 is composed of two internal and external coil groups (not shown), and these two internal and external coil groups have a spatial gradient in the region of the subject 43. It is configured to generate a magnetic field and to output each other so that the magnetic field does not leak to the external region of the gradient magnetic field generation device 41.

4 and 5 show the pattern of a saddle type coil which is attached to the gradient magnetic field generator 41 shown in FIG. 3 and which generates a radial gradient magnetic field. FIG. 4 shows the inner coil. FIG. 5 shows an example of the outer coil pattern.

When the nuclear magnetic resonance imaging apparatus is used, a tomographic image of the subject 43 can be obtained by the following procedure. The subject 43 is placed in the static magnetic field generated by the main magnet 40. The magnetic field generated by the gradient magnetic field generator 41 is applied to the subject 43 to determine the imaging cross-section position. An electromagnetic field having a frequency at which nuclear magnetic resonance occurs at the magnetic field strength at the imaging cross-section position is applied to cause nuclear magnetic resonance in the subject 43. The magnetic field generated by the gradient magnetic field generator 41 is applied to the nuclear magnetic resonance signal from the subject 43, and position information is given to the nuclear magnetic resonance signal. The nuclear magnetic resonance signal is received by the antenna 44, the computer 43 performs image processing on the basis of the received signal, and the subject 43
Obtain a cross-sectional image of.

In the above steps, the magnetic field generated by the gradient magnetic field generator 41 is high speed (for example, about 1 millisecond).
Is switched on. At this time, an induced current flows through the main magnet 40 and the like so as to generate a gradient magnetic field having good spatial linearity in the region of the subject 43 and to prevent leakage to the outside region of the gradient magnetic field generation device 41. This prevents the magnetic field from being disturbed by the induced current.

The conventional gradient magnetic field generator 41 generates a gradient magnetic field having a good spatial linearity in the subject 43 as described above, and also has a predetermined surface so as not to leak the magnetic field to the external region. The coil pattern that satisfies the current distribution condition is determined.

On the other hand, in the determination of the coil pattern based on the above surface current distribution condition, each coil is shown as a closed loop current pattern. Therefore, in order to form an actual coil, adjacent turns are connected in series and driven by a power supply. Input and output terminals are provided. And the conventional gradient magnetic field generator 4
In No. 1, when connecting the adjacent coils in series, as shown in FIGS. 4 and 5, a twist portion is provided between the coil turns. FIG. 6 shows a coil of the same kind as the coil shown in FIGS. 4 and 5, and this coil 45 has a lead connecting portion 45A serving as an input end, an inter-turn twist portion 45B, and a lead connecting portion 45C serving as an output end. There is.

[0010]

However, since the conventional gradient magnetic field generator 41 is constructed as described above, the current flows in each coil 45 in the direction C, and the twisted portion 45B between the turns causes an incorrect magnetic field. Is generated, and there is a problem that the linearity of the magnetic field is deteriorated. Furthermore, in order to take out the current lead from the lead connecting portion 45C at the center of each coil 45, it is necessary to crawl the current lead above or below each coil 45. Is required, and when another coil 45 is above or below the coil 45, an insulator or the like for correcting the radial height of the cylinder is required.
A large coil 45 is formed in the cylindrical direction, and the coil 4 is
However, there is a problem in that the structure of the image forming apparatus using NMR for inserting 5 becomes large.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a gradient magnetic field generating device which is excellent in linearity of a magnetic field and can be miniaturized.

[0012]

In the gradient magnetic field generator according to claim 1 of the present invention, each coil is constituted by an even number of normal conductor coils which are insulated from each other, and between the normal conductive coils of each layer, respectively. Connected in series at the center end or the outer end, and the winding directions of the odd-numbered layer normal conductive coil and the even-numbered layer normal conductive coil are reversed, and the twisted portions between the turns of the normal conductive coil of each layer are crossed at approximately the same position. It is constructed by overlapping.

Further, in the gradient magnetic field generating device according to the second aspect of the present invention, the cylindrical unit is composed of a large-diameter cylindrical unit and a small-diameter cylindrical unit arranged coaxially, and the large-diameter cylindrical unit has a small-diameter unit. The magnetic field to the outside is shielded by generating a magnetic field output opposite to that of the cylindrical unit, and the coils of the cylindrical units are composed of even-numbered layers of normal-conducting coils insulated from each other and centered between the normal-conducting coils of each layer. Connect in series at the end or outer end, reverse the winding directions of the odd-numbered layer normal conductive coil and the even-numbered layer normal conductive coil, and intersect the twisted portions between the turns of the normal conductive coils of the above layers at substantially the same positions. It is constructed by overlapping.

[0014]

According to the first aspect of the present invention, the twisted portions between the turns of the normal conducting coil can be overlapped by overlapping the layers to cancel the generation of an incorrect magnetic field, and the center end of the normal conducting coil or Since the outer end crosses the layers, each normal conducting coil can be connected only by pulling out the lead from the end of the normal conducting coil.

According to the present invention as defined in claim 2,
The magnetic field to the outside is shielded by generating a magnetic field output opposite to that of the small-diameter cylindrical unit to the large-diameter cylindrical unit, and the twisted part between the turns of the normal-conducting coil is crossed between the layers and overlapped to form an incorrect magnetic field. Can be canceled out, and since the interlayer is crossed at the center end or the outer end of the normal conducting coil, each normal conducting coil can be connected only by pulling out the lead from the end of the normal conducting coil.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the embodiments shown in FIGS. 1 is a perspective view showing an essential part of one embodiment of the gradient magnetic field generator of the present invention, and FIG. 2 is a front view of a normal conducting coil which constitutes a distributed winding coil of the gradient magnetic field generator shown in FIG. , (A) is a diagram showing the normal conducting coil of the first layer, and (b) is a diagram showing the normal conducting coil of the second layer.

As shown in FIG. 1, the gradient magnetic field generator according to the present embodiment has four distributed winding coils 1 on the surface of a cylinder 11.
2, 13 (other coils are omitted because they are located on the opposite side of the paper) to form the cylindrical unit 10, and current is passed through the coils 12, 13 of the cylindrical unit 10 to form the cylinder. A magnetic field having a substantially uniform magnetic field component in the Z-axis direction is formed within a plane perpendicular to an arbitrary axis perpendicular to the Z-axis as the axis of the unit 10, for example, the X-axis or the Y-axis,
In addition, the magnetic field in the plane is configured so that the magnetic field strength changes substantially in proportion to the distance between the plane and the origin O to form the gradient of the magnetic field.

Thus, each coil 12, 13 of the distributed winding is
Are formed in the same size such as an elliptical shape or a substantially rectangular shape, and one coil 12 is composed of two layers of normal conducting coils 121 and 122 insulated from each other, as shown in FIG. Then, the normal conducting coils 121, 1 of each layer
As shown in FIGS. 2A and 2B, the winding No. 22 is formed by the numerically controlled machine tool so that the winding directions thereof are opposite to each other. Further, each normal conducting coil 121, 122 has lead connecting portions 121A, 122A formed at the outer ends thereof, and is wound inward from each of the lead connecting portions 121A, 122A and twisted between turns 121B, 122B between turns. Is formed, and the inner end portion connects the layers to each other to form the crossover portion 121.
It is formed as C and 122C. Then, as shown in FIGS. 2 (a) and 2 (b), a current is applied to the normal conducting coil 121 in the direction of arrow A, and the normal conducting coil 122 is indicated by arrow B.
The electric current is made to flow in the direction. Of course, the distributed winding coil 13 is also constructed in the same manner as the coil 12.

The distributed winding coil 12 shown in FIG.
As shown in FIG. 5, the normal conducting coil 121 is turned over and is superposed on the normal conducting coil 122 via an insulating material (not shown). , 122B intersect with each other as shown in FIG. Further, the normal conducting coils 121 and 122 of each layer are electrically connected by means of brazing or the like at the interlayer connecting portions 121C and 122C located at the same position at the centers thereof.

Therefore, according to this embodiment, the cylindrical unit 1
If a current in the direction of arrow A is applied from the lead connecting portion 121A to the normal conducting coil 121 of the distributed winding coil 0 of 0, this current flows from the interlayer connecting portion 121C to the interlayer connecting portion 122C of the normal conducting coil 122. It flows in the direction of the arrow B through the lead connecting portion 122A, and during this period, the incorrect magnetic field in the inter-turn twist portion 121B is canceled by the reverse magnetic field in the inter-turn twist portion 122B. In addition, if an electric current is applied to the coils of the other three sets of distributed windings, the irregular magnetic field is similarly canceled out, and a uniform gradient magnetic field excellent in linearity of the magnetic field can be obtained. The accuracy of the NMR image of the image forming apparatus using can be improved. Further, according to the present embodiment, the normal conducting coil 121 and the normal conducting coil 122 are respectively connected to the interlayer connecting portion 121.
Since the connection is made by C and 122C, it is not necessary to pull out the lead from the center of the coil as in the conventional case, and the device can be downsized with a more compact structure than in the conventional case.

In the above embodiment, the coil pattern was machined using the numerically controlled machine tool, and the coil pattern was attached to the cylinder. However, a coil-shaped groove is formed on the surface of the cylindrical bobbin. The coil may be embedded in this groove.

In the above embodiment, the distributed winding coil is constructed by turning over the normal conducting coil of the same shape, but even if the turns are different between the upper and lower layers, the twisted portions between the turns are overlapped to generate an incorrect magnetic field. May be offset.

Furthermore, in the above-described embodiment, the coil turn-to-turn twist portion is provided at the cylinder end away from the magnetic field center, but the coil-to-turn twist portion is provided near the center of the magnetic field. May be.

In the above embodiment, the number of distributed winding coils is two.
Although only the layers are described, it is needless to say that the present invention can be applied to a distributed winding coil composed of four or more even layers.

[0025]

As described above, according to the invention as set forth in claim 1 of the present invention, each coil on the cylindrical surface is constituted by the even-numbered layers of the normal-conducting coils, and the normal-conducting coils between the respective layers are centered. Connected in series at the end or outer end, the winding directions of the odd-numbered layer normal conductive coil and the even-numbered layer normal conductive coil are reversed, and the twisted portions between the turns of the normal conductive coil of each layer are overlapped at approximately the same position. Therefore, it is possible to provide a gradient magnetic field generation device which is excellent in linearity of a magnetic field and can be downsized.

According to the second aspect of the present invention, the cylindrical unit is composed of a large-diameter cylindrical unit and a small-diameter cylindrical unit coaxially arranged, and the large-diameter cylindrical unit has a small-diameter cylinder. The magnetic field to the outside is shielded by generating a magnetic field output opposite to that of the unit, and since the coil according to claim 1 is used as the coil, a gradient magnetic field generation device further improving the linearity of the magnetic field is provided. be able to.

[Brief description of drawings]

FIG. 1 is a perspective view showing a main part of an embodiment of a gradient magnetic field generator of the present invention.

2 is a front view of a normal conducting coil that constitutes a distributed winding coil of the gradient magnetic field generator shown in FIG. 1, (a) showing the first conducting coil, and (b) showing its two layers. It is a figure which shows the normal conducting coil of an eye.

FIG. 3 is a sectional view showing a main part of a conventional nuclear magnetic resonance imaging apparatus.

FIG. 4 is a pattern diagram showing an inner coil of a saddle type coil of the gradient magnetic field generator used in the nuclear magnetic resonance imaging apparatus shown in FIG.

5 is a pattern diagram showing an outer coil of a saddle coil of the gradient magnetic field generator used in the nuclear magnetic resonance imaging apparatus shown in FIG.

FIG. 6 is a front view showing another coil of the conventional gradient magnetic field generator.

[Explanation of symbols]

 10 Cylinder Unit 11 Cylinder 12 Coil 13 Coil 121 Normal Conduction Coil 122 Normal Conduction Coil 121B Turn Twist Part 121C Interlayer Transfer Part 122B Interturn Twist Part 122C Interlayer Transfer Part

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[Procedure amendment]

[Submission date] January 22, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

Claims (2)

[Claims] 1. A cylindrical unit is formed by providing a plurality of distributed winding coils on a cylindrical surface, and an electric current is caused to flow through each coil of the cylindrical unit so that the coil is perpendicular to an arbitrary axis perpendicular to the axis of the cylindrical unit. The magnetic field component in the axial direction makes a substantially uniform magnetic field inside the plane that intersects with, and the magnetic field in the plane changes the magnetic field strength in proportion to the distance between the plane and the origin to form a magnetic field gradient. In the gradient magnetic field generator, the above-mentioned coils are composed of even-layer normal conductor coils insulated from each other, and the normal-conducting coils of each layer are connected in series at their respective central ends or outer ends, and the odd-numbered layers are normally connected. A gradient magnetic field generator characterized in that the winding directions of the normal conducting coil and the even-numbered normal conducting coil are reversed and the twisted portions between turns of the normal conducting coils of the respective layers are crossed and overlapped at substantially the same position. 2. A plurality of coils of distributed winding are provided on a surface of a cylinder to form a cylinder unit, and an electric current is passed through each coil of the cylinder unit, whereby the cylinder unit is perpendicular to an arbitrary axis perpendicular to the axis of the cylinder unit. The magnetic field component in the axial direction makes a substantially uniform magnetic field inside the plane that intersects with, and the magnetic field in the plane changes the magnetic field strength in proportion to the distance between the plane and the origin to form a magnetic field gradient. In the gradient magnetic field generating device, the cylindrical unit is composed of a large-diameter cylindrical unit and a small-diameter cylindrical unit coaxially arranged, and the large-diameter cylindrical unit generates a magnetic field output opposite to that of the small-diameter cylindrical unit. The magnetic field to the outside is shielded by the coil, and the coils of each of the cylindrical units are composed of even-numbered layers of normal-conducting coils, and the normal-conducting coils of each layer are separated from each other by their central ends or outer ends. And the odd-numbered normal-conducting coils and the even-numbered normal-conducting coils were reversed in their winding directions, and the twisted portions between the turns of the normal-conducting coils of the above layers were crossed at approximately the same position and overlapped. A gradient magnetic field generator characterized by: