JPS5873850A - Method and apparatus for generating magnetic field - Google Patents

Abstract

PURPOSE:To minimize the occupation space of a coil with minimization of the entire coils and enlargement of the internal space of the coils by arranging the coil for generating gradient field on a common cylindrical surface in an NMR imaging or the like. CONSTITUTION:A cylindrical bobbin 50 is wrapped with an flexible electric insulation sheet 51 on which a Z-axis magnetic field generating coil having a gradient in direction of X, Y and Z. A small diameter radius difference with a necessary range is provided between a group of the coils, for example, the coils (21-24) overlapping each other in the position and a group of the coils 11 and 12 for electric insulation therebetween. Coils for generating gradient field in various directions and an offsetting coils are formed in an integral coil device 52 and a coil 53 is arranged coaxially in a cylindrical space inside a static field generating air core coil 53 maintaining a clearance 54. In this manner, the various coils for generating gradient field are constructed by combining coil elements containing a circular arc having the common axis.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for generating a gradient magnetic field used in nuclear magnetic resonance tomography imaging (hereinafter referred to as "NMR imaging"), and a method for manufacturing the same.

For example, in NMR imaging, one common method is used to determine the resonance position in an object: 1. In addition to a magnetic field that is uniform in location and constant in time (hereinafter referred to as ``static magnetic field''), there is also a magnetic field that varies in size locally and has a gradient (hereinafter referred to as ``gradient magnetic field'' or [gradient magnetic field]). j) is applied 1. In order to limit the resonance position to a certain value, a magnetic field with gradients in three orthogonal axes is required, and if the static magnetic field direction is the Iz-axis direction, its magnitude is linear in the X, Y, and 73-axis directions. Conventionally, as a gradient magnetic field generating coil to which a magnetic field in the Z-axis direction which varies as shown in FIG.

A method of arranging them on the Y and Z axes is used. Coil (61), (62), Coil (63), (6
4) , coil (65), (66) are
This is a coil that generates a Z@force direction magnetic field having gradients in the axial direction, the X-axis direction, and the Z-axis direction. However, with this configuration, a large coil is required to obtain a magnetic field with good linearity over a wide sample space, and the NMR imaging apparatus as a whole becomes huge to accommodate it.

The present invention solves the above-mentioned problems and provides a gradient magnetic field generating device that occupies a small space and is suitable for NMH imaging devices and the like, and a method for manufacturing the same.
``・l・゛・ The first feature of the present invention is that the customer coils for generating gradient magnetic fields can be arranged on a common cylindrical surface.

If an air-core coil is used as the electromagnet for generating a uniform magnetic field, a cylindrical space will be left in the air-core portion. Therefore, if the shape and arrangement of the gradient magnetic field generating coils are housed on the same cylindrical surface, the entire magnetic field generating coil of the NMR imager can be made compact, and the gradient magnetic field generating coils can be made compact. In the present invention, which allows the internal space of the coil to be large, it is preferable that each coil for generating a magnetic field having a gradient in the direction of orthogonal axes is arranged on a common cylindrical surface. The space occupied by the coil for generating a strong gradient magnetic field can be made extremely small.

The second feature of the present invention is that, as a coil manufacturing method suitable for a gradient magnetic field generating coil, a pattern corresponding to the expansion diagram of each coil is formed on a flexible sheet.
1 After that, wrap the CRT directly or on a cylindrical bobbin:・
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The point is to form a cylindrical coil.

Embodiments of the present invention will be described below based on the drawings.

Figure 1 shows a biaxial magnetic field ('''2
It is a coiled iron rope for generating a directional gradient magnetic field (abbreviated as "'M, axwell Pa1r").
In other words, two circular coils 11. of the same radius with the Z axis as the axis are placed symmetrically on a plane (XY plane) containing the X axis and the Y axis (1 m or The current flows in the opposite direction.(In principle, it is sufficient that the coil bend and the coil (12 ampere turns) are equal, but in the present invention, the same number of turns and the same current value will be explained.

) In the calculation result, the relationship between the -5 radius 1 and the spacing 2ds of 1 imaginary coil is, for example, d, -72JI
Power: Appropriate.

By this, if we separate the static magnetic field, we have a uniform gradient that is zero at the origin (0) and whose intensity changes linearly in the positive and negative directions of the Z-axis symmetrically at the origin. Z-axis direction magnetic field (9
A force S (shown at the bottom of Figure 1) is generated.

Figure 2 shows the configuration of a coil element for generating a Z-axis magnetic field with a gradient in the X-axis direction (abbreviated as "X-axis gradient magnetic field"). Consists of @ line parts parallel to the two axes [same shape, same size as saddle shape-1,
411il coils a, ■, cs, + with the same number of turns
241 is placed symmetrically on the XY plane and symmetrically on the Yz plane 1
．． Currents of the same magnitude (generally, currents of the same ampere-turn) flow in the direction shown.

The axial component Hz of the resultant magnetic field according to this configuration is equal to the inner circular arc interval 2f1. It has been found that by appropriately selecting the outer arc interval 2f2, it changes linearly along the 4Z axis symmetrically to the origin. (It is shown in the lower part of Fig. 2.) When we calculated the magnetic field fraction for various values of 11·f2 by considering the magnitude of the static magnetic field, we concluded that the optimum value is near the following formula.

L+==0.4a f2=1.4a (11
α=1.20- Note that the generated magnetic field is not only the Z component (although some X component is also generated, its magnitude does not depend on the X and Y coordinates and the Z component
It was also found that it only depends on the coordinates.

The coil element for generating a magnetic field in the Z4h direction (Y-direction gradient magnetic field) having a gradient in the Rotate 90° around the Z axis [11. Coil (2), coil to coil ■, and coil (to) are arranged in a symmetrical state on the nXz plane.1. The symbol G, mother, @, cllA in the 4th section below 1. ing. Note that the optimal value of *'1+'2+α is the same as in the case of FIG.

Figure 3 shows the zero point 1a of the gradient magnetic field! This is an offset coil for varying the position of the field zero point).

It consists of a pair of circular coils (311, W) arranged symmetrically at the origin with the Z axis as the axis. Calculation result jld2Q
) The optimal value was found to be d, = a. Koi J
As shown in the figure, the same ampere-turn [ff] is applied to the coil 31) and the coil @ in the same direction. , When this current value is changed, the off-sail/magnetic field becomes 6if according to this value.
For example, two-way gradient magnetic field generating coil 5. At the same time as shown in Fig. 1), the position of the zero point of the Z-direction gradient magnetic field Q) is changed by 5J.

Note that one or more gradient magnetic field generating coils (11+) between each direction.

Mouth, C! 11~ and offset coil (311,
At t32.

A pulsed current is applied and the magnitude of the magnetic field gradient is.

Pulse height etc. fl! *Next change and switch.

FIG. 4 shows a schematic configuration diagram of the magnetic field generator of the present invention in which the axes of the arcs constituting each of the coils described above are common, and each coil is projected onto the Xz plane. . What does each symbol mean?

It is the same as the case of lIl~3 factors.

Since the gradient magnetic field generation coils and offset coils in each direction described above all have a common axis (Z-axis), it is possible to arrange them almost on a common cylinder.

(There may be cases where it is necessary to have a slight radius difference to prevent the coils from overlapping, but this is not a practical problem.)
Therefore, each of these coils can be formed into an inner cylindrical coil device and housed inside an air-core coil for generating a static magnetic field. 1), the space occupied by the coil as a whole can be made very small, and a wide cylindrical space can be secured inside the coil, making it extremely suitable for use in NMR imaging devices.

FIG. 5 shows a specific example of the construction and a preferred manufacturing method of the coil I for magnetic field invention according to the present invention. This is a cylindrical bobbin for holding the ω-th coil, and is made of plastic or other suitable non-magnetic electrically insulating material. (51) is a flexible electrically insulating sheet wound on a bobbin ω, which is a thin metal plate σ) (lj!) insulated, or a sheet made of plastic or other electrically insulating material. Sheet 61) 1 Illustrated Figures 1 to 4 have been described. A Z-axis magnetic field generating phase coil J and bS having gradients in each of the x, y, and z directions is formed.

(The diagram only shows a part of the coil in Figure 2 for simplicity.

) The arrangement relationship of each coil is basically determined by the force 5. Each child 4 jl
It is desirable to select the optimal value of z as described above.
A minute radius difference is provided between the groups of coils (1 to 24) and the groups of coils (111 and (121), and electrical insulation is provided between them. Both grays can be separated at the same position on the same sheet by an electrical insulating layer, or they can be laminated after forming a separate sheet field/upper coil group.T+1°For generating gradient magnetic fields in each direction. Coil f-? and offset coil are integrated coil device: F
+3I formed 11. As shown in the cross-sectional view on the right side of Fig. 5, the air-core coil 1 for static magnetic field generation is
The coil is placed coaxially with the coil in the cylindrical space inside the coil. Special number for use ζ How to handle the cooling method, coil position, etc. (in terms of N).

63 & @ is a separate 1 nib (closed direction 5 L).

Seat f! Since L material also forms a coil on top of 0, it becomes cloudy and C.
Yo.

For example, as shown in the upper part of Fig. 5, conductor 1 < turn cm, + fishing, which corresponds to the developed view of each coil.
Form each sheet member 61) in a flat state, and wind this 1 on a cylindrical bobbin ω with a force S. 0) Only a part is shown.) The above method makes it easy to create coils with complex shapes.

It can be mass-produced economically. This method is especially suitable for saddle-shaped coils! Suitable for producing i-■. This is because the deployment pattern of the saddle shape coil itself forms a closed circuit.

Circular-z 4 le1llI, (121, (Ill,
When winding the cylindrical coil (1-61) into a cylindrical shape, the position of the unfolded pattern will change.In order to form a continuous coil, pay attention to the positional relationship of the ends of the conductor pattern, and when assembling the cylindrical coil. It is necessary to connect the ends of the conductive patterns as appropriate.

In addition, each coil is manufactured using Purin I circuit technology.

It goes without saying that IM projection may be formed on the cylindrical bobbin ω.

As can be seen from the above description, in the present invention, by configuring each coil for generating a gradient magnetic field by a combination of coil elements including arcs having a common axis, the following remarkable effects can be obtained.

1, 2) Therefore, it is possible to form 4 cylindrical surfaces with a common force of 1 coil, and the total size of the coil can be reduced to 1 v, 5 units, ÷ extremely small. Therefore, it is possible to significantly reduce the size of the entire NMR imaging device.

In this case, since a wide cylindrical space can be secured inside the coil, it is suitable for accommodating an object having the same length as a human body.

3) Since the coils are formed within a cylindrical surface, a conductor pattern corresponding to the developed view of each coil is formed on a flexible flat plate. Direct winding or winding: It can be constructed by winding it around a cylindrical body. Therefore, complex-shaped coils for generating gradient magnetic fields can be simplified.

It can be produced economically and is also suitable for production.

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[Brief explanation of drawings]

11 [Figures 1 to 3 are schematic configuration diagrams of each element of the gradient magnetic field generation coil according to the present invention, Figure 4 is a schematic configuration diagram of the gradient magnetic field generation coil according to the present invention, and Figure 5 is a schematic configuration diagram of each element of the gradient magnetic field generation coil according to the present invention. A specific example of the configuration of a magnetic field generator, FIG. 6 shows one of the conventional gradient magnetic field generators.
This is an example diagram. 111+, tlB... Coil for generating gradient magnetic field in two-axis direction ~ (to)... Coil for generating gradient magnetic field in X-axis direction (c)
~■... Y-axis direction gradient magnetic field generation coil ci11. ■
...Offset coil cm, as...Conductor pattern ω...Cylindrical bobbin 69...Flexible insulation JETRO...Gradient magnetic field generation phase coil device -...Static magnetic field generation coil・Patent application Person Shimadzu Corporation Representative Patent Attorney Hatahiko Takeishi

Claims (5)

[Claims] (1) A plurality of coil elements including circular arcs having a common axis and generating magnetic flux in the same direction as the common axis are combined so that the magnetic field strength of each coil changes in a direction perpendicular to the common axis. ←It is characterized by Device for generating magnetic field. (2) The magnetic field generating device according to claim 1, wherein each of the coil elements is arranged in a common cylinder having the common axis as the axis. (3) A portion of the coil element is comprised of a plurality of saddle-shaped coil pieces arranged symmetrically in a plane including the common axis. Device for generating magnetic field. (4) The magnetic field generating device according to claim 1 or 2, wherein the coil element is arranged inside a cylindrical air-core coil coaxial with the common axis. (5) After forming a conductor pattern in a shape corresponding to the developed view of the coil element on the flexible insulating sheet. It is characterized by forming this n into a cylindrical shape. A method of manufacturing a device for generating a magnetic field. +61 The method for producing a magnetic field generating coil 0) according to claim 5, wherein the coil element is a saddle-shaped coil.