JPH05220127A - Magnet device - Google Patents

Abstract

PURPOSE:To enable the easy execution of magnetic field correction with high accuracy and good efficiency by equally dividing a cylindrical magnetic material mounting mechanism for supporting a magnetic material for magnetic field correction to 24n (where (n) is an integer) in a circumferential direction. CONSTITUTION:The members constituting the magnetic material mounting mechanism are groove shape members 2 which are arrounded in parallel with the central axis of the middle hole of a magnet body 1 consisting of a superconducting coil, etc., to a cylindrical shape in the positions equally dividing the circumference to 24 to the shape of the inside surface of the magnetic middle hole and slide plates (mounting members) 3 which are supported by the grooves of the groove shape members 2 and are arounded within the middle hole of the magnet body 1. The magnetic materials 4 for magnetic field correction to be mounted are fixed onto the slide plates 3 by means, such as adhesive bonding or screwing and are so considered as to prevent the positions of the magnetic materials 4 from being changed by the electromagnetic force generated in the magnetic materials 4 in the middle hole of the magnet body 1. The mounting positions on the inside surface of the middle hole of the magnetic materials 4 are freely settable by selecting the mounting positions on the slide plates 3 and the groove shape members 2 to be inserted with the slide plates 3.

Description

Detailed Description of the Invention

[0001]

The present invention relates to NMR (nuclear magnetic resonance).
A magnetic body mounting mechanism (a shim mechanism) that supports a magnetic field correcting magnetic body for correcting an error magnetic field component of a main magnetic field generated by a main coil, in particular, a magnet device such as a device magnet. The present invention relates to a provided magnet device.

[0002]

2. Description of the Related Art Generally, in a magnet for an NMR apparatus, one of the important characteristics is the homogeneity of a spatial magnetic field in a region where an object is to be examined. Therefore, in order to make the magnetic field highly uniform, various modifications have been made to the shape of the main coil for generating the output magnetic field or the current density distribution, but the magnet internal conditions such as the manufacturing accuracy and temperature conditions of the main coil, Alternatively, due to external conditions such as the placement of a ferromagnetic material near the magnet,
Highly uniform magnetic fields are easily disturbed.

Therefore, for example, in the prior art, Japanese Patent Laid-Open No. 1-22
As shown in No. 80447 “Nuclear Spin Resonance Tomography Apparatus”, a method of correcting an error magnetic field component by a magnetic material arranged appropriately is adopted. That is, the magnetic field in the spherical region inside the magnet hole is expanded by the Legendre function and the Legendre function, and by appropriately arranging the magnetic substance, the expansion term (Zonal term) by the Legendre function and the expansion term by the Legendre function The magnetic field correction is performed by using a method in which the term) is generated in an arbitrary size and the expansion coefficient of the magnetic field except the constant term in the measurement region is made as close to 0 as possible.

In the magnetic field correction by this magnetic material, the arrangement of the magnetic material on the circumference of the magnetic material is such that the Zonal term is annular and the Tesseral is
The terms are generally placed at specific angular positions on the circumference to output only specific adjoint orders. Also Tess
Although the eral term forms a magnetic field distribution having a phase in the circumferential direction, conventionally, magnetic materials are arranged in two arrangements in which the phase in the circumferential direction differs by π / 2, such as the sin θ term for the cos θ term. The magnetic field output of a specific phase is obtained by mounting and superposing the magnetic field outputs of the two arrangements.

[0005]

The conventional magnetic field correction by the magnet device having the magnetic body mounting mechanism (shim mechanism) for magnetic field correction) has the following three drawbacks.

First, in order to realize expansion of the highly uniform magnetic field space of the magnet device, of the expansion coefficients, higher-order terms that have not been conventionally subjected to magnetic field correction, especially in the Legendre function. In some cases, it may be necessary to correct terms with an adjoint order of 3 or more, but no specific method for correcting these higher-order terms has been proposed, which is a cause of hindering the expansion of the highly uniform magnetic field space.

Secondly, in the correction of the Tesseral term, in order to obtain a magnetic field output of a specific phase in the circumferential direction, superposition of magnetic field outputs in two arrangements in which the phases in the circumferential direction are different by π / 2 is used. Therefore, for example, Tesseral with phase π / 4
In the case of term correction, the amount of the magnetic pair is √2 times the amount of the magnetic substance when the magnetic substance is attached to the arrangement for directly outputting the phase, and the efficiency is low.

Third, in the conventional magnetic shim mechanism, Tess
Since the arrangement of the eral term on the circumference is special, it is arranged in an annular shape.
It requires a mounting mechanism different from the Zonal term, and narrows the effective area inside the magnet device bore.

According to the present invention, the mounting mechanism of the magnetic material for correcting the Tesseral term and the mounting mechanism of the magnetic material for correcting the Zonal term, which are capable of correcting the higher order terms of the expansion coefficient and have a high degree of freedom in phase setting in the circumferential direction, are integrated. It is an object of the present invention to provide a magnet device which can easily perform highly accurate and efficient magnetic field correction.

[0010]

In order to achieve the above-mentioned object, a magnet device according to the present invention has a cylindrical magnetic body for supporting a cylindrical magnetic body for magnetic field correction arranged in a bore of a magnet. It is characterized in that the body attachment mechanism is equally divided into 24n (where n is an integer) in the circumferential direction.

[0011]

In the magnetic shim device constructed as described above, since the magnetic body mounting mechanism is equally divided into 24n in the circumferential direction, an equal amount of magnetic body is arranged on the circumference at an angle of 2π / 24n.
Zonal terms can be generated by arranging them at equal intervals, and Tess of the conventional adjoint order 1 or 2
In addition to the eral term, the magnetic material can be arranged at the specific angular positions necessary to generate the Tesseral terms of the adjoint orders 3 and 4 without excess or deficiency. The phase of the Tesseral term in the circumferential direction is 24n.
In the case of division, the phase can be easily changed in units of mπ / 12n with respect to the adjoint order m, so that the phase position with high correction efficiency can be freely selected.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

On the inner surface of the inner hole of the cylindrical magnet body 1 made of a superconducting coil or the like, the groove-shaped member 2 is arranged parallel to the central axis of the inner hole at a position where the circumference is divided into 24 equal parts, and the slide plate ( The mounting member 3 is supported by the groove of the groove-shaped member 2 and is arranged in the inner hole of the magnet body 1. The channel member 2 and the slide plate 3 are made of a non-magnetic material,
Both constitute a magnetic body attachment mechanism.

The magnetic body 4 for magnetic field correction to be attached is
As shown in FIG. 2, it is fixed on the slide plate 3 by means such as adhesion or screwing so that the position of the magnetic body 4 does not change due to the electromagnetic force generated in the magnetic body 4 in the inner hole of the magnet body 1. It is considered. By selecting the mounting position on the slide plate 3 and the groove-shaped member 2 into which the slide plate 3 is inserted, the mounting position on the inner surface of the inner hole of the magnetic body 4 can be freely set.

In order to correct the Zonal term, the magnetic bodies 4 are made to face each other by 180 ° on an appropriate section perpendicular to the central axis of the bore, and the magnetic bodies 4 are made to face each other by an equal amount. Deploy. Similarly, in order to correct the Tesseral terms of the adjoint orders 1, 2, 3, and 4, the magnetic bodies 4 are arranged in equal amounts in the arrangements shown in FIGS. 4, 5, 6, and 7, respectively. The phase of the Tesseral term in the circumferential direction is mπ / 12 with respect to the adjoint order m by changing the arrangement shown in FIGS. 4 to 7 in steps of 15 ° in the circumferential direction.
It can be changed in units. Zonal term and each Tesse
The polynomial order and the output value of the ral term are adjusted by the mounting position on the slide plate 3 in the central axis direction and the amount of the magnetic body 4.

The mounting position and amount of the magnetic body 4 can be easily determined by using various mathematical programming methods based on the measured data of the magnetic field distribution, and magnetic field correction is performed until a predetermined uniform magnetic field is achieved. Be seen.

In the embodiment, the magnetic member mounting mechanism is composed of the groove-shaped member and the slide plate, but it is also possible to form a unitary structure of a hexagonal prism and dispose the magnet-shaped member inside the magnet. Further, the magnetic body attachment mechanism may be divided into 48 integer divisions, 72 equal divisions, or the like, which is an integral multiple of 24, and the larger the number of divisions, the more accurately the magnetic field can be corrected.

[0018]

According to the present invention, the correction of the Tesseral terms of the adjoint orders 3 to 4, which could not be conventionally corrected, can be performed easily with high accuracy and efficiently, and the phase position with high correction efficiency can be freely set. Can be selected.

Further, since the same magnetic body mounting mechanism is used regardless of the order of the expansion coefficient, the effective area inside the inner hole of the magnet device can be widened and the number of parts can be reduced. ..

Further, if the mounting member of the magnetic body mounting mechanism can be moved (slide) in the axial direction of the cylinder as in the embodiment, the mounting and removal of the magnetic body can be easily performed, so that the magnetic field correction work can be performed. Can be done efficiently.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a perspective view showing a configuration of a magnetic body attachment mechanism of FIG.

FIG. 3 is a diagram showing a circumferential arrangement of magnetic bodies for outputting a Zonal term.

FIG. 4 is a diagram showing a circumferential arrangement of magnetic bodies for outputting a Tesseral term of an adjoint order 1.

FIG. 5 is a diagram showing a circumferential arrangement of magnetic bodies for outputting a Tesseral term of an adjoint order 2.

FIG. 6 is a diagram showing a circumferential arrangement of magnetic materials for outputting a Tesseral term of an adjoint order 3.

FIG. 7 is a diagram showing a circumferential arrangement of magnetic bodies for outputting a Tesseral term of an adjoint order 4.

[Explanation of symbols]

 1 ... Magnet body 2 ... Groove member 3 ... Slide plate (mounting member) 4 ... Magnetic material

Claims (2)

[Claims] 1. A magnet device having a cylindrical magnet for generating a main magnetic field and a cylindrical magnetic body mounting mechanism for supporting a magnetic body for magnetic field correction arranged on the inner peripheral side of the magnet,
A magnet device, wherein the magnetic body mounting mechanism is equally divided into 24n (where n is an integer) in the circumferential direction. 2. The magnet device according to claim 1, wherein each of the divided mounting members of the magnetic body mounting mechanism is movable in the cylindrical axis direction.