JP2000357608A - Magnetic field generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small and lightweight magnetic field generator which can form a strong and uniform magnetic field of 1T or above stably with high accuracy for an MRI(magnetic resonance imaging) apparatus, an NMR(nuclear magnetic resonance for chemical analysis) apparatus, and an ESR(electron spin resonance for chemical analysis) apparatus. SOLUTION: Since a first field generating section 1 comprising a yokeless magnetic circuit 3 generating a strong field of Bg>=1T is disposed in the air gap of a second field generating section 10 having a structure where the uniformity of field can be regulated easily on the order of Bg<=0.2 T, a total field strength can be obtained in the air gap of the yokeless magnetic circuit 3. Since the uniformity of field is regulated at the second field generating section 10, a strong and uniform magnetic field of Bg>=1T can be obtained with high accuracy in the air gap of the yokeless magnetic circuit 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic field generator used for nuclear magnetic resonance, electron spin resonance, and the like, and more particularly to a yokeless magnetic field generator in which a required gap is formed and opposed to each other. A small and lightweight magnetic field generator that can arrange a magnetic field generator for a magnetic circuit to improve the uniformity of the strong magnetic field obtained by a yokeless magnetic circuit and obtain a strong magnetic field of 1T or more with high precision uniformity. About.

[0002]

2. Description of the Related Art Medical magnetic resonance tomography (MRI), nuclear magnetic resonance (NMR), and electron spin resonance (ESR) for chemical analysis are very powerful. An object of the present invention is to obtain a tomographic image of an object in a gap of a magnetic field generator that forms a strong magnetic field and to depict the properties of the tissue.

[0003] In the MRI apparatus, the gap needs to be large enough to allow a part or all of the subject to be inserted, and in order to obtain a clear tomographic image, usually, an imaging field of view in the gap is
It is required to form a stable and strong uniform magnetic field having an accuracy of 0.02 to 2.0 T and an accuracy of 1 × 10 ⁻⁴ or less.

[0004] As a magnetic field generator for an MRI apparatus capable of obtaining a high-precision uniform magnetic field, a pair of plate-shaped yokes are connected and supported by four cylindrical yokes so as to face each other with a predetermined gap formed. In addition, a configuration in which a pole piece is arranged together with a permanent magnet on the gap facing surface of each of a pair of plate-like yokes (actually 2-44483)
Has been put to practical use.

[0005]

Recently, in the MRI, NMR, and ESR systems, a configuration has been developed in which elements other than H such as P are to be searched. This requires a strong magnetic field of 1T or more.

[0006] The permanent magnet type using the pair of plate yoke
In magnetic field generators for MRI equipment, for example, 0.2T
In order to obtain 1T, a device having a weight of several tens to 100 tons is required for the configuration for obtaining the magnetic field, and a permanent magnet type magnetic field generating device for generating a strong magnetic field has not been put to practical use. Even in an NMR apparatus having a relatively small gap size, there is a problem that the apparatus becomes large and heavy in order to obtain a strong magnetic field.

An object of the present invention is to provide a magnetic field generator capable of forming a magnetic field of 1 T or more for use in an MRI apparatus, an NMR apparatus, and an ESR apparatus. It is an object of the present invention to provide a magnetic field generator capable of reducing the size and weight of the magnetic field generator.

[0008]

Means for Solving the Problems The inventors of the present invention have proposed various magnetic field generating sources and magnetic circuits for the purpose of providing a high-precision and stable uniform magnetic field having a magnetic field strength of 1 T or more in a required gap. As a result of the study, we focused on the fact that a magnetic field generator composed of a yokeless magnetic circuit in which permanent magnets were arranged in a cylindrical shape was compact and lightweight and could generate a strong magnetic field. It has been found that by arranging in a gap of a magnetic field generator using a columnar yoke, a highly accurate, stable and strong uniform magnetic field can be formed, and the device can be reduced in size and weight.

In other words, the magnetic field generator according to the present invention comprises a first magnetic field generator comprising a yokeless magnetic circuit having a high magnetic efficiency which forms most of the magnetic field in the air gap where the device to be measured is arranged, and a magnetic field in the air gap. It is characterized by comprising a second magnetic field generation unit having a structure that makes it easy to finely adjust the magnetic field uniformity.

[0010] Specifically, the magnetic field generator according to the present invention comprises:
For example, a first magnetic field comprising a yokeless magnetic circuit capable of generating a strong magnetic field of Bg ≧ 0.5 to 1T in an air gap of a second magnetic field generating section having a structure that can easily adjust the magnetic field uniformity of about Bg ≦ 0.2T. Since the relative permeability of the yokeless magnetic circuit substantially consisting of permanent magnets is close to 1 by arranging the generator, the magnetic field strength of the sum of both magnetic field generators is obtained in the air gap in the yokeless magnetic circuit. Can be In addition, by adjusting the magnetic field uniformity in the second magnetic field generating unit, a highly accurate uniform magnetic field and a strong magnetic field of Bg ≧ 1T can be obtained in the gap in the yokeless magnetic circuit. Further, since the yokeless magnetic circuit, which is a main magnetic field generating source, is small and light, the size and weight of the entire apparatus can be easily reduced.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of a magnetic field generator according to the present invention will be described in detail with reference to the drawings. The magnetic field generation device shown in FIG. 1 has a configuration in which the first magnetic field generation unit 1 is formed of a rectangular cylindrical yokeless magnetic circuit 3 and the first magnetic field generation unit 1 is disposed in the magnetic field generation gap 11 of the second magnetic field generation unit 10. Become.

The first magnetic field generating section 1 is a yokeless magnetic circuit 3 formed by combining a plurality of permanent magnets 2 having a triangular cross section into a quadrangular cylindrical shape, and has a magnetization direction as shown (in the direction of the arrow in the figure).
By combining the respective permanent magnets 2 having the above, an upward magnetic field is generated in the gap 4 in the yokeless magnetic circuit 3 in the figure. A gradient magnetic field coil 17 is arranged close to the upper and lower permanent magnets 2 in the gap 4.

The second magnetic field generating unit 10 has a configuration in which two plate yokes 12 are opposed to each other and connected by a columnar yoke 13, and a permanent magnet 14 is provided on the opposing surfaces of the upper and lower plate yokes 12. As shown in FIG.1B, the projections 15
The pole piece 16 having the following is mounted.

A feature of the magnetic field generator according to the present invention is that the yokeless magnetic circuit 3 constituting the first magnetic field generator 1 is composed of only permanent magnets and has a relative magnetic permeability of 1, that is, the same as the relative magnetic permeability in a vacuum. That is.

When assembling the yokeless magnetic circuit 3, or in the magnetic field generating gap 11 of the second magnetic field generating section 10, the first magnetic field generating section
Although a support material is appropriately used for disposing 1, the use of a magnetic material for holding impairs the above characteristics. That is, the relative magnetic permeability of the yokeless magnetic circuit 3 constituting the first magnetic field generation unit 1 becomes larger than 1, and the strength and uniformity of the magnetic field formed in the gap are disturbed. The above assembly
It is preferable to use a non-magnetic material for holding.

Considering the generation of eddy current by the gradient magnetic field coil, the above-mentioned support material is preferably a non-magnetic material and is preferably a non-metal, and most preferably FRP, bakelite, synthetic resin and the like. Further, when assembling the permanent magnet 2, it is preferable that the permanent magnet 2 is bonded and fixed with an adhesive made of an insulating resin and reinforced with the above-mentioned nonmetallic material.

In the above configuration, the first magnetic field generating unit 1 is disposed in the magnetic field generating gap 11 of the second magnetic field generating unit 10, and the gap 4 in the first magnetic field generating unit 1 is provided with the gap in which the object to be measured is disposed. Become. Here, the magnetic field generated by the magnetic circuit of the second magnetic field generation unit 10 is superimposed on the magnetic field generated by the yokeless magnetic circuit 3 having high magnetic efficiency that forms the majority of the magnetic field in the air gap 4, and a strong magnetic field is formed. .

It is difficult for the yokeless magnetic circuit 3 itself to adjust the uniformity of the magnetic field in the air gap 4 to the required accuracy, and in the magnetic circuit of the second magnetic field generating unit 10, the configuration and shape of the pole piece 16 The magnetic field is adjusted by adopting various known means such as selection, arrangement of permanent magnet pieces and other magnetic material pieces to the magnetic pole pieces 16 or the permanent magnets 14, for example, magnet pieces such as iron pieces, and the like. Uniformity can be obtained.

Therefore, as shown in FIG. 1, it is easier to adjust the magnetic field when the first magnetic field generator 1 and the second magnetic field generator 10 are separated from each other. Further, the gradient magnetic field coil 17 may be disposed in the gap 4 of the first magnetic field generator 1 as shown in the drawing,
Since the relative magnetic permeability of 1 is 1, it can be disposed between the first magnetic field generating section 1 and the second magnetic field generating section 10, which is preferable in securing a space in the gap 4.

The configuration of the magnetic field generator shown in FIG. 2 is similar to the configuration shown in FIG. 1 except that a yokeless magnetic circuit 5 constituting the first magnetic field generator 1 is provided between the pole pieces 16, 16 of the second magnetic field generator 10. And place
The configuration is such that a gradient magnetic field coil 17 is arranged close to each pole piece 16.

The pole piece 16 of the second magnetic field generator 10 includes the above-described FIG.
As shown in (1), a configuration in which projections are provided at both ends on the short side or long side of the plate-shaped magnetic pole piece, or a configuration in which annular projections are provided on the outer peripheral portion of the plate-shaped magnetic pole piece can be adopted.

The yokeless magnetic circuit 5 shown in FIG. 2 has a configuration in which permanent magnets 6 each having a trapezoidal cross section are combined to form an octagonal cylinder, and each of the permanent magnets 6 having a magnetization direction (the direction of the arrow in the figure) as shown in the figure. Generates an upward magnetic field in the air gap 7 in the yokeless magnetic circuit 5 in the figure.

In the magnetic field generator having the above configuration, most of the magnetic field in the gap 7 where the device under test is placed is a magnetic field generated by the yokeless magnetic circuit 5 having high magnetic efficiency.
The magnetic field of the second magnetic field generation unit 10 having a structure that can easily adjust the magnetic field uniformity that finely adjusts the internal magnetic field is applied, and a strong and highly accurate magnetic field of 1T or more is obtained.

[0024] In the present invention, the yokeless magnetic circuit constituting the first magnetic field generating section has a plurality of permanent magnets arranged so that the magnetization vectors form a closed circuit. Therefore, there is substantially no leakage magnetic flux to the outside. The same effect is obtained regardless of whether the second magnetic field generating section is in contact with or apart from the permanent magnet or the pole piece.

The configuration of the yokeless magnetic circuit is as described in the above-described diagram.
1, the configuration shown in a perspective view in FIG.
No. 940, US Pat. No. 4,994,777), and various other configurations can be employed. For example, a yokeless magnetic circuit (EPA 0467437A1) assembled by combining twelve triangular permanent magnets having a predetermined magnetization direction shown in FIG. 4 and forming a rectangular cylinder, which forms an air gap with a smaller magnetic field than the configuration of FIG. It is a magnetic circuit that is effective for

Also, in addition to the yokeless magnetic circuit having a configuration in which permanent magnets having a trapezoidal cross section having a predetermined magnetization direction shown in FIG. 2 are assembled and assembled in an octagonal cylindrical shape, in this configuration, as shown in FIG. A configuration in which the thickness of the magnets at both ends is increased (JP-A-3-82447) can also be employed.

In the present invention, the yoke (yoke) constituting the magnetic circuit of the second magnetic field generating section is employed in FIGS.
In addition to the configuration in which two plate-shaped yokes are opposed to each other and connected and supported by a cylindrical yoke, a configuration in which four plate-shaped yokes are combined to form a square tube or a hexagonal tube (Japanese Patent Application Laid-Open No. 5-326252) Any known configuration such as a configuration in which a vertical cross section opened on three sides is C-shaped (Japanese Patent Laid-Open No. 8-45729, etc.) can be adopted.

[0028] In short, the second magnetic field generating unit may have a configuration having a pair of magnetic field generating means opposed to each other with the first magnetic field generating unit interposed therebetween. Any type such as a wound electromagnet (including a normal magnet and a superconducting magnet) can be adopted.

When the intensity of the magnetic field generated by the second magnetic field generating unit is small and is adopted mainly for the purpose of adjusting the uniformity of the magnetic field, only an electromagnetic coil may be arranged as the magnetic field generating means. 1 and 2, it is also possible to arrange and use an electromagnetic coil around the outer periphery of the permanent magnet or the pole piece.

[0030]

Embodiment 1 The configuration shown in FIG. 1, that is, a magnetic field generator according to the present invention comprising a second magnetic field generator (configuration 2) and a yokeless magnetic circuit (configuration A), and a second magnetic field generator according to the present invention Only a comparative magnetic field generator (configuration 1) having the same configuration as the conventional
It was manufactured using an Nd-based permanent magnet.

The magnetic field generating device according to the present invention and the comparative device are as follows. The gap distance for inserting an object to be measured is 300 mm, the set magnetic field strength (Bg) in this gap is 1.0 T, and the center diameter is 10 mm.
Table 1 shows the total weight of the magnetic field generator manufactured by performing the magnetic field adjustment so that the magnetic field uniformity within 0 mm is almost equal.

The outer shape of the yokeless magnetic circuit is 600 × 600.
It is 00 x 600 mm in length. Therefore, the second magnetic field generator (Configuration 2)
The gap distance was set to 650 mm, a yokeless magnetic circuit was arranged in the gap distance, and the magnetic field of the second magnetic field generation unit was adjusted so that the magnetic field uniformity became 60 ppm.

[0033]

【table 1】

As is clear from Table 1, the conventional magnetic field generator has a device weight of 40 tons for obtaining 1.0T, whereas the magnetic field generator according to the present invention can be significantly reduced to 17.5 tons. I understand.

Embodiment 2 A magnetic field generator according to the present invention having the structure shown in FIG.
Fabricated using eB-Nd permanent magnet. The yokeless magnetic circuit of the first magnetic field generator has an outer diameter of 100 mm, a length of 80 mm, and a gap distance of 2
At 0 mm, Bg = 1.6T was generated. In addition, the second magnetic field generator for adjusting the magnetic field uniformity generated Bg = 0.05T by setting the pole piece facing distance to 120 mm. When the second magnetic field generating section was assembled in the configuration of FIG. 2 in which the first magnetic field generating section was arranged in the second magnetic field generating section and the magnetic field was adjusted, a magnetic field of 1.65 T and a center diameter of 5 mm were formed in the gap in the first magnetic field generating section. Within which a homogeneity of 20 ppm was obtained.

[0036]

According to the magnetic field generator of the present invention, the first magnetic field generator of the yokeless magnetic circuit having high magnetic efficiency, which forms the majority of the magnetic field in the gap in which the device under test is arranged, is used to reduce the magnetic field in the gap. Since the yokeless magnetic circuit is composed of only permanent magnets and has a relative magnetic permeability of 1 by being arranged in the second magnetic field generating section having a structure that makes it easy to adjust the uniformity of the magnetic field to be adjusted, the magnetic field in the air gap is equal to both magnetic fields. The sum of the magnetic fields generated by the generating units can be provided, and a device can be provided in which a strong magnetic field can be easily obtained.

According to the present invention, when the magnetic field strength of the required air gap is set to 1 T or more and the size and weight are reduced, the magnetic field strength formed by the second magnetic field generating part is less than 0.5 T, preferably 0.2 T
Below, the magnetic field strength formed by the first magnetic field generation part is 0.5T
As described above, preferably, by setting the magnetic field intensity formed by the first magnetic field generation unit to 1 T or more, it is possible to significantly reduce the size and weight as compared with the related art.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a configuration of a magnetic field generating device according to the present invention, wherein A shows an entire configuration, and B shows a pole piece configuration.

FIG. 2 is an explanatory diagram showing another configuration of the magnetic field generator according to the present invention.

FIG. 3 is a perspective explanatory view illustrating a configuration of a yokeless magnetic circuit.

FIG. 4 is a perspective explanatory view showing another configuration of the yokeless magnetic circuit.

FIG. 5 is a perspective explanatory view showing another configuration of the yokeless magnetic circuit.

[Explanation of symbols]

 1 First magnetic field generation part 2,6,14 Permanent magnet 3,5 Yokeless magnetic circuit 4,7 Air gap 10 Second magnetic field generation part 11 Magnetic field generation air gap 12 Plate yoke 13 Cylindrical yoke 14 Permanent magnet 15 Projection 16 Magnetic pole Piece 17 gradient magnetic field coil

Continued on the front page (72) Inventor Masaaki Aoki 2-15-17 Egawa, Shimamoto-cho, Mishima-gun, Osaka Sumitomo Special Metals Co., Ltd. Yamazaki Works F-term (reference) 4C096 AB32 AB42 AD08 CA05 CA07 CA16 CA24 CA58 CA70

Claims (8)

[Claims] A first magnetic field generating unit comprising a yokeless magnetic circuit that arranges a plurality of permanent magnets magnetized in a predetermined direction in a cylindrical shape and forms a magnetic field in a predetermined direction in a gap in the cylindrical permanent magnet; A magnetic field generator having a second magnetic field generator having a pair of magnetic field generators disposed at least outside the first magnetic field generator via the first magnetic field generator. 2. The magnetic field generation device according to claim 1, wherein the second magnetic field generation unit includes a magnetic circuit in which a pair of permanent magnets disposed to face each other via the first magnetic field generation unit. 3. The magnetic field generator according to claim 2, wherein a pole piece is arranged on each of the pair of permanent magnets on the side facing the first magnetic field generator. 4. The second magnetic field generator includes a pair of electromagnetic coils disposed to face each other with the first magnetic field generator interposed therebetween.
The magnetic field generator according to 1. 5. The magnetic field generator according to claim 1, wherein the second magnetic field generator includes a magnetic circuit having a pair of permanent magnets disposed to face each other via the first magnetic field generator and a pair of electromagnetic coils. 6. The magnetic field generator according to claim 1, wherein a gradient magnetic field coil is disposed between the first magnetic field generator and the second magnetic field generator. 7. The magnetic field generator according to claim 1, wherein a magnetic field intensity formed by the first magnetic field generation unit is 0.5T or more, and a magnetic field intensity formed by the second magnetic field generation unit is less than 0.5T. 8. The magnetic field generator according to claim 7, wherein a magnetic field intensity formed by the first magnetic field generation unit is 1T or more, and a magnetic field intensity formed by the second magnetic field generation unit is 0.2T or less.