JP2001070280A - Magnetic field generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic field generator improved in safety and intensity of the magnetic field. SOLUTION: A device main body 22 to be housed in a case includes a permanent magnet 24, and magnet blocks 26a and 26b are stood in both sides of the permanent magnet 24. The magnet block 26a includes a permanent magnet 28a formed on the magnet block 24, permanent magnets 30a, 32a and 34a formed on the permanent magnet 28a, and a permanent magnet 36a formed thereon. The magnet block 26b is similarly formed. A permanent magnet 38 is arranged so as to ride over the permanent magnets 36a and 36b. The permanent magnets 30a, 34a are arranged in both sides of the permanent magnet 32a, and the permanent magnets 30b and 34b are arranged in both sides of the permanent magnet 32b so as to form magnetic circuits (C1-C4) in addition to magnetic circuits B1 and B2.

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, and more particularly to a small permanent magnet type magnetic field generator for MRI used for examining a part of a body such as a finger or the contents of food.

2. Description of the Related Art In a conventional magnetic field generator for MRI of this type, a yoke is generally used to construct a magnetic circuit, so that the weight increases (for example, 1.4 tons). In view of the above, for example, a magnetic field generating device having a magnetic circuit composed of only a Halbach magnet has been proposed, as disclosed in Japanese Patent No. 2787509 and Japanese Patent No. 2596836.

[0002]

However, in this magnetic field generator, since magnetic flux leaks at the end of the magnetic circuit, there is a problem that the magnetic field intensity is reduced in the imaging area. Therefore, a main object of the present invention is to provide a magnetic field generator having an improved magnetic field strength.

[0003]

According to a first aspect of the present invention, there is provided a magnetic field generator comprising: a first magnetic circuit having a closed circuit formed by a magnet; and a magnetic flux direction of the first magnetic circuit. A second magnetic circuit configured by connecting a magnet magnetized in the orthogonal direction to a magnet constituting the first magnetic circuit, wherein magnetic fluxes generated by the first magnetic circuit and the second magnetic circuit are superimposed; Is what is done. In the magnetic field generation device according to the first aspect, a magnet having a magnetization direction different by 90 degrees is connected to a magnet constituting the first magnetic circuit to form a second magnetic circuit, which leaks from an end of the first magnetic circuit. The magnetic flux passes through the second magnetic circuit and is superimposed on the magnetic flux generated by the first magnetic circuit. Therefore, the magnetic flux can be concentrated on the imaging region, and the magnetic field intensity is improved.

[0004]

Embodiments of the present invention will be described below with reference to the drawings. Referring to FIG. 1, an MRI magnetic field generator 10 according to an embodiment of the present invention
And the like. Case 1
2 is a lower plate 14, a side plate 1 erected from both sides of the lower plate 14.
6a and 16b, and an upper plate 18 provided on the side plates 16a and 16b, each plate being connected by screws 20 such as hexagon screws.

[0005] The case 12 houses an apparatus main body 22. The dimensions of the apparatus main body 22 are set to, for example, about 210 mm in width × 260 mm in depth × 280 mm in height. Referring to FIG. 2, device main body 22 includes a permanent magnet 24 having a trapezoidal cross section mounted on lower plate 14. Permanent magnet 24
The magnet blocks 26a and 26b attached to the side plates 16a and 16b, respectively, are provided upright on both sides. The magnet block 26a includes a permanent magnet 28a having a trapezoidal cross section formed on the permanent magnet 24, and permanent magnets 30a, 32a, and 3 having a substantially rectangular parallelepiped shape formed on the permanent magnet 28a.
4a, trapezoidal permanent magnet 3 formed on them
6a. The magnet block 26b is also a magnet block 26.
Since it is formed in the same manner as a, the reference number “a” is replaced with “b”.
And a duplicate description will be omitted. And
The permanent magnet 38 attached to the upper plate 18 is
It is arranged so that it may straddle 6a and 36b. In this way, the apparatus main body 22 is formed in a substantially rectangular parallelepiped shape having the opening 37.

The direction of magnetization of each permanent magnet is indicated by an arrow in FIG. As can be seen from FIG. 2, when the direction of magnetization is also taken into consideration, the apparatus main body 22 includes the permanent magnets 24, 3
8, permanent magnets 28a, 36a, permanent magnets 28b, 3
6b, permanent magnets 30a, 30b, 34a, 34b (not shown), and permanent magnets 32a, 32b. Here, it should be noted that the magnetization directions of the permanent magnets 30a and 34a are orthogonal to the magnetization direction of the permanent magnet 32a, and similarly, the magnetization directions of the permanent magnets 30b and 34b are orthogonal to the magnetization direction of the permanent magnet 32b. That is. Further, in the apparatus main body 22, the magnetic flux flows from the magnetic pole plates 40b toward 40a.

In the apparatus main body 22, a pair of magnetic pole plates 40a and 40b are arranged with a gap G formed therein. Magnetic pole plate 4
0a and 40b are permanent magnets 32a and 3b, respectively.
2b, the interval between the pole plates 40a and 40b is set to, for example, approximately 60 mm. The magnetic pole plates 40a and 40b can improve the uniformity of the magnetic field in the gap G.

[0008] Such a magnetic field generator 10 is assembled as follows. With reference to FIG.
A subassembly 42a in which the magnet block 26a is fixed to the magnet block 6a with an adhesive or the like, and similarly, the magnet block 2 is attached to the side plate 16b.
A subassembly 42b with the 6b fixed, a subassembly 44 with the permanent magnet 38 fixed to the upper plate 18, and a subassembly with the permanent magnet 24 fixed to the lower plate 14 (not shown in FIG. 3). ) Are formed respectively. Then, the semi-assembled products 42a and 42b are fixed on the table 46 by fixtures 50a and 50b, respectively, with a spacer 48 made of a non-magnetic material interposed therebetween. Six holes 52 are formed in each of the side plates 16a and 16b, and guide pins 54 are attached to the holes 52 at both ends.

The subassembly 44 is connected to the subassemblies 42a and 42b arranged as described above. Six holes 56 corresponding to the holes 52 are formed on both sides of the upper plate 18, respectively. First, for example, four setscrews 58, two on each side of the upper plate 18, are passed through the holes 56 and screwed into the corresponding holes 52, and the subassembly 44 is positioned. Then, the upper plate 18 of the subassembly 44 is pressed in the direction of arrow A by the pusher 60. At this time, the sub-assembly 44 is gradually brought closer to the sub-assemblies 42a and 42b by tightening the set screw 58 little by little so that the sub-assembly 44 is not sucked all at once, and the position of the sub-assembly 44 is regulated. . When the pusher 60 is not used, the tension screw is screwed into the hole 52 further inside the hole into which the push screw 58 is screwed, and the subassembly 44 is gradually moved.

When the subassembly 56 comes into contact with the subassemblies 42a and 42b, the screws 20 are screwed into the holes 56 and 52 provided on both sides of the upper plate 18. Thereafter, the guide pin 54 and the push screw 58 are pulled out, the screw 20 is screwed into the holes 56 and 52, and the sub-assembly 44 is connected to the sub-assemblies 42a and 42b. Subassembly and subassembly 42a with permanent magnet 24 bonded to lower plate 14
The connection with the sub-assembly 44 may be made, for example, by rotating the table 42 by 180 degrees thereafter and in the same manner as in the case of the sub-assembly 44. In this way, the subassemblies 42a, 42
After b, 44, etc. are assembled, fixtures 50a and 5
Ob is removed, and the magnetic field generator 10 is completed. The magnetic field generator 10 can be easily assembled by the above-described method.

In the magnetic field generator 10, as shown in FIG. 4, the permanent magnets 32a → 36a → 38 → 36b → 32b
→ magnetic pole plate 40b → 40a → permanent magnet 32a, magnetic circuit B1, permanent magnet 32a → 28a → 24 → 28b → 3
The magnetic circuit B2 is formed in the path of 2b → pole plate 40b → 40a → permanent magnet 32a. Further, the permanent magnets 32a → 30a → 36a → 38 → 36b → 30b → 3
2b → pole plate 40b → 40a → permanent magnet 32a, magnetic circuit C1, permanent magnet 32a → 30a → 28a → 24
The magnetic circuit C2 is formed in the path of → 28b → 30b → 32b → pole plate 40b → 40a → permanent magnet 32a. Although not shown, similarly, the permanent magnets 32a → 34a
→ 36a → 38 → 36b → 34b → 32b → Pole plate 40
b → 40a → magnetic circuit C3 along the path of permanent magnet 32a, permanent magnet 32a → 34a → 28a → 24 → 28b → 34b
The magnetic circuit C4 is formed in the path of → 32b → pole plate 40b → 40a → permanent magnet 32a.

That is, the permanent magnets 30a and 34a are arranged on both sides of the permanent magnet 32a, and the permanent magnets 30b and 34b are arranged on both sides of the permanent magnet 32b.
a and 32b can be taken into the magnetic circuits C1 to C4, and can be taken into the magnetic circuit B1.
And B2 superimposed on the magnetic flux generated.

Therefore, according to the magnetic field generator 10,
The magnetic field strength between the magnetic pole plates 40a and 40b, that is, in the imaging region can be increased. The magnetic field strength between the pole plates 40a and 40b is, specifically, the permanent magnets 30a, 34a,
When there was no 30b and 34b, it was 0.66T, whereas the permanent magnets 30a, 34a, 30b and 34
By adding b and adding the magnetic circuits C1 to C4, it was possible to improve to 1.02T. Therefore, a clear captured image can be obtained.

Further, the apparatus main body 22 is constructed by combining permanent magnets having a simplified rectangular parallelepiped shape or a substantially trapezoidal cross section.
By forming the outer shape of the device main body 22 into a substantially rectangular parallelepiped shape, the assembling work becomes easier than before, and the cost can be reduced. Furthermore, since only five types of permanent magnets having different magnetization directions are sufficient as the permanent magnets to be used, the productivity can be improved as compared with the related art requiring many types of magnets.

Further, the magnetic field generator 10 does not use a yoke, so that it can be reduced in weight and can be more easily carried. Specifically, the weight of the device main body 22 is approximately 100 kg, the weight of the case 12 is approximately 60 kg, and the weight of the magnetic field generator 10 can be approximately 160 kg. Thus, the magnetic field generator 1
Since the weight of zero can be reduced, the magnetic field strength can be further increased by slightly increasing the amount of permanent magnet used.
Further, by surrounding the device main body 22 with the case 12, the strength of the magnetic field generator 10 can be improved and safety can be ensured.

The apparatus main body 22a as shown in FIG. 5 may be used. In the device main body 22a, the permanent magnets 24a to 24d are used instead of the permanent magnets 24 of the device main body 22 shown in FIG.
24c, permanent magnets 38a-38 instead of permanent magnets 38
By using c respectively, the magnetic flux flows smoothly,
The magnetic field strength in the imaging region is improved. Permanent magnet 24a
24c and 38a to 38c are shown in FIG.
Are indicated by arrows. For other configurations, the main unit 2
2, the description thereof is omitted.

When a magnetic field generator is constructed using the apparatus main body 22a, the same effect as that of the magnetic field generator 10 shown in FIG. 1 can be obtained. However, in the device body 22a, more types of permanent magnets must be prepared than in the case of the device body 22, but the leakage magnetic flux can be further reduced and the magnetic field strength can be further increased. Specifically, the magnetic field intensity between the pole plates 40a and 40b was able to be 1.12T. Note that case 12
Although aluminum is light and can reduce cost if it is made of Al, stainless steel is desirable if emphasis is placed on strength.
Case 12 may be made of any non-magnetic material. Also, openings 3 on the front and rear surfaces of the apparatus main bodies 22, 22a.
A cover made of a non-magnetic material may be provided on portions other than 7 to improve safety.

[0018]

According to the present invention, since the magnetic flux of the second magnetic circuit can be superimposed on the magnetic flux of the first magnetic circuit, the magnetic flux can be concentrated on the imaging area, and the magnetic field strength is improved.

[Brief description of the drawings]

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

FIG. 2 is a perspective view illustrating an example of an apparatus main body.

FIG. 3 is an illustrative view for explaining an assembling method of the embodiment in FIG. 1;

FIG. 4 is an illustrative view showing a magnetic circuit;

FIG. 5 is a perspective view showing another example of the apparatus main body.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Magnetic field generator 12 Case 22, 22a Device main body 24, 24a, 24b, 24c, 28a, 28b, 30
a, 30b, 32a, 32b, 34a, 34b, 36
a, 36b, 38, 38a, 38b, 38c Permanent magnet 40a, 40b Magnetic pole plate B1, B2, C1-C4 Magnetic circuit

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tsuyoshi Tsuzaki 2-15-17 Egawa, Shimamoto-cho, Mishima-gun, Osaka Prefecture Inside the Yamazaki Works, Sumitomo Special Metals Co., Ltd. (72) Akio Nakanishi 2 Egawa, Shimamoto-cho, Mishima-gun, Osaka F-term (reference) at Yamazaki Works, Sumitomo Special Metals Co., Ltd.

Claims (1)

[Claims] 1. A first magnetic circuit having a closed circuit formed by magnets, and a magnet magnetized in a direction orthogonal to a magnetic flux direction of the first magnetic circuit is connected to a magnet forming the first magnetic circuit. A magnetic field generator comprising: a second magnetic circuit configured by: a magnetic flux generated by each of the first magnetic circuit and the second magnetic circuit.