JP4816690B2 - Magnetic field generator for MRI - Google Patents

Description

  The present invention relates to a magnetic field generator for MRI, and more particularly to a magnetic field generator for MRI in which a permanent magnet group has a protruding portion protruding outward from a contact portion with a pole piece.

  Conventionally, in a permanent magnet type MRI magnetic field generator, each permanent magnet constituting a group of permanent magnets is bonded to an adjacent permanent magnet, a plate yoke, or both using an adhesive.

  However, according to such a configuration, when a mechanical load exceeding a normal design value is applied to the permanent magnet group due to vibration or impact during transportation of the magnetic field generator, the permanent magnets constituting the permanent magnet group are In some cases, the permanent magnets cannot be sufficiently held, and the permanent magnets are separated from the adjacent permanent magnets or plate yokes, and thus separated from the group of permanent magnets. In this case, the magnetic field uniformity of the MRI magnetic field generator cannot be maintained, and the magnetic field strength decreases.

Therefore, a technique of providing a molding material on the side surface of the permanent magnet group has been proposed (see, for example, Patent Document 1).
Moreover, the technique using the magnet cover which protects a permanent magnet group is proposed (for example, refer patent document 2).
Japanese Patent No. 2699250 JP-A-11-178808

  The technique of Japanese Patent No. 2699250 is effective in preventing the permanent magnet from being separated from the adjacent permanent magnet or plate yoke because the molding material directly holds the permanent magnet.

  However, in order to provide such a molding material, a mold frame composed of a plurality of members is provided at a predetermined position of the plate yoke to form a sealed space, and the molding material is filled in the space, and then the mold frame is formed. Need to be removed, which requires many steps.

  In addition, this technique can be applied to a magnetic field generator having a space for placing a mold around a group of permanent magnets, but cannot be applied to a magnetic field generator that does not have such a space. It was not a general-purpose technology that could be used for the device.

  In the technique of JP-A-11-178808, the permanent magnet group can be protected from the outside by a magnet cover arranged so as to cover the outer peripheral surface of the permanent magnet group, but between the magnet cover and the permanent magnet group. Since there is a gap and the permanent magnet group is not directly held by the magnet cover, it is impossible to prevent the permanent magnet from being separated from other permanent magnets and plate yokes in the magnet cover.

  Therefore, a main object of the present invention is to provide an MRI magnetic field generator that can be applied to various magnetic field generators and can prevent separation of permanent magnets constituting a permanent magnet group.

In order to achieve the above-mentioned object, an MRI magnetic field generator according to claim 1 includes a pair of permanent magnet groups each including a plurality of permanent magnets bonded to each other and arranged to face each other in a gap. , A yoke for magnetically coupling the pair of permanent magnet groups, and a pair of magnetic pole pieces provided on the respective gap side main surfaces of the pair of permanent magnet groups, In the MRI magnetic field generator configured to have a protruding portion that protrudes outward from the contact portion and generates a magnetic field in the gap between the pair of magnetic pole pieces, the permanent magnets arranged in the protruding portion are from the permanent magnet group. comprises a permanent magnet fixing member for preventing the disengagement, the permanent magnets solid constant-member, of the protrusions to connect between the permanent magnets part of an adjacent one of the plurality of permanent magnets which constitute the projecting portions Between a pair of permanent magnet groups arranged opposite to each other Wherein the part of the outer peripheral surface of a portion or the protruding portion of the surface facing the gap formed a plate-like member made of a nonmagnetic metal attached.

  The magnetic field generator for MRI according to claim 2 is the magnetic field generator for MRI according to claim 1, wherein the plate-like member extends to the yoke and is fixed.

  A magnetic field generator for MRI according to claim 3 is the magnetic field generator for MRI according to claim 1 or 2, further comprising a ring member surrounding a protrusion provided with a permanent magnet fixing member. And

  The magnetic field generator for MRI according to claim 4 is the magnetic field generator for MRI according to claim 3, further comprising a molding material filled in a space between the ring member and the protrusion. .

  In the magnetic field generator for MRI according to claim 1, by providing the permanent magnet fixing member, for example, even if vibration or impact occurs during transportation of the magnetic field generator for MRI, the permanent magnets constituting the permanent magnet group Can be prevented from separating from adjacent permanent magnets and plate yokes, that is, the permanent magnets can be prevented from separating from the permanent magnet group, and the magnetic field generator for MRI can be operated stably for a long period of time. Further, the permanent magnet fixing member can be used not only for a magnetic field generator to be provided in the future, but also for an existing magnetic field generator, and is suitable for reinforcing the magnetic field generator.

  Moreover, in the magnetic field generator for MRI according to claim 1, by using a plate-like member that connects a plurality of permanent magnets constituting the protruding portion as a member for fixing the permanent magnet, the MRI magnetic field generating device is provided at a place where the protruding portion is required. A plate-like member can be easily provided to reinforce the fixing of the permanent magnet.

  In the magnetic field generator for MRI according to the second aspect, the plate-like member extends to the yoke and is fixed, whereby the connection between the permanent magnet and the yoke can be strengthened and the permanent magnet can be more strongly fixed.

  In the magnetic field generator for MRI according to claim 3, by further providing a ring member surrounding the protruding portion, the permanent magnet can be prevented from falling off the magnetic field generator, and the permanent magnet group can be protected from the outside. Can do.

  In the magnetic field generator for MRI according to claim 4, the permanent magnets constituting the projecting portions of the permanent magnet group can be more firmly held by filling the molded body between the ring member and the projecting portions. .

According to the present invention, it is possible to prevent the permanent magnets from leaving the permanent magnet group.
The present invention can be applied not only to a magnetic field generator to be provided in the future, but also to an existing magnetic field generator.

Embodiments of the present invention will be described below with reference to the drawings.
Referring to FIG. 1, an MRI magnetic field generation apparatus 10 according to an embodiment of the present invention is an open type MRI magnetic field generation apparatus, and includes a pair of magnetic pole units 11a and 11b that are arranged to face each other while forming a gap. Including.

  The magnetic pole units 11a and 11b include plate yokes 12a and 12b, respectively. Permanent magnet groups 14a and 14b are arranged on the opposing surface sides of the pair of plate yokes 12a and 12b, and magnetic pole pieces 16a and 16b are fixed to the opposing surface sides of the permanent magnet groups 14a and 14b. .

  At this time, the outer peripheral portion of the permanent magnet group 14a protrudes outward from the contact portion with the magnetic pole piece 16a to form a protruding portion 18, and the outer peripheral portion of the permanent magnet group 14b is outward from the contact portion with the magnetic pole piece 16b. Protrusions 18 are formed to project.

  The height of the permanent magnet groups 14a and 14b is, for example, 100 mm. As shown in FIG. 2, the permanent magnet groups 14 a and 14 b are obtained by integrating a plurality of rectangular or cubic permanent magnets 20 by bonding. Further, the permanent magnets 20 constituting the permanent magnet group 14a are arranged so that the magnetization directions are the same direction, and the permanent magnets 20 constituting the permanent magnet group 14b are arranged so that the magnetization directions are the same direction. . In this embodiment, the permanent magnet 20 of the permanent magnet group 14a is arranged so that the air gap side is an N pole, and the permanent magnet 20 of the permanent magnet group 14b is arranged so that the air gap side is an S pole.

  For the permanent magnet 20, for example, a high magnetic flux density type R—Fe—B type magnet such as NEOMAX-47 (manufactured by Sumitomo Special Metal Co., Ltd.) is used, and the permanent magnet 20 is obtained by assembling a single magnet (not shown). .

  The pole piece 16a includes a disk-shaped base plate 22 made of, for example, iron and disposed on the permanent magnet group 14a. On the base plate 22, a silicon steel plate 24 for preventing the generation of eddy current is formed. The silicon steel plate 24 is fixed on the base plate 22 with an adhesive. An annular projection 26 made of, for example, iron and increasing the magnetic field strength of the peripheral portion to obtain a uniform magnetic field is formed on the peripheral portion of the base plate 22. The annular projection 26 includes, for example, a plurality of annular projection pieces, and the annular projection 26 is formed by fixing each annular projection piece to the peripheral edge portion of the silicon steel plate 24.

  The plate yokes 12 a and 12 b are magnetically coupled by a single plate-like support yoke 28. That is, the support yoke 28 is positioned such that the upper surface on one end edge side of the plate-like yoke 12a is located on the lower end surface of the support yoke 28, and the upper end surface of the support yoke 28 is located on the lower surface on one end edge side of the plate-like yoke 12b. Connected to the plate yokes 12a and 12b. Accordingly, the plate yokes 12a and 12b and the support yoke 28 are connected so that the connecting portion has an angle of approximately 90 degrees and is U-shaped in a side view.

Referring also to FIG. 3, the farthest position from the permanent magnet group 14 a on the inner surface side of the connecting portion between the plate-like yoke 12 a and the supporting yoke 28 (in this embodiment, the plate-like yoke 12 a and the supporting yoke 28. Reinforcing members 30 are respectively formed on both ends of the connecting portion on the inner surface side. Similarly, the position farthest from the permanent magnet group 14b on the inner surface side of the connecting portion between the plate yoke 12b and the supporting yoke 28 (in this embodiment, the inner surface of the connecting portion between the plate yoke 12b and the supporting yoke 28). Reinforcing members 30 are respectively formed at both ends of the side. Accordingly, the reinforcing member 30 fixes the plate yoke 12a and the support yoke 28, and the plate yoke 12b and the support yoke 28 more firmly.
Four leg portions 32 are attached to the lower surface of the plate yoke 12a.

In such a magnetic field generator 10, a magnetic field is generated in the gap between the magnetic pole pieces 16a and 16b, and a magnetic field strength of, for example, 0.2 T or more is required in the uniform magnetic field space F (see FIG. 1).
Such a magnetic field generator 10 includes a hook-shaped member 34 as shown in FIG. 3 as a permanent magnet fixing member.

  3, 5, 7, 8, and 10, the magnetic pole unit 11 b side is omitted. However, like the magnetic field generator 10 shown in FIG. 1, it has a vertically symmetrical structure with a gap in between. Needless to say. However, the permanent magnets 20 constituting the permanent magnet group 14a are arranged so as to have the magnetization direction A1, and the permanent magnets 20 constituting the permanent magnet group 14b are arranged so as to have the magnetization direction A2.

  As shown in FIG. 3, the hook-shaped member 34 is attached to the outer peripheral surface of the pole piece 16 a in a hook shape, and the gap-side surface 18 a (see FIG. 1) of the protrusion 18 is covered with the hook-shaped member 34. At the time of assembly, first, the pole piece 16a may be assembled on the permanent magnet group 14a, and then the flange member 34 may be attached to the outer peripheral surface of the pole piece 16a by welding or the like. The same applies to the magnetic pole unit 11b side.

  The bowl-shaped member 34 has a thickness of about 4 mm to 10 mm, and is preferably a nonmagnetic metal such as aluminum or stainless steel. Such a nonmagnetic metal has excellent strength and does not affect the magnetic field generated in the magnetic field generator 10. Further, when emphasizing suppression of the eddy current, the hook-shaped member 34 made of nonmagnetic metal is divided into a plurality of pieces, and an electric wire is provided between each hook-shaped member piece and the adjacent hook-shaped member piece and the pole piece 16a. Insulation may be achieved by disposing a material having high resistance or by forming a gap in each. Alternatively, it is preferable to use a material having a large electrical resistance, such as resin or ceramic, as the bowl-shaped member 34. The reinforcing material 38, the cover member 40, the plate-like members 42 and 44, and the ring member 46, which will be described later, are similarly configured with such thickness and material.

  According to such a magnetic field generator 10, even when a load exceeding the design value is applied to the bonded portion of the permanent magnet 20 due to an external impact or the like, the bowl-shaped member 34 holds the permanent magnet 20 from the air gap side surface 18a. In addition, it is possible to prevent the permanent magnet 20 from being separated from the adjacent permanent magnet 20 and the plate yokes 12a and 12b. Thus, by fixing the permanent magnet 20 with the hook-shaped member 34 in addition to fixing with the adhesive, the magnetic field generator 10 can be used stably for a long period of time.

  Further, by attaching the flange-shaped member 34 to the outer peripheral surfaces of the magnetic pole pieces 16a and 16b, the permanent magnet fixing member can be used even if there is no space on the surface of the plate yokes 12a and 12b on which the permanent magnet groups 14a and 14b are arranged. Can be used.

  Furthermore, if the hook-shaped member 34 is used, the permanent magnet fixing member can be attached to the magnetic field generator more easily (with fewer steps) than in the past. By attaching the hook-shaped member 34 to the magnetic pole pieces 16a and 16b in advance, the number of assembly steps can be further reduced.

In addition, you may perform the attachment operation | work of the collar-shaped member 34 as follows.
When the annular protrusions 26 of the magnetic pole pieces 16a and 16b are composed of a plurality of annular protrusion pieces, the hook-shaped member 34 is also divided in correspondence with each of the annular protrusion pieces, and the hook-shaped member is attached to each annular protrusion piece. After the pieces are attached, the annular protrusion pieces with the hook-like member pieces attached are arranged on the base plate 22 and assembled into an annular shape.

  Further, as shown in FIG. 4, the flange-shaped member 34 is formed so as to extend not only to the air gap side surface 18a in the protrusion 18 of the permanent magnet group 14a but also to the outer peripheral surface 18b and further to the upper surface of the plate yoke 12a. May be. The same applies to the permanent magnet group 14b side.

Then, as shown in FIG. 5, a belt-like member 36 may be used as a permanent magnet fixing member.
As the belt-like member 36, for example, a flexible metal belt is used, and a nonmagnetic metal such as stainless steel is preferable. Such a nonmagnetic metal has excellent strength and does not affect the magnetic field generated in the magnetic field generator 10. Moreover, when importance is attached to suppression of eddy current, it is desirable to use a nonmetal such as polyester fiber. The strength can be further improved by adding glass fiber or carbon fiber to the nonmetal. Further, for example, it is desirable that the band-shaped member 36 has a thickness of 0.1 mm to 1.0 mm and a width of 90 mm, and is wound around the outer peripheral surface 18b of the protrusion 18 in multiple layers. Further, the belt-like member 36 may be one or plural.

By winding such a belt-shaped member 36 around the outer peripheral surface 18b of the protrusion 18, the fixation of the permanent magnet 20 can be reinforced.
Moreover, in any magnetic field generator in which the outer peripheral surface 18b of the protruding portion 18 is exposed, the belt-like member 36 can be easily attached to the outer peripheral surface 18b of the protruding portion 18.

  In addition, when the outer peripheral surface 18b of the protrusion part 18 is uneven | corrugated shape, the permanent magnet 20 which the fixing force of the strip | belt-shaped member 36 does not reach can arise. Therefore, as shown in FIG. 6, all the permanent magnets constituting the outer peripheral portion 18 b of the protruding portion 18 by inserting the reinforcing member 38 between the belt-like member 36 and the permanent magnet 20 (permanent magnet group 14 a). 20 can be firmly fixed.

  The shape of the reinforcing member 38 is preferably a shape that fills the gap between the belt-like member 36 and the permanent magnet 20 that constitutes the protrusion 18, but the belt-like member 36 is a permanent that constitutes the protrusion 18 of the permanent magnet group 14 a. Any shape can be used as long as the force for holding the magnet 20 can be increased.

  Further, as shown in FIG. 7, a cover member 40 may be used as a permanent magnet fixing member. The cover member 40 is shaped along the protrusion 18. The cover member 40 is preferably fixed to the plate yoke 12a with a screw or the like, and may be divided into a plurality of parts in the circumferential direction in consideration of assembly efficiency.

  By using the cover member 40, it is possible to fix all the surfaces (the gap side surface 18 a and the outer peripheral surface 18 b) of the permanent magnet 20 that constitutes the protruding portion 18. The cover member 40 is more easily manufactured and effective as the protrusion 18 has a simple shape.

  As shown in FIGS. 8 and 9A, a plate-like member 42 that connects the plurality of permanent magnets 20 to the air gap side surface 18a and the outer peripheral surface 18b of the protrusion 18 is provided as a permanent magnet fixing member. It may be attached. By bonding the plurality of permanent magnets 20 with the plate-like member 42, it is possible to prevent one of the permanent magnets 20 from separating from the adjacent permanent magnets 20. In addition, the magnitude | size of a plate-shaped member may be arbitrary, for example, it may be cyclically | annularly formed in the said space | gap side surface 18a so that the space | gap side surface 18a of the protrusion part 18 may wrap around.

  Further, as shown in FIGS. 8 and 9B, for example, an L-shaped plate-like member 44 extending from the permanent magnet 20 to the upper surface of the plate yoke 12a may be used. In this case, the permanent magnet 20 can be more strongly fixed by connecting the permanent magnet 20 to the plate yoke 12a, and the permanent magnet 20 can be prevented from being separated from the plate yoke 12a.

Furthermore, since such plate-like members 42 and 44 can be easily attached to a necessary portion of the protrusion 18, the fixation of the permanent magnet 20 can be easily reinforced.
The same applies to the magnetic pole unit 11b side.

  The saddle-shaped member 34, the band-shaped member 36, the reinforcing member 38, the cover member 40, and the plate-shaped members 42 and 44 are the same as the permanent magnet 20, the adjacent permanent magnet 20, the plate yokes 12a and 12b, or both of them. It is also effective as a means for reinforcing a magnetic field generator that is not provided with a measure for separation from the device, and can be used for general purposes.

Furthermore, as shown in FIG. 10 and FIG. 11A, a ring member 46 may be disposed so as to cover the protruding portion 18 to which the flange-shaped member 34 is attached.
By using such a ring member 46, it is possible to prevent the permanent magnet 20 from falling off the magnetic field generator 10, and it is possible to protect the permanent magnet group 14a from the outside. In consideration of assembly efficiency and the like, the ring member 46 may be divided into a plurality of parts in the circumferential direction.

Moreover, as shown in FIG.11 (b), if the molding material 48 is filled in the ring member 46, the force which hold | maintains the permanent magnet 20 which comprises the protrusion part 18 of the permanent magnet group 14a will be made still stronger. Can do.
The same applies to the magnetic pole unit 11b side.

  In consideration of thermal demagnetization of the permanent magnet 20, the molding material 48 needs to have a temperature during the curing reaction of 100 ° C. or lower, more preferably 60 ° C. or lower. Specifically, urethane foam is used. preferable. Urethane foam is cured at room temperature and is excellent in terms of workability and economy, and is effective for reinforcing existing magnetic field generators.

  Needless to say, the ring member 46 and the molding material 48 shown in FIGS. 10 and 11 can also be applied to the embodiment using the belt-like member 36, the reinforcing material 38, or the plate-like members 42 and 44.

  Moreover, although the above-mentioned embodiment described the case where a yoke is formed by a pair of plate-like yokes 12a and 12b and one supporting yoke 28, it is not limited to this, and a pair of permanent magnet groups 14a and 14b. For example, a C-shaped integrated yoke may be used.

It is a schematic side view which shows the magnetic field generator for MRI to which this invention is applied. It is a perspective view which shows an example of a permanent magnet group. It is a fragmentary perspective view which shows an example of embodiment which attached the bowl-shaped member. It is an illustration figure which shows the modification of a bowl-shaped member. It is a fragmentary perspective view which shows an example of embodiment which attached the strip | belt-shaped member. It is an illustration figure which shows the state which inserted the reinforcing material in the clearance gap between a strip | belt-shaped member and a protrusion part. It is a fragmentary perspective view which shows an example of embodiment which attached the cover member. It is a fragmentary perspective view which shows an example of embodiment which attached the plate-shaped member. It is an illustration figure for demonstrating a plate-shaped member. It is a fragmentary perspective view which shows an example of embodiment which attached the ring member. (A) is an illustration figure which shows an example of embodiment which attached the ring member, (b) is an illustration figure which shows an example of embodiment which filled the molding material in the ring member.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 MRI magnetic field generator 11a, 11b Magnetic pole unit 12a, 12b Plate-like yoke 14a, 14b Permanent magnet group 16a, 16b Magnetic pole piece 18 Protruding part 18a Air gap side surface of protruding part 18b Outer peripheral surface of protruding part 20 Permanent magnet 28 Support Yoke 34 bowl-shaped member 36 band-shaped member 38 reinforcing material 40 cover member 42, 44 plate-shaped member 46 ring member 48 molding material

Claims (4)

A pair of permanent magnet groups each including a plurality of permanent magnets bonded to each other and forming an air gap; a yoke for magnetically coupling the pair of permanent magnet groups; A pair of magnetic pole pieces provided on the respective gap side principal surfaces of the permanent magnet group, and the permanent magnet group is configured to have a protruding portion protruding outward from a contact portion with the magnetic pole piece, In the magnetic field generator for MRI that generates a magnetic field in the gap between the pair of magnetic pole pieces,
A permanent magnet fixing member for preventing the permanent magnet disposed in the protruding portion from being detached from the permanent magnet group;
The permanent magnet fixing member is a pair of permanent magnets that are arranged opposite to each other in the projecting portion in order to connect a part of the permanent magnets among the plurality of permanent magnets constituting the projecting portion . A magnetic field generator for MRI, which is a plate-like member made of a non-magnetic metal that is attached to a part of a surface facing the gap formed therebetween or a part of an outer peripheral surface of the protrusion.   The magnetic field generator for MRI according to claim 1, wherein the plate-like member extends and is fixed to the yoke.   The magnetic field generator for MRI according to claim 1, further comprising a ring member surrounding the protruding portion provided with the permanent magnet fixing member.   The magnetic field generator for MRI according to claim 3, further comprising a molding material filled in a space between the ring member and the protrusion.

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