JP4813645B2 - Magnetic pole unit, method for assembling the same, and magnetic field generator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic pole unit, an assembling method thereof, and a magnetic field generator, and more particularly, to a magnetic pole unit, an assembling method thereof, and a magnetic field generator used in an MRI apparatus that requires a strong magnetic field exceeding 0.3T. .
[Prior art]
In this type of large magnetic field generator, such as an MRI magnetic field generator, in order to prevent the leakage of magnetic flux from the magnetic pole plates and to concentrate the magnetic flux effectively in the gap between the magnetic pole plates, the applicant has applied Japanese Utility Model No. 2-49683. As shown in the above, a configuration has been proposed in which a permanent magnet for repelling leakage magnetic flux is provided on the outer surface of the annular protrusion.
[0002]
[Problems to be solved by the invention]
When a strong magnetic field is required in this prior art, an R—Fe—B magnet having a strong magnetic force is used as a permanent magnet. In this case, another permanent magnet to be bonded to the already bonded permanent magnet. A strong repulsive force works when the is moved closer. Therefore, it is difficult to bond the permanent magnet to the annular projection formed as a single body, and there is a problem that productivity is poor.
Further, in the above-described prior art, the magnetization direction of the permanent magnet for repelling leakage magnetic flux is parallel to the main surface of the permanent magnet for generating a magnetic field. There is a problem that the cost is increased.
[0003]
Furthermore, although the above-described conventional technology can improve the magnetic field generation efficiency, it is expensive because it uses a bow-shaped leakage magnetic flux repulsion magnet, and the cost cannot be reduced.
Therefore, a main object of the present invention is to provide a magnetic pole unit, an assembling method thereof, and a magnetic field generator capable of improving productivity.
Another object of the present invention is to provide a magnetic field generator capable of increasing the uniform space without increasing the cost.
Furthermore, another object of the present invention is to provide a magnetic field generator capable of reducing the cost by using a relatively inexpensive permanent magnet for preventing leakage magnetic flux.
[0004]
[Means for Solving the Problems]
  In order to achieve the above object, a magnetic pole unit according to claim 1 is provided on a plate yoke, a permanent magnet group for generating a magnetic field provided on a main surface of the plate yoke, and a main surface of the permanent magnet group. The magnetic pole plate includes an annular projection including a plurality of annular projection pieces and a permanent magnet for preventing leakage magnetic flux provided on the outer surface of each annular projection piece.The outer surface of the annular projecting piece is formed in a flat shape, the inner surface of the annular projecting piece is curved in an arc shape, and the permanent magnet for preventing leakage magnetic flux has a square shape.Is.
  A magnetic field generator according to a second aspect includes the pair of magnetic pole units according to the first aspect and a columnar yoke that magnetically couples the pair of magnetic pole units.
  According to a third aspect of the present invention, there is provided a magnetic pole unit assembling method for preventing a leakage magnetic flux provided on a base plate, an annular projection including a plurality of annular projection pieces fixed to the main surface of the base plate, and an outer surface of each annular projection piece. A method for assembling a magnetic pole unit including a permanent magnet, wherein a first step of fixing the permanent magnet to the outer surface of the annular projection piece and a second step of fixing the annular projection piece to which the permanent magnet is fixed to the main surface of the base plate With stepsThe outer surface of the annular projecting piece is formed in a flat shape, the inner surface of the annular projecting piece is curved in an arc shape, and the permanent magnet for preventing leakage magnetic flux has a square shape..
[0005]
  The method for assembling the magnetic pole unit according to claim 4 is the method for assembling the magnetic pole unit according to claim 3, wherein the annular projecting piece has a guide hole, and the second step is a step A for attaching the guide bar to the base plate. And a step B in which the guide hole is passed through the guide rod and the annular projection piece to which the permanent magnet is fixed is guided to the main surface of the base plate..
[0007]
  ContractClaim5The magnetic field generator described in 1 includes a plate-shaped yoke, a permanent magnet group for generating a magnetic field provided on the main surface of the plate-shaped yoke, and a magnetic pole plate provided on the main surface of the permanent magnet group. Each of the annular projection pieces and a permanent magnet for preventing leakage magnetic flux provided on the outer side surface of each annular projection piece. The outer side surface of the annular projection piece is formed in a flat shape, The permanent magnet for preventing leakage magnetic flux has an angular shape, and the magnetization direction of the permanent magnet for preventing leakage magnetic flux is perpendicular to the outer surface of the annular protrusion.
  Claim6The magnetic field generator described in 1 includes a plate-shaped yoke, a permanent magnet group for generating a magnetic field provided on the main surface of the plate-shaped yoke, and a magnetic pole plate provided on the main surface of the permanent magnet group. Each of the annular projection pieces and a permanent magnet for preventing leakage magnetic flux provided on the outer side surface of each annular projection piece. The outer side surface of the annular projection piece is formed in a flat shape, The permanent magnet for preventing magnetic flux leakage is curved in a circular arc shape, and the permanent magnet for preventing magnetic flux leakage is drawn from the annular projection piece.
  Claim7The MRI apparatus according to claim 2, whereinAnd 6The magnetic field generator described in any of the above is used.
  Claim8The method for assembling the magnetic pole unit described in 1) includes a base plate, an annular protrusion including a plurality of annular protrusions fixed to the main surface of the base plate, and a permanent magnet for preventing leakage magnetic flux provided on the outer surface of each annular protrusion. A first step of fixing the permanent magnet to the outer surface of the annular projection piece, and a second step of fixing the annular projection piece to which the permanent magnet is fixed to the main surface of the base plate. The annular projection piece has a guide hole, and the second step is a step A for attaching the guide rod to the base plate, and the annular projection piece with the permanent magnet fixed to the main surface of the base plate by passing the guide hole through the guide rod. Step B to guide is included.
[0008]
In the magnetic pole unit according to the first aspect, the permanent magnet is fixed in advance to the outer surface of each annular projection piece, and a predetermined number of the annular projection pieces in that state may be assembled. There is no need to attach a permanent magnet to the annular projection. Therefore, the assembly of the magnetic pole unit is facilitated, and the productivity of the magnetic pole unit can be improved. The same applies to the method of assembling the magnetic pole unit according to the third aspect.
In the magnetic field generator according to claim 2, the magnetic field generator can be easily obtained by using the magnetic pole unit according to claim 1, which is easy to assemble, and productivity is improved.
[0009]
  In the method of assembling the magnetic pole unit according to claim 4, the annular projection piece can be guided to a desired position on the base plate by passing the guide hole of the annular projection piece through the guide rod attached to the base plate. Easy positioning and easy assembly of magnetic pole unit.
[0010]
  NaIn this specification, the “magnetization angle of the permanent magnet for preventing leakage magnetic flux” refers to an angle formed between the main surface of the permanent magnet group and the magnetization direction of the permanent magnet for preventing leakage magnetic flux. “Uniform space” refers to a magnetic field space in which the degree of uniformity of the magnetic field falls within 100 ppm. “Center magnetic field strength” refers to the magnetic field strength in the central portion of the uniform space.
[0011]
  Claim5In the magnetic field generator described in 1), the magnetization direction of the permanent magnet for preventing leakage magnetic flux only needs to be perpendicular to the outer surface of the annular projection piece. It is possible to use a normal permanent magnet that is easily magnetized and whose direction is parallel or perpendicular to each surface. Therefore, since a relatively inexpensive permanent magnet can be used, the manufacturing cost can be reduced.
  Claim6In the magnetic field generator described in 1), a space for forming a heat insulating material for heat-shielding the magnetic circuit can be secured by retracting the permanent magnet for preventing leakage magnetic flux from the annular projection piece, and the living space of the subject can be secured. The feeling of pressure can be reduced without damage.
  If such a magnetic field generator is used, a useful MRI apparatus can be obtained without increasing the cost.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
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, and includes a pair of magnetic pole units 11a and 11b that are opposed to each other so as to form a gap. The magnetic pole units 11a and 11b include plate yokes 12a and 12b, respectively. The plate-like yoke 12a has a substantially disc-shaped main body portion 14a and two coupling portions 16a and 18a extending from the main body portion 14a. Similarly, the plate-like yoke 12b has a substantially disc-shaped main body portion 14b and two coupling portions 16b and 18b extending from the main body portion 14b.
[0013]
Permanent magnet groups 20a and 20b are arranged on the opposing surfaces of the main body portion 14a of the plate yoke 12a and the main body portion 14b of the plate yoke 12b, and the opposing surfaces of the permanent magnet groups 20a and 20b. On the side, the magnetic pole plates 22a and 22b are fixed.
As shown in FIG. 2, the permanent magnet group 20 b includes a plurality of magnet units 24 each having a rectangular parallelepiped shape made of, for example, an R—Fe—B magnet. The same applies to the permanent magnet group 20a.
The magnetic pole plate 22b includes a disk-shaped base plate 26 made of, for example, iron disposed on the permanent magnet group 20b. A silicon steel plate 28 for preventing the generation of eddy current is formed on the base plate 26. The silicon steel plate 28 is fixed on the base plate 26 with an adhesive.
[0014]
An annular projection 32 made of, for example, iron and for increasing the magnetic field strength of the peripheral portion is formed on the peripheral portion of the base plate 26. As shown in FIG. 3, the annular protrusion 32 includes a plurality (eight in this embodiment) of annular protrusions 34. Each annular projecting piece 34 has an inner surface curved in an arc shape and an outer surface formed in a flat shape, and each annular projecting piece 34 is fixed to the peripheral edge of the silicon steel plate 28 with a screw 36 to form an annular shape. A protrusion 32 is formed. In this way, the annular protrusion 32 is formed by dividing radially. The annular protrusion 32 is formed with two guide holes 38 for assembly penetrating in the vertical direction. A female screw into which a later-described screw 92 is screwed is formed on the inner surface of the guide hole 38.
[0015]
A permanent magnet 40 for preventing leakage magnetic flux is formed on the outer surface of each annular projection piece 34. The permanent magnet 40 can induce a magnetic flux between the magnetic pole plates 22a and 22b to reduce the leakage magnetic flux. As shown in FIG. 4, the permanent magnet 40 includes a plurality of rectangular parallelepiped magnets 42 made of, for example, an R—Fe—B magnet. In this embodiment, 2 × 2 × 4 = 16 magnets 42. Are stacked to form a rectangular permanent magnet 40. In addition, the through-hole 44 is formed by notching the corner | angular part of the magnet single-piece | unit 42. FIG.
As can be seen from FIG. 5, a pressing plate 46 made of a non-magnetic material such as SUS304 or aluminum is formed on the outer surface of the permanent magnet 40 formed on the outer surface of the annular projection piece 34. The permanent magnet 40 and the pressing plate 46 are fixed to the annular projecting piece 34 by a fixing screw 48 so as to be disposed and inserted through the through hole 44. Further, as can be seen from FIGS. 2 and 5, the lower part of the permanent magnet 40 extends until the bottom part of the permanent magnet 40 comes into contact with the permanent magnet group 20 b so that the magnetic flux does not leak from the bottom part of the permanent magnet 40. Is desirable. The same applies to the magnetic pole plate 22a.
[0016]
  As shown in FIGS. 3 and 5, the magnetization direction A of the permanent magnet 40 is set perpendicular to the outer surface of the annular projection piece 34. Therefore, the permanent magnet 40, that is, the magnet alone 42, is square and has a magnetization direction parallel or perpendicular to each surface.MagnetismEasy normal permanent magnets can be used. Since such a relatively inexpensive and easily available permanent magnet can be used, the device can be easily manufactured and the manufacturing cost can be reduced. The magnetization direction A shown in FIG. 3 and FIG. 5 indicates the magnetization direction in the lower magnetic pole plate 22b, and the magnetization direction in the upper magnetic pole plate 22a is outwardly opposite to the magnetization direction A.
[0017]
Returning to FIG. 1, a movable yoke 50 for fine adjustment of the magnetic field is arranged at the center of the plate yoke 12a. The position of the movable yoke 50 is adjusted by the three bolts 52 and the position is regulated by the three stoppers 54. The plate yoke 12b is also formed in the same manner. A screw hole 56 for attaching a lifting hook is formed in each of the connecting portions 16a and 18a of the plate yoke 12a.
The plate yokes 12a and 12b are magnetically coupled by two columnar column yokes 58. At this time, the columnar yoke 58 is disposed between the coupling portions 16a and 16b and between the coupling portions 18a and 18b, and is fixed to the coupling portions 16a and 18a of the plate-shaped yoke 12a by the fixing bolt 60. Connected and fixed respectively. Moreover, the leg part 62 is each attached to the position corresponding to the two columnar yokes 58 among the lower surface front part of the plate-shaped yoke 12b, and the lower surface of the plate-shaped yoke 12b.
[0018]
Next, an assembly process of the permanent magnet 40 and the presser plate 46 to the annular projection piece 34 in the magnetism generator 10 will be described with reference to FIG.
First, the annular projection piece 34 is fixed on the work table 64 by the fixing screw 66 so that the outer surface thereof faces upward. A positioning jig 68 made of a plate-like and non-magnetic member is erected on the work table 64 so as to abut on the terminal portion of the outer surface serving as the magnet fixing surface of the annular protrusion 34. The positioning jig 68 is fixed to the work table 64 with screws (not shown), for example. On the other hand, a slide base 70 is connected to the start end of the outer surface of the annular protrusion piece 34. The outer surface of the annular projecting piece 34 and the upper surface of the slide table 70 are substantially flush with each other.
[0019]
The first magnet block 72 is arranged on the slide table 70. The magnet block 72 is formed by laminating and bonding 2 × 2 × 2 = 8 magnet single bodies 42 shown in FIG. In a state where such a magnet block 72 is firmly held by the holding portion 74, the arm 76 is pushed out from the slide base 70 onto the outer surface of the annular projection piece 34, and slides on the annular projection piece 34 to be positioned. It abuts on the jig 68 and stops.
[0020]
At this time, since the annular projection piece 34 is made of soft iron, the magnet block 72 is strongly attracted to the annular projection piece 34. Then, the first magnet block 72 is strongly adsorbed and is pushed up by a screw 78 screwed from the lower part of the work table 64, and an adhesive is applied to the gap between the annular projection piece 34 and the magnet block 72. The Thereafter, the annular projection piece 34 and the magnet block 72 are bonded together by turning in the direction in which the screw 78 is pulled out. Next, the second magnet block 72 is also firmly held by the holding portion 74 in the same manner, and is pushed out by the arm 76 toward the outer surface of the annular protruding piece 34 and stopped before the fixed position. Then, an adhesive is applied to the final fixing position on the annular protrusion piece 34 and the side surface of the first magnet block 72. Thereafter, the second magnet block 72 is pushed out and fixed to the final fixing position by the arm 76. If a repulsive force is generated between the already fixed magnet block 72 and the magnet block 72 to be fixed and the magnet block 72 to be fixed is lifted, an air cylinder is formed above the holding portion 74. (Not shown) may be provided to press the magnet block 72 downward. In this way, the magnet block 72, that is, the permanent magnet 40 is fixed to the outer surface of the annular projecting piece 34. At this time, since the outer side surface of the annular projecting piece 34 is flat, the magnet block 72 can be easily slid linearly with respect to the outer side surface. Therefore, the magnet block 72 can be easily transported and fixed at a desired position on the outer surface of the annular projecting piece 34.
Thereafter, the presser plate 46 is disposed on the upper surface of the magnet block 72 and attached by a fixing screw 48.
[0021]
Next, the assembly process of the magnetic pole plate 22b will be described with reference to FIG.
First, as shown in FIG. 7A, a guide bar 80 is screwed into the base plate 26 of the magnetic pole plate 22b in advance. Next, the guide hole 38 of the annular projection piece 34 is passed through the guide rod 80, and the annular projection piece 34 to which the permanent magnet 40 is attached is lowered onto the guide plate 26. If a repulsive force is generated between the annular projection piece 34 and the annular projection piece 34 that cannot be lowered easily, a male screw is formed on the guide rod 80 and the guide rod 80 is screwed. A nut (not shown) to be joined may be disposed on the annular protrusion 34, and the annular protrusion 34 may be lowered by tightening the nut. The lowered annular protrusion 34 is fixed on the base plate 26 by screws 36. Thereafter, the guide rod 80 is removed.
[0022]
As shown in FIG. 7B, the assembly order of the annular projecting pieces 34 is such that every other annular projecting piece 34 is attached, and further, as shown in FIG. The annular protrusions 34 are respectively attached between the annular protrusions 34 formed. At this time, since a considerably strong repulsive force is generated, it is desirable to tighten with screws.
The magnetic pole plate 22b assembled in this way is fixed on the permanent magnet group 20b using, for example, an elevator 82 as shown in FIG. The elevator 82 includes an elevator 84 made of a non-magnetic material such as SUS304. The elevator 84 can be moved up and down by the rotation of a screw-type drive shaft 88 standing on the base 86. A turntable 90 is disposed on the base 86, and a plate yoke 12b and a permanent magnet group 20b are disposed thereon. The magnetic pole plate 22 b is suspended by a screw 92 that passes through the lifting platform 84. At this time, the screw 92 is screwed into the guide hole 38 of the magnetic pole plate 22b. Then, the pole plate 22b is disposed on the permanent magnet group 20b by lowering the elevator 84, and is fixed on the permanent magnet group 20b by screws (not shown). The same applies to the pole plate 22a side.
[0023]
As described above, according to the magnetic field generator 10, the permanent magnet 40 is fixed to the outer surface of each annular projection piece 34 in advance, and a predetermined number of the annular projection pieces 34 in that state may be assembled on the base plate 26. Therefore, unlike the prior art, it is not necessary to attach the permanent magnet 40 to the annular protrusion 32 disposed on the base plate 26. That is, the permanent magnet 40 can be easily fixed by dividing the annular protrusion 32. As a result, even when a strong magnetic field is required and an R—Fe—B magnet is used as a single magnet, assembly of the magnetic pole units 11a and 11b and the magnetic field generator 10 is facilitated, and productivity is improved.
[0024]
Further, since the annular projection piece 34 can be guided to a desired position on the base plate 26 by passing the guide hole 38 of the annular projection piece 34 through the guide rod 80, the positioning of the annular projection piece 34 is facilitated.
For such a magnetic field generator 10 and the conventional example, a magnetic circuit was configured such that a 0.4 T magnetic field was generated in the gap between the magnetic pole plates. As a result, in the conventional example that does not use the permanent magnet 40 for preventing leakage magnetic flux, the amount of permanent magnet used increases as the leakage magnetic flux increases, and a 4.9-ton permanent magnet is required. On the other hand, in the magnetic field generator 10, since the leakage magnetic flux can be reduced by using the permanent magnet 40, it can be realized by a permanent magnet of 3.9 tons. Therefore, according to the magnetic field generator 10, the usage-amount of a permanent magnet can be decreased and cost can be reduced.
[0025]
Next, referring to FIG. 9, an MRI magnetic field generation apparatus 100 according to another embodiment of the present invention includes a pair of magnetic pole units 102 a and 102 b that are opposed to each other so as to form a gap. The magnetic pole units 102a and 102b include plate yokes 104a and 104b, respectively.
Permanent magnet groups 106a and 106b are arranged on the opposing surface sides of the plate yokes 104a and 104b, and magnetic pole plates 108a and 108b are fixed to the opposing surface sides of the permanent magnet groups 106a and 106b. .
Each of the permanent magnet groups 106a and 106b includes, for example, a plurality of cube-shaped magnets 110 made of R-Fe-B magnets and having a side of 50 mm, and the magnets 110 are stacked in three stages.
[0026]
The magnetic pole plate 108a includes a disk-shaped base plate 112 made of, for example, iron and disposed on the main surface of the permanent magnet group 106a. A silicon steel plate 114 for preventing generation of eddy current is formed on the main surface of the base plate 112. The silicon steel plate 114 is fixed on the base plate 112 with an adhesive.
An annular projection 116 made of, for example, iron and used to increase the magnetic field strength of the peripheral portion is formed on the peripheral portion of the base plate 112. The annular protrusion 116 is formed in the same manner as the annular protrusion 32 described above, and is formed by, for example, a plurality of annular protrusion pieces 34 as shown in FIG.
[0027]
A permanent magnet 118 for preventing leakage magnetic flux is formed on the outer surface of the annular protrusion 116, that is, each annular protrusion piece 34. The permanent magnet 118 can induce a magnetic flux between the magnetic pole plates 108a and 108b to reduce the leakage magnetic flux. The permanent magnet 118 is formed in a square shape by laminating a plurality of rectangular parallelepiped magnets made of, for example, R-Fe-B magnets. What should be noted here is the magnetization direction A1 of the permanent magnet 118. As shown in FIG. 9, the permanent magnet 118 is formed such that the magnetization direction A <b> 1 intersects the main surface 120 of the permanent magnet 118 at an acute angle. Therefore, each magnet constituting the permanent magnet 118 is similarly formed such that its magnetization direction intersects the main surface of the magnet alone at an acute angle. By disposing such a permanent magnet 118 so as to contact the main surface of the permanent magnet group 106a and the outer peripheral surfaces of the base plate 112 and the annular protrusion 116, the permanent magnet 118 is fixed to the main surface of the permanent magnet group 106a. The magnetization direction A1 can be tilted. For example, the above-described presser plate 46 is disposed on the outer surface of the permanent magnet 118. In this case, the permanent magnet 118 and the presser plate 46 are fixed to the annular projecting piece 34 with a fixing screw or the like. The same applies to the magnetic pole plate 108b.
[0028]
The permanent magnet 118 is retracted from the annular protrusion 116, that is, each annular protrusion piece 34. Thereby, a space for forming the heat insulating material 121 for heat shielding the magnetic circuit can be secured, and the feeling of pressure can be reduced without impairing the living space of the subject. In FIG. 9, a part of the heat insulating material 121 is illustrated in order to avoid complication of the drawing.
The plate yokes 104a and 104b are magnetically coupled by two columnar column yokes 58, as in the magnetic field generator 10 shown in FIG. At this time, the plate yokes 104a and 104b and the columnar yoke 58 are connected and fixed by, for example, fixing bolts.
[0029]
Here, the magnet simple substance used for the permanent magnet 118 is manufactured, for example using the press apparatus 200 as shown in FIG.
The press device 200 includes a pair of opposing yokes 202 (only one is shown in FIG. 10). A coil 204 is arranged around the yoke 202. A magnetic field is generated by energizing the coil 204.
Between the pair of yokes 202, a die 206 made of a nonmagnetic material or a weak magnetic material is provided. A plurality of through holes 208 having a square cross section extending in the vertical direction are formed in the die 206. The direction of the through hole 208 is inclined by the magnetization angle θ with respect to the orientation direction B by the yoke 202.
[0030]
  A die set 210 is disposed between the pair of yokes 202 with a die 206 interposed therebetween. Further, the base plate 212 is disposed so as to sandwich the die 206 and the die set 210 and to be orthogonal to the orientation direction B. Here, the upper surfaces of the die 206, the die set 210, and the base plate 212 are flush with each other. Further, a powder supply box 214 storing powder is disposed on the base plate 212 so as to be able to advance and retreat in the direction of the die 206.
  In such a press apparatus 200, a molded body is obtained by pressing powder with a prismatic upper punch and a lower punch (not shown) in the through hole 208, and further sintered.Its magnetization direction is relative to its main surfaceAngle θMeet atA magnet alone is obtained. A method of making a magnet is disclosed in US Pat. No. 4,770,723.
[0031]
Next, an experimental example using the magnetic field generator 100 will be described.
Here, the thickness T1 of the permanent magnet groups 106a and 106b is 150 mm, the total thickness T2 of the base plate 112 and the silicon steel plate 114 is 65 mm, the height H1 of the annular protrusion 116 is 64 mm, the thickness T3 is 65 mm, and the height of the permanent magnet 118 H2 was 80 mm, thickness T4 was 120 mm, inner diameter D1 of annular protrusion 116 was 855 mm, outer diameter D2 was 983 mm, and distance d between magnetic pole plates 108a and 108b was 405 mm. A uniform space is formed between the magnetic pole plates 108a and 108b, shaped like a sphere crushed in the vertical direction.
[0032]
  First, in the magnetic field generation device 100, the magnetization angle θ of the permanent magnet 118 was changed, and the horizontal diameter D3 of the uniform space and its central magnetic field strength were measured.
  From FIG. 11A, it can be seen that the uniform space increases as the magnetization angle θ of the permanent magnet 118 increases. Thus, magnetizationDirection A1By arranging the permanent magnet 118 so that the magnetic field is inclined with respect to the main surfaces of the permanent magnet groups 106a and 106b, more magnetic flux can be guided to the imaging space, and the uniform space can be enlarged. Therefore, the uniform space can be enlarged without increasing the usage amount of the permanent magnet 118 and without increasing the cost. Further, by adjusting the magnetization angle θ, a desired uniform space and central magnetic field strength can be obtained.
[0033]
Next, in the magnetic field generator 100, the diameters of the magnetic pole plates 108a and 108b and the thickness of the annular protrusion 116 are set according to the change in the magnetization angle θ of the permanent magnet 118 so that the diameter D3 in the horizontal direction of the uniform space is constant. At the same time, the central magnetic field strength was measured. The permanent magnet groups 106a and 106b are constant.
As described above, as the magnetization angle θ is increased, the uniform space is expanded. Therefore, in order to make the diameter D3 of the uniform space constant, the dimensions of the magnetic pole plates 108a and 108b are increased according to the increase of the magnetization angle θ of the permanent magnet 118. What is necessary is just to make small, and this can raise the magnetic field intensity in a space | gap. Therefore, when the use efficiency of the permanent magnet 118 is improved and a magnetic field having the same strength is generated, the amount of magnet use corresponding to the increase in the magnetic field strength can be reduced, so that the cost can be reduced and the magnetic field generator 100 can be lightened. it can.
[0034]
  From FIG. 11B, the magnetization angle θ is 0 degree.Bigger and60 degreesLess thanIf so, it can be seen that the above-mentioned central magnetic field strength can be obtained when the magnetization angle θ = 0 °. In particular, if the magnetization angle θ is in the range of 10 degrees to 50 degrees, the central magnetic field strength is 0.42 T or more, and a stronger magnetic field is obtained. Further, the magnetization angle θ is preferably within a range of 15 degrees to 45 degrees.
  Further, from the other experimental results shown in FIG. 12, when the central magnetic field strength and the distance d between the magnetic pole plates 108a and 108b are constant, if the magnetization angle θ is set to 30 degrees, the total magnet weight can be 2313 kg, and the magnetization angle It can be seen that the total magnet weight can be reduced by 100 kg compared to when θ = 0 degrees, and by 610 kg compared with when no permanent magnet 118 is provided. In this case, the diameter D3 of the uniform space is 400 mm.
  Furthermore, since a magnet whose magnetization direction A1 is inclined in advance is used as the permanent magnet 118, it is easy to simply place the permanent magnet 118 directly on the main surface of the permanent magnet group 106a, 106b.Permanent magnet 118 for preventing magnetic flux leakageHaving the desired magnetization angle θlikeCan be placed.
[0035]
Further, a magnetic field generator 100a as shown in FIG. 13 may be used.
In the magnetic field generator 100a, a magnet whose magnetization direction A2 is parallel or perpendicular to each surface of the permanent magnet 124 is used as the permanent magnet 124 for preventing leakage magnetic flux included in the magnetic pole plates 122a and 122b. In this case, the permanent magnet 124 is disposed in a state where the magnetization direction A2 of the permanent magnet 124 is inclined with respect to the main surfaces of the permanent magnet groups 106a and 106b using the trapezoidal members 126 and 128. The other configuration is the same as that of the magnetic field generator 100 shown in FIG.
[0036]
According to the magnetic field generator 100a, the permanent magnet 124 itself is inclined with respect to the main surfaces of the permanent magnet groups 106a and 106b. Therefore, as a permanent magnet for preventing leakage flux, a permanent magnet having an arbitrary magnetization direction, in particular, a normal permanent magnet whose magnetization direction is parallel or perpendicular to each surface of the permanent magnet can be used. Magnets can be easily obtained. Also, the magnetic field generator 100a can obtain the same effects as the magnetic field generator 100.
In addition, the outer peripheral surface of the annular protrusion 116 may be inclined, and the permanent magnets 118 and 124 for preventing leakage magnetic flux may be attached to the outer peripheral surface. In this case, the same effect as the magnetic field generator 100 can be obtained.
[0037]
The magnetic field generator as described above can be applied to an MRI apparatus 300 as shown in FIG. Here, the case where the magnetic field generator 10 shown in FIG. 1 is used will be described.
Referring to FIG. 14, an MRI apparatus 300 obtains a tomographic image of a subject 302 using a magnetic resonance (NMR) phenomenon, and includes a magnetic field generator 10 having a necessary and sufficient size, a center A processing device (hereinafter referred to as a CPU) 304, a sequencer 306, a transmission system 308, a gradient magnetic field generation system 310, a reception system 312 and a signal processing system 314 are included.
The magnetic field generator 10 generates a uniform magnetic flux around the subject 302 in the body axis direction or in a direction perpendicular to the body axis.
[0038]
The sequencer 306 is operated by the control of the CPU 304, and sends various commands necessary for collecting tomographic image data of the subject 302 to the transmission system 308, the gradient magnetic field generation system 310, and the reception system 312.
The transmission system 308 includes a high-frequency oscillator 316, a modulator 318, a high-frequency amplifier 320, and a transmission-side high-frequency coil 322b. The high-frequency pulse output from the high-frequency oscillator 316 is amplitude-modulated by the modulator 318 in accordance with an instruction from the sequencer 306, and the amplitude-modulated high-frequency pulse is amplified by the high-frequency amplifier 320 and then placed close to the subject 302. By being supplied to the high-frequency coil 322b, the object 302 is irradiated with electromagnetic waves.
[0039]
The gradient magnetic field generation system 310 includes gradient magnetic field coils 324a and 324b wound in three directions of X, Y, and Z, and a gradient magnetic field power source 326 that drives the respective coils. The gradient magnetic field power supply 326 of each coil is driven in accordance with a command from the sequencer 306, whereby gradient magnetic fields Gx, Gy, and Gz in three directions of X, Y, and Z are applied to the subject 302. The slice plane for the subject 302 can be set by adding the gradient magnetic fields Gx, Gy, and Gz.
The high-frequency coil 322b and the gradient magnetic field coil 324b are disposed on the main surface of the silicon steel plate 28 of the magnetic pole plate 22b (see FIG. 2). Similarly, the high-frequency coil 322a (described later) and the gradient magnetic field coil 324a are The silicon steel plate 28 is disposed on the main surface.
[0040]
The reception system 312 includes a reception-side high-frequency coil 322a, an amplifier 328, a shifter 330, a quadrature detector 332, and an A / D converter 334. The subject 302 is irradiated with electromagnetic waves from the high-frequency coil 322b on the transmission side, and a response electromagnetic wave (NMR signal) from the subject 302 is detected by the high-frequency coil 322a disposed close to the subject 302, and the amplifier 328, The signal is input to the A / D converter 334 via the shifter 330 and the quadrature detector 332 and converted into a digital quantity. At this time, the A / D converter 334 samples the two series of signals output from the quadrature detector 332 at the timing according to the command from the sequencer 306, and outputs the two series of digital signals. Those digital signals are sent to the signal processing system 314 and subjected to Fourier transform.
[0041]
The signal processing system 314 includes a CPU 304, a recording device such as a magnetic disk 334 and a magnetic tape 336, and a display 338 such as a CRT. The digital signal is used to perform processing such as Fourier transform, correction coefficient calculation, image reconstruction, etc., and a signal intensity distribution of an arbitrary cross section or a distribution obtained by performing an appropriate operation on a plurality of signals is imaged, and a display 338 is obtained. Is displayed.
If the magnetic field generator 10 is used, a useful MRI apparatus 300 can be obtained without increasing the cost.
Note that the magnetic field generator 100 shown in FIG. 9 and the magnetic field generator 100a shown in FIG. 13 may be applied to the MRI apparatus 300. In this case, the same effect as when the magnetic field generator 10 is used can be obtained.
[0042]
【The invention's effect】
  According to the present invention, the permanent magnet can be easily fixed, and the magnetic pole unit and thus the magnetic field generator can be easily assembled. In addition, by making the outer surface of the annular projection piece flat, it is easy to transport the permanent magnet, and the magnetic pole unit can be easily assembled. Therefore, the productivity of the magnetic pole unit and the magnetic field generator is improved.
  Magnetization of permanent magnets for preventing leakage magnetic fluxdirectionBy arranging the permanent magnets for preventing leakage magnetic flux so as to be inclined with respect to the main surface of the permanent magnet group, more magnetic flux can be guided to the imaging space, and the uniform space can be enlarged. Therefore, the uniform space can be enlarged without increasing the amount of permanent magnets used and without increasing costs.
  Furthermore, since the magnetization direction of the permanent magnet for preventing leakage magnetic flux only needs to be perpendicular to the outer surface of the annular projection piece, a relatively inexpensive permanent magnet can be used and the manufacturing cost can be reduced.
  Moreover, by retracting the permanent magnet for preventing leakage magnetic flux from the annular protrusion, a space for forming the heat insulating material can be secured, and the feeling of pressure can be reduced without impairing the living space of the subject.
  If such a magnetic field generator is used, a useful MRI apparatus can be obtained without increasing the cost.
[Brief description of the drawings]
FIG. 1 is a perspective view schematically showing an embodiment of the present invention.
FIG. 2 is an illustrative view showing a main part of a magnet unit.
FIG. 3 is a plan view showing a magnetic pole plate.
FIG. 4 is a perspective view showing a permanent magnet.
FIG. 5A is a perspective view showing an annular projecting piece to which a permanent magnet is attached, and FIG. 5B is a plan view thereof.
FIG. 6 is an illustrative view showing a step of attaching a permanent magnet to the annular projecting piece.
7A is an illustrative view showing a method of attaching an annular projection piece on a base plate, and FIGS. 7B and 7C are illustrative views showing an attachment order of the annular projection piece. FIG.
FIG. 8 is an illustrative view showing a method of attaching a magnetic pole plate on the permanent magnet group.
FIG. 9 is an illustrative view showing an outline of another embodiment of the present invention.
FIG. 10 is an illustrative view showing one example of a press apparatus.
11A is a graph showing the relationship between the magnetization angle, the central magnetic field strength, and the uniform space diameter, and FIG. 11B is a graph showing the magnetization angle, the central magnetic field strength, and the uniform magnetic field when the uniform space diameter is constant. It is a graph which shows the relationship.
FIG. 12 is a table showing a comparative example of the total magnet weight when the central magnetic field strength and the distance between the magnetic pole plates are constant.
FIG. 13 is an illustrative view showing an outline of another embodiment of the present invention.
FIG. 14 is a block diagram showing an example of an MRI apparatus.
[Explanation of symbols]
10, 100, 100a Magnetic field generator
11a, 11b, 102a, 102b Magnetic pole unit
12a, 12b, 104a, 104b Plate yoke
20a, 20b, 106a, 106b Permanent magnet group
22a, 22b, 108a, 108b, 122a, 122b Pole plate
24, 42, 110 Magnet alone
26, 112, 212 Base plate
32, 116 annular projection
34 Annular protrusion
38 Guide hole
40, 118, 124 Permanent magnet
58 columnar yoke
80 guide bar
120 Main surface of permanent magnet
300 MRI system
A, A1, A2 Magnetization direction
θ Magnetization angle

Claims (8)

Plate yoke,
A permanent magnet group for generating a magnetic field provided on the main surface of the plate-shaped yoke, and a magnetic pole plate provided on the main surface of the permanent magnet group,
The magnetic pole plate includes an annular protrusion including a plurality of annular protrusions and a permanent magnet for preventing leakage magnetic flux provided on an outer surface of each annular protrusion;
The outer surface of the annular projection piece is formed in a planar shape,
The inner surface of the annular projection piece is curved in an arc shape,
The magnetic pole unit, wherein the permanent magnet for preventing leakage magnetic flux has a square shape. A magnetic field generator comprising: a pair of magnetic pole units according to claim 1; and a columnar yoke that magnetically couples the pair of magnetic pole units. A magnetic pole unit assembly method comprising: a base plate; an annular protrusion including a plurality of annular protrusions fixed to the main surface of the base plate; and a permanent magnet for preventing leakage magnetic flux provided on an outer surface of each annular protrusion. There,
A first step of fixing the permanent magnet to an outer surface of the annular projection piece; and a second step of fixing the annular projection piece to which the permanent magnet is fixed to the main surface of the base plate,
The outer surface of the annular projection piece is formed in a planar shape,
The inner surface of the annular projection piece is curved in an arc shape,
The method for assembling a magnetic pole unit, wherein the permanent magnet for preventing leakage magnetic flux has a square shape. The annular projection piece has a guide hole,
The second step includes a step A in which a guide bar is attached to the base plate, and a step B in which the guide hole is passed through the guide bar to guide the annular projecting piece to which the permanent magnet is fixed to the main surface of the base plate. The method of assembling the magnetic pole unit according to claim 3, comprising: Plate yoke,
A permanent magnet group for generating a magnetic field provided on the main surface of the plate-shaped yoke, and a magnetic pole plate provided on the main surface of the permanent magnet group,
The magnetic pole plate includes an annular protrusion including a plurality of annular protrusions and a permanent magnet for preventing leakage magnetic flux provided on an outer surface of each annular protrusion;
The outer surface of the annular projection piece is formed in a planar shape,
The inner surface of the annular projection piece is curved in an arc shape,
The permanent magnet for preventing leakage magnetic flux has a square shape,
The magnetic field generator in which the magnetization direction of the permanent magnet for preventing leakage magnetic flux is perpendicular to the outer surface of the annular projection piece. Plate yoke,
A permanent magnet group for generating a magnetic field provided on the main surface of the plate-shaped yoke, and a magnetic pole plate provided on the main surface of the permanent magnet group,
The magnetic pole plate includes an annular protrusion including a plurality of annular protrusions and a permanent magnet for preventing leakage magnetic flux provided on an outer surface of each annular protrusion;
The outer surface of the annular projection piece is formed in a planar shape,
The inner surface of the annular projection piece is curved in an arc shape,
The permanent magnet for preventing leakage magnetic flux has a square shape,
The magnetic field generator which draws in the permanent magnet for the said magnetic flux leakage prevention from the said annular protrusion piece. Using a magnetic field generator according to any of the claims 2, 5 and 6, MRI device. A magnetic pole unit assembly method comprising: a base plate; an annular protrusion including a plurality of annular protrusions fixed to the main surface of the base plate; and a permanent magnet for preventing leakage magnetic flux provided on an outer surface of each annular protrusion. There,
A first step of fixing the permanent magnet to an outer surface of the annular projection piece; and a second step of fixing the annular projection piece to which the permanent magnet is fixed to the main surface of the base plate,
The annular projection piece has a guide hole,
The second step includes a step A in which a guide bar is attached to the base plate, and a step B in which the guide hole is passed through the guide bar to guide the annular projecting piece to which the permanent magnet is fixed to the main surface of the base plate. A method for assembling the magnetic pole unit.

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