JP6046560B2 - Magnet apparatus and magnetic resonance imaging apparatus - Google Patents

Description

  The present invention relates to a magnet apparatus and a magnetic resonance imaging apparatus (hereinafter referred to as an MRI (Magnetic Resonance Imaging) apparatus) including the magnet apparatus.

  An MRI apparatus uses a nuclear magnetic resonance phenomenon that occurs when an object is placed in an imaging space in which a uniform static magnetic field is formed and the object is irradiated with a high-frequency pulse. Can be obtained. This image is mainly used for medical purposes. From the viewpoint of the direction of the static magnetic field, the MRI apparatus can be roughly classified into a horizontal type in which the direction is in the horizontal direction and a vertical type in which the direction is in the vertical direction. In the former horizontal MRI apparatus, there is an imaging space in a tunnel penetrating in the horizontal direction, and the subject enters the tunnel for examination. For this reason, a subject may receive a feeling of pressure. On the other hand, in the latter vertical MRI apparatus, since an imaging space is formed between a pair of magnetic poles arranged opposite to each other, and the subject enters between the magnetic poles, You can feel open. For this reason, the vertical MRI apparatus is also referred to as an open MRI apparatus.

  In order to take advantage of the features of the vertical MRI apparatus and open a large space around the subject, the shape of the yoke connected to the pair of magnetic poles is C-shaped or U-shaped (for example, patents) Reference 1 etc.). In the present specification, the C-shape or U-shape refers to a shape in which a part of a substantially annular shape is cut open. However, when a C-shaped or U-shaped yoke is used, the distribution of the magnetic material including the yoke as viewed from the imaging space is biased, so that the static magnetic field in the imaging space tends to be non-axisymmetric, and in the imaging space. The magnetic field strength of the static magnetic field tends to be non-uniform. Therefore, in Patent Document 1, the C-shaped or U-shaped yoke has a structure in which the thickness of the pair of upper and lower horizontal portions extending in the horizontal direction is reduced toward the distal end side, so that the C-shape in the imaging region is obtained. Alternatively, the magnetic field strength on the U-shaped opening side and the column side is adjusted.

JP 2005-168772 A

  The vertical MRI apparatus includes a magnet device in order to generate a uniform static magnetic field in the imaging space. And the permanent magnet and the superconducting coil are used for the magnet apparatus. Generally, a permanent magnet is used if the magnetic field strength required in the imaging space is less than 0.5T, and a superconducting coil is used if it is 0.5T or more.

  In addition to the magnetic field strength and the magnetic field uniformity, important parameters of the magnet device for the MRI apparatus include the size of the region where the leakage magnetic field spreads. As a measure of the size of the area where the leakage magnetic field spreads, it is common to use the size of the space required until the magnetic field strength is attenuated to 0.5 mT. It is necessary to suppress the leakage magnetic field to such an extent that the size of this space is made smaller than the room where the MRI apparatus is installed. If the magnetic field intensity in the imaging space is 1.0 T or less, the leakage magnetic field can be suppressed to such an extent by arranging only a magnetic material such as iron. When the magnetic field intensity exceeds 1T, a magnetic material of several tens of tons is required to suppress the leakage magnetic field by arranging only the magnetic material, and it is not practical to suppress the leakage magnetic field by arranging the magnetic material. In this case, the leakage magnetic field can be suppressed by using a superconducting coil called a shielding coil.

  In summary, in a vertical MRI apparatus in which the magnetic field strength in the imaging space is within a range of 0.5 T or less, a permanent magnet is used as a magnetic pole for generating a static magnetic field, and a leakage magnetic field is suppressed. A magnetic material can be used. Specifically, an iron yoke can be used as the magnetic body. In addition, in a vertical MRI apparatus that is in the range of 0.5 T or more and 1.0 T or less, a superconducting coil is used separately from the magnetic pole for the generation of a static magnetic field, and the leakage magnetic field is suppressed. A magnetic material can be used separately from the magnetic material of the magnetic pole.

  In Patent Document 1, since a superconducting coil and a continuous iron yoke with a small gap are used, a static magnetic field having a high magnetic field strength can be generated while suppressing a leakage magnetic field. Furthermore, a method for reducing the non-axial symmetry of the magnetic field by reducing the thickness of the horizontal portion of the C-shaped or U-shaped yoke toward the tip side is described.

  However, there is non-axisymmetric property that cannot be corrected by the method of adjusting the thickness of the tip of the horizontal portion of the yoke. That is, with respect to the circumferential angle of the vertical axis passing through the center of the imaging region, when the C-shaped or U-shaped column side is set to 0 degrees and the C-shaped or U-shaped opening side is set to 180 degrees, 0 degrees and 180 degrees are set. Even if a mechanism for aligning the strength of the magnetic field in the direction of degrees with the thickness of the tip side of the horizontal portion of the yoke is used, this mechanism does not match the strength of the magnetic fields in the directions of 0 degrees, 90 degrees, and 270 degrees. Can not.

  Further, in Patent Document 1, when the thickness of the tip of the horizontal portion of the yoke is reduced, for example, the upper horizontal portion has a shape in which the outer surface of the horizontal portion is convex downward, that is, a concave shape when viewed from above. The indented shape is the basic shape. Such a convex shape toward the lower side of the outer surface causes the magnetic flux flowing in the vertical upward direction to be sharper toward the C-shaped or U-shaped column side than the convex shape toward the upper side. Since it is bent, the distance that the magnetic field on the opening side of the C-shaped or U-shaped flow in the vertically upward direction is shortened, and therefore the imaging area that requires a uniform magnetic field is reduced.

  Therefore, the problem to be solved by the present invention is to provide a magnet device that can reduce non-axial symmetry of a static magnetic field and improve uniformity. Moreover, it is providing the MRI apparatus which mounts this.

In order to solve the above problems, the present invention provides:
A pair of substantially disk-shaped magnetic poles arranged opposite to each other;
A yoke that is C-shaped or U-shaped in a side view, and that both ends of the C-shaped or U-shaped are arranged close to the magnetic poles,
The yoke has a yoke-side facing portion facing the magnetic pole in the vicinity;
The yoke side facing portion is
A central zone region including a portion of a vertical symmetry plane that substantially bisects the yoke;
Having both side band regions located on both sides of the central band region away from the vertical symmetry plane;
In height from the yoke side facing surface facing in proximity to the magnetic pole of the yoke-side facing portion, the central strip region is magnet apparatus that is higher than the two side zones.
And this invention is characterized by the said center belt | band | zone area | region being near the outer periphery of the said magnetic pole compared with the said both-sides belt | band | zone area | region. Alternatively, the present invention is characterized in that the distance from the yoke-side facing portion to the outer periphery of the magnetic pole continuously decreases as the distance from the tip of the yoke-side facing portion approaches.

The present invention also provides this magnet device,
A bed for transporting a subject between a pair of magnetic poles;
The magnet apparatus is an MRI apparatus that generates a uniform static magnetic field between the pair of magnetic poles to form an imaging space.

  According to the present invention, since the magnetic flux flowing through the magnetic pole to the yoke-side facing portion has a directional component toward the vertical symmetry plane, the non-axial symmetry of the static magnetic field is reduced while suppressing the leakage magnetic field. It is possible to provide a magnet apparatus that can improve uniformity and an MRI apparatus equipped with the magnet apparatus. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

1 is a perspective view of a magnetic resonance imaging apparatus (MRI apparatus) according to a first embodiment of the present invention. It is the longitudinal cross-sectional view which cut | disconnected the magnet apparatus which concerns on the 1st Embodiment of this invention by the vertical symmetry plane. It is a top view of the magnet apparatus which concerns on the 1st Embodiment of this invention. It is the longitudinal cross-sectional view which cut | disconnected the upper half of the magnet apparatus which concerns on the 1st Embodiment of this invention with the plane orthogonal to a vertical symmetry plane and a horizontal symmetry plane. It is a top view of the magnet apparatus which concerns on the 1st Embodiment of this invention, and is the figure which showed the flow of the produced magnetic flux. It is the longitudinal cross-sectional view which cut | disconnected the upper half of the magnet apparatus which concerns on the 1st Embodiment of this invention with the plane orthogonal to a vertical symmetry plane and a horizontal symmetry plane, and is the figure which showed the flow of the generated magnetic flux. It is the longitudinal cross-sectional view which cut | disconnected the upper half of the magnet apparatus which concerns on the 1st Embodiment of this invention by the vertical symmetry plane, and is the figure which showed the flow of the generated magnetic flux. It is the longitudinal cross-sectional view which cut | disconnected the upper half of the magnet apparatus of the comparative example with the perpendicular symmetry plane, and is the figure which showed the flow of the generated magnetic flux. It is a perspective view of the upper half of the yoke of the magnet apparatus which concerns on the 2nd Embodiment of this invention. It is a top view of the magnet apparatus which concerns on the 2nd Embodiment of this invention. It is the longitudinal cross-sectional view which cut | disconnected the upper half of the magnet apparatus which concerns on the 2nd Embodiment of this invention by the plane orthogonal to a vertical symmetry plane and a horizontal symmetry plane. It is the longitudinal cross-sectional view which cut | disconnected the upper half of the magnet apparatus which concerns on the 2nd Embodiment of this invention with the perpendicular symmetry plane. It is a perspective view of the upper half of the yoke of the magnet apparatus which concerns on the 3rd Embodiment of this invention. It is the longitudinal cross-sectional view which cut | disconnected the magnet apparatus at the time of using a permanent magnet by the vertical symmetry plane.

  Next, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. In each figure, common portions are denoted by the same reference numerals, and redundant description is omitted.

(First embodiment)
FIG. 1 is a perspective view of a magnetic resonance imaging apparatus (MRI apparatus) 1 according to the first embodiment of the present invention. The MRI apparatus 1 includes a magnet device 2 that generates a static magnetic field having a uniform magnetic field intensity in the imaging space 9, a bed 8 that transports the subject to the imaging space 9 while lying, and an MRI of the magnet device 2, the bed 8, and the like. And a control unit 7 that controls the entire apparatus 1 and obtains an image representing the physical and chemical properties of the subject by utilizing a nuclear magnetic resonance phenomenon that occurs when the subject is irradiated with a high-frequency pulse. Yes.

  The control unit 7 is connected to the magnet device 2, the bed 8, and the like. The control unit 7 includes an operation unit 72 that can be operated by an operator to adjust the content of the control, and a display unit 71 that displays the acquired image. The operation unit 72 can accept an operator's operation with a key, a rotary switch, or the like. The display unit 71 displays the operation information and displays the acquired image. The control unit 7 receives various operations of the operator by the operation unit 72, controls the magnet device 2 to generate a static magnetic field based on the operations, controls the bed 8, and images the subject in the horizontal direction. Transport to space 9.

  The bed 8 includes a drive unit 81 provided at a lower portion and a top plate 82 that moves horizontally in the direction of the imaging space 9 by the drive unit 81. A subject can lie on the top plate 82. The drive unit 81 moves the subject together with the top plate 82, and enables photographing of a cross-sectional image (MRI image) of a desired part. By capturing a cross-sectional image each time the top plate 82 is moved by a minute predetermined amount, a continuous cross-sectional image, that is, a three-dimensional image can be obtained.

  In the MRI apparatus 1, the magnet apparatus 2 generates a uniform static magnetic field and forms an imaging space 9. In the magnet device 2, a pair of disk-shaped magnetic poles 4U and magnetic poles 4L, which are magnetic field generation sources, are arranged so as to face each other vertically. A torus (annular) coil storage container 5U is disposed close to the upper magnetic pole 4U. A torus (annular) superconducting coil 6U (see FIG. 2) is stored in the coil storage container 5U together with the refrigerant. A torus (annular) coil storage container 5L is arranged close to the lower magnetic pole 4L. A torus (annular) superconducting coil 6L (see FIG. 2) is stored in the coil storage container 5L together with the refrigerant. A disc-shaped gradient magnetic field coil 10 is disposed on the inner peripheral surface side of the coil storage container 5L (5U). The gradient coil 10 can generate a gradient magnetic field with a magnetic field strength gradient in the imaging space 9.

  The magnetic pole 4U and the magnetic pole 4L are supported by an iron yoke 3. The yoke 3 is substantially C-shaped or U-shaped when viewed from the side. The yoke 3 has a vertical symmetry plane (symmetry plane) α that bisects the yoke 3 and is plane-symmetric with respect to the vertical symmetry plane α. The magnetic poles 4U and 4L are arranged close to both ends of the C-shaped or U-shaped yoke 3. The yoke 3 is close to the magnetic pole 4U (4L) and is opposed to a yoke-side facing portion (yoke horizontal portion) 15U (15L) and a yoke connecting portion (yoke vertical) that connects a pair of upper and lower yoke horizontal portions 15U and 15L. Part) 13. The yoke horizontal portion 15U (15L) has a tapered yoke horizontal front end portion 14U (14L, see FIG. 2) and a yoke horizontal rear portion 12U (12L, see FIG. 2) connected to the yoke horizontal portion 12U (see FIG. 2). Yes. The yoke horizontal rear portions 12U and 12L are connected by a yoke vertical portion 13. In addition, when assembling the yoke 3 from several parts, it does not necessarily limit that it is divided | segmented for every component of this structure, and the yoke 3 may be manufactured as an integral thing.

  FIG. 2 shows a longitudinal sectional view of the magnet device 2 according to the first embodiment of the present invention cut along a vertical symmetry plane α. The yoke 3 is substantially C-shaped or U-shaped when viewed from the side. For this reason, the yoke 3 has a horizontal symmetry plane β and is plane-symmetric with respect to the horizontal symmetry plane β. The substantially disk-shaped magnetic pole 4U and the magnetic pole 4L are disposed so as to face each other with the imaging space 9 interposed therebetween. The imaging space 9 has a substantially spherical shape, the center of which is located on the common central axis 101 of the disk-shaped magnetic pole 4U and the magnetic pole 4L, and on the horizontal symmetry plane β and the vertical symmetry plane α. positioned. A coil storage container 5U is coupled to the magnetic pole 4U, and a superconducting coil 6U is accommodated in the coil storage container 5U. Similarly, a coil storage container 5L is coupled to the magnetic pole 4L, and a superconducting coil 6L is accommodated in the coil storage container 5L. A magnetic field is generated by passing a current through the pair of upper and lower superconducting coils 6U and 6L, and a magnetic field with a uniform magnetic field strength can be generated in the imaging space 9 by magnetizing the magnetic pole 4U and the magnetic pole 4L. When the magnetic field strength is smaller than 0.5T, as shown in FIG. 14, permanent magnets 16U and 16L are provided between the magnetic pole 4U and the yoke horizontal tip 14U and between the magnetic pole 4L and the yoke horizontal tip 14L. Can be omitted, the superconducting coils 6U and 6L can be omitted. Thus, since the magnet apparatus 2 has a plane-symmetrical structure with respect to the horizontal symmetry plane β, the structure on the upper side of the horizontal symmetry plane β will be described below, and the description on the lower side will be omitted.

  As shown in FIG. 2, the opposite outer surface 15e of the yoke-side facing surface 15a coupled to the magnetic pole 4U of the yoke horizontal front end portion 14U has a smooth curved surface, and is convexly curved outward. ing. The height W1 of the yoke horizontal front end portion 14U from the yoke-side facing surface 15a decreases monotonously in a broad sense as it approaches the tip 15d of the yoke horizontal front end portion 14U, that is, moves away from the yoke vertical portion 13, and smoothly decreases. It has become. In the present specification, monotonic decreasing in a broad sense refers to not increasing in a corresponding section.

  In FIG. 3, the top view of the magnet apparatus 2 which concerns on the 1st Embodiment of this invention is shown. It can be seen that the yoke 3, in particular, the yoke vertical portion 13 is unevenly distributed in one direction with respect to the disk-shaped magnetic pole 4U. That is, the angle θ at which the yoke vertical portion 13 is viewed from the center axis 101 on a plane that is normal to the center axis 101, for example, on the horizontal symmetry plane β (see FIG. 2), is greater than 0 degree and less than 180 degrees. It has become.

  Moreover, the yoke horizontal front end portion 14U has a tapered shape. Specifically, the width W2 in the normal direction of the vertical symmetry plane α decreases continuously and smoothly as it approaches the tip 15d (away from the yoke vertical portion 13). Strictly speaking, the width W2 may be monotonously decreased in a broad sense and the maximum value and the minimum value may be different.

  The maximum width W2 (equal to the width of the yoke horizontal rear portion 12U) is smaller than the diameter of the disk-shaped magnetic pole 4U. There is a region having a radius of curvature smaller than the radius of the disk-shaped magnetic pole 4U on the outer peripheral line of the yoke horizontal front end portion 14U. In particular, the radius of curvature is smaller than the radius of the disk-shaped magnetic pole 4U at the outer peripheral line of the yoke horizontal tip portion 14U around the tip 15d. As a result, the distance W4 from the yoke horizontal front end portion 14U to the outer periphery 4a of the magnetic pole 4U decreases continuously and smoothly as it approaches the tip end 15d (as it moves away from the yoke vertical portion 13). Yoke horizontal front end portion 14U (yoke side facing portion 15U) is divided into a central band region 15b including a part of vertical symmetry plane α and both side band regions 15c located on both sides of central band region 15b away from vertical symmetry plane α. In other words, the distance W4b from the central band region 15b to the outer periphery 4a of the magnetic pole 4U is shorter than the distance W4c from the both-side band region 15c to the outer periphery 4a of the magnetic pole 4U.

  FIG. 4 shows a longitudinal sectional view of the upper half of the magnet device 2 according to the first embodiment of the present invention cut along a plane γ (see FIG. 3) perpendicular to the vertical symmetry plane α and the horizontal symmetry plane β. The height W3 of the yoke horizontal front end portion 14U (yoke side facing portion 15U) from the yoke side facing surface 15a decreases continuously and smoothly as the distance from the vertical symmetry plane α increases. Strictly speaking, the height W3 only needs to decrease monotonously in a broad sense as the distance from the vertical symmetry plane α increases, and the maximum value and the minimum value are different. In the height W3, the height W3b of the central band region 15b is higher than the height W3c of the both-side band region 15c.

  The principle of improving the uniformity by suppressing the non-axial symmetry of the static magnetic field in the imaging space 9 (see FIG. 2) by the shape of the yoke horizontal front end portion 14U (yoke side facing portion 15U) as described above will be described later. .

  In FIG. 5, the top view of the magnet apparatus 2 which concerns on the 1st Embodiment of this invention is shown. In FIG. 5, the flow of magnetic flux generated by the magnet device 2 is indicated by arrows. In the flow of magnetic flux (arrow), the flow starts from the vicinity of the outer periphery 4a of the magnetic pole 4U, passes through the yoke horizontal front end portion 14U, and reaches the yoke horizontal rear portion 12U. Since the yoke horizontal front end portion 14U spreads in an arc shape (substantially parabolic shape) toward the yoke horizontal rear portion 12U, the magnetic resistances in the paths for each magnetic flux (arrow) can be made uniform (equal). As a result, the magnetic flux (arrow) flowing from the magnetic pole 4U to the yoke horizontal tip portion 14U flows in a balanced manner from the circumferential direction of the magnetic pole 4U. Then, the magnetic flux (arrow) flowing from the circumferential direction does not go straight to the yoke horizontal rear portion 12U at the yoke horizontal front end portion 14U, but goes not only to the direction component toward the yoke horizontal rear portion 12U but also to the vertical symmetry plane α. It also has a directional component.

  FIG. 6 shows a longitudinal sectional view of the upper half of the magnet device 2 according to the first embodiment of the present invention cut along a plane γ (see FIG. 5). In FIG. 6, the flow of magnetic flux generated by the magnet device 2 is indicated by arrows. In the flow of magnetic flux, the flow starts from the horizontal symmetry plane β, passes through the magnetic pole 4U, and reaches the yoke horizontal front end portion 14U. As shown in FIG. 6, since the yoke horizontal front end portion 14U becomes higher as it approaches the vertical symmetry plane α, the magnetic flux (arrow) has a directional component toward the vertical symmetry plane α.

  As a result, the yoke horizontal front end portion 14U has a shape that expands in an arc shape (substantially parabolic shape) toward the yoke horizontal rear portion 12U, and becomes higher as it approaches the vertical symmetry plane α. The magnetic flux (arrow) flowing from the magnetic pole 4U into the yoke horizontal tip portion 14U is distributed in a balanced manner in the circumferential direction and flows toward the vertical symmetry plane α, thereby reducing the non-axisymmetric property of the magnetic flux in the imaging region 9. be able to. Further, since the structure is provided to reduce the non-axisymmetric property without increasing the magnetic resistance by providing a gap at the tip of the yoke, the function of the iron yoke for suppressing the leakage magnetic field is not impaired.

  FIG. 7 shows a longitudinal sectional view of the upper half of the magnet device 2 according to the first embodiment of the present invention cut along a vertical symmetry plane α, and FIG. 8 shows the upper half of the magnet device 2 of the comparative example vertically symmetric. A longitudinal sectional view cut along the plane α is shown. 7 and 8, the flow of magnetic flux generated by the magnet device 2 is indicated by arrows. In the flow of magnetic flux (arrow), the flow starts from the horizontal symmetry plane β, passes through the magnetic pole 4U and the yoke horizontal front end portion 14U (14Ua), and reaches the yoke horizontal rear portion 12U.

  The outer surface 15e of the yoke horizontal front end portion 14U (yoke horizontal portion 15U) of the first embodiment of FIG. 7 is convex upward, whereas the yoke horizontal front end portion 14Ua (yoke horizontal portion of the comparative example) is convex. The outer surface 15e of 15Ua) is different in that it is convex downward. In the comparative example, the flow of magnetic flux (arrow) is obliquely incident on the yoke horizontal front end portion 14Ua, and the incident position is also shifted to the yoke vertical portion 13 (yoke horizontal rear portion 12U) side. On the other hand, in the first embodiment, as compared with the comparative example, the magnetic flux flow (arrow) is incident on the yoke horizontal front end portion 14U at an angle closer to the vertical. Thereby, the direction component toward the vertical direction of the magnetic flux in the space between the magnetic poles 4U and 4L is increased, and the non-axial symmetry of the magnetic field in the vicinity of the imaging region 9 can be reduced. From the above, according to the present embodiment, the magnetic flux (arrow) can be guided in the vertical axis direction in the imaging region 9 by the yoke horizontal front end portion 14U, so that the leakage magnetic field suppression efficiency is not impaired in the imaging region 9. The non-axial symmetry of the magnetic field can be reduced and the imaging area can be widened.

(Second Embodiment)
FIG. 9 is a perspective view of the upper half of the yoke 3 of the magnet device according to the second embodiment of the present invention. The difference between the second embodiment and the first embodiment is the shape of the yoke 3, and among them, the shape of the yoke horizontal front end portion 14U. The outer surface 15e of the yoke horizontal tip 14U of the first embodiment is configured using a curved surface, but the outer surface 15e of the yoke horizontal tip 14U of the second embodiment has a plurality of different inclination angles. It is comprised using the inclined surface.

  In FIG. 10, the top view of the magnet apparatus 2 which concerns on the 2nd Embodiment of this invention is shown. The yoke horizontal front end portion 14U has a tapered shape. Specifically, the width W2 in the normal direction of the vertical symmetry plane α decreases in two steps by approaching the tip 15d (by moving away from the yoke vertical portion 13). Strictly speaking, the width W2 only needs to decrease monotonously in a broad sense as it approaches the tip 15d, and its maximum value and minimum value are different. The maximum value of the width W2 is equal to the width of the yoke horizontal rear portion 12U. The width W2 is narrowed in two steps. In the second embodiment, the width W2 is set in two stages. However, the width W2 is not limited to this and may be set in multiple stages.

  Further, the yoke horizontal front end portion 14U (yoke side facing portion 15U) includes a central band region 15b including a part of the vertical symmetry plane α, and both side band regions 15c located on both sides of the central band region 15b apart from the vertical symmetry plane α. In other words, the distance W4b from the central band region 15b to the outer periphery 4a of the magnetic pole 4U is closer than the distance W4c from the both-side band region 15c to the outer periphery 4a of the magnetic pole 4U. The central band region 15b of the yoke horizontal front end portion 14U extends from the both side band regions 15c in the direction opposite to the yoke vertical portion 13.

  FIG. 11 is a longitudinal sectional view of the upper half of the magnet device 2 according to the second embodiment of the present invention cut along a plane γ (see FIG. 10). The height W3 from the yoke-side facing surface 15a of the yoke horizontal front end portion 14U (yoke-side facing portion 15U) decreases stepwise as it moves away from the vertical symmetry plane α. Strictly speaking, the height W3 only needs to decrease monotonously in a broad sense as the distance from the vertical symmetry plane α increases, and the maximum value and the minimum value are different. The height W3b in the central band region 15b is higher than the height W3c in the both-side band region 15c. In the second embodiment, the height W3 is set in two stages, but the present invention is not limited to this, and may be set in multiple stages.

  FIG. 12 shows a longitudinal sectional view of the upper half of the magnet device 2 according to the second embodiment of the present invention cut along a vertical symmetry plane α. The outer surface 15e of the yoke horizontal front end portion 14U is configured by using two inclined surfaces having different inclination angles θ1 and θ2. The inclination angle θ1 of the lower inclined surface is larger than the inclination angle θ2 of the upper inclined surface (θ1> θ2). As a result, the outer surface 15e is convex outward (upward). In the second embodiment, the inclination angles θ1 and θ2 are set in two stages. However, the present invention is not limited to this and may be set in multiple stages. The height W1 of the yoke horizontal front end portion 14U from the yoke-side facing surface 15a decreases monotonously in a broad sense as the distance from the yoke vertical portion 13 increases, and the level decreases smoothly.

  Also in the second embodiment, the shape of the yoke horizontal front end portion 14U has a common point with the first embodiment, and due to this common point, as in the first embodiment, the static magnetic field is non-axisymmetric. Property can be suppressed and uniformity can be improved.

(Third embodiment)
FIG. 13 is a perspective view of the upper half of the yoke 3 of the magnet device according to the third embodiment of the present invention. The difference between the third embodiment and the second embodiment is the shape of the yoke 3, and among them, the shape of the yoke vertical portion 13. In the second embodiment, the yoke vertical portion 13 is a single column, but in the third embodiment, there are a plurality of columns (two in the example of FIG. 13). According to this, between the plurality of adjacent yoke vertical portions 13, pipes for connecting the coil storage containers 5U and 5L, wiring connected to the superconducting coils 6U and 6L, a refrigerator, and the like can be installed. By arranging a pipe, wiring, or the like in a region between adjacent yoke vertical parts, a region through which the bed 8 passes can be widened, and a wider degree of freedom of movement of the bed 8 can be secured. Further, by installing a refrigerator between adjacent yoke vertical portions, the refrigerator can be installed near the superconducting coil, and the superconducting coil can be cooled more efficiently.

  The present invention is not limited to the first to third embodiments described above, and includes various modifications. For example, the first to third embodiments described above have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of an embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of an embodiment. Moreover, it is also possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 1 Magnetic resonance imaging (MRI) apparatus 2 Magnet apparatus 3 Yoke 4U, 4L Magnetic pole 4a Magnetic pole outer periphery 5U, 5L Coil storage container 6U, 6L Superconducting coil 7 Control part 8 Bed 9 Imaging space (uniform static magnetic field)
10 Gradient coil 12U, 12L Yoke horizontal rear part 13 Yoke vertical part (Yoke coupling part)
14U, 14L Yoke horizontal tip 15U, 15L Yoke horizontal part (yoke side facing part)
15a Yoke-side facing surface of the yoke-side facing portion 15b Central band region of the yoke-side facing portion 15c Both-side band regions of the yoke-side facing portion 15d Tip of the yoke-side facing portion 15e Outer surface of the yoke-side facing portion 101 Central axis of the superconducting coil W1 Height from the yoke-side facing surface of the yoke-side facing portion W2 Width in the normal direction of the vertical symmetry plane of the yoke-side facing portion W3 Height from the yoke-side facing surface of the yoke-side facing portion W3b Height at the central band region W3c Height on both side belt regions W4 Distance from the yoke side facing part to outer periphery of magnetic pole W4b Distance from center belt region W4c Distance from both side belt regions α Vertical symmetry plane of the yoke (symmetric plane)
β Horizontal symmetry plane of the yoke γ Plane orthogonal to α and β θ Angle to expect the yoke connection

Claims (13)

A pair of substantially disk-shaped magnetic poles arranged opposite to each other;
A yoke that is C-shaped or U-shaped in a side view, and that both ends of the C-shaped or U-shaped are arranged close to the magnetic poles,
The yoke has a yoke-side facing portion facing the magnetic pole in the vicinity;
The yoke side facing portion is
A central zone region including a portion of a vertical symmetry plane that substantially bisects the yoke;
Having both side band regions located on both sides of the central band region away from the vertical symmetry plane;
In the height from the yoke-side facing surface facing the magnetic pole of the yoke-side facing portion close to the magnetic pole, the central band region is higher than the both-side band regions ,
The magnet device according to claim 1, wherein the central band region is closer to the outer periphery of the magnetic pole than the both side band regions . A pair of substantially disk-shaped magnetic poles arranged opposite to each other;
A yoke that is C-shaped or U-shaped in a side view, and that both ends of the C-shaped or U-shaped are arranged close to the magnetic poles,
The yoke has a yoke-side facing portion facing the magnetic pole in the vicinity;
The yoke side facing portion is
A central zone region including a portion of a vertical symmetry plane that substantially bisects the yoke;
Having both side band regions located on both sides of the central band region away from the vertical symmetry plane;
In the height from the yoke-side facing surface facing the magnetic pole of the yoke-side facing portion close to the magnetic pole, the central band region is higher than the both-side band regions ,
The magnet apparatus according to claim 1, wherein a distance from the yoke-side facing portion to the outer periphery of the magnetic pole continuously decreases as approaching a tip of the yoke-side facing portion .   The width in the normal direction of the yoke-side facing portion with respect to the vertical symmetry plane decreases monotonously in a broad sense as it approaches the tip of the yoke-side facing portion, and the maximum value and the minimum value thereof are different. Or the magnet apparatus of Claim 2. Height from the yoke side facing the surface of the yoke-side facing portion, the broad monotonically decreasing with distance from the vertical plane of symmetry, and claim 1 or claim, characterized in that the maximum and minimum values are different 2. The magnet device according to 2 . The height of the yoke-side facing portion from the yoke-side facing surface decreases monotonously in a broad sense as it approaches the tip of the yoke-side facing portion, and
The magnet device according to claim 1 or 2 , wherein an outer surface of the yoke-side facing portion facing the yoke-side facing surface is convex outward. The yoke has a yoke coupling part that couples a pair of yoke side facing parts,
From the central axis common to the pair of the magnetic poles, the angle anticipating the yoke connecting portion on a plane that said central axis and normals, claim 1, characterized in that not more than 180 degrees greater than 0 degrees or The magnet device according to claim 2 . 3. The magnet device according to claim 1, wherein a width in a normal direction of the yoke-side facing portion with respect to the vertical symmetry plane continuously decreases as approaching a tip of the yoke-side facing portion. . Height from the yoke side facing the surface of the yoke-side facing portion which faces in proximity to the pole, according to claim 1 or claim 2, characterized in that continuously decreases with distance from the vertical plane of symmetry Magnet device. 3. The magnet device according to claim 1, wherein a width in a normal direction of the yoke-side facing portion with respect to the vertical symmetry plane decreases in a stepwise manner toward a tip of the yoke-side facing portion. . 3. The height from the yoke-side facing surface of the yoke-side facing portion that faces the magnetic pole in the vicinity of the magnetic pole gradually decreases as the distance from the vertical symmetry plane increases. Magnet device. Magnet as claimed in any one of claims 1 to 10, characterized in that it comprises a pair of substantially annular superconducting coil is arranged close to the pair of the magnetic poles. Magnet as claimed in any one of claims 1 to 10, characterized in that it comprises a pair of substantially disc-shaped permanent magnet is arranged close to the pair of the magnetic poles. A magnet device according to any one of claims 1 to 12 ,
A bed for transporting a subject between a pair of magnetic poles;
The magnet apparatus generates a uniform static magnetic field between the pair of magnetic poles to form an imaging space.

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