CN105208929B - Magnet arrangement and MR imaging apparatus - Google Patents

Abstract

The magnet device (2) includes: a pair of substantially disk-shaped magnetic poles (4U) disposed opposite to each other; in a side view, it is C-shaped or U-shaped, and both ends of the C-shaped or U-shaped are close to the magnetic poles (4U). A yoke (3) arranged in the ground, the yoke (3) has a yoke-side opposing portion (15U) closely facing the magnetic pole (4U), and the yoke-side opposing portion (15U) has a yoke ( 3) the central band region (15b) of a part of the vertical symmetry plane (α); the two side band regions (15c) on both sides of the central band region (15b) away from the vertical symmetry plane (α), in the magnetic In the height (W3) of the yoke-side facing part (15U) from the yoke-side facing surface (15a) which is closely opposed to the magnetic pole (4U), the central band area (15b, W3b) is larger than the side band areas (15c, W3c) high. The height (W3) of the yoke-side opposing portion (15U) from the yoke-side opposing surface (15a) decreases monotonously in a generalized sense with distance from the vertical symmetry plane (α) and its maximum value and minimum value differ .

Description

Magnet device and magnetic resonance imaging device

technical field

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

Background technique

The MRI device places the subject in an imaging space formed with a uniform static magnetic field, and uses the nuclear magnetic resonance phenomenon generated when the subject is irradiated with high-frequency pulses to obtain images representing the physical and chemical properties of the subject. Also, the image is mainly used for medical purposes. The MRI apparatus is roughly classified into a horizontal type in which the direction of the static magnetic field is oriented horizontally, and a vertical type in which the direction is oriented vertically. In the former, that is, the horizontal type MRI apparatus, the imaging space is in a tunnel penetrating in the horizontal direction, and the subject enters the tunnel to be examined. Therefore, the subject sometimes feels oppressed. On the other hand, the latter vertical type MRI apparatus has a structure in which an imaging space is formed between a pair of magnetic poles arranged to face up and down, and the subject enters the space between the magnetic poles, so that the subject can obtain a sense of openness. Therefore, a vertical type MRI apparatus is also called an open type MRI apparatus.

In order to take advantage of the advantages of the vertical MRI apparatus and open the space around the subject to a large extent, the shape of the yoke connected to the pair of magnetic poles is C-shaped or U-shaped (for example, refer to Patent Document 1, etc.). In this specification, a C-shape or a U-shape refers to a shape in which a part of a substantially circular ring shape is cut away and opened. However, when a C-shaped or U-shaped yoke is used, the distribution of the magnetic body including the yoke seen from the imaging space will be biased, so the static magnetic field in the imaging space is likely to form non-axisymmetric, and the static magnetic field in the imaging space The magnetic field strength tends to become non-uniform. For this reason, in Patent Document 1, the thickness of the pair of upper and lower horizontal parts extending in the horizontal direction of the C-shaped or U-shaped yoke is gradually reduced toward the front end side, thereby reducing the thickness of the imaging area. Adjust the magnetic field intensity on the opening side and column side of the C-shaped or U-shaped.

prior art literature

patent documents

Patent Document 1: Japanese Patent Laid-Open No. 2005-168772

Contents of the invention

The problem to be solved by the invention

The vertical MRI apparatus has a magnet device for generating a uniform static magnetic field in the imaging space. Also, permanent magnets or superconducting coils are used in this magnet device. Usually, permanent magnets are used when the required magnetic field strength is less than 0.5T in the imaging space, and superconducting coils are used if the magnetic field strength is more than 0.5T.

Furthermore, as an important parameter of the magnet device for an MRI apparatus, in addition to the above-mentioned magnetic field strength and the above-mentioned magnetic field uniformity, there is also the size of the leakage field diffusion region. The size scale of the leakage magnetic field diffusion area generally adopts the size of the space required for the magnetic field intensity to decay to 0.5mT. It is necessary to suppress the leakage magnetic field so that the size of this space is smaller than the room where the MRI apparatus is installed. In addition, if the magnetic field intensity in the imaging space is 1.0 T or less, suppression of the leakage field to that extent can be achieved by arranging only a magnetic material such as iron. On the other hand, when the magnetic field strength exceeds 1 T, tens of tons of magnetic materials are required to suppress the leakage field only by arranging the magnetic materials, and it is not practical to arrange the magnetic materials to suppress the leakage field. In this case, the leakage magnetic field can be suppressed by using a superconducting coil called a shield coil.

Summarizing the above, in a vertical MRI apparatus in which the magnetic field strength in the imaging space is within the range of 0.5T or less, permanent magnets are used for the magnetic poles to generate static magnetic fields, and magnetic materials are used to suppress leakage magnetic fields. As the magnetic body, specifically, an iron yoke can be used. In addition, in the vertical MRI apparatus in the range of 0.5 T to 1.0 T, a static magnetic field is generated by using a superconducting coil with a different magnetic pole than the magnetic material, and a leakage magnetic field is suppressed by using a magnetic material different from the magnetic material of the magnetic pole.

In addition, in Patent Document 1, a superconducting coil and a magnetic body, that is, a continuous iron yoke with few gaps are used, so that leakage magnetic fields can be suppressed and a static magnetic field with high magnetic field strength can be generated. In addition, the thickness of the horizontal portion of the C-shaped or U-shaped yoke is gradually reduced toward the tip side, thereby reducing the non-axisymmetric nature of the magnetic field.

However, the method of adjusting the thickness of the front end side of the horizontal portion of the yoke has non-axisymmetric properties that cannot be corrected. That is, when the circumferential angle of the vertical axis passing through the center of the imaging area is set to 0 degrees on the column side of the C-shaped or U-shaped shape and 180 degrees on the opening side of the C-shaped or U-shaped shape, even if it is equipped with 0 The mechanism in which the strengths of the magnetic fields in the directions of 0 degrees and 180 degrees are equal in the thickness of the front end side of the horizontal portion of the yoke cannot make the strengths of the magnetic fields in the directions of 0 degrees, 90 degrees, and 270 degrees equal.

Furthermore, in Patent Document 1, when the thickness of the front end side of the horizontal portion of the yoke is made thinner, then, for example, the upper horizontal portion has a shape in which the outer surface of the horizontal portion is convex downward, that is, viewed from above. The concave shape is the basic shape. Compared with the upward convex shape, the convex shape downward on the outer surface will cause the magnetic flux flowing vertically upward to the side of the C-shaped or U-shaped column to bend sharply, so the C-shaped or U-shaped Since the vertically upward distance of the magnetic field at the opening side is shortened, the imaging area in which a uniform magnetic field is required is reduced.

Therefore, the problem to be solved by the present invention is to provide a magnet device which can reduce the non-axisymmetric nature of the static magnetic field and improve the uniformity. Furthermore, an MRI apparatus equipped with the magnet apparatus is provided.

method used to solve the problem

In order to solve the above-mentioned problems, the present invention is a magnet device characterized in that it includes:

a pair of substantially disc-shaped magnetic poles arranged oppositely; and

A yoke that is C-shaped or U-shaped in side view and whose two ends of the C-shaped or U-shaped shape are arranged close to the above-mentioned magnetic poles,

The yoke has a yoke-side opposing portion closely facing the magnetic pole,

The above-mentioned yoke-side opposing portion has:

a central band region comprising a portion of a vertical plane of symmetry that roughly bisects said yoke; and

the side band regions located on both sides of the aforementioned central band region away from the above-mentioned plane of symmetry,

In the height of the yoke-side facing portion from the yoke-side facing surface closely facing the magnetic pole, the central band region is higher than the side-band regions.

And, the present invention is a kind of MRI apparatus, is characterized in that, has:

the magnet device; and

Transport the subject to the bed between a pair of magnetic poles,

The magnet device generates a uniform static magnetic field between the pair of magnetic poles to form an imaging space.

The effect of the invention

According to the present invention, it is possible to provide a magnet device and an MRI apparatus equipped with the magnet device. Since the magnetic flux flowing through the magnetic poles to the yoke-side opposing portion has a direction component toward the vertical symmetry plane, it is possible to suppress the leakage field and make the The non-axisymmetric nature of the static magnetic field is reduced to improve uniformity. In addition, problems, configurations, and effects other than those described above will be clarified by the following description of the embodiments.

Description of drawings

FIG. 1 is a perspective view of a magnetic resonance imaging apparatus (MRI apparatus) according to a first embodiment of the present invention.

2 is a longitudinal sectional view of the magnet device according to the first embodiment of the present invention, taken along a vertical symmetry plane.

Fig. 3 is a plan view of the magnet device according to the first embodiment of the present invention.

4 is a longitudinal sectional view of the upper half of the magnet device according to the first embodiment of the present invention, taken along a plane perpendicular to the vertical symmetry plane and the horizontal symmetry plane.

5 is a plan view of the magnet device according to the first embodiment of the present invention, showing the flow of generated magnetic flux.

6 is a longitudinal sectional view of the upper half of the magnet device according to the first embodiment of the present invention, taken along a plane perpendicular to the vertical symmetry plane and the horizontal symmetry plane, showing the flow of generated magnetic flux.

7 is a longitudinal cross-sectional view of the upper half of the magnet device according to the first embodiment of the present invention, taken along a vertical symmetry plane, showing the flow of generated magnetic flux.

8 is a longitudinal cross-sectional view of the upper half of the magnet device of the comparative example cut along the vertical symmetry plane, and is a view showing the flow of generated magnetic flux.

9 is a perspective view of an upper half of a yoke of a magnet device according to a second embodiment of the present invention.

Fig. 10 is a plan view of a magnet device according to a second embodiment of the present invention.

11 is a longitudinal sectional view of the upper half of the magnet device according to the second embodiment of the present invention, taken along a plane perpendicular to the vertical symmetry plane and the horizontal symmetry plane.

12 is a longitudinal sectional view of the upper half of the magnet device according to the second embodiment of the present invention, taken along the vertical symmetry plane.

13 is a perspective view of an upper half of a yoke of a magnet device according to a third embodiment of the present invention.

Fig. 14 is a longitudinal sectional view cut along a vertical symmetry plane of a magnet device using a permanent magnet.

Detailed ways

Next, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. In addition, the same code|symbol is attached|subjected to the common part in each figure, and overlapping description is abbreviate|omitted.

(first embodiment)

FIG. 1 shows a perspective view of a magnetic resonance imaging apparatus (MRI apparatus) 1 according to a first embodiment of the present invention. The MRI apparatus 1 has: a magnet device 2 that generates a static magnetic field with uniform magnetic field strength in the imaging space 9; a bed 8 that transports the subject to the imaging space 9 in a supine state; and a magnet device 2, the bed 8, etc. The entire MRI apparatus 1 is controlled, and the control unit 7 acquires images representing the physical and chemical properties of the subject by utilizing the nuclear magnetic resonance phenomenon generated when the subject is irradiated with high-frequency pulses.

The control unit 7 is connected to the magnet device 2, the bed 8, and the like. The control unit 7 has an operation unit 72 that can be operated by an operator to adjust the control content thereof, and a display unit 71 that displays an acquired image. The operation unit 72 accepts operations by the operator through keys, rotary switches, and the like. The display unit 71 displays the operation information and the acquired image. The control unit 7 receives various operations from the operator through the operation unit 72 , controls the magnet device 2 to generate a static magnetic field based on the operations, and controls the bed 8 to transport the subject to the imaging space 9 in the horizontal direction.

The bed 8 includes a drive unit 81 provided at the lower portion, and a table 82 horizontally moved in the direction of the imaging space 9 by the drive unit 81 . The subject can lie flat on the table top 82 . The driving unit 81 moves the subject along with the table 82 to capture a cross-sectional image (MRI image) of the target site. Continuous cross-sectional images, that is, three-dimensional images can be obtained by capturing cross-sectional images by moving the platen 82 by a small predetermined amount at a time.

The magnet device 2 generates a uniform static magnetic field in the MRI apparatus 1 to form an imaging space 9 . In the magnet device 2 , a set of disk-shaped magnetic poles 4U and 4L as a magnetic field generating source are arranged to face up and down. A ring (annulus)-shaped coil storage container 5U is arranged closely below the upper magnetic pole 4U. A refrigerant and a ring (annulus)-shaped superconducting coil 6U are accommodated in the coil storage container 5U (see FIG. 2 ). An annular (annular)-shaped coil storage container 5L is disposed close to and above the lower magnetic pole 4L. A refrigerant and a ring (annulus)-shaped superconducting coil 6L (see FIG. 2 ) are accommodated in the coil storage container 5L. A disk-shaped gradient magnetic field coil 10 is arranged on the inner peripheral surface side of the coil storage container 5L ( 5U ). The gradient magnetic field coil 10 can generate a gradient magnetic field in which the magnetic field intensity is inclined in the imaging space 9 .

Magnetic pole 4U and magnetic pole 4L are supported by iron yoke 3 . The yoke 3 is substantially C-shaped or U-shaped in side view. The yoke 3 has a vertical symmetry plane (symmetry plane) α that roughly bisects the yoke 3 , and is symmetrical with respect to the vertical symmetry plane α. Furthermore, the above-mentioned magnetic poles 4U and 4L are disposed adjacent to both ends of the C-shaped or U-shaped yoke 3 . The yoke 3 has a yoke-side opposing portion (yoke horizontal portion) 15U (15L) that is close to and faces the magnetic pole 4U (4L), and a yoke connecting portion that connects the pair of upper and lower yoke horizontal portions 15U, 15L. (Yoke vertical 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 thereto to form a substantially rectangular parallelepiped. The yoke horizontal rear parts 12U and 12L are connected by a yoke vertical part 13 . Also, in the case where the yoke 3 is composed of several parts, not limited to each part divided into the structure, the yoke 3 may also be manufactured as an integral piece.

FIG. 2 is a vertical cross-sectional view of the magnet device 2 according to the first embodiment of the present invention, taken along the vertical symmetry plane α. The yoke 3 is substantially C-shaped or U-shaped in side view. Therefore, the yoke 3 has a horizontal symmetry plane β and is symmetrical with respect to the horizontal symmetry plane β. The substantially disc-shaped magnetic poles 4U and 4L are disposed vertically opposite to each other across the imaging space 9 . The imaging space 9 has a substantially spherical shape, and its center is located on the common central axis 101 of the disc-shaped magnetic poles 4U and 4L, and is located on the horizontal symmetry plane β and the vertical symmetry plane α. 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 current is passed through the pair of upper and lower superconducting coils 6U, 6L to generate a magnetic field to magnetize the magnetic pole 4U and the magnetic pole 4L, thereby generating a static magnetic field with uniform magnetic field strength in the imaging space 9 . In addition, when the magnetic field intensity is less than 0.5T, as shown in FIG. 14 , permanent magnets 16U, 16U, 16L and save the superconducting coils 6U, 6L. In this way, the magnet device 2 adopts a symmetrical structure with respect to the horizontal symmetry plane β, so that the upper side structure of the horizontal symmetry plane β will be described below, and the description of the lower side will be omitted.

As shown in FIG. 2 , an outer surface 15 e of the horizontal front end portion 14U of the yoke opposite to the yoke-side facing surface 15 a coupled to the magnetic pole 4U is convexly curved outward in a smooth curved shape. The height W1 of the yoke horizontal front end portion 14U from the yoke side opposing surface 15a decreases monotonically in a broad sense and becomes smooth as it approaches the front end 15d of the yoke horizontal front end portion 14U, that is, as it moves away from the yoke vertical portion 13 lowered. In the present specification, monotonic decreasing (monotonic decreasing) in a broad sense means not increasing in the interval.

FIG. 3 shows a top view of the magnet device 2 according to the first embodiment of the present invention. It can be seen that the yoke 3 , especially the yoke vertical portion 13 is offset in one direction with respect to the disk-shaped magnetic pole 4U. That is, from the central axis 101, on a plane normal to the central axis 101, such as a horizontal symmetry plane β (refer to FIG. 2 ), the angle of view θ when observing the vertical portion 13 of the yoke is greater than 0 degrees and not more than 180 degrees. .

In addition, 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 front end 15 d (as it moves away from the yoke vertical portion 13 ). Strictly speaking, the width W2 generally decreases monotonously as long as its maximum value and minimum value are different.

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

4 is a longitudinal cross-sectional view of the upper half of the magnet device 2 according to the first embodiment of the present invention, taken along a plane γ (see FIG. 3 ) orthogonal to the vertical symmetry plane α and the horizontal symmetry plane β. The height W3 of the yoke horizontal front end portion 14U (the yoke-side opposing portion 15U) from the yoke-side opposing surface 15a decreases continuously and smoothly as it moves away from the vertical symmetry plane α. Strictly speaking, the height W3 generally decreases monotonically as it moves away from the vertical symmetry plane α, and it only needs to have different maximum and minimum values. In the height W3, the height W3b of the central belt region 15b is higher than the height W3c of the side belt regions 15c.

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

FIG. 5 shows a plan view of the magnet device 2 according to the first embodiment of the present invention. The flow of the magnetic flux generated by the magnet device 2 is indicated by arrows in FIG. 5 . The flow direction (arrow) of the magnetic flux shows the flow direction from the vicinity of the outer periphery 4 a of the magnetic pole 4U to the yoke horizontal rear portion 12U via the yoke horizontal front end portion 14U. Since the yoke horizontal front end portion 14U gradually expands in an arc shape (substantially parabolic shape) toward the yoke horizontal rear portion 12U, the reluctance on each magnetic flux (arrow) path can be made uniform (equal). Accordingly, the magnetic flux (arrow) flowing from the magnetic pole 4U to the yoke horizontal front end portion 14U flows in a balanced manner from the circumferential direction of the magnetic pole 4U. And, the magnetic flux (arrow) flowing in from this circumferential direction does not go straight toward the yoke horizontal rear portion 12U on the yoke horizontal front end portion 14U, but except for the direction component toward the yoke horizontal rear portion 12U, There is also a direction component towards the vertical symmetry plane α.

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

As a result, the horizontal front end portion 14U of the yoke has a shape that gradually expands into an arc shape (substantially parabolic shape) toward the horizontal rear portion 12U of the yoke, and becomes higher as it gets closer to the vertical symmetry plane α, so that it flows into the yoke from the magnetic pole 4U. The magnetic flux (arrow) of the horizontal front end portion 14U is evenly distributed in the circumferential direction and flows toward the vertical symmetry plane α, thereby reducing the non-axisymmetric nature of the magnetic flux in the imaging region 9 . In addition, since the non-axisymmetric structure is not reduced by providing a gap at the front end of the yoke to increase the magnetic resistance, the function of suppressing the leakage field of the ferromagnetic yoke is not affected.

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 the vertical symmetry plane α, and FIG. 8 shows the upper half of the magnet device 2 of the comparative example along the vertical symmetry plane. Longitudinal sectional view of α cut. The flow of the magnetic flux generated by the magnet device 2 is indicated by arrows in FIGS. 7 and 8 . The flow direction (arrow) of the magnetic flux shows the flow direction from the horizontal symmetry plane β to the yoke horizontal rear portion 12U via the magnetic pole 4U and the yoke horizontal front end portion 14U ( 14Ua ).

The outer surface 15e of the yoke horizontal front end portion 14U (yoke horizontal portion 15U) of the first embodiment in FIG. then protrude downward. In the comparative example, the flow direction (arrow) of the magnetic flux enters the yoke horizontal front end portion 14Ua obliquely, and the incident position also shifts toward the yoke vertical portion 13 (yoke horizontal rear portion 12U) side. On the other hand, in the first embodiment, the flow direction (arrow) of the magnetic flux enters the yoke horizontal front end portion 14U at an angle closer to the vertical than in the comparative example. This increases the vertical direction component of the magnetic flux in the space between the magnetic poles 4U and 4L, and reduces the non-axisymmetric nature of the magnetic field in the vicinity of the imaging region 9 . As can be seen from the above, according to this embodiment, the magnetic flux (arrow) can be guided in the direction of the vertical axis in the imaging region 9 by using the horizontal front end portion 14U of the yoke, so that the suppression efficiency of the leakage field is not affected, and the magnetic flux in the imaging region 9 can be reduced. The non-axisymmetric nature of the magnetic field expands the imaging area.

(second embodiment)

FIG. 9 shows 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 point of difference between the second embodiment and the first embodiment lies in the shape of the yoke 3, among them the shape of the horizontal front end portion 14U of the yoke. The outer surface 15e of the horizontal front end portion 14U of the yoke in the first embodiment is formed using a curved surface, whereas the outer surface 15e of the horizontal front end portion 14U of the yoke in the second embodiment is formed using a plurality of inclined surfaces with different inclination angles.

FIG. 10 shows a plan view of a magnet device 2 according to a second embodiment of the present invention. The horizontal front end portion 14U of the yoke has a tapered shape. Specifically, the width W2 in the normal direction of the vertical symmetry plane α decreases in two stages as it approaches the front end 15 d (farther from the yoke vertical portion 13 ). Strictly speaking, the width W2 generally decreases monotonously as it gets closer to the front end 15d and only needs to have different maximum and minimum values. The maximum value of the width W2 is equal to the width of the horizontal rear portion 12U of the yoke. The width W2 is narrowed in two stages. In addition, although the width W2 is set in two steps in the second embodiment, it is not limited thereto and may be set in multiple steps.

Furthermore, if the yoke horizontal front end portion 14U (yoke-side facing portion 15U) is divided into a central zone region 15b including a part of the vertical symmetry plane α, and a central zone region 15b located away from the vertical symmetry plane α The distance W4b from the central belt region 15b to the outer periphery 4a of the magnetic pole 4U is shorter than the distance W4c from the both side belt regions 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 in a direction opposite to the yoke vertical portion 13 with respect to the both side band regions 15c.

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

FIG. 12 is a vertical cross-sectional view of the upper half of the magnet device 2 according to the second embodiment of the present invention, taken along the vertical symmetry plane α. The outer surface 15e of the horizontal front end portion 14U of the yoke is configured 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). Thereby, the outer surface 15e protrudes outward (up). In addition, although the inclination angles θ1 and θ2 are set in two stages in the second embodiment, they are not limited thereto and may be set in multiple stages. The height W1 of the yoke horizontal front end portion 14U from the yoke-side opposing surface 15a decreases monotonously and smoothly in a broad sense as it moves away from the yoke vertical portion 13 .

In the second embodiment, the shape of the horizontal front end portion 14U of the yoke also has something in common with the first embodiment. Using this common point, similar to the first embodiment, the non-axisymmetric nature of the static magnetic field can be suppressed and the uniformity can be improved. sex.

(third embodiment)

FIG. 13 shows 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 lies in the shape of the yoke 3 , which is also the shape of the yoke vertical portion 13 . In the second embodiment, the yoke vertical portion 13 is one column, but in the third embodiment, it is a plurality of columns (two in the example of FIG. 13 ). Accordingly, a pipe connecting the coil storage containers 5U and 5L, wiring connecting the superconducting coils 6U and 6L, a refrigerator, and the like can be provided between the plurality of adjacent yoke vertical portions 13 . By arranging pipes, wiring, and the like in the area between adjacent yoke vertical portions, the area through which the bed 8 passes can be enlarged and the degree of freedom of movement of the bed 8 can be ensured more widely. In addition, by providing a refrigerator between adjacent yoke vertical portions, it is possible to provide a refrigerator near the superconducting coil to cool the superconducting coil more efficiently.

In addition, the present invention is not limited to the first to third embodiments described above and includes various modified examples. For example, the above-mentioned first to third embodiments are used to describe the present invention in detail to facilitate understanding and are not limited to having all the structures described. Furthermore, it is also possible to substitute a part of the structure of a certain embodiment with the structure of another embodiment, and to add the structure of another embodiment to the structure of a certain embodiment. In addition, addition, deletion, and replacement of other configurations can also be performed on part of the configurations of the respective embodiments.

Symbol Description

1—magnetic resonance imaging (MRI) device; 2—magnet device; 3—yoke; 4U, 4L—magnetic pole; 4a—outer circumference of magnetic pole; 5U, 5L—coil storage container; 6U, 6L—superconducting coil; 7— Control part; 8—bed platform; 9—camera space (uniform static magnetic field); 10—inclined magnetic field coil; 12U, 12L—horizontal rear part of yoke; 13—vertical part of yoke (yoke connecting part); 14U, 14L—horizontal front end portion of the yoke; 15U, 15L—horizontal portion of the yoke (yoke side facing portion); 15a—yoke side facing surface of the yoke side facing portion; 15b—yoke side facing portion Central belt area; 15c—the two side belt areas of the yoke-side opposing portion; 15d—the front end of the yoke-side opposing portion; 15e—the outer surface of the yoke-side opposing portion; 101—the central axis of the superconducting coil; W1—the height of the yoke side opposite part from the yoke side opposite surface; W2—the width of the normal direction of the vertical symmetry plane of the yoke side opposite part; W3—the height of the yoke side opposite part from The height from the opposite surface of the yoke side; W3b—the height on the central belt area; W3c—the height on both sides of the belt area; W4—the distance from the opposite part of the yoke side to the outer periphery of the magnetic pole; W4b—from the central belt area W4c—the distance from the belt area on both sides; α—the vertical symmetry plane (symmetry plane) of the yoke; β—the horizontal symmetry plane of the yoke; γ—the plane orthogonal to α and β; θ —The angle of view when observing the yoke joint.

Claims (13)

1. A magnet device, characterized in that it possesses: a pair of substantially disc-shaped magnetic poles arranged oppositely; and A yoke that is C-shaped or U-shaped in side view and whose two ends of the C-shaped or U-shaped shape are arranged close to the above-mentioned magnetic poles, The yoke has a yoke-side opposing portion closely facing the magnetic pole, The above-mentioned yoke-side opposing portion has: a central zone region comprising a portion of a vertical plane of symmetry that roughly bisects said yoke; and the two side zone regions, which are separated from the above-mentioned vertical symmetry plane and located on both sides of the above-mentioned central zone region, In the height of the yoke-side facing portion from the yoke-side facing surface closely facing the magnetic poles, the central band region is higher than the side-band regions, The central zone region is closer to the outer periphery of the magnetic pole than the both side zone regions. 2. A magnet device, characterized in that, possesses: a pair of substantially disc-shaped magnetic poles arranged oppositely; and A yoke that is C-shaped or U-shaped in side view and whose two ends of the C-shaped or U-shaped shape are arranged close to the above-mentioned magnetic poles, The yoke has a yoke-side opposing portion closely facing the magnetic pole, The above-mentioned yoke-side opposing portion has: a central zone region comprising a portion of a vertical plane of symmetry that roughly bisects said yoke; and the two side zone regions, which are separated from the above-mentioned vertical symmetry plane and located on both sides of the above-mentioned central zone region, In the height of the yoke-side facing portion from the yoke-side facing surface closely facing the magnetic poles, the central band region is higher than the side-band regions, The distance from the yoke-side opposing portion to the outer circumference of the magnetic pole decreases continuously as the front end of the yoke-side opposing portion approaches. 3. The magnet arrangement according to claim 1 or 2, characterized in that, The width of the yoke-side opposing portion in the normal direction with respect to the vertical symmetry plane decreases monotonously in a broad sense as the front end of the yoke-side opposing portion approaches, and the maximum and minimum values of the width are different. 4. The magnet arrangement according to claim 1 or 2, characterized in that, The height of the yoke-side opposing portion from the yoke-side opposing surface decreases monotonously in a broad sense as the distance from the vertical symmetry plane increases, and the maximum and minimum values of the height are different. 5. The magnet arrangement according to claim 1 or 2, characterized in that, The height of the above-mentioned yoke-side opposing portion from the yoke-side opposing surface decreases monotonously in a broad sense as approaching the front end of the above-mentioned yoke-side opposing portion, In addition, an outer surface of the yoke-side facing portion facing the yoke-side facing surface protrudes outward. 6. The magnet arrangement according to claim 1 or 2, characterized in that, The yoke has a yoke connecting portion connecting a pair of the yoke-side opposing portions, A viewing angle of the yoke connecting portion viewed from a central axis common to the pair of magnetic poles on a plane normal to the central axis is greater than 0° and not more than 180°. 7. The magnet arrangement according to claim 1 or 2, characterized in that, The width of the yoke-side opposing portion in the normal direction with respect to the vertical symmetry plane decreases continuously as the front end of the yoke-side opposing portion approaches. 8. The magnet arrangement according to claim 1 or 2, characterized in that, The height of the yoke-side facing portion closely facing the magnetic pole from the yoke-side facing surface decreases continuously as it moves away from the vertical symmetry plane. 9. The magnet arrangement according to claim 1 or 2, characterized in that, The width of the yoke-side opposing portion in the direction of the normal line with respect to the vertical symmetry plane decreases stepwise as the front end of the yoke-side opposing portion approaches. 10. The magnet arrangement according to claim 1 or 2, characterized in that, The height of the yoke-side facing portion closely facing the magnetic pole from the yoke-side facing surface decreases stepwise as it moves away from the vertical symmetry plane. 11. The magnet arrangement according to claim 1 or 2, characterized in that, A pair of substantially annular superconducting coils arranged close to the pair of magnetic poles are provided. 12. The magnet arrangement according to claim 1 or 2, characterized in that, It includes a pair of substantially disk-shaped permanent magnets disposed close to the pair of magnetic poles. 13. A magnetic resonance imaging device, characterized in that it has: A magnet arrangement as claimed in any one of claims 1 to 12; and Transport the subject to the bed between a pair of magnetic poles, The magnet device generates a uniform static magnetic field between the pair of magnetic poles to form an imaging space.