JP3080603B2 - Static magnetic field generator for MRI equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a static magnetic field generator used for a magnetic resonance imaging apparatus (hereinafter, referred to as an MRI apparatus).

[0002]

2. Description of the Related Art A magnetic resonance imaging apparatus is an apparatus that obtains a tomographic image of a subject to be examined using a so-called nuclear magnetic resonance (NMR) phenomenon.

[0003] As one means for causing the NMR phenomenon in the examination region of the subject, there is provided a static magnetic field generator for forming a static magnetic field in the measurement space into which the subject is inserted.

This static magnetic field generator has conventionally been configured as follows.

For example, as shown in FIG.
First yoke 92A, 92 opposed to each other with 1 in between
B, and these first yokes 92A, 92B are provided at the portions (each corner of the first yoke) corresponding to both sides of the subject inserted in the direction of the arrow α in the figure (the second yoke 93A). , 93B, 9
3C, 93D, the first yoke 92A,
Disc-shaped permanent magnets 94A (not shown) and 94B are provided at substantially the center of a surface of the measurement space 91 on the side of the measurement space 91B.
Is fixed.

[0006]

However, in the magnetic circuit configured as described above, the insertion port of the subject into the measurement space 91 is provided with the second yoke positioned in front of the first yoke 92A, 92B. 93A and 93B, the frontage was relatively narrow.

For this reason, when the subject is inserted into the measurement space 91, it is inevitable that a so-called oppressive feeling is generated. For example, this causes a great sense of anxiety for the subject with claustrophobia. .

In recent years, it is often the case that a special part of a subject is diagnosed. In this case, if the frontage of the insertion port into the measurement space 91 is narrow, a doctor or the like directly touches the subject while the doctor or the like directly touches the subject. There remains a problem that it is difficult to freely diagnose a special site in a specimen.

Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to provide a method in which a doctor or the like directly touches a subject without giving a feeling of oppression to the subject. It is an object of the present invention to provide a static magnetic field generator capable of constituting a magnetic resonance imaging apparatus capable of freely diagnosing a special site in a subject.

[0010]

In order to achieve such an object, a static magnetic field generator for an MRI apparatus according to the present invention is vertically opposed to each other across a space in which a subject can be inserted, A set of magnetic field sources for generating a uniform magnetic field having a predetermined intensity and a spatial size to be a measurement space in the space, and a set of magnetic field sources for supporting these magnetic field sources behind the space; A first yoke and a second yoke arranged between the first yoke and configured to maintain a distance between the pair of magnetic field generation sources at a predetermined value and configure a magnetic circuit with the magnetic field generation source and the first yoke. In the static magnetic field generator for MRI apparatus having two yoke, each of the first yokes has an external plane larger than the diameter of the magnetic field generation source when the static magnetic field generator is viewed in plan, and Visually align the magnetic field source on a straight line passing through the center of the magnetic field source. Protrusions whose ends have a smaller width than the diameter of said magnetic field generating source is formed at both ends Nde, the second
A yoke is provided between each of the first yoke in the vertical direction and between the protrusions, and one of the yoke is provided on the outside of the magnetic field generating source so as to face each other. Are open to the external space on both sides orthogonal to the facing direction. (Claim 1)

In order to achieve the above object, the present invention is arranged so as to be vertically opposed to each other across a space in which a subject can be inserted, and has a predetermined strength and spatial A set of magnetic field sources for generating a uniform magnetic field having a magnitude, a set of first yoke supporting each of these magnetic field sources behind the space, and a first yoke arranged between the first yoke. A static magnetic field generator for an MRI apparatus, comprising: a second yoke that forms a magnetic circuit with the magnetic field generation source and the first yoke while maintaining an interval between the pair of magnetic field generation sources at a predetermined value. Each of the first yoke has a contour plane larger than the diameter of the magnetic field source when viewed in plan view of the static magnetic field generator, and is divided by a first straight line passing through a center point of the magnetic field source. A protrusion having a width smaller than the diameter of the magnetic field source in one of the The portion is formed symmetrically with respect to a second straight line that is orthogonal to the first straight line and passes through the center of the magnetic field generating source, and the second yoke is opposed to each of the first yoke in a vertical direction. One each standing between the protruding portions and outside the magnetic field generating source, wherein the measurement space is open to the outside space on both sides orthogonal to the facing direction of the second yoke portion. It is. (Claim 2)

Further, in order to achieve the above object, according to the present invention, the first yoke is formed so that a portion coupled to the second yoke is formed to protrude beyond the outer diameter of the magnetic field generating source. The portion is characterized by being formed in a polygonal shape or an arc shape approximating the outer diameter of the magnetic field generation source. (Claim 3)

[0013] In the static magnetic field generator for an MRI apparatus thus configured, both ends of the first yoke in the magnetic circuit protrude from the magnetic field source and are formed with a width smaller than the diameter of the magnetic field source. A second yoke is erected between the protrusions of the first yoke with the magnetic field generation source interposed therebetween, and the measurement space is two second yoke.
Since both sides in the opposing direction of the yoke are open, even if the subject is put in the measurement space, the subject feels a better open feeling than the conventional device. Further, a doctor or the like can make a diagnosis while directly touching the subject through the opening.

When the apparatus is viewed in a plan view, a second yoke is provided on one side of a region divided by a straight line passing through the center of the magnetic field source, passing through the center of the magnetic field source and orthogonal to the center line. By symmetrically arranging the openings, one of the openings can be made wider than the other, which further increases the sense of openness felt by the subject and makes it easier for a doctor or the like to access the center of the measurement space from both sides of the bed.

[0015]

FIG. 1 is a perspective view showing an embodiment of a static magnetic field generator provided in an MRI apparatus according to the present invention.

In FIG. 1, a static magnetic field generator 10 has a measurement space 11 into which a subject (not shown) is inserted from the direction of arrow α in the figure. The first yokes 12A and 12B are arranged to face each other with the measurement space 11 therebetween, and the first yokes 12A and 12B are supported by portions corresponding to both sides of the subject into which the first yokes 12A and 12B are inserted. And the second yoke 13A, 13B,
Permanent magnets 14A (not shown) and 14B are fixed to substantially the center of the surface of the first yoke 12A and 12B on the measurement space 11 side, respectively.

FIG. 2 is a view showing a cross section taken along line II-II of FIG. 1 and further shows a magnetic path crossing the measurement space 11. In the same figure, opposed permanent magnets 14A, 1
The magnetic flux generated by one of the permanent magnets 14B of 4B is
The pole piece 15B passes through the measurement space 11, and the pole piece 15A,
The magnetic circuit forms two closed loops that pass through the permanent magnet 14A, the first yoke 12A, pass through the second yoke 13A, 13B, and the first yoke 12B, and return to the permanent magnet 14B. I have.

Hereinafter, the first yoke 12A, 12B,
The yoke 13A, 13B, the permanent magnets 14A, 14B, etc. will be described in further detail.

The first yoke 12A, 12B each of the first yoke 12A, 12B has a plane shape, has a shape which is cut out nearly each corner of the rectangle. The first yokes 12A and 12B are arranged so as to face each other with the measurement space 11 therebetween, and their major axis directions are positioned so as to be orthogonal to the insertion direction of the subject (the α direction in the figure). I have.

Thus, the width of each of the first yokes 12A and 12B along the insertion direction α of the subject becomes smaller on both sides of the subject to be inserted.

The second yoke 13A, 13B is provided at both sides of the subject to be inserted so as to mutually support the first yoke 12A, 12B arranged opposite to each other. Is arranged.

The width of the second yoke 13A, 13B along the insertion direction α of the subject is smaller than the width of a permanent magnet 14 described later in the same direction.

That is, at the longitudinal ends of the first yokes 12A and 12B, in other words, the width along both sides of the inserted subject along the inserting direction α of the subject is formed small. The first yoke 12A, 1
2B is supported by the second yoke 13A, 13B.

The second yoke 13A, 13B passes through the center of the permanent magnet 14 in a plan view and the subject insertion direction α
Are positioned symmetrically with respect to a straight line orthogonal to the virtual line and passing through the center of the permanent magnet 14.

The permanent magnets 14A (not shown), 1
The 4B permanent magnets 14A and 14B each have a disk shape and are fixed to the surface of the first yoke 12A and 12B on the measurement space 11 side.

The diameters of the permanent magnets 14A, 14B are equal, and are sufficiently large without protruding from the first yoke 12A, 12B.

Here, referring to FIG. 3, the first yoke 1
The respective sizes of the cross sections of the 2A, the permanent magnet 14A, and the second yoke 13A, 13B will be described. In the figure,
The width L1 of the second yoke 13A, 13B along the subject insertion direction α is approximately 50% of the width (slightly larger than the diameter of the permanent magnet 14A) L2 of the first yoke 12A in the same direction. . Then, the width T of the second yoke 13A, 13B in the direction orthogonal to the insertion direction α of the subject is taken, and T × L1
Assuming that the area determined by × 2 (since two are multiplied by two) is approximately the same as the total cross-sectional area of the second yoke of the apparatus having four second yoke shown in FIG. The characteristics are comparable to those of the conventional device. For this purpose, the first yoke 1
The width L3 of 2A in the direction orthogonal to the subject insertion direction α may be larger than before, but this does not particularly cause any adverse effect.

Magnetic pole pieces 15A (not shown) and 15B are arranged on the surfaces of the permanent magnets 14A and 14B on the measurement space 11 side, respectively, and a gradient for forming a gradient magnetic field in the measurement space is provided. Magnetic field coils 16A (not shown) and 16B are arranged.

FIG. 4 shows an envelope 40 enclosing the magnetic circuit 10, and an insertion port 41 into the measurement space of the envelope 40 is formed in accordance with the shape of the magnetic circuit 10. , Both sides 4 of the subject to be inserted
In 1A and 41B, it is possible to have a shape in which it is recessed rearward as compared with the central portion, and thus the frontage of the insertion port can be made substantially larger than in the conventional case. In addition,
In FIG. 4, a bed 42 for placing a subject is disposed in front of the insertion port 41.

According to the magnetic circuit 10 of the above-described embodiment, the width of the second yoke 13A, 13B along the subject insertion direction α is reduced, and the permanent magnet 14
A and 14B are located on an imaginary line passing through the center of the object and orthogonal to the subject insertion direction α. And the first yoke 12
A and 12B have their widths along the subject insertion direction α reduced at locations supported by the second yokes 13A and 13B.

For this reason, the insertion opening into the measurement space 11 can have a shape in which both sides are recessed as compared with the central portion. As a result, the frontage of the insertion port becomes substantially large, so that the subject inserted into the measurement space 11 does not have a feeling of oppression, and at the same time, the first yoke 12
A doctor or the like stands on the recessed portion of A, 12B and can easily access the affected part of the subject located in the measurement space.

Further, since the insertion opening of the measurement space 11 has a shape slightly larger in the side direction on both sides, the subject can be inserted from the side direction, in other words, the bed can be inserted. The degree of freedom in the arrangement direction can be increased, and a special site in the subject can be freely diagnosed.

The shapes of the first yokes 12A and 12B and the second yokes 13A and 13B are not limited to those shown in FIG. 1, but may be various as shown in FIGS. It goes without saying that deformation can be brought about.

In the above embodiments, the first yoke 12A,
The planar shape of 12B is almost an octagon,
The present invention is not necessarily limited to this, and it goes without saying that each corner may be cut to form a smooth arc. In short, it is only necessary that the width of the subject along the insertion direction α be small at a position supporting the second yoke.

In the above-described embodiment, the second yoke 13
A and 13B are positioned on a virtual line passing through the centers of the permanent magnets 14A and 14B and orthogonal to the subject insertion direction α. However, the present invention is not limited to this, and it goes without saying that it may be moved and positioned directly behind the virtual line. Even in this case, the frontage of the insertion port of the subject into the measurement space 11 can be made sufficiently large. In this case, the opening is larger at the front where the bed is arranged than at the rear, so that a doctor or the like can easily access the affected part in the center of the measurement space from the front bedside.

[0036]

As is apparent from the above description,
ADVANTAGE OF THE INVENTION According to the static magnetic field generator for MRI apparatus by this invention, the MRI apparatus which does not give a feeling of oppression to a subject, and which can freely diagnose a special part in a subject while a doctor etc. touches a subject directly is provided. Will be able to do it.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of a static magnetic field generator provided in a magnetic resonance imaging apparatus according to the present invention.

FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1 and is an explanatory diagram showing a magnetic path crossing a measurement space.

FIG. 3 shows a first yoke in the static magnetic field generator shown in FIG.
It is explanatory drawing for demonstrating each size of a 2nd yoke and a permanent magnet.

FIG. 4 is a perspective view showing an embodiment of an envelope including a static magnetic field generator provided in the magnetic resonance imaging apparatus according to the present invention.

FIG. 5 is a plan view showing another embodiment of the static magnetic field generator provided in the magnetic resonance imaging apparatus according to the present invention.

FIG. 6 is a plan view showing another embodiment of the static magnetic field generator provided in the magnetic resonance imaging apparatus according to the present invention.

FIG. 7 is a plan view showing another embodiment of the static magnetic field generator provided in the magnetic resonance imaging apparatus according to the present invention.

FIG. 8 is a plan view showing another embodiment of the static magnetic field generator provided in the magnetic resonance imaging apparatus according to the present invention.

FIG. 9 is a perspective view showing an example of a static magnetic field generator provided in a conventional magnetic resonance imaging apparatus.

[Explanation of symbols]

 11 Measurement space 12 First yoke 13 Second yoke 14 Permanent magnet

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-1-283905 (JP, A) JP-A-2-218344 (JP, A) JP-A-2-243132 (JP, A) JP-A-2- 21846 (JP, A) Shokai Sho 62-101205 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) A61B 5/055

Claims (3)

(57) [Claims] 1. A uniform magnetic field having a predetermined strength and a spatial magnitude, which is arranged in a vertical direction across a space into which a subject can be inserted, and serves as a measurement space in the space. A set of magnetic field sources, a set of first yoke supporting each of these magnetic field sources behind the space, and a distance between the first set of magnetic field sources arranged between the first yoke. In a static magnetic field generator for an MRI apparatus having a predetermined value and a second yoke constituting a magnetic circuit with the magnetic field generation source and the first yoke, each of the first yoke is a static magnetic field. The generator has an external plane larger than the diameter of the magnetic field generation source when viewed in plan, and the end of the magnetic field generation is located on a straight line passing through the center of the magnetic field generation source in plan view with the magnetic field generation source interposed therebetween. Protrusions having a width smaller than the diameter of the source are formed at both ends,
The second yoke is located between the protrusions of each of the first yoke in the vertical direction, and each of the second yoke is erected on the outside of the magnetic field generation source so as to be opposed to each other. A static magnetic field generator for an MRI apparatus, characterized in that both sides orthogonal to the direction of the yoke are open to the external space. 2. A uniform magnetic field having a predetermined strength and a spatial magnitude, which is arranged in a vertical direction across a space in which a subject can be inserted, and serves as a measurement space in the space. A set of magnetic field sources, a set of first yoke supporting each of these magnetic field sources behind the space, and a distance between the first set of magnetic field sources arranged between the first yoke. In a static magnetic field generator for an MRI apparatus having a predetermined value and a second yoke constituting a magnetic circuit with the magnetic field generation source and the first yoke, each of the first yoke is a static magnetic field. When the generator is viewed in a plan view, the magnetic field source has an external plane larger than the diameter of the magnetic field source and is located within one of regions divided by a first straight line passing through the center point of the magnetic field source. The protrusion having a width smaller than the diameter of the magnetic field is perpendicular to the first straight line. The second yoke is formed symmetrically with respect to a second straight line passing through the center of the source, and the second yoke is provided between the vertically opposed protrusions of each of the first yoke and outside the magnetic field generation source. Wherein the measurement space is open to the outside space on both sides perpendicular to the direction in which the second yoke portion faces each other. 3. The first yoke is formed such that a portion coupled to the second yoke protrudes beyond the outer diameter of the magnetic field generation source, and a portion excluding the protruding portion approximates the outer diameter of the magnetic field generation source. The static magnetic field generator for an MRI apparatus according to claim 2, wherein the apparatus is formed in a polygonal shape or an arc shape.