JPH0850170A - Magnetic resonance imaging device - Google Patents

Abstract

PURPOSE:To provide a magnetic resonance imaging device having a magnetic circuit freely accessible to a subject placed in a measuring space without giving a feeling of uneasiness to the subject. CONSTITUTION:Two first yokes 1a, 1b to which a pair of permanent magnets 3a, 3b for forming an uniform magnetic field in a measuring space 6 are fixed thereto, respectively, have disc body parts having the permanent magnets 3a, 3b fixed thereto and connecting parts extended in the rear, and supported by two second yokes 2a, 2b in each connecting part to form the measuring space 6 semicircularly opened in the front of the second yokes 2a, 2b. Thus, the sense of oppression to a subject placed in the semicircular measuring space 6 cart be eliminated, and a medical treatment can be performed closer to the subject under photographing from the peripheral part of the opened measuring space 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging apparatus (hereinafter referred to as "MRI apparatus"), and more particularly to an MRI apparatus having an improved magnetic circuit structure.

[0002]

2. Description of the Related Art An MRI apparatus uses a nuclear magnetic resonance (NMR) phenomenon to obtain a tomographic image at an examination site of a subject,
The MRI apparatus is provided for diagnosis and is provided with a magnetic circuit that forms a static magnetic field in the measurement space into which the subject is inserted in order to cause an NMR phenomenon in the examination site of the subject. .

FIG. 8 shows an example of the configuration of a magnetic circuit in a conventional MRI apparatus, and the structure of the magnetic circuit in the conventional apparatus will be briefly described below with reference to FIG. First, the magnetic circuit includes flat plate yokes 20a and 20b arranged in parallel and facing each other, and flat plate yokes 20a and 20b.
columnar yokes 21a to 21d supporting b, and a plate yoke 20
permanent magnets 22a, 22 provided on the facing surfaces of a, 20b.
b, the pole pieces 23a and 23b, and the gradient coil 24a,
24b and 24b as main constituent elements.

The flat plate yokes 20a and 20b are made of magnetic members formed in a substantially rectangular shape, and are supported by columnar yokes 21a to 21d provided in the vicinity of the four corners thereof so as to face each other in substantially parallel. That is, the columnar yokes 21a to 21d formed in a columnar shape are made of a magnetic member, and one end of each columnar yoke 21a to 21d has a flat plate yoke 20a in the vicinity of a corner of the flat plate yoke 20a. Inserted into
The columnar yokes 21a to 21d are connected to each other, and the other ends of the columnar yokes 21a to 21d are inserted and connected to the plate yoke 20b near the corners of the other plate yoke 20b.

The other plate yoke 20b is, so to speak, equivalent to a bottom plate, and is placed on the installation surface on which the magnetic circuit is installed via legs (not shown). Further, the flat magnets 20a and 20b are provided on their respective flat surface portions facing each other, and each of the permanent magnets 22 is formed in a disk shape.
a, 22b are joined together, and the diameter of the permanent magnets 22a, 22b is slightly smaller than the diameter of the permanent magnets 22a, 22b on the other surface (on the surface opposite to the surface joined to the flat plate yokes 20a, 20b). Magnetic pole pieces 23a and 23b each having a diameter and having an annular projection formed on the periphery thereof are provided. Further, gradient magnetic field coils 24a and 24b for generating a gradient magnetic field to be superimposed on the static magnetic field are provided in the hollow portions of the magnetic pole pieces 23a and 23b. In the figure, a permanent magnet 22a and a magnetic pole piece 23a
Also, the gradient magnetic field coil 24a is on the lower surface of the flat plate yoke 20a and is not shown.

In such a structure, the magnetic circuit has a magnetic pole piece 23a → a permanent magnet 22a → a flat plate yoke 20a → a columnar yoke → a flat plate yoke 20b → a permanent magnet 22b → a magnetic pole piece 23b →
In the measurement space 25 formed by the path of the measurement space 25 → the pole piece 23a and sandwiched by the pole pieces 23a and 23b,
Generates a uniform static magnetic field. Although not shown in FIG.
Flat plate yokes 20a, 20b and two columnar yokes 21a, 21
The portion other than the rectangular opening formed with b is covered with, for example, a gantry cover, and the plate yoke 20
The rectangular opening 26 formed by a and 20b and the two columnar yokes 21a and 21b serves as the entrance and exit of the subject.

[0007]

However, as described above, the openings 26 which form the entrance and exit in the above-mentioned conventional apparatus have flat plate yokes 20a, 20b and columnar yokes 2 around the openings.
Since it is configured to be surrounded by 1a and 21b, there is a problem that not only the physical oppressive feeling but also the psychological oppressive feeling is given to the subject, which makes the subject uneasy.

In order to solve such a problem, the present inventors have made the flat plate yoke a plane shape in which each corner of a substantially rectangular shape is cut out, and the insertion direction of the subject is set to the flat plate yoke. By making the direction orthogonal to the longitudinal direction, a device that widens the opening and reduces the feeling of pressure on the subject is proposed. By the way, in recent years, there has been a demand for using a so-called interventional MRI apparatus that diagnoses a specific part of a subject during MRI imaging and performs a medical treatment while checking an image. Since the doorway is only the opening 26, there is a problem that it is difficult to perform such medical treatment and the usability is poor. Therefore, attempts have been made to remove the feeling of pressure felt by the examinee and to make a doctor or the like accessible to the subject in the measurement space. For example, JP-A-62-26052 proposes a C-shaped magnet. There is.

However, even in the technique disclosed in Japanese Patent Laid-Open No. 62-26052, since the bed is arranged in front of the open portion of the C-shaped magnet, there remains a problem to be solved in the approach of the doctor or the like to the subject. It is considered to have been done. The present invention
In consideration of the above situation, a magnetic circuit having a structure that does not cause anxiety to the subject, is easy for the operator or operator to approach the subject, and has a high degree of freedom in disposing the bed with respect to the gantry. An object of the present invention is to provide an MRI apparatus having the above.

[0010]

The MRI apparatus of the present invention which achieves the above object is provided with a magnetic field circuit for forming a static magnetic field in a measurement space into which a subject is inserted, and the magnetic field circuit includes a pair of magnets. And a pair of first yokes that fix each magnet, and a second yoke that supports the first yoke so that the pair of magnets are arranged to face each other with a measurement space in between. In the MRI apparatus having the above, the first yoke has a substantially disc-shaped main body portion to which a magnet is fixed, and a joint portion extending rearward from the center of the main body portion, and the joint portion has two The second second yoke is provided, and preferably the diameters of the two second yokes are smaller than the diameter of the main body of the first yoke.

Further, in a preferred aspect of the MRI apparatus of the present invention, the thickness of the main body of the first yoke is gradually reduced from the peripheral portion to the central portion of the disk. Furthermore, in a preferred aspect of the MRI apparatus of the present invention, a through hole through which a subject lying on the bed can enter is provided between the two second yokes.

[0012]

The second yoke that supports the pair of first yokes so that the disk-shaped main body portions face each other is arranged rearward from the center of the main body portion, so that the second yoke Since the front measurement space can be opened to the outside in a semicircular shape with a spread of 180 degrees or more, a sense of pressure is given to the subject when the subject is inserted into the measurement space from the front. Never. Further, in the interventional state, while the subject is placed in the apparatus, it is possible to approach any part from the semicircular peripheral part, and it is possible to easily perform medical actions such as diagnosis and treatment. .

Further, by making the diameter of the two second yokes smaller than the diameter of the main body portion of the first yoke, the entire apparatus can be designed compactly, and the two second yokes are also provided. Since a relatively large opening can be provided behind the yoke, the feeling of pressure on the subject can be further reduced, and the subject can be approached from the rear opening. Furthermore the first
With the configuration in which the thickness of the yoke is gradually reduced toward the central portion, the weight of the device can be reduced without affecting the characteristics of the magnetic field.

Further, by providing a through hole through which the subject lying on the bed can enter between the two second yokes, the bed is arranged parallel to the gantry cover with respect to the gantry cover. A method such as a method of arranging the bed so that the bed enters the through hole of the gantry is possible, and the degree of freedom of arrangement is increased. Moreover, this through hole can also be used by a doctor or the like to approach the subject.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the MRI apparatus according to the present invention will be described below with reference to FIGS. here,
1 is an overall perspective view of an embodiment of a magnetic circuit 10 for an MRI apparatus according to the present invention, FIG. 2 is a plan view of the magnetic circuit of FIG. 1, and FIG. 3 is a vertical sectional view taken along the line AA of FIG.

The members, arrangements, etc. described below do not limit the present invention, but can be variously modified within the scope of the gist of the present invention. The magnetic circuit 10 for an MRI apparatus of this embodiment includes two first yokes 1a and 1b facing each other in parallel in a plane portion and two first yokes 1a and 1b.
Second yokes 2a, 2b for supporting the first yoke 1a, 1b
Permanent magnets 3a, 3b and pole pieces 4a, 4b provided on the
And have. The space between the permanent magnets of the first yokes 1a and 1b and the portion where the magnetic pole pieces are arranged is the measurement space 6, and the subject is inserted from the direction indicated by the arrow α in the figure to perform diagnosis. At this time, the whole or part of the subject is positioned in the measurement space 6.

Each of the first yokes 1a and 1b is made of a magnetic member and has a main body portion 11 having a disk-like planar shape (the shape shown in FIG. 2) and a part of the peripheral edge of the main body portion 11. The two coupling portions 12a and 12b are extended from the above. The angle β formed by the line connecting the centers of the coupling portions 12a and 12b and the center of the main body portion 11 is smaller than 180 degrees, and the vertical width L ₁ of the coupling portions 12a and 12b (vertical direction in FIG. 2) is the main body portion. It is set smaller than the diameter L _{2 of} 11. In the illustrated embodiment, L ₁ is about 50% of L ₂ . The second yoke 2 is attached to the joints 12a and 12b.
The end faces of a and 2b are joined together, so that they are sandwiched between the two first yokes 1a and 1b, and the joint portions 12a and 1b are joined together.
A measurement space having an arcuate opening is formed in front of 2b. Further, by making the vertical width L ₁ of the coupling portion smaller than the diameter L _{2 of the} main body portion, the size (L ₃ , L ₂ ) in the width direction and the depth direction of the entire device can be kept relatively compact and a solid support structure can be obtained. Can be

The second yokes 2a and 2b serve as a support member for the first yoke and form a magnetic path, and are formed in a columnar shape using a magnetic member, and the diameter thereof is the first yoke 1a. ,
It is smaller than the vertical width L ₁ of the coupling portion 12 in 1b. However, it is preferable that the sum of the cross-sectional areas of the two second yokes 2a and 2b be substantially the same as the sum of the cross-sectional areas of the conventional four columnar yokes. Second yoke 2a, 2b
By making the sum of the cross-sectional areas of (1) as large as possible, a solid support structure can be obtained and the leakage of the magnetic field from the measurement space can be minimized.

On the opposing flat sides of the first yokes 1a, 1b, the body 11 is provided with disk-shaped permanent magnets 3a, 3b concentrically with the disk center of the body 11. Arranged and joined. Permanent magnet 3 of this embodiment
The diameters of a and 3b are set to be slightly smaller than the diameter of the main body portion 11 of the first yoke 1a and 1b. Each of the permanent magnets 3a and 3b is formed by stacking rectangular blocks, and magnetic poles are formed in the thickness direction (vertical direction of the paper in FIG. 3). The magnetic poles on the surface side facing each other via magnetic pole pieces 4a and 4b described later. Are arranged so as to have different polarities (see FIG. 3).

Magnetic pole pieces 4a and 4b are joined to the measurement spaces of the permanent magnets 3a and 3b, respectively. This pole piece 4
Although not shown in detail, a and 4b are formed in a flat hollow bottomed cylindrical shape using a magnetic member, and are provided in the permanent magnets 3a and 3b so that their hollow portions face each other. A gradient magnetic field coil 5 (a part of which is shown by a broken line) for generating a gradient magnetic field to be superimposed on the static magnetic field is arranged in the hollow portion. The pole piece 4a of the present embodiment,
The diameter of 4b is set to be slightly smaller than the diameter of the permanent magnets 3a and 3b, but they may be set to have substantially the same size.

As shown by the dotted line in FIG. 3, the magnetic circuit in the above structure has one magnetic pole piece 4a, one permanent magnet 3a, one first yoke 1a, one second yoke 2a, and two.
b, the other first yoke 1b, the other permanent magnet 3b, the other magnetic pole piece 4b, and the measurement space 6 to return to the one magnetic pole piece 4a again. In this case, since the first yokes 1a and 1b are coupled by the two second yokes 2a and 2b having a relatively large cross-sectional area as described above, the leakage magnetic field can be reduced and the measurement space can be reduced. A uniform magnetic field can be formed at 6.

The first yoke 1a, 1 having the above structure
b, the second yokes 2a and 2b, the permanent magnets 3a and 3b, the pole pieces 4a and 4b, and the gradient coil are covered by the gantry cover 7 as shown in FIG. A through hole through which a subject lying on the bed can enter is provided between the second yokes 2a and 2b, and the front and rear of the second yoke 2a and 2b are open to the outside. The bed 8 and the transfer mechanism 9 for loading and unloading the subject into and out of the measurement space are the second yokes 2a and 2b.
Is installed in front of the main body portion 11 in front of, and the subject is inserted into the measurement space in a direction orthogonal to an imaginary line connecting the two second yokes 2a and 2b as indicated by an arrow α. In this case, since the magnetic field center where the measurement site of the subject is located is located substantially equidistant from the through-holes on both sides 6a and 6b in the front of the second yoke and in the rear 6c of the second yoke, any of them is used. Also, the subject can be approached, the degree of freedom of the operator in the interventional use is increased, and the act of diagnosing and treating the problem site can be easily performed. Moreover, the physical and psychological pressure on the subject inserted into the measurement space 6 can be minimized, and the subject can enter and leave the measurement space 6 without feeling anxiety. ing.

In the figure, the bed 8 and its transfer mechanism 9 are arranged with respect to the gantry in such a manner that the bed enters the through hole of the gantry. It is also possible to arrange the beds so that they are parallel. 5 and 6 show another embodiment of the present invention.

In these embodiments, the second yokes 2a and 2b connected to the first yokes 1a and 1b are arranged further rearward with respect to the insertion side of the subject. The other components are
Since it is the same as the embodiment shown in FIGS. 1 to 3, the description thereof will be omitted. In the embodiment shown in FIG. 5, the angle β formed by the line connecting the centers of the coupling portions 12a and 12b and the center of the main body portion 11 is 120 degrees or less.
The measurement space in front of the yokes 2a and 2b has an arc-shaped opening close to approximately 240 degrees. Therefore, it is easier to approach the subject from the front side. Further, the device of this embodiment has a longer size (L ₄ ) in the depth direction than the device of the embodiment shown in FIG. 2, but the size (L ₅ ) in the width direction can be made smaller. It can be designed according to the installation location. Also in this case as well, by making the diameter of the second yoke smaller than the diameter of the main body portion, an opening width (L ₆ ) that allows the bed to move sufficiently is provided behind the second yokes 2a and 2b. It is possible to secure.

In the embodiment shown in FIG. 6, the second yoke 2a,
The connecting portion 12 to which 2b is connected is integrally provided behind the disk-shaped main body 11, and in these cases also, a sufficiently wide open opening is provided in the measurement space formed between the main bodies 11. Since it is possible to approach the subject, it is possible to arrange the bed in a direction parallel to the gantry cover (direction parallel to the line connecting the two second yokes 2a and 2b). . Further, by providing a through hole between the two second yokes 2a and 2b, it is possible to adopt a method of arranging the bed so that the bed enters the through hole, thereby increasing the degree of freedom of arrangement.

In the above embodiments, the main body of the first yoke has a circular planar shape and the second yoke has a cylindrical shape. However, these shapes have various modifications. For example, the main body of the first yoke may have an elliptical shape or a rounded rectangular shape, or a second shape.
The yoke may have a prismatic shape. Further, in the above examples, the case where the thickness of the first yoke is uniform in the surface direction is shown.
It can be arbitrarily changed within a range that does not affect the magnetic circuit. Such an embodiment is shown in FIG.

The magnetic circuit of the MRI apparatus shown in FIG. 7 has the same planar shape as that shown in FIG. 2, 5 or 6 (a), but the thickness of the first yoke is within the yoke. It is carved from the periphery to the center of the body to the extent that the passing magnetic flux is not saturated. As a result, the weight of the entire device is reduced. The thickness of the main body portion can be reduced to about half the thickness of the peripheral portion at the center portion, and in this case, the weight can be reduced by about 10% of the total weight. That is, it is possible to reduce the weight of the magnetic circuit of about 10 tons to 9 tons or less. This embodiment is applicable to any of the other embodiments of the invention.

[0028]

As described above, according to the present invention,
By adopting a structure in which the rear of the disk-shaped main body portion of the first yoke is supported by two second yokes, it is possible to take in and out of the measurement space as wide as possible, and thereby, the subject can be inspected. The effect is that the user can smoothly enter and exit without feeling physical pressure or psychological pressure.

Further, since the magnetic field center of the measurement space can be approached from anywhere on the outer circumference of the semicircle, it becomes possible for a doctor to perform medical treatment on an arbitrary part of the subject while performing image diagnosis on the subject. The effect is that more effective medical treatment can be provided. In particular, by providing a through-hole between the two second yokes and through which a subject lying in the bed can enter, the degree of freedom in arranging the bed with respect to the gantry is increased, and a doctor can be provided through this through-hole. Etc. can easily approach the subject.

[Brief description of drawings]

FIG. 1 is an overall perspective view of an embodiment of a magnetic circuit of an MRI apparatus according to the present invention.

FIG. 2 is a plan view of the magnetic circuit shown in FIG.

FIG. 3 is a vertical sectional view taken along the line AA of the magnetic circuit of FIG.

4 is an overall perspective view of an MRI apparatus including the magnetic circuit of FIG.

FIG. 5 is a plan view showing another embodiment of the MRI apparatus according to the present invention.

FIG. 6 is a plan view showing another embodiment of the MRI apparatus according to the present invention.

FIG. 7 is a front view showing another embodiment of the MRI apparatus according to the present invention.

FIG. 8 is an overall perspective view showing an example of a magnetic circuit in a conventional device.

[Explanation of symbols]

 1a, 1b ..... First yoke 2a, 2b ..... Second yoke 3a, 3b ..... Permanent magnets 4a, 4b ........ Pole piece 11. ...... Main body 12a, 12b, 12 ... Connection part 6 ... Measurement space

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideya Sakurai 2-15-17 Egawa, Mishima archipelago, Osaka Prefecture Sumitomo Special Metals Co., Ltd. Yamazaki Works

Claims (4)

[Claims] 1. A magnetic field circuit for forming a static magnetic field in a measurement space into which a subject is inserted, the magnetic field circuit comprising a pair of magnets and a pair of first yokes for fixing the respective magnets. And a second yoke that supports the first yoke so that the pair of magnets are arranged to face each other with the measurement space in between, a magnetic resonance imaging apparatus comprising: The iron has a substantially disk-shaped main body portion to which the magnet is fixed, and a joint portion extending rearward from the center of the main body portion, and the second yoke is provided in the joint portion by two pieces. A magnetic resonance imaging apparatus characterized by being provided. 2. The magnetic resonance imaging apparatus according to claim 1, wherein the diameter of the two second yokes is smaller than the diameter of the main body portion of the first yoke. 3. The magnetic resonance imaging apparatus according to claim 1, wherein the body of the first yoke has a thickness that gradually decreases from the peripheral portion to the central portion of the disk. 4. The magnetic resonance according to claim 1, wherein a through hole through which a subject lying on a bed can enter is provided between the two second yokes. Imaging equipment.