JP2003159230A - Superconducting magnet and magnetic resonance imaging apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a superconducting magnet and a magnetic resonance imaging apparatus using the same, which suppress deflection of generated magnetic flux of a superconducting coil so as to be prevented from adversely affecting an image, by reducing transmission of vibrations from a refrigerating machine to a coil container housing the superconducting coil, and which can secure a large space for allowing the entry of a subject, so as to be prevented from giving a sense of oppression to the subject, even if the apparatus is downsized. <P>SOLUTION: A cooling medium tank for supplying a cooling medium to the coil container is provided separately from the coil container and a passage for circulating the cooling medium makes the cooling medium tank communicate with the coil container. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting magnet and a magnetic resonance imaging (MRI) apparatus using the superconducting magnet. It relates to the MRI apparatus used.

[0002]

2. Description of the Related Art An example of a conventional superconducting magnet used in an MRI apparatus is described in Japanese Patent Application Laid-Open No. 10-179546. In the conventional superconducting magnet described in this, the coil container, which is immersed in liquid helium as a cooling medium and stores the superconducting coil, also serves as a helium tank for storing liquid helium. A refrigerator for cooling is installed directly in a coil container (helium container).

Further, as a countermeasure against the vibration of the refrigerator, there is a system in which a flexible portion such as a bellows is installed between the refrigerator and a cryostat portion in which the refrigerator is installed.
No. 19 publication. This method will certainly provide vibration isolation between the cryostat and the cold head of the refrigerator, but in order to provide reliable vibration isolation while ensuring cooling performance, various methods such as those described in the patents mentioned above are used. It is necessary to devise a device, which causes an increase in cost.

[Patent Document 1] Japanese Patent Laid-Open No. 10-179546

[Patent Document 2] JP-A-11-16719

[0004]

However, the conventional superconducting magnet for an MRI apparatus has the following problems.

That is, since the refrigerator for cooling liquid helium is directly installed in the coil container, the vibration of the refrigerator is directly transmitted to the coil container, and this vibration also vibrates the superconducting coil housed inside. The generated magnetic flux fluctuates, which adversely affects the image, and a clear image cannot be obtained.

Further, conventionally, since the cooling medium tank and the coil container are integrally formed, the device inevitably becomes large, and when the device becomes large, the space into which the object to be examined is restricted is narrow. However, there is a problem in that the subject feels a sense of pressure during the examination.

The present invention has been made in view of the above points, and an object thereof is to reduce the transmission of vibrations from a refrigerator to a coil container in which the superconducting coil is housed, and to generate a magnetic flux of the superconducting coil. Of a superconducting magnet that suppresses the shake of the image and does not adversely affect the image and MRI using the same
To provide a device.

It is another object of the present invention to provide an MRI apparatus which can take a large space for a subject and does not give a feeling of pressure to the subject even if the device is miniaturized. .

[0009]

In order to achieve the above object, according to the present invention, a cooling medium tank for supplying a cooling medium to a coil container accommodating a superconducting coil together with a cooling medium is provided separately from the coil container. A refrigerator for cooling the cooling medium is installed in the cooling medium tank, the cooling medium tank and the coil container are connected by a passage for circulating the cooling medium, and an annular space is formed in the coil container. At the same time, a ferromagnetic magnetic pole is arranged in the space.

In order to achieve another object, according to the present invention, a cooling medium tank for supplying a cooling medium for a coil container accommodating the superconducting coil together with a cooling medium is provided separately from the coil container, and , The cooling medium in the coil container is set to the minimum necessary amount for maintaining superconductivity, or at the vertical angle limited by the magnetic poles when the opening of the upper and lower coil containers is seen from the center of the superconducting magnet. A certain viewing angle is 30 ° or more, or a cooling medium tank for supplying a liquid refrigerant to the coil container is provided separately from the coil container, and both are connected by a passage, and a crossover wire from the superconducting coil is provided. Is wired in the cooling medium tank, and the crossover and the permanent current switch are connected in the cooling medium tank.

Further, the present invention provides a superconducting magnet according to any one of claims 1 to 8, a bed on which a subject is placed and which is movable between coil containers of the superconducting magnet facing each other, and a nucleus from the subject. It is characterized in that it is an MRI apparatus provided with a control device for analyzing a magnetic resonance signal.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

First, a schematic structure of the MRI apparatus will be described. As shown in FIG. 18, the MRI apparatus includes a superconducting coil (not shown), coil containers 11 and 12 that house the superconducting coil together with a cooling medium (for example, liquid helium), a cooling medium tank 41 that cools the cooling medium, and a cooling. It is composed of a refrigerator 51 for cooling the medium, a superconducting magnet 80, a bed 90 on which a subject is placed, and a controller 100 for analyzing a nuclear magnetic resonance signal from the subject, and the coil containers 11 and 12 are separated from each other. Then, a magnetic field space is formed between the coil containers 11 and 12 while facing each other, and tomography is performed through the subject on the bed 90.

Next, each embodiment of the superconducting magnet used in the MRI apparatus will be described below.

FIGS. 1, 2 and 3 show a first embodiment of the superconducting magnet. FIG. 3 shows the magnetic pole support members 71, 7 from FIG.
2, the magnetic poles 81 and 82, and the support member 63 are removed.

As shown in the figure, in this embodiment, a cooling medium tank (hereinafter referred to as He tank) 41 for supplying a cooling medium to the coil containers 11 and 12 is provided separately from the coil containers 11 and 12. The refrigerator 51 is added to the He tank 41.
And the He tank 41 and the coil container 1 are installed.
1 and 12 are passages 31 and 32 for circulating the cooling medium, respectively.
(Piping) is connected. And the coil containers 11, 1
2 is supported by the He tank 41 via the passages 31 and 32.

An annular space is formed in the coil containers 11 and 12, and magnetic poles 81 and 82 made of a ferromagnetic material are installed in the space to support the upper coil portion and the lower coil portion including the magnetic poles 81 and 82. Is performed by the support member 63.

That is, the upper and lower coil containers 11 and 12 having the magnetic poles 81 and 82 are supported by the magnetic pole support members 71 and 72, and the upper and lower coil containers 11 and 12 are supported by the support member 63 via the magnetic pole support members 71 and 72. . This magnetic pole support member 71,
72 is made of a ferromagnetic material.

The coil containers 11 and 12 and the He tank 41 are connected by passages 31 and 32, respectively, whereby liquid He is supplied from the He tank 41 to the coil containers 11 and 12. As described above, the refrigerator 51 is installed in the He tank 41, and the refrigerator 51 is for liquefying the gasified refrigerant.

Next, as shown in FIG. 2, the coil container 11,
12 is the superconducting coil 11 in the He containers 112 and 122.
3, 123 are housed together with a cooling medium, and further provided with shield plates 111, 121, which are vacuum-insulated and cooled by the refrigerator 51. Superconducting coils 113, 123
From here, a superconducting crossover 711 is wired to the inside of the He tank 41, where the superconducting switch 602 and the protective resistor 60 are connected.
It is connected to 1. Superconducting coil is liquid He (4.2
It is cooled by K) and has a zero resistance to current flow at this temperature. The superconducting coil can also be formed of any material, such as a low temperature or high temperature superconductor that becomes superconducting below the superconducting transition temperature (ie exhibits near zero resistance to the flow of current).

Generally, a low-temperature superconductor makes a superconducting transition at a temperature close to 0 degrees absolute. High-temperature superconductors make superconducting transitions at temperatures well above absolute 0 degrees.

As an example, as the low-temperature superconductor, niobium-titanium is used as a filament and copper is used as a matrix. Alternatively, any material suitable for superconductivity can be utilized for this application, such as other materials categorized as low temperature or high temperature superconductors.

The superconducting coils 113 and 123 are excited by connecting a power source 805 to the power lead 811. After the excitation, the power source 805 is disconnected from the power lead 811.

The power lead 811 is connected to the permanent current switch 602 and the protection resistor 6 via the low temperature part current introduction terminal 812.
01 is connected to a superconducting crossover 711.

A pressure sensor 801 is installed in the He tank 41, and an output signal from the pressure sensor 801 is fetched into a control box 802, and the energization amount of the heater 803 is controlled, whereby the tank internal pressure can be made substantially constant. Therefore, the amount of liquid He is maintained at an appropriate amount.

That is, the refrigerator 51 is continuously operated, and the liquid He amount is detected by the pressure in the He tank 41 and the heater 8 is detected.
Controlled by 03.

According to this configuration, the coil containers 11, 12 and H
Since the e-tank is located away from each other via the passages 31 and 32, the vibration of the refrigerator 51 does not easily propagate to the coil containers 11 and 12. Therefore, it is possible to reduce the influence on the magnetic field homogeneity in the magnetic field space formed by the superconducting coil. Further, since the magnetic poles 81 and 82 are provided, a uniform magnetic field can be formed without increasing the number of magnets in the central magnetic field, which tends to become non-uniform, so that the MRI can be constructed at low cost.

Further, since the He tank 41 is moved away from the magnetic field space, the permanent magnetic switch 602 and the superconducting connection 701 of the persistent current switch are installed inside the He tank 41 to reduce the empirical magnetic field. It is possible to set a low value (a large margin), cost reduction is achieved, and reliability is improved. Further, by disposing the permanent current switch and the superconducting connection portion in the He tank, it becomes possible to minimize the size of the coil container. That is, the amount of liquid helium in the coil container can be reduced by setting the necessary minimum amount of liquid helium to hold the coil in superconductivity, so that the size of the coil container can be reduced. This makes it possible to take a wider space for the subject,
The subject feels less oppressive. Furthermore, it becomes easier to perform a medical operation such as performing an operation while seeing an image, that is, a subject under examination.

FIG. 4 is a schematic view showing the periphery of the coil shown in FIG. The viewing angle is defined using this figure. That is, the magnet 8
When viewing the open portions of the upper coil 11 and the lower coil 12 from the center 0 of 1, 82, the vertical angle limited by the magnetic poles is called the viewing angle. In this embodiment, as described in the first embodiment, by making the coil container compact, the height of the coil container (dimension a in the figure) is lower than the height of the magnetic pole portion (dimension a in the figure). You can take a wide viewing angle,
For example, a configuration of 30 ° or more is possible.

In the second embodiment of FIG. 5, vibration isolation means 33, 34 such as bellows are provided in the middle of the passages 31, 32 connecting the coil containers 11, 12 and the He tank 41 described in the first embodiment. This is an example provided. The present invention relates to a cooling medium tank 41 in which a refrigerator is installed and a coil container 11,
Since a passage is provided between the passage 12 and 12 and the distance is secured, the structure is essentially resistant to vibration of the refrigerator. However, by providing the above-mentioned vibration isolation means in the passages 31 and 32, vibration isolation can be achieved. Will be certain.

This makes it possible to more effectively suppress transmission of refrigerating machine vibration to the coil container.

FIG. 6 shows a third embodiment of the superconducting magnet.

In this embodiment, a cooling medium tank for supplying a cooling medium to the coil containers 11 and 12 (hereinafter referred to as He tank).
41 is provided separately from the coil containers 11 and 12, and
The refrigerator 51 is installed in the He tank 41, and the He tank 41 and the coil containers 11 and 12 are connected by a passage 31 (pipe) for circulating a cooling medium.
The coil containers 11 and 12 are supported by the He tank 41 via the support member 61.

Further, the upper and lower coil containers 11 and 12 are connected by a connection passage 21, through which liquid He and He gas pass, as well as coil connection lines and the like. Further, the coil container 11 and the He tank 41 are connected by the passage 31, so that the liquid He is transferred from the He tank 41 to the coil container 11.
Is supplied and the He gas is collected in the He tank 41. As mentioned above, He tank 4
1 has a refrigerator 51 installed.
Is for condensing the He gas collected in the He tank 41.

According to this configuration, the coil containers 11, 12 and H
Since the e-tank is located at a position separated via the passage 31, the vibration of the refrigerator 51 is difficult to propagate to the coil containers 11 and 12. Therefore, it is possible to reduce the influence on the magnetic field homogeneity in the magnetic field space formed by the superconducting coil.

FIG. 7 shows a fourth embodiment of the superconducting magnet.

In this embodiment, a coil container support member 62 for supporting the upper and lower coil containers 11 and 12 in the third embodiment is prepared separately from the He tank 41. Even if configured in this way, the effect is similar to that of the first embodiment, but if the He tank 41 can be made compact, it is more rational to provide the coil container support member 62 than the first embodiment. .

FIG. 8 shows a fifth embodiment of the superconducting magnet.

In addition to the structure of the third embodiment, this embodiment
This is a case where the ferromagnetic members 71 and 72 are arranged outside the coil containers 11 and 12 (on the side opposite to the coil facing surface). Even with this configuration, the effect is similar to that of the first embodiment, but by arranging the ferromagnetic members 71 and 72 at this position, it is possible to reduce the leakage magnetic field. In some cases, the active shield coil may be replaced by the ferromagnetic members 71, 72.
It is also possible to arrange it on the top surface to improve the magnetic field shield performance. The coil container 11 and the He tank 41 are connected via a passage (not shown).

9 and 10 show a sixth embodiment of the superconducting magnet. FIG. 10 shows the magnetic pole support members 71, 72 from FIG.
The magnetic pole and the support member 63 are removed.

In this embodiment, the coil containers 11 and 12 having the ferromagnetic members 71 and 72 arranged outside are supported by a member 63 different from the He tank 41.

As described in the fourth embodiment, the He tank 4
When 1 can be configured compactly, it is cheaper to provide the support 63 separately from the He tank 41. Also,
When this support is made of a ferromagnetic material (iron material), the magnetic circuit is configured together with the upper and lower ferromagnetic material members 71 and 72, so that the leakage magnetic field can be more effectively suppressed.

FIG. 11 shows a seventh embodiment of the superconducting magnet.

In this embodiment, an annular space is formed in the coil containers 11a and 12a, and a magnetic pole 8 made of a ferromagnetic material is formed in the space.
1, 82 are installed, and the He tank 41 also serves to support the upper coil portion and the lower coil portion including the magnetic poles 81 and 82. That is, the He tank 41 supports the coil containers 11a and 12a in which the magnetic poles 81 and 82 are installed via the support members 64 and 65. This support member 6
Reference numerals 4 and 65 are made of a non-magnetic material.

In the structure of this embodiment, the same effects as those of the above-mentioned third embodiment can be obtained. Of course, since the magnetic poles 81 and 82 are provided, depending on the magnetic field strength and the magnetic field homogeneity, the magnetic pole 81, If 82 is provided, the cost can be reduced.

FIG. 12 shows an eighth embodiment of the superconducting magnet.

In this embodiment, the coil containers 11 and 12 are not supported by the He tank 41, but by a support member 63 provided separately from the He tank 41, and the support members 64 and 65 are integrally supported. The effect of this embodiment is similar to that of the first embodiment described above, and the He tank 41
If it can be configured compactly, the cost can be reduced.

FIG. 13 shows a ninth embodiment of the superconducting magnet.

In this embodiment, the upper and lower coil containers 11 and 12 having magnetic poles are covered with magnetic pole supporting members 71 and 72, and the He tank 41 is supported via the magnetic pole supporting members 71 and 72. The magnetic pole support members 71 and 72 are made of a ferromagnetic material. With the configuration of this embodiment, the same effects as those of the above-described embodiments can be obtained, and it is effective to reduce the leakage magnetic field. Further, in order to reduce the leakage magnetic field, it is more effective to install the magnetic field shield coil outside the ferromagnetic material.

14 and 15 show a tenth embodiment of a superconducting magnet. FIG. 15 shows the magnetic pole support members 71,
72, the magnetic pole, and the support member 63 are removed.

In this embodiment, a support member 63 is provided separately from the He tank 41, and the magnetic pole support members 71 and 72 provided so as to cover the coil containers 11 and 12 are integrated to form the coil containers 11 and 12. In this case, the magnetic pole support members 71 and 72 are made of a ferromagnetic material and are also used as the support member 63 that connects the upper and lower coil containers 11 and 12.

With the structure of this embodiment, the same effects as those of the above-mentioned embodiment can be obtained, and the magnetic pole 8 can be obtained.
By combining a magnetic circuit with 1, 82, the magnetic flux can be contained and the leakage magnetic field can be further reduced.

The embodiment shown in FIG. 16 is a case where there are a plurality of upper and lower coil portion supports 63 (two in this example).

The embodiment shown in FIG. 17 is an example in which the magnets are horizontally arranged so that the coil containers 11 and 12 facing each other face each other on the left and right sides. In the present embodiment, it is possible to configure an apparatus capable of inspecting a subject while standing.

[0055]

According to the present invention described above, the influence of the refrigerator vibration on the superconducting coil can be suppressed, so that the image disturbance can be prevented. Further, even if the apparatus is downsized, a large space for the subject can be taken, so that the MRI can be performed without giving a feeling of pressure to the subject.
It is effective when it is adopted in the device.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a superconducting magnet of the present invention.

FIG. 2 is a perspective view of a superconducting magnet which is another embodiment of the present invention.

FIG. 3 is a perspective view of a superconducting magnet which is another embodiment of the present invention.

FIG. 4 is a perspective view of a superconducting magnet which is another embodiment of the present invention.

FIG. 5 is a perspective view of a superconducting magnet which is another embodiment of the present invention.

FIG. 6 is a perspective view of a superconducting magnet which is another embodiment of the present invention.

FIG. 7 is a perspective view of a superconducting magnet which is another embodiment of the present invention.

FIG. 8 is a perspective view of a superconducting magnet which is another embodiment of the present invention.

FIG. 9 is a perspective view of a superconducting magnet which is another embodiment of the present invention.

FIG. 10 is a perspective view of a superconducting magnet which is another embodiment of the present invention.

FIG. 11 is a perspective view of a superconducting magnet which is another embodiment of the present invention.

FIG. 12 is a perspective view of a superconducting magnet which is another embodiment of the present invention.

FIG. 13 is a perspective view of a superconducting magnet which is another embodiment of the present invention.

FIG. 14 is a perspective view of a superconducting magnet which is another embodiment of the present invention.

FIG. 15 is a perspective view of a superconducting magnet which is another embodiment of the present invention.

FIG. 16 is a perspective view of a superconducting magnet which is another embodiment of the present invention.

FIG. 17 is a perspective view of a magnetic resonance imaging apparatus using the superconducting magnet of the present invention.

[Explanation of symbols]

11, 12 ... Coil container, 21 ... Connection passage, 31, 32
... passage, 41 ... He tank, 51 ... refrigerator, 64, 65
... Support member, 81, 82 ... Magnetic pole, 111 ... Shield plate,
112 ... He container for coil, 113 ... Superconducting coil winding, 601 ... Protective resistance, 602 ... Permanent current switch, 7
01 ... Superconducting connection, 711 ... Superconducting crossover.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI Theme Coat (reference) G01N 24/06 510D (72) Inventor Tsutomu Yamamoto 3-1-1 Sachimachi, Hitachi City, Ibaraki Stock Company Hitachi, Ltd. Nuclear Business Division (72) Inventor Yoshihide Wadayama 7-1, Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Hirotaka Takeshima 1-1, Uchikanda, Chiyoda-ku, Tokyo No. 14 Inside the Hitachi Medical Co. (72) Inventor Kenji Sakakibara 1-14-1 Uchida Kanda, Chiyoda-ku, Tokyo Inside the Hitachi Medical Co. (72) Inventor Takao Hona 885-16 Ichige Ichika, Hitachinaka City, Ibaraki Prefecture Term (reference) 4C096 AA20 AB32 AB50 AD02 AD08 CA02 CA16 CA34 CA36 CA54

Claims (9)

[Claims] 1. A superconducting coil, a coil container for accommodating the superconducting coil together with a cooling medium, and a refrigerator for cooling the cooling medium, wherein the coil containers are spaced apart from each other and arranged to face each other. Together with the superconducting magnet that forms a magnetic field space between both coil containers, a cooling medium tank for supplying a cooling medium to the coil container is provided separately from the coil container, and the refrigerator is provided in the cooling medium tank. In addition to being installed, the cooling medium tank and the coil container are connected by a passage for circulating the cooling medium, an annular space portion is formed in the coil container, and a ferromagnetic magnetic pole is arranged in the space portion. And a superconducting magnet. 2. The superconducting magnet according to claim 1, wherein a ferromagnetic member is provided on the side opposite to the surfaces of the coil containers facing each other. 3. The coil vessels are connected to each other by a connecting passage, and a lead wire for connecting a superconducting coil in each of the coil vessels passes through the inside of the connecting passage. The superconducting magnet according to any one of 2 and 3. 4. The superconducting magnet according to claim 1, wherein a flexible portion is provided in the middle of the passage for circulating the cooling medium. 5. A superconducting coil, a coil container for accommodating the superconducting coil together with a cooling medium, and a refrigerator for cooling the cooling medium, and the coil containers are arranged so as to be spaced apart from each other and face each other. Together with the superconducting magnet that forms a magnetic field space between both coil containers, a cooling medium tank for supplying a cooling medium to the coil container is provided separately from the coil container, and the cooling medium in the coil container is superconducting. A superconducting magnet characterized by having a minimum necessary amount to be maintained. 6. A superconducting coil, a coil container for accommodating the superconducting coil together with a cooling medium, and a refrigerator for cooling the cooling medium, wherein the coil containers are spaced apart from each other and arranged to face each other. In addition, in a superconducting magnet that forms a magnetic field space between both coil containers, an annular space portion is formed in the coil container, a ferromagnetic magnetic pole is arranged in the space portion, and the center of the superconducting magnet. A superconducting magnet having a viewing angle of 30 ° or more, which is an angle in the vertical direction limited by the magnetic poles when the open portions of the upper and lower coil containers are viewed from above. 7. The superconducting magnet according to claim 4, wherein each coil container including the magnetic poles is supported by the cooling medium tank via a non-magnetic support member. 8. A superconducting coil, a coil container for accommodating the superconducting coil together with a cooling medium, and a refrigerator for cooling the cooling medium, wherein the coil containers are spaced apart from each other and arranged to face each other. Along with, in a superconducting magnet that forms a magnetic field space between both coil containers, a cooling medium tank for supplying a liquid refrigerant to the coil container is provided separately from the coil container, and both are connected by a passage,
A superconducting magnet in which a connecting wire from the superconducting coil is wired in the cooling medium tank 4 and a connecting wire and a permanent current switch are connected in the cooling medium tank. 9. A superconducting magnet according to any one of claims 1 to 8, a bed on which a subject is placed and movable between coil coils of the superconducting magnet facing each other, and a nuclear magnetic resonance signal from the subject. A magnetic resonance imaging apparatus having a controller for analyzing.