JPH047808A - Cryogenic container for superconducting magnets in nuclear magnetic resonance tomography equipment - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention A. Industrial Field of Application The present invention relates to a cryogenic container for a superconducting magnet that houses a superconducting magnet used to generate a static magnetic field in a nuclear magnetic resonance tomography device (hereinafter simply referred to as the device). Regarding.

B. Conventional technology Nuclear magnetic resonance tomography equipment generates a uniform static magnetic field in the space surrounding the object inserted into the device, and adds a rotating magnetic field in pulses to this to excite spins within the object. It is known to detect and image the electromagnetic waves emitted when the excited spins return to their original state, and superconducting magnets are used to generate the static magnetic field. In order to maintain the 1ill state of this superconducting magnet, the superconducting magnet is housed in a low-temperature container as described below.

The low-temperature container includes an inner container that stores an annular superconducting magnet immersed in a cryogenic cryogen (such as liquid helium), and a plurality of heat shield plates that cover the inner container.
It consists of a vacuum container that encloses these, and conventional low-temperature containers are formed as an integral cylindrical body.

C3 Problems to be Solved by the Invention However, the above-mentioned conventional low temperature container has the following problems.

In other words, since it is formed of a one-piece cylindrical body, when a subject is inserted into the device (into the cavity of the cryocontainer), the space around the subject is blocked by the cryocontainer, and the subject is mentally incapacitated. There is a problem that it gives a feeling of pressure.

Generally, the cavity radius of a cryocontainer is about 40 to 50 cm, and the time a subject is inserted into the apparatus for one imaging session is about 40 minutes on average. In this way, confining a subject in a narrow space for a certain period of time sometimes causes claustrophobia, making imaging impossible.

Furthermore, a gradient magnetic field generating coil for detecting three-dimensional positional information of excited spins within the subject is arranged within the cavity of the low temperature container. Around this time, the gradient magnetic field generated by the gradient magnetic field generating coil induces eddy currents in the conductor parts such as the vacuum container and heat shield plate that make up the low temperature container, and the eddy current magnetic field due to the eddy current is generated by the static magnetic field and the gradient magnetic field. There is a problem in that the magnetic field is superimposed on the magnetic field, resulting in a decrease in image quality and a decrease in imaging speed.

This invention was made in view of these circumstances, and by opening the peripheral wall of the cavity of the cryogenic container,
It is an object of the present invention to provide a cryogenic container for a superconducting magnet that can reduce the psychological pressure on a subject and reduce the influence of eddy currents.

09 Means for Solving the Problems The present invention has the following configuration to achieve the above object.

That is, the present invention provides an inner container filled with a cryogenic cryogen for immersing an annular superconducting magnet, a heat shield plate that covers the periphery of the inner container, and a cylindrical container that includes the inner container and the heat shield plate. In the cryo-container for a superconducting magnet of a nuclear magnetic resonance tomography apparatus, the cryo-container is divided into a plurality of pieces along its cylindrical axis, in which a coil for generating a gradient magnetic field is arranged in a cavity of the cryo-container having a vacuum container. However, the periphery of each divided low-temperature container is covered with a magnetic shield plate, and a plurality of rod-shaped magnetic shield members are attached at a required gap to connect the magnetic shield plates.

E1 Effect According to the present invention, a cylindrical cryogenic container is divided into a plurality of parts along its cylindrical axis, and the connection between the magnetic shielding plates surrounding each cryogenic container for superconducting magnets is made by forming a connection with a required gap. Since this is done using a plurality of bar-shaped magnetic shielding materials separated by a gap, the peripheral wall of the cavity of the cryogenic container is opened by the gap while suppressing leakage of the static magnetic field generated by the superconducting magnet to the outside. .

Furthermore, since the low temperature container has a divided structure, the conductor area is reduced compared to an integrated low temperature container. Therefore, the area in which eddy currents are induced by the gradient magnetic field generating coil is narrowed, so that the influence of eddy currents is reduced.

F. Example Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a perspective view showing a schematic configuration of a low temperature container for a superconducting magnet according to an embodiment of the present invention.

In the figure, reference numeral 1 denotes a magnetic shield plate disposed so as to cover the low-temperature container 2 from the end surface to the circumferential surface of the low-temperature container 2. The low-temperature container 2 is divided into two along its cylindrical axis, and each low-temperature container is designated by reference numerals 2a and 2b.

The low temperature containers 2a and 2b are arranged to face each other with a predetermined distance D1 between them. Each cryocontainer 2a.

The magnetic shielding plates 1a and lb are attached to the outer periphery of each opposing end surface of the magnetic shielding plate 2b, and the magnetic shielding plates 1a and lb are spaced at a predetermined interval D2 in the circumferential direction so as to connect the magnetic shielding plates 1a and lb to each other. A plurality of bar-shaped iron shield plates 4 are attached. Each magnetic shield Fila, lb and the bar-shaped iron shield plate 4 are made of a ferromagnetic material such as iron or nickel.

The cavity of each cryogenic container 2a, 2b, which is a cylindrical body, accommodates the subject M.
This is a through hole 5 for inserting the into the device. A bed 6 that moves forward and backward with respect to the inside of the through hole 5 is installed on the floor on the end face side of the cryocontainer 2a, and the subject M lying supine on this head 6 is moved inside the through hole 5 by the movement of the bed 6. The device is inserted into the body, and nuclear magnetic resonance tomography is performed.

In the figure, reference numeral 7 indicates a leg for installing each of the low-temperature containers 2a, 2b on the floor, and 8 indicates a base that supports the bed 6 and is provided with a mechanism for moving the bed 6 inside.

FIG. 2 is a cross-sectional view of the cryocontainer. Referring to this diagram,
The configuration inside the low temperature container will be explained.

In addition, since the internal structure of each of the low-temperature vessels 2a and 2b is composed of the same parts, they are indicated by the same reference numerals in this figure without distinguishing them by the suffixes a and b.

In the through hole 5 into which the subject M is inserted, there is a superconducting magnet 10 that generates a uniform static magnetic field in the body axis direction of the subject M, and a superconducting magnet 10 that cancels the external leakage magnetic field of the static magnetic field generated by the superconducting magnet 10. A shielding coil 15 that generates a magnetic field in the opposite direction to the static magnetic field is housed in the annular inner container 11 while being immersed in liquid helium as a cryogen. The inner container 11 is surrounded by a second heat shield 12 made of a highly thermally conductive material such as aluminum, and the second heat shield 12 is surrounded by a first heat shield 13 made of a similar material. covered by. The second heat shield 12 includes a refrigerator (not shown)
The temperature of the first heat shield 13 is maintained at approximately 20K, and the temperature of the first heat shield 13 is maintained at approximately 80K. Inner container 11, second
The heat shield 12 and the first heat shield 13 are housed in a vacuum container 14 at room temperature. This vacuum container 14 serves as a casing for the low temperature container 2, and the above-mentioned magnetic shield 1 is arranged on the outer peripheral surface of the vacuum container 14.

In the figure, reference numeral 16 is a gradient coil arranged on the inner peripheral surface forming the through hole 5 of the cryogenic chamber 2. A gradient coil is used to obtain three-dimensional position information of excited spins in the specimen M. Generates a magnetic field.

According to the low-temperature container 2 having such a configuration, the low-temperature container 2 is divided into two low-temperature containers 2a and 2b, and the rod-shaped iron shield plates 4 are attached at a predetermined distance D2, so that no damage is caused in the through hole 5. A necessary open space can be secured without completely blocking the space around the inserted subject M, and nuclear magnetic resonance tomography can be performed without putting mental pressure on the subject M.

In addition, the low-temperature container 2 according to this embodiment has a magnetic shield plate 1 made of a ferromagnetic material and a bar-shaped iron shield plate 4 as means for suppressing external leakage magnetic fields caused by dividing the container into two. The leakage magnetic field to the outside due to the static magnetic field generated by the superconducting magnet 10 is suppressed. This can prevent adverse effects on electronic devices placed around the device.

In addition, as a device to cancel the external leakage magnetic field, the inner container ll
A shielding coil 15 is provided inside, but this shielding coil 15 is provided for the purpose of reducing the number of rod-shaped iron shield plates 4, and there is no particular need to provide this shielding coil 15.

However, if the shielding coil 15 is provided, the number of rod-shaped iron shield plates 4 to be attached can be reduced to the extent that the external leakage magnetic field is canceled out by this coil, so that the open feeling of the subject M is further enhanced.

Further, by making the low temperature container 2 have a divided structure, the following effects can be obtained.

The low temperature container 2 has a divided structure, and each low temperature container 2a.

By forming a gap between 2b, the area of the conductor where eddy current is induced can be significantly reduced compared to a conventional integrated low temperature container. This makes it possible to reduce eddy currents induced in conductors such as the vacuum vessel 14 and heat shields 11 and 12 by the gradient magnetic field generated by the gradient coil 16 provided on the inner peripheral surface forming the through hole 5 of the low temperature vessel 2. , it is possible to suppress deterioration in image quality and imaging speed of tomographic images caused by superimposition of eddy current magnetic fields generated by eddy currents on static magnetic fields and gradient magnetic fields.

Effects of the G1 Invention As is clear from the above explanation, the cryo-container for superconducting magnet of the nuclear magnetic resonance tomography apparatus according to the present invention has a cylindrical cryo-container divided into a plurality of pieces along the axis of the cylinder. However, since the connection between the magnetic shield plates surrounding each low-temperature container is made using multiple bar-shaped magnetic shield materials separated by a required air gap, leakage of the static magnetic field generated by the superconducting magnet to the outside is reduced. In the suppressed state, the space around the subject is opened by the void. This makes it possible to reduce the psychological pressure on the subject.

Furthermore, since the low temperature container is divided, the conductor area can be reduced compared to conventional low temperature containers that are integrated. Therefore, the vortex 1itfJL induced in the conductor can be reduced by the gradient coil installed on the inner circumferential surface forming the through hole of the cryogenic container, and the deterioration of the image quality of the tomographic image and the decrease in the imaging time speed can be suppressed. .

[Brief explanation of drawings]

1 and 2 relate to one embodiment of the present invention, in which FIG. 1 is a perspective view showing a schematic structure of a cryogenic container for a superconducting magnet, and FIG. 2 is a longitudinal sectional view thereof. 1...Magnetic shield plate 2...Low temperature container 4...
Rod-shaped iron shield plate End...Through hole 10...Superconducting magnet IL 12...Heat shield 14...Vacuum vessel 1
6... Gradient coil patent applicant Shimadzu Corporation

Claims (1)

[Claims] (1) An inner container filled with a cryogenic cryogen for immersing an annular superconducting magnet, a heat shield plate that covers the periphery of the inner container, and a cylindrical vacuum container containing the inner container and the heat shield plate. In a cryocontainer for a superconducting magnet of a nuclear magnetic resonance tomography apparatus in which a coil for generating a gradient magnetic field is disposed in a cavity of the cryocontainer, the cryocontainer is divided into a plurality of pieces along its cylindrical axis; Nuclear magnetic resonance tomography characterized in that each cryogenic container is covered with a magnetic shielding plate, and a plurality of rod-shaped magnetic shielding members are attached at a required gap to connect the magnetic shielding plates. A cryogenic container for the superconducting magnet of the device.