JP2009004693A - Superconductive magnet device and magnetic resonance imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reliable superconductive magnet device and a magnetic resonance imaging device, in which structure is simple, and a persistent current of a superconductive coil can be stably retained for the long term. <P>SOLUTION: A superconductive magnet device 1 includes: a pair of coil containers 4 and 4 which accommodate a circularly-shaped superconductive coil 2 with a cooling medium; a pair of vacuum containers 1A and 1B which accommodate coil containers 4 and 4, respectively; a connecting tube 1C which supports the vacuum containers 1A and 1B, while opposing them to each other in the vertical direction, using a space between the vacuum containers 1A and 1B as a magnetic field space; a superconductive wire 2A which is connected between the superconductive coil 2 and 2 of a pair of the coil containers 1A and 1B through the connecting tube 1C; and a permanent current switch 7 which is connected to the superconductive wire 2A and passes permanent current to the superconductive coil 2. The permanent current switch 7 is arranged in the connecting tube 1C. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a superconducting magnet device and a magnetic resonance imaging apparatus.

The superconducting coil and the permanent current switch constituting the superconducting magnet device are cooled with a liquefied refrigerant for cooling the superconducting magnet device, such as liquid helium, and stored in the coil container, and the coil container has a heat insulating vacuum layer. It is stored in a vacuum container to be formed. A heat shield is provided between the coil container and the vacuum container, and the coil container is further insulated and protected by the heat shield.
In general, in a superconducting magnet device applied to a magnetic resonance imaging apparatus, a permanent current switch is known that is disposed inside an upper coil container among a pair of upper and lower coil containers. Moreover, what is arrange | positioned in the tank provided separately from a pair of coil container is known (for example, refer patent document 1, 2).

By the way, when the superconducting coil is energized and a magnetic field is generated, a part of the coil conductor of the superconducting coil moves, or the impregnating material covering the coil conductor cracks. When a disturbance occurs, this becomes a thermal disturbance, and a part of the superconducting coil rises in temperature and transitions to normal conduction. When the temperature rise due to such thermal disturbance greatly exceeds the cooling by the surrounding refrigerant, a phenomenon in which the normal conduction transition reaches the entire superconducting coil, so-called quenching, occurs.
When such a quench occurs, a large amount of heat is generated from the superconducting coil. In addition, even when a normal transition occurs due to mechanical disturbance or the like in the permanent current switch, the permanent current circuit cannot maintain a closed circuit and may be quenched.

  In recent years, a magnetic resonance imaging apparatus constituted by such a superconducting magnet apparatus has been developed with a high-intensity magnetic field, and even in a permanent current switch as a component, a disturbance in an operating state is prevented. High electromagnetic stability is required.

JP 2002-190406 A JP 2003-159230 A

However, in Patent Document 1 described above, since the permanent current switch is arranged inside the upper coil container, there is a risk of being affected by a high-intensity magnetic field due to the upper superconducting coil or the like. Therefore, the reliability of the superconducting magnet device and the magnetic resonance imaging device may be lowered, for example, because the closed circuit cannot be maintained and quenching occurs.
Further, in Patent Document 2 described above, the permanent current switch is disposed in a tank provided separately, and thus has a problem that the structure becomes complicated.

  From such a point of view, the present invention provides a highly reliable superconducting magnet device and magnetic resonance imaging apparatus that have a simple structure and can stably maintain the permanent current of the superconducting coil for a long period of time. This is the issue.

  As a means for solving the above-described problems, the present invention provides a pair of vacuum containers that accommodate coil containers, which are supported by a connecting pipe in a state of facing each other in the vertical direction, and a permanent current is supplied to the superconducting coils in each coil container. Because the permanent current switch that flows the current is arranged in this connecting pipe, the structure is simplified, and the magnetic field is stronger than the conventional one in which the permanent current switch is arranged inside the upper coil container. As a result, the permanent current switch is less likely to be affected, and the permanent current of the superconducting coil can be stably maintained for a long period of time, thereby improving the reliability.

  According to the present invention, it is possible to obtain a highly reliable superconducting magnet device and magnetic resonance imaging apparatus that have a simple structure and can stably maintain the permanent current of the superconducting coil for a long period of time.

Next, an embodiment of a magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus) provided with the superconducting magnet apparatus of the present invention will be described with reference to the drawings.
(First embodiment)
As shown in FIG. 1, the MRI apparatus includes a superconducting magnet apparatus 1, a bed B on which a subject (not shown, the same applies hereinafter) is placed, and a subject placed on the bed B in a magnetic field space. Conveying means B1 provided with a drive mechanism (not shown) for conveying to the imaging region F, and equipment such as a computer for analyzing nuclear magnetic resonance signals from the subject conveyed to the imaging region F by the conveying means B1. It comprises an analyzing means 30 and performs tomography through a subject placed on a bed B.

  As shown in FIG. 2, the superconducting magnet device 1 includes a coil container 4 that houses an annular superconducting coil 2 together with a refrigerant 3, and a pair of vacuum containers 1A and 1B that are held in a vacuum. In addition, the coil container 4 is enclosed and accommodated via the heat shield 5. A pair of connecting pipes 1C and 1C are connected to each other in a state where the vacuum containers 1A and 1B are opposed to each other in a vertical direction with a magnetic field space between the pair of vacuum containers 1A and 1B (only one is shown in FIG. 2). It is supported by.

  The superconducting coil 2 uses, for example, an NbTi wire as a coil wire, and is supported inside the coil container 4 by a support body (not shown). As the refrigerant 3, for example, liquid helium is used.

  The coil container 4 is formed of a sealable container and serves as a tank for storing the refrigerant 3. Such a coil container 4 is shown in order to discharge a gas phase refrigerant gas (helium gas) inside the coil container 4 and an injection pipe (not shown) for injecting the refrigerant 3 into the coil container 4. Not connected to the exhaust line. In addition, several pipes (not shown) such as pipes (not shown) for detecting the pressure inside the coil container 4 pass through the vacuum container 1A and are connected to the coil container 4.

  The connecting pipes 1 </ b> C and 1 </ b> C are arranged on both sides in the radial direction of the superconducting magnet device 1 across a central axis (not shown) of the superconducting magnet device 1. The upper vacuum container 1A and the lower vacuum container 1B are connected to each other inside the connecting pipes 1C and 1C, and the coil container 4 and the heat shield 5 housed in the vacuum containers 1A and 1B. Are connected inside the connecting pipes 1C and 1C, respectively. Thus, the refrigerant 3 is configured to flow between the vacuum containers 1A and 1B. The upper vacuum vessel 1A and the lower vacuum vessel 1B are formed with a recess so as to face the imaging region F, and a gradient magnetic field coil or the like (not shown) is provided in the recess.

In the present embodiment, a superconducting wire 2A (crossover wire, partially omitted) connected to the superconducting coils 2 and 2 and the superconducting wire 2A are connected to the inside of one connecting tube 1C. A permanent current switch 7 is arranged. That is, the superconducting wire 2A and the permanent current switch 7 are immersed in the refrigerant 3 that can flow inside the connecting pipe 1C.
The permanent current switch 7 allows a permanent current to flow through the superconducting coils 2 and 2, and is brought into a normal conduction state or a superconducting state by energization / non-energization of a permanent current switch heater 7B described later. , 2 excitation / demagnetization.

  Specifically, as shown in FIG. 3, the superconducting magnet device 1 is connected to an excitation power supply E1 and a heater power supply E2 in a circuit in which a superconducting coil 2, a permanent current switch 7, and an optional protective resistor 8 are connected in parallel. The excitation circuit is formed. The permanent current switch 7 includes a superconductor 7A and a permanent current switch heater 7B that heats the superconductor 7A. When the permanent current switch heater 7B is turned on / off by the heater power supply E2, the normal state of the superconductor 7A is reached. Or it controls the superconducting state.

The procedure for setting such an excitation circuit to permanent current operation is as follows.
First, the permanent power switch heater 7B is energized by the heater power supply E2, and the superconductor 7A is transitioned to normal conduction by heating the permanent current switch heater 7B, and the permanent current switch 7 is turned off.
Thereafter, the superconducting coils 2 and 2 are energized by the excitation power source E1, and the superconducting coils 2 and 2 are excited to the rated current. When the superconducting coils 2 and 2 are excited to the rated current, the permanent current switch heater 7B is deenergized and the permanent current switch 7 is turned on. By this operation, a current flows through a permanent current circuit (closed circuit) composed of the superconducting coils 2 and 2 and the permanent current switch 7.
Thereafter, the current of the excitation power source E1 is lowered to zero.
The excitation circuit can be shifted to the permanent current operation by the procedure as described above.

  The superconductor 7A used for the permanent current switch 7 is a composite made of bare wire, cupronickel or the like.

  FIG. 4 shows a magnetic field state around the permanent current switch 7. In this embodiment, the magnetic field strength existing between the upper and lower superconducting coils 2 and 2 is lower than the others. In other words, the permanent current switch 7 is disposed in the low-intensity region R1 in which the magnetic field generated by the superconducting coils 2 and 2 cancels each other to generate a magnetic field having a lower intensity than the surroundings. Thereby, the permanent current switch 7 is arranged at a position that is substantially in the center in the vertical direction of the connecting pipe 1C.

The superconducting wire 2A is routed from the connecting pipe 1C in the circumferential direction of the superconducting coils 2 and 2 and connected through a connection port (not shown) provided in the superconducting coils 2 and 2.
The superconducting magnet device 1 can be assembled, for example, by first assembling the vacuum containers 1A and 1B and then connecting these vacuum containers 1A and 1B with connecting pipes 1C and 1C, respectively. . That is, the superconducting magnet device 1 is assembled by performing assembly in which the connection of the connection pipe 1C in the connection process is close to the final stage of the assembly process.

Below, the effect acquired in this embodiment is demonstrated.
(1) According to the present embodiment, since the permanent current switch 7 is disposed inside the connecting pipe 1C, the superconducting wire 2A connected to the superconducting coils 2 and 2 can be routed short, and superconducting The entire wiring length of the line 2A can be shortened. In addition, it is possible to shorten the routing distance of the superconducting wire 2A with respect to the circumferential direction of the superconducting coils 2 and 2, and accordingly, generation of an irregular magnetic field caused by the routing of the superconducting wire 2A can be suitably suppressed. . Therefore, the influence on the uniform magnetic field created by the superconducting magnet apparatus 1 can be minimized, and a highly reliable superconducting magnet apparatus 1 and MRI apparatus can be obtained.
(2) Since the permanent current switch 7 is arranged in the connecting pipe 1C, the soundness of the entire circuit is obtained at the time of connecting the vacuum vessels 1A and 1B, which are the final stage of assembly, with the connecting pipes 1C and 1C, respectively. An electrical test performed for confirmation, such as a withstand voltage test or an insulation resistance test, can be performed. Therefore, the number of electrical tests in the excitation circuit including the permanent current switch 7 can be reduced. Thereby, cost can be reduced.
In addition, since the number of electrical tests can be reduced, the number of times a high voltage is applied to the permanent current switch 7 in the test is naturally reduced. Thereby, failure of the permanent current switch 7 due to insulation deterioration or the like can be suitably prevented.
(3) Since the permanent current switch 7 is disposed inside the connecting pipe 1C, it is possible to always immerse the permanent current switch 7 in the refrigerant 3 that can flow through the connecting pipe 1C, which occurs during the permanent current operation. Thermal disturbance, for example, thermal disturbance due to exposure of the permanent current switch 7 to evaporative gas generated when the refrigerant 3 is replenished can be prevented. Thereby, the permanent current switch 7 is suitably cooled and protected, and the permanent current of the superconducting coils 2 and 2 is stably maintained for a long time. Therefore, the reliability of the superconducting magnet apparatus 1 and the MRI apparatus can be improved.
(4) Since the permanent current switch 7 is disposed in the region R1 in the connecting pipe 1C where a magnetic field having a lower strength than the surroundings is generated, instability during permanent current operation can be reduced. The permanent current of the superconducting coils 2 and 2 can be stably maintained for a long time. Thereby, the superconducting magnet apparatus 1 and the MRI apparatus with high reliability can be obtained.
In addition, since it can be suitably applied to the superconducting magnet device 1 that forms a high-intensity magnetic field, in combination with the reduction of instability during permanent current operation, improvement in diagnostic accuracy and An MRI apparatus capable of shortening the diagnosis time is obtained.
(5) Since the permanent current switch 7 is arranged inside the connecting pipe 1C, there is no need to install a separate tank as in the conventional case, and the structure is complicated as when a separate tank is provided. Never become. Therefore, the structure is simple and the assembly is easy.
(6) Since the permanent current switch 7 is arranged inside the connecting pipe 1C, it is not necessary to provide a special space in the superconducting magnet device 1 for providing the permanent current switch 7; Contributes to downsizing.

(Second Embodiment)
FIG. 5 shows a superconducting magnet device 1 ′ of the second embodiment. This embodiment is different from the first embodiment in that superconducting shield coils 10 and 10 that generate a magnetic field opposite to the superconducting coils 2 and 2 (superconducting main coil) are provided. The other points remain the same.
That is, the superconducting shield coils 10 and 10 are configured such that a current in the second direction that is opposite to the current in the first direction flowing through the superconducting coils 2 and 2 flows.

  Superconducting shield coils 10 and 10 are arranged on the upper end side in the vicinity of the outer peripheral portion in vacuum container 1A, and are arranged on the lower end side in the vicinity of the outer peripheral portion in vacuum container 1B. That is, the superconducting shield coils 10 and 10 are located in a portion far from the imaging region F of the superconducting magnet device 1, and thereby act to suppress a leakage magnetic field that leaks to the side of the superconducting magnet device 1. To do.

  In the superconducting magnet device 1 ′ having such superconducting shield coils 10, 10, the permanent current switch 7 disposed in the connecting pipe 1 </ b> C includes the superconducting coils 2, 2 and the axis of the superconducting shield coils 10, 10. When viewed from the direction (extension direction of the axis of the central axis O), in the radial direction of the superconducting coils 2 and 2 and the superconducting shield coils 10 and 10, the superconducting coils 2 and 2 and the superconducting shield coil 10 and 10 are arranged.

  FIG. 6 shows a magnetic field state around the permanent current switch 7 in the superconducting magnet device 1 ′ having such superconducting shield coils 10 and 10. Also in this embodiment, the magnetic field strength existing between the upper and lower superconducting coils 2 and 2 and the superconducting shield coils 10 and 10 is lower than the other regions, that is, the superconducting coils 2 and 2, The permanent current switch 7 is arranged in a low magnetic field region R2 where a magnetic field having a lower strength than the surroundings is generated by canceling out the magnetic fields generated by the superconducting shield coils 10 and 10. Also in this case, as in the first embodiment, the permanent current switch 7 is arranged at a position that is substantially in the center in the vertical direction of the connecting pipe 1C.

  Also in the superconducting magnet device 1 ′ as described above, the same effects as the effects (1) to (6) described in the first embodiment can be obtained, and the presence of the superconducting shield coils 10 and 10 makes it permanent. The empirical magnetic field experienced by the current switch 7 is further reduced, the instability during permanent current operation is reduced, and a highly reliable active shield superconducting magnet device 1 ′ and MRI device are obtained.

In the first and second embodiments, the permanent current switch 7 is arranged in the low strength regions R1 and R2 where the magnetic field strength is lower than the others inside the connecting tube 1C. The invention is not limited to this, and for example, it may be configured to be arranged in the low-strength region R3 (see FIG. 6) where the magnetic field strength is low on the side outside the connecting pipe 1C. In this case, the permanent current switch 7 can be cooled by extending a pipe (not shown) from the inside of the connecting pipe 1C to the side of the connecting pipe 1C. That is, the permanent current switch 7 disposed on the side of the connecting pipe 1C can be suitably cooled using the refrigerant 3 provided so as to be able to flow inside the connecting pipe 1C. Therefore, it is not necessary to provide a separate cooling device or the like, and the cost is excellent. In addition, since the permanent current switch 7 is disposed on the side of the connecting pipe 1C, the above-described electrical test is more easily performed.
Even in such a configuration, the permanent current switch 7 is disposed in the low-strength region R3 where the magnetic field strength is lower than the others, so that the superconducting coils 2 and 2 (superconducting shield coils 10 and 10) The permanent current is stably maintained for a long time. Therefore, the reliability of the superconducting magnet device 1 (1 ′) and the MRI apparatus can be improved.

It is explanatory drawing which shows the magnetic resonance imaging device provided with the superconducting magnet apparatus of 1st Embodiment of this invention. It is a schematic cross section which shows the superconducting magnet apparatus of 1st Embodiment. It is a circuit diagram which shows the excitation circuit which excites a superconducting coil. It is a schematic diagram which shows the magnetic field state in the superconducting magnet apparatus of 1st Embodiment. It is a schematic cross section which shows the superconducting magnet apparatus of 2nd Embodiment of this invention. It is a schematic diagram which shows the magnetic field state in the superconducting magnet apparatus of 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,1 'Superconducting magnet apparatus 1A, 1B Vacuum container 1C Connecting pipe 2 Superconducting coil 3 Refrigerant 4 Coil container 5 Heat shield 7 Permanent current switch 7A Superconductor 7B Permanent current switch heater 8 Protection resistance 10 Superconducting shield coil 30 Analysis means B Bed B1 Transport means E1 Excitation power supply E2 Heater power supply F Imaging area R1 to R3 Low intensity area

Claims (6)

A pair of coil containers for storing a superconducting coil formed in an annular shape together with a refrigerant;
A pair of vacuum containers for respectively accommodating the coil containers;
A connecting pipe that supports each vacuum container in a state of facing each other in the vertical direction, with the space between the vacuum containers as a magnetic field space,
A superconducting wire connected between the superconducting coils of the pair of coil containers via the connecting pipe;
A permanent current switch connected to the superconducting wire and for passing a permanent current through the superconducting coil;
A superconducting magnet device comprising:
A superconducting magnet device, wherein the permanent current switch is disposed in the connecting pipe.   The permanent current switch is provided inside the connecting pipe, and is disposed in a low-strength region where the strength of the magnetic field inside the connecting pipe is lower than the others. 2. The superconducting magnet device according to 1.   3. The refrigerant is provided so that the refrigerant can flow between the pair of coil containers through the connection pipe, and the superconducting wire and the permanent current switch are immersed in the refrigerant. A superconducting magnet device according to claim 1. The superconducting coil includes a superconducting main coil through which a current in a first direction flows, and a superconducting shield coil through which a current in a second direction opposite to the first direction flows.
The permanent current switch is disposed between the superconducting main coil and the superconducting shield coil in the radial direction of the superconducting coil when viewed from the axial direction of the superconducting coil. The superconducting magnet device according to any one of claims 1 to 3.   The superconducting magnet device according to any one of claims 1 to 4, wherein the refrigerant is liquid helium. A magnetic resonance imaging apparatus comprising the superconducting magnet device according to any one of claims 1 to 5,
A bed on which the subject is placed, transport means for transporting the subject placed on the bed to the imaging region between the pair of vacuum containers, and a nucleus from the subject transported to the imaging region by the transport means A magnetic resonance imaging apparatus comprising: an analysis unit that analyzes a magnetic resonance signal.

Images