JPH0479304A - Superconducting magnet apparatus - Google Patents

Abstract

PURPOSE:To obtain a light and compact apparatus, and relieve the anxiety of a patient as best as possible, by installing a small refrigerator generating a temperature higher than or equal to 4.2K, a heat conduction plate cooled by the refrigerator, and a superconducting coil which is in thermal contact with the heat conduction plate via insulator. CONSTITUTION:The cooling surface of a small refrigerator 7 capable of cooling at the liquid helium temperature or at a temperature lower than or equal to the liquid helium temperature is brought into thermal contact with one end of a plate 8 made of high purity aluminum excellent in thermal conductivity or the like. The aluminum plate 8 is brought into thermal contact, via electric insulator, with the outer periphery or the inner periphery or both of a superconducting coil 1. The coil is cooled by the small refrigerator 7 via the insulator and the aluminum plate, thereby obtaining the superconducting state. Since liquid helium is excluded, a helium vessel is unnecessitated. The helium vessel is excluded and further a heat insulated retaing member for retaining a heavy object can be reduced, so that the heat insulating space is shortened and the axial length of an apparatus also can be reduced.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention is directed to magnetic resonance (MR)
The present invention relates to a superconducting magnet device that generates a static magnetic field in an MRI device (magnetic resonance imaging device), etc., which uses the phenomenon of magnetic resonance imaging to obtain morphological information such as slice images of a subject (biological body) or morphological information such as spectroscopy.

(Prior art) Magnetic resonance is a phenomenon in which an atomic nucleus with non-zero spin and magnetic moment placed in a static magnetic field resonantly absorbs and emits only electromagnetic waves of a specific frequency. The angular frequency ω shown in (ω.=2πVIIIVI
It resonates at the I-Niramor frequency).

ω. =γB0 Here, γ is the gyromagnetic ratio specific to the type of atomic nucleus,
Further, Bo is the strength of the static magnetic field.

An MRI apparatus that performs biological diagnosis using the above-mentioned principle processes the electromagnetic waves of the same frequency as above, which are induced after the above-mentioned resonance absorption, to determine nuclear density, longitudinal relaxation time T□, transverse relaxation time T2, and so on. Diagnostic information that reflects information such as flow and chemical shift, such as slice images of a subject, can be obtained non-invasively.

Although the collection of diagnostic information by magnetic resonance is able to excite all parts of the subject placed in a static magnetic field and collect signals, there are limitations in the equipment configuration and clinical problems with imaging images. Due to these demands, actual devices excite a specific region and collect its signals.

In this case, what is the specific area to be imaged?

In general, the slice region has a certain thickness, and the echo signal from this slice region and the magnetic resonance signal (MR multiplied signal) of the FID signal are processed by multiple data encoding processes in the phase encoding method. The image of the specific slice region is generated by performing image reconstruction processing on these data groups using, for example, a two-dimensional Fourier transform method.

In such an MRI apparatus, B, that is, the static magnetic field strength, is
It requires several thousand to gauss, and generally a superconducting magnet or a normal conducting magnet is used.

On the other hand, superconducting magnets are popular because the higher the static magnetic field formed in the diagnostic space within the magnet, the higher the image quality. The superconducting magnet is as shown in FIG. For example, in the literature (J, Alcor
n, etal+ IEEE Transactions
onMagnetics, Vol 24. No2
t March 1988. p1280). That is, the superconducting coil (g) is immersed in liquid helium (3) at 1 atm, and there is a helium container (3) that holds the liquid helium. The temperature of liquid helium is about 4.2 K, and in order to reduce the radiant heat from the room temperature part, a heat shield plate (2) is inserted between the helium container (2) and the vacuum container 4 which is at room temperature. The heat shield plate is generally about 20
Shield plate (51) on 20 held by K, about 80K
It is often composed of a shield plate (52) held at 80, but in some cases it is composed of a single heat shield plate.

The heat shield plate (2) is generally brought into thermal contact with the cooling surface of the small refrigerator (2) to maintain its temperature.

Therefore, the temperature of the heat shield plate is balanced with the capacity of the small refrigerator and the amount of heat entering the heat shield plate. 80
In the case of a small refrigerator with two cooling stages, two heat shield plates can be used.

On the other hand, if a small refrigerator is not used, one side of the heat shield plate uses approximately 77% liquid nitrogen. Alternatively, a method is used to keep the temperature of the heat shield plate low by circulating helium gas that is evaporated from liquid helium.

Furthermore, although not shown, a multilayer heat insulating layer is placed between the liquid helium container (3), the heat shield plate (3), and the vacuum container (4) to reduce the intrusion of heat to the low temperature side. .

The space between the liquid helium container (1) and the vacuum container 4 is kept in a vacuum to suppress heat convection from room temperature.

A conventional superconducting magnet device is mainly composed of the above-mentioned components.

(Problems to be Solved by the Invention) In the superconducting magnet device described above, the liquid helium container stores liquid helium at 1 atmosphere.

In addition, in order to have enough strength to withstand the vacuum region outside, the helium container has the disadvantage of being thick and heavy at the same time. Furthermore, the axial length of the superconducting magnet device also increases. Furthermore, in the radial direction, a space is required to store liquid helium in the helium container, which has the disadvantage of increasing the height of the superconducting magnet device. In addition, a space is required to insert the transaer tube used to inject liquid helium, and a space is required above the height of the superconducting magnet device, which increases the indoor height of the building housing the superconducting magnet device. The disadvantage was that it was expensive. In addition, since patients receiving diagnosis undergo imaging in the diagnostic region located approximately in the center of the superconducting magnet device, the long axis length has the disadvantage of causing a sense of anxiety.

In view of the above problems, it is an object of the present invention to provide a lightweight and compact superconducting magnet device, and to eliminate patients' sense of anxiety as much as possible.

[Structure of the invention]

(Means for Solving the Problems) The superconducting magnet device of the present invention is equipped with a small refrigerator that can be cooled to liquid helium temperature or lower, and the cooling surface is made of high-purity aluminum or the like with good heat conduction. The superconducting coil is cooled by bringing the plates into thermal contact and by bringing the heat transfer plate into thermal contact with the superconducting coil.

(Function) With this configuration, the superconducting coil is cooled by thermal conduction of the heat exchanger plate, so liquid helium and a container for storing the liquid helium are unnecessary, and an overall lightweight and compact superconducting magnet device can be obtained. , the axial length also becomes shorter.

(Example) An embodiment of the present invention will be described with reference to FIG.

The cooling surface of a small refrigerator ■ that can be cooled to liquid helium temperature or lower is thermally brought into contact with one end of a plate (5) made of high-purity aluminum with a purity of 99% or higher and good thermal conductivity. let The aluminum plate (8) is brought into thermal contact with the outer circumference, inner circumference, or both of the superconducting coil (2) via an electrical insulator. Fes for electrical insulators,
If an adhesive such as epoxy is used to fill the space between the superconducting coil and the aluminum plate, thermal contact will be improved.

With this configuration, the superconducting coil (2) is cooled by the small refrigerator (2) via the insulator and the aluminum plate, and a superconducting state is obtained.

In such a configuration, since there is no liquid helium, a helium container is not required, and a lightweight and compact superconducting magnet device can be obtained. In addition, since the helium container is eliminated, the heat insulating support material that supports the heavy object can be made smaller, and the heat insulating space is shortened, so the axial length of the device is also shortened, which has the effect of reducing the patient's sense of anxiety.

Although the small refrigerator (2) is mounted above in FIG. 1, the same effect can be obtained even if it is mounted in any position.

A plate of copper or oxygen-free copper may be used instead of the aluminum plate.

(Other Example 1) Another example is shown in FIG. One end of the aluminum plate (8), which has good thermal conductivity, is brought into thermal contact with the cooling surface of a small refrigerator (2) that can be cooled to below 462K. Further, the aluminum plate (8) is brought into thermal contact with the superconducting coil (2) via an insulator. A slit (9) is made in the aluminum plate in the same direction as the axial direction of the superconducting coil. The slit 0) may be thermally connected only at one end. Alternatively, the slit 0 may be cut to both ends in the portion that contacts the superconducting coil, but is joined at a position away from the superconducting coil.

With this configuration, the superconducting coil (2) is cooled by the small refrigerator (2) via the aluminum plate (3), and becomes a superconducting state. Furthermore, by inserting the slit e) into the aluminum plate (3), when the superconducting coil quenches, the induced current flowing through the aluminum plate (c) is reduced, eliminating excessive heating.

Furthermore, eddy currents due to pulsed magnetic fields generated by gradient magnetic field coils used to take both MR images are also reduced.

In this way, by inserting the slit (2) in the aluminum plate (8), the same effect as in the previous embodiment can be obtained, and furthermore, the influence of the quench or the gradient magnetic field coil is reduced. In addition, in Fig. 2, the aluminum plate (8)
is placed on the outside of the superconducting coil, but the same effect can be obtained even if it is placed on the inside or on both sides.

(Other Example 2) Another example is shown in FIG. When the superconducting coil is divided into multiple pieces, the aluminum plate (8) is thermally contacted with the multiple superconducting coils via an insulator. In addition, one end or part of the aluminum plate etc.) is 4.
It is in thermal contact with the cooling surface of a small refrigerator ω that can be cooled to 2K or less.

With this configuration, a large number of superconducting coils ■ are cooled by a small refrigerator ■ through an aluminum plate (c),
A superconducting state is obtained.

Therefore, since a helium container having a complicated structure for cooling a large number of superconducting coils (1) is not required, the same effect as in the previous embodiment can be obtained. In addition, aluminum plate (
You may also make a slit in 8).

(Other Embodiment 3) Another embodiment is shown in FIG. The aluminum plate (c) is placed between the layers of the superconducting coil (2).

With this configuration, thermal contact between the aluminum plate (8) and the superconducting coil is improved, so that in addition to obtaining the same effect as the previous embodiment, there is also the effect of speeding up cooling.

(Other Embodiment 4) Another embodiment is shown in FIG. A pipe (10) made of aluminum, copper, or stainless steel is wrapped around the superconducting coil ■, and one end is attached to a small refrigerator ■, where the helium is cooled and liquefied, using the gravity of the liquid helium to Cool the superconducting coil. Helium may be normal 4He or its isotope 'He.

Further, the pipe (10) may be brought into thermal contact with an aluminum plate with good thermal conductivity attached to the surface of the superconducting coil (2) via an insulator.

With this configuration, the same effects as the previous embodiment can be obtained.

(Other Example 5) Another example is shown in FIG. In a superconducting magnet composed of multiple superconducting coils, the coils at both ends have a larger diameter than the other coils, and are configured to generate a magnetic field in the opposite direction to that of the other coils. A magnetic body (11) having a diameter smaller than the center diameter is arranged.

When arranged in this way, the magnetic body (11) strengthens the magnetic field at the center, and the weight of the superconducting coil can be reduced.

The same effect as the previous embodiment can be obtained, and it can also contribute to weight reduction.

(Other Embodiment 6) Another embodiment is shown in FIG. The superconducting coil (2) is divided in the center of the diagnostic space (102), and the aluminum plate (3) is brought into thermal contact with the superconducting coil (2) via an insulator. One end of the aluminum plate (8) is brought into thermal contact with the cooling surface of the small refrigerator. A hole (101) penetrating to the outside of the superconducting magnet device is provided directly above the diagnostic space (102).

The shape of the hole (101) may be made wider as the diameter becomes larger. Alternatively, it may be opened in a fan shape in the circumferential direction.

Also, the length from the end of the vacuum container to the hole (101) should be within 1 m.

With this configuration, in addition to obtaining the effects of the previous embodiment, the patient can see the outside from the diagnostic space, which has the effect of reducing anxiety. Furthermore, if the length of the vacuum vessel in the axial direction was made to be 1 m or less, the magnetomotive force of the superconducting coil became large, but by dividing the vacuum vessel into two parts, the magnetomotive force also decreases, thereby reducing the sense of anxiety.

〔Effect of the invention〕

As explained above, in the present invention, a heat transfer plate such as a high-purity aluminum plate is brought into thermal contact with the cooling surface of a small refrigerator that can be cooled to below the temperature of liquid helium, and a superconducting coil is connected via an insulator. Because of the thermal contact structure, a helium container is not required, a lightweight and compact superconducting magnet device can be obtained, and the patient's anxiety can be alleviated.

[Brief explanation of drawings]

FIG. 1 is a sectional view of the upper half of a superconducting magnet device showing one embodiment of the present invention, FIG. 2 is a perspective view showing the arrangement of a superconducting coil, an aluminum plate, and a small refrigerator in another embodiment, and FIG.
6 to 6 are sectional views of main parts of other embodiments, and FIG.
The figure is a sectional view of still another embodiment, and FIG. 8 is a sectional view of the upper half of a conventional superconducting magnet device.

Claims (1)

[Scope of Claims] (1) A small refrigerator that generates a temperature of 4.2 K or less, a heat exchanger plate cooled by the refrigerator, and a heat exchanger plate that is in thermal contact with the heat exchanger plate through an insulator. A superconducting magnet device characterized by comprising a superconducting coil. (2) The superconducting magnet device according to claim (1), wherein the heat transfer plate is made of high-purity aluminum or oxygen-free copper. (3) The superconducting magnet device according to claim (1), wherein the heat transfer plate has a slit in the same direction as the axis of the cylindrical superconducting coil. (4) The superconducting magnet device according to claim (1), wherein the superconducting coil is composed of a large number of winding parts, each of which is provided with a heat transfer plate. (5) Each axis of the multiple coil blocks forming the cylindrical superconducting coil is the same, the coil blocks at both ends are arranged with a larger diameter than the inner coil block, and a magnetic material is arranged around the outer periphery of the inner coil block. The superconducting magnet device according to claim 4, characterized in that: (6) The superconducting magnet device according to claim 4, characterized in that in the cylindrical superconducting coil composed of a plurality of coaxial blocks, a hole for room temperature space is formed in the center in the axial direction of the coil. (7) Claim (6) characterized in that the length from the hole in the room temperature space to the end of the superconducting magnet device is within 1 m.
) The superconducting magnet device described. (8) The superconducting magnet device according to claim (1), wherein the heat transfer plate is inserted between one or more layers of the superconducting coil winding. (9) One end of the pipe containing helium is 4.2
A superconducting magnet device, characterized in that it is brought into contact with a small refrigerator that generates a temperature of K or less, and the other end is wound around a superconducting coil.