JPS62169311A - Superconductive magnet device for nmar imaging - Google Patents

Abstract

PURPOSE:To enable a leaking magnetic field to be extremely suppressed with superior reproducibility and productivity, by enabling superconductive coils and their shield to be cooled to a superconductive state. CONSTITUTION:Superconductive coils 1...1 and a shield 2 are housed to be cooled inside a cryostat. Circular superconductive coils 1...1 are housed inside a coolant vessel 4 arranged inside a cryostat vacuum vessel 3, and immersed in a coolant such as liquid helium. The shield 2 of superconductive material formed in a cage shape is wound around the peripheral surface of the coolant vessel 4. Therefore, the shield 2 is cooled through the wall surface of the coolant vessel 4 to the temperature near the inside coolant temperature, so that it is cooled to the superconductive temperature together with the superconductive coils 1...1, with a superconductive phase being maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a superconducting magnet device for generating a static magnetic field for NMR imaging (imaging using nuclear magnetic resonance phenomena).

<Prior Art> In NMR imaging, it is necessary to apply a strong and uniform static magnetic field to a space in which an object such as a human body is placed (hereinafter referred to as a measurement space). Generally, a ring-shaped resistive coil or superconducting coil is arranged to surround the measurement space to obtain the above-mentioned static magnetic field.

When a current is passed through a ring-shaped coil, a magnetic field is generated inside the ring, that is, within the measurement space, and at the same time, a magnetic field is also generated outside the ring, causing various adverse effects. As a method to reduce this leakage of magnetic fields to the outside, a conventional method has been proposed in Japanese Patent Application Laid-Open No. 60-9
There are techniques described in No. 8344 and Japanese Unexamined Patent Publication No. 123756/1983. These basically consist of an electromagnet (resistive coil or superconducting coil) that generates a static magnetic field in an IQ constant space, and a second electromagnet (resistive coil or superconducting coil) concentrically and radially outside the electromagnet (resistive coil or superconducting coil). By providing this, the structure is such that a strong static magnetic field is generated in the measurement space, and a weak leakage static magnetic field is generated outside.

<Problems to be solved by the invention> Although the above-mentioned conventional technology has a sufficiently persuasive argument, it is necessary to significantly improve the mechanical accuracy (dimensional accuracy, etc.) when manufacturing the actual machine. However, there is a problem that the desired effect cannot be achieved.

The object of the present invention is to provide an NMR imaging system in which manufacturing tolerances do not affect the intended effect of reducing leakage magnetic fields, and thereby the leakage magnetic fields can be extremely suppressed with good reproducibility and productivity. An object of the present invention is to provide a superconducting magnet device for use.

Means for Solving the Problems> A configuration for achieving the above object will be described with reference to FIGS. 1 and 2, which are embodiment drawings. This is a magnet device for generating , which surrounds the measurement space A with superconducting coils 1--1, and has superconducting coils ■...-■ outside of the superconducting coils 1--l. A shield 2 made of a superconducting material formed into a stripe shape is provided to surround the superconducting coil tow.
1 and its shield 2 can be cooled to a superconducting state.

The superconducting coil 1-1 and the shield 2 form an equivalent circuit as shown in Fig. It becomes impossible for magnetic flux to enter and exit between the space surrounded by 2 and the external space. Therefore, leakage of the magnetic field to the outside of the coil, which is generated by passing a current through the superconducting coil 1-1, to the outside of the shield 2 is extremely suppressed. Furthermore, due to its principle, manufacturing errors in terms of mechanical precision do not affect the intended effect of preventing magnetic field leakage.

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

FIG. 1 is a partially cutaway exploded perspective view of an embodiment of the present invention, and FIG. 2 is a central vertical sectional view of a refrigerant tank 4 around which a shield 2 is wound.

This embodiment shows an example in which a superconducting coil 1-1 and a shield 2 are housed inside one taliostat and cooled. That is, a ring-shaped superconducting coil 1 is placed inside a refrigerant tank 4 disposed in a vacuum tank 3 of a cryostat.
-1 is contained and immersed in a coolant such as liquid helium. A shield 2 made of a superconducting material formed into a stripe shape is wound around the outer peripheral surface of the refrigerant tank 4. Therefore, this shield 2 is cooled to near the temperature of the refrigerant inside it through the wall surface of the refrigerant tank 4, and together with the superconducting coil 1-1, it is cooled to the superconducting temperature (below the superconducting critical temperature). and can maintain the superconducting phase.

The vacuum chambers 3 each have a cylindrical outer wall 3a coaxial with each other.
Both end surfaces of the inner wall 3b are closed by side walls 3c and 3c', and the inside of the inner wall 3b forms a cylindrical measurement space A into which a measurement object such as a human body can be inserted.

The refrigerant tank 4, like the vacuum tank 3, has a substantially double cylindrical shape, and the shield 2 is wrapped around the portion excluding the inner wall 4a. The shield 2 has a structure in which a superconducting material such as Pb or Nb-Tt is formed into a flat plate, and then a large number of small holes are punched to form a so-called punch metal shape, or a superconducting material wire is woven into a striped shape. The structure can be made as follows. In addition, when adopting the latter structure, either a structure in which the overlapping portions of the wires are superconductingly short-circuited or insulated may be used.

FIG. 3 is an equivalent circuit diagram of an embodiment of the present invention. With superconducting coil 1 and shield 2 cooled to a superconducting state,
By operating the persistent current switch 10, a persistent current flows through the superconducting coil 1, and a static magnetic field is generated inside and outside the coil. Due to the magnetic field inside the coil, 4F+
A uniform static magnetic field is applied to one constant space A. Since the shield 2 is in a superconducting state, the magnetic field to the outside of the coil cannot go outside the shield 2 due to the Meissner effect, and there is almost no static magnetic field leaking to the outside.

FIG. 4 is a sectional view of a main part of another embodiment of the present invention. This embodiment shows an example in which another cryostat is provided outside the cryostat for cooling the superconducting coils I--I so as to surround the cryostat, and a shield 2 is housed inside the cryostat.

That is, the superconducting coil 1-1 is housed in the first refrigerant tank 14, and the first refrigerant tank 14 is housed in the first vacuum tank 13 to form the measurement space A.

A second vacuum tank 23 is provided so as to surround the outer periphery and side wall of the first vacuum tank 13, and a second refrigerant tank 24 is accommodated therein. A streak-shaped shield 2 made of superconducting material is housed inside the second refrigerant tank 24 . Even if the shield 2 is cooled to a superconducting state with this structure, the Meissner effect causes the shield 2 to
It is possible to prevent the static magnetic field from leaking to the outside.

<Effects of the Invention> As explained above, according to the present invention, the outside of the superconducting coil for creating a uniform static magnetic field in the measurement space A for NMR imaging is covered with a shield made of superconducting material in the shape of a stripe. , and the shield is configured so that it can be cooled to a superconducting state together with the superconducting coil.Because of the perfect diamagnetism (Meissner effect), which is a basic property of superconductivity, the static magnetic field towards the outside of the superconducting coil is cannot pass through the shield, and leakage of the static magnetic field to the outside of the device is extremely suppressed. Moreover, in principle, unlike conventional devices, the strength of the leakage static magnetic field does not affect the mechanical precision during manufacturing, so the reproducibility is good and manufacturing is easy. Furthermore, the structure prevents disturbances caused by fluctuations in the external magnetic field of the superconducting magnet device or changes in the effective magnetic path due to the approach of objects with different magnetic permeability, such as iron, from reaching the inside, so the measurement space is Static magnetic field stability can also be improved.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway exploded perspective view of an embodiment of the present invention, FIG. 2 is a central vertical sectional view of a refrigerant tank 4 around which the shield 2 is wound, and FIG. 3 is an equivalent circuit diagram of the embodiment of the present invention. FIG. 4 is a sectional view of a main part of another embodiment of the present invention. 1-m-superconducting coil 2-shield 3.13.2
3...Vacuum tank 4.14.24-Refrigerant tank 10--Persistent current switch A--Measurement space

Claims (3)

[Claims] (1) A magnet device for generating a static magnetic field for NMR imaging, in which a measurement space is surrounded by a superconducting coil, and a superconducting material is placed outside the superconducting coil so as to surround the coil. Provide a shield formed into a mold,
NMR characterized in that the shield is configured to be cooled to a superconducting state together with the superconducting coil.
Superconducting magnet device for imaging. (2) The superconducting magnet device for NMR imaging according to claim 1, wherein the superconducting coil and the shield are arranged in the same cryostat. (3) Claim 1, characterized in that another cryostat is coaxially provided outside the cryostat housing the superconducting coil so as to surround the cryostat, and the shield is housed inside the cryostat. A superconducting magnet device for NMR imaging as described in 1.