JPH0428349A - Static magnetic field magnet for mri device - Google Patents

Abstract

PURPOSE:To reduce the axial length in order to prevent a patient from being given with uneasy feeling and generate the highly uniform magnetic field by using a superconductive coil and normal conductive coils for generating a main magnetic field and arranging the superconductive coil at the center part and the normal conductive coils at both the sides. CONSTITUTION:A vacuum container 6 is constituted by using only a superconductive coil 1b having a short axis, and the normal conductive coils 1a' and 1c' are installed outside the vacuum container 6, and a vacuum heat- shielding space 3 including the heat shielding plates 2a and 2b is formed. Accordingly, for the normal electric conductive coils 1a' and 1c', the need of the container having a heat shielding space is obviated, and it is enough only to take account of the space for an electric insulating member 7, etc., and the length of the axis can be shortened in compassion with the constituted case only of the superconductive coil. Further, since each of the coils, 1a', 1b, and 1c' for generating a main magnetic field B is at the same position to the conventional device and has the equal magnetomotive force, the magnetic field uniformity in a diagnosis space 5 is equal to that in the conventional device.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a static magnetic field magnet 1- used in a medical magnetic resonance imaging apparatus (MRI apparatus).

(Prior art vfI) Static magnetic field magnet 1-1 used in an MRI apparatus In particular, a magnet using a superconducting coil has a long axial length due to its configuration. That is, a coil arrangement for generating a highly uniform magnetic field in a space necessary for diagnosing a patient, an insulating space for keeping the superconducting coil at an extremely low temperature, etc. are required, and the axial length becomes long. An example of a conventional superconducting magnet for an MRI apparatus is shown in FIG. In this way, the conventional system uses three superconducting coils to generate a highly uniform magnetic field.1. a, lb, l
c, and a vacuum insulation space 3 including heat shield plates 2a and 2b.
has. A magnetic shield 4 (made of a magnetic material such as iron) is attached to this, resulting in a device with a total length of approximately 2 m.

(Magnetic shielding is used to prevent the influence of magnetic fields on peripheral equipment.) (Problem to be solved by the invention) In this way, an MRI apparatus using a superconducting magnet can:
Although it has advantages such as being able to generate a high magnetic field and having a stable magnetic field over time, it has the problem that the magnet axis is long and large, giving the patient a sense of anxiety. If the axial length is shortened, the uniformity of the magnetic field within the diagnostic space 5 deteriorates, and in order to maintain the uniformity, a coil is required to flow a current in the opposite direction to cancel the error magnetic field, resulting in an increase in cost. be.

SUMMARY OF THE INVENTION An object of the present invention is to provide a static magnetic field magnet for an MRI apparatus that has a short axial length and has a highly uniform magnetic field that does not give a patient a feeling of anxiety.

[Structure of the invention]

(Means for Solving the Problems) In the present invention, a superconducting coil and a normal conducting coil are used to generate the main magnetic field. Preferably, a superconducting coil is disposed at the center and a normal conductive coil is disposed at the ends, so that both coils generate a highly uniform main magnetic field.

(Function) Normally conductive coils do not require a container with an insulating space, and only need to consider the space for electrical insulating material, etc.
As a result, the axial length is shorter than when constructed with only superconducting coils.

(Example) FIG. 1 shows an embodiment of the present invention.

A vacuum vessel is constructed using only the short-axis superconducting coil 1b. Since this superconducting coil Ib alone cannot form a highly uniform magnetic field in the diagnostic space 5, normal conducting coils Ia' and 1c' are provided outside the vacuum container, and the coil arrangement is as shown in Fig. 6, La, Ib, lc. Do the same.

In addition, the vacuum insulation space is between the coils la' and lb and between the coils la' and lb.
.

It can be configured using the space between Ic'. A normal conducting coil does not require a container with an insulating space, and the space for the electrical insulating material 7, etc. can be taken into account, so the axial length will be shorter than when it is composed only of superconducting coils. . In other words, the short axis corresponds to the adiabatic space outside the coils], a, and lc shown in FIG. 6, and the magnetic shield 4 can be miniaturized accordingly.

FIG. 2 shows the normal conducting coil core body 9. This conductor has
There is a hole 10 for passing cooling water, and water is allowed to flow through this hole to cool the conductor.

(Operation of the embodiment) Coils 1a' and lb that generate the main magnetic field B shown in FIG.
.

1c' has the same magnetomotive force at the same position as in the conventional case (FIG. 6), so the magnetic field uniformity within the diagnostic space 5 is the same as in the conventional case. The vacuum insulation space 3 is between the coils 1a' and 1b and between the coils 1b and 1b.
lc', and heat shield plates 2a and 2b are arranged to minimize the amount of evaporation of liquid helium, which is a cooling medium for the superconducting coil. Furthermore, a magnetic shield 4 is placed outside of the magnetic shield 4 to reduce leakage magnetic fields. With such a configuration, the axial length is shortened by the vacuum insulation space outside the superconducting coil. Conventionally, the insulation space is approximately 100 to 15
0mm was required, so the total length was 200-300m.
This means that the m-axis length can be shortened.

(Effects of Example) In this way, among the superconducting coils that generate the main magnetic field,
The coil near the center of the magnet is composed of a superconducting coil,
The coil located at the end is composed of a normal conducting coil. This eliminates the need for a vacuum insulation space at both ends, and the magnet 1
- Has the effect of shortening the axial length.

(Other Embodiments) FIG. 3 shows another embodiment of the present invention. In this example, the normally conducting coil is used as a canceling coil that reduces leakage magnetic field.

In the axial direction of the superconducting coil 1b, there is a normal conducting coil 1a″1c″.
Place. Since the normal conducting coils 1a", lc" are used as canceling coils to reduce leakage magnetic fields, their diameters are made large to improve the shielding effect. That is, normally conducting coil la', 1. The leakage magnetic field generated by the superconducting coil 1b is canceled by the magnetic field generated by the superconducting coil 1b, but if the diameter of the normal conducting coil 1a is made larger than the diameter of the superconducting coil 1b, the axial and radial This means that the leakage magnetic field can be efficiently reduced.

With such a configuration, the vacuum insulation space at both ends of the magnet can be omitted, so the axial length of the magnet can be shortened similarly to the example shown in FIG. In addition, since the normal conduction coil is used as a canceling coil that acts as a magnetic shield,
The magnetic seal 1 made of magnetic material is no longer necessary, and the axial length of the magnet can be further shortened accordingly.

FIG. 4 shows another embodiment using the present invention. This consists of a vacuum container containing a superconducting coil 1b made of a magnetic material,
This is a magnetic vacuum container 6'.

In this way, the vacuum container 6' also becomes a part of the magnetic shield, so that the magnetic shield 4 disposed outside the magnet can be thinner than in the embodiment shown in FIG. Therefore, the axial length of the magnet is further shortened, and the magnetic shield 4 is also lightweight, which has the effect of facilitating assembly and installation.

Figure 5 shows an example in which a superconducting coil and a permanent magnet are used in the present invention. Permanent magnets 8 are arranged. Even with this configuration, the axial length of the magnet is shorter than that of the prior art (FIG. 6).

=8- All of the above embodiments have shown normal conducting coils or permanent magnets arranged at both ends of the superconducting coil in the axial direction.
These may be placed at one end.

If this is done, the main magnetic field will be asymmetrical, which may improve the space utilization of the room in which the MRI apparatus is installed.

〔Effect of the invention〕

As described above, in the present invention, of the coil group that generates the main magnetic field, the coil located near the center of the magnet is composed of a superconducting coil, and the coils on the end side are composed of normal conducting coils or permanent magnets. The total length of the magnet can be shortened, which has the effect of alleviating patients' anxiety.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention, a cross-sectional view showing a normal conducting coil arranged on both sides of a superconducting coil, FIG. 2 is a diagram showing a conductor for a normal conducting coil used in the above embodiment, and FIG. The figure shows an example in which a normal conducting coil is used as a canceling coil in the present invention, Figure 4 shows an example in which the vacuum container is made of a magnetic material in the present invention, and Figure 5 shows a permanent magnet and a superconducting coil in the present invention. 6th diagram of an embodiment using a coil
The figure shows conventional superconducting magnets 1 to 1. la, lb, lc...superconducting coils 18', 1c
'...Normal conduction coil 1a'' ]cH...Normal conduction canceling coil 2a, 2
b...Heat shield plate 3...Vacuum insulation space 4...
・Magnetic shield 5...Diagnostic space 6...Vacuum container 6'...Magnetic vacuum container 7...Electrical insulating material 8...Permanent magnet 9...Conductor for normal conducting coil 10...For cooling water 6B...Main magnetic field
Z...Z axis (center axis) agent Patent attorney Nori Chika
Kensuke Qt

Claims (9)

[Claims] (1) A static magnetic field magnet for an MRI apparatus, comprising a superconducting coil and a normal conducting coil as main magnetic field generating coils, both coils generating a predetermined main magnetic field. (2) The static magnetic field magnet for an MRI apparatus according to claim (1), characterized in that a permanent magnet is used in place of the normally conducting coil. (3) The MRI apparatus according to claim (1), wherein the normal conductive coil is a canceling coil that flows a current in the opposite direction to that of the superconducting coil in order to reduce the leakage magnetic field generated by the superconducting coil. Static magnetic field magnet. (4) The static magnetic field magnet for an MRI apparatus according to claim (1), wherein the diameter of the normal conducting coil is larger than the diameter of the superconducting coil. (5) The static magnetic field magnet for an MRI apparatus according to claim (1), wherein the normal conducting coils are arranged on both sides of the superconducting coil in the axial direction. (6) The static magnetic field magnet for an MRI apparatus according to claim (5), wherein the normal conductive coils arranged on both sides of the superconducting coil in the axial direction can be individually excited. (7) Normal conducting coils have a larger diameter than superconducting coils,
The static magnetic field magnet for an MRI apparatus according to claim 5, characterized in that the magnet is a canceling coil that reduces leakage magnetic field of the superconducting coil by passing a current in the opposite direction to that of the superconducting coil. (8) The static magnetic field magnet for an MRI apparatus according to claim (7), wherein the leakage magnetic field is axially asymmetric. (9) The static magnetic field magnet for an MRI apparatus according to claim (1), wherein the vacuum container housing the superconducting coil is made of a magnetic material.