JPH07100125A - Magnetic resonance imaging system - Google Patents

Abstract

PURPOSE:To effectively hold in check a magnetic field leaked from the means of generating a static magnetic field, easily and at a low cost, without a need for enlarging an examination room or use of a magnetic shield made of expensive material with high magnetic im-permeability in order to prevent the spread of harmful effects of a leaked magnetic field on electric equipment outside the examination room and human bodies. CONSTITUTION:A coil 4 to counteract the effect of a leaked magnetic field is installed at a position surrounding the area where the leaked magnetic field resulting from the means of generating a static magnetic field exists. A DC constan-current power supply circuit 5 is installed to supply current to the coil 4 to generate a magnetic field oriented in the opposite direction of the leaked magnetic field and in the magnitude sufficient to cancel out the effect of the leaked magnetic field.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to nuclear magnetic resonance (NMR).
The present invention relates to a magnetic resonance imaging apparatus that obtains a tomographic image of an inspection region of a subject by using a phenomenon.

[0002]

2. Description of the Related Art A magnetic resonance imaging apparatus requires a static magnetic field to cause an NMR phenomenon and is provided with a static magnetic field generating means for generating a static magnetic field. The static magnetic field generated by the static magnetic field generating means is very large, and its leakage magnetic field, especially the leakage magnetic field to the outside of the examination room (apparatus installation room) poses a problem.

That is, the leakage magnetic field may damage electronic devices and human bodies outside the examination room. In order to avoid this, in the conventional magnetic resonance imaging apparatus,
Enlarge the inspection room itself to reduce the leakage magnetic field to the outside of the inspection room, or enclose the surface of the inspection room where the leakage magnetic field is large with an extremely expensive high permeability material such as permalloy, amorphous, silicon steel sheet, etc. I was dealing with it by shielding.

[0004]

As described above, in the prior art, in order to avoid the damage due to the stray magnetic field from the static magnetic field generating means, the size of the test chamber is increased or the surface of the test chamber on the side where the stray magnetic field is increased is increased. In the past, improvement of this point has been demanded, not a simple and inexpensive countermeasure such as enclosing a magnetic shield with an extremely expensive high magnetic permeability material.

The object of the present invention is to easily and inexpensively suppress the leakage magnetic field of the static magnetic field generated from the static magnetic field generating means, and to prevent the leakage magnetic field from affecting the electronic equipment outside the examination room and the human body. It is an object of the present invention to provide a magnetic resonance imaging apparatus that can achieve the above without enlarging the examination room and surrounding the surface of the examination room on the side where the leakage magnetic field is large with an extremely expensive high magnetic permeability material.

[0006]

In the magnetic resonance imaging apparatus for obtaining a tomographic image of an examination region of a subject by using the nuclear magnetic resonance phenomenon, a static magnetic field necessary for causing the nuclear magnetic resonance phenomenon is generated. A leakage magnetic field canceling magnetic field generating coil disposed at a position surrounding a region in which a leakage magnetic field from the static magnetic field generating means is present, and in this magnetic field generating coil, a direction for generating a magnetic field in a direction of canceling the leakage magnetic field, Further, it is achieved by providing a DC constant current power supply circuit for supplying a DC constant current of a magnitude that cancels the leakage magnetic field.

[0007]

The magnetic field generating coil for canceling the leakage magnetic field is arranged at a position surrounding the region where the leakage magnetic field from the static magnetic field generating means for generating the static magnetic field necessary for the occurrence of the nuclear magnetic resonance phenomenon exists.
The DC constant current power supply circuit supplies a DC constant current in a direction in which a magnetic field is generated in a direction in which the leakage magnetic field is canceled and in a magnitude that cancels the leakage magnetic field. Therefore, in the leakage magnetic field canceling magnetic field generating coil, an appropriate magnetic field in the direction of canceling the leakage magnetic field from the static magnetic field generating means is generated, and the leakage magnetic field is canceled.

As a result, the leakage magnetic field of the static magnetic field generated from the static magnetic field generating means can be suppressed easily and inexpensively, and the influence of the leakage magnetic field on the electronic equipment outside the examination room and the human body can be prevented. This can be achieved without enlarging the inspection room and using an extremely expensive high magnetic permeability material.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing an embodiment of a magnetic resonance imaging apparatus according to the present invention. This magnetic resonance imaging apparatus obtains a tomographic image of a desired examination region of a subject (not shown) by utilizing a nuclear magnetic resonance phenomenon, and includes a gantry unit 1 and a table unit 2.

The gantry unit 1 causes nuclear magnetic resonance (NMR) to occur at an inspection site of an object to be inspected, and detects an NMR signal emitted from the object. And a static magnetic field generating means for giving a gradient magnetic field and a gradient magnetic field generating means, and further a transmitting system for irradiating the subject with a high frequency signal and a receiving system for detecting an NMR signal emitted from the subject. A table section 2 is provided on the front side of the gantry section 1. The table portion 2 lays a subject on the table and slides it back and forth and left and right.

Here, the static magnetic field generating means provided in the gantry unit 1 has a higher S magnetic field strength as the magnetic field strength increases.
/ N ratio is improved, and the central magnetic field is usually 0.2T
Many are in the range of (2000G) to 2T (20000G), but when the magnetic field strength becomes strong, the leakage magnetic field to the outside of the inspection room 3 becomes large.

FIG. 2 shows a leakage magnetic field distribution of a magnetic resonance imaging apparatus of a central magnetic field 0.3T vertical magnetic field type. The magnetic field strength that does not affect the human body, electronic devices, etc. is 1 G or less and must be separated from the center of the gantry unit 1 by 3 m or more.

Here, in the present invention, as shown in FIGS. 1 and 3, a position surrounding the region where the leakage magnetic field from the static magnetic field generating means for generating the static magnetic field exists, here, the ceiling of the inspection room 3. Is provided with a magnetic field generating coil 4 for canceling a leaky magnetic field, and the magnetic field generating coil 4 has a size that cancels the leaky magnetic field in a direction to generate a magnetic field F in a direction that cancels the leaky magnetic field. And a DC constant current power supply circuit 5 for supplying a DC constant current. The magnetic field F is generated by a DC constant current of a magnitude that cancels the leakage magnetic field, and is a constant magnetic field having the same strength as the direction opposite to the leakage magnetic field. As a result, the leakage magnetic field from the gantry unit 1 is canceled and the leakage magnetic field to the upper part of the inspection room 3 is reduced.

The DC constant current power supply circuit 5 is composed of a DC constant current power supply body and a current value adjusting volume, and the magnitude of the constant current I can be adjusted by adjusting the volume. The DC constant current power supply circuit 5 may be installed anywhere, but if it is installed outside the inspection room 3, it does not affect the NMR signal receiving system in the gantry unit 1 and is an inexpensive and compact switching power supply. Can also be used.

In the above-mentioned embodiment, the case where the present invention is applied to the magnetic resonance imaging apparatus of the vertical magnetic field type has been described. Therefore, the vertical leakage magnetic field is large, and the leakage magnetic field upward of the gantry portion 1 is reduced. As an example,
It is not limited to this. When applied to a horizontal magnetic field type magnetic resonance imaging apparatus, the leakage magnetic field canceling magnetic field generating coil 4 may be provided on both the left and right wall surfaces in order to reduce the leakage magnetic field in the horizontal direction. Of course, in the above-described embodiment, in order to reduce the leakage magnetic field in the vertical direction, the leakage magnetic field canceling magnetic field generating coil 4 may be provided on the ceiling and floor surfaces. That is, if the surface on the side where a large leakage magnetic field from the static magnetic field generating means is generated, it can be effectively installed on any of the ceiling, floor, left and right wall surfaces, and front and rear wall surfaces of the inspection room 3.

The static magnetic field generating means may be of any type such as a permanent magnet type or a superconducting type.

[0017]

As described above, according to the present invention, the leakage magnetic field of the static magnetic field generated from the static magnetic field generating means can be suppressed with a simple coil and power supply circuit, that is, easily and inexpensively. There is an effect that it is possible to prevent the spread of harm to electronic devices and human bodies outside the inspection room due to the method without enlarging the inspection room or magnetically shielding with an extremely expensive high magnetic permeability material.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of the device of the present invention.

FIG. 2 is a trihedral view showing a leakage magnetic field from a gantry unit.

FIG. 3 is a view showing a main part of the device of the present invention taken out.

[Explanation of symbols]

 1 Gantry part 2 Table part 3 Inspection room 4 Magnetic field generating coil for canceling leakage magnetic field 5 DC constant current power supply circuit I Constant current (DC) F Constant magnetic field

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H01F 7/20 A 8105-2J G01N 24/06 510 Z

Claims (1)

[Claims] 1. In a magnetic resonance imaging apparatus for obtaining a tomographic image of an examination region of a subject by using a nuclear magnetic resonance phenomenon, leakage from a static magnetic field generating means for generating a static magnetic field necessary for causing the nuclear magnetic resonance phenomenon. A magnetic field generating coil for canceling a leakage magnetic field arranged in a position surrounding a region where a magnetic field exists, and a direction in which a magnetic field is generated in the magnetic field generating coil in a direction of canceling the leakage magnetic field, and to the extent of canceling the leakage magnetic field. A magnetic resonance imaging apparatus comprising: a DC constant current power supply circuit for supplying a DC constant current of a magnitude.