JPH11137535A - Magnetic resonance imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce noises generated from a gradient magnetic field coil which imparts a gradient magnetic field to a specimen in a magnetic resonance imaging device. SOLUTION: A gradient magnetic field coil 2 is arranged in a pole piece 1, and the pole piece 1 is sealed, and air in the pole piece 1 is drawn out by a vacuum pump, and the inside of the pole piece 1 is vacuumized. By the vacuumization, the transmission in air of hitting noises generated in such a manner that wires 7 being packed in grooves which are cut on the surface of the gradient magnetic field coil 2 in a manner to form a gradient magnetic field generating pattern, vibrate by a pulse current, and hit the internal wall surfaces of the grooves, can be reduced. For this reason, an uncomfortable feeling or anxiety due to the noises for a specimen being located in a measurement space which is formed in a magnetic field generating means, can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a subject (human body) utilizing a nuclear magnetic resonance (hereinafter abbreviated as "NMR") phenomenon.
More particularly, the present invention relates to a magnetic resonance imaging apparatus capable of reducing noise generated from a gradient coil that applies a gradient magnetic field to a subject.

[0002]

2. Description of the Related Art A magnetic resonance imaging apparatus measures a nuclear spin (hereinafter, simply referred to as "spin") density distribution, relaxation time distribution, and the like at a desired inspection site in a subject by utilizing an NMR phenomenon. An arbitrary section of the subject is displayed as an image based on the measurement data. As shown in FIG. 6, the conventional magnetic resonance imaging apparatus performs a magnetic field generating means 61 for applying a static magnetic field and a gradient magnetic field to a subject, and a nuclear magnetic resonance to the nuclei of the atoms constituting the living tissue of the subject. A transmission system having a transmission high-frequency coil for irradiating a high-frequency signal to wake up the signal; a reception system having a reception high-frequency coil 62 for detecting an echo signal emitted by the nuclear magnetic resonance; And a signal processing system 63 for performing an image reconstruction operation using the echo signals thus obtained.

In FIG. 6, reference numeral 64 denotes a bed for placing a subject on the bed and moving it into the opening of the magnetic field generating means 61. Although not shown, the magnetic field generating means 61 includes a static magnetic field generating magnet for generating a uniform static magnetic field, and a gradient magnetic field provided near the static magnetic field generating magnet for generating a gradient magnetic field. The transmission coil includes a coil and a transmission high-frequency coil that is provided near the gradient coil and irradiates a high-frequency signal for exciting nuclear magnetic resonance to the subject.

A conventional gradient magnetic field coil 2 as shown in FIGS. 7 and 8 has, for example, a groove formed in an integral insulating plate 5 formed in a disk shape in a gradient magnetic field generating pattern.
A wire 7 made of, for example, a copper stranded wire is packed into the groove so as to be crushed, and one current path having one end of the wire 7 as an input end and the other end as an output end is formed, and an X-direction gradient magnetic field is formed. The coil 3 and the Y-direction gradient magnetic field coil 4 were formed. The sound absorbing members 6a and 6b are respectively attached to both surfaces of the insulating plate 5 having the X and Y direction gradient magnetic field coils 3 and 4 formed as described above. And prevents noise generated by the vibration of the wire 7 from being absorbed. Further, on the lower surface side of the insulating plate 5, a Z-direction gradient magnetic field coil 71 formed in a ring shape is attached with a sound absorbing member 6b interposed therebetween. The gradient magnetic field coil 2 configured as described above is provided with a screw 73 through a coil mounting plate 72 on an annular protrusion on the outer periphery of the pole piece 21 mounted on one surface of the permanent magnet 20 as a static magnetic field generating magnet. It is attached by.

When an electric current is applied to the gradient magnetic field coils 3 and 4 in the X and Y directions in a state where the gradient magnetic field coil 2 is placed in the static magnetic field space by the permanent magnet 20, a certain value is determined by Fleming's left-hand rule. A force is generated in the direction, and the current flows in a pulsed manner, so that the wire 7 of each gradient coil 2 vibrates and strikes the inner wall surface of the groove formed in the insulating plate 5,
Noise was generated. In contrast,
A wire 7 having a diameter slightly larger than the width of the groove is used. The wire 7 is crushed and packed into the groove, and a certain amount of play is provided to allow the vibration of the wire 7 to be transmitted non-linearly. , 6b absorbed the noise caused by the vibration of the wire.

[0006]

However, in such a gradient coil in such a conventional magnetic resonance imaging apparatus, as shown in FIG. 8, an insulating plate 5 as a base member is formed in a plate-like integral body. At the same time, since the groove is cut in the groove, the vibrating wire 7 directly hits the inner wall surface of the groove, and a large noise is generated by the impact of the rigid insulating plate 5. Further, since the insulating plate 5 is formed in a large diameter, for example, in a disk shape, a striking sound on the inner wall surface of the groove by the vibrating wire 7 spreads in all directions through the insulating plate 5, and the noise is reduced. May be enlarged. Therefore, the generation of the noise may cause discomfort or anxiety to the subject located in the measurement space formed inside the magnetic field generating means 61.

Accordingly, an object of the present invention is to provide a magnetic resonance imaging apparatus capable of addressing such problems and reducing noise generated from a gradient coil that applies a gradient magnetic field to a subject.

[0008]

In order to achieve the above object, there is provided a magnetic field generating means for applying a static magnetic field and a gradient magnetic field to a subject, and nuclear magnetic resonance is generated in nuclei of atoms constituting a living tissue of the subject. A signal system for irradiating a high-frequency signal, a receiving system for detecting an echo signal emitted by the above-described nuclear magnetic resonance, and a signal processing system for performing an image reconstruction operation using the echo signal detected by the receiving system. And a gradient magnetic field coil as a magnetic field generating means for applying the gradient magnetic field is disposed in a closed space. (Claim 1)

[0009] Further, the magnetic resonance imaging apparatus is characterized in that the space for disposing the gradient magnetic field is further reduced in pressure. (Claim 2)

[0010] Furthermore, the gradient magnetic field coil is supported in a pole piece by a shock absorbing material, and a cover for covering and sealing the gradient magnetic field coil, and a pressure reducing member provided on the pole piece for depressurizing by removing air. A magnetic resonance imaging apparatus according to claim 1. (Claim 3)

In the magnetic resonance imaging apparatus thus configured, a wire rod packed in a groove cut in a gradient magnetic field generating pattern on the surface of the gradient coil vibrates by a pulse current, and the inner wall surface of the groove is removed. It is possible to reduce transmission of the hitting sound due to tapping to the outside.

[0012]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a plan view showing an embodiment in which a gradient coil is arranged inside a pole piece in a magnetic resonance imaging apparatus of the present invention, and FIG. 2 is a central sectional view thereof. FIG. 3 is a partially enlarged sectional view showing a part of the central sectional view shown in FIG. 2 in an enlarged manner.

First, a magnetic resonance imaging apparatus to which a pole piece having the above-described gradient magnetic field coil disposed therein is applied, as in the conventional example shown in FIG.
, A transmission system, a reception system, and a signal processing system 63. The magnetic field generating means 61 applies a static magnetic field and a gradient magnetic field to the subject, and generates a static magnetic field generating magnet (about) which generates a uniform static magnetic field around the subject in the body axis direction or the direction perpendicular to the body axis. (Not shown) and a gradient magnetic field coil (not shown) formed in the X, Y, and Z axes for applying a gradient magnetic field in the X, Y, and Z axes to the subject. I have. As the static magnetic field generating magnet, a permanent magnet type, a normal conducting magnet type, or a superconducting magnet type magnetic field generating means is arranged in a certain space around the subject.

The transmission system irradiates a high-frequency signal to cause nuclear magnetic resonance in the nuclei of the atoms constituting the living tissue of the subject. Although not shown, the transmitting system applies the high-frequency signal to the subject inside the gradient magnetic field coil. The transmission high-frequency coil is disposed in close proximity to the transmission high-frequency coil. The transmission high-frequency coil supplies a high-frequency pulse to the transmission high-frequency coil.

The receiving system detects an echo signal (NMR signal) emitted by nuclear magnetic resonance of an atomic nucleus of a living tissue of the subject, and responds to the subject by a high-frequency signal emitted from the transmitting high-frequency coil. And a high-frequency coil for reception arranged in close proximity to the subject to detect the electromagnetic wave (NMR signal), and an amplifier, a quadrature phase detector, and an A / D converter (not shown).

The signal processing system 63 performs an image reconstruction operation using the echo signal detected by the reception system. The image data obtained from the echo signal is Fourier-transformed to calculate correction coefficients, image reconstruction, and the like. Central processing unit (C
PU), a recording device such as a magnetic disk and a magneto-optical disk, and a display such as a CRT for displaying an image of the obtained tomographic image data of an arbitrary cross section.

In FIG. 6, reference numeral 64 denotes a bed for placing the subject on the bed and moving it into the opening of the magnetic field generating means 61, and reference numeral 65 supplies a high-frequency pulse to the transmitting high-frequency coil. And a device unit accommodating a high-frequency power supply and a power supply for the gradient coil 2 for
Reference numeral 66 denotes a multi-format camera that captures the obtained magnetic resonance imaging image on a film or the like.

Here, as shown in FIGS. 1 to 3, a pole piece 1 which is a feature of the present invention and has a gradient magnetic field coil provided inside a magnetic field generating means 61 shown in FIG. A gradient magnetic field coil 2 is arranged inside the piece 1. The gradient magnetic field coil 2 has X and Y direction gradient magnetic field coils 3 and 4 as in the conventional example. As shown in FIG. 2, sound absorbing members 6a and 6b are attached to prevent the respective gradient magnetic field coils 3 and 4 from dropping out of the groove and absorb noise generated by the vibration of the wire 7. Has become. The gradient magnetic field coil 2 is attached to the D piece 8 with screws (not shown) so as to avoid the X and Y direction gradient magnetic field generation patterns. Further, the D-piece 8 is attached to the pole piece 1 through a non-magnetic and non-conductive material, for example, a rubber D-piece 9 to prevent vibration from being transmitted to the outside through the pole piece 1. doing. Then, air is drawn out to the outer peripheral portion of the pole piece 1.
A pipe 10 for reducing the pressure inside and a valve 11 are attached. The inner wall surface of the pole piece 1 is entirely sealed with a sealing material or the like in order to increase the degree of sealing inside the pole piece 1. A groove 13 for disposing the O-ring 12 is provided in the annular projection of the pole piece 1, and is entirely covered with a cover 14 made of a non-magnetic and highly rigid material such as glass fiber resin. The cover 14 is fixed to the pole piece 1 with screws 15.

Then, the pole piece 1 is sealed, and the air inside the pole piece 1 is drawn out from the valve 11 by a vacuum pump to reduce the pressure inside the pole piece 1. By reducing the pressure, the wire 7 packed in the groove cut in a gradient magnetic field generating pattern on the surface of the gradient magnetic field coil 2 vibrates due to the pulse current, and the hitting sound caused by hitting the inner wall surface of the groove is reduced. Can be done. That is, the vibration to the outside can be reduced by sealing, and the vibration to the air can be reduced by further reducing the pressure, so that the noise due to the impact sound can be suppressed.

The pole piece 1 configured as described above
FIG. 4 shows the inside of the magnetic field generator 61 (see FIG. 6).
It is mounted as shown. That is, an upper yoke 41 and a lower yoke 42 made of a material having a high magnetic permeability, for example, low carbon steel, and a side yoke 4 connecting these two feelings.
3 and disk-shaped permanent magnets 20, 20 fixed to the inner surfaces of the upper yoke 41 and the lower yoke 42 facing each other.
And a magnetic circuit for generating a static magnetic field.
The pole piece 1 is disposed above and below the measurement space with the measurement space of the subject formed between the opposing inner surfaces of the magnets 0 and 20, and attached near the permanent magnet 20. I have. In FIG. 4, the arrow Bo indicates the direction of the static magnetic field generated by the permanent magnets 20, 20.

FIG. 5 is an internal configuration diagram showing an example of the application of the pole piece container of the present invention to another magnetic field generating means 61 in which the gradient coil is hermetically closed and decompressed. This embodiment uses an electromagnet instead of a permanent magnet as a magnet constituting a magnetic circuit for generating a static magnetic field. That is, the exciting coil 53 is wound around the iron core 51 a plurality of times to form the electromagnet 52, and the electromagnet 52 is fixed to the inner surfaces of the upper yoke 41 and the lower yoke 42 so as to face each other. The gradient coil is sealed above and below the measurement space of the subject formed between the opposed inner surfaces of the electromagnets 52, 52, and the decompressed pole piece containers are arranged to face each other. Attached to. And
A static magnetic field is generated in the direction indicated by the arrow Bo by flowing a current in the direction of the arrow through the exciting coil 53 of each of the electromagnets 52, 52. Also in this case, the vibration to the outside can be reduced by sealing as in the above-described embodiment, and the vibration to the air can be reduced by further reducing the pressure, so that the noise due to the impact sound can be suppressed.

[0022]

Since the present invention is constructed as described above, the wire 7 packed in the groove cut into the gradient magnetic field generating pattern on the surface of the gradient magnetic field coil 2 vibrates by a pulse current, The transmission of the impact sound in the air by hitting the inner wall surface of the groove can be reduced. That is, vibration to the outside can be reduced by sealing, and vibration to the air can be reduced by reducing the pressure. From this, the magnetic field generating means 61
Since noise can be suppressed with respect to the subject located in the measurement space formed therein, discomfort and anxiety can be eliminated.

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of a pole piece in a magnetic resonance imaging apparatus of the present invention.

FIG. 2 is a cross-sectional view of a center of the pole piece.

FIG. 3 is an enlarged partial sectional view showing a part of the pole piece.

FIG. 4 is an internal configuration diagram showing an attached state of the pole piece inside the magnetic field generating means.

FIG. 5 is an internal configuration diagram showing an application example of the pole piece of the present invention to another magnetic field generating means.

FIG. 6 is a perspective view showing the appearance of a magnetic resonance imaging apparatus according to the present invention and a conventional example.

FIG. 7 is a plan view showing a gradient magnetic field coil and a pole piece in a conventional example.

FIG. 8 is a central transverse sectional view of a gradient coil and a pole piece in a conventional example.

FIG. 9 is an enlarged partial sectional view showing a part of a gradient magnetic field coil and a pole piece in a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pole piece 2 Gradient magnetic field coil 3 Signal processing system 6a, 6b Sound absorbing member 9 D piece 11 Valve 12 O ring 14 Cover 20 Permanent magnet 61 Magnetic field generating means 62 High frequency coil for reception 63 Signal processing system 64 Bed

Claims (3)

[Claims] A magnetic field generating means for applying a static magnetic field and a gradient magnetic field to a subject; a signal system for irradiating a high-frequency signal to cause nuclear magnetic resonance in nuclei of atoms constituting the living tissue of the subject; A magnetic resonance imaging apparatus comprising: a receiving system that detects an echo signal emitted by the above-described nuclear magnetic resonance; and a signal processing system that performs an image reconstruction operation using the echo signal detected by the receiving system. A magnetic resonance imaging apparatus, wherein a gradient magnetic field coil as a magnetic field generating means for applying a gradient magnetic field is arranged in a closed space. 2. A magnetic resonance imaging apparatus, wherein the space in which the gradient magnetic field is arranged is further reduced in pressure. 3. A cover for supporting the gradient magnetic field coil in a pole piece with a shock absorbing material, covering the gradient magnetic field coil and sealing, and a decompression member provided on the pole piece for depressurizing by removing air. The magnetic resonance imaging apparatus according to claim 1.