JPH04231935A - Magnetic resonance imaging device - Google Patents

Abstract

PURPOSE:To reduce the heat and the noise generated from a gradient magnetic field coil which provides a gradient magnetic field to a body to a examined. CONSTITUTION:In grooves 17a, 17b cut by forming a gradient magnetic field generation pattern on the surface of an insulating plate 16 consisting of a non- magnetic and electric insulating material, coil wire rods 18a, 18b are embedded so as to roughly fill a cross section of said grooves, and also, the inside of the grooves 17a, 17b in which these coil infrared wire rods 18a, 18b are embedded is filled with damping materials 22a, 22b, by which gradient magnetic field coils 4a, 4b are constituted. In such a state, a gradient magnetic field is provided to a body to be examined being an inspection object by these gradient magnetic field coils 4a, 4b.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to nuclear magnetic resonance (hereinafter referred to as "N"
This invention relates to a magnetic resonance imaging device that obtains a tomographic image of a desired part of a subject (human body) using the phenomenon (abbreviated as MR), and in particular reduces heat and noise generated from gradient magnetic field coils that apply gradient magnetic fields to the subject. The present invention relates to a magnetic resonance imaging apparatus that can perform

0002

[Prior Art] A magnetic resonance imaging apparatus uses the NMR phenomenon to measure the density distribution, relaxation time distribution, etc. of nuclear spins at a desired inspection site in a subject, and calculates and processes the measured signals. The image is displayed as a tomographic image of the examination site. Here, when measuring a wide spatial range such as the human body, approximately 0.05 to 2 T (tesla; 1 tesla is 10,000 gauss) in the measurement space consisting of a spherical space with a diameter of 30 to 50 cm. The static magnetic field of
A static magnetic field generator is required that generates a static magnetic field with a uniformity of 0 ppm or less.

[0003]The conventional magnetic resonance imaging apparatus using a permanent magnet as the above-mentioned static magnetic field generating device has a pair of magnetic resonance imaging devices facing each other forming a gap A into which the subject can enter, as shown in FIGS. 2 and 3. permanent magnets 1a, 1b and yokes 2a, 2 that magnetically couple these permanent magnets 1a, 1b.
b, and magnetic pole pieces 3a fixed to the opposing surfaces of the permanent magnets 1a and 1b on the air gap A side, respectively, for generating a uniform magnetic field.
, 3b, and the magnetic pole piece 3a.
, 3b, which generate a gradient magnetic field to be added to the uniform magnetic field generated by the magnetic pole pieces 3a, 3b, and the gradient magnetic field coils 4a, 4b, which are disposed close to each other inside the magnetic pole pieces 3a, 3b, and which are arranged in the air gap A, It comprises an irradiation coil 5 for applying electromagnetic waves to the specimen, a receiving coil 6 for receiving nuclear magnetic resonance signals emitted from the specimen, and a temperature adjustment means 7 for keeping the temperature of the static magnetic field generating magnetic circuit constant. It was done.

A conventional gradient magnetic field coil in such a magnetic resonance imaging apparatus is as shown in FIG.
, only the lower gradient magnetic field coil 4a is shown), an X-direction gradient magnetic field coil 12 is formed on one side of the air gap A side, and a Y-direction gradient magnetic field coil 13 is formed on the opposite side. A Z-direction gradient magnetic field coil 14 is formed on the back surface of the Y-direction gradient magnetic field coil 13, and is arranged close to the inside of the annular protrusion 15 above the magnetic pole piece 3a with almost no gap. In this case, the Z-direction gradient magnetic field coil 14 is, for example, a Helmholtz coil made of a formal copper wire wound in a circle, but the X-direction and Y-direction gradient magnetic field coils 12 and 13 have complicated shapes.

That is, as shown in FIGS. 5 and 6, on one side of an integral insulating plate 16 formed into a disk shape, for example,
Gradient magnetic field generation pattern in the X direction (see solid line 12 in Figure 5)
A coil wire 18a made of stranded copper wire, for example, is buried in the groove 17a, and one end of the coil wire 18a is used as an input end 20, and the other end is used as an output end 21. The X-direction gradient magnetic field coil 12 was configured by forming one current path. Further, on the opposite side of the insulating plate 16, a Y-direction gradient magnetic field generation pattern (see broken line 13 in FIG. 5), which is rotated 90 degrees with respect to the X-direction gradient magnetic field generation pattern, is cut out. A coil wire 18b also made of stranded copper wire is buried in this groove 17b to form one current path in the same manner as above, and as shown by the broken line in FIG. A directional gradient magnetic field coil 13 was configured. Then, the X-direction and Y-direction gradient magnetic field coils 12 formed as described above,
Sound absorbing members 19a,
19b are pasted on each of the gradient magnetic field coils 12 and 13 to prevent them from falling off the grooves 17a and 17b, and to absorb the noise generated by the vibrations of the coil wires 18a and 18b. .

[0006] Here, in the static magnetic field generating magnetic circuit using the permanent magnets 1a and 1b in the magnetic resonance imaging apparatus, the strength of the static magnetic field tends to change with changes in ambient temperature. Generally, its temperature coefficient is -1000p
pm/℃, and when the temperature increases by 1℃, the magnetic field strength increases by 100.
It was 0 ppm weaker. In this way, when the magnitude of the static magnetic field changes due to the influence of temperature, a gradient magnetic field is applied to the static magnetic field by the gradient magnetic field coils 4a and 4b to make the position correspond to the magnitude of the magnetic field, and resonance according to the position is generated. Errors occur in the operation of generating a frequency and detecting an NMR signal having this resonant frequency to specify a position. This deviation in position detection also causes image distortion and blurring.

[0007] However, with recent magnetic resonance imaging devices, there has been a demand for high-speed imaging and improved patient throughput, and with this, new high-speed sequences such as the gradient echo method have come to be used. As the current applied to the gradient magnetic field coils 4a and 4b shown in FIG. 3 has become larger, the frequency of their use (duty) has also become higher. Here, since the gradient magnetic field coils 4a and 4b are basically made of copper wire, they have a finite electrical resistance value, and when a current is passed to generate a gradient magnetic field, the current value Heat was generated in proportion to the square of

Furthermore, when current is applied to the X-direction and Y-direction gradient magnetic field coils 12 and 13 with the gradient magnetic field coils 4a and 4b placed in the static magnetic field space created by the permanent magnets 1a and 1b, Fleming's left hand Since force is generated in a certain direction according to the law of
8b vibrates and grooves 17a, 1 formed in the insulating plate 16
It struck the inner wall surface of 7b, producing noise.

[0009]

However, in the gradient magnetic field coils 4a and 4b in such a conventional magnetic resonance imaging apparatus, as shown in FIG. It was about 50% smaller than the cross-sectional area of . This is mainly done by connecting the coil wires 18a, 18b to the grooves 17a, 17.
This is to improve the ease of work when forming the X-direction and Y-direction gradient magnetic field coils 12 and 13, respectively, by embedding them in the coil wires 18a and 18b. When a large current is passed and a high duty is used as in recent years, the heat generated from the gradient magnetic field coils 4a and 4b increases. This heat is then transferred to the static magnetic field generating magnetic circuit, and the static magnetic field strength changes, causing deviations in position detection of NMR signals and distortion and blurring of images.

Furthermore, as mentioned above, the gradient magnetic field coil 4
By supplying a pulse current to a, 4b, the vibrating coil wires 18a, 18b hit the inner wall surfaces of the grooves 17a, 17b, and the impact of the rigid insulating plate 16 generated large noise. . Further, since the insulating plate 16 is formed into a disk shape with a large diameter, for example, the grooves 17 formed by the vibrating coil wires 18a and 18b
The sound of impact against the inner wall surfaces of a and 17b spreads in all directions via the insulating plate 16, and the noise may be amplified. Therefore, the generation of the noise may give a feeling of discomfort or anxiety to the subject located in the measurement space formed inside the static magnetic field generating magnetic circuit.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a magnetic resonance imaging apparatus that can address such problems and reduce heat and noise generated from gradient magnetic field coils that apply gradient magnetic fields to a subject. shall be.

0012

[Means for Solving the Problems] In order to achieve the above object, a magnetic resonance imaging apparatus according to the present invention has a pair of static magnetic field generating means arranged opposite each other to form a gap into which a subject can enter. A static magnetic field generating magnetic circuit having magnetic pole pieces each fixed to the opposing surface on the air gap side of the static magnetic field generating means for generating a uniform magnetic field, and a static magnetic field generating magnetic circuit having magnetic pole pieces for generating a uniform magnetic field, and a static magnetic field generating magnetic circuit disposed close to the inside of the magnetic pole piece to add to the uniform magnetic field generated by the magnetic pole piece. A gradient magnetic field coil that generates a gradient magnetic field, an irradiation coil that applies electromagnetic waves to the subject within the air gap inside the gradient magnetic field coil, and a receiving coil that receives nuclear magnetic resonance signals emitted from the subject. In the magnetic resonance imaging apparatus, the gradient magnetic field coil is arranged such that the coil wire is inserted into grooves cut in a gradient magnetic field generation pattern on the surface of the base member made of a non-magnetic and electrically insulating material. Embed it so that it almost fills the cross-sectional area, and
The groove in which the coil wire is embedded is filled with a damping material.

[0013]

[Operation] The magnetic resonance imaging apparatus configured as described above has grooves cut in a gradient magnetic field generation pattern on the surface of the base member made of a non-magnetic and electrically insulating material.
A coil wire is embedded in the cross-sectional area of the groove so that it almost fills the cross-sectional area, and the groove in which the coil wire is embedded is filled with a damping material. It operates to provide a gradient magnetic field. This is equivalent to increasing the diameter of the wire by embedding the coil wire almost completely in the cross-sectional area of the groove, so even if a large current is passed through the coil wire, heat generation from the gradient magnetic field coil is reduced. be able to. In addition, by filling the groove in which the coil wire is embedded with a damping material, even if the coil wire tries to vibrate due to the supply of pulse current, the vibration is suppressed, and the vibration is suppressed by striking the inner wall surface of the groove. The noise of the gradient magnetic field coil can be reduced.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a partially enlarged sectional view showing an embodiment of gradient magnetic field coils 4a, 4b in a magnetic resonance imaging apparatus of the present invention. First, the gradient magnetic field coil 4a
, 4b is applied to the magnetic resonance imaging apparatus shown in FIG.
The configuration is similar to the conventional example shown in FIG. This magnetic resonance imaging apparatus uses a permanent magnet as a static magnetic field generating means and utilizes the NMR phenomenon to obtain a tomographic image of an examination area of a subject. In FIGS. 2 and 3, a pair of permanent magnets 1a and 1b are , are arranged vertically to face each other, forming a gap A between which the subject can enter. These permanent magnets 1a and 1b are for generating a static magnetic field within the air gap A, and are formed, for example, in the shape of a disk, and are supported by upper and lower yokes 2a and 2b, respectively. These yokes 2a, 2b have the permanent magnets 1a, 1b and magnetic pole pieces 3a, 3b (described later) facing each other at a predetermined interval and form a magnetic path.For example, the depth is larger than the width. It is formed into a short rectangle. The upper and lower yokes 2a, 2b are supported by a plurality of vertical yokes 2c, 2c, . . . . These vertical yokes 2c are for arranging the upper and lower yokes 2a and 2b facing each other at a predetermined interval and closing the magnetic path formed by the permanent magnets 1a and 1b, and are members that allow magnetic flux to easily pass through the inside. For example, a total of four yokes are installed, one at each of the four corners of the upper and lower yokes 2a and 2b, each forming a return circuit for magnetic flux passing through the measurement space set within the gap A.

Magnetic pole pieces 3a and 3b are magnetically and mechanically fixed to opposing surfaces of the pair of permanent magnets 1a and 1b on the air gap A side, respectively. These magnetic pole pieces 3a and 3b are set in a predetermined area within the air gap A to improve the uniformity of the static magnetic field in the measurement space in which the test part of the subject enters, and are formed approximately in the shape of a disk. The peripheral edge is provided with an annular projection. A static magnetic field generating magnetic circuit generates a uniform static magnetic field in the measurement space into which the subject is inserted by the pair of permanent magnets 1a, 1b, yokes 2a, 2b, 2c, and magnetic pole pieces 3a, 3b. It consists of

As shown in FIG. 3, gradient magnetic field coils 4a, 4 are provided on the inner sides of the magnetic pole pieces 3a, 3b facing the air gap A side.
b are arranged close to each other. These gradient magnetic field coils 4a and 4b generate a gradient magnetic field that is added to the uniform static magnetic field produced by the magnetic pole pieces 3a and 3b, and by adding this gradient magnetic field, the position is made to correspond to the magnitude of the magnetic field, and the position is It is designed to generate a corresponding resonant frequency. And, these gradient magnetic field coils 4a, 4b are connected to the magnetic pole pieces 3a,
It is constructed by arranging three types of coils in the X direction, Y direction, and Z direction on the front and back surfaces of a circular plate that can fit inside the annular projection 3b.

Further, an irradiation coil 5 is provided inside the gradient magnetic field coils 4a, 4b. The irradiation coil 5 applies electromagnetic waves to cause nuclear magnetic resonance in the subject located within the gap A.
It is formed into a cylindrical shape surrounding the periphery. A receiving coil 6 is arranged inside this irradiation coil 5. The receiving coil 6 receives nuclear magnetic resonance signals emitted from the subject, and is formed to surround the subject located in the gap A.

A temperature adjusting means 7 is provided around the static magnetic field generating magnetic circuit. This temperature adjustment means 7 is for keeping the temperature of the static magnetic field generating magnetic circuit constant, and is made of, for example, styrofoam or sponge, which covers the entire permanent magnets 1a, 1b, yokes 2a, 2b, 2c, and magnetic pole pieces 3a, 3b. The heat insulating material 8 consists of a heat insulating material 8, and a planar heater 9 fixed to the inside of an aluminum plate 10 attached to the inner surface of the heat insulating material 8. Note that the heat insulating material 8 is shaped so that the center thereof is open so that the subject can enter the gap A. In addition, the entire static magnetic field generating magnetic circuit described above is
As shown in FIG. 2, it is covered with a gantry cover 11a for the front surface, a gantry cover 11b for the rear surface, a gantry cover 11c for the side surface, and a gantry cover 11d for the top surface.

Here, the gradient magnetic field coils 4a and 4b, which is a feature of the present invention, have an X on one side on the air gap A side, as shown in FIG. A direction gradient magnetic field coil 12 is formed, a Y direction gradient magnetic field coil 13 is formed on one side on the opposite side, and a Z direction gradient magnetic field coil 14 is further formed on the back side of this Y direction gradient magnetic field coil 13. . In this case, the above Z
The directional gradient magnetic field coil 14 is, for example, a Helmholtz coil made of a formal copper wire wound in a circle, but the X-direction and Y-direction gradient magnetic field coils 12 and 13 have complicated shapes.

That is, as shown in FIGS. 5 and 1, a gradient magnetic field generation pattern in the (See the solid line 12 in FIG. 5).The insulating plate 16 has a groove 17a cut therein, and a groove 17a formed on the opposite side of the insulating plate 16 has a shape rotated by 90 degrees with respect to the gradient magnetic field generation pattern in the X direction. Another groove 17 cut to form a gradient magnetic field generation pattern in the Y direction (see broken line 13 in FIG. 5)
It has b.

In this state, as shown in FIG. 1, a coil wire 18a made of, for example, copper strands is inserted into the groove 17a cut in the X-direction gradient magnetic field generation pattern. As shown in FIG. 5, one end of this coil wire 18a is used as an input end 20, and the other end is used as an output end 21, forming one current path. A gradient magnetic field coil 12 is configured. Here, in order to embed the coil wire 18a so that the cross-sectional area of the groove 17a is almost completely filled, for example, a large number of annealed copper wires are twisted together to form a coil wire 18a having a large cross-sectional area, and this coil wire 18a is inserted into the groove 17a. 17a in a compressed manner, or make a coil wire 18a from annealed copper wire with a small cross-sectional area, and push a number of coil wires 18a into the groove 17a in a stacked manner so that the groove 17a is filled with the coil wire 18a. Just embed it. In addition, a coil wire 18b formed in the same manner as described above is embedded in the groove 17b cut in a gradient magnetic field generation pattern in the Y direction so as to fill the cross-sectional area of the groove 17b. Similarly, one current path is formed, and as shown by the broken line in FIG.
A directional gradient magnetic field coil 13 is configured. In this case, it is equivalent to increasing the wire diameter of each of the coil wires 18a, 18b, the resistance value of the coil wires 18a, 18b becomes smaller, and the gradient magnetic field coils 4a, 4b when a current is supplied.
It is possible to reduce the heat generated from the

Furthermore, as described above, each coil wire 18a
, 18b are filled with damping materials 22a, 22b so as to close the openings of the grooves 17a, 17b. This braking material 22
a, 22b are made of silicon, for example, and the coil wire 18 is filled with melted silicon into each of the grooves 17a, 17b.
The grooves 17a, 17 with the grooves a, 18b embedded
By filling and solidifying the coil wire material 1 in b.
8a, 18b are fixed in the respective grooves 17a, 17b. In this case, due to the presence of the damping materials 22a and 22b, even if the coil wires 18a and 18b try to vibrate due to the supply of pulse current, the vibration is suppressed, and the noise generated from the gradient magnetic field coils 4a and 4b can be reduced. . Sound absorbing members 19a and 19b are attached to both surfaces of the insulating plate 16 having the X-direction and Y-direction gradient magnetic field coils 12 and 13 formed as described above, respectively. 13 is the groove 17a,
It prevents the coil wire material 1 from falling off from the coil wire material 17b.
It is designed to absorb noise generated by vibrations of 8a and 18b.

In the above explanation, permanent magnets 1a and 1b are used as the static magnetic field generating means, but the present invention is not limited to this. Instead of the permanent magnets 1a and 1b, an iron core An electromagnet formed by winding an excitation coil multiple times around the magnet may also be used.

[0024]

[Effects of the Invention] Since the present invention is configured as described above,
Base member (16) made of non-magnetic and electrically insulating material
) Groove 1 cut in a gradient magnetic field generation pattern on the surface of
The coil wire rods 18a, 18b are inserted into the grooves 17a, 17b.
A gradient magnetic field coil 4a is embedded so as to fill almost the entire cross-sectional area of the coil wires 18a and 17b, and the grooves 17a and 17b in which the coil wires 18a and 18b are embedded are filled with damping materials 22a and 22b. , 4b, it is possible to apply a gradient magnetic field to the subject to be examined. Since this is equivalent to increasing the wire diameter by embedding the coil wires 18a and 18b so as to fill the cross-sectional area of the grooves 17a and 17b almost completely, even when a large current is passed through the coil wires 18a and 18b, Heat generation from the gradient magnetic field coils 4a and 4b can be reduced. In addition, the coil wire 18a
, 18b are filled with damping materials 22a, 22b, so that even if the coil wires 18a, 18b try to vibrate due to the supply of pulse current, the vibration is suppressed, and the grooves 17a, 17b are filled with damping materials 22a, 22b. Gradient magnetic field coils 4a, 4 generated by hitting the inner wall surface of
b. Noise can be reduced.

In this way, since the heat generation from the gradient magnetic field coils 4a and 4b is reduced, the temperature of the static magnetic field generating magnetic circuit is stabilized, and the uniformity of the static magnetic field strength is improved, so that the NMR signal is improved. Discrepancies in position detection, image distortion, blur, etc. can be removed. Furthermore, since the noise generated from the gradient magnetic field coils 4a and 4b is reduced,
It is possible to eliminate discomfort and anxiety for the subject located in the measurement space set within the gap A.

[Brief explanation of the drawing]

FIG. 1 is a partially enlarged sectional view showing an embodiment of a gradient magnetic field coil in a magnetic resonance imaging apparatus of the present invention;

FIG. 2 is an exploded perspective view showing a magnetic resonance imaging apparatus according to the present invention and a conventional example;

[FIG. 3] A central vertical cross-sectional view of the magnetic resonance imaging apparatus,

[Figure 4] Enlarged cross-sectional view of main parts showing the installation state of the gradient magnetic field coil,

[Fig. 5] A plan view showing a gradient magnetic field coil in the present invention and a conventional example,

FIG. 6 is a partially enlarged sectional view showing a gradient magnetic field coil in a conventional example.

[Explanation of symbols]

1a, 1b...Permanent magnet, 3a, 3b...Magnetic pole piece,
4a, 4b... Gradient magnetic field coil, 5... Irradiation coil,
6... Receiving coil, 16... Insulating plate, 17a, 1
7b...Groove, 18a, 18b...Coil wire, 22
a, 22b...braking material, A...void.

Claims (1)

[Claims] Claim 1: A pair of static magnetic field generating means arranged opposite to each other forming a gap into which a subject can enter, and fixed to opposing surfaces of the static magnetic field generating means on the side of the gap to generate a uniform magnetic field. a static magnetic field generating magnetic circuit having a magnetic pole piece; a gradient magnetic field coil disposed close to the inside of the magnetic pole piece to generate a gradient magnetic field to be added to the uniform magnetic field by the magnetic pole piece; In a magnetic resonance imaging apparatus comprising an irradiation coil that applies electromagnetic waves to a subject, and a receiving coil that receives nuclear magnetic resonance signals emitted from the subject, the gradient magnetic field coil is non-magnetic and electrically insulated. A coil wire is embedded in a groove cut in a gradient magnetic field generation pattern on the surface of a base member made of a magnetic material so that the cross-sectional area of the groove is almost completely filled, and the groove in which the coil wire is embedded is A magnetic resonance imaging device characterized in that the inside is filled with a damping material.