JP2006141613A - Magnet system and magnetic resonance image diagnostic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the vibration of a gradient magnetic coil and to improve the quality of an MR image in a magnetic system for a magnetic resonance image diagnostic apparatus. <P>SOLUTION: The magnet system comprises a superconductive magnet with a pair of superconductive coil groups for generating uniform static magnetic fields, a pair of vacuum containers for storing the pair of superconductive coil groups respectively and a vacuum container connection member for connecting the pair of vacuum containers, and a pair of gradient magnetic field coils for generating gradient magnetic fields with a gradient in the uniform static magnetic field region. The pair of gradient magnetic field coils are connected to each other by a gradient magnetic field coil connection member, and the gradient magnetic field coil connection member and one vacuum container of the superconductive magnet are connected to each other by a support member. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention belongs to the technical field of a magnetic resonance imaging diagnosis apparatus (MRI apparatus), and relates to a superconducting electromagnet that generates a uniform static magnetic field and a magnet apparatus having a gradient magnetic field coil that generates a gradient magnetic field.

  An MRI apparatus is an image diagnostic apparatus that applies a magnetic resonance phenomenon of a nucleus of a substance, and images a component or structure in the body of a subject placed in a uniform static magnetic field generated by a superconducting electromagnet or the like. Is.

  The MRI apparatus includes a superconducting electromagnet that generates a uniform static magnetic field region and a pair that generates a gradient magnetic field having gradients in three directions X, Y, and Z (the uniform static magnetic field direction is the Z direction) in the uniform static magnetic field region. A high-frequency coil and a high-frequency magnetic field generator for receiving a nuclear magnetic resonance signal from the subject by irradiating a subject placed in a uniform static magnetic field region with a high-frequency radio wave, And a computer that digitizes the nuclear magnetic resonance signal received by the high-frequency coil and performs image processing.

  In the first conventional MRI apparatus (see, for example, Patent Document 1), the vacuum vessel that accommodates the superconducting coil is annular, and the gradient magnetic field coil is disposed in the central space of the vacuum vessel to provide the gradient coil support. Via an iron yoke.

  In the second conventional MRI apparatus (see, for example, Patent Document 2), the vacuum vessel that accommodates the superconducting coil is annular, and the gradient magnetic field coil is disposed in the central space of the vacuum vessel so as to have a cylindrical inclination. It is being fixed to the flat gradient magnetic field coil support body via the magnetic field coil support body. The flat gradient coil support is connected to the fixed column so as not to contact the vacuum vessel.

Japanese Patent Laid-Open No. 2002-17705 (FIG. 2) JP 2002-52004 A (FIGS. 1 and 6)

  When the gradient magnetic field is generated, a pulse current of several hundred amperes flows through the gradient magnetic field coil. At this time, an electromagnetic force close to several hundred kgf to 1000 kgf is applied between the upper and lower gradient magnetic field coils in the vertical and horizontal directions. Therefore, the gradient magnetic field coil vibrates violently.

  In the conventional technique, since the upper and lower gradient coils are supported on separate supports, if the vibration forms of the upper and lower gradient coils are greatly different, the symmetry of vibration may not be ensured. In this case, the vibration of the gradient magnetic field coil is transmitted to the superconducting coil, and the magnetic field strength of the uniform static magnetic field fluctuates by several ppm.

  The present invention has been made to solve the above problems, and aims to reduce the vibration of the gradient coil and to improve the image quality of the magnetic resonance image.

  A magnet apparatus according to the present invention includes a pair of superconducting coils that generate a uniform static magnetic field, a pair of vacuum containers that respectively accommodate the pair of superconducting coils, and a vacuum container connecting member that connects the pair of vacuum containers. A pair of gradient magnetic field coils that generate a gradient magnetic field having a gradient in a uniform static magnetic field region, a gradient magnetic field coil coupling member that couples the pair of gradient magnetic field coils, a gradient magnetic field coil coupling member, and the superconducting electromagnet And a support member for connecting one of the vacuum containers.

  The magnet device according to the present invention includes a pair of superconducting coil groups that generate a uniform static magnetic field, a pair of vacuum containers that respectively accommodate the pair of superconducting coil groups, and a vacuum container connecting member that connects the pair of vacuum containers. A superconducting electromagnet, a pair of gradient coils that generate a gradient magnetic field having a gradient in a uniform static magnetic field region, a gradient coil coupling member that couples the pair of gradient coils, the gradient coil coupling member, and the superconductivity And a support member that connects the vacuum vessel connecting member of the electromagnet.

  According to the present invention, since the pair of gradient magnetic field coils are connected and integrated, the electromagnetic force acting between the gradient magnetic field coils is canceled out. Therefore, since the vibration of the gradient coil is reduced, the vibration transmitted to the superconducting coil is also reduced. As a result, the magnetic field intensity fluctuation of the uniform static magnetic field generated by the superconducting coil is suppressed, and the image quality of the magnetic resonance image is improved.

Embodiment 1 FIG.
FIG. 1 is a schematic configuration diagram for explaining Embodiment 1 in an MRI apparatus to which the present invention is applied. As shown in FIG. 1, the MRI apparatus generates a magnetic field having a gradient in a uniform static magnetic field region, a bed 110 for placing the subject, a superconducting electromagnet 100 that generates a uniform static magnetic field applied to the subject, and the like. The gradient magnetic field coils 8a and 8b and the gradient magnetic field power source 120, the high frequency coils 130a and 130b and the high frequency magnetic field generator 140 for transmitting a high frequency magnetic field to the subject and receiving a nuclear magnetic resonance signal from the subject, A computer 150 that can perform image processing from a nuclear magnetic resonance signal and a display device 160 that displays an image signal processed by the computer 150 as a tomographic image are provided.

  FIG. 2 is a partial cross-sectional view of the magnet device according to this embodiment. The left side is a cross section. The magnet device has a superconducting electromagnet 100 and a pair of gradient coils 8a and 8b. Here, the magnet device is fixed to the foundation base 10 by the anchor 13.

  First, the superconducting electromagnet 100 will be described. A superconducting coil group made up of a plurality of superconducting coils 1a arranged on the upper side of the figure and a superconducting coil group made up of a plurality of superconducting coils 1b arranged on the lower side of the figure are paired, and about 0.7 to 1 Tesla Generate a uniform static magnetic field. In particular, in the uniform static magnetic field region 2, a static magnetic field uniformity of about several ppm is required. Imaging by the MRI apparatus is performed by arranging a part of the subject to be imaged in the uniform static magnetic field region 2.

  The upper superconducting coil group is housed in the upper helium container 3a, and the lower superconducting coil group is housed in the lower helium container 3b. Liquid helium as a refrigerant stored in the helium containers 3a and 3b cools the superconducting coils 1a and 1b to 4.2 K which is an extremely low temperature at which the superconducting coils 1a and 1b are brought into a superconducting state.

  Further, for vacuum insulation, the upper helium container 3a is accommodated in the upper vacuum container 4a, and the lower helium container 3b is accommodated in the lower vacuum container 4b. The vacuum vessels 4a and 4b have an annular shape facing each other. The upper heat shield 5a is disposed between the helium vessel 3a and the vacuum vessel 4a and shields radiant heat from the vacuum vessel 4a to the helium vessel 3a. Similarly, the lower heat shield 5b is disposed between the helium vessel 3b and the vacuum vessel 4b and shields radiant heat from the vacuum vessel 4b to the helium vessel 3b. The heat shields 5a and 5b are made of a material such as aluminum having good thermal conductivity. Moreover, although not shown in figure, the multilayer heat insulating material which laminated | stacked the aluminum vapor deposition film and the net | network about 20-40 layers alternately is arrange | positioned between the vacuum vessel 4a and the heat shield 5a, and between the vacuum vessel 4b and the heat shield 5b. Has been. As a result, the amount of heat entering the ultra-low temperature helium containers 3a and 3b from the vacuum containers 4a and 4b can be reduced.

  The pair of helium containers 3a and 3b are connected by a helium container connecting member 6a. The helium vessel connecting member 6a supports the electromagnetic force acting between the helium vessels 3a and 3b, and has a superconducting wire (not shown) connecting the upper and lower superconducting coil groups therein. The pair of heat shields 5a and 5b are connected by a heat shield connecting member 6b. The heat shield connecting member 6b transfers the heat that has entered the heat shield 5b to the heat shield 5a by connecting the upper and lower heat shields 5a and 5b. The pair of vacuum vessels 4a and 4b are connected by a vacuum vessel connecting member 6c. The vacuum container connecting member 6c is evacuated to insulate the helium containers 3a and 3b from vacuum, and supports the weight of the vacuum container 4a and the electromagnetic force acting between the vacuum containers 4a and 4b. In addition, although helium container connecting member 6a, heat shield connecting member 6b, and vacuum container connecting member 6c are illustrated as two cases in total in the drawing, the number and arrangement position thereof can be appropriately selected.

  The heat shields 5a and 5b and the helium containers 3a and 3b are cooled by a combination of the refrigerator 7 and a compressor (not shown). In addition, although the case where the heat shields 5a and 5b are single was shown, it is not limited to this. Normally, the heat shields 5a and 5b are arranged in a double, and the heat shield on the vacuum vessel side is cooled to about 70K and the heat shield on the helium vessel side is cooled to about 20K by the shield refrigerator 7. Is reduced to about 0.1 liter / hour or less. Further, by installing the refrigerator 7 that can cool the helium containers 3a and 3b to 4.2K or less, the liquid helium consumption can be reduced to approximately 0 liter / hour.

  Next, the pair of gradient magnetic field coils 8a and 8b will be described. The gradient magnetic field coil 8a is disposed in the recess on the opposing surface of the vacuum vessel 4a, and the gradient magnetic field coil 8b is disposed in the recess on the opposing surface of the vacuum vessel 4b with the uniform static magnetic field region 2 interposed therebetween. The gradient magnetic field coils 8 a and 8 b generate gradient magnetic fields having gradients in three directions of X, Y, and Z with respect to the uniform static magnetic field region 2.

  The gradient coil connecting member 9a is made of a high-strength nonmagnetic material such as stainless steel having a length of about 500 mm, and connects the gradient coils 8a and 8b so as to be mechanically integrated. . Further, the support member 11 a connects the gradient coil connecting member 9 a and the vacuum container 4 b below the superconducting electromagnet 100. Thereby, the gradient magnetic field coils 8a and 8b are fixed to the vacuum vessel 4b via the gradient magnetic field coil connecting member 9a and the support member 11a. In addition, although the gradient magnetic field coil coupling member 9a and the support member 11a are illustrated as being two in total in the drawing, the number and arrangement position thereof can be appropriately selected.

  Next, the operation will be described. The gradient coils 8a and 8b generate a gradient magnetic field having a pulsed gradient of about 20 millitesla / m in the three directions X, Y, and Z with respect to the uniform static magnetic field region 2. For example, in the case of a gradient magnetic field in the Z direction, which is a uniform static magnetic field direction, the gradient magnetic field coil shape is a disk shape having a surface perpendicular to the Z direction, so that the gradient magnetic field coils 8a and 8b repel each other. Force or suction force is generated. Since the electromagnetic force becomes several hundred kgf to 1000 kgf, the gradient coils 8a and 8b vibrate vigorously.

  In this embodiment, the oscillating gradient coils 8a and 8b are connected and integrated by a pair of left and right gradient coil connecting members 9a, so that the opposite electromagnetic force acting between the gradient coils 8a and 8b is generated. Be countered. Therefore, the vibrations of the gradient magnetic field coils 8a and 8b are reduced, and the vibrations transmitted to the superconducting coils 1a and 1b are also reduced. As a result, the magnetic field intensity fluctuation of the uniform static magnetic field generated by the superconducting coils 1a and 1b is suppressed, and the image quality of the magnetic resonance image is improved.

Embodiment 2. FIG.
FIG. 3 is a partial cross-sectional view of the magnet device for explaining the second embodiment. In this embodiment, the configuration of the gradient coil connecting member in the first embodiment is changed. The changed part will be described.

  The gradient coil connecting member 9b includes a pair of beam-like portions 12a and 12b and a columnar portion 12c. The upper beam-like portion 12a is composed of a contact area that contacts the inside of the outer diameter of the gradient magnetic field coil 8a and a non-contact area that protrudes outside of the outer diameter of the gradient magnetic field coil 8a. Similarly, the lower beam-like portion 12b includes a contact area that contacts the inside of the outer diameter of the gradient magnetic field coil 8b and a non-contact area that protrudes outside of the outer diameter of the gradient magnetic field coil 8b. The columnar part 12c connects the non-contact areas of the pair of beam-like parts 12a and 12b.

  By using such a gradient coil connecting member 9b, the columnar portion 12c is disposed outside the outer diameter of the gradient coils 8a and 8b. That is, since the columnar part 12c can be moved away from the uniform static magnetic field region 2, the space for the subject to enter becomes wider in the horizontal direction in the figure, and the openness is improved.

  Further, as the columnar portion 12 c moves away from the uniform static magnetic field region 2, the support member 11 b that connects the gradient coil connecting member 9 b and the vacuum vessel 4 b also moves away from the uniform static magnetic field region 2. In this embodiment, the support member 11b is connected to the outer edge portion of the facing surface of the vacuum vessel 4b. Since this outer edge is in the vicinity of the joint between the outer cylinder of the vacuum vessel 4b and the opposing surface, it is a highly rigid part. Thus, by fixing the support member 11b to the outer edge portion of the opposing surface of the highly rigid vacuum vessel 4b, the vibration of the gradient magnetic field coils 8a and 8b can be further reduced. As a result, the magnetic field intensity fluctuation of the uniform static magnetic field generated by the superconducting coils 1a and 1b is suppressed, and the image quality of the magnetic resonance image is improved.

Embodiment 3 FIG.
FIG. 4 is a partial cross-sectional view of the magnet device for explaining the third embodiment. In this embodiment, the shape of the support member in the second embodiment is changed. The changed part will be described.

  The support member 11c is connected to the central portion of the columnar portion 12c of the gradient coil connecting member 9b, and has a vertically long shape as compared with the second embodiment. Here, the electromagnetic force acting between the gradient magnetic field coils 8a and 8b is generated symmetrically in all directions such as up and down, front and rear, and left and right with the uniform static magnetic field region 2 as the center. Therefore, the gradient magnetic field coils 8a and 8b vibrate symmetrically in all directions such as up and down, front and rear, and left and right with the uniform static magnetic field region 2 as the center, but are integrated by the gradient magnetic field coil coupling member 9b. Counteract vibrations.

  In FIG. 4, the central portion of the columnar portion 12 c of the gradient coil connecting member 9 b is at the same height as the central portion of the uniform static magnetic field region 2. That is, the support member 11c is connected to the central portion of the gradient coil connecting member 9b that is a neutral point of vibration of the gradient coils 8a and 8b. Since the support member 11c is fixed at the neutral point of the vibration with the smallest vibration, the required rigidity may be low.

  Thus, since the support member 11c is connected to the neutral point of the vibration of the gradient magnetic field coils 8a and 8b, the electromagnetic force in the opposite direction that acts between the gradient magnetic field coils 8a and 8b even if the support member 11c has a low rigidity. Can be effectively counteracted. Therefore, vibrations of the gradient magnetic field coils 8a and 8b can be effectively reduced. As a result, the magnetic field intensity fluctuation of the uniform static magnetic field generated by the superconducting coils 1a and 1b is suppressed, and the image quality of the magnetic resonance image is improved.

  In addition, a buffer material 13a is provided between the support member 11c and the vacuum vessel 4c. Since the buffer material 13a absorbs the vibration of the gradient magnetic field coils 8a and 8b, the vibration transmitted to the vacuum vessel 4b can be reduced. Even if the buffer material 13a is provided between the support member 11c and the gradient coil connecting member 9b, the same effect can be obtained.

Embodiment 4 FIG.
FIG. 5 is a partial cross-sectional view of a magnet device for explaining the fourth embodiment. In this embodiment, the shape and connection destination of the support member in the second embodiment are changed. The changed part will be described.

  The support member 11d connects the gradient magnetic field coil coupling member 9b and the vacuum vessel coupling member 6c. In this embodiment, the support member 11d can be shortened to such an extent that the shortest distance between the gradient coil connecting member 9b and the vacuum vessel connecting member 6c can be connected. Here, since the rigidity of the support member 11d is inversely proportional to the cube of the length, shortening the support member 11d increases the rigidity and is advantageous for reducing vibration. Thus, the vibration of the gradient magnetic field coils 8a and 8b can be further reduced by increasing the rigidity of the support member 11d. As a result, the magnetic field intensity fluctuation of the uniform static magnetic field generated by the superconducting coils 1a and 1b is suppressed, and the image quality of the magnetic resonance image is improved.

  Further, a buffer material 13b is provided between the support member 11d and the vacuum vessel connecting member 6c. Since the buffer material 13b absorbs the vibration of the gradient magnetic field coils 8a and 8b, the vibration transmitted to the vacuum vessel connecting member 6c can be reduced. Even if the buffer material 13b is provided between the support member 11d and the gradient coil connecting member 9b, the same effect can be obtained.

Embodiment 5. FIG.
FIG. 6 is a partial cross-sectional view of a magnet device for explaining the fifth embodiment. In this embodiment, a stainless steel ring is attached to the outer periphery of the gradient coil. Here, although it demonstrates as a modification of Embodiment 3, it cannot be overemphasized that it can apply also to other Embodiment. The changed part will be described.

  The upper stainless steel ring 14a is attached to the outer periphery of the upper gradient magnetic field coil 8a. Similarly, the lower stainless steel ring 14b is attached to the outer periphery of the lower gradient coil 8b. Stainless steel rings 14a and 14b are non-magnetic.

  By attaching such a stainless steel ring, the mass of the gradient magnetic field coils 8a and 8b is increased, and at the same time, the rigidity is improved. As a result, the gradient coils 8a and 8b are less likely to vibrate if the electromagnetic force acting between them is the same. Therefore, the vibration of the gradient magnetic field coils 8a and 8b can be further reduced. As a result, the magnetic field intensity fluctuation of the uniform static magnetic field generated by the superconducting coils 1a and 1b is suppressed, and the image quality of the magnetic resonance image is improved.

1 is a schematic configuration diagram of an MRI apparatus for explaining Embodiment 1. FIG. FIG. 3 is a partial cross-sectional view of a magnet device for explaining the first embodiment. FIG. 5 is a partial cross-sectional view of a magnet device for explaining a second embodiment. FIG. 6 is a partial cross-sectional view of a magnet device for explaining a third embodiment. FIG. 10 is a partial cross-sectional view of a magnet device for explaining a fourth embodiment. FIG. 10 is a partial cross-sectional view of a magnet device for explaining a fifth embodiment.

Explanation of symbols

1a, 1b Superconducting coil, 4a, 4b Vacuum container, 6c Vacuum container connecting member, 8a, 8b Gradient magnetic field coil, 9a, 9b Gradient magnetic field coil connecting member, 11a-11d Support member, 12a, 12b Beam-shaped part, 12c Columnar part , 13a, 13b Buffer material, 14a, 14b Stainless steel ring, 100 superconducting electromagnet, 120 gradient magnetic field power source, 130a, 130b high frequency coil, 140 high frequency magnetic field generator, 150 computer, 160 display device.

Claims (9)

  A superconducting electromagnet having a pair of superconducting coils that generate a uniform static magnetic field, a pair of vacuum containers that respectively accommodate the pair of superconducting coils, and a vacuum container connecting member that connects the pair of vacuum containers; and a uniform static magnetic field region Connecting a pair of gradient magnetic field coils that generate a gradient magnetic field having a gradient, a gradient coil coupling member that couples the pair of gradient coil, and one vacuum vessel of the gradient coil coupling member and one of the superconducting magnets A magnet device comprising a supporting member.   The gradient coil connecting member includes a pair of beam-shaped portions each formed of a contact region that contacts the pair of gradient magnetic field coils and a non-contact region that protrudes outside an outer diameter of the pair of gradient coil. The magnet device according to claim 1, further comprising: a columnar portion that connects non-contact regions of the beam-shaped portion.   3. The magnet device according to claim 1, wherein the pair of vacuum containers are in an annular shape facing each other, and the support member is connected to an outer edge portion of an opposing surface of the one vacuum container.   The magnet device according to claim 1, wherein the support member is connected to a central portion of the gradient coil connecting member.   The magnet device according to any one of claims 1 to 4, further comprising a buffer material interposed between the support member and the one vacuum vessel or between the support member and the gradient coil connecting member.   A superconducting electromagnet having a pair of superconducting coils that generate a uniform static magnetic field, a pair of vacuum containers that respectively accommodate the pair of superconducting coils, and a vacuum container connecting member that connects the pair of vacuum containers; and a uniform static magnetic field region A pair of gradient magnetic field coils that generate a gradient magnetic field having a gradient, a gradient magnetic field coil coupling member that couples the pair of gradient magnetic field coils, the gradient magnetic field coil coupling member, and the vacuum vessel coupling member of the superconducting electromagnet. A magnet device comprising a supporting member to be connected.   The magnet apparatus according to claim 6, further comprising a buffer material interposed between the support member and the vacuum vessel connecting member or between the support member and the gradient coil connecting member.   The magnet device according to claim 1, wherein the pair of gradient coils includes a stainless steel ring attached to each outer periphery. A superconducting electromagnet that generates a uniform static magnetic field to be given to a subject, a magnet apparatus including a gradient magnetic field coil that generates a gradient magnetic field having a gradient in the uniform static magnetic field region, a gradient magnetic field power source connected to the gradient magnetic field coil, A high-frequency coil and a high-frequency magnetic field generator for transmitting a high-frequency magnetic field to the subject and receiving a nuclear magnetic resonance signal from the subject; a calculator capable of performing image processing from the nuclear magnetic resonance signal; In a magnetic resonance diagnostic imaging apparatus comprising a display device that displays an image signal image-processed by the computer as a tomographic image,
The said magnet apparatus is a magnetic resonance diagnostic imaging apparatus which is a magnet apparatus described in any one of Claims 1-8.

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