JP2002238874A - Magnet device and magnetic resonance imaging apparatus using the same, and adjuster of magnetic field uniformity coefficient, and method of adjusting the magnetic field uniformity coefficient - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnet device, a magnetic resonance imaging apparatus, an adjuster of the magnetic field uniformity coefficient, and a method of adjusting the uniformity coefficient for optimizing the adjusting sensitivity in adjusting the magnetic field uniformity coefficient, adjusting irregular magnetic components in lower orders without detaching/attaching a gradient magnetic coil, improving the work efficiency, and easily performing the work in the fine adjustment of the magnetic field uniformity coefficient in the space for measurement. SOLUTION: The magnet device comprises a pair of magnetic poles facing each other with the space for measurement in-between, superconducting coils disposed around the outer periphery of each magnetic pole, and containers for storing each superconducting coil. In the magnet device, the adjuster of the magnetic field uniformity coefficient including a plurality of magnetic pieces is disposed adjacent to the containers. The adjuster of the magnetic field uniformity coefficient is shaped in a ring consisting of the plurality of magnetic pieces disposed on the same circle or concentric circles relative to the center axis of the magnetic field. The magnetic resonance imaging apparatus has the adjuster of the magnetic field uniformity coefficient, and the magnetic field uniformity coefficient in the space for measurement is adjusted by adjusting the magnetic pieces as the adjuster of the magnetic field uniformity coefficient.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel magnet device,
The present invention relates to a magnetic resonance imaging apparatus using the same, a magnetic field uniformity adjusting body thereof, and a method of adjusting the uniformity thereof, and more particularly to a magnetic field uniformity adjustment of an open magnet having a wide opening.

[0002]

2. Description of the Related Art Magnetic resonance imaging (hereinafter, referred to as MRI)
The apparatus) obtains an image representing the physical properties of the test object by utilizing a nuclear magnetic resonance phenomenon that occurs when the test object placed in a uniform static magnetic field space is irradiated with electromagnetic waves, and is used particularly for medical purposes.

[0003] The open type MRI apparatus which is the object of the present invention is:
Since the pair of magnetic poles are arranged facing each other across the uniform magnetic field region, the feeling of obstruction received by the subject is small, and the inspector has easy access to the subject.
It is the mainstream of MRI equipment. In addition, with the advancement of medical technology, higher resolution and higher functionality of the captured images are required, and in particular, the magnetic assembly applied to the measurement There is a demand for improved uniformity.

[0004] In order for these MRI apparatuses to maintain the magnetic field uniformity required for medical use, a process called shimming, which is means for correcting the non-uniformity of the magnetic field, is required. The method includes coarse adjustment of the magnetic field uniformity performed after assembly, fine adjustment performed after being carried into a medical facility, and the like. In the latter process, even if the initial setting of the uniform magnetic field is completely completed in the factory, the uniformity varies slightly depending on the installation space conditions in the medical facility. Manual work such as placement at a position is essential.

FIG. 5 shows the structure of a conventional example of an open type MRI apparatus. The main components of the device are: magnetic poles (1a, 1b) for applying a uniform magnetic field to the measurement space, superconducting coils (2a, 2b) as a magnetomotive force source, containers (3a, 3b) for storing the superconducting coils,
Gradient magnetic field coils (4a, 4b) for applying a gradient magnetic field to give positional information on resonance phenomena, RF for irradiating and receiving electromagnetic waves
There are a coil system (5a, 5b), a uniformity adjusting unit (6a, 6b) for adjusting the magnetic field uniformity in the measurement space, and the like, which are arranged to face each other across the measurement space.

As a known technique for adjusting the magnetic field uniformity of an open type MRI apparatus, a method of providing a plurality of adjustable radial segments called a magnetic flux field adjustment control device on a magnetic pole projection (Japanese Patent Laid-Open No. 5-251231). A method of raising and lowering a ring on the outer periphery of a magnetic pole (Japanese Patent Application Laid-Open No. 63-165743), a method of arranging a magnetic substance or a small piece of permanent magnet on a surface facing a magnetic pole (Japanese Patent Application Laid-Open Nos. 3-131234, 8-172010, 9) -313458), and a method of moving a magnetic piece disposed on the magnetic pole opposing surface in parallel with the direction of magnetic flux (Japanese Patent Laid-Open No. 7-171131).

A magnetic device using a permanent magnet is disclosed in both the magnetic field generator of JP-A-2-117106 and the magnetic field generator for MRI of JP-A-10-146326.

[0008]

However, these uniformity adjusting means change the shape and arrangement of the magnetic poles on the opposing surface close to the measurement space, or change the arrangement of the magnetic pieces in a region adjacent to the opposing surface. Therefore, the sensitivity to the change in the magnetic field uniformity is extremely high and can be applied to the coarse adjustment, but is not always suitable as the fine adjustment.

In these means, since the magnetic field uniformity adjusting body is arranged inside the magnetic pole, the magnetic field constituting the magnetic field uniformity adjusting body is removed by removing the gradient magnetic field coil and the like every time fine adjustment of the uniformity is performed. The arrangement of the pieces has to be changed, which complicates the work and consumes a considerable amount of work time. In addition, in the case of a magnet assembly using a superconducting coil as a magnetomotive force source, the electromagnetic force acting on the plate-shaped magnetic field uniformity adjuster is extremely large, so that when the magnet assembly is removed, the superconducting coil in the excited state is demagnetized. Therefore, there is also a problem that the loss of liquid helium as a refrigerant is large due to AC loss, which is an electromagnetic phenomenon of the coil body during excitation and demagnetization of the superconducting coil.

In these means, since the magnetic shim is arranged in the area adjacent to the gradient coil, the temperature change caused by the pulse operation of the gradient coil causes the magnetization of the magnetic material constituting the magnetic field uniformity adjusting body. The characteristics were changed, and as a result, the uniformity of the magnetic field during imaging was adversely affected.
This is the case of passive uniformity adjustment using a magnetic piece.
This is because the temperature dependence of the magnetization characteristics of the magnetic material is large.

As a method for fine adjustment of the magnetic field uniformity without removing the gradient magnetic field coil and the like, there is a method of raising and lowering the magnetic pole from the outside with a worm gear or the like (JP-A-8-69913). However, this method has a limit on the irregular magnetic field component that can be adjusted for uniformity by moving the entire magnetic pole up and down.

An object of the present invention is to optimize the adjustment sensitivity when finely adjusting the magnetic field uniformity, and to adjust the low-order irregular magnetic field without detaching the gradient coil in the fine adjustment of the magnetic field uniformity in the measurement space. Provided are a magnet device capable of adjusting components, improving the work efficiency thereof, and easily performing the work, a magnetic resonance imaging apparatus using the same, a magnetic field uniformity adjusting body thereof, and a method of adjusting the uniformity thereof. It is in.

[0013]

SUMMARY OF THE INVENTION The present invention comprises a pair of magnetic poles which are opposed to each other across a measurement space, a pair of superconducting coils, and a pair of containers for accommodating the superconducting coils.
In the magnet apparatus for an MRI apparatus, a magnetic field uniformity adjuster including a plurality of magnetic pieces is arranged in a region adjacent to the superconducting coil storage container. In this configuration, since the uniformity adjustment area is separated from the gradient magnetic field coil, the magnetic piece for magnetic field uniformity is less susceptible to the heat generated by the pulsed current supplied to the gradient magnetic field coil. Becomes stable. In addition, since the uniformity can be adjusted in a region away from the measurement space, fine adjustment of the irregular magnetic field component is possible. According to the present invention, the magnetic field uniformity adjuster is arranged in a region adjacent to the superconducting coil and has a divided structure.

In the present invention, it is preferable that the magnetic field uniformity adjuster has an annular shape arranged on the same circle or concentric circle with respect to the center axis of the magnetic field. The magnetic field uniformity adjuster is arranged concentrically with respect to the central axis of the magnetic field, and the asymmetric magnetic field component in the measurement space is displaced from the central axis of the magnetic field. The magnetic field component can be adjusted.

Further, according to the present invention, the magnetic field uniformity adjusting member is provided on the outer peripheral side with respect to the central axis of the magnetic field with respect to the space where the pair of magnetic poles are opposed, and on the surface opposite to the central axis of the magnetic field with the adjacent superconducting coil housing. It was arranged outside. In addition, this magnetic field uniformity adjuster is constituted by segments divided in the circumferential direction, and has a structure detachable to the outer peripheral side in the radial direction. With this configuration, even in the final step of fine-tuning the magnetic field, the divided segments can be exchanged without attaching and detaching the gradient magnetic field coil and the RF coil, so that the workability can be significantly improved. In addition, by appropriately reducing the volume of the segment to be divided, even when a static magnetic field is applied to the measurement space, the electromagnetic force acting on these segments can be reduced, so even when the superconducting coil is excited. , The segments can be attached and detached.

In the present invention, it is preferable that the magnetic field uniformity adjusting member is composed of a composite of a non-magnetic material and a magnetic material, and the magnetic material is a ferromagnetic material or a permanent magnet. With this configuration, it is possible to finely control the magnetic flux generated from the superconducting coil which is the magnetomotive force source. In addition, the magnetic field uniformity adjuster has a structure in which the magnetic flux passes through the magnetic field uniformity adjuster, which is composed of a composite of a nonmagnetic / electric insulator and a magnetic / electrical conductor piece, so that it can be used in a measurement space. Since a static magnetic field with extremely high magnetic field homogeneity can be applied, a captured image suitable for medical use as an MRI apparatus can be obtained.

More specifically, the present invention relates to a pair of magnetic poles which are arranged opposite to each other with a subject serving as a measurement space therebetween and provide a static magnetic field, and a superconducting coil arranged on the outer periphery of each of the magnetic poles; A storage container for storing each of the superconducting coils, a pair of gradient magnetic fields for forming a gradient magnetic field in the static magnetic field, a gradient power supply connected to the gradient magnetic field coil for applying a voltage, A probe that transmits to and receives a nuclear magnetic resonance signal from the subject, a high-frequency magnetic field generator that is connected to the probe and generates a high-frequency magnetic field, and that is connected to the high-frequency magnetic field generator and the gradient magnetic field power supply. A magnetic resonance imager having a computer for controlling a high-frequency magnetic field and a gradient magnetic field and controlling the acquisition of the nuclear magnetic resonance signal to perform image processing, and a bed for transporting the subject In the device, a magnetic field equal to an annular shape formed by a plurality of non-magnetic material pieces adjacent to the storage container, wherein a plurality of ferromagnetic material insertion cylindrical holes are regularly arranged in the non-magnetic material pieces. The adjusting body is disposed so as to be once detachable, and the above-mentioned cylindrical hole is preferably formed substantially parallel to the annular central axis.

Further, the present invention provides an annular shape formed by a plurality of non-magnetic material pieces, wherein the non-magnetic material pieces have a plurality of ferromagnetic material insertion straight formed straight with respect to the annular central axis. The cylindrical holes are regularly arranged, and the aforementioned cylindrical holes are preferably formed substantially parallel to the central axis of the ring, and the magnetic field uniformity adjustment for a nuclear magnetic resonance imaging apparatus is characterized in that: In the body.

The present invention also provides a pair of magnetic poles disposed opposite to each other with a subject serving as a measurement space therebetween, a pair of superconducting coils disposed on the outer periphery of each of the magnetic poles, and each of the superconducting coils. Magnetic resonance comprising: a storage container for storing the magnetic field; a pair of gradient magnetic field coils disposed on the measurement space side of the magnetic pole; and a pair of high-frequency magnetic field generation coils disposed on the measurement space side of the gradient magnetic field coil. In the magnetic field uniformity adjusting method of the imaging apparatus, the plurality of nonmagnetic material pieces are formed on the outer peripheral side of the magnetic pole while being adjacent to the storage container with the gradient magnetic field coil and the high frequency magnetic field generating coil mounted. A magnetic field uniformity adjuster in which a plurality of ferromagnetic material insertion cylindrical holes formed substantially in parallel to the center axis of the non-magnetic material piece are arranged in the non-magnetic material piece so as to be detachable. And location, and adjusting the magnetic field uniformity of the measurement space by adjusting the insertion of the ferromagnetic body in the said cylindrical bore.

By applying the present invention, the magnetic field center strength in the measurement space is 0.5 T or more, the magnetic field uniformity in 40 cm DSV is 20 ppm or less, and the gap between the opposing surfaces of the upper and lower magnetic poles is 700
An MRI apparatus having a diameter of not less than mm can be realized.

[0021]

(Embodiment 1) FIG. 1 is an overall structural view of a magnet assembly for MRI according to the present invention. In FIG. 1, a pair of magnetic poles 1a and 1b are vertically opposed to each other across a measurement space 8, and a pair of superconducting coils 2a and 2 as a magnetomotive force source.
b, and storage containers 3a and 3b for storing respective superconducting coils
Is arranged. These magnetic poles 1a, 1b and superconducting coils 2a, 2
b, the storage containers 3a and 3b are magnetically driven by base plates 10a and 10b and two yoke columns 7 made of a ferromagnetic material such as pure iron.
Mechanically coupled. Further, on the side facing the magnetic poles, gradient magnetic field coils 4a and 4b for applying a gradient magnetic field to the measurement space,
In this embodiment, the RF coils 5a and 5b for irradiating electromagnetic waves and the magnetic field uniformity adjusters 6a and 6b for adjusting the magnetic field uniformity in the measurement space are superconducting. The storage containers 3a and 3b for storing the coils 2a and 2b are detachably disposed adjacent to the opposite sides of the surfaces facing each other. A refrigerator or the like is connected to the storage containers 3a and 3b of the superconducting coil, and a structure for reducing evaporation of a low-temperature refrigerant such as liquid helium filled therein is taken, but not shown here. The superconducting coil storage containers 3a and 3b have the magnetic pole 1a,
It is preferable that it is provided at a position slightly away from the projecting surface on the opposite side of the ring 1b so as not to be seen from the measurement space 8.

The magnetic field uniformity adjusters 9a and 9b have the advantage that only the magnetic component to be adjusted can be adjusted by disposing them at the position of this embodiment. In this position, fine adjustment is possible, and a more uniform magnetic field can be formed.
It is preferable to be located at a position away from the center of the magnetic field and outside the annular portion of the magnetic pole. From the viewpoint of workability, the magnetic field can be adjusted without attaching and detaching the gradient magnetic field coils 4a and 4b and the RF coils 5a and 5b.

The material of the magnetic poles 1a and 1b is a ferromagnetic material. For example, a single material of pure iron or iron alloy or a composite thereof is used. In FIG. 1, the magnetic poles 1a and 1b are shown as cup-shaped integral structures. However, when viewed from the surfaces facing each other, the magnetic poles 1a and 1b are each divided into an outer side made of a disk-shaped ferromagnetic material and an inner side in contact with the outer side. The ring-shaped ferromagnetic material can be divided into three parts, that is, an annular ferromagnetic material that is in contact with the end of the outer disk-shaped ferromagnetic material and is in contact with the outer peripheral surface of the inner disk-shaped ferromagnetic material. The outer side has the same outer diameter as the outer diameter of the annular member, and the inner side has the same outer diameter as the inner diameter of the annular member. An annular ferromagnetic material is effective in forming a uniform magnetic field.

The gradient magnetic field coils 4a and 4b are formed of flat coils whose magnetic field application directions correspond to three directions of X, Y and Z. A three-dimensional gradient magnetic field is applied to a uniform magnetic field space to change the magnetic field strength and acquire position information. A copper plate is slit to form a board-shaped coil pattern, and the upper and lower surfaces are covered with FRP or the like and used for insulation treatment.

The RF coil has a flat plate shape and is composed of a conductor and an insulator for irradiating a high-output (high voltage, large current) excitation pulse.

The magnetic field uniformity adjusters 6a and 6b insert a ferromagnetic material such as pure iron or the like into a circular straight hole regularly arranged on a flat surface of a disk-shaped non-magnetic material. Thus, the magnetic field is adjusted. The flat disk-shaped non-magnetic material is preferably a fiber-reinforced plastic.

Generally, the magnetic field uniformity in the measurement space of the MRI apparatus is obtained by measuring the magnetic field strength at an arbitrary point in the measurement space as Legend.
Although expressed by the expansion formula of the re function, as a result of many studies leading to the present invention, the following became clear. That is, the uniformity adjustment in the magnetic field uniformity adjusters 6a and 6b arranged in the region where the magnetic poles face each other has a high sensitivity to the uniformity, and furthermore, from the low order (second order) to the high order (Eg 14th order)
Affected magnetic field components up to wide.

Further, the uniformity adjustment in the magnetic field uniformity adjusters 9a and 9b arranged in a region adjacent to the superconducting coil which is a magnetomotive force source distant from the measurement space maintains the sensitivity substantially equal to the above. While the unfolded low-order irregular magnetic field component
(About the second to sixth order).
This result, without changing the expandable higher-order components in the medical facility, which is the final magnetic field adjustment step of the MRI apparatus,
It is extremely useful for fine-tuning low order components.

In addition, by arranging the magnetic field uniformity adjusters 9a and 9b concentrically with respect to the magnetic field center axis, an axially symmetric irregular magnetic field component is obtained, and the center of the annular body is slightly shifted from the magnetic field center axis. A non-axisymmetric irregular magnetic field component can be adjusted efficiently.

FIG. 2 shows a magnetic field uniformity adjuster 9a of this embodiment.
It is a perspective view of 9b. Has an annular shape as shown in FIG. 2,
It is preferable that the center axis is arranged so as to coincide with the center axis of the magnetic field in the measurement section. However, the center axis may be slightly shifted. This effect is as described above. The superconducting coils 2a and 2b are mechanically fixed by a support mechanism from the base plate, and this support mechanism interferes with the magnetic field uniformity adjusters 9a and 9b. This can be avoided by forming the magnetic field uniformity adjusters 9a and 9b into a cutout structure. Note that notching the magnetic field uniformity adjusters 9a and 9b has little effect on the magnetic field uniformity in the measurement space. If this effect cannot be ignored, the magnetic field uniformity adjuster 9a arranged near the defect site,
This can be dealt with by adjusting the amount of magnetic material pieces included in 9b.

The annular magnetic field uniformity adjusters 9a and 9b are composed of segments divided in the circumferential direction, and can be detached and pulled out to the outer peripheral side in the radial direction. It became easy. That is, when adjusting the magnetic field uniformity only with the plate-shaped magnetic field uniformity adjusters 6a and 6b as in the conventional example, it is necessary to remove the gradient magnetic field coils 4a and 4b and the RF coils 5a and 5b for irradiating electromagnetic waves. However, by applying the present invention, in the final adjustment step of the magnetic field uniformity, the uniformity can be adjusted without removing them. In addition, since the volume of the segment has been reduced, the segment can be replaced even when the superconducting coils 2a and 2b are excited.

The annular magnetic field uniformity adjuster shown in FIG. 2 has a plurality of semi-circular blocks of glass fiber reinforced resin having through holes formed substantially parallel to the center axis of the circle. By inserting a rod-shaped magnetic material into the through hole, the uniformity of the magnetic field in the measurement space can be adjusted. The adjustment can be performed while the gradient magnetic field coil and the RF coil for irradiating the electromagnetic wave are mounted as described above. Further, the through holes are regularly arranged, so that the magnetic field can be easily adjusted.

FIG. 3 is an enlarged view of a part of the segment of the magnetic field uniformity adjusters 9a and 9b divided in the circumferential direction. The magnetic field uniformity adjusters 9a and 9b directly contribute to the magnetic field uniformity adjustment. And a base 12 for supporting these. As a method of attaching the magnetic material piece 11 to the base 12, a large number of screw holes are regularly provided in advance in the base 12, and the magnetic material piece 11 having the male screw portion is screwed into a portion necessary for adjusting the magnetic field uniformity. is there. In the process of obtaining the desired uniformity by this method, it is easy to repeatedly attach and detach the magnetic piece 11. The shapes of the magnetic pieces 11 need not all be the same size, and it is effective to use pieces having different volumes, preferably with different lengths, according to the situation of uniformity adjustment. In the figure, the magnetic piece 11 is shown as being arranged over the entire surface of the base 12, but in practice, there are often gaps where the magnetic piece 11 is not arranged. That is, the arrangement of the magnetic material pieces 10 can vary greatly depending on the situation of uniformity adjustment. Here, a ferromagnetic material such as pure iron or an alloy thereof is used as a material of the magnetic material piece 11, but if it is desired to increase the change in uniformity adjustment, a permanent magnet can be used. . Use a non-magnetic material with high electrical insulation such as FRP as the base material.

The magnetic piece 11 is inserted into a hole formed straight and parallel to the center axis of the magnetic field of the annular base 12. The magnetic piece 11 depends on the presence or absence of the magnetic piece 11 and its size. Once the adjustment is made. This uniformity adjustment is performed by inserting the magnetic piece 11 when the entire magnet device is installed and assembled. The holes are regularly arranged so that the uniformity can be easily adjusted.

Since the uniformity adjusting body 9 is composed of segments divided in the circumferential direction, when adjusting the uniformity, the segments are pulled out to the outer peripheral side in the radial direction, and then the base 12 is removed.
The uniformity of the magnetic field can be adjusted by changing the arrangement of the magnetic pieces 11. By providing a hole for inserting the magnetic piece 11 on the side surface of the base 12, that is, by providing this hole in the direction toward the center axis of the annular body, the uniformity adjusters 9a, 9
b from the side of the base 9 without pulling out the magnetic piece 1
It is also possible to replace 1 and adjust the uniformity.

Further, in this embodiment, the magnetic field center strength in the measurement space is 0.5 T or more, the gap between the opposing surfaces of the magnetic poles is 700 mm or more, and the magnetic field uniformity at 40 cm DSV can be 20 ppm or less.

Further, in this embodiment, the magnet assembly for the MRI apparatus in the case where the number of the yoke columns 7 is two has been described. However, even when the number of the yoke columns is one or three or more, the effect of the present invention is sufficient. Can be demonstrated in.

(Embodiment 2) FIG. 4 is a cross-sectional view of a magnet assembly in which magnetic field uniformity adjusters 9a and 9b according to the present invention are arranged on a surface facing a measurement space with respect to superconducting coil housings 3a and 3b. FIG. FIG. 1 shows a magnetic field uniformity adjuster 9 according to the present invention.
Although a and 9b are arranged outside the facing surface, which is the measurement space, with respect to the superconducting coil storage containers 3a and 3b, the effect can be exhibited even if they are arranged on the facing surface side. When applying this arrangement, also from the viewpoint of ensuring the openness of the open type MRI apparatus, the magnetic field uniformity adjusters 9a and 9b are positioned on a straight line 1 defining the viewing angle.
It is preferable to be inside than 3.

The magnetic field uniformity adjusters 9a and 9b have an annular shape as shown in FIG. 2 as in the first embodiment, and are preferably arranged so that the central axis thereof coincides with the magnetic field central axis of the measurement section. However, the center axis may be slightly shifted. This effect is as described above. In the case of this embodiment, the support mechanism for coupling the superconducting coils 2a, 2b and the base plates 10a, 10b does not interfere with the magnetic field uniformity adjusters 9a, 9b. In addition, since access from the measurement space side is possible,
The annular adjuster can be detached without being divided into circumferential segments, and the magnetic piece 11 can also be directly attached to the base 12.

The annular magnetic field uniformity adjusters 9a and 9b may be constituted by segments divided in the circumferential direction, and may be detached by pulling the segments toward the outer periphery in the radial direction. That is, in the conventional example, when the magnetic field uniformity is adjusted only by the plate-shaped magnetic field uniformity adjusters 9a and 9b, the gradient coil 4 is used.
Although a and 4b and the RF coils 5a and 5b for irradiating the electromagnetic waves had to be removed, in the present embodiment, the uniformity can be adjusted without removing them in the final adjustment step of the magnetic field uniformity. In addition, since the volume of the segment is reduced, the segment can be replaced even when the superconducting coils 2a and 2b are excited.

Also in this embodiment, as shown in FIG. 3, a part of the segments of the magnetic field uniformity adjusters 9a and 9b divided in the circumferential direction is enlarged. , 9b are composed of magnetic material pieces 11 that directly contribute to the adjustment of the magnetic field uniformity and a base 12 that supports them. Although the figure shows that the magnetic material pieces 11 are arranged over the entire surface of the base 12, in practice, there are often gaps where the magnetic material pieces 11 are not arranged. In other words, the arrangement of the magnetic pieces 11 can vary greatly depending on the situation of uniformity adjustment. Here, as a material of the magnetic body piece 11,
Although a ferromagnetic material such as iron or an alloy thereof is used, a permanent magnet can be used when a change in uniformity is desired to be increased. Use a non-magnetic material with high electrical insulation such as FRP as the base material.

Further, in this embodiment, the magnet assembly for the MRI apparatus in the case where the number of the yoke columns 7 is two is shown. However, even when the number of the yoke columns is one or three or more, the effect of the present invention is sufficient. Can be demonstrated in.

(Embodiment 3) FIG. 6 is a block diagram of an MRI apparatus using the magnet apparatus of Embodiment 1 or 2. MRI
The apparatus measures the nuclear spin density distribution, relaxation time distribution, and the like at a desired inspection site in a subject by using the NMR phenomenon, and displays an arbitrary cross section of the subject from the measurement data as an image. As shown in FIG. 6, the MRI apparatus includes a static magnetic field generating means 22 for applying a static magnetic field to the subject 21.
A gradient magnetic field generator 23 for generating a gradient magnetic field by inclining the static magnetic field strength of the magnetic field generated by the static magnetic field generating means 22; and a gradient magnetic field power supply 24 connected to the gradient magnetic field generator 23 and applying a voltage. And the high-frequency magnetic field
, A radio frequency magnetic field generator 26 connected to the probe 25 for generating a radio frequency magnetic field, a radio frequency magnetic field generator 6 and a gradient magnetic field power supply 24 The computer 27 controls the high-frequency magnetic field and the gradient magnetic field and controls the acquisition of nuclear magnetic resonance signals to perform image processing.
And a bed 29 on which the subject 21 is placed and which is transported into a static magnetic field by the drive of the drive mechanism 28. Further, the display device 20 receives the image signal generated by the computer 27 and displays it as a tomographic image.
RT. The movement of the bed 29 by the drive mechanism 28 in such an MRI apparatus is set to a constant speed in order to avoid a mechanical impact on the subject 21. Reference symbol L is a magnet center indicating the center line of the static magnetic field generating means 22.

In the present MRI apparatus, a pair of magnetic poles, a pair of superconducting coils as a magnetomotive force source, and a storage container for accommodating the respective superconducting coils are arranged vertically facing each other across the measurement space. The magnetic field uniformity adjusting body shown in FIG. 2 is disposed outside the facing surface side of the storage container as in the first embodiment.

According to this embodiment, in the final step of finely adjusting the magnetic field in the measurement space, a low-order irregular magnetic field component can be adjusted without detaching the gradient magnetic field coil, and the work can be easily performed. Further, the adjustment sensitivity when finely adjusting the magnetic field uniformity is optimized, and high working efficiency can be obtained.

[0046]

According to the present invention, the adjustment sensitivity in finely adjusting the uniformity of the magnetic field is optimized, and in the final step of finely adjusting the magnetic field in the measurement space, the gradient magnetic field coil can be reduced without being detached. The next irregular magnetic field component can be adjusted, and the operation can be easily performed. Further, the adjustment sensitivity when finely adjusting the magnetic field uniformity can be optimized, and the working efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the overall configuration of a magnet assembly according to the present invention.

FIG. 2 is an enlarged sectional view of a main part in FIG.

FIG. 3 is a schematic diagram of a main part in FIG. 2;

FIG. 4 is a cross-sectional view of an overall configuration showing an example of another magnet assembly according to the present invention.

FIG. 5 is a cross-sectional view showing the entire structure of a conventional MRI apparatus.

FIG. 6 is a block diagram showing the overall configuration of the MRI apparatus according to the present invention.

[Explanation of symbols]

1a, 1b: magnetic poles, 2a, 2b: superconducting coils, 3a, 3b: superconducting coil storage containers, 4a, 4b: gradient coils, 5a, 5b: R
F coil, 6a, 6b: uniformity adjusting body, 7: yoke pillar, 8: measuring space, 9, 9a, 9b: uniformity adjusting body, 10a, 10b: base plate, 11: magnetic piece, 12: base, 13 ... viewing angle defining straight line, 20 ... display, 21 ... subject, 22 ... static magnetic field generating means, 23 ... gradient magnetic field generator, 24 ... gradient magnetic field power supply, 2
5: Probe, 26: High frequency magnetic field generating coil, 27: Computer, 28: Drive mechanism, 29: Bed.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shigeru Kadokawa 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Takeshi Wakuda 7-1 Omikacho, Hitachi City, Ibaraki Prefecture No. 1 Inside Hitachi, Ltd.Hitachi Research Laboratories (72) Inventor Hirotaka Takeshima 1-1-14 Uchikanda, Chiyoda-ku, Tokyo, Japan Inside Hitachi Medical Co., Ltd. (72) Kenji Sakakibara, Uchikanda, Chiyoda-ku, Tokyo No. 1-114, Hitachi Medical Co., Ltd. (72) Inventor Takeshi Yao 1-1-1 Uchikanda, Chiyoda-ku, Tokyo F-term, Hitachi Medical Co., Ltd. F-term (reference) 4C096 AA01 AB32 AB45 AD08 CA02 CA16 CA24 CA25 CA32 CA36

Claims (12)

[Claims] 1. A magnetic head comprising: a pair of magnetic poles disposed to face each other across a subject as a measurement space; a superconducting coil disposed on an outer periphery of each of the magnetic poles; and a storage container for storing each of the superconducting coils. The magnet device, wherein a magnetic field uniformity adjuster having a plurality of magnetic pieces is arranged adjacent to the storage container. 2. A magnetic head comprising: a pair of magnetic poles disposed to face each other across a subject as a measurement space; a superconducting coil disposed on an outer periphery of each of the magnetic poles; and a storage container for storing each of the superconducting coils. In the magnet device, an annular magnetic field uniformity adjuster formed by a plurality of non-magnetic material pieces is detachably disposed adjacent to the storage container and on the outer periphery of the magnetic pole, and the non-magnetic material piece is provided. Wherein a plurality of cylindrical holes for inserting a ferromagnetic material are regularly arranged. 3. The magnet device according to claim 1, wherein the magnetic field uniformity adjusting member is formed of a composite of a non-magnetic material and a magnetic material piece. 4. The magnet device according to claim 3, wherein the magnetic piece is a ferromagnetic material or a permanent magnet. 5. A magnet device according to claim 1, wherein said magnetic field uniformity adjusting member is composed of a composite of a nonmagnetic electric insulator and a magnetic electric conductor piece. 6. A magnet according to claim 1, wherein said magnetic field uniformity adjuster is annular, and is arranged on the same circle or concentric circle with respect to the magnetic field center axis. apparatus. 7. The magnetic field uniformity adjuster according to claim 1, wherein the magnetic field uniformity adjuster is provided on an outer periphery of the magnetic pole, and is disposed on at least one of an opposing surface side and the outer side of the opposing surface across the container. A magnet device characterized in that: 8. The method according to claim 1, wherein the magnetic field center strength in the measurement space is 0.5 T or more, the magnetic field uniformity in 40 cm DSV is 20 ppm or less, and the gap between the opposing surfaces of the magnetic poles is 700 mm or more. Characteristic magnet device. 9. A pair of magnetic poles which are arranged opposite to each other with a subject serving as a measurement space to provide a static magnetic field, a superconducting coil disposed on an outer periphery of each of the magnetic poles, and a storage container for accommodating each of the superconducting coils. A pair of gradient magnetic field applying means for forming a gradient magnetic field in the static magnetic field, a high frequency transmitting / receiving means for transmitting a high frequency magnetic field to the subject and receiving a magnetic resonance signal from the subject, and the high frequency transmitting / receiving means And a means for controlling the high-frequency magnetic field and the gradient magnetic field connected to the gradient magnetic field applying means, and controlling the acquisition of the nuclear magnetic resonance signal to perform image processing. An annular magnetic field uniformity adjuster formed by a plurality of non-magnetic material pieces is detachably disposed, and the non-magnetic material piece has a plurality of ferromagnetic material insertion circles. Magnetic resonance imaging apparatus characterized by pores are regularly arranged. 10. The magnetic resonance apparatus according to claim 9, wherein the magnetic field center intensity in the measurement space is 0.5 T or more, the magnetic field uniformity at 40 cm DSV is 20 ppm or less, and the gap between the facing surfaces of the magnetic poles is 700 mm or more. Imaging device. 11. A ring formed by a plurality of non-magnetic material pieces, wherein the non-magnetic material piece has a plurality of cylindrical ferromagnetic material insertion holes formed in parallel with the center axis of the ring. A magnetic field uniformity adjuster for a magnetic resonance imaging apparatus, wherein the magnetic field uniformity adjuster is arranged in a uniform manner. 12. A pair of magnetic poles disposed opposite to each other with a subject as a measurement space therebetween, a pair of superconducting coils disposed on the outer periphery of each of the magnetic poles, and a housing for accommodating each of the superconducting coils. A magnetic field of a magnetic resonance imaging apparatus including a container, a pair of gradient magnetic field coils disposed on the measurement space side of the magnetic pole, and a pair of high-frequency magnetic field generation coils disposed on the measurement space side of the gradient magnetic field coil In the uniformity adjusting method, in a state in which the gradient magnetic field coil and the high frequency magnetic field generating coil are mounted, an annular shape formed by a plurality of nonmagnetic material pieces is provided adjacent to the storage container and on the outer peripheral side of the magnetic pole. The magnetic field uniformity adjuster in which the ferromagnetic material insertion cylindrical holes are regularly arranged is detachably arranged, and the insertion of the ferromagnetic material into the cylindrical hole is adjusted to adjust the magnetic field uniformity in the measurement space. Magnetic field homogeneity adjusting method for a magnetic resonance imaging apparatus characterized by adjusting the degree.