JP3983984B2 - Magnet apparatus, nuclear magnetic resonance imaging apparatus using the same, and magnetic field uniformity adjustment method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a novel magnet apparatus, a magnetic resonance imaging apparatus using the same, and its magnetic field uniformity adjustment. Arrangement In particular, the present invention relates to magnetic field uniformity adjustment of an open magnet having a wide opening.
[0002]
[Prior art]
A magnetic resonance imaging device (hereinafter referred to as an MRI device) obtains an image representing the physical properties of a specimen by utilizing the nuclear magnetic resonance phenomenon that occurs when an electromagnetic wave is irradiated onto a specimen placed in a uniform static magnetic field space. , Especially for medical use.
[0003]
The open-type MRI apparatus that is the subject of the present invention has a structure in which a pair of magnetic poles are arranged to face each other across a uniform magnetic field region, so that the subject feels less obstruction and the subject's subject Recently, the MRI system has become the mainstream because it is easy to access. In addition, with the advancement of medical technology, there has been a demand for higher resolution and higher functionality of captured images, and the magnetic field applied to the measurement space, especially for the magnet assembly that is a component of an open MRI system, is required. There is a demand for improved uniformity.
[0004]
In order for these MRI devices to ensure the magnetic field uniformity required for medical use, a process called shimming, which is a means for correcting the magnetic field inhomogeneity, is necessary, and is mainly performed after the assembly of the magnet assembly. Coarse adjustment of the magnetic field uniformity, fine adjustment performed after being brought into the medical facility, and the like. Even if the initial setting of the uniform magnetic field is completely completed in the factory, the latter process is due to the fact that the uniformity varies slightly depending on the installation space conditions in the medical facility. Manual work, such as placing it in position, is essential.
[0005]
FIG. 5 shows the structure of a conventional example of an open MRI apparatus. The main components of the device are the magnetic poles (1a, 1b) for applying a uniform magnetic field to the measurement space, the superconducting coils (2a, 2b) as the magnetomotive force source, the containers (3a, 3b) for storing the superconducting coils, Gradient magnetic field coils (4a, 4b) that apply a gradient magnetic field to provide positional information of the resonance phenomenon, RF coil systems (5a, 5b) that irradiate and receive electromagnetic waves, and an average to adjust the magnetic field uniformity in the measurement space Once there are adjustment sections (6a, 6b), etc., these are arranged so as to face each other across the measurement space.
[0006]
As a known technique for adjusting the magnetic field uniformity of an open type MRI apparatus, there is a method of providing a plurality of adjustable radial segments called a magnetic field adjustment control device on a magnetic pole protrusion (Japanese Patent Laid-Open No. 5512231), Method of moving up and down the ring (Japanese Patent Laid-Open No. 63-165743), method of disposing a magnetic material or permanent magnet piece on the magnetic pole facing surface (Japanese Patent Laid-Open No. 3-131234, Japanese Patent Laid-Open No. 8-172010, Japanese Patent Laid-Open No. 9-313458) For example, there is a method (Japanese Patent Laid-Open No. 7-11131) in which a magnetic piece arranged on the magnetic pole facing surface is moved in parallel with the magnetic flux direction.
[0007]
A magnetic device using a permanent magnet is disclosed in both the magnetic field generator disclosed in Japanese Patent Laid-Open No. 2-117106 and the magnetic field generator for MRI disclosed in Japanese Patent Laid-Open No. 10-146326.
[0008]
[Problems to be solved by the invention]
However, these uniformity adjustment means change the shape and arrangement of the magnetic poles on the opposite surface side close to the measurement space, or change the magnetic piece arrangement in the region adjacent to the opposite surface side. Although the sensitivity to changes is extremely high and can be applied to coarse adjustment, it is not always suitable for fine adjustment.
[0009]
In these means, since the magnetic field uniformity adjusting body is arranged inside the magnetic pole, the magnetic field pieces constituting the magnetic field uniformity adjusting body are removed by removing the gradient magnetic field coil and the like for each fine adjustment work of the uniformity. As a result, the work becomes complicated and a considerable amount of work time is spent. 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 adjusting body is very large. As a result, there has been a problem that the loss of liquid helium, which is a refrigerant, is large due to the AC loss that is an electromagnetic phenomenon of the coil body in the excitation / demagnetization of the superconducting coil.
[0010]
In addition, since these magnetic means shims are arranged in a region adjacent to the gradient magnetic field coil, the temperature change caused by the pulse operation of the gradient magnetic field coil changes the magnetization characteristics of the magnetic material constituting the magnetic field uniformity adjusting body. As a result, the magnetic field uniformity during photographing was adversely affected. This is because in the case of passive uniformity adjustment using a magnetic piece, the temperature dependence of the magnetization characteristics of the magnetic substance is large.
[0011]
In addition, as a method for finely adjusting the magnetic field uniformity without removing the gradient magnetic field coil or the like, there is a method of moving the magnetic pole up and down from the outside with a worm gear or the like (JP-A-8-69913). However, this method has a limitation in the irregular magnetic field component that can adjust the uniformity by moving the whole magnetic pole up and down.
[0012]
The purpose of the present invention is to optimize the adjustment sensitivity when finely adjusting the magnetic field homogeneity, and to adjust the low-order irregular magnetic field components without detaching the gradient magnetic field coil in the fine adjustment of the magnetic field homogeneity in the measurement space. A magnetic device that can improve the work efficiency and can easily carry out the work, a magnetic resonance imaging device using the magnet device, and a magnetic field uniformity adjustment thereof. Arrangement To provide a law.
[0013]
[Means for Solving the Problems]
The present invention relates to a magnet apparatus for an MRI apparatus including a pair of magnetic poles arranged opposite to each other with a measurement space interposed therebetween, a pair of superconducting coils, and a pair of containers for housing the superconducting coils. Non-divided in the circumferential direction Magnetic piece Formed by the annular Magnetic field uniformity adjuster But Area adjacent to the superconducting coil storage container At the outer periphery of the magnetic pole Placed in The nonmagnetic piece is detachable, and a plurality of ferromagnetic material insertion cylindrical holes are regularly arranged in the nonmagnetic piece. It is characterized by that. In this configuration, the uniformity adjustment region is separated from the gradient magnetic field coil, so that the magnetic piece for homogenizing the magnetic field is not easily affected by the heat generated by the pulse current of the gradient magnetic field coil. Is stable. In addition, since the uniformity can be adjusted in a region away from the measurement space, the irregular magnetic field component can be finely adjusted. In the present invention, the magnetic field uniformity adjusting body is disposed in a region adjacent to the superconducting coil and has a divided structure.
[0014]
In the present invention, the magnetic field uniformity adjusting body is arranged with respect to the magnetic field central axis. Same It is preferable to have an annular shape arranged on the center circle. By arranging the magnetic field homogeneity adjustment body concentrically with respect to the magnetic field center axis, the asymmetrical magnetic field component of the measurement space is asymmetrical. The magnetic field component can be adjusted.
[0015]
In the present invention, the magnetic field uniformity adjusting body is arranged on the outer peripheral side with respect to the magnetic field center axis from the space where the pair of magnetic poles face each other, and on the outer side from the facing surface with respect to the magnetic field center axis from the adjacent superconducting coil storage container. Arranged. In addition, the magnetic field uniformity adjusting body is composed of segments divided in the circumferential direction, and has a structure that can be detached from the outer circumferential side in the radial direction. With this configuration, even in the final magnetic field fine adjustment step, the divided segments can be exchanged without detaching the gradient magnetic field coil or the RF coil, so that workability can be significantly improved. In addition, by appropriately reducing the volume of the segment to be divided, the electromagnetic force acting on these segments can be reduced even when a static magnetic field is applied to the measurement space, so even when the superconducting coil is excited. The segment can be detached.
[0016]
In the present invention, it is preferable that the magnetic field uniformity adjusting body is composed of a composite of a non-magnetic material and a magnetic material piece, and the magnetic material piece is a ferromagnetic material or a permanent magnet. With this configuration, the magnetic flux generated from the superconducting coil, which is a magnetomotive force source, can be finely controlled. In addition, the magnetic field uniformity adjusting body has a structure in which magnetic flux passes through a magnetic field uniformity adjusting body composed of a composite of non-magnetic / electrical insulator and magnetic / electrical conductor pieces, so that it can be used in the measurement space. Since a static magnetic field with extremely high magnetic field uniformity can be applied, a captured image suitable for medical use as an MRI apparatus can be obtained.
[0017]
More specifically, the present invention relates to a pair of magnetic poles that are arranged opposite to each other with a subject serving as a measurement space to give a static magnetic field, a superconducting coil arranged on the outer periphery of each of the magnetic poles, and the superconducting coil A storage container for storing each of the above, a pair of gradient magnetic field coils for forming a gradient magnetic field in the static magnetic field, a gradient magnetic field power source connected to the gradient magnetic field coil for applying a voltage, and a high-frequency magnetic field transmitted to the subject And a probe that 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 the high-frequency magnetic field that is connected to the high-frequency magnetic field generator and the gradient magnetic field power supply In a magnetic resonance imaging apparatus comprising: a computer that controls a gradient magnetic field and controls image acquisition by controlling the capture of the nuclear magnetic resonance signal; and a bed that conveys the subject , Adjacent to the receiving container As well as , On the outer periphery of the magnetic pole, plural Divided in the circumferential direction Annulus formed by nonmagnetic pieces The magnetic field uniformity adjustment body is arranged , The non-magnetic piece is detachable, A plurality of ferromagnetic material insertion cylindrical holes are regularly arranged in the non-magnetic piece. Please In addition, the aforementioned cylindrical hole is preferably formed substantially parallel to the annular central axis.
[0018]
Furthermore, the present invention provides a plurality of Divided in the circumferential direction Annulus formed by nonmagnetic pieces The magnetic field uniformity adjusting body is arranged on the outer periphery of the magnetic pole in the region adjacent to the superconducting coil storage container. , The non-magnetic piece is removable The non-magnetic piece is regularly arranged with a plurality of ferromagnetic material insertion cylindrical holes formed straight with respect to the annular central axis, and the above-mentioned cylindrical holes are preferably Formed substantially parallel to the annular central axis. Nuclear Magnetic field homogeneity adjuster for magnetic resonance imaging apparatus Make up It is in.
[0019]
In addition, the present invention houses a pair of magnetic poles arranged opposite to each other with an object serving as a measurement space, a pair of superconducting coils arranged on the outer periphery of each of the magnetic poles, and each of the superconducting coils. A magnetic resonance imaging apparatus comprising: a storage container; a pair of gradient magnetic field coils arranged on the measurement space side of the magnetic pole; and a pair of high-frequency magnetic field generating coils arranged on the measurement space side of the gradient magnetic field coil In the magnetic field homogeneity adjustment method, a plurality of gradient magnetic field coils and high-frequency magnetic field generating coils are attached to the outer peripheral side of the magnetic pole and adjacent to the storage container. Divided in the circumferential direction Annulus formed by nonmagnetic pieces The magnetic field uniformity adjustment body is arranged , Making the non-magnetic piece removable; The non-magnetic piece is regularly arranged with a plurality of ferromagnetic material insertion cylindrical holes formed substantially parallel to the annular central axis. Before The magnetic field uniformity of the measurement space is adjusted by adjusting the insertion of the ferromagnetic material into the cylindrical hole.
[0020]
By applying the present invention, it is possible to realize an MRI apparatus in which 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 opposing surfaces of the upper and lower magnetic poles is 700 mm or more.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Example 1
FIG. 1 is an overall structural view of an MRI magnet assembly according to the present invention. In FIG. 1, a pair of magnetic poles 1a and 1b, a pair of superconducting coils 2a and 2b which are magnetomotive force sources facing each other in the vertical direction across a measurement space 8, and a storage container 3a for storing each superconducting coil. 3b is arranged. The magnetic poles 1a and 1b, the superconducting coils 2a and 2b, and the storage containers 3a and 3b are magnetically and mechanically coupled by the base plates 10a and 10b made of a ferromagnetic material such as pure iron and the two yoke columns 7. Further, on the opposite surface side of the magnetic pole, the gradient magnetic field coils 4a and 4b that apply a gradient magnetic field to the measurement space, the RF coils 5a and 5b that irradiate electromagnetic waves, and the magnetic field uniformity for adjusting the magnetic field uniformity of the measurement space. Once the adjusting bodies 6a and 6b are in this embodiment, the magnetic field uniformity adjusting bodies 9a and 9b according to the present invention are detachable on the opposite side of the opposing surfaces of the storage containers 3a and 3b for storing the superconducting coils 2a and 2b. Adjacent to each other. The superconducting coil storage containers 3a and 3b are connected to a refrigerator or the like to reduce the evaporation of a low-temperature refrigerant such as liquid helium filled therein, which is not shown here. The superconducting coil storage containers 3a and 3b are preferably provided at positions slightly away from the annular projecting surfaces of the magnetic poles 1a and 1b so that they cannot be seen from the measurement space 8.
[0022]
The magnetic field homogeneity adjusters 9a and 9b have the advantage that only the magnetic component to be adjusted can be adjusted by arranging them at the positions of this embodiment. In this position, fine adjustment is possible and a more uniform magnetic field can be formed. It is preferable that they are located 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 adjustment can be performed without removing the gradient magnetic field coils 4a and 4b and the RF coils 5a and 5b.
[0023]
The magnetic poles 1a and 1b are made of a ferromagnetic material. For example, pure iron or an iron alloy single material or a composite of these materials is used. In FIG. 1, the magnetic poles 1a and 1b are shown as a cup-shaped integrated structure. However, when viewed from opposite surfaces, 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 it. It can be divided into three parts, which are divided into an annular ferromagnet in contact with the end of the outer disk-shaped ferromagnet and in contact with the outer peripheral surface of the inner disk-shaped ferromagnet. 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 ferromagnet is effective in forming a uniform magnetic field.
[0024]
The gradient magnetic field coils 4a and 4b are constituted by flat-plate coils whose magnetic field application directions correspond to three directions of X, Y and Z. The position information is obtained by applying a three-dimensional gradient magnetic field to the uniform magnetic field space and changing the magnetic field strength. A copper plate is slit to form a disk-like coil pattern, and the upper and lower surfaces are covered with FRP or the like for insulation treatment.
[0025]
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.
[0026]
The magnetic field uniformity adjusting bodies 6a and 6b are formed by inserting a ferromagnetic material of a cylindrical rod such as pure iron into a circular straight hole regularly arranged on a flat plate surface of a flat disk-like nonmagnetic material. To be adjusted. The flat disk-like nonmagnetic material is preferably a fiber reinforced plastic.
[0027]
In general, the magnetic field homogeneity in the measurement space of the MRI apparatus is expressed by the expansion formula of the Legendre function of the magnetic field strength at an arbitrary point in the measurement space. As a result of numerous studies up to the present invention, the following has become clear. In other words, the uniformity adjustment in the magnetic field uniformity adjusting bodies 6a and 6b arranged in the areas where the magnetic poles are opposed has a high sensitivity to the uniformity, and moreover, from the low-order (secondary) to the high-order of the above-described expansion type. It affects even wide irregular magnetic field components up to (for example, 14th order).
[0028]
In addition, adjusting the uniformity in the magnetic field uniformity adjusting bodies 9a and 9b arranged in the region adjacent to the superconducting coil, which is a magnetomotive force source away from the measurement space, can be developed while maintaining almost the same sensitivity as above. It was found that only the low order irregular magnetic field components (about 2 to 6th order) of the equation greatly affect. This result is extremely useful for fine-tuning the low-order component without changing the deployable high-order component in the medical facility that is the final magnetic field adjustment process of the MRI apparatus.
[0029]
In addition, the magnetic field uniformity adjusting bodies 9a and 9b are arranged concentrically with respect to the magnetic field central axis, so that the asymmetric magnetic field component is axisymmetric, and the center of the annular body is slightly shifted from the magnetic field central axis to make it non-axisymmetric. It is possible to efficiently adjust the irregular magnetic field component.
[0030]
FIG. 2 is a perspective view of the magnetic field uniformity adjusting bodies 9a and 9b of the present embodiment. As shown in FIG. 2, it is preferable to have an annular shape and to arrange the central axis so that it coincides with the magnetic field central axis of the measurement section, but the central axis may be slightly shifted. This effect is as described above. The superconducting coils 2a and 2b are mechanically fixed by the 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 adopting a structure in which the magnetic field uniformity adjusting bodies 9a and 9b are cut out. Note that the effect on the magnetic field uniformity of the measurement space by cutting out the magnetic field uniformity adjusting bodies 9a and 9b is small. If this influence cannot be ignored, it can be dealt with by adjusting the amount of the magnetic piece contained in the magnetic field uniformity adjusting bodies 9a, 9b arranged near the defect site.
[0031]
Also, the annular magnetic field uniformity adjusting bodies 9a and 9b are divided in the circumferential direction. Non-magnetic piece Since it consists of segments and can be pulled out to the outer peripheral side in the radial direction, replacement and adjustment are very easy. That is, when adjusting the magnetic field uniformity only with the plate-like magnetic field uniformity adjusting bodies 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 that irradiate electromagnetic waves. However, by applying the present invention, 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 exchanged even when the superconducting coils 2a and 2b are excited.
[0032]
The annular magnetic field uniformity adjusting body in FIG. 2 has a through hole that is opened substantially parallel to the central axis of a plurality of semicircular blocks of glass fiber reinforced resin. The magnetic field homogeneity of the measurement space can be adjusted by inserting a rod-shaped magnetic body inside. In the adjustment, as described above, the gradient magnetic field coil and the RF coil for irradiating electromagnetic waves can be attached. Further, the through holes are regularly arranged, whereby the magnetic field adjustment can be easily performed.
[0033]
FIG. 3 is an enlarged view of one part of the segments of the magnetic field uniformity adjusting bodies 9a and 9b divided in the circumferential direction. The magnetic field uniformity adjusting bodies 9a and 9b are magnetic bodies that directly contribute to the magnetic field uniformity adjustment. It consists of a piece 11 and a base 12 that supports them. As a method of attaching the magnetic piece 11 to the base 12, a large number of screw holes are regularly provided in the base 12 in advance, and the magnetic piece 11 having the male screw portion is screwed into a place 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 desorb the magnetic piece 11. The shapes of the magnetic pieces 11 need not all have the same size, and it is effective to use pieces having different volumes, preferably those having different lengths, depending on the situation of uniformity adjustment. In the figure, the magnetic piece 11 is shown to be disposed over the entire surface of the base 12, but in practice, there are often void portions where the magnetic piece 11 is not disposed. In other words, the arrangement of the magnetic piece 10 can vary greatly depending on the state of uniformity adjustment. Here, a ferromagnetic material such as pure iron or an alloy thereof is used as the material of the magnetic piece 11, but a permanent magnet can also be used to increase the change in the uniformity adjustment. . Use non-magnetic and high electrical insulation such as FRP as the base material.
[0034]
The magnetic piece 11 is inserted into a hole formed in a straight line parallel to the magnetic field central axis of the annular base 12, and the uniformity can be adjusted depending on whether or not the magnetic piece 11 is inserted and its size. Done. This uniformity adjustment is performed by inserting the magnetic piece 11 when the entire magnet apparatus is installed and assembled. The holes are regularly arranged so that the uniformity can be easily adjusted.
[0035]
Since the uniformity adjusting body 9 is composed of segments divided in the circumferential direction, when adjusting the uniformity, after the segment is pulled out to the outer peripheral side in the radial direction, the arrangement of the magnetic pieces 11 of the base 12 is changed. The magnetic field can be adjusted uniformly. A hole for inserting the magnetic material piece 11 is provided on the side surface of the base 12, that is, the hole is provided in a direction toward the central axis of the annular body, so that the uniformity adjusting bodies 9a and 9b are not pulled out. It is also possible to exchange the magnetic piece 11 from the side surface and adjust the uniformity.
[0036]
Furthermore, in this embodiment, the magnetic field center intensity 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.
[0037]
Furthermore, although the present Example showed about the magnet assembly for MRI apparatuses in case the number of the yoke columns 7 is two, the effect of this invention can fully be exhibited, even when the number of yoke columns is one or three or more. .
[0038]
(Example 2)
FIG. 4 is a cross-sectional view of a magnet assembly in which the magnetic field uniformity adjusting bodies 9a and 9b according to the present invention are arranged on the facing surface side which is a measurement space with respect to the superconducting coil storage containers 3a and 3b. In FIG. 1, the magnetic field uniformity adjusting bodies 9a and 9b according to the present invention are arranged outside the facing surface which is a measurement space with respect to the superconducting coil storage containers 3a and 3b. The effect can be demonstrated. When applying this arrangement, it is preferable that the magnetic field uniformity adjusting bodies 9a and 9b are located inside the straight line 13 that defines the viewing angle from the viewpoint of ensuring the openness of the open MRI apparatus.
[0039]
The magnetic field uniformity adjusting bodies 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. The shaft may be arranged with a slight shift. This effect is as described above. In the case of the present embodiment, the support mechanism for coupling the superconducting coils 2a, 2b and the base plates 10a, 10b and the magnetic field uniformity adjusting bodies 9a, 9b do not interfere with each other. Further, since access from the measurement space side is possible, the annular adjustment body can be attached and detached without being divided into circumferential segments, and the magnetic piece 11 can also be directly attached to the base 12.
[0040]
The annular magnetic field uniformity adjusting bodies 9a and 9b may be constituted by segments divided in the circumferential direction, and the desorption may be performed by pulling out to the outer circumferential side in the radial direction. That is, in the conventional example, when the magnetic field uniformity is adjusted only by the plate-like magnetic field uniformity adjusting bodies 9a and 9b, it is necessary to remove the gradient magnetic field coils 4a and 4b and the RF coils 5a and 5b that irradiate electromagnetic waves. However, in this 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 exchanged even when the superconducting coils 2a and 2b are excited.
[0041]
Also, in this embodiment, as shown in FIG. 3, one part of the segments of the magnetic field uniformity adjusting bodies 9a and 9b divided in the circumferential direction is enlarged, but the magnetic field uniformity adjusting bodies 9a and 9b are It comprises a magnetic piece 11 that directly contributes to magnetic field uniformity adjustment and a base 12 that supports them. In the figure, the magnetic piece 11 is shown as being disposed over the entire surface of the base 12, but in practice, there are often void portions where the magnetic piece 11 is not disposed. That is, the arrangement of the magnetic material pieces 11 can vary greatly depending on the situation of the uniformity adjustment. Here, a ferromagnetic material such as iron or an alloy thereof is used as the material of the magnetic piece 11, but a permanent magnet can also be used when it is desired to increase the change in the uniformity adjustment. . Use non-magnetic and high electrical insulation such as FRP as the base material.
[0042]
Furthermore, in this embodiment, the magnet assembly for an MRI apparatus in the case where there are two yoke columns 7 is shown, but the effect of the present invention can be sufficiently exerted even when the number of yoke columns is one or three or more. .
[0043]
(Example 3)
FIG. 6 is a block diagram of an MRI apparatus using the magnet apparatus according to the first or second embodiment. The MRI apparatus measures the density distribution, relaxation time distribution, etc. of nuclear spins at a desired examination site in a subject 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 forms a gradient magnetic field by inclining a static magnetic field generating means 22 for applying a static magnetic field to a subject 21, and a static magnetic field intensity of the magnetic field generated by the static magnetic field generating means 22. A gradient magnetic field generator 23, a gradient magnetic field power source 24 that is connected to the gradient magnetic field generator 23 and applies a voltage, and a probe that transmits a high-frequency magnetic field to the subject 21 and receives a nuclear magnetic resonance signal from the subject 21 25, a high-frequency magnetic field generator 26 that is connected to the probe 25 and generates a high-frequency magnetic field, and is connected to the high-frequency magnetic field generator 6 and the gradient magnetic field power source 24 to control the high-frequency magnetic field and the gradient magnetic field, and at the same time nuclear magnetic resonance A computer 27 that controls signal acquisition and performs image processing, and a bed 29 that is placed on the subject 21 and is carried into a static magnetic field by driving of a drive mechanism 28. It is. Further, the display device 20 receives the image signal generated by the computer 27 and displays it as a tomographic image, and is composed of, for example, a CRT. The movement of the bed 29 by the drive mechanism 28 in such an MRI apparatus is set at a constant speed in order to avoid a mechanical impact on the subject 21. Reference symbol L denotes a magnet center indicating a center line of the static magnetic field generating means 22.
[0044]
In this MRI apparatus, a pair of magnetic poles, a pair of superconducting coils that are magnetomotive force sources, and a storage container that stores each superconducting coil are arranged facing each other in the vertical direction across the measurement space. Similar to Example 1, the magnetic field uniformity adjusting body shown in FIG. 2 is arranged outside the opposing surface of the storage container.
[0045]
According to the present embodiment, in the final magnetic field fine adjustment step of the measurement space, the low-order irregular magnetic field component can be adjusted and the operation can be easily performed without detaching the gradient magnetic field coil. In addition, it is possible to optimize the adjustment sensitivity when finely adjusting the magnetic field uniformity and to obtain high working efficiency.
[0046]
【The invention's effect】
According to the present invention, the adjustment sensitivity at the time of fine adjustment of the magnetic field homogeneity is optimized, and in the final magnetic field fine adjustment process of the measurement space, the low-order irregular magnetic field component without removing the gradient magnetic field coil. Can be adjusted and the operation can be carried out easily. In addition, it is possible to optimize the adjustment sensitivity when finely adjusting the magnetic field uniformity and improve the working efficiency.
[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 cross-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 the overall configuration showing an example of another magnet assembly according to the present invention.
FIG. 5 is a cross-sectional view showing the overall 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 pole, 2a, 2b ... Superconducting coil, 3a, 3b ... Superconducting coil storage container, 4a, 4b ... Gradient magnetic field coil, 5a, 5b ... RF coil, 6a, 6b ... Uniformity adjuster, 7 ... Relay column 8 ... Measurement space 9,9a, 9b ... Uniformity adjusting body, 10a, 10b ... Base plate, 11 ... Magnetic body piece, 12 ... Base, 13 ... Line of view angle regulation, 20 ... Display device, 21 ... Subject, DESCRIPTION OF SYMBOLS 22 ... Static magnetic field generation means, 23 ... Gradient magnetic field generator, 24 ... Gradient magnetic field power supply, 25 ... Probe, 26 ... High frequency magnetic field generator coil, 27 ... Computer, 28 ... Drive mechanism, 29 ... Bed.

Claims (9)

  A magnet apparatus comprising a pair of magnetic poles arranged opposite to each other with a measurement space interposed therebetween, a superconducting coil arranged on the outer periphery of each of the magnetic poles, and a storage container for storing each of the superconducting coils. An annular magnetic field uniformity adjusting body formed by a plurality of circumferentially divided nonmagnetic body pieces is arranged on the outer periphery of the magnetic pole, and the nonmagnetic body piece is detachable, A magnet device comprising a plurality of ferromagnetic material insertion cylindrical holes regularly arranged in a magnetic piece.   2. The magnet device according to claim 1, wherein the magnetic piece is a ferromagnetic material or a permanent magnet.   3. The magnet apparatus according to claim 1, wherein the magnetic field uniformity adjusting body is composed of a composite of a nonmagnetic electrical insulator and a magnetic electrical conductor piece.   4. The magnet device according to claim 1, wherein the magnetic field uniformity adjusting body is annular and is disposed concentrically with respect to a magnetic field central axis.   5. The magnetic field uniformity adjusting body according to claim 1, wherein the magnetic field uniformity adjusting body is disposed on an outer periphery of the magnetic pole, and is disposed on at least one of an opposing surface side and an outer side of the opposing surface side with the container interposed therebetween. Magnet device.   6. The magnet device according to claim 1, wherein the magnetic field center strength 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 opposing surfaces of the magnetic poles is 700 mm or more. .   A pair of magnetic poles arranged opposite to each other with a subject arranged in the measurement space to give a static magnetic field, a superconducting coil arranged on the outer periphery of each of the magnetic poles, and a storage container for storing 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 transmission / reception means for transmitting a high frequency magnetic field to the subject and receiving a magnetic resonance signal from the subject; the high frequency transmission / reception means; and In a nuclear magnetic resonance imaging apparatus that is connected to a gradient magnetic field applying means and has an image processing means for controlling the high-frequency magnetic field and the gradient magnetic field and controlling the capture of the nuclear magnetic resonance signal to perform image processing, adjacent to the storage container In addition, an annular magnetic field uniformity adjusting member formed by a plurality of nonmagnetic pieces divided in the circumferential direction is disposed on the outer periphery of the magnetic pole, and the nonmagnetic Piece is detachable, wherein the nonmagnetic body pieces magnetic resonance imaging apparatus, wherein a plurality of ferromagnetic insertion cylindrical holes are regularly arranged.   8. The magnetic resonance imaging apparatus according to claim 7, 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 opposing surfaces of the magnetic poles is 700 mm or more.   A pair of magnetic poles arranged opposite to each other with a measurement space interposed therebetween, a pair of superconducting coils arranged on the outer periphery of each of the magnetic poles, a storage container for storing each of the superconducting coils, and the measurement space for the magnetic poles In the magnetic field homogeneity adjusting method of a magnetic resonance imaging apparatus, comprising the pair of gradient magnetic field coils arranged on the side and the pair of high-frequency magnetic field generating coils arranged on the measurement space side of the gradient magnetic field coil, the gradient magnetic field An annular magnetic field uniformity adjusting body formed of a plurality of circumferentially divided non-magnetic pieces on the outer periphery of the magnetic pole, with the coil and the high-frequency magnetic field generating coil mounted. By disposing the non-magnetic body piece so as to be removable, and inserting the ferromagnetic body into the cylindrical hole of the non-magnetic body piece in which a plurality of ferromagnetic body insertion cylindrical holes are regularly arranged. Magnetic field homogeneity adjusting method for a magnetic resonance imaging apparatus characterized by adjusting the magnetic field uniformity of the serial measurement space.

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