JP6368625B2 - Magnetic resonance imaging system - Google Patents

Description

The present invention relates to a method for reducing an unnecessary fluctuation magnetic field generated when a magnetic resonance imaging apparatus is used.

  A magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus) uses a nuclear magnetic resonance phenomenon that occurs when an object placed in a uniform static magnetic field is irradiated with a high-frequency pulse, and thereby the physical and chemical properties of the object. It is an apparatus for obtaining a cross-sectional image showing properties, and is particularly used for medical purposes.

  An MRI apparatus generates a magnetic field that generates a uniform static magnetic field mainly in an imaging space into which a subject is inserted, and a magnetic field that is spatially gradient in intensity to give positional information to the imaging space. A gradient magnetic field coil, an RF coil that irradiates a subject with a high frequency pulse, a receiving coil that receives a magnetic resonance signal from the subject, and a computer system that processes the received signal and displays an image.

  As a means for improving the performance of the MRI apparatus, there is an improvement in the strength or uniformity of the static magnetic field generated by the magnet apparatus. The stronger the static magnetic field, the clearer the image can be obtained, and the more uniform in the wide space of the static magnetic field, the clearer image can be obtained over a wide range. Development is being continued with the aim of improving performance. As other means for improving performance, there are improvement of gradient magnetic field accuracy and high-speed driving of gradient magnetic field pulses. These contribute to improvement of image quality and reduction of imaging time. In particular, with the diversification of imaging methods, a current waveform that generates a gradient magnetic field pulse tends to be a pulse waveform with a fast time change.

Since a pulsed current flows through the gradient magnetic field coil, not only a gradient magnetic field in the imaging space but also a leakage magnetic field is generated outside the imaging space, and an eddy current is generated by generating a variable magnetic field in the metal structure constituting the magnet device. Let The eddy current generates a fluctuating magnetic field in the imaging space, which affects the distribution of the static magnetic field and the gradient magnetic field and adversely affects the image quality. In particular, in recent MRI apparatuses, with the advancement of imaging methods, a highly accurate magnetic field is required, so reducing eddy current is an important issue. For this reason, in general, a high magnetic field (0.5 Tesla or higher) MRI magnet with a superconducting static magnetic field magnet adopts a self-shielding gradient magnetic field coil to reduce the leakage magnetic field outside the imaging space. It has been adopted. On the other hand, in an MRI apparatus having a static magnetic field magnet with a medium to low magnetic field (less than 0.5 Tesla), since the gradient magnetic field coil is used with a drive power source with a small output, it does not have a shield coil, but instead a static magnetic field. A magnetic pole piece serving as a magnetic flux path such as a silicon steel plate and generating less eddy current is provided on the magnetic pole face of the magnet. Further, iron magnetic poles, which are magnetic materials, are often used for medium and low magnetic field magnets. In this case, the fluctuation magnetic field due to the gradient magnetic field not only affects the magnetic field due to the eddy current, but also the residual magnetic field due to the magnetization of the iron magnetic pole having the hysteresis characteristic of the magnetic material adversely affects the image. It has become.
As a background art in this technical field, there is a publication (Japanese Patent Laid-Open No. 05-182821) (Patent Document 1). This public information discloses a technique for reducing eddy current caused by a gradient magnetic field coil by using a pole piece in which soft ferrite and a laminated silicon steel plate are laminated on the surface of a static magnetic field magnetic pole from the gradient magnetic field side. In addition, in JP 2004-65714 A (Patent Document 2), a pole piece of a silicon steel plate laminated on the surface of a static magnetic field magnetic pole is installed in a small shape in a surface layer portion with respect to a deep layer portion, There is a technique for reducing the leakage magnetic field of the gradient magnetic field.

JP 05-182821 PR JP 2004-65714 A

  As shown in Patent Document 1, by installing a soft ferrite having a large resistance value and a small hysteresis characteristic on the surface of a static magnetic field magnetic pole closest to the gradient magnetic field coil, a variable magnetic field due to an eddy current and a magnetization change can be reduced. However, the saturation magnetization of soft ferrite is lower than that of a silicon steel plate or the like, and the thickness of the laminate is necessary so that the magnetic flux is not saturated. If the combined thickness of soft ferrite and silicon steel plate is not sufficient, the leakage magnetic field of the gradient magnetic field reaches the surface of the static magnetic field magnetic pole (iron magnetic pole), and the eddy current and the fluctuation magnetic field due to the magnetization change affect the image quality. Cause.

  In Patent Document 2, the eddy current generated on the surface of the silicon steel sheet is reduced by reducing the magnetic steel pole piece made of the silicon steel sheet on the surface portion of the static magnetic field magnetic pole. Since silicon steel has a saturation magnetization larger than that of soft ferrite, it is easy to suppress the lamination thickness. However, if the pole pieces are made smaller in order to suppress the generation of eddy current, the apparent electrical resistance increases, but the gap for insulation increases, the space factor decreases, and the apparent saturation. Magnetization also decreases. For this reason, in order to suppress the leakage magnetic field of the gradient magnetic field that reaches the iron magnetic pole, it is necessary to increase the thickness of the silicon steel sheet by the amount that the space factor is reduced.

  As described above, in the prior art, it is possible to reduce the generation of eddy currents on the surface of the static magnetic field magnetic pole, while it is necessary to install a thick silicon steel plate or soft ferrite on the surface of the iron magnetic pole. In order to widen the imaging space, it is more efficient to reduce the distance between the gradient magnetic field coil and the iron magnetic pole as much as possible because it is not necessary to increase the magnetic energy of the static magnetic field magnet. On the other hand, in order for the gradient coil to effectively generate a gradient magnetic field in the imaging space, it is preferable that the gap between the gradient coil and the surface of the soft ferrite or silicon steel plate is wide.

  As described above, in the prior art, it is possible to reduce the eddy current generated on the surface of the static magnetic field magnetic pole, while the leakage magnetic field of the gradient magnetic field to the iron magnetic pole tends to increase. As a result, the eddy current generated in the iron magnetic pole and the fluctuating magnetic field due to the magnetization change may affect the image quality.

The present invention has been made in view of such circumstances, and at the time of generating a gradient magnetic field, in an iron magnetic pole, the generation of an eddy current magnetic field due to a leakage magnetic field and a fluctuation magnetic field due to a magnetization change are suppressed, and at the same time, an imaging space is widened. Thus, an object of the present invention is to provide an MRI apparatus provided with means for obtaining a good image while improving the comfort of a subject.

In order to solve the above-described problems, in the present invention, in an MRI apparatus having a static magnetic field magnet having a magnetic pole and a gradient magnetic field coil, the magnetic pole facing the imaging space includes a substantially disc-shaped iron magnetic pole and a substantially annular ring. It is composed of a magnetic iron pole of a shape and a magnetic pole piece of a substantially tile-shaped silicon steel plate, and the magnetic pole piece of the tile-shaped silicon steel plate is laminated on the surface of the disk-shaped iron magnetic pole, and the disk-shaped iron magnetic pole Divided in directions and insulated from each other by insulators or voids. In particular, it is divided in the circumferential direction at the outer peripheral portion of the disk shape.

According to the MRI apparatus of this configuration, it is possible to suppress the eddy current generated in the magnetic pole without increasing the distance between the disc-shaped iron magnetic pole constituting the static magnetic field magnet and the gradient magnetic field coil. That is, an MRI apparatus that can suppress the eddy current magnetic field and the residual magnetic field and obtain a good image quality is realized.

FIG. 2 is a partial front view showing a static magnetic field magnetic pole part of the MRI apparatus according to the first embodiment of the present invention. 1 is a vertical external perspective view of an MRI apparatus according to a first embodiment of the present invention. FIG. 2 is a partial cross-sectional view showing the configuration of the MRI apparatus according to the first embodiment of the present invention and the distribution of magnetic flux in a gradient magnetic field.

It is a fragmentary sectional view which shows the static magnetic field distribution and gradient magnetic field distribution, and eddy current flow path in the magnetic pole structure of the MRI apparatus which has a superconducting coil by a prior art as a static magnetic field generation source. It is a fragmentary sectional view which shows the static magnetic field distribution and gradient magnetic field distribution, and eddy current flow path in the magnetic pole structure of the MRI apparatus which has the permanent magnet as a main static magnetic field generation source by a prior art. 3 is a comparison of temporal changes in magnetic flux density due to eddy currents in the magnetic pole structure of the prior art and the magnetic pole structure of the first embodiment by numerical simulation of an MRI apparatus. It is a partial front view which shows the magnetic pole structure of the static magnetic field magnet of 2nd Embodiment. It is a fragmentary sectional view which shows the magnetic pole structure of the static magnetic field magnet of 2nd Embodiment. It is a partial front view which shows the magnetic pole structure of the static magnetic field magnet of 3rd Embodiment. It is a fragmentary sectional view which shows the magnetic pole structure of the static magnetic field magnet of 3rd Embodiment. It is a partial front view which shows the magnetic pole structure of the static magnetic field magnet of 4th Embodiment. It is a fragmentary sectional view which shows the magnetic pole structure of the static magnetic field magnet of 4th Embodiment. It is a partial front view which shows the magnetic pole structure of the static magnetic field magnet of 5th Embodiment. It is a fragmentary sectional view which shows the magnetic pole structure of the static magnetic field magnet of 5th Embodiment. It is a partial front view which shows the magnetic pole structure of the static magnetic field magnet of 6th Embodiment. It is sectional drawing of the static magnetic field magnet of 6th Embodiment. It is a partial front view of the static magnetic field magnet of 7th Embodiment in a permanent magnet type | mold MRI apparatus. It is a fragmentary sectional view of the static magnetic field magnet of a 7th embodiment. It is a fragmentary sectional view of the static magnetic field magnet which shows another example of implementation of 7th Embodiment.

  Hereinafter, embodiments will be described with reference to the drawings.

  As shown in FIG. 2, a general medium magnetic field MRI apparatus has a shape in which a disk-shaped upper and lower magnetic poles 1 are connected by a substantially C-shaped return yoke 2, and is located between the upper and lower magnetic poles 1. A static magnetic field is generated in the imaging space 3 in the direction indicated by the arrow 4. The subject 5 is carried to the imaging space 3 by the movable bed 6 and acquires an image. Due to this shape, the MRI apparatus with medium magnetic field is not surrounded by structures in the imaging space 3 into which the subject 5 is inserted with respect to a general high magnetic field horizontal magnetic field type MRI. The person 5 can obtain a feeling of liberation more. As a result, the anxiety of the subject 5 can be removed, and the affected part can always be imaged at the center of the imaging space 3 by moving the bed 6, and further, an operator or the like can be examined from outside the apparatus during imaging. It has the feature that it can assist the person's 5 imaging.

  As shown in FIG. 3, the magnetic pole 1 includes a magnetic pole disc portion 7 using a magnetic material such as iron, a magnetic pole projection portion 8 having a substantially annular shape and using the same magnetic material as the magnetic pole disc portion, and a transparent material such as a silicon steel plate. A silicon steel plate block 9 in which sheet-shaped magnetic bodies having a large magnetic susceptibility and electrical resistance are laminated in a substantially tile shape forms a magnetic circuit together with a return yoke that connects the upper and lower magnetic poles. The static magnetic field is generated by a substantially annular coil 10 using a superconducting material or the like, or a magnetized permanent magnet not shown in the figure. When a superconducting coil is used for an annular coil, as shown in FIG. 3, the coil 10 is housed in a container having a heat insulating structure such as a vacuum container 11, a radiation shield 12, and a liquid helium container 13 from the outside. It is kept at a very low temperature by liquid helium and a refrigerator not shown.

  On the imaging space 3 side of the silicon steel plate block 9, a gradient magnetic field coil 14 is installed in the imaging space 3 to generate a gradient magnetic field 15 in the same direction as the static magnetic field direction 4 in a pulse shape with an intensity proportional to the distance from the center. Has been. In order to generate a gradient magnetic field independently in three orthogonal directions in the imaging space 3, the gradient magnetic field coil is composed of three pairs of upper and lower coils. For example, in FIG. If the direction is y and the vertical direction of the paper is z, the magnetic flux generated by the X gradient magnetic field coil 16 that generates the gradient magnetic field 15 in the x direction in the imaging space 3 has a distribution as indicated by the broken line 17. The Y gradient magnetic field coil that generates the gradient magnetic field in the y direction, which is the vertical direction of the paper, is indicated by 18, and the Z gradient magnetic field coil in the z direction is indicated by 19, and these three coils are formed into a single, substantially disk shape by resin or the like. In addition, a pair of gradient magnetic field coils 14 is constituted by the upper and lower magnetic poles. Further on the imaging space 3 side of the gradient coil 14, an approximately disk-shaped RF coil 20 that generates high-frequency electromagnetic pulses is installed. These are covered with a cover 21 made of FRP resin or the like to constitute the magnetic pole 1. The RF coil 20 may be integrated with the gradient coil 14 or may also serve as the cover 21.

  In addition, although not shown, the MRI apparatus has a power supply device for driving the gradient coil 14 and the RF coil 20, a power supply control, and an image of the signal obtained by the RF coil 12. A computer system is included.

  In FIG. 1, among the lower magnetic poles, the magnetic disk part 7 and the magnetic pole protrusion 8, the silicon steel plate block 9, the heat insulating structure container, the superconducting coil 10 housed therein, the magnetic pole protrusion 8 and the silicon steel plate block 9 are shown. FIG. 2 is a partial front view showing the configuration of a gap or an insulating structure installed between the magnetic pole disk portion 7 divided in the circumferential direction and the magnetic pole disk portion according to the first embodiment of the present invention.

  As shown in FIG. 1, an eddy current is generated in the magnetic pole disk portion 7 as a path 23 by a time-varying gradient magnetic field, but an insulating structure is provided on the surface of the magnetic pole disk portion 7 facing the imaging space. Alternatively, an insulating structure such as FRP prevents the eddy current 23 from forming a large eddy current flow path in the entire magnetic disk part 7. Since the magnetic disk 7 is usually composed of a member having a small electrical resistance such as iron and a large magnetic hysteresis characteristic, the eddy current 23 generated here generates an eddy current magnetic field in the imaging space, and at the same time, A residual magnetic field is generated by a fluctuating magnetic field with time change, which causes image quality degradation.

  For this reason, although the silicon steel plate block 9 having a large electrical resistivity and a large relative magnetic permeability compared to iron or the like is attached to the surface of the magnetic pole disk portion 7, the relative magnetic permeability of the silicon steel plate is approximately not saturated magnetically. It is large at 1.7-1.8 Tesla or less, and it becomes small rapidly at more than that. Further, since a silicon steel plate is generally a thin plate having a thickness of 1 mm or less, and it is necessary to process and use a laminated one, iron having a large saturation magnetization is used for the magnetic pole disc portion 7 as a base for structural attachment. .

  As shown in FIG. 4, in a conventional medium magnetic field MRI apparatus, magnetic pole projections 8 are concentrically arranged in the circumferential direction on an integral iron magnetic pole disk part 7. The magnetic pole protrusion has a structure in which the circular ring is divided into several parts in the circumferential direction for easy manufacture and reduction of eddy current. In this configuration, the magnetic flux 17 generated by the gradient coil generates a large eddy current path 24 in the entire magnetic pole disk.

  In particular, since the magnetic disk part 7 has a larger cross-sectional area in the circumferential direction than the magnetic pole protrusion 8 and is made of magnetically unsaturated iron, it is an important issue to prevent eddy currents from being generated. For this purpose, the silicon steel plate block 9 is installed so that the gradient magnetic field does not directly pass through the magnetic pole disk. However, the present inventor has discovered that an eddy current 24 is generated by a leakage magnetic field that cannot be shielded only by a silicon steel plate block, and the magnetic field and residual magnetic field due to the eddy current affect the image.

  In particular, the magnetic flux density 25 of the static magnetic field using the superconducting coil 10 as the source is high near the outer periphery of the magnetic pole disk part, and the magnetization of this part is also large. This is because the plate thickness of the magnetic pole disk part is about several centimeters to several tens of centimeters. Therefore, when the magnetization increases, the relative permeability decreases, the cross-sectional area of the flow path through which eddy current flows increases, and the flow path resistance decreases. For this reason, it is considered that an eddy current flow path having a long time constant can be easily formed particularly in the outer peripheral portion of the magnetic pole disk portion.

  On the other hand, as shown in FIG. 5, when the permanent magnet 26 is used as the generation source of the static magnetic field 25, the magnetic flux density does not increase even at the outer peripheral portion of the surface of the magnetic pole disc portion 7 on the gradient magnetic field side. For this reason, the magnetization does not increase on the outer peripheral side, and the relative permeability does not decrease. Therefore, even when an eddy current is generated, it is attenuated with a short time constant. Therefore, the superconducting coil in FIG. The impact on is small.

    On the other hand, as shown in FIG. 1 and FIG. 3, in the first embodiment of the present invention, the magnetic pole disk portion 7 is divided in the circumferential direction, and an insulating structure 22 is installed between them, thereby removing the gradient magnetic field coil. Even if an eddy current is generated in the magnetic pole disk part by the magnetic flux 17 like the flow path 23, the eddy current path makes a round within the range divided by the insulating structure 22 on the surface of the magnetic pole disk part 7, and the generated amount And the time constant can be kept short. In particular, by dividing the magnetic pole disk portion 7 in the circumferential direction at the outer peripheral portion, generation of eddy currents having a long time constant can be reduced. If the potential is the same even if the magnetic pole protrusion is divided, the insulating structure may be an extremely thin sheet (about 1 mm or less) or a coating when the member is disposed as an insulating structure. The shape of the magnetic disk and the magnetic disk may be the same as the conventional one, and the influence on the static magnetic field uniformity due to the change in shape can be ignored.

  FIG. 6 shows an example of simulating the temporal change of the eddy current magnetic field for one point in the imaging space. The time change 27 of the eddy current magnetic flux density of the magnetic pole structure according to the prior art and the time change 28 and 29 of the eddy current magnetic field of the magnetic pole structure according to the first embodiment of the present invention are analyzed and compared by magnetic field simulation. Each 28 is a result when the circumferential division is 45 °, and 29 is a result when the circumferential division is 90 °. According to the present invention, it was found that the eddy current magnetic field can be reduced to about 60 to 70% in both the time constant and the value by the magnetic pole shape according to the present invention.

  FIG. 7 is a partial front view of the second embodiment of the present invention, and FIG. 8 is a partial cross-sectional view thereof. In FIG. 7, only the gap or the insulating structure due to the division of the magnetic pole disc portion 7, the magnetic pole projection portion 8, and the magnetic pole disc portion is shown.

  FIG. 8 shows a cross-sectional view in a plane at the position of the insulating structure 22 including the X axis of the three gradient magnetic field axes. The magnetic disk portion is divided in the circumferential direction by a radial insulating structure 22, and each portion has a substantially fan shape. In this embodiment, since all the insulating structures are provided as gaps and are formed in a plane, it is easy to process and assemble, but the effect of reducing eddy currents by the slits on the outer peripheral portion is the same as that of the first embodiment. Can be expected. In addition, by matching the circumferential division with the circumferential division position of the magnetic pole protrusion 8, no eddy current is generated across the divided portion. In the figure, although the division is performed every 90 ° in the circumferential direction, an angle such as 45 ° or 180 ° can be arbitrarily selected in consideration of the effect of reducing eddy currents.

  A partial front view of a third embodiment of the present invention is shown in FIG. 9, and a partial cross-sectional view is shown in FIG. In FIG. 9, only the gap or the insulating structure 22 due to the division of the magnetic disk part 7, the magnetic pole protrusion 8, and the magnetic disk part is shown. FIG. 10 shows a cross-sectional view in a plane including the X axis and at the position of the gap portion 22. In this embodiment, the magnetic disk part 7 is divided into a disk inner part 7a and a disk outer part 7b. The inner disk portion has an integral disk shape, and the outer disk portion has a fan shape with a convex portion on the surface. In other words, in this embodiment, the outer disk portion has a structure in which the inner disk portion is fitted, and the outer disk portion is formed by combining four fan-shaped magnetic members in FIG. Further, the inner part of the disk and the outer part of the disk are electrically insulated by a gap or insulating members 22a and 22b. According to the present embodiment, the central portion of the magnetic pole disk portion having relatively small magnetization is formed into a disk shape, so that the influence on the static magnetic field distribution due to the air gap can be avoided. Generation of a long time constant eddy current can be suppressed at the outer peripheral portion of the magnetic pole disk portion by a radial gap or an insulating structure.

  FIG. 11 is a partial front view of a fourth embodiment of the present invention, and FIG. 12 is a partial cross-sectional view thereof. In FIG. 10, only a gap or an insulating structure due to the division of the magnetic pole disk part, the magnetic pole protrusion part, and the magnetic pole disk part is shown. FIG. 12 shows a cross-sectional view in a plane including the X axis and in the space position. In the present embodiment, the magnetic disk part is divided into a disk center part 7c and a disk outer periphery part 7d. Further, the center of the disk and the outer periphery of the disk are electrically insulated by a gap or an insulating member 22c. According to the present embodiment, by not providing a gap or an insulating member in the central portion where the time constant of the eddy current is short, the eddy current having a long time constant is not affected without affecting the uniformity of the magnetic flux density distribution of the static magnetic field. Can be suppressed.

  FIG. 13 is a partial front view of the fifth embodiment of the present invention, and FIG. 14 is a partial cross-sectional view thereof. In FIG. 13, only a gap or an insulating structure due to the division of the magnetic pole disc portion, the magnetic pole projection portion, and the magnetic pole disc portion is shown. FIG. 14 shows a cross-sectional view at a gap position by a plane including the X axis. In the present embodiment, the magnetic disk portion is the same as the fourth embodiment, but the magnetic pole protrusion 8 has a shape rotated by 22.5 degrees in the circumferential direction around the Z axis of the gradient magnetic field axis. Further, a gap or an insulating structure 22d is disposed between the magnetic pole protrusion and the magnetic pole disk. The magnetic pole protrusion part connects the magnetic pole disk parts by an insulating bolt 30 that stops the magnetic pole protrusion part. However, since a conductive member such as iron is used for the magnetic pole projection, the insulating structure 22d and the insulating bolt 30 prevent a large eddy current flow path from being formed between the divided magnetic pole disks. It is out. The present embodiment can be similarly adopted in any of the first, second, third, and fourth cases. Moreover, the angle divided | segmented into the circumference direction of a magnetic pole protrusion part and a magnetic pole disc part can be arbitrarily selected in addition to 90 degree | times or 45 degree | times shown in Examples 1-5.

  FIG. 15 is a partial front view of the sixth embodiment of the present invention, and FIG. 16 is a partial cross-sectional view thereof. In FIG. 15, only a gap or an insulating structure due to the division of the magnetic disk part, the magnetic pole protrusion part, and the magnetic disk part is shown. FIG. 16 shows a cross-sectional view of a vertical plane including the Y axis. In this case, the Y axis is a direction from the imaging center to the return yoke side. In the present embodiment, the gap or insulating structure 22 on the outer peripheral side of the magnetic pole disc part is not circularly symmetric but is dense on the return yoke side and sparse on the opposite side of the return yoke. This is because the magnetic flux density of the static magnetic field is concentrated and distributed in the direction of the return yoke in the magnetic pole disc portion, so that a lot of gaps or insulating structures are arranged on the return yoke side where the magnetic flux density is large and the relative permeability is small. As a result, the generation of eddy currents with a long time constant can be suppressed, and at the same time, the magnitude and time constant of the eddy current can be made uniform in the circumferential direction of the magnetic pole disk part. In the present embodiment, the structure of the magnetic pole disk part is the fourth example, but the present invention can also be applied to the magnetic pole disk part structure of any of the first to fifth examples.

FIG. 17 is a partial front view of the seventh embodiment of the present invention, and FIGS. 18 and 19 are partial cross-sectional views of the seventh embodiment. In FIG. 17, only a gap or an insulating structure by dividing the magnetic pole disk part, the silicon steel plate block, the magnetic pole protrusion part, and the magnetic pole disk part is shown. The seventh embodiment shows a case where a permanent magnet 26 is used as a generation source of a static magnetic field. Also in this embodiment, the generation of eddy currents with a long time constant can be reduced by dividing the magnetic pole disk part in the circumferential direction, but the magnetic flux density distribution by the permanent magnet does not change significantly between the outer peripheral part and the central part of the magnetic pole disk part. Therefore, the effect is not large in the gap or the insulating structure only in the outer peripheral portion. Accordingly, the long time constant eddy current can be reduced by the radial gap or the insulating structure 22 from the central portion to the outer peripheral portion as shown in FIG. Compared to the case where a superconducting coil is used as a static magnetic field generation source, the magnetization of the surface circle on the imaging area side of the magnetic pole disk is small and the relative permeability is large, so the leakage magnetic field of the gradient magnetic field is close to the surface of the magnetic pole disk. Decreases rapidly at. For this reason, as shown in FIG. 19, the magnetic disk part is divided into a disk part imaging region side 7e and a disk part magnetic pole side 7f, and only the disk part imaging region side is divided by a gap or an insulating structure in the circumferential direction. Further, the disk part imaging region side and the disk part magnetic pole side are electrically insulated from each other by a gap or an insulating structure 22e. According to the present embodiment, it is possible to reduce the gaps or insulating structures generated by dividing the magnetic pole disk portion, and to reduce the influence on the uniform static magnetic field distribution.

DESCRIPTION OF SYMBOLS 1 Magnetic pole 2 Return yoke 3 Imaging space 4 Static magnetic field and arrow which shows the direction 5 Subject 6 Movable bed 7 Magnetic pole disk part
7a Inside the disk
7b Disc outer side
7c Disk center
7d disk outer periphery
7e Disk part imaging area side
7f Disk part magnetic pole side 8 Magnetic pole projection part 9 Silicon steel plate block 10 Substantially circular coil 11 Vacuum container 12 Radiation shield 13 Helium container 14 Gradient magnetic field coil 15 Arrow 16 indicating the strength of the X direction gradient magnetic field X Gradient magnetic field coil 17 X Gradient magnetic field Magnetic flux by coil 18 Y gradient magnetic field coil 19 Z gradient magnetic field coil 20 RF coil 21 Exterior cover 22, 22a, 22b, 22c, 22d, 22e Insulation structure gap or insulation structure 23 Eddy current 24 generated in magnetic disk part Eddy current generated in magnetic pole disk of technology 25 Magnetic flux density by static magnetic field magnet 26 Static magnetic field generating source by permanent magnet 27 Simulation result 28 of eddy current magnetic field by conventional magnetic pole structure 28 Eddy current magnetic field by magnetic pole structure of the present invention Time change simulation result (when the angle of the circular direction division of the magnetic disk part is 45 degrees)
29 Simulation results of time variation of eddy current magnetic field by the magnetic pole structure of the present invention (when the angle of the rotation direction division of the magnetic pole disk is 90 degrees)
30 Insulation bolt

Claims (7)

A pair of static magnetic field magnets arranged opposite to each other centering on the imaging space;
A pair of gradient coils arranged opposite to each other centering on the imaging space;
An RF coil for generating a high-frequency magnetic field in the imaging space;
Have
The static magnetic field magnet is
Has a superconducting magnet as a magnetic field source,
Having a substantially disc-shaped magnetic pole plate having an insulating structure on the surface facing the imaging space;
The insulating structure is provided radially with respect to the central axis of the magnetic pole disc part ,
An annular magnetic pole projection in which the surface of the magnetic pole disc portion facing the imaging space is covered with a silicon steel plate laminated in a tile shape, and protrudes toward the imaging space and is divided in a circumferential direction with respect to the central axis Part
The magnetic resonance imaging apparatus , wherein the magnetic pole protrusion is provided along an inner diameter surface of the superconducting magnet and is fixed to the magnetic magnetic pole disk through an insulating structure . The magnetic resonance imaging apparatus according to claim 1, wherein the insulating structure is made of a thin film-like insulating material such as a sheet or paint . Claim the magnetic pole disc portion, which in point located inside in the direction of the central axis, characterized in that the disc-shaped insulating structure having a vertical bottom with respect to the central axis is provided The magnetic resonance imaging apparatus according to claim 1 or 2 . The magnetic magnetic pole disk part is divided into a disk center part and a disk outer peripheral part,
An insulating structure is provided between the disc central portion and the disc outer peripheral portion,
Magnetic resonance imaging apparatus according to any one of claims 1 to 3, characterized in that said disc outer peripheral portion is Oite divided in the circumferential direction with respect to the central axis. The magnetic pole disk unit according to claim claim 1, before Symbol pole protrusions, characterized in that the insulating structure along an angular same, or angle of an integral multiple being divided is provided radially 5. The magnetic resonance imaging apparatus according to any one of 4 above . The magnetic resonance imaging apparatus according to claim 5 , wherein the magnetic magnetic pole disk parts divided in the circumferential direction are fastened to each other by magnetic pole protrusions divided in the circumferential direction . The magnetic pole disk unit, a magnetic resonance imaging apparatus according to any one of claims 1 to 4, characterized in that it comprises the insulating structure at different angular positions in the circumferential direction.