JP4254921B2 - Magnetic shield room for magnetic resonance imaging equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic shield room for a magnetic resonance imaging apparatus.
[0002]
[Prior art]
The magnetic resonance imaging device (MRI device) is a device that forms a strong magnetic field in the central space of the magnetic field, and if the generated strong magnetic field leaks to the surroundings, a cardiac pacemaker is used with a magnetic field strength of 0.5 mT or more. May adversely affect the patient who is living, and may adversely affect the surrounding display at a magnetic field strength of 0.1 mT or more.
[0003]
Further, when an external magnetic field enters the MRI apparatus, it becomes difficult to stably maintain a uniform magnetic field.
[0004]
Therefore, in order to avoid the influence of the magnetic field on the surroundings and the influence of the external magnetic field, the MRI apparatus needs to be installed in the magnetic shield room.
[0005]
This magnetic shield room will be described below.
13 and 14 are schematic external views of a magnetic shield room for an MRI apparatus.
[0006]
As shown in FIG. 13, plate-like magnetic shielding materials (for example, silicon steel plate, iron, permalloy, etc.) are arranged on the ceiling surface, wall surface, and floor surface of the magnetic shield room 8. The plate-like magnetic shielding materials arranged on each surface such as the ceiling surface are magnetically joined to each other. A magnetic shield room as shown in FIG. 13 is described in Non-Patent Document 1.
[0007]
FIG. 14 shows the spread of the leakage magnetic field 13 in the plane of the shield room shown in FIG. 13 and the horizontal direction of the MRI apparatus.
[0008]
As shown in FIG. 14, if an opening such as an inspection window 9 is provided in a portion of the wall surface of the magnetic shield room 8 where the magnetic flux density of the leakage magnetic field 13 from the MRI apparatus 12 is high, the leakage magnetic field from the MRI apparatus 12 is provided. Will spread outside the magnetic shield room 8.
[0009]
For this reason, it is necessary to make the inspection window 9 as small as possible. In the conventional magnetic shield room 8, the sizes of the inspection window 9, the entrance 10, the apparatus entrance 11, and the like are limited. (Patient) gets a closed impression because the shield room 8 is narrow.
[0010]
In addition, it is difficult for an operator (radiologist) of the MRI apparatus 12 to observe the inside of the magnetic shield room 8, and the work efficiency is poor.
[0011]
Therefore, Patent Document 1 describes a method of canceling a vertical (top and bottom direction (Z-axis direction)) leakage magnetic field from the MRI apparatus 12 using a canceling coil.
[0012]
15 and 16 are explanatory diagrams of the technique described in Patent Document 1. FIG. 15 shows a case where one canceling coil 14 is used, and FIG. 16 shows a plurality of canceling coils 15, 16 and 17. It is an example in the case of using.
[0013]
The technique described in Patent Publication 1 is a technique that has a suppression effect on the leakage magnetic field in the magnetic field central axis direction of the main coil 1 of the magnet 2 in the MRI apparatus.
[0014]
[Non-Patent Document 1]
“Examination of magnetic field analysis method for magnetic shield room design”, Journal of Applied Magnetics Society of Japan, Vol.18, No.5, 1994, 934-939 [Patent Publication 1]
Japanese Patent Laid-Open No. 2002-143126
[Problems to be solved by the invention]
However, although the technique described in Patent Document 1 has the effect of suppressing the vertical leakage magnetic field from the MRI apparatus, it has the effect of suppressing the leakage magnetic field in the circumferential direction (side direction) of the magnetic field center. Is small.
[0016]
For this reason, in the case of the technique described in Patent Document 1, it is necessary to use a magnetic shield material for the leakage magnetic field in the circumferential direction (side direction) of the magnetic field center as in the conventional magnetic shield room. Subjected to the size of the inspection window and entrance, subjects in the magnetic shield room are still subject to a closed impression.
[0017]
Moreover, it was difficult for the operator of the MRI apparatus to observe the inside of the magnetic shield room, and the work efficiency was poor.
[0018]
An object of the present invention is to realize a magnetic shield room for a magnetic resonance imaging apparatus in which the wall surface of the magnetic shield room is open, and the size of the inspection window and the entrance / exit and the restriction on the installation position can be reduced.
[0019]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is configured as follows.
(1) In the magnetic shield room for a magnetic resonance imaging apparatus that houses the magnetic resonance imaging apparatus, part or all of the side surface of the magnetic shield room is formed of an RF shield material, and among the side surfaces formed of the RF shield material , A cross section of the magnetic field center of the magnetic resonance imaging apparatus is provided with one or more sets of magnetic field suppression coils in which currents flowing in opposite directions flow on the surface formed in a direction parallel to the central magnetic field direction of the magnetic resonance imaging apparatus. And the coil surface is arranged parallel to the magnetic shield room surface .
(2) In the magnetic shield room for a magnetic resonance imaging apparatus that houses the magnetic resonance imaging apparatus, part or all of the side surface of the magnetic shield room is formed of an RF shield material, and among the side surfaces formed of the RF shield material, One of the two regions divided by the cross-section of the central magnetic field of the magnetic resonance imaging apparatus is placed on a surface formed in a direction parallel to the central magnetic field direction of the magnetic resonance imaging apparatus. Place in one of these areas .
(3) Preferably, in the above (1) and (2), the RF shield material is a permeable shield material .
(4) Preferably, in the above (1) and (2), the magnetic field suppression coil is a planar coil.
[0022]
( 5 ) Preferably, in the above (1) or (2), the coil is disposed on a portion of the surface forming the magnetic shield room where no ferromagnetic material is disposed .
[0023]
( 6 ) Preferably, in the above ( 5 ), the portion where the ferromagnetic material is not disposed is a window or an entrance portion.
( 7 ) Moreover, Preferably, in said (1)-( 6 ), the center part of the said magnetic field suppression coil is transparent.
[0024]
A magnetic field suppression coil is provided, and the magnetic field suppression coil is disposed in each or only one of the two regions separated by the equator plane of the central magnetic field by the magnet of the magnetic resonance imaging apparatus. The magnetic field generating coil generates a magnetic field toward the inside of the magnetic shield room or a magnetic field toward the outside of the magnetic shield room, and suppresses the generated magnetic field from the magnet.
[0025]
Therefore, the circumferential leakage magnetic field at the center of the magnetic field can be efficiently suppressed, and the restriction on the size of the inspection window on the wall surface and the entrance / exit can be relaxed. A magnetic shield room can be realized.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram showing a magnet 2 used in a magnetic resonance imaging apparatus and a leakage magnetic field of the magnet 2 alone. In FIG. 1, the direction of the central magnetic field of the magnet 2 is the positive direction of the Z axis, and the transverse direction of the central magnetic field of the magnet 2 is the X axis.
[0027]
As shown in FIG. 1, the main component of the leakage magnetic field springs in the + Z direction of the magnet 2, proceeds in the X-axis direction, passes the side of the magnet 2, and follows the path returning from the −Z direction to the magnet 2. (This magnetic flux flow is called the primary component).
[0028]
The present invention efficiently suppresses the leakage magnetic field in the X-axis direction shown in FIG.
[0029]
2 and 3 are schematic configuration explanatory views of the first embodiment of the present invention.
2 and 3, a set of coils 3a and 3b (hereinafter referred to as room coils) is formed on the X-axis direction surface (side surface) of the magnetic shield room, and the surface of the coils 3a and 3b and the side surface of the magnetic shield room are connected. Arrange them so that they are parallel.
[0030]
Each of the pair of room coils (magnetic field suppression coils) 3a and 3b is arranged in a + Z region and a −Z region, respectively, separated by the equator plane of the central magnetic field by the magnet 2.
[0031]
At this time, a current is passed through the room coil 3a arranged on the + Z side so as to generate a magnetic field directed toward the inside (indicated by an arrow) of the magnetic shield room.
[0032]
Further, a current in the direction opposite to that of the room coil 3a on the + Z side is passed through the room coil 3b on the −Z side, and a magnetic field directed to the outside (indicated by an arrow) of the magnetic shield room is generated.
[0033]
The magnetic flux generated from one set of room coils 3a and 3b follows a path indicated by a dotted line in FIG. The direction of the magnetic flux generated by the room coils 3a and 3b is a direction in which the primary component, which is the main component of the leakage magnetic field from the magnet 2, is suppressed.
[0034]
That is, the direction of the leakage magnetic field in the + Z side region is the downward direction outside the shield room, and the direction of the leakage magnetic field in the −Z side region is the downward direction inside the shield room.
[0035]
Therefore, as described above, if the room coil 3a is configured to generate a magnetic field directed to the inside of the magnetic shield room, and the room coil 3b is configured to generate a magnetic field directed to the outside of the magnetic shield room, 0. The 5 mT (5 gauss) line is suppressed as shown by the two-dot chain line.
[0036]
Here, the reason why the line is defined as a 0.5 mT line is that in a general magnetic shield room, a 0.5 mT (5 gauss) line is accommodated in the magnetic shield room for the leakage magnetic field of the magnet 2.
[0037]
5 and 6 are diagrams showing calculation results of magnetic field analysis. FIG. 5 shows a leakage magnetic field (ZX plane) in a single magnet without a magnetic shield, and FIG. 6 shows a set of room coils in the side direction of the magnet. The leakage magnetic field (ZX plane) when 3a and 3b are arranged is shown.
[0038]
As apparent from FIGS. 5 and 6, the leakage magnetic field outside the room coil is suppressed from 5.0 mT (50 gauss) to 2.5 mT (25 gauss).
[0039]
This result indicates that, in principle, the leakage magnetic field can be arbitrarily controlled by the current values and the number of turns of the room coils 3a and 3b.
[0040]
Further, the magnetic field strength locally increases in the vicinity of the + Z side region end and the −Z side region end of the room coil. However, since the magnetic field of the room coil is attenuated faster than the leakage magnetic field from the magnet, there is no problem at a position several tens of centimeters away from the room coil.
[0041]
As described above, according to the first embodiment of the present invention, the room coil 3a includes a pair of room coils 3a and 3b, and the room coil 3a is disposed in the + Z region separated by the equatorial plane of the central magnetic field by the magnet 2. The room coil 3b is disposed in the −Z region. The room coil 3a generates a magnetic field toward the inside of the magnetic shield room, and the room coil 3b generates a magnetic field toward the outside of the magnetic shield room.
[0042]
Therefore, according to the first embodiment of the present invention, the circumferential leakage magnetic field at the center of the magnetic field by the magnet 2 can be efficiently suppressed, and the size limit of the inspection window and the entrance / exit on the wall surface can be relaxed. It is possible to realize a magnetic shield room for a magnetic resonance imaging apparatus in which the wall surface of the magnetic shield room is open.
[0043]
FIG. 4 is a schematic explanatory diagram of a main part of a magnetic shield room according to the second embodiment of the present invention. The second embodiment is an example in the case of using two sets of room coils 4a and 4b, and further includes a set of coils similar to the room coils 3a and 3b in the first embodiment in the Y-axis direction (Z It is an example of being arranged additionally in the direction orthogonal to the axial direction and the X-axis direction. This example is a coil arrangement example that suppresses a leakage magnetic field in a region extending in the Y-axis direction.
[0044]
In the example shown in FIG. 4, the direction of the central magnetic field of the magnet 2 is the + Z-axis direction, as in the examples shown in FIGS. A plurality of room coils are arranged in the Y direction in a region (+ Z side or −Z side) separated by a cross section of the central magnetic field.
[0045]
At this time, currents in the same direction are passed through the coils in the same region among the regions separated by the cross section of the central magnetic field. That is, magnetic fluxes are generated in the −X-axis direction in the room coil 4a in the + Z side region and in the + X-axis direction in the room coil 4b in the −Z side region.
[0046]
FIG. 7 is a diagram illustrating a calculation example when the coil arrangement for suppressing the leakage magnetic field in the region extending in the Y direction according to the second embodiment of the present invention is performed.
[0047]
According to the second embodiment, the same effects as those of the first embodiment can be obtained, the size of each room coil can be reduced, and the manufacturability and installation workability can be improved.
[0048]
FIG. 8 is a schematic explanatory diagram of a main part of a magnetic shield room according to the third embodiment of the present invention. This third embodiment is an example in which the leakage magnetic field on only one side of the region separated by the cross section of the magnetic field center of the magnet 2 is suppressed.
[0049]
This third embodiment is an example of suppressing the leakage magnetic field of the portion in the region on the + Z side separated by the cross section of the central magnetic field of the magnet 2 in the surface other than the Z-axis direction.
[0050]
An example in the case of arranging one single-side room coil 5 is shown in FIG. 9, and an example in the case of arranging two single-sided room coils 6 is shown in FIG.
[0051]
These room coils 5 and 6 are arranged in the vicinity of the portion that suppresses the leakage magnetic field so that all of the one-side room coils are within the + Z side region. The direction of the current at this time is a direction in which a magnetic field directed toward the inside of the magnetic shield room is generated.
[0052]
Further, the direction of the current when suppressing the leakage magnetic field in the portion in the −Z side region separated by the equator plane of the central magnetic field is a direction in which a magnetic field directed to the outside of the magnetic shield room is generated.
[0053]
In the third embodiment as well, the magnetic shield room for the magnetic resonance imaging apparatus can be realized in which the wall surface of the magnetic shield room is open and the size of the inspection window and the entrance / exit and the restriction on the installation position can be reduced.
[0054]
As described above, a permeable magnetic shield room can be configured by the room coil arrangement method according to the embodiment of the present invention.
[0055]
In other words, by using an RF shield material having transparency such as a metal mesh for the magnetic shield room, a magnetic shield room for an MRI apparatus having transparency can be configured. If this RF shield material is configured to support the above-described room coil of the present invention, it is excellent in transparency and can suppress the leakage magnetic field in the direction of the side surface of the central magnetic field caused by the magnet 2. Miniaturization is possible.
[0056]
FIG. 11 is a diagram showing an arrangement example of room coils when a vertical (vertical magnetic field type) magnet 2 is arranged in the magnetic shield room 7.
[0057]
The direction of the magnetic field of the vertical magnet is the + Z direction. In this case, room coils are arranged on the sides of the magnet 2, that is, in the X and Y directions. In FIG. 11, the boundary line where the cross section of the central magnetic field intersects the wall surface is indicated by a one-dot chain line. At this time, a magnetic flux directed in the −X direction is generated in the room coil located on the + Z side (upper side) of the alternate long and short dash line.
[0058]
On the other hand, the room coil located on the −Z side (lower side) generates a magnetic flux in the opposite direction to the room coil on the + Z side.
[0059]
Moreover, about the door part of a room coil, one set of coils is arrange | positioned in the area | region separated by the dashed-dotted line. Also in this case, a magnetic flux directed in the −X direction is generated in the room coil positioned on the + Z side (upper side) of the alternate long and short dash line. Then, a magnetic flux in the opposite direction to the room coil on the + Z side is generated in the room coil located on the −Z side (lower side).
[0060]
FIG. 12 is a diagram illustrating an example of suppressing a leakage magnetic field from a portion where no magnetic shield material is disposed, for example, a window portion. The example shown in FIG. 12 shows a case where a vertical magnet having a central magnetic field direction of + Z axis is arranged. Furthermore, in FIG. 12, the boundary line where the cross section of the central magnetic field intersects the wall surface is indicated by a one-dot chain line. At this time, a magnetic flux in the −X direction is generated in the room coil located on the + Z side (upper side) of the one-dot chain line.
[0061]
On the other hand, the room coil located on the −Z side (lower side) generates a magnetic flux in the opposite direction to the room coil on the + Z side.
[0062]
Thus, the present invention is effective when a large window or entrance is provided in a ferromagnetic magnetic shield room.
[0063]
In general, there are the following three methods for suppressing the leakage magnetic field of a magnet used in a magnetic resonance imaging apparatus.
[0064]
(1) Passive shield method using a ferromagnetic material (2) Active shield method using only a coil (3) Hybrid method using both a ferromagnetic material and a coil The present invention is any of the above (1) to (3) The method can also be applied. Of course, the present invention is also effective for a magnet having no magnetic field leakage field suppressing means.
[0065]
The present invention is applicable to either a horizontal magnetic field type magnet in which the Z-axis direction is a horizontal direction or a vertical magnetic field type magnet in which the Z-axis direction is a vertical direction.
[0066]
【The invention's effect】
According to the present invention, it is possible to realize a magnetic shield room for a magnetic resonance imaging apparatus in which the wall surface of the magnetic shield room is open and the size of the inspection window and the entrance / exit and the restriction on the installation position can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a magnet used in a magnetic resonance imaging apparatus and a leakage magnetic field of the magnet alone.
FIG. 2 is an explanatory diagram of a schematic configuration of a first embodiment of the present invention.
FIG. 3 is a schematic configuration explanatory view of a first embodiment of the present invention. FIG. 4 is a schematic explanatory diagram of a main part of a magnetic shield room according to a second embodiment of the present invention.
FIG. 5 is a diagram showing a leakage magnetic field (ZX plane) in a single magnet without a magnetic shield.
FIG. 6 is a diagram showing a leakage magnetic field (ZX plane) when a pair of room coils are arranged in the side surface direction of the magnet.
FIG. 7 is a diagram illustrating a calculation example in a case where a coil arrangement that suppresses a leakage magnetic field in a region extending in the Y direction according to the second embodiment of the present invention is used.
FIG. 8 is a schematic explanatory diagram of a main part of a magnetic shield room according to a third embodiment of the present invention.
FIG. 9 is a diagram showing an example in which one single-side room coil is arranged in the third embodiment.
FIG. 10 is a diagram showing an example in the case of arranging two one-side room coils in the third embodiment.
FIG. 11 is a diagram showing an arrangement example of a room coil when a vertical magnet is arranged in a magnetic shield room.
FIG. 12 is a diagram illustrating an example of suppressing a leakage magnetic field from a portion where a magnetic shield material is not disposed.
FIG. 13 is a schematic external view of a general magnetic shield room.
FIG. 14 is an explanatory diagram of a plane of a general magnetic shield room and a leakage magnetic field.
FIG. 15 is a diagram illustrating an arrangement example of leakage magnetic field suppression coils in the prior art.
FIG. 16 is a diagram illustrating an arrangement example of leakage magnetic field suppression coils in the prior art.
[Explanation of symbols]
1 Main coil 2 Magnet 3a, 3b Room coil 4a, 4b Room coil 5, 6 Room coil 7 Magnetic shield room

Claims (7)

In a magnetic shield room for a magnetic resonance imaging apparatus that houses the magnetic resonance imaging apparatus,
Part or all of the side surface of the magnetic shield room is formed of an RF shield material, and of the side surfaces formed of the RF shield material, the surface is formed in a direction parallel to the central magnetic field direction of the magnetic resonance imaging apparatus. One or a plurality of sets of magnetic field suppression coils that have mutually opposite currents are sandwiched across the cross section of the magnetic field center of the magnetic resonance imaging apparatus, and the surface of the coil is parallel to the surface of the magnetic shield room A magnetic shield room for a magnetic resonance imaging apparatus. In a magnetic shield room for a magnetic resonance imaging apparatus that houses the magnetic resonance imaging apparatus,
Part or all of the side surface of the magnetic shield room is formed of an RF shield material, and of the side surfaces formed of the RF shield material, the surface is formed in a direction parallel to the central magnetic field direction of the magnetic resonance imaging apparatus. A magnetic shield room for a magnetic resonance imaging apparatus, wherein one or a plurality of magnetic field suppression coils are arranged in one of two areas divided by a cross section of a central magnetic field of the magnetic resonance imaging apparatus . In a magnetically shielded room for a magnetic resonance imaging apparatus according to claim 1 or 2 wherein, the magnetically shielded room for a magnetic resonance imaging apparatus said RF shielding material which is a transparent shielding material.   3. The magnetic shield room for a magnetic resonance imaging apparatus according to claim 1, wherein the magnetic field suppression coil is a planar coil.   3. The magnetic shield room according to claim 1, wherein the coil is disposed on a portion of the surface forming the magnetic shield room where no ferromagnetic material is disposed. 6. The magnetic shield room according to claim 5, wherein the portion where the ferromagnetic material is not disposed is a window or an entrance portion. In a magnetically shielded room according to any one claim of claims 1 to 6, the magnetic shield room, wherein the central portion of the magnetic field suppression coils is transparent.

Images