JP2016123802A - Superconducting magnet apparatus and magnetic resonance imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize uniform high magnetic field without enlarging a superconducting coil.SOLUTION: The superconducting magnet apparatus of the present invention comprises a superconducting coil 111 generating magnetic flux of a predetermined direction in space at the side of internal diameter, and a superconducting member 122 which make the magnetic flux in the space at the side of the internal diameter to converge at the side of central axis of the magnetic flux, and it is characterized by the shape of the inner wall of the cylindrical superconducting member 122. That is, when the superconducting member 122 is sectioned into plane surface vertical to the central axis of the cylinder, the area of a region surrounded by the superconducting member 122 is changed according to the position along with direction of the magnetic flux from one end part of the cylindrical superconducting member 122 to the other end part in a manner where at least 2 positions having minimum value are provided on the way reaching the other end part.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a superconducting magnet apparatus and a magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus) using the superconducting magnet apparatus.

  An MRI (Magnetic Resonance Imaging) apparatus is an indispensable apparatus in the medical field. When a high-resolution captured image, for example, a clear captured image of a blood vessel in the brain, is required, an MRI apparatus that can apply a high magnetic field to the subject is used. In the medical field, MRI apparatuses capable of generating a magnetic field of several Tesla have already been put into practical use.

  In an MRI apparatus, when a high magnetic field is to be realized, there is a problem that the superconducting magnet that generates the high magnetic field is enlarged. When the superconducting magnet is increased in size, the manufacturing cost increases due to the material cost of the material constituting the superconducting magnet, and a large space is also required for installing the MRI apparatus, which increases the operation cost. Therefore, there is a need for an MRI apparatus that can realize a high magnetic field without increasing the size of the superconducting magnet.

  Patent Document 1 discloses a technique for realizing a high magnetic field by causing a magnetic flux generated by a superconducting magnet or the like to pass through and converge inside a cylindrical or hollow conical superconducting member having a wide inlet and a narrow outlet. . Patent Document 2 discloses a technique for making a magnetic field uniform in a cylinder of the superconducting member by disposing a cylindrical superconducting member inside a coil of a superconducting magnet such as a solenoid coil. . In these prior arts, the so-called Meissner effect is commonly used, in which superconductors in a superconducting state exhibit complete diamagnetism and magnetic flux does not enter the superconductor.

Japanese Patent No. 5158799 Japanese Patent No. 3184678

  Patent Document 1 discloses a technique for realizing a high magnetic field by converging a magnetic flux, but does not disclose a technique for making the magnetic flux uniform in the high magnetic field. Patent Document 2 does not disclose a technique for realizing a high magnetic field, but discloses a technique for using a superconducting cylindrical member inserted in a solenoid coil to equalize the magnetic flux inside the cylinder. ing. However, as shown below, even if the techniques disclosed in Patent Documents 1 and 2 are combined, an MRI apparatus capable of obtaining a uniform high magnetic field without increasing the size of the superconducting magnet can be realized. Not exclusively.

  Incidentally, according to Paragraph 0032, FIG. 2, Paragraph 0035, FIG. 5 and the like of Patent Document 2, the length of 128 mm in the magnetic flux direction of the cylindrical member (24, 23) in the superconducting state used for uniformizing the magnetic flux has its inner diameter. It is about 4 times 30mm. That is, the length of the cylindrical member is sufficiently larger than its inner diameter. In addition, the length of the cylindrical members (24, 23) is longer than the length of the solenoid coil 11 of 96 mm, and a part of the cylindrical member protrudes outside the solenoid coil 11. If the superconducting magnet having such a configuration is assumed, the influence of the non-uniformity of the magnetic flux at the end of the cylinder is mitigated at the central portion inside the cylinder. .

  On the other hand, in an actual MRI apparatus, the length of the cylindrical member for equalizing the magnetic flux cannot always be made sufficiently larger than the inner diameter, and the cylindrical member is projected to the outside of the superconducting magnet. It is not always possible. Therefore, it cannot be said that the conventional technique alone can realize an MRI apparatus capable of obtaining a uniform high magnetic field without increasing the size of the superconducting magnet.

  In view of the above-described problems of the prior art, the present invention provides a superconducting magnet device capable of realizing a uniform high magnetic field without increasing the size of the superconducting coil, and an MRI apparatus using the superconducting magnet device. The purpose is to do.

  A superconducting magnet device according to the present invention has a superconducting coil that generates a magnetic flux in a fixed direction in a space on the inner diameter side, and a superconducting member that converges the magnetic flux in the inner diameter side space of the superconducting coil to the central axis side of the magnetic flux. A cylindrical magnetic flux converging portion, and when the cylindrical magnetic flux converging portion is cut along a plane perpendicular to the central axis of the magnetic flux, the cylindrical magnetic flux converging portion is surrounded by a superconducting member included in the cylindrical magnetic flux converging portion The area of the region changes from one end of the cylindrical magnetic flux converging portion to the other end along the direction of the magnetic flux, and at least 2 until the other end is reached. It takes two minimum values.

  ADVANTAGE OF THE INVENTION According to this invention, the superconducting magnet apparatus which can implement | achieve a uniform high magnetic field, without enlarging a superconducting coil, and the MRI apparatus using the superconducting magnet apparatus are provided.

The figure which showed the example of the external appearance perspective view of the MRI apparatus which concerns on the 1st Embodiment of this invention. The figure which showed typically the example of the cross-section in the position of AA of the MRI apparatus of FIG. It is the figure which showed the example of the shape of the superconducting member of a magnetic flux convergence part, (a) is an example of the perspective view of a superconducting member, (b) is the example of the side view seen from the direction of the central axis B of a superconducting member, (C) is the figure which showed the example of the cross-section when cut | disconnecting in the plane containing the central axis B of a superconducting member. It is a figure explaining the effect of the magnetic flux equalization by the superconducting member which concerns on 1st Embodiment, (a) is a figure which showed the mode of the magnetic flux in the cylinder of the superconducting member of a comparative example, (b) is this The figure which showed the mode of the magnetic flux in the cylinder of the superconducting member which concerns on embodiment. The figure which showed the modification of the cross-sectional shape of a superconducting member. The figure which showed the other modification of the cross-sectional shape of the superconducting member. The figure which showed the example of the external appearance perspective view of the MRI apparatus which concerns on the 2nd Embodiment of this invention. The figure which showed typically the example of the cross-section in the position of CC of the MRI apparatus of FIG. The figure which showed the example of the perspective view of the superconducting member of the magnetic flux converging part (lower magnetic flux converging part) attached to a lower superconducting magnet. The figure explaining the effect of the magnetic flux convergence by the superconducting member which concerns on 2nd Embodiment, and magnetic flux equalization.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, in each drawing, the same code | symbol is attached | subjected to a common component and the overlapping description is abbreviate | omitted.

<First Embodiment>
FIG. 1 is a view showing an example of an external perspective view of the MRI apparatus 100 according to the first embodiment of the present invention, and FIG. 2 is a cross-sectional view of the MRI apparatus 100 in FIG. It is the figure which showed the example typically. As shown in FIGS. 1 and 2, the main part of the MRI apparatus 100 is configured such that a cylindrical superconducting magnet 11 is accommodated in a cylindrical gantry 10 that is a support housing. In this embodiment, the magnetic flux converging part 12 is further attached to the inner diameter side of the cylindrical superconducting magnet 11.

  Here, the space in the cylinder of the cylindrical magnetic flux converging unit 12 is called a subject insertion region 15, and the subject 4 placed on the table 2 is inserted therein. The table driving unit 3 inserts and removes the table 2 on which the subject 4 is placed in accordance with an instruction from the control device 5.

  In addition to the magnetic flux converging unit 12, a magnetic field gradient coil (not shown), a high-frequency coil for acquiring a magnetic resonance signal, and the like are disposed in the cylinder (inner diameter side) of the cylindrical superconducting magnet 11. The control device 5 controls currents and signals supplied to these coils, generates a two-dimensional or three-dimensional image of the subject 4 using a magnetic resonance signal obtained from the high-frequency coil, and displays the generated image as a display device. 6 is displayed.

  Further, as shown in FIG. 2, the superconducting magnet 11 is housed in a vacuum vessel 112 and is constituted by a superconducting coil 111 surrounded by a radiation shield (not shown). At this time, the superconducting coil 111 may be cooled via a refrigerant such as liquid helium supplied from the first cooling unit 13 or may be cooled via a heat conducting member connected to the first cooling unit 13. Good. When the superconducting coil 111 is cooled via a refrigerant, the superconducting coil 111 is accommodated in a refrigerant container (not shown) provided inside a radiation shield (not shown).

  Further, the magnetic flux converging unit 12 is configured such that a superconducting member 122 attached to an installation base 121 is housed in a vacuum vessel 124 and is further surrounded by a radiation shield 123. The vacuum vessel 124 is fixed to the inner diameter surface of the vacuum vessel 112 of the cylindrical superconducting magnet 11 via a fastening member (not shown), and the installation table 121 to which the superconducting member 122 is attached attaches the load support 120. And is attached to the surface of the vacuum vessel 124 on the superconducting magnet 11 side. At this time, the superconducting member 122 may be cooled via a refrigerant such as liquid helium supplied from the second cooling unit 14 or may be cooled via a heat conducting member connected to the second cooling unit 14. Good. When the superconducting member 122 is cooled via a refrigerant, the superconducting member 122 is assumed to be accommodated in a refrigerant container (not shown) provided inside the radiation shield 123.

Here, the first cooling unit 13 and the second cooling unit 14 are controlled and operated independently of each other, and the vacuum vessel 112 and the vacuum vessel 124 are not in communication with each other. Therefore, the cooling temperature of the superconducting coil 111 and the cooling temperature of the superconducting member 122 may be different from each other. Therefore, for example, niobium titanium (NbTi), niobium tin (Nb ₃ Sn) or the like is used as the wire of the superconducting coil 111, and a high-temperature superconducting material is used as the superconducting member 122 of the magnetic flux converging unit 12. Also good.

  Further, as shown in FIG. 2, the heater 16 may be disposed in the middle of the refrigerant path or the heat conduction path connecting the second cooling unit 14 and the superconducting member 122. The role of the heater 16 in this case will be described later.

  As described above, in the MRI apparatus 100 having the configuration as shown in FIGS. 1 and 2, the cylindrical superconducting magnet 11 has a direction substantially parallel to the central axis of the cylinder, that is, the body of the subject 4. Magnetic flux is generated in a direction substantially parallel to the axis. Such an MRI apparatus 100 is often referred to as a horizontal MRI apparatus. In the present embodiment, as described above, the cylindrical magnetic flux converging unit 12 including the superconducting member 122 is further disposed in the cylinder of the superconducting magnet 11.

  Here, the installation base 121 and the vacuum vessel 124 of the magnetic flux converging unit 12 are made of nonmagnetic stainless steel or the like, and the superconducting member 122 is made of a superconductor that is in a superconducting state below a predetermined critical temperature. Therefore, when the superconducting member 122 becomes a predetermined critical temperature or less, the magnetic flux passing through the cylinder of the superconducting magnet 11 is rejected to the outside of the superconducting member 122 of the magnetic flux converging unit 12 and converged to the central axis side of the magnetic flux. It is done. As a result, the magnetic flux density (magnetic field strength) in the cylindrical space of the cylindrical magnetic flux converging unit 12, that is, the subject insertion region 15, is increased.

  Furthermore, the shape of the superconducting member 122 of the magnetic flux converging unit 12 will be described in detail with reference to FIG. Here, FIG. 3 is a diagram showing an example of the shape of the superconducting member 122, (a) is an example of a perspective view of the superconducting member 122, and (b) is a view from the direction of the central axis B of the superconducting member 122. (C) is a diagram showing an example of a cross-sectional structure when cut along a plane including the central axis B of the superconducting member 122.

  As shown in FIGS. 3A to 3C, the superconducting member 122 has a cylindrical appearance, but has the following two features. One of them is that a slit 125 is provided in a cylindrical superconducting member 122. The slit 125 is a gap provided on the cylindrical side surface of the superconducting member 122 along the central axis B, and prevents the circulating current generated around the magnetic flux by the magnetic flux passing through the cylinder of the superconducting member 122. It is. Note that the slit 125 is not a mere gap, but is usually filled with an insulating resin or the like in the gap. Further, the number of slits 125 provided in the superconducting member 122 is not limited to one and may be two or more.

  Another feature of the shape of the superconducting member 122 according to this embodiment is that irregularities are formed on the cylindrical inner wall of the cylindrical superconducting member 122. The unevenness is formed in order to improve the uniformity of the magnetic flux in the cylinder of the superconducting member 122, that is, in the subject insertion region 15. Therefore, the shape of the unevenness is substantially rotationally symmetric about the central axis B of the superconducting member 122, and the cross-sectional shape when cut along a plane including the central axis B is, for example, shown in FIG. It has a shape like this. That is, the superconducting member 122 has a cross-sectional structure that gradually increases in thickness from one end portion toward the back of the cylinder, becomes thinner near the center, and becomes thicker again at the other end portion.

  In other words, when the superconducting member 122 is cut along a plane perpendicular to the central axis B, the area of the region surrounded by the superconducting member 122 (however, it is assumed that there is no slit 125) is one of the cylinders of the superconducting member 122. Between the end portion and the other end portion, two minimum values and one maximum value are taken. In other words, the path of the magnetic flux passing through the cylinder of the superconducting member 122 becomes gradually narrower from one end to the back and gradually becomes wider from a certain point. And after passing the central part vicinity of a cylinder, it will become narrow again, and it will become wide again before the other edge part.

  4A and 4B are diagrams for explaining the effect of uniforming the magnetic flux by the superconducting member 122. FIG. 4A is a diagram showing an example of the magnetic flux in the cylinder of the superconducting member 122a of the comparative example, and FIG. It is the figure which showed the example of the magnetic flux in the cylinder of the superconducting member 122 which concerns on a form. In FIGS. 4A and 4B, illustrations of the non-magnetic installation base 121, the vacuum vessel 124, and the like are omitted.

  In the comparative example of FIG. 4A, it is assumed that the inner wall of the superconducting member 122a is not uneven. Accordingly, the cross-sectional area through which the magnetic flux (streamlines shown with arrows) on the inner diameter side of the superconducting magnet 11 can pass is reduced by the Meissner effect in the subject insertion region 15 whose side is surrounded by the superconducting member 122a. The magnetic flux density, that is, the magnetic field strength in that region increases. However, the cross-sectional area through which the magnetic flux can pass in the cylinder of the superconducting member 122a becomes a substantially constant cross-sectional area once it becomes smaller as it goes deeper. Therefore, the magnetic flux in the subject insertion region 15 at the center of the cylinder of the superconducting member 122a tends to be closer to the central axis side of the magnetic flux due to the influence of the end effect of the superconducting member 122a. As a result, the magnetic flux uniformity in the subject insertion region 15 is not sufficiently ensured.

  On the other hand, in the case of FIG. 4B as an example of the present embodiment, the cross-sectional area through which the magnetic flux can pass in the cylinder of the superconducting member 122 becomes smaller as it goes further, and then becomes larger again. That is, the inner wall of the superconducting member 122 has a convex portion in the vicinity of both end portions and a concave portion in the central portion. Therefore, the magnetic flux passing through the cylinder of the superconducting member 122 is converged by the convex portion near the end portion, and the magnetic field strength is increased. In addition, in the concave portion at the center of the cylinder of the superconducting member 122, the space through which the magnetic flux can pass spreads outward, so the magnetic flux also spreads outward slightly. Therefore, in the comparative example (FIG. 4A), the magnetic flux tends to be close to the central axis of the magnetic flux in the subject insertion region 15, but in the present embodiment (FIG. 4B), the magnetic flux is outside. Therefore, the uniformity of the magnetic flux can be improved.

  Note that more detailed shapes of the convex portions and concave portions provided on the inner wall of the superconducting member 122 as shown in FIGS. 3 and 4B can be obtained in advance by computer simulation, for example. Further, as another example of the shape of the superconducting member 122, modifications as shown in FIGS. 5 and 6 can be assumed.

  FIG. 5 is a view showing a modification of the cross-sectional shape of the superconducting member 122. The superconducting member 122b according to this modification has three convex portions and two concave portions on the inner wall along the central axis B as shown in FIG. At this time, the effect of the central convex portion can be easily understood by assuming that a new convex portion is provided in the concave portion at the central portion of the superconducting member 122 shown in FIG. That is, when the magnetic flux in the subject insertion region 15 is excessively spread outward by the central concave portion provided in the superconducting member 122 shown in FIG. 3 (FIG. 4B), the concave portion The magnetic flux in the subject insertion region 15 can be pushed back to the central axis B side by the convex portion newly provided in FIG. Therefore, the uniformity of the magnetic flux in the subject insertion region 15 can be improved.

  When the above idea is expanded, the number of convex portions provided on the inner wall of the superconducting member 122b may be four or more, and the number of concave portions may be three or more. Even in such a case, the shape can be appropriately determined by computer simulation.

  FIG. 6 is a view showing another modification of the cross-sectional shape of the superconducting member 122. As shown in FIG. 6, in this modification, the present embodiment shown in FIG. 4B is provided in that a new superconducting member 122c is provided on the inner wall of the cylindrical end portion of the cylindrical superconducting magnet 11. This is different from the shape of the superconducting member 122 according to the embodiment. In FIG. 6, the superconducting member 122c is separated from the superconducting member 122, but may have a structure in which both are connected.

  In this modification, since the magnetic flux passing through the inner diameter side of the superconducting magnet 11 is converged in advance by the superconducting member 122c provided at the end of the superconducting magnet 11, the degree of convergence can be small in the superconducting member 122. Thus, the uniform magnetic flux is promoted.

  In the present modification, the superconducting member 122c is provided only at one end of the superconducting magnet 11, but may be provided at both ends. The reason why the superconducting member 122c is provided only at one end of the superconducting magnet 11 is that the subject 4 placed on the table 2 is inserted into the subject insertion region 15 from the end where the superconducting member 122c is not provided. This is for convenience.

The superconducting members 122, 122b, and 122c according to the first embodiment and the modification described above are assumed to be composed of a bulk superconductor that becomes a superconducting state below a predetermined critical temperature. . However, since a bulk material of a general superconductor is fragile, a superconductor solidified with a resin is used here. In that case, it is preferable that the resin is as close as possible to the temperature expansion coefficient of the superconductor whose temperature expansion coefficient is solidified. Further, from the viewpoint of the cooling efficiency of the magnetic flux converging part 12, a resin having a high thermal conductivity is preferable.
Further, the superconducting members 122, 122b, and 122c may be formed by depositing a superconductor on the surface of metal or ceramic. Moreover, what stuck the tape material which contains a superconductor to a metal, ceramics, or a resin molding may be used.

  At the end of the description of the first embodiment, a supplementary description will be given of how to cool and operate the superconducting coil 111 and the superconducting member 122. That is, in the present embodiment, the superconducting member 122 is cooled by the second cooling unit 14 (see FIG. 2) until it is in the superconducting state, and then cooled by the first cooling unit 13 and already in the superconducting state. And a magnetic flux is generated on the inner diameter side of the superconducting coil 111. By doing so, the Meissner effect in the superconducting member 122 is surely expressed, and the magnetic flux generated on the inner diameter side of the superconducting coil 111 is reliably converged by the superconducting member 122.

  As shown in FIG. 2, the heater 16 provided in the middle of the refrigerant path or the heat conduction path connecting the second cooling unit 14 and the superconducting member 122 is a magnetic field generated on the inner diameter side of the superconducting coil 111. It is used to switch the strength (magnetic flux density). That is, if the temperature of the superconducting member 122 is raised to a critical temperature or higher by the heater 16, the magnetic flux converging effect by the superconducting member 122 disappears, so that the magnetic field strength in the subject insertion region 15 can be switched from a high magnetic field to a low magnetic field. . Moreover, the magnitude of the Meissner effect of the superconducting member 122 can be adjusted by adjusting the temperature.

  As described above, according to the first embodiment of the present invention, the cylindrical magnetic flux converging portion 12 including the superconducting member 122 is disposed in the radial space of the cylindrical superconducting coil 111. However, the magnetic flux is converged in the space surrounded by the superconducting member 122, that is, the subject insertion region 15, and the magnetic field strength is increased. Further, the magnetic flux in the subject insertion region 15 can be made uniform by appropriately determining a cross-sectional area when cut along a plane perpendicular to the magnetic flux direction of the space surrounded by the superconducting member 122, that is, a cross-sectional area through which the magnetic flux can pass. Can be achieved. Therefore, in the horizontal MRI apparatus 100, it is possible to obtain a uniform high magnetic field without increasing the magnetomotive force of the superconducting coil 111, that is, without increasing the size of the superconducting magnet 11.

<Second Embodiment>
FIG. 7 is a view showing an example of an external perspective view of the MRI apparatus 200 according to the second embodiment of the present invention. FIG. 8 is a cross-sectional view of the MRI apparatus 200 in FIG. It is the figure which showed the example typically. As shown in FIG. 7 and FIG. 8, the main part of the MRI apparatus 200 is a horizontal annular superconductor that forms upper and lower magnetic poles inside a sturdy disk-shaped gantry 20 that is a support housing separated vertically. The magnet 21 is accommodated and configured. The present embodiment is characterized in that the magnetic flux converging portions 22 separated in the vertical direction are attached to the lower surface and the upper surface of the upper and lower horizontal annular superconducting magnets 21, respectively.

  Here, the central portion of the space sandwiched between the upper and lower magnetic flux converging portions 22 is called a subject insertion region 25, and the subject 4 placed on the table 2 is inserted. Then, insertion / extraction of the table 2 on which the subject 4 is placed is performed by the table driving unit 3 in accordance with an instruction from the control device 5 as in the case of the first embodiment.

  In addition to the magnetic flux converging unit 22, a magnetic field gradient coil (not shown) and a high-frequency coil for acquiring a magnetic resonance signal are disposed on the lower and upper surfaces of the upper and lower horizontal annular superconducting magnets 21. . The control device 5 controls currents and signals supplied to these coils, generates a two-dimensional or three-dimensional image of the subject 4 using a magnetic resonance signal obtained from the high-frequency coil, and displays the generated image as a display device. 6 is displayed.

  Further, as shown in FIG. 8, the superconducting magnets 21 separated in the upper and lower directions are each housed in a vacuum vessel 212 and are constituted by a superconducting coil 211 surrounded by a radiation shield (not shown). At this time, the superconducting coil 211 may be cooled via a refrigerant such as liquid helium supplied from the first cooling unit 23 or may be cooled via a heat conducting member connected to the first cooling unit 23. Good. In addition, when the superconducting coil 211 is cooled via a refrigerant, the superconducting coil 211 is accommodated in a refrigerant container (not shown) provided inside a radiation shield (not shown).

  In addition, the magnetic flux converging portions 22 separated in the vertical direction are configured such that the superconducting member 222 attached to the installation base 221 is accommodated in the vacuum vessel 224 and is further surrounded by the radiation shield 223. The upper and lower vacuum containers 224 are fixed to the lower surface or upper surface of the vacuum container 212 of the upper and lower disk-shaped superconducting magnets 21 via a fastening member (not shown). The installation base 221 to which the superconducting member 222 is attached is attached to the surface of the vacuum vessel 224 on the superconducting magnet 11 side via the load support 220. At this time, the superconducting member 222 may be cooled via a refrigerant such as liquid helium supplied from the second cooling unit 24 or may be cooled via a heat conducting member connected to the second cooling unit 24. Good. When the superconducting member 222 is cooled via a refrigerant, the superconducting member 222 is accommodated in a refrigerant container (not shown) provided inside the radiation shield 223.

Here, the first cooling unit 23 and the second cooling unit 24 are controlled and operated independently of each other, and the vacuum vessel 212 and the vacuum vessel 224 are not in communication with each other. Therefore, the cooling temperature of the superconducting coil 211 and the cooling temperature of the superconducting member 222 may be different from each other. Therefore, for example, niobium titanium (NbTi), niobium tin (Nb ₃ Sn) or the like is used as the wire of the superconducting coil 211, and a high-temperature superconducting material is used as the superconducting member 222 of the magnetic flux converging unit 22. Also good.

  Further, as shown in FIG. 8, the heater 26 may be disposed in the middle of the refrigerant path or the heat conduction path connecting the second cooling unit 24 and the superconducting member 122. In this case, the role of the heater 26 is the same as the role of the heater 16 (see FIG. 2) of the first embodiment.

  As described above, in the MRI apparatus 200 having the configuration as shown in FIGS. 7 and 8, the cylinder is formed on the inner diameter side of the superconducting coil 211 in the cylinder that virtually connects the two superconducting magnets 21 separated vertically. Is generated in a direction substantially parallel to the central axis of the subject 4, that is, in a direction substantially perpendicular to the body axis of the subject 4. Such an MRI apparatus 200 is often called a vertical MRI apparatus. And in this embodiment, the magnetic flux converging part 22 provided with the superconducting member 222 is arrange | positioned in the both ends in the cylinder which connects the two superconducting magnets 21 virtually.

  Further, the shape of the superconducting member 222 of the magnetic flux converging portion 22 will be described in detail with reference to FIG. 9 in addition to FIG. Here, FIG. 9 is a view showing an example of a perspective view of the superconducting member 222 of the magnetic flux converging portion 22 attached to the lower superconducting magnet 21. As can be seen from FIGS. 8 and 9, the superconducting member 222 has a hollow semiconical shape, that is, a semiconical tube in which the diameter of one end is smaller than the diameter of the other end. is there. The end portion of the superconducting member 222 having the larger diameter is attached to the installation base 221, and the installation base 221 is attached to a predetermined position of the superconducting magnet 21.

  Here, since the installation table 221 is attached to the lower surface or the upper surface of the upper and lower superconducting magnets 21, the magnetic flux generated on the inner diameter side of the superconducting coil 211 passes through the installation table 221 substantially vertically. Therefore, here, the superconducting member 222 attached to the installation base 221 is disposed at a position where the central axis of the half cone substantially coincides with the central axis of the magnetic flux. Furthermore, in this embodiment, it is assumed that a plurality of hollow semiconical superconducting members 222 having different diameters are attached to the installation base 221 concentrically around the central axis of the magnetic flux. In that case, the height of each half cone may be different.

  Similarly to the case of the first embodiment, the installation base 221 and the vacuum vessel 224 of the magnetic flux converging unit 22 are made of nonmagnetic stainless steel or the like, and the superconducting member 222 is in a superconducting state below a predetermined critical temperature. It is assumed that it is composed of a superconductor. Therefore, when the superconducting member 222 is below a predetermined critical temperature, the magnetic flux passing through the inner diameter side of the superconducting coil 211 (the magnetic flux in the vertical direction) is converged to the central axis side of the magnetic flux by the semiconical superconducting member 222. . As a result, the magnetic field strength in the subject insertion region 25 sandwiched between the upper and lower magnetic flux converging units 22 is increased.

  Further, as shown in FIG. 9, a slit 225 is provided in the semiconical superconducting member 222. The slit 225 is a gap provided on the side surface of the superconducting member 222, and is intended to prevent the circulating current generated in the superconducting member 222 by the magnetic flux passing through the inside of the superconducting member 222 along its central axis. Note that the slit 225 is not a mere gap, but is usually one in which an insulating resin or the like is packed in the gap. Further, the number of slits 225 provided in the superconducting member 222 is not limited to one and may be two or more.

  As in the case of the first embodiment, the superconducting member 222 as described above is configured by a superconductor bulk material that becomes a superconducting state at a predetermined critical temperature or lower and is solidified with a resin. . Alternatively, the superconducting member 222 may be a superconductor deposited on the surface of a metal or ceramic. Moreover, what stuck the tape material which contains a superconductor to a metal, ceramics, or a resin molding may be used.

  FIG. 10 is a diagram for explaining the effect of magnetic flux convergence and magnetic flux equalization by the superconducting member 222 according to the second embodiment. As shown in FIG. 10, in the second embodiment, the magnetic flux (streamlines shown with arrows) generated by two upper and lower horizontal annular superconducting coils 211 and passing through the inner diameter side thereof is directed in the vertical direction. . In the present embodiment, when the superconducting member 222 is in a superconducting state, the magnetic flux is converged to the central axis side of the magnetic flux by the effect of eliminating the magnetic flux of the hollow semiconical superconducting member 222 (Meissner effect). . As a result, the magnetic flux density (magnetic field strength) in the subject insertion region 25 increases.

  In the second embodiment, the side portion of the subject insertion region 25 is open. Therefore, the magnetic flux at the outer peripheral portion of the magnetic flux converged by the superconducting member 222 tends to bulge outward from the central axis of the magnetic flux. In order to correct the swelling, in this embodiment, a plurality of superconducting members 222 having different diameters are concentrically arranged with the central axis of the magnetic flux as the central axis. At this time, the heights of the plurality of superconducting members 222 may be different.

  In other words, the magnetic flux in the subject insertion region 25 can be made uniform by appropriately adjusting the size of the plurality of semiconical superconducting members 222, the inclination of the side surfaces, the height, and the like. . It should be noted that conditions such as the diameter of the semiconical superconducting member 222 for achieving the uniform magnetic flux, the inclination of the side surface, and the height can be obtained in advance by computer simulation or the like.

  As described above, according to the second embodiment of the present invention, the upper and lower horizontal annular superconducting magnets 21 have their magnetic flux converging portions separated vertically as described with reference to FIGS. By attaching 22, the magnetic field strength of the subject insertion region 25 can be increased and the magnetic flux can be made uniform. Therefore, in the vertical MRI apparatus 200, a uniform high magnetic field can be obtained without increasing the magnetomotive force of the superconducting coil 211, that is, without increasing the size of the superconducting magnet 21.

  Finally, the difference between the shape of the superconducting member 122 according to the first embodiment and the shape of the superconducting member 222 according to the second embodiment will be supplemented. The external shape of the superconducting member 122 according to the first embodiment has a cylindrical shape along the direction of magnetic flux, and has irregularities formed on its inner wall surface. As described with reference to FIGS. 3 to 6, the unevenness of the inner wall is characterized by the area of the region surrounded by the superconducting member 122 when the superconducting member 122 is cut along a plane perpendicular to the central axis B of the magnetic flux. Is characterized in that it takes at least two minimum values from one end of the cylindrical superconducting member 122 to the other end along the direction of the magnetic flux.

  On the other hand, in the second embodiment, a pair of superconducting members 222 divided vertically by the subject insertion region 25 can be associated with the superconducting member 122 in the first embodiment. In this case, the upper and lower semiconical superconducting members 222 have an effect of converging the passing magnetic flux toward the center of the magnetic flux, and are thus provided at both ends of the cylindrical inner wall of the superconducting member 122 according to the first embodiment. It can be said that it is a component corresponding to the provided convex part (refer FIG.4 (b)). Further, the portion of the subject insertion region 25 that divides the superconducting member 222 according to the second embodiment into the upper and lower parts means that the magnetic flux passing therethrough spreads outward, so that the cylindrical portion of the superconducting member 122 according to the first embodiment is expanded. It can be said that it is a component corresponding to the recessed part provided in the center part of the inner wall.

  Therefore, in the region in which the superconducting member 222 is divided vertically in the second embodiment (subject insertion region 25), the superconducting member 222 does not appear on a plane perpendicular to the central axis of the magnetic flux, so the superconducting member 222 on that plane The area surrounded by can be considered as infinite. Then, the area of the region surrounded by the superconducting member 122 when the superconducting member 222 according to the second embodiment is cut perpendicularly to the central axis of the magnetic flux is from one end of the magnetic flux converging unit 22 to the magnetic flux. It can be said that it has the same characteristics as the first embodiment in that it has two minimum values before reaching the other end along the direction.

  The present invention is not limited to the embodiments and modifications described above, and includes various modifications. For example, the above-described embodiments and modifications have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. In addition, a part of the configuration of an embodiment or modification can be replaced with the configuration of another embodiment or modification, and the configuration of another embodiment or modification can be replaced with another embodiment or modification. It is also possible to add the following configuration. In addition, with respect to a part of the configuration of each embodiment or modification, the configuration included in another embodiment or modification may be added, deleted, or replaced.

2 Table 3 Table drive unit 4 Subject 5 Control device 6 Display device 10, 20 Gantry 11, 21 Superconducting magnet 12, 22 Magnetic flux converging unit 13, 23 First cooling unit 14, 24 Second cooling unit 15, 25 Subject insertion Region 16, 26 Heater 100, 200 MRI apparatus 111, 211 Superconducting coil 112, 212 Vacuum vessel 120, 220 Load support 121, 221 Installation base 122, 222 Superconducting member 123, 223 Radiation shield 124, 224 Vacuum vessel 125, 225 Slit

Claims (11)

A superconducting coil that generates a magnetic flux in a certain direction in the space on the inner diameter side;
A cylindrical magnetic flux converging portion having a superconducting member for converging the magnetic flux in the space on the inner diameter side of the superconducting coil to the central axis side of the magnetic flux;
With
When the cylindrical magnetic flux converging part is cut along a plane perpendicular to the central axis of the magnetic flux, the area of the region surrounded by the superconducting member included in the cylindrical magnetic flux converging part is the area of the cylindrical magnetic flux converging part. A superconducting magnet device characterized in that it changes as it reaches the other end along the direction of the magnetic flux from one end, and takes at least two local minimum values before reaching the other end. . A first cooling part for cooling the superconducting coil; and a second cooling part for cooling the superconducting member of the magnetic flux converging part, wherein the second cooling part operates independently of the first cooling part. The superconducting magnet device according to claim 1, wherein the superconducting member of the magnetic flux converging portion is cooled. The superconducting member of the magnetic flux converging unit is cooled to a temperature lower than the critical temperature of superconducting through the second cooling unit, and then the superconducting coil that is cooled and is in a superconducting state is energized. The superconducting magnet device described. The superconducting magnet apparatus according to claim 2, wherein a heater is provided in a part of a heat conduction path or a refrigerant path connecting the second cooling part and the superconducting member of the magnetic flux converging part. When the superconducting coil is used in a vertical magnetic resonance imaging apparatus, the magnetic flux converging part includes an upper magnetic flux converging part attached to the superconducting coil part on the upper electrode side along the direction of the magnetic flux. A space that separates the upper magnetic flux converging portion and the lower magnetic flux converging portion along the direction of the magnetic flux. The superconducting magnet device according to any one of claims 1 to 4, wherein the superconducting magnet device is an insertion space. Each of the superconducting members included in each of the upper magnetic flux converging part and the lower magnetic flux converging part has a semiconical cylindrical shape, and each of the semiconical cylindrical superconducting members has a wide opening surface side. The superconducting magnet apparatus according to claim 5, wherein the superconducting magnet apparatus is attached to the superconducting coil side, and a narrow opening surface side is in contact with the subject insertion space. Each of the upper magnetic flux converging part and the lower magnetic flux converging part is formed by concentrically arranging a plurality of semi-cylindrical superconducting members having different inclinations and heights around the central axis of the magnetic flux. The superconducting magnet device according to claim 6. The superconducting magnet device according to any one of claims 1 to 7, wherein the superconducting member of the magnetic flux converging part is a superconductor made of a bulk material solidified with a resin. The superconducting magnet device according to any one of claims 1 to 7, wherein the superconducting member of the magnetic flux converging unit is a superconducting member deposited on a metal or ceramics. The superconducting magnet according to any one of claims 1 to 7, wherein the superconducting member of the magnetic flux converging part is a nonmagnetic member with a tape material made of a superconductor attached thereto. apparatus. A magnetic resonance imaging apparatus comprising the superconducting magnet device according to any one of claims 1 to 10.

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