JP4886482B2 - Superconducting magnet apparatus and nuclear magnetic resonance imaging apparatus - Google Patents

Description

  The present invention relates to a superconducting magnet apparatus that generates a static magnetic field by circulating a permanent current through a superconducting coil, and further relates to a nuclear magnetic resonance imaging apparatus to which this superconducting magnet apparatus is applied as a generation source of a static magnetic field.

Nuclear Magnetic Resonance Imaging (Magnetic Resonance Imaging; hereinafter referred to as MRI) measures the electromagnetic waves emitted when the spin state of a hydrogen nucleus changes due to the nuclear magnetic resonance (Nuclear Magnetic Resonance; hereinafter referred to as NMR) phenomenon. By processing the signal, the tomogram of the subject is imaged as an image depending on the density distribution of the hydrogen nuclei.
When performing measurement using this MRI apparatus, the superconducting magnet device, which is the source of the static magnetic field, generates a static magnetic field (about 10 ppm) with high magnetic field strength (0.2 T or more) and high magnetic field density uniformity. Need to be formed.

Such a superconducting magnet device used as a source of a high-intensity and highly uniform static magnetic field includes a pair of opposing superconducting coils that induce a static magnetic field by circulating a permanent current, and the induced static magnetic field A pair of opposing magnetized members that amplify or improve uniformity and a refrigerant container that holds a refrigerant that cools the superconducting coil are included at least as components. Furthermore, these components are held inside a vacuum vessel that insulates heat from the outside of the MRI apparatus (see Patent Documents 1 and 2).
The MRI apparatus is required to further improve the strength of the static magnetic field formed in the imaging region for the purpose of clarifying the tomographic image and increasing the amount of information necessary for diagnosis.
JP-A-9-153408 (pages 3 to 5, FIG. 1) Special table 2003-513436 gazette

By the way, if the strength of the static magnetic field of the MRI apparatus is further improved, the above-described components are increased in size, and it is inevitably necessary to improve the rigidity of the support members that mutually support these components.
However, improving the rigidity of such a support member facilitates simultaneous heat entry from the outside normal temperature part of the MRI apparatus to the inside cooling part, and the capacity of the refrigerator required to maintain the liquefaction of the refrigerant (liquid helium). And load (operating power, etc.) increases. As a result, the cost for maintaining the operation of the MRI apparatus also increases.
For this reason, the rigidity of the support member is to have a sufficient rigidity with respect to a load accompanying generation of a stationary static magnetic field of the MRI apparatus, and it is desired to configure the support member with low rigidity while minimizing the margin.

However, in the MRI apparatus, when a static magnetic field is raised or when a phenomenon (so-called quenching) in which destruction of the superconducting state is propagated, a current with temporal fluctuation flows in the superconducting coil. Then, an eddy current is induced in the circumferential direction of the magnetized member, and a Lorentz force is generated by the interaction between the eddy current and the magnetic field. And the electromagnetic force which this Lorentz force was newly added and strengthened may act on a support member.
As described above, the support member may be subjected to a larger overload than when the MRI apparatus generates a stationary static magnetic field, and needs to have extra rigidity to withstand it.

  An object of the present invention is to solve such a problem, and realizes a configuration that reduces an overload acting on a support member even if a current in a superconducting coil fluctuates with time. Accordingly, it is possible to provide a superconducting magnet and a nuclear magnetic resonance imaging apparatus in which the rigidity of the support member is allowed to be reduced and heat intrusion is suppressed from the outside normal temperature portion to the inside cooling portion.

The present invention for solving the above problem is, static induced a pair of opposing superconducting coil for inducing a static magnetic field by circulating a permanent current, the centrally disposed axis and the axis of the superconducting coil by the permanent current e Bei a pair of opposed magnetic member to magnetize the magnetic field, and the prior SL magnetized member, the opposite surface is a surface opposite to the facing surface is a surface of the magnetization member opposite to the side to be paired, bottom of the slit extending in a radial direction is formed, one end of the slit formed in the opposite surface is a superconducting magnet apparatus according to claim and Wataru Turkey the side peripheral surface of the magnetic member.
By configuring the invention in this way, even if the current in the superconducting coil fluctuates with time, the eddy current flowing in the circumferential direction of the magnetized member is blocked at the portion where the slit is provided. That is, when the magnetized member is viewed in cross section, the slit has an opening on the opposite surface side, so that the current density of the eddy current is relatively lower on the opposite surface side than on the opposite surface side. Thereby, among the electromagnetic force generated by the interaction between the eddy current and the static magnetic field, the components attracted by the pair of magnetized members are reduced .

  According to the present invention, even if the current in the superconducting coil fluctuates with time, for example, during quenching, it is possible to reduce the overload that acts on the support member that supports each component. Accordingly, it is possible to provide a superconducting magnet and a nuclear magnetic resonance imaging apparatus in which the rigidity of the support member is allowed to be reduced and heat intrusion is suppressed from the outside normal temperature portion to the inside cooling portion.

(First embodiment)
Hereinafter, a nuclear magnetic resonance imaging apparatus (MRI apparatus) according to a first embodiment of the present invention will be described with reference to the drawings.
As shown in the overall side view of FIG. 1, the MRI apparatus 10 includes a first static magnetic field generation unit 30 and a second static magnetic field generation unit 40 such that the central axis Z facing the vertical direction is a rotationally symmetric axis. Are placed on a superconducting magnet device 11 (see FIG. 2) which is fixed to the support column 12 and the gradient magnetic field generators 13 and 13 arranged so as to sandwich the imaging region R and the subject P are placed on the imaging region. And a bed table D positioned at R.
In this superconducting magnet device 11 (see FIG. 2), a static magnetic field with high magnetic field strength and high magnetic field density uniformity is formed in the imaging region R in the same direction as the central axis Z.

Further, the MRI apparatus 10 receives, as components not shown, an RF (Radio Frequency) coil that irradiates an electromagnetic wave having a resonance frequency that causes an NMR phenomenon toward the imaging region R, and a response signal from the imaging region R. A coil, a control device that controls these components, and an analysis device that processes and analyzes the received signal are provided.
With this configuration, the MRI apparatus 10 causes the NMR phenomenon to appear only in the region of interest (usually a slice surface having a thickness of 1 mm) in the imaging region R, and based on the electromagnetic wave emitted from the hydrogen nuclear spin, the subject P The tomogram is imaged.

  The gradient magnetic field generators 13 and 13 are disposed in a pair of depressions U and U (see FIG. 2) provided on the surfaces where the first static magnetic field generator 30 and the second static magnetic field generator 40 face each other. The gradient magnetic field generators 13 and 13 apply a gradient magnetic field to the static magnetic field formed by the superconducting magnet device 11 in the imaging region R to give position information of the NMR phenomenon.

As shown in FIG. 2, the first static magnetic field generator 30 includes a main coil 31, a shield coil 32, a coil bobbin 33, a refrigerant container 35, a radiation plate 36, a vacuum container 37, and a first magnetizing member. 21, the second magnetizing member 22, and the supporting members 23 and 24 as at least constituent elements.
The inside of the second static magnetic field generation unit 40 is configured to share the central axis Z with respect to the first static magnetic field generation unit 30 and to be mirror-symmetric with respect to the imaging region R.

  The support column 12 supports the pair of first static magnetic field generation units 30 and second static magnetic field generation units 40 so as to face each other in the vertical direction. As shown in the cross section of FIG. 2, the inside of the support column 12 is configured such that the refrigerant container 35 communicates the first static magnetic field generation unit 30 and the second static magnetic field generation unit 40. Similarly, the vacuum vessel 37 communicates the first static magnetic field generation unit 30 and the second static magnetic field generation unit 40 inside the support column 12.

The main coil 31 is a superconducting coil that generates a static magnetic field for measurement in the imaging region R by circulating a permanent current in a predetermined direction (forward direction), and around the coil bobbin 33 arranged around the central axis Z. A superconducting wire is wound around the wire.
Here, the superconducting coil is changed from the normal conducting state to the superconducting state when cooled to a temperature lower than the critical temperature by the refrigerant L (for example, liquid helium) filled in the refrigerant container 35, and the electric resistance becomes zero. The annular current circulates permanently without decaying.

The shield coil 32 is wound around the coil bobbin 33 so as to share the central axis Z with the main coil 31 and to have a large diameter. An annular permanent current flows through the shield coil 32 in the direction opposite to the forward direction flowing through the main coil 31.
Further, the shield coil 32 is arranged at a position farther from the imaging region R than the main coil 31 and acts to cancel the measurement magnetic field leaking outside the superconducting magnet device 11.

The vacuum container 37 holds the refrigerant container 35 via a member (not shown) inside the vacuum state, and prevents heat from entering the refrigerant container 35 due to conduction and convection.
The refrigerant container 35 contains a refrigerant L (liquid helium) that keeps the main coil 31 and the shield coil 32 at a temperature equal to or lower than the critical temperature at which the superconducting phenomenon occurs.
The radiation plate 36 is provided between the vacuum container 37 and the refrigerant container 35 and shields heat radiation from the vacuum container 37 toward the refrigerant container 35.

  In this way, the refrigerant container 35, the radiation plate 36, and the vacuum container 37 are arranged in a layer structure and exhibit a heat insulation effect, so that they are immersed in the refrigerant L from the outer surface of the superconducting magnet device 11 exposed to the atmosphere and exhibiting normal temperature. Thus, the temperature gradient up to the superconducting coils 31 and 32 maintained at an extremely low temperature is constantly maintained.

The first magnetizing member 21 and the second magnetizing member 22 (hereinafter may be referred to as magnetizing members 21 and 22) share the central axis Z and are coaxial, outside the refrigerant container 35 and inside the vacuum container 37. It is fixed to. Typically, as illustrated, the magnetized members 21 and 22 are disposed on the inner radius side of the refrigerant container 35.
The magnetized members 21 and 22 are made of a ferromagnetic material such as pure iron, for example, and are paired so as to sandwich the imaging region R in a magnetic circuit that is formed in a closed loop shape with a permanent current flowing through the main coil 31 in an annular shape. Be placed. In this way, the magnetizing members 21 and 22 reduce the magnetic resistance of the magnetic circuit and induce many magnetic lines of force in the imaging region R to increase the strength of the static magnetic field.

  As shown in FIG. 3, the first magnetizing member 21 is provided with a flange portion 21e that extends from the side peripheral surface 21a in a hook shape and further expands the outer periphery of the opposite surface 21b. By providing such a heel part 21e, as shown in FIG. 4, the curvature of the magnetic field Bb passing through the first magnetizing member 21 is increased, and the loop of the magnetic circuit is reduced. As a result, it is possible to increase the strength of the static magnetic field in the imaging region R and reduce the leakage magnetic field to the outside.

Returning to FIG. 2, the description will be continued.
The magnetizing members 21 and 22 are configured by a first magnetizing member 21 and a second magnetizing member 22 that is separated from the first magnetizing member 21 and configured in an annular shape as shown in the drawing, so that the imaging region R The effect of improving the uniformity of the magnetic field and expanding the imaging region R can be obtained.
For the purpose of further improving such an effect, the first magnetizing member 21 has a hollow ring shape or a plurality of first magnetized members 21 inside the ring shape, other than the case where it is a flat plate as shown in the figure. In some cases, the annular magnetized members are arranged coaxially in multiple stages.
The magnetized members 21 and 22 will be described later with respect to their shapes and functions with reference to FIGS. 3 to 5.

The support member 23 is formed by arranging a plurality of rod-like bodies at intervals around the axis of the central axis Z and aligning the longitudinal direction thereof in the axial direction of the central axis Z. One end of the support member 23 is fixed to the first magnetizing member 21, and the other end is fixed to the inner peripheral surface of the vacuum vessel 37.
The support member 23 is preferably made of a material having high rigidity and a small heat transfer coefficient. Specifically, the support member 23 is made of fiber reinforced plastic (FRP). The fixing position of the other end of the support member 23 is not particularly limited, and may be fixed to the refrigerant container 35, for example.
By configuring the support member 23 in this way, it is possible to prevent heat intrusion from the normal temperature portion on the outer surface of the superconducting magnet device 11 toward the first magnetization member 21.
Note that the support member 24 that supports the second magnetizing member 22 outside the refrigerant container 35 and inside the vacuum container 37 is also the same as the support member 23, and thus the description thereof is omitted.

  By the way, these support members 23 and 24 support and fix members having extremely different temperatures (the magnetized members 21 and 22 and the vacuum vessel 37 in FIG. 2). It is necessary to configure a large. Thus, in order to make a member with a large thermal resistance, it is necessary to make it from a material having a low heat transfer coefficient, and to make the cross section of the heat inflow path small and the entire length long. However, when the support members 23 and 24 are configured in this manner, their mechanical rigidity generally decreases, and when the mechanical overload described in the section of [Problems to be solved by the invention] is applied, the magnetizing member 21 , 22 may be out of position. Since the positional accuracy of the magnetized members 21 and 22 is closely related to the uniformity of the magnetic field, if this uniformity is out of order, readjustment will be required, and the efficiency of adjustment work of the apparatus will be reduced. Become.

However, in the present invention, since the support members 23 and 24 have a characteristic structure as described later, the overload applied to the support members 23 and 24 can be kept low. Therefore, even if the support members 23 and 24 are configured to have low rigidity, they do not adversely affect an unexpected accident such as a quench. The components of the superconducting magnet apparatus 11 by the thermal resistance of the support members 23 and 24 is increased (in this case the magnetization member 21, 22) allowing Rukoto Soo more adiabatically coercive a.

Further, the support members 23 and 24 are configured to dispose the magnetized members 21 and 22 outside the refrigerant container 35. For this reason, the magnetized members 21 and 22 are not held at the extreme temperature, but are held at normal temperature or an intermediate temperature from the normal temperature to the temperature of the refrigerant L without temperature fluctuation.
Since the magnetizing members 21 and 22 have a large heat capacity and iron, which is a constituent material, has a property that the magnetization change with respect to the temperature change is large, it is variously different for the MRI apparatus 10 to be held at a temperature close to normal temperature without temperature fluctuation. This is advantageous in terms of points (for example, it is possible to suppress fluctuations in the intensity of the static magnetic field, to suppress consumption of the refrigerant L, and to reduce the size of the cooling device that suppresses vaporization of the refrigerant L).

Next, the shape of the magnetized members 21 and 22 will be described with reference to FIG.
FIG. 3A is a perspective view of the first magnetizing member 21 and the second magnetizing member 22. For the sake of explanation, both positions are displaced along the central axis Z by a predetermined amount. FIG. 3B is a cross-sectional view orthogonal to the XY direction of FIG.
The first magnetizing member 21 has a rotationally symmetrical shape with respect to the central axis Z, and has a flange portion 21e in which a part of the side peripheral surface 21a extends in a hook shape as described above. The flange portion 21e is configured to be Ri by opposing surface 21d that faces an imaging region side which is not shown the outer periphery of the opposite surface 21b is extended.

A slit 21f is provided so as to open from the opposite surface 21b of the magnetizing member 21 to the side peripheral surface 21a. Further, in the drawing, the slit 21f linearly intersects the central axis Z, and is provided so that the start end and the end thereof both reach the side peripheral surface 21a and open to the side peripheral surface 21a.
It is preferable from the viewpoint of the uniformity of the magnetic field in the imaging region R (see FIG. 1) that the plurality of slits 21f be equally arranged so as to have rotational symmetry with respect to the central axis Z.

  However, the slit 21f may be terminated at an arbitrary position in the opposite surface 21b as long as the start end of the slit 21f opens on the side peripheral surface 21a. Further, the groove-shaped direction of the slit 21f does not need to be completely coincident with the direction in which the extension line intersects the central axis Z, and may be substantially coincident. Further, the groove shape of the slit 21f does not need to be linear or planar, and as will be described later, the progress of the eddy current Ja (see FIG. 4A) generated in the circumferential direction of the first magnetizing member 21 is interrupted. As long as it does, it may have a curved or curved shape. Furthermore, in the first embodiment, the first magnetizing member 21 does not include the heel part 21e as an essential component, and can be preferably applied if it has a rotationally symmetric shape with respect to the central axis Z. For example, a simple cylindrical shape is also included.

The slit 21f preferably has a depth in the range of one third to two thirds of the thickness direction of the first magnetizing member 21 in a sectional view as shown in FIG.
When the depth of the slit 21f is smaller than one third in the thickness direction, the current density of eddy currents Ja and Jb (see FIG. 4A) generated in the circumferential direction of the first magnetizing member 21 as will be described later. The effect of deviating from the opposing surface 21d side cannot be obtained.
When the depth of the slit 21f is larger than two thirds of the thickness direction, the rigidity of the first magnetizing member 21 is lowered, and there is a concern that the first magnetizing member 21 may be elastically deformed in a suspended state as shown in FIG. Is done. However, as long as a measure that does not cause such deformation is performed, it is not necessary to define the upper limit of the depth of the slit 21f, and the slit 21f may penetrate to the facing surface 21d side.
Rather, it is preferable that the depth of the slit 21f is large from the viewpoint of effectively blocking the eddy current generated in the rotating direction, in that the area of the eddy current blocking surface is widened.

Moreover, it is preferable that the width | variety of the slit 21f is formed in the range of 0.5 mm to 10 mm.
The lower limit of the width of the slit 21f is 0.5 mm because it is not appropriate to form the slit 21f narrower than that from the viewpoint of cost effectiveness.
Moreover, when the slit 21f width is larger than 10 mm, it is not preferable from the viewpoint of affecting the uniformity of the magnetic field in the imaging region R (see FIG. 2).

Returning to FIG. 3, the description will be continued.
The second magnetizing member 22 has a rotationally symmetric shape with respect to the central axis Z, and is configured in an annular shape larger in the radial direction than the outer periphery of the second magnetizing member 22.
The slit 22f provided in the second magnetizing member 22 has a starting end that forms one opening of the side peripheral surface 22a of the second magnetizing member 22 and extends in a direction that intersects the central axis Z linearly. The end is provided so as to form an opening in the inner peripheral surface 22c. However, the slit 22f may be provided with an opening extending from the opposite surface 22b to the side peripheral surface 22a even if it does not penetrate to the inner peripheral surface 22c side.
In addition, since the preferable requirement which the slit 22f provided in the 2nd magnetization member 22 should have, the range which can be deform | transformed, etc. are the same as the slit 21f provided in the 1st magnetization member 21, the applicable part of the description is quoted. As a matter of fact, the description is omitted.

Next, with reference to FIGS. 4 and 5, the operation of the magnetizing members 21 and 22 will be described.
FIG. 4A is a diagram showing a first quadrant portion on the coordinates of the X (Y) -Z cross section in the first embodiment of the superconducting magnet device 11, and is a schematic diagram showing an example of the first magnetizing member 21. FIG.
FIG. 4B is a schematic diagram showing a comparative example when the magnetized member 21 ′ is not provided with the slit 21f.

  Here, it is assumed that the permanent current Jc flows in the main coil 31 in a ring shape in a direction from the front surface to the back surface in the cross-sectional view. Then, it is assumed that the magnetic field Bb is guided by the annular permanent current Jc and penetrates through the first magnetization members 21 and 21 ′ as shown in the figure.

  Next, it is assumed that a phenomenon (for example, a quench phenomenon) in which the permanent current Jc attenuates rapidly occurs. Then, the eddy currents Ja, Jb, Ja ′, Jb ′ are supplied to the main coil as shown in the first magnetizing member 21 which is also an electric conductor so as to compensate for the decrease in the magnetic field Bb accompanying the decay of the permanent current Jc. This occurs in the same direction as 31.

Here, in the embodiment shown in FIG. 4A, the eddy current Ja generated on the opposite surface 21b side is interrupted by the slit 21f, so that the value is extremely small, and it can be said that the relationship Ja << Jb is established. That is, in the first magnetizing member 21, it can be said that the eddy current Ja on the opposite surface 21b side has a relatively lower current density than the eddy current Jb on the facing surface 21d side.
On the other hand, in the embodiment shown in FIG. 4 (b), the eddy current Ja 'generated on the opposite surface 21b side does not obstruct the flow, and therefore it can be said that the relationship Ja' = Jb 'is substantially established. That is, in the magnetized member 21 ′ of the comparative example, it can be said that there is no difference in current density between the eddy current Ja on the opposite surface 21b ′ side and the eddy current Jb ′ on the opposite surface 21d ′ side.

  By the way, if the tangential vector of the eddy currents Ja and Jb at an arbitrary point is J and the tangential vector of the magnetic field Bb is B, the electromagnetic force F generated at this arbitrary point is the outer product of J and B, It is known that F = J × B.

  Here, in the embodiment shown in FIG. 4A, the electromagnetic force Fa generated by the eddy current Ja on the opposite surface 21b side is obliquely downward in the direction toward the main coil 31, as shown. On the other hand, the electromagnetic force Fb generated by the eddy current Jb on the facing surface 21d side is obliquely upward in the direction toward the main coil 31, and the amount is | Fa | <| Fb from the relationship of Ja << Jb. |.

The force acting on the entire first magnetizing member 21 is expressed as a resultant force of the electromagnetic force Fa and the electromagnetic force Fb. Of these resultant forces, the radial component cancels out with the component on the opposite side of the central axis Z and does not appear as an external force.
On the other hand, the vertical component Fg of the resultant force applied to the first magnetizing member 21 is the difference between the vertical component of the electromagnetic force Fa and the vertical component of the electromagnetic force Fb. The component Fg in the vertical direction of the resultant force is determined by the shape of the first magnetizing member 21 and the main coil 31 and the positional relationship in the height direction, but typically, a small load that faces the imaging region R side as illustrated. Or load in the reverse direction.

Next, in the comparative example shown in FIG. 4B, when the same examination is performed, the electromagnetic force Fa ′ generated by the eddy current Ja ′ on the opposite surface 21b ′ side, and the eddy current Jb ′ on the opposite surface 21d ′ side. The vertical component Fg ′ of the resultant force with the electromagnetic force Fb ′ generated by the above is | Fa ′ |> | Fb ′ | from the relationship of Ja ′ = Jb ′ and the magnitude relationship of the magnetic flux density.
Therefore, the component Fg ′ in the vertical direction of the resultant force is typically a large load that faces the imaging region R as illustrated.

Usually, when the permanent current Jc flowing through the main coil 31 is in a steady state, the force acting on the magnetizing member 21 ′ is directed toward the imaging region R in the first place.
When the permanent current Jc flowing through the main coil 31 is attenuated, in the comparative example, the electromagnetic force Fg ′ is further superimposed by the generation of the eddy currents Fa ′ and Fb ′ and acts on the magnetizing member 21 ′, and the support member 23 (FIG. 2) is overloaded.
On the other hand, in the embodiment, since the eddy currents Ja and Jb generated in the first magnetizing member 21 have a relatively low current density on the opposite surface 21b side than on the facing surface 21d side, the superimposed electromagnetic force Fg has a small load. Therefore, the support member 23 (FIG. 2) is not overloaded.

FIG. 5A is a diagram illustrating a first quadrant portion on the coordinates of the X (Y) -Z cross section in the first embodiment of the superconducting magnet device 11, and is a schematic diagram illustrating an example of the second magnetization member 22. FIG.
FIG. 5B is a schematic diagram showing a comparative example in which the slit 22f is not provided in the magnetizing member 22 ′.
In FIG. 5, the difference in action and effect due to the presence or absence of the slit 22 f provided in the second magnetizing member 22 is the same as the case of the presence or absence of the slit 21 f in the first magnetizing member 21 (see FIG. 4). In the description referring to, the description of the corresponding configuration is replaced and used as the description of FIG. 5, and the description is omitted.

(Second Embodiment)
Next, the shape of the magnetizing member 26 applied to the second embodiment of the present invention will be described with reference to FIG.
6A is a perspective view of the magnetizing member 26, and FIG. 6B is a cross-sectional view orthogonal to the XY direction of FIG.
The magnetized member 26 has a rotationally symmetric shape with respect to the central axis Z, and has a flange portion 26e in which a part of the side peripheral surface 26a extends in a hook shape as described above. The heel part 26e is configured such that the outer periphery of the opposite surface 26b is expanded rather than the facing surface 26d facing the imaging region (not shown).

  A plurality of slits 26f are provided in the flange portion 26e in a groove shape. The plurality of slits 26f are preferably arranged evenly so as to have rotational symmetry with respect to the central axis Z from the viewpoint of magnetic field uniformity in the imaging region R (see FIG. 1).

The slit 26f preferably has a depth covering the entire range in the thickness direction of the heel portion 26e in a sectional view as shown in FIG. 6B. However, the shape of the slit 26f is not particularly limited as long as the effect that the eddy current generated in the magnetizing member 26 does not circulate in the flange portion 26e is obtained.
Moreover, it is preferable that the slit 26f is formed in the range whose width is 0.5 mm to 10 mm.

  Further, the magnetizing member 26 applied to the second embodiment may be arranged alone, or may be used together with the second magnetizing member 22 as shown in FIG. In addition to the flat plate as described above, there may be a hollow annular shape, or a plurality of annular magnetic members may be coaxially arranged in multiple stages inside the annular shape.

Next, the operation of the magnetizing member 26 will be described with reference to FIG.
FIG. 7 is a diagram showing a first quadrant portion on the coordinates of the X (Y) -Z cross section in the second embodiment of the superconducting magnet device 11 (see FIG. 2), and is a schematic diagram showing an example of the magnetizing member 26. FIG.
Hereinafter, the description will be continued in comparison with the comparative example shown in FIG.

  It is assumed that a phenomenon (for example, a quench phenomenon) in which the permanent current Jc attenuates rapidly occurs. Then, eddy currents Ja and Jb are generated in the same circumferential direction as the main coil 31 as shown in the magnetizing member 26 which is also an electric conductor so as to compensate for the decrease in the magnetic field Bb accompanying the decay of the permanent current Jc. .

  Here, in the embodiment shown in FIG. 7, it can be said that the eddy current does not flow in the heel portion 26e because it is blocked by the slit 26f. Instead, it can be said that there is no difference in the eddy current density on the opposite surface 26b side and the opposing surface 26d side in the portion of the magnetized member 26 where the slit 26f is not provided (Ja = Jb).

Here, the electromagnetic force Fa generated by the eddy current Ja on the opposite surface 26b side in the embodiment shown in FIG. 7 and the electromagnetic force generated by the eddy current Ja ′ on the opposite surface 21b ′ side in the comparative example shown in FIG. 4B. Contrast with force Fa '. Then, it can be said that the vertical component of the electromagnetic force Fa of the embodiment of FIG. 7 is smaller than the vertical component of the electromagnetic force Fa ′ of the comparative example of FIG.
For this reason, it can be said that the vertical component Fg of the resultant force of the electromagnetic forces Fa and Fb of the example is smaller than the vertical component Fg ′ of the resultant force of the electromagnetic forces Fa ′ and Fb ′ of the comparative example.
As described above, in the example of the second embodiment, since the electromagnetic force Fg superimposed on the magnetizing member 26 is small due to the decay of the permanent current Jc, the support member 23 (FIG. 2) is not overloaded.

  In the above description, the superconducting magnet apparatus constituting the nuclear magnetic resonance imaging apparatus is described on the premise that the subject is positioned so that the static magnetic field faces in a direction perpendicular to the direction in which the subject is inserted into the imaging region. Went. However, the present invention is not limited to this, and in the nuclear magnetic resonance imaging apparatus, a configuration in which the superconducting magnet apparatus is positioned such that the static magnetic field faces in a parallel direction with respect to the direction in which the subject is inserted into the imaging region can be taken.

1 is a longitudinal sectional view showing an embodiment of a nuclear magnetic resonance imaging apparatus of the present invention. It is a fragmentary sectional view which shows 1st Embodiment of the superconducting magnet apparatus of this invention. (A) is a perspective view of the 1st magnetization member and the 2nd magnetization member applied to 1st Embodiment of the superconducting magnet apparatus of this invention, (b) is XY orthogonal sectional drawing. (A) is a figure explaining the Example of the 1st magnetization member applied to 1st Embodiment of the superconducting magnet apparatus of this invention, (b) is a figure explaining a comparative example. (A) is a figure explaining the Example of the 2nd magnetization member applied to 1st Embodiment of the superconducting magnet apparatus of this invention, (b) is a figure explaining a comparative example. (A) is a perspective view of the magnetization member applied to 2nd Embodiment of the superconducting magnet apparatus of this invention, (b) is XY orthogonal sectional drawing. It is a figure explaining the Example of the magnetization member applied to 2nd Embodiment of the superconducting magnet apparatus of this invention.

Explanation of symbols

10 MRI system (nuclear magnetic resonance imaging system)
11 Superconducting magnet device 21, 26 First magnetizing member (magnetizing member)
21a, 22a, 26a Side peripheral surface 21b, 22b, 26b Opposite surface 21d, 26d Opposing surface 21e, 26e Saddle part 21f, 22f, 26f Slit 22 Second magnetizing member (magnetizing member)
23, 24 Support member 31 Main coil (superconducting coil)
35 Refrigerant container 37 Vacuum container L Refrigerant P Subject R Imaging area Z Center axis

Claims (10)

A pair of opposing superconducting coils that circulate a permanent current to induce a static magnetic field;
A pair of opposing magnetized members disposed coaxially with the central axis of the superconducting coil and magnetized by a static magnetic field induced by the permanent current,
The front Symbol magnetization member,
The opposing surface is a surface of the magnetization member opposite to the side forming a pair on the opposite surface is a surface opposite to a bottom of the slit extending in a radial direction is formed,
One end of the slit formed in the opposite surface is Ru Wataru the side peripheral surface of the magnetic member
Superconducting magnet apparatus according to claim and this. That has a flange portion to further extend the outer circumference of the extending out the opposite side to the flange shape is provided from the side peripheral surface of the magnetic member
Superconducting magnet apparatus according to claim 1, wherein the this. The slit is that provided as the start and end are both open to the side peripheral surface
Superconducting magnet apparatus according to claim 1 or claim 2, wherein the this. The slits, that have only provided in the flange portion
Superconducting magnet apparatus according to claim 2, wherein the this. The slit is
The depth is included in the range of 1/3 to 2/3 of the thickness direction of the magnetized member,
Width Ru is included in the range from 0.5mm to 10mm
Superconducting magnet apparatus according to any one of claims 4 and this claim, wherein. The magnetized member includes a first magnetized member and a second magnetized member that is separated from the first magnetized member and configured in an annular shape,
Even that has one said slit is provided together less of the first magnetization member and the second magnetization member
Superconducting magnet apparatus as claimed in any one of claims 5, wherein the this. A refrigerant container for holding therein the superconducting coil and a refrigerant for cooling the superconducting coil;
A vacuum container that insulates and holds the refrigerant container inside;
A support member for supporting the magnetic member within the outer and and the vacuum vessel of the coolant vessel, Ru with a
Superconducting magnet apparatus as claimed in any one of claims 6, wherein the this. The superconducting magnet apparatus according to any one of claims 1 to 7 is applied as a source of the static magnetic field, capture an image of a subject using a magnetic resonance phenomenon
A nuclear magnetic resonance imaging apparatus. To the direction in which the subject is inserted into the imaging region, the static magnetic field is the superconducting magnet apparatus so as to face the vertical direction that are positioned
Nuclear magnetic resonance imaging apparatus according to claim 8, wherein the this. To the direction in which the subject is inserted into the imaging area, that the static magnetic field is located is the superconducting magnet apparatus so as to face the parallel
Nuclear magnetic resonance imaging apparatus according to claim 8, wherein the this.

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