JP6510874B2 - Magnet device - Google Patents

Description

  The present invention relates to a cylindrical superconducting magnet including a positive magnetic field generating coil that generates a positive magnetic field and a reverse magnetic field generating coil that generates a reverse magnetic field, and a magnet apparatus including the superconducting magnet.

  For example, a medical MRI (Magnetic Resonance Imaging) apparatus equipped with a superconducting magnet performs tomographic imaging (MRI imaging) using nuclear magnetic resonance, and is exposed compared to tomographic imaging using X-rays. Have no problems and are widely used as medical applications. However, in the conventional MRI apparatus, since the magnetic field uniform space suitable for diagnosis is usually at the central portion in the longitudinal direction (axial direction) of the apparatus, it is necessary to put the subject in a tunnel-like elongated space as shown in Patent Document 1. was there. Therefore, it was a problem that the subject felt a sense of oppression and a fear of closing.

  Therefore, for example, as in the MRI apparatus described in Patent Document 2, if the diagnosis site is specialized for the head and the magnetic field uniform space is generated at the end of the apparatus, the subject's head is inserted to the back of the apparatus Since it is not necessary, the subject's sense of oppression and fear can be greatly relieved. Such an MRI apparatus specialized for the head is said to be effective for diagnosis of dementia, which is increasing worldwide, and the size of the apparatus is much smaller than that for the whole body. There is also the merit of being able to

JP 2001-212107 A JP, 2009-259923, A

  Here, the MRI apparatus of Patent Document 2 arranges the reverse magnetic field generating coil between two positive magnetic field generating coils at one end, thereby reducing the force acting on the coil wire. It is believed that However, when the coils provided at the one side are arranged in the axial direction as described above, there is a possibility that the device can be easily enlarged in the axial direction, and the merit that the device size can be reduced can not be sufficiently achieved.

  Therefore, an object of the present invention is to suppress the dimension in the axial direction in a superconducting magnet that generates a magnetic field uniform space at the end in the axial direction.

  In order to achieve the above object, the present invention is a cylindrical superconducting magnet provided with a positive magnetic field generating coil for generating a positive magnetic field and a reverse magnetic field generating coil for generating a reverse magnetic field. A mixed layer in which the positive magnetic field generation coil and the reverse magnetic field generation coil are mixed and disposed, a positive magnetic field layer in which the positive magnetic field generation coil is disposed, and a reverse magnetic field layer in which the reverse magnetic field generation coil is disposed The positive magnetic field generating coil of the positive magnetic field layer is disposed at one end of the axial direction, and the reverse magnetic field generating coil is opposed to the positive magnetic field generating coil of the positive magnetic field layer in the mixed layer. It is characterized by being arranged.

  In the present invention, a mixed layer in which a positive magnetic field generating coil and a reverse magnetic field generating coil are mixed and arranged, a positive magnetic field layer in which the positive magnetic field generating coil is arranged, and a reverse magnetic field layer in which the reverse magnetic field generating coil is arranged are in this order It has a configuration provided from the inner side in the radial direction. The positive magnetic field generating coil of the positive magnetic field layer is disposed at one end of the axial direction, and the reverse magnetic field generating coil is disposed in the mixed layer so as to face the positive magnetic field generating coil of the positive magnetic field layer. There is. As such, by providing two coils for generating magnetic fields in opposite directions at the axial end, a magnetic field uniform space can be formed at the end. Moreover, since these two coils are arranged in the radial direction, it is possible to suppress the dimension in the axial direction.

It is a schematic cross section of the MRI apparatus concerning the embodiment of the present invention. It is a schematic diagram which shows distribution of magnetic field intensity. It is a schematic diagram which shows distribution of magnetic field intensity. It is a schematic diagram which shows distribution of magnetic field intensity. 5 is a schematic cross-sectional view of an MRI apparatus of Comparative Example 1. FIG. FIG. 7 is a schematic cross-sectional view of an MRI apparatus of Comparative Example 2;

  An embodiment of an MRI apparatus (magnet apparatus) according to the present invention will be described with reference to the drawings. As shown in FIG. 1, the MRI apparatus 1 of this embodiment includes a superconducting magnet 10 in which a plurality of coils 21 to 28 are accommodated in a liquid helium container 11, and a radiation shield 12 provided outside the liquid helium container 11. , And an insulated vacuum vessel 13 provided on the outside of the radiation shield 12, and is an MRI apparatus specialized in diagnosis of the head. The superconducting magnet 10, the radiation shield 12, and the adiabatic vacuum vessel 13 constituting the MRI apparatus 1 are all cylindrical with the same central axis, and extend in the radial direction central portion of the MRI apparatus 1 in the axial direction. An internal space 14 is formed.

  The superconducting magnet 10 has a magnetic field strength in the internal space 14 by supplying a current from an electric circuit (not shown) to coils 21 to 28 configured by winding a wire around a cylindrical winding frame (not shown). A uniform magnetic field uniform space S is generated. The magnetic field uniform space S is generally formed in a spherical shape, and MRI imaging is performed in a state where the subject's head (diagnosis region) is located in the magnetic field uniform space S.

  The wire constituting the coils 21 to 28 is a superconducting wire in which an extremely fine wire material of niobium titanium (NbTi) alloy is embedded in a copper base material, and the bare wire diameter is about φ0.65 mm, and the covered wire diameter is about φ0. It is 88 mm. The superconducting wire is wound around the winding frame, treated by impregnation, and immersed in liquid helium (about 4.2 K) in the liquid helium container 11. The electric circuit provided in the superconducting magnet 10 has a role of a supply circuit for supplying current to the coils 21 to 28 and a role of a protection circuit for protecting the coils 21 to 28 from quenching and the like.

  The superconducting magnet 10 has a plurality of coils 21 to 28, in which a positive magnetic field generating coil for generating a positive magnetic field and a reverse magnetic field generating coil for generating a reverse magnetic field reverse to the positive magnetic field are present. . What is illustrated by a thick frame in each figure is a positive magnetic field generating coil, and what is illustrated by a narrow frame is a reverse magnetic field generating coil. Note that the positive magnetic field and the reverse magnetic field have only a relative relationship, and when the magnetic field in a certain direction is determined to be a positive magnetic field, the reverse magnetic field is only defined as the reverse magnetic field. That is, in the present invention, the direction of the magnetic field generated by the positive magnetic field generating coil and the reverse magnetic field generating coil is not absolutely determined.

  The superconducting magnet 10 has a mixed layer 10A in which the positive magnetic field generating coils 21 to 24 and the reverse magnetic field generating coils 25 and 26 are mixed and arranged in order from the inner side in the radial direction, and a positive magnetic field layer 10B in which the positive magnetic field generating coil 27 is arranged. And a reverse magnetic field layer 10C in which the reverse magnetic field generating coil 28 is disposed is a three-layer structure. The mixed layer 10A and the positive magnetic field layer 10B mainly function as a main coil layer for generating the magnetic field uniform space S in the internal space 14. On the other hand, the reverse magnetic field layer 10C mainly functions as a shield coil layer for preventing the magnetic field generated from the main coil layer from leaking to the outside.

  In the mixed layer 10A, the positive magnetic field generating coils 21 to 24 are disposed close to the back side in the axial direction, while the reverse magnetic field generating coils 25 and 26 are disposed close to the front side in the axial direction. In addition, the positive magnetic field generating coil 27 of the positive magnetic field layer 10B is disposed at an end on the near side so as to face the reverse magnetic field generating coil 26 disposed closest to the near side in the mixed layer 10A. In addition, "opposing" here refers to the form by which two coils are arrange | positioned so that at least one part may overlap in an axial direction. The same applies to the following.

  The positive magnetic field generating coil 27 of the positive magnetic field layer 10B is a coil that generates a magnetic field stronger than any of the coils 21 to 26 provided in the mixed layer 10A, and is the most effective for generating a strong magnetic field in the internal space 14 It is a coil with a large degree of contribution. By arranging such a positive magnetic field generating coil 27 at the end on the front side in the axial direction, it is possible to form a magnetic field uniform space S having a high magnetic field strength near the front side of the internal space 14. In order to strengthen the magnetic field, the number of turns of the coil may be increased or the current may be increased.

  Here, the effect of providing the reverse magnetic field generating coil 26 inward in the radial direction of the positive magnetic field generating coil 27 of the positive magnetic field layer 10B will be described in detail with reference to FIGS. 2A to 2C. FIG. 2A schematically shows the distribution of magnetic flux density (magnetic field strength) in the case where only one coil is provided, and FIG. 2B is an axial alignment of two coils generating magnetic fields of the same direction. FIG. 3C schematically shows the distribution of the magnetic flux density in the case, and FIG. 3C schematically shows the distribution of the magnetic flux density in the case where two coils generating opposite magnetic fields are arranged in the radial direction.

  As shown in FIG. 2A, in the case where only one positive magnetic field generating coil 31 is provided, the distribution of the magnetic flux density B is substantially elliptical arc-shaped, and a region where the magnetic flux density B is uniform can not be secured. Therefore, conventionally, as shown in FIG. 2B, by arranging two positive magnetic field generating coils 31 in the axial direction, a region having uniform magnetic flux density B can be secured in the central portion of the two positive magnetic field generating coils 31. It was done. However, such a coil arrangement has been a factor that promotes the upsizing of the device in the axial direction.

  Therefore, in the superconducting magnet 10 of the present embodiment, as shown in FIG. 2C, the reverse magnetic field generating coil 26 is provided radially inside the positive magnetic field generating coil 27 that generates the strongest positive magnetic field. By doing this, it is possible to smooth the peak region of the positive magnetic field generated by the positive magnetic field generating coil 27 by the relatively weak reverse magnetic field generated by the reverse magnetic field generating coil 26, and secure a region where the magnetic flux density B is uniform. . Furthermore, as compared with the coil arrangement of FIG. 2B, due to the configuration in which the coils 26, 27 are arranged in the radial direction, the apparatus can be prevented from being enlarged in the axial direction.

  Although the reverse magnetic field generating coil 26 of the mixed layer 10A has been described, the other coils 21 to 25 of the mixed layer 10A also contribute to the formation of the uniform magnetic field space S. For example, although the reverse magnetic field generation coil 25 is not disposed to face the positive magnetic field generation coil 27, the reverse magnetic field generation coil 25 is disposed close to the front side in the axial direction. It contributes to the uniformization of the uniform space S. Further, in the mixed layer 10A, the plurality of positive magnetic field generating coils 21 to 24 are arranged close to the back in the axial direction, so that the magnetic field uniform space by the reverse magnetic field generating coils 25 and 26 arranged on the front side of the axial direction Adjustment of the magnetic field intensity and the axial direction position of the magnetic field uniform space S by the positive magnetic field generating coils 21 to 24 can be performed while suppressing interfering with the homogenization action of S.

  The reverse magnetic field generating coil 28 of the reverse magnetic field layer 10C is disposed radially outside the positive magnetic field generating coil 27 so as to face the positive magnetic field generating coil 27 of the positive magnetic field layer 10B. Such an arrangement can effectively suppress the leakage of the magnetic field generated by the positive magnetic field generating coil 27 that generates the strongest magnetic field to the outside. In addition, since the reverse magnetic field generation coil 28 is disposed at the near end of the axial direction together with the positive magnetic field generation coil 27, the coil on the back side in the axial direction of the positive magnetic field layer 10B and the reverse magnetic field layer 10C. There will be free space where is not placed. In order to narrow this empty space, as shown in FIG. 1, the axially rear and radially outer portions of the liquid helium container 11, the radiation shield 12 and the adiabatic vacuum container 13 are notched to obtain an MRI. Further miniaturization of the device 1 is possible. In addition, the amount of liquid helium required can be reduced, which is economical.

Each specification of the embodiment of the present invention will be described in comparison with a comparative example. FIG. 3A is a schematic cross-sectional view of an MRI apparatus 101 of Comparative Example 1, and FIG. 3B is a schematic cross-sectional view of an MRI apparatus 102 of Comparative Example 2. Table 1 compares the specifications of the example and the comparative examples 1 and 2.

  The specifications required for the MRI apparatus specialized for the head will be described. Here, it is assumed that the shape of the magnetic field uniform space S is spherical. In order to reduce the sense of oppression and fear of the subject, the distance a from the front side in the axial direction of the superconducting magnet to the center of the magnetic field uniform space S is preferably 195 mm or less. Further, by limiting the distance a to 195 mm or less, it is not necessary to put the shoulders of the subject into the internal space 14, and the miniaturization of the MRI apparatus becomes easy.

  In addition, in the MRI apparatus specialized for the head, it is preferable to suppress the diameter r2 of the inner space 14 to 350 mm or less to achieve miniaturization because only the head of the subject needs to enter the inner space 14. In order to suppress the diameter r2 of the internal space 14 to 350 mm or less, as shown in Table 1, the inner diameter r1 of the superconducting magnet 10 is required to be 385 mm or less. Moreover, from other viewpoints such as diagnostic accuracy, the conduction current is 100A or less, the magnetic field strength of the magnetic field uniform space S is 1.5T or more, the sphere diameter of the magnetic field uniform space S is about 200 mm, the magnetic field uniformity of the magnetic field uniform space S is It is preferable that it is 5 ppm or less.

  As shown to FIG. 3A, B, the MRI apparatus 101 of the comparative example 1 and the MRI apparatus 102 of the comparative example 2 are equipped with the superconducting magnet 110 which consists of main coil layer 110A and shield coil layer 110B. The superconducting magnet 110 has a plurality of coils arranged symmetrically with respect to the axial center, and as a result, it is a conventional type in which a magnetic field uniform space S is formed at the central portion in the axial direction.

  As apparent from Table 1, according to the embodiment of the present invention, the MRI apparatus 1 could be designed to satisfy all the specifications described above. On the other hand, in Comparative Examples 1 and 2 of the conventional type, it was not possible to design to satisfy all the specifications. Specifically, in Comparative Example 1 in which the main object was to make the distance a from the front side in the axial direction of the superconducting magnet 110 to the center of the magnetic field uniform space S 195 mm or less, the magnetic field of the magnetic field homogeneous space S was The intensity was 0.5 T, the magnetic field uniformity was 13 ppm, and a high quality magnetic field uniform space S could not be formed. Further, in Comparative Example 2 designed to satisfy the specifications of the magnetic field strength of the magnetic field uniform space S and the magnetic field uniformity, the center of the magnetic field uniform space S is 247.5 mm from the front side in the axial direction, and the target value is 195 mm. Significantly beyond.

  That is, in the conventional type MRI apparatuses 101 and 102, the requirement to form the magnetic field uniform space S at the end in the axial direction and the requirement to improve the magnetic field strength and the magnetic field uniformity of the magnetic field uniform space S are both compatible. I couldn't let it go. On the other hand, according to the embodiment of the present invention, it is possible to simultaneously satisfy these two requirements, and to provide an MRI apparatus 1 suitable for head diagnosis that does not cause the subject to feel pressure and fear. The

(effect)
As described above, in the superconducting magnet 10 of the present embodiment, the positive magnetic field generating coil 27 of the positive magnetic field layer 10B is disposed at the end on the near side (one side) in the axial direction, and the mixed layer 10A is positive. The reverse magnetic field generating coil 26 is disposed to face the positive magnetic field generating coil 27 of the magnetic field layer 10B. Thus, the magnetic field uniform space S can be formed in the said edge part by providing two coils 26 and 27 which generate | occur | produce a reverse magnetic field in the axial direction edge part. Moreover, since these two coils 26 and 27 are arranged in the radial direction, it is possible to suppress the axial dimension.

  Further, in the present embodiment, in the mixed layer 10A, since the plurality of reverse magnetic field generating coils 25 and 26 are disposed close to the front side (one side) in the axial direction, the positive magnetic layer is disposed at the front end The uniformity of the magnetic field generated by the magnetic field generating coil 27 can be effectively improved. As a result, it is possible to form a good magnetic field uniform space S.

  Further, in the present embodiment, in the mixed layer 10A, since the plurality of positive magnetic field generating coils 21 to 24 are disposed close to the back side (the other side) in the axial direction, the magnetic field uniformity by the reverse magnetic field generating coils 25 and 26 is uniform. The magnetic field strength and the axial position of the magnetic field uniform space S can be adjusted by the positive magnetic field generating coils 21 to 24 while suppressing interference with the homogenization action of the space S.

  Further, in the present embodiment, since the reverse magnetic field generating coil 28 of the reverse magnetic field layer 10C is disposed to face the positive magnetic field generating coil 27 of the positive magnetic field layer 10B, the magnetic field generated by the positive magnetic field generating coil 27 is a device. Can be effectively suppressed. Further, according to such an arrangement, since a vacant space where the coil is not disposed is generated on the back side of the positive magnetic field layer 10B and the reverse magnetic field layer 10C, the liquid helium container 11 and the radiation shield 12 are made narrow. Further, by configuring the adiabatic vacuum vessel 13, further miniaturization is possible. In addition, the amount of liquid helium required can be reduced, which is economical.

(Other embodiments)
The present invention is not limited to the above embodiment, and the elements of the above embodiment can be appropriately combined or various modifications can be made without departing from the scope of the invention.

  For example, although the superconducting magnet 10 has a three-layer structure including the mixed layer 10A, the positive magnetic field layer 10B, and the reverse magnetic field layer 10C in the above embodiment, the superconducting magnet 10 may have four or more layers.

  Further, in the above embodiment, as shown in FIG. 1, the apparatus is miniaturized by forming the liquid helium container 11, the radiation shield 12, and the corner of the heat insulating vacuum container 13 in a cutaway shape. However, such a notch shape is not essential.

1 MRI system (Magnet system)
10 superconducting magnet 10A mixed layer 10B positive magnetic field layer 10C reverse magnetic field layer 21-24 positive magnetic field generating coil 25, 26 reverse magnetic field generating coil 27 positive magnetic field generating coil 28 reverse magnetic field generating coil S magnetic field uniform space

Claims (3)

Positive magnetic field generating coil generates a positive magnetic field, and a cylindrical superconducting magnet having a reverse magnetic field generation coil for generating a reverse magnetic field, a magnet system and a liquid helium vessel containing the superconducting magnet ,
In the superconducting magnet, a mixed layer in which the positive magnetic field generating coil and the reverse magnetic field generating coil are mixed and arranged in order from the inner side in the radial direction, a positive magnetic field layer in which the positive magnetic field generating coil is arranged, and the reverse magnetic field A reverse magnetic field layer in which a generation coil is disposed;
The positive magnetic field generating coil of the positive magnetic field layer is disposed at one end in the axial direction,
In the mixed layer, a plurality of the reverse magnetic field generation coils are disposed close to the one side, and a plurality of the positive magnetic field generation coils are disposed close to the other side in the axial direction,
In the mixed layer, at least one reverse magnetic field generating coil is disposed to face the positive magnetic field generating coil of the positive magnetic field layer ,
The shape of the liquid helium container as viewed from the circumferential direction of the positive magnetic field generating coil is a shape in which a portion on the other side in the axial direction and a radially outer side is cut away,
The magnet device, wherein the shape of the other side portion in the axial direction of the liquid helium container is a shape that narrows radially inward toward the other side in the axial direction . The magnet apparatus according to claim 1, wherein at least one reverse magnetic field generation coil is disposed in the mixed layer without facing the positive magnetic field generation coil of the positive magnetic field layer . It said reverse magnetic field generation coil of the reversed field layer Ma Gunetto device according the to claim 1 or 2 are arranged to face the positive magnetic field generating coils of the positive magnetic field layer.

Images