Superconducting magnet and magnetic resonance imaging apparatus

Abstract

To inhibit disturbance in the static magnetic field distribution generated by a superconducting magnet.SOLUTION: In one embodiment, a superconducting magnet includes: at least one primary superconducting coil configured to generate a primary magnetic field; at least one secondary superconducting coil configured to generate a secondary magnetic field in a direction opposite to a direction of the primary magnetic field; and a superconducting shim coil configured to cover part or all of an outer surface of at least one of the at least one primary superconducting coil and the at least one secondary superconducting coil, and to correct the distribution of a static magnetic field generated by both the at least one primary superconducting coil and the at least one secondary superconducting coil.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The embodiments disclosed in this specification and the drawings relate to a superconducting magnet and a magnetic resonance imaging apparatus. [Background technology]

[0002] A magnetic resonance imaging device is an imaging device that excites the nuclear spins of a subject placed in a static magnetic field with a radio frequency (RF) signal at the Larmor frequency, and generates an image by reconstructing the magnetic resonance (MR) signals generated from the subject in response to the excitation.

[0003] Many magnetic resonance imaging (MRI) devices have a configuration called a gantry, in which a cylindrical space is formed. An object (e.g., a patient) lying on a tabletop is carried into the cylindrical space and imaged. A cylindrical superconducting magnet, a cylindrical gradient magnetic field coil, and a cylindrical transmitting / receiving coil (i.e., a WB (Whole Body) coil) are housed inside the gantry. In many conventional magnetic resonance imaging devices of this type, the superconducting magnet, the gradient magnetic field coil, and the transmitting / receiving coil are cylindrical, and therefore, hereinafter, this type of magnetic resonance imaging device will be referred to as a cylindrical magnetic resonance imaging device.

[0004] In a cylindrical magnetic resonance imaging apparatus, imaging is performed in a cylindrical closed space, and therefore imaging may be difficult for some patients, such as those who suffer from claustrophobia.

[0005] In response to this, magnetic resonance imaging devices have been proposed and developed that use flat superconducting magnets and gradient coils, and are configured to image a subject such as a patient in an open space between, for example, two flat superconducting magnets. This type of magnetic resonance imaging device will be referred to as a planar open-type magnetic resonance imaging device (or simply an open-type magnetic resonance imaging device) below. In an open-type magnetic resonance imaging device, imaging is performed in an open space, making it possible to image claustrophobic patients.

[0006] In either a cylindrical magnetic resonance imaging apparatus or a planar open type magnetic resonance imaging apparatus, high winding precision is required for the superconducting coils that constitute the superconducting magnet in order to obtain a desired static magnetic field distribution.

[0007] The winding positions of the wire that constitutes the superconducting coil may be slightly misaligned due to manufacturing errors, thermal deformation, etc., and such misalignment of the windings causes a disturbance in the static magnetic field distribution generated by the superconducting magnet. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent Publication No. 2021-136300 Summary of the Invention [Problem to be solved by the invention]

[0009] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to suppress disturbances in the static magnetic field distribution generated by a superconducting magnet. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problem. Problems corresponding to the effects of each configuration shown in each embodiment described later can also be positioned as other problems. [Means for solving the problem]

[0010] A superconducting magnet in one embodiment includes at least one main superconducting coil that generates a main magnetic field, at least one secondary superconducting coil that generates a secondary magnetic field opposite to the main magnetic field, and a superconducting shim coil arranged to cover a part or all of an outer circumferential surface of at least one of the at least one main superconducting coil and the at least one secondary superconducting coil, and corrects a static magnetic field distribution generated by the at least one main superconducting coil and the at least one secondary superconducting coil. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram showing a first example of the arrangement of a magnetic resonance imaging apparatus according to an embodiment. [Diagram 2] FIG. 2 is a diagram showing a second example of the arrangement of a magnetic resonance imaging apparatus according to an embodiment. [Diagram 3] FIG. 2 is a diagram showing an example of the internal configuration of a superconducting magnet according to an embodiment. [Figure 4] FIG. 2 is a diagram showing an example of a method of winding a wire that constitutes a superconducting coil. [Diagram 5] FIG. 2 is a diagram showing a first embodiment of a superconducting shim coil. [Figure 6] FIG. 4 is a diagram showing a second embodiment of a superconducting shim coil. [Figure 7] FIG. 13 is a diagram showing a third embodiment of a superconducting shim coil. [Figure 8] FIG. 13 is a diagram showing a fourth embodiment of a superconducting shim coil. [Figure 9] FIG. 13 is a diagram showing a fifth embodiment of a superconducting shim coil. [Figure 10] 1 is a diagram showing an example of the configuration of a magnetic resonance imaging apparatus according to an embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0013] (Superconducting magnet) Fig. 1 is a diagram showing a first arrangement example of superconducting magnets 10 used in an open-type magnetic resonance imaging apparatus 1 according to an embodiment. As illustrated in Fig. 1, the magnetic resonance imaging apparatus 1 has, for example, two superconducting magnets 10 each having a circular flat plate shape (in other words, a thin cylindrical shape).

[0014] Each superconducting magnet 10 is arranged so that the central axis of the superconducting magnet 10, i.e., the axis passing through the center of the circle at each end face of the cylindrical shape, is parallel to, for example, the floor surface. The two superconducting magnets 10 are arranged so as to sandwich the subject. By arranging the superconducting magnets 10 in this manner, a magnetic field is formed in the open space between the two superconducting magnets 10. The subject is imaged in this open space, for example, in an upright position.

[0015] Fig. 2 is a diagram showing a second arrangement example of superconducting magnets 10 used in the open-type magnetic resonance imaging apparatus 1. While Fig. 1 shows an arrangement example for imaging a subject in an upright position, Fig. 2 shows an arrangement example for imaging a subject in a supine position lying on a top plate 80 of a bed 81. When imaging a subject in a supine position, the two superconducting magnets 10 are arranged so that their central axes are in the vertical direction as shown in Fig. 2, and for example, one superconducting magnet 10 is arranged below the top plate 80 and the other superconducting magnet 10 is arranged above the top plate 80.

[0016] As shown in FIGS. 1 and 2, in imaging using the superconducting magnet 10 of the embodiment, imaging of a subject in an open magnetic field space is possible, so that even a claustrophobic patient can be imaged.

[0017] Although Figures 1 and 2 show the subject being imaged in an open area outside the superconducting magnet 10 including the superconducting coil, the subject may be imaged with at least a portion of the subject placed in the open area outside the superconducting coil.

[0018] 3 is a diagram showing an example of the internal configuration of the superconducting magnet 10 of the embodiment. Each superconducting magnet 10 incorporates a main superconducting coil 100 that generates a main magnetic field, and a sub-superconducting coil 200 that generates a sub-magnetic field. A current flows in the sub-superconducting coil 200 in the opposite direction to that of the main superconducting coil 100 so that the sub-magnetic field is in the opposite direction to the main magnetic field.

[0019] Hereinafter, the main superconducting coil 100 may be referred to as the main coil 100, and the secondary superconducting coil 200 may be referred to as the secondary coil 200. In addition, since the secondary magnetic field generated by the secondary superconducting coil acts in a direction that cancels the main magnetic field, the secondary superconducting coil 200 may be referred to as the cancel coil 200.

[0020] Furthermore, as described below, each of the superconducting magnets 10 has a superconducting shim coil 110. The superconducting shim coil 110 is configured to correct the static magnetic field distribution of a composite magnetic field obtained by combining the main magnetic field generated by the main superconducting coil 100 and the sub-magnetic field generated by the sub-superconducting coil 200.

[0021] In addition, while FIG. 3 illustrates an example in which there is one main superconducting coil 100 and one auxiliary superconducting coil 200, the superconducting magnet 10 may be configured to have two or more main superconducting coils 100, or may be configured to have two or more auxiliary superconducting coils 200.

[0022] In the excitation mode, each of the main superconducting coil 100 and the auxiliary superconducting coil 200 generates a static magnetic field by passing a current supplied from a static magnetic field power supply (not shown), and then the static magnetic field power supply is disconnected and the mode transitions to the persistent current mode. Once the mode transitions to the persistent current mode, each of the main superconducting coil 100 and the auxiliary superconducting coil 200 continues to generate a large static magnetic field for a long period of time, for example, for more than one year.

[0023] 4 is a diagram showing an example of a method of winding the winding 101 constituting the main superconducting coil 100 or the winding 201 constituting the auxiliary superconducting coil 200. The main superconducting coil 100 and the auxiliary superconducting coil 200 are each configured by, for example, winding one winding 101, 201 so that a cylindrical layer is formed in a direction parallel to the cylindrical axis, and windings are provided such that a plurality of cylindrical layers are provided from the innermost layer to the outermost layer. Although the diameter of the generated ring and the number of turns of the winding 101 and the winding 201 are different from each other, the winding method itself is substantially the same, so that the winding 101 of the main superconducting coil 100 will be described below.

[0024] 4(b) shows multiple small hatched rectangles. Each rectangle represents the cross section of one of the windings 101, and the multiple rectangles represent the windings 101 wound coaxially multiple times around the cylindrical shaft 10a.

[0025] Each winding 101 can be constructed by, for example, forming a superconducting wire such as niobium titanium (Nb-Ti) or a rare earth or bismuth high temperature superconducting wire into a number of thin filaments or thin tapes and embedding them in a normally conductive base material such as copper.

[0026] By winding the winding 101 multiple times, the main superconducting coil 100 is formed into a circular ring shape having a predetermined thickness in a direction parallel to the cylindrical axis 10a shown in Figure 4(a) and a predetermined width in a direction perpendicular to the cylindrical axis 10a (i.e., the radial direction).

[0027] The winding 101 is wound coaxially multiple times, for example, from one end (e.g., the bottom end of the innermost layer) of the annular innermost layer (the layer closest to the cylindrical axis 10a) to the other end (e.g., the top end of the innermost layer) of the innermost layer. When the position of the winding 101 reaches the top end of the annular ring, the winding changes direction and is wound from the top end to the bottom end of the annular ring to form a second layer. By repeating this winding method from the innermost layer to the outermost layer in the radial direction of the annular ring, the main superconducting coil 100 is formed, having an annular cross section of a predetermined thickness and width.

[0028] Usually, the winding 101 is wound while being coated with a viscous material such as resin to prevent misalignment of the winding position.

[0029] Meanwhile, in order to obtain a desired static magnetic field distribution, the winding position and the number of turns of each of the windings 101 are determined in advance by calculation and simulation. In order to obtain a desired static magnetic field distribution, it is necessary to align the winding position of the winding 101 with a predetermined position with extremely high accuracy. For example, the present inventors have found through simulations and the like that if an error of, for example, a few tenths of a millimeter occurs between the actual winding position of the winding 101 and the predetermined position, it may not be possible to obtain a desired static magnetic field distribution.

[0030] However, for example, in the manufacturing process of winding 101 while applying a viscous material such as resin, it is extremely difficult to ensure a positional accuracy of about 0.05 mm, and there is a strong possibility that deviations in the winding position will occur as manufacturing errors.

[0031] Furthermore, since winding 101 wound in a room temperature environment (eg, an environment of 300K) will operate in a cryogenic environment (eg, an environment of 4K) in a superconducting state, deviation in winding position due to thermal contraction cannot be ignored.

[0032] In order to address such problems, the superconducting magnet 10 of the embodiment is configured to include a superconducting shim coil 110 in addition to the main superconducting coil 100 and the sub superconducting coil 200. The superconducting shim coil 110 is used to efficiently correct errors in the static magnetic field distribution (i.e., deviation from a desired static magnetic field distribution) caused by misalignment of the winding 101 due to manufacturing errors, thermal shrinkage, or the like.

[0033] Hereinafter, several embodiments of the superconducting shim coil 110 provided in the superconducting magnet 10 will be described with reference to FIGS.

[0034] The superconducting shim coil 110 is provided so as to cover a part or the whole of the outer circumferential surface of at least one of the main superconducting coil 100 and the auxiliary superconducting coil 200. The superconducting shim coil 110 is configured so as to correct the static magnetic field distribution generated by the main superconducting coil 100 and the auxiliary superconducting coil 200 by passing a correction current through the superconducting shim coil 110.

[0035] The superconducting shim coil 110 may be provided in both the main superconducting coil 100 and the auxiliary superconducting coil 200, or may be provided in either the main superconducting coil 100 or the auxiliary superconducting coil 200. In the following, each embodiment of the superconducting shim coil 110 will be described using an example in which the superconducting shim coil 110 is provided in the main superconducting coil 100, but the same applies to the superconducting shim coil 210 (see FIG. 10) provided in the auxiliary superconducting coil 200.

[0036] 5 is a diagram showing a first embodiment of the superconducting shim coil 110. As described above, the winding 101 of the main superconducting coil 100 is wound so as to form a plurality of layers from the innermost layer to the outermost layer of the annular shape. In the first embodiment of the superconducting shim coil 110, the superconducting shim coil 110 is provided adjacent to the outermost layer on the outer circumferential surface of the main superconducting coil 100 so as to cover the outermost layer of the winding 101.

[0037] It is considered that the positional deviation of the winding 101 due to manufacturing error, thermal contraction, etc. is larger on the outer circumferential side than on the inner circumferential side of the ring of the main superconducting coil 100, and that the positional deviation of the outermost layer of the winding 101 may be the largest. It is considered that the error of the magnetic field caused by the positional deviation can be corrected most efficiently by disposing the superconducting shim coil 110 adjacent to the position where the positional deviation is the largest. From this viewpoint, the superconducting shim coil 110 of the first embodiment is provided adjacent to the outermost layer of the winding 101 on the outer circumferential surface of the main superconducting coil 100 so as to cover the outermost layer.

[0038] The outer peripheral surface of the main superconducting coil 100 is composed of a cylindrical surface adjacent to the innermost layer, a cylindrical surface adjacent to the outermost layer, and two parallel planes perpendicular to the cylindrical axis 10a, which cover the top and bottom of the main superconducting coil 100.

[0039] In addition, as illustrated in FIG. 5(b), the superconducting shim coil 110 may be formed by winding the winding of the superconducting shim coil 110 (hereinafter referred to as the shim coil winding) so as to cover the outermost layer of the winding 101, like a single-layer solenoid coil, or may be formed by winding in multiple layers.

[0040] 6 is a diagram showing a second embodiment of the superconducting shim coil 110. The superconducting shim coil 110 of the second embodiment is provided adjacent to each of the two parallel planes so as to cover not only the cylindrical surface adjacent to the outermost layer among the outer circumferential surfaces of the main superconducting coil 100 but also two parallel planes perpendicular to the cylindrical axis 10a. In other words, the superconducting shim coil 110 of the second embodiment is provided adjacent to each of the three outer circumferential surfaces so as to cover three outer circumferential surfaces among the four outer circumferential surfaces of the main superconducting coil 100 except for the surface facing the innermost layer.

[0041] The reason for providing the superconducting shim coils 110 adjacent to each of the two parallel planes is that it is believed that misalignment of the winding 101 due to manufacturing errors, thermal contraction, etc. will be greatest at the positions of the two parallel planes perpendicular to the cylindrical axis 10a, next to the cylindrical surface of the outermost layer of the winding 101.

[0042] The superconducting shim coil 110 in the portion covering two parallel planes perpendicular to the cylinder axis 10a can be formed, for example, by winding a shim coil wire in a spiral shape.

[0043] In addition, the superconducting shim coil 110 may be configured with either one of two parallel planes perpendicular to the cylindrical axis 10a and a cylindrical surface adjacent to the outermost layer. Alternatively, the superconducting shim coil 110 may be configured with only two parallel planes perpendicular to the cylindrical axis 10a. Alternatively, the superconducting shim coil 110 may be configured with one or more of four surfaces: two parallel planes perpendicular to the cylindrical axis 10a, a cylindrical surface adjacent to the outermost layer of the winding 101, and a cylindrical surface adjacent to the innermost layer of the winding 101.

[0044] 7 is a diagram showing a third embodiment of the superconducting shim coil 110. The superconducting shim coil 110 of the third embodiment is formed so as to cover all four surfaces of the outer circumferential surface of the main superconducting coil 100.

[0045] 8 is a diagram showing a fourth embodiment of the superconducting shim coil 110. The main superconducting coil 100 of the fourth embodiment includes a winding form 120. The winding form 120 is provided as a guide for the winding 101 in order to increase the efficiency of the winding operation of the winding 101 of the main superconducting coil 100 or to increase the accuracy of the winding position of the winding 101. As shown in FIG. 8, the winding frame 120 may be provided so as to surround the entire outer circumferential surface of the winding 101, or may be provided so as to surround three sides of the outer circumferential surface of the winding 101 excluding the outermost layer.

[0046] In the fourth embodiment, the superconducting shim coil 110 is provided outside the winding frame 120, for example, adjacent to the winding frame 120. In this case, the superconducting shim coil 110 may be provided so as to surround the entire outer peripheral surface of the winding frame 120 as shown in Fig. 8, but may be provided so as to cover the surface of the winding frame 120 on the outermost layer side of the winding 101 as in the first embodiment, or may be provided so as to cover three surfaces of the winding frame 120 corresponding to the three surfaces excluding the innermost layer of the winding 101 as in the second embodiment.

[0047] FIG. 9 is a diagram showing a fifth embodiment of the superconducting shim coil 110. The main superconducting coil 100 of the fifth embodiment also includes a reel 120. The reel 120 can be configured to be removable from the winding 101 after the winding of the winding 101 is completed. In the main superconducting coil 100 having such a reel 120, the superconducting shim coil 110 can be provided inside the reel 120, i.e., between the reel 120 and the winding 101, as shown in FIG. 9. In such a configuration, the superconducting shim coil 110 may be provided so as to surround the entire outer circumferential surface of the winding 101 as shown in FIG. 9, or may be provided so as to cover the surface of the outermost layer of the winding 101, or may be provided so as to cover three outer circumferential surfaces of the winding 101 excluding the surface of the innermost layer.

[0048] (Magnetic Resonance Imaging Device) 10 is a diagram showing a configuration example of a magnetic resonance imaging apparatus 1 in an embodiment in which superconducting magnets 10 having the main superconducting coil 100 and the sub-superconducting coil 200 according to each of the above-mentioned embodiments are arranged above and below a lying subject P. An imaging region, or FOV (Field of View), is formed between the two superconducting magnets 10.

[0049] The main superconducting coil 100 and the auxiliary superconducting coil 200 provided in each of the two superconducting magnets 10 are provided with superconducting shim coils 110, 210 that cover the outer periphery of the respective windings. Here, the superconducting shim coil 110 covers the outer periphery of the winding of the main superconducting coil 100 (hereinafter referred to as the main coil 100), and the superconducting shim coil 210 covers the outer periphery of the winding of the auxiliary superconducting coil 200 (hereinafter referred to as the auxiliary coil 200).

[0050] The main coil 100 and the sub-coil 200, whose outer peripheries are covered with the superconducting shim coils 110 and 210, are housed, for example, in a cooling vessel 10b called a cryostat.

[0051] The magnetic resonance imaging apparatus 1 shown in FIG. 10 has, in addition to the two superconducting magnets 10 mentioned above, a tabletop 80 on which a subject P lies, a local coil 20 placed in close proximity to the subject, a gradient magnetic field coil 60, and an RF (radio frequency) coil 62.

[0052] The magnetic resonance imaging apparatus 1 also includes a magnetic field sensor 300, a shim coil power supply 40, a control circuit 42, an imaging condition setting circuit 50, a sequence controller 51, a gradient magnetic field power supply 52, a transmission circuit 53, a reception circuit 54, and a reconstruction processing circuit 55.

[0053] The magnetic field sensor 300 is disposed at a predetermined position outside the cooling container 10b, and measures magnetic field information such as the intensity of the static magnetic field, the static magnetic field distribution, etc. Although one magnetic field sensor 300 is shown in Fig. 10, the number of the magnetic field sensors 300 may be multiple, and these multiple magnetic field sensors 300 are disposed at a predetermined position outside the cooling container 10b, for example, adjacent to the imaging space.

[0054] The imaging condition setting circuit 50 sets imaging conditions, such as the type of pulse sequence and the values ​​of various parameters, inputted via a user interface (not shown), in a sequence controller 51 .

[0055] The sequence controller 51 scans the subject based on the set imaging conditions by driving the gradient magnetic field power supply 52 and the transmission circuit 53. The gradient magnetic field power supply 52 applies a gradient magnetic field current to the gradient magnetic field coil 60 based on a drive signal from the sequence controller 51.

[0056] The transmission circuitry 53 generates an RF pulse based on a drive signal from the sequence controller 51, and applies the RF pulse to the RF coil 62. In response to this application, an MR (Magnetic Resonance) signal emitted from the subject P is received by the local coil 20. The MR signal received by the local coil 20 is converted from an analog signal to a digital signal by the reception circuitry 54. The MR signal converted to a digital signal is supplied to the reconstruction processing circuitry 55 as k-space data. The reconstruction processing circuitry 55 performs reconstruction processing such as an inverse Fourier transform process on the k-space data to generate a magnetic resonance image.

[0057] As described above, in the excitation mode, a current supplied from a static magnetic field power supply (not shown) flows through the main coil 100 and the sub-coil 200, and then the static magnetic field power supply is disconnected and the mode transitions to the persistent current mode. After the transition to the persistent current mode, the static magnetic field distribution of the composite magnetic field, which is the composite of the static magnetic field generated by the main coil 100 and the sub-magnetic field generated by the sub-coil 200, is maintained.

[0058] The outer circumferential surfaces of the main coil 100 and the secondary coil 200 are covered with superconducting shim coils 110 and 210, respectively.

[0059] 10, the superconducting shim coils 110, 210 cover the entire outer circumferential surfaces of the main coil 100 and the secondary coil 200, but as described above, they may cover only a part of the outer circumferential surfaces. Also, in FIG. 10, the outer circumferential surfaces of both the main coil 100 and the secondary coil 200 are covered with the superconducting shim coils 110, 210, but it is also possible to cover only one of them, for example, the main coil 100, with the superconducting shim coil 110.

[0060] A current is supplied to the superconducting shim coils 110, 210 from a shim coil power supply 40 under the control of a control circuit 42. The control circuit 42 determines, for example, by feedback control, the current to be applied to the superconducting shim coils 110, 210 so as to correct the static magnetic field distribution generated by the main coil 100 and the sub coil 200 based on information about the magnetic field measured by the magnetic field sensor 300. Then, the shim coil power supply 40 supplies the current determined by the control circuit 42 to the superconducting shim coils 110, 210.

[0061] The superconducting shim coils 110 and 210 can be configured such that a shim coil power supply 40 is constantly connected and the static magnetic field distribution is corrected by a current constantly supplied from the shim coil power supply 40 .

[0062] On the other hand, a configuration may be adopted in which a persistent current switch (PCS) is provided between the superconducting shim coils 110, 210 and the shim coil power supply 40. In this configuration, before switching to the persistent current mode, the superconducting shim coils 110, 210 correct the static magnetic field distribution with a current supplied from the shim coil power supply 40 via the persistent current switch, and then switch off the persistent current switch to switch to the persistent current mode. After switching to the persistent current mode, the static magnetic field distribution corrected immediately before switching to the persistent current mode is maintained.

[0063] As described above, current is passed through the main coil 100 and the secondary coil 200 so that the direction of the magnetic field generated by the secondary coil 200 is opposite to the direction of the magnetic field generated by the main coil 100. Therefore, when the sign of the magnetic field generated by the main coil 100 is positive, the sign of the magnetic field generated by the secondary coil 200 is negative.

[0064] As a result, in the composite magnetic field, the magnetic field generated by the main coil 100 and the magnetic field generated by the sub-coil 200 cancel each other out, and it becomes possible to generate a region with uniform magnetic field strength (i.e., a region where the magnetic field strength hardly changes) or a magnetic field region with a very gentle gradient in the cylinder axial direction (the vertical direction in Figs. 2 and 10). Such a region where the magnetic field strength hardly changes can be used as the FOV during MR imaging.

[0065] On the other hand, as described above, if the winding positions of the main coil 100 or the sub-coil 200 are slightly misaligned due to manufacturing errors, thermal deformation, or the like, such misalignment of the windings will cause a disturbance in the static magnetic field distribution generated by the main coil 100 or the sub-coil 200. As the size of the gap between adjacent windings increases, the behavior of the magnetic field will gradually deviate from that when there is no gap error.

[0066] For this reason, a situation may occur in which a region where the magnetic field strength hardly changes (that is, a region that can be used as the FOV during MR imaging), which exists when there is no gap error, no longer exists due to the gap error.

[0067] In order to avoid such a situation, the superconducting magnet 10 of this embodiment is provided with the above-mentioned superconducting shim coils 110 and 210, and the disturbance of the static magnetic field distribution due to manufacturing errors, thermal deformation, etc. is corrected by controlling the current flowing through the superconducting shim coils 110 and 210. For example, an ideal static magnetic field distribution when there are no manufacturing errors, thermal deformation, etc. is stored in an appropriate memory, and the current flowing through the superconducting shim coils 110 and 210 is feedback-controlled so that the magnetic field measured by the magnetic field sensor 300 becomes the ideal static magnetic field distribution stored in the memory, thereby making it possible to correct the disturbance of the static magnetic field distribution due to manufacturing errors, thermal deformation, etc.

[0068] In addition, the magnetic resonance imaging apparatus 1 of the above-mentioned embodiment (e.g., Figures 2 and 10) is configured to include two static magnetic field magnets 10 facing each other, and images of the subject are captured in the space sandwiched between the two static magnetic field magnets 10.

[0069] Alternatively, a configuration may be adopted in which only one of the two static magnetic field magnets 10 is provided. For example, the magnetic resonance imaging apparatus 1 of the embodiment may be configured by removing the static magnetic field magnet 10 above the tabletop 80 from the configuration of the magnetic resonance imaging apparatus 1 shown in Fig. 2 or 10. Even with such a configuration, each of the technical effects described above can be achieved.

[0070] According to at least one of the embodiments described above, it is possible to suppress disturbance in the static magnetic field distribution generated by the superconducting magnet.

[0071] Although some embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations of embodiments can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents as described in the claims, as well as in the scope and spirit of the invention. [Explanation of symbols]

[0072] 1. Magnetic resonance imaging equipment 10 Superconducting magnets 10a Cylindrical shaft 10b Cooling vessel 20 Local Coil 40 Shim coil power supply 42 Control circuit 60 Gradient magnetic field coil 62 RF coil 100 Main superconducting coil (main coil) 110, 210 Superconducting shim coil 200 Secondary superconducting coil (secondary coil)

Claims

1. at least one main superconducting coil for generating a main magnetic field; At least one secondary superconducting coil for generating a secondary magnetic field in a direction opposite to that of the main magnetic field; a superconducting shim coil provided so as to cover a part or the whole of an outer circumferential surface of at least one of the at least one main superconducting coil and the at least one auxiliary superconducting coil, the superconducting shim coil correcting a static magnetic field distribution generated by the at least one main superconducting coil and the at least one auxiliary superconducting coil; A superconducting magnet comprising:

2. Each of the main superconducting coil and the auxiliary superconducting coil is configured such that a winding is wound so that a cylindrical layer is formed in a direction parallel to a cylindrical axis, and the cylindrical layer is wound so that a plurality of layers are provided from the innermost layer to the outermost layer.

2. The superconducting magnet according to claim 1.

3. the superconducting shim coil is provided adjacent to the outermost layer so as to cover the outermost layer of the outer circumferential surface of at least one of the main superconducting coil and the auxiliary superconducting coil; 3. The superconducting magnet according to claim 2.

4. the superconducting shim coil is provided adjacent to a surface perpendicular to the cylindrical axis so as to further cover a surface perpendicular to the cylindrical axis of at least one of the outer circumferential surfaces of the main superconducting coil and the auxiliary superconducting coil.

4. The superconducting magnet according to claim 3.

5. Each of the main superconducting coil and the secondary superconducting coil further includes a winding form, The superconducting shim coil is provided outside the winding body.

2. The superconducting magnet according to claim 1.

6. Each of the main superconducting coil and the secondary superconducting coil further includes a winding form, The superconducting shim coil is provided inside the winding frame.

2. The superconducting magnet according to claim 1.

7. a shim coil power supply that supplies a current to the superconducting shim coil; A magnetic field sensor for measuring a magnetic field, the shim coil power supply supplies a current to the superconducting shim coil so as to correct the static magnetic field distribution generated by the main superconducting coil and the sub superconducting coil based on the magnetic field measured by the magnetic field sensor.

2. The superconducting magnet according to claim 1.

8. the cooling vessel further includes a cylindrical cooling vessel having two parallel planes or a cylindrical cooling vessel having a central hollow portion, the cylindrical cooling vessel housing the main superconducting coil, the auxiliary superconducting coil, and the superconducting shim coil; The magnetic field sensor is provided outside the cylindrical cooling vessel or in the central hollow portion of the cylindrical cooling vessel. The superconducting magnet according to claim 7.

9. The superconducting shim coil is constantly connected to the shim coil power supply, and corrects the static magnetic field distribution by the current supplied from the shim coil power supply. The superconducting magnet according to claim 7.

10. a persistent current switch is provided between the superconducting shim coil and the shim coil power supply; The superconducting shim coil comprises: Before switching to a persistent current mode, the static magnetic field distribution is corrected by the current supplied from the shim coil power supply via the persistent current switch; Thereafter, the persistent current switch is turned off to transition to the persistent current mode. The superconducting magnet according to claim 7.

11. 11. The superconducting magnet according to claim 1, wherein the superconducting shim coils are arranged in a coil arrangement that shares a central axis with the main superconducting coil or the sub superconducting coil.

12. A magnetic resonance imaging apparatus comprising the superconducting magnet according to any one of claims 1 to 10.

Images