Static magnetic field magnet, magnetic resonance imaging device, and method for adjusting static magnetic field

Abstract

To reduce a weight of a static magnetic field magnet, reduce demagnetization works, and reduce consumption of liquid helium while improving uniformity of a static magnetic field while making an iron shim unavailable.SOLUTION: A cylindrical-shape static magnetic field magnet that generates a static magnetic field includes a plurality of superconductive coils and a position adjustment part. The superconductive coils are split at a transverse section of the cylindrical shape. The position adjustment part changes and fixes a relative physical relationship of the plurality of superconductive coils. The position adjustment part slides the whole or part of the plurality of superconductive coils along a height direction of the cylindrical shape.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The embodiments disclosed in this specification and the drawings relate to a static magnetic field magnet, a magnetic resonance imaging (MRI) apparatus, and a static magnetic field adjustment method. [Background technology]

[0002] An MRI device is an imaging device that excites the nuclear spins of a subject placed in a static magnetic field generated by a static magnetic field magnet with radio frequency (RF) signals at the Larmor frequency, and generates images by reconstructing the magnetic resonance signals (MR (Magnetic Resonance) signals) generated from the subject in response to the excitation. Magnetic resonance imaging devices can collect magnetic resonance signals from the subject non-invasively.

[0003] In order to obtain high-quality images from an MRI system, it is necessary to homogenize the static magnetic field formed by the superconducting coil that serves as the static magnetic field magnet. One method of correcting the non-uniformity of the static magnetic field is to install magnetic materials called iron shims in multiple locations inside the superconducting coil. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2008-289717 A Summary of the Invention [Problem to be solved by the invention]

[0005] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to improve the uniformity of the static magnetic field without using iron shims, while reducing the weight of the static magnetic field magnet by not using iron shims, reducing the demagnetization work, and reducing the consumption of liquid helium. 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 the embodiments described later can also be positioned as other problems. [Means for solving the problem]

[0006] A cylindrical static magnetic field magnet that generates a static magnetic field according to an embodiment includes a plurality of superconducting coils and a position adjustment unit. The plurality of superconducting coils are divided at the cross section of the cylindrical shape. The position adjustment unit is for changing and fixing the relative positional relationship of the plurality of superconducting coils. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a block diagram showing the overall configuration of a magnetic resonance imaging apparatus equipped with a static magnetic field magnet according to an embodiment. [Diagram 2] FIG. 2 is a cross-sectional view showing a first configuration example of a static magnetic field magnet according to an embodiment. [Diagram 3] FIG. 3 is a cross-sectional view showing a portion of a first configuration example of a static magnetic field magnet according to an embodiment. [Figure 4] FIG. 4 is a cross-sectional view showing a second configuration example of the static magnetic field magnet according to the embodiment. [Diagram 5] FIG. 5 is a cross-sectional view showing a part of a second configuration example of a static magnetic field magnet according to an embodiment. [Figure 6] 6 is a diagram for explaining the operation of the configuration shown in FIG. 5 in the static magnetic field magnet according to the embodiment. [Figure 7] FIG. 7 is a cross-sectional view showing a part of a second configuration example of the static magnetic field magnet according to the embodiment. [Figure 8] FIG. 8 is a cross-sectional view showing a part of a second configuration example of a static magnetic field magnet according to an embodiment. [Figure 9]FIG. 9 is a cross-sectional view showing a part of a second configuration example of a static magnetic field magnet according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, embodiments of a static magnetic field magnet, an MRI apparatus, and a static magnetic field adjusting method will be described in detail with reference to the drawings.

[0009] FIG. 1 is a block diagram showing the overall configuration of an MRI apparatus including a high-frequency coil unit according to an embodiment.

[0010] 1 shows an MRI apparatus 1 according to an embodiment. The MRI apparatus 1 includes a magnet gantry 10, a local coil 20 (e.g., chest coil 20A), a bed 30, a control cabinet 40, and an image processing unit (e.g., a console) 50. The magnet gantry 10, the local coil 20, and the bed 30 are usually arranged in an examination room, which is a shielded room. Meanwhile, the control cabinet 40 is arranged in a room called a machine room, for example, and the console 50 is arranged in an operation room.

[0011] 1 illustrates a case where the MRI apparatus 1 adopts a method (head first) in which a subject, for example, a patient U, is transferred into a bore formed by the magnet gantry 10 from the head side, but the present invention is not limited to this case. For example, the MRI apparatus 1 may adopt a method (foot first or feet first) in which the patient U is transferred into a bore formed by the magnet gantry 10 from the foot side. The bore refers to the space inside the cylinder of the magnet gantry 10.

[0012] The magnet gantry 10 includes a static magnetic field magnet 11, a gradient magnetic field coil 12, a WB (Whole Body) coil 13, etc. The static magnetic field magnet 11 of the magnet gantry 10 is broadly classified into a tunnel type in which the magnet has a cylindrical magnetic structure, and an open type in which a pair of magnets are arranged above and below with an imaging space in between. Here, a case in which the static magnetic field magnet 11 is of the tunnel type will be described, but the present invention is not limited to this case.

[0013] The static magnetic field magnet 11 has a roughly cylindrical shape and generates a static magnetic field in a bore to which a patient U is transported. As shown in Figs. 2 and 4, the static magnetic field magnet 11 includes a plurality of superconducting coils 60, a position adjustment unit 70, a helium container 80, a plurality of coil support units 90, and a refrigerator (not shown) that cools the liquid helium in the helium container 80 to an extremely low temperature. The position adjustment unit 70 has a function of adjusting the relative positional relationship of the plurality of superconducting coils 60 by changing and fixing the relative positional relationship of the plurality of superconducting coils 60. For example, the position adjustment unit 70 slides all or a portion of the plurality of superconducting coils 60 along the height direction (Z-axis direction) of the cylindrical shape.

[0014] The multiple coil support parts 90 are disposed between each of the multiple superconducting coils 60 and the inner wall of the helium vessel 80, and hold each of the multiple superconducting coils 60 so that they can slide in the Z-axis direction. For example, by providing wheels (not shown) on the inner wall side of the helium vessel 80 for the multiple superconducting coils 60, the multiple superconducting coils 60 can be configured to run on rails along the Z-axis direction provided on the inner wall of the helium vessel 80. The static magnetic field magnet 11 may be formed of a permanent magnet. Below, a case where the static magnetic field magnet 11 has multiple superconducting coils 60 will be described.

[0015] In the static magnetic field magnet 11, multiple superconducting coils 60 are cooled to extremely low temperatures by liquid helium. In the excitation mode, the static magnetic field magnet 11 applies a current supplied from a static magnetic field power supply to each of the multiple superconducting coils 60 to generate a static magnetic field. After that, when the mode is switched to the persistent current mode, the static magnetic field power supply is disconnected. Once the mode is switched to the persistent current mode, the static magnetic field magnet 11 continues to generate a static magnetic field for a long period of time, for example, for more than one year.

[0016] 2 and 4, the multiple superconducting coils 60 have a shape (roughly cylindrical shape) in which a roughly cylindrical superconducting coil unit having a height in the Z-axis direction is divided at a cross section (XY cross section). For example, the static magnetic field magnet 11 has a superconducting coil unit including two superconducting coils 60 divided at one cross section (XY cross section) (superconducting coils 61 and 62 shown in FIG. 2). Also, for example, the static magnetic field magnet 11 has a superconducting coil unit including three superconducting coils 60 divided at two cross sections (XY cross sections) (superconducting coils 63 to 65 shown in FIG. 4).

[0017] In addition, a position adjustment unit 70 is provided between the multiple superconducting coils 60 to change and fix the relative positional relationship between the multiple superconducting coils 60. For example, the static magnetic field magnet 11 is provided with a position adjustment unit 70 between the two superconducting coils 61, 62 (position adjustment unit 71 shown in FIG. 2). For example, the static magnetic field magnet 11 is provided with a position adjustment unit 70 between the two superconducting coils 63, 64 (position adjustment unit 73 shown in FIG. 4), and is also provided with a position adjustment unit 70 between the two superconducting coils 64, 65 (position adjustment unit 74 shown in FIG. 4). The detailed configuration of the static magnetic field magnet 11 will be described later with reference to FIGS. 2 to 9.

[0018] Returning to the explanation of Fig. 1, the gradient magnetic field coil 12 has a roughly cylindrical shape similar to the static magnetic field magnet 11, and is placed inside the static magnetic field magnet 11. The gradient magnetic field coil 12 generates a gradient magnetic field by a current (power) supplied from a gradient magnetic field power supply 41 described later, and applies the gradient magnetic field to the patient U. The gradient magnetic field coil 12 includes an Xch coil that generates a gradient magnetic field in the X-axis direction, a Ych coil that generates a gradient magnetic field in the Y-axis direction, and a Zch coil that generates a gradient magnetic field in the Z-axis direction. Here, the Z-axis direction is the direction along the static magnetic field, the Y-axis direction is the vertical direction, and the X-axis direction is the direction perpendicular to both the Z-axis and the Y-axis.

[0019] Here, since an eddy magnetic field generated by an eddy current generated with the generation of a gradient magnetic field interferes with imaging, for example, an actively shielded gradient coil (ASGC) for the purpose of reducing eddy currents may be used as the gradient magnetic field coil 12. The ASGC is a gradient magnetic field coil in which a shield coil for suppressing leakage magnetic fields is provided on the outside of a main coil for forming each of the gradient magnetic fields in the X-axis, Y-axis, and Z-axis directions.

[0020] The WB coil 13 is also called a whole-body coil, and is disposed inside the gradient coil 12 in a generally cylindrical shape so as to surround the patient U. The WB coil 13 functions as a transmitting coil. That is, the WB coil 13 transmits RF pulses to the patient U in accordance with an RF pulse signal transmitted from an RF transmitter 42, which will be described later. Meanwhile, the WB coil 13 may also function as a receiving coil in addition to the function as a transmitting coil that transmits RF pulses. In that case, the WB coil 13 serves as a receiving coil to receive MR signals emitted from the patient U due to excitation of atomic nuclei. The WB coil 13 is an example of an RF coil.

[0021] The MRI apparatus 1 may include a local coil 20 in addition to the WB coil 13. The local coil 20 is placed close to the body surface of the patient U. The local coil 20 may include a plurality of coil elements. A coil in which a plurality of coil elements are arranged in an array is sometimes called a PAC (Phased Array Coil).

[0022] There are several types of local coils 20. For example, the local coils 20 include a body coil placed on the chest (or abdomen or leg) of a patient U as shown in FIG. 1, and a spine coil placed on the back of the patient U. Other types of local coils 20 include a head coil for imaging the head of the patient U and a foot coil for imaging the legs. Other types of local coils 20 include a wrist coil for imaging the wrist, a knee coil for imaging the knee, and a shoulder coil for imaging the shoulder. In this embodiment, a case will be described in which the local coil 20 is a chest coil 20A, but the present invention is not limited to this case.

[0023] The local coil 20 functions as a receiving coil. That is, the local coil 20 receives the above-mentioned MR signal. However, the local coil 20 may be a transmitting / receiving coil having a function as a transmitting coil that transmits RF pulses in addition to the function as a receiving coil that receives MR signals. For example, the head coil and knee coil as the local coil 20 also include a transmitting / receiving coil. That is, the local coil 20 may be a transmitting-only coil, a receiving-only coil, or a coil for both transmitting and receiving. In this specification, the case where the local coil 20 is a chest coil 20A will be described, but the present invention is not limited to this case. The local coil 20 is an example of an RF coil.

[0024] In this specification, the local coil 20 is described as one of the components of the MRI apparatus 1, but there may be cases where the local coil 20 is not included in the configuration of the MRI apparatus 1. In this case, although the local coil 20 is not included in the configuration of the MRI apparatus 1, the local coil 20 and the MRI apparatus 1 are configured to be connectable to each other. More specifically, the local coil 20 and the bed top 32 of the MRI apparatus 1 are configured to be connectable to each other.

[0025] The bed 30 comprises a bed body 31 and a bed top 32. The bed body 31 is capable of moving the bed top 32 in the vertical and horizontal directions, and moves the patient U placed on the bed top 32 to a predetermined height before imaging. Thereafter, during imaging, the bed top 32 is moved horizontally to move the patient U into the bore. The bed top 32 is provided on the upper side of the bed body 31, and is used to position the patient U in a supine position.

[0026] The control cabinet 40 includes gradient magnetic field power supplies 41 (for the X-axis 41x, for the Y-axis 41y, and for the Z-axis 41z), an RF transmitter 42, an RF receiver 43, and a sequence controller 44.

[0027] The gradient magnetic field power supply 41 includes gradient magnetic field power supplies 41x, 41y, and 41z for each channel that drive coils that generate gradient magnetic fields in the X-axis direction, the Y-axis direction, and the Z-axis direction, respectively. The gradient magnetic field power supplies 41x, 41y, and 41z output required currents independently for each channel in response to a command from a sequence controller 44. This enables the gradient magnetic field coil 12 to apply gradient magnetic fields (also called "gradient magnetic fields") in the X-axis direction, the Y-axis direction, and the Z-axis direction to the patient U.

[0028] The RF transmitter 42 generates an RF pulse signal based on an instruction from the sequence controller 44. The RF transmitter 42 transmits the generated RF pulse signal to an RF coil (the WB coil 13 or the local coil 20).

[0029] The MR signals received by the WB coil 13 and the local coil 20, more specifically, the MR signals received by each coil element in the local coil 20, are transmitted to the RF receiver 43. The output line of each coil element and the output line of the WB coil 13 are called channels. For this reason, the MR signals output from each coil element and the WB coil 13 are sometimes called channel signals. The channel signals received by the WB coil 13 are also transmitted to the RF receiver 43.

[0030] The RF receiver 43 performs AD (Analog to Digital) conversion on the channel signals from the WB coil 13 and the local coil 20, i.e., the MR signals, and outputs the signals to a sequence controller 44. The digitally converted MR signals are sometimes called raw data.

[0031] The sequence controller 44 performs imaging of the patient U by driving the gradient magnetic field power supply 41, the RF transmitter 42, and the RF receiver 43 under the control of the console 50. When raw data is received from the RF receiver 43 by imaging, the sequence controller 44 transmits the raw data to the console 50.

[0032] The sequence controller 44 includes a processing circuit (not shown). The processing circuit is configured with hardware such as a processor that executes a predetermined program, a field programmable gate array (FPGA), and an application specific integrated circuit (ASIC).

[0033] The console 50 comprises a processing circuit 51, a memory 52, an input interface 53 and a display 54.

[0034] The processing circuit 51 refers to a processor such as a dedicated or general-purpose CPU (Central Processing Unit) or MPU (Micro Processor Unit), as well as an application specific integrated circuit (ASIC) and a programmable logic device. Examples of the programmable logic device include a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA). The processing circuit 51 reads and executes a program stored in the memory 52 or directly incorporated in the processing circuit 51, thereby controlling the operation of the sequence controller 44 and realizing a function of performing imaging according to a pulse sequence to generate an MR image. The processing circuit 51 is an example of a processing unit.

[0035] Furthermore, the processing circuit 51 may be configured by a single processing circuit, or may be configured by a combination of multiple independent processing circuit elements. In the latter case, multiple memories 52 may store programs corresponding to the functions of the multiple processing circuit elements, respectively, or one memory 52 may store programs corresponding to the functions of the multiple processing circuit elements.

[0036] The memory 52 includes a semiconductor memory element such as a random access memory (RAM) or a flash memory, a hard disk, an optical disk, etc. The memory 52 may include a portable medium such as a universal serial bus (USB) memory or a digital video disk (DVD). The memory 52 stores various processing programs (including application programs, an operating system (OS), etc.) used in the processing circuit 51, data required for executing the programs, and medical images. The OS may also include a graphical user interface (GUI) that uses a lot of graphics to display information to the operator on the display 54 and allows basic operations to be performed by the input interface 53. The memory 52 is an example of a storage unit.

[0037] The input interface 53 includes an input device that can be operated by an operator, and an input circuit that inputs a signal from the input device. The input device can be realized by a trackball, a switch, a mouse, a keyboard, a touchpad that performs an input operation by touching the operation surface, a touchscreen in which a display screen and a touchpad are integrated, a non-contact input device using an optical sensor, a voice input device, etc. When the input device is operated by the operator, the input circuit generates a signal according to the operation and outputs it to the processing circuit 51. The input interface 53 is an example of an input unit.

[0038] The display 54 is configured by a general display output device such as a liquid crystal display, an OLED (Organic Light Emitting Diode) display, etc. The display 54 displays various information under the control of the processing circuit 51. The display 54 is an example of a display unit.

[0039] Under the control of the processing circuitry 51, the console 50 arranges the raw data transmitted from the sequence controller 44 in k-space and stores it in the memory 52. ​​Under the control of the processing circuitry 51, the console 50 performs reconstruction processing such as an inverse Fourier transform on the k-space data stored in the memory 52 to generate desired MR images of the inside of the patient U. Then, under the control of the processing circuitry 51, the console 50 stores the generated various MR images in the memory 52.

[0040] Here, in order to correct the non-uniformity of the static magnetic field, there is a method of providing a magnetic material called an iron shim inside the superconducting coil 60. However, the installation of this iron shim increases the weight of the static magnetic field magnet 11. Furthermore, when adjusting the uniformity of the static magnetic field using an iron shim, it is necessary to demagnetize the magnet when installing the iron shim. The demagnetization process not only takes time, but also consumes liquid helium.

[0041] Therefore, the static magnetic field magnet 11 includes a plurality of superconducting coils 60 divided in cross section, and a position adjustment unit 70 for changing and fixing the relative positional relationship of the plurality of superconducting coils 60. This improves the uniformity of the static magnetic field without using iron shims, while reducing the weight of the static magnetic field magnet by not using iron shims, reducing the demagnetization work, and reducing the consumption of liquid helium.

[0042] FIG. 2 is a cross-sectional view showing a first configuration example of the static magnetic field magnet 11. The left side of FIG. 2 shows a longitudinal cross-sectional view of the static magnetic field magnet 11, and the right side of FIG. 2 shows a transverse cross-sectional view (AA cross-sectional view on the left side) of the static magnetic field magnet 11. The static magnetic field magnet 11 includes two superconducting coils 60 (e.g., superconducting coils 61 and 62), a position adjustment unit 70 (e.g., position adjustment unit 71) between the two superconducting coils 61 and 62, a helium container 80, and a coil support unit 90 (e.g., a coil support unit 91 supporting the superconducting coil 61 and a coil support unit 92 supporting the superconducting coil 62). Note that, on the right side of FIG. 2, the position adjustment units 70 (as well as the coil support unit 90) are arranged at eight locations along the circumference of the cylinder of the static magnetic field magnet 11, but are not limited to eight locations. The position adjustment units 70 may be arranged at multiple locations at approximately equal intervals along the circumference of the cylinder of the static magnetic field magnet 11.

[0043] Fig. 3 is an enlarged view of the upper configuration in the left diagram of Fig. 2. As shown in Fig. 3, the static magnetic field magnet 11 includes members 61, 62, and 71, as well as a winding form F1 for the superconducting coil 61 and a winding form F2 for the superconducting coil 62. The winding forms F1 and F2 are each connected to a coil support portion 90 (shown in Fig. 2), and wire, arrange, and fix the superconducting coils 61 and 62.

[0044] The position adjustment unit 70, for example, the position adjustment unit 71, includes a ball screw 71A and an ultrasonic motor 71B, which is a non-magnetic motor, in order to change the position of the reel F1. The position adjustment unit 71 includes a ball screw 71C and an ultrasonic motor 71D, which is a non-magnetic motor, in order to change the position of the reel F2. That is, the static magnetic field magnet 11 has a structure in which the reels F1 and F2 are connected by the members 71A to 71D of the position adjustment unit 71. When a motor is mounted inside the static magnetic field magnet 11, there is a restriction that the motor should not generate magnetism and should not be affected by magnetism. Therefore, in order to satisfy these restrictions, the ultrasonic motors 71B and 71D are adopted. It is assumed that the ultrasonic motors 71B and 71D are integrated.

[0045] After assembling the superconducting coil 60, the eight ultrasonic motors 71B arranged along the circumference are controlled by the processing circuit 51 of the MRI apparatus 1 (or a control device, not shown, outside the MRI apparatus 1) to rotate the eight ball screws 71A arranged along the circumference. This causes the superconducting coil 61 to be attracted to or pulled away from the ultrasonic motor 71B, so that the relative positional relationship in the Z-axis direction of the winding frames F1 and F2 (i.e., the superconducting coils 61 and 62) on the ball screw 71A can be changed. The relationship between the ball screw 71C and the ultrasonic motor 71D is the same as the relationship between the ball screw 71A and the ultrasonic motor 71B.

[0046] In addition, after one of the multiple superconducting coils 60 (for example, the superconducting coil 61) is fixed to the helium container 80 (not slidable), only the position of the superconducting coil 62 may be slid relative to the superconducting coil 61, or the positions of the superconducting coils 61 and 62 may be slid relative to each other. Since the uniformity of the static magnetic field can be adjusted while changing the relative positional relationship of the superconducting coils 61 and 62, the uniformity of the static magnetic field can be improved without using iron shims. Furthermore, once the relative positional relationship of the superconducting coils 61 and 62 is changed, the ultrasonic motors 71B and 71D have a high torque retention, so that the positions after the relative positional relationship is changed, that is, after the superconducting coils 61 and 62 are slid in the Z-axis direction, can be fixed.

[0047] In addition, the eight ball screws 71A arranged along the circumference are rotated by the same number of rotations to move the superconducting coil 61 in parallel in the Z-axis direction, but the present invention is not limited to this case. The eight ball screws 71A arranged along the circumference are rotated by different numbers of rotations to change the 90° angle that the superconducting coil 61 makes with the XZ plane, thereby tilting the superconducting coils 61 and 62.

[0048] FIG. 4 is a cross-sectional view showing a second configuration example of the static magnetic field magnet 11. The left side of FIG. 4 shows a longitudinal cross-sectional view of the static magnetic field magnet 11, and the right side of FIG. 4 shows a transverse cross-sectional view (BB cross-sectional view on the left side) of the static magnetic field magnet 11. The static magnetic field magnet 11 includes three superconducting coils 60 (for example, superconducting coils 63 to 65), a position adjustment unit 70 (for example, position adjustment unit 73) between the two superconducting coils 63 and 64, a position adjustment unit 70 (for example, position adjustment unit 74) between the two superconducting coils 64 and 65, a helium container 80, and a coil support unit 90 (for example, a coil support unit 93 supporting the superconducting coil 63, a coil support unit 94 supporting the superconducting coil 64, and a coil support unit 95 supporting the superconducting coil 65). In addition, on the right side of FIG. 4, the position adjustment units 70 (as well as the coil support unit 90) are arranged at eight locations along the circumference of the cylinder of the static magnetic field magnet 11, but are not limited to eight locations. The position adjustment units 70 may be arranged at a plurality of locations at approximately equal intervals along the circumference of the cylinder of the static magnetic field magnet 11 .

[0049] Fig. 5 is an enlarged view of the upper configuration in the left diagram of Fig. 4. As shown in Fig. 5, the static magnetic field magnet 11 includes, in addition to members 63-65, 73, and 74, a winding form F3 for the superconducting coil 63, a winding form F4 for the superconducting coil 64, and a winding form F5 for the superconducting coil 65. The winding forms F3-F5 are each connected to a coil support portion 90 (shown in Fig. 4), and wire, arrange, and fix the superconducting coils 63-65.

[0050] The position adjustment unit 70, for example, the position adjustment unit 73, includes a wedge 73A provided on the reel F4 and an elastic body (for example, a spring) 73B connected to the wedge 73A. The position adjustment unit 74 includes a wedge 74A provided on the reel F4 and an elastic body 74B connected to the wedge 74A. In other words, the static magnetic field magnet 11 has a structure in which the wedge 73A of the position adjustment unit 73 connects the reel F3 and F4, and the wedge 74A of the position adjustment unit 74 connects the reel F4 and F5.

[0051] By passing current through the multiple superconducting coils 63 to 65, it is possible to generate attractive and repulsive forces of any magnitude between the superconducting coils 63 and 64 and between the superconducting coils 64 and 65, as shown in Fig. 6. Figs. 6(A) and (B) are detailed views of the range S in Fig. 5. Fig. 6(A) shows the repulsive force between the superconducting coils 64 and 65, and Fig. 6(B) shows the attractive force between the superconducting coils 64 and 65.

[0052] After the superconducting coil 60 is assembled, the current flowing through the superconducting coils 63 to 65 is controlled by the processing circuit 51 of the MRI apparatus 1 (or a control device, not shown, outside the MRI apparatus 1). Here, the relationship between the superconducting coils 64 and 65 will be described as an example. By controlling the current flowing through the superconducting coils 64 and 6, the superconducting coil 65 is moved away from the superconducting coil 64 to change its position (as shown in FIG. 6(A)), and the wedge 74A is lowered by the elastic force of the elastic body 74B stretching, and the position is fixed. Even after the current supply to the superconducting coils 64 and 65 is stopped, the superconducting coil 65 is fixed to the superconducting coil 64 with the wedge 74A lowered.

[0053] Meanwhile, the current flowing through the superconducting coils 64, 65 is controlled to attract the superconducting coil 65 to the superconducting coil 64 to change its position (as shown in FIG. 6(B)), and the wedge 74A rises and is fixed in position by the sliding force (to the left on the page) of the spool F5. Even after the current supply to the superconducting coils 64, 65 is stopped, the superconducting coil 65 is fixed to the superconducting coil 64 with the wedge 74A in the raised state. By calculating the relationship between the frictional force of the wedges 73A, 74A and the electromagnetic force, the superconducting coils 63 to 65 can be slid in the Z-axis direction to any position.

[0054] In addition, after fixing any one of the multiple superconducting coils 60 (for example, the superconducting coil 64) to the helium container 80 (not slidable), only the positions of the superconducting coils 63 and 65 may be slid relative to the superconducting coil 61, or the positions of the superconducting coils 63 to 65 may be slid relative to each other. Since the uniformity of the static magnetic field can be adjusted while changing the relative positional relationship of the superconducting coils 63 to 65, the uniformity of the static magnetic field can be improved without using iron shims. In addition, once the relative positional relationship of the superconducting coils 63 to 65 is determined, the positions of the superconducting coils 63 to 65 after sliding in the Z-axis direction can be maintained by the function of the wedges 73A and 74A.

[0055] Fig. 7 is an enlarged view of the upper configuration in the left diagram of Fig. 4. As shown in Fig. 7, the static magnetic field magnet 11 includes, in addition to members 63-65, 73, and 74, a winding form F3 for the superconducting coil 63, a winding form F4 for the superconducting coil 64, and a winding form F5 for the superconducting coil 65. The winding forms F3-F5 are each connected to a coil support portion 90 (shown in Fig. 4), and wire, arrange, and fix the superconducting coils 63-65.

[0056] The position adjustment unit 70, for example, the position adjustment unit 73, includes a tough body (highly tough material, for example, resin, carbon tool steel (SK material)) 73C connected between the reel F4, F5. The position adjustment unit 74 includes a tough body 74C connected between the reel F4, F5. In other words, the static magnetic field magnet 11 has a structure in which the tough body 73C of the position adjustment unit 73 connects the reel F3, F4, and the tough body 74C of the position adjustment unit 74 connects the reel F4, F5.

[0057] By passing current through the superconducting coils 63 to 65, it is possible to generate attractive and repulsive forces of any magnitude between the superconducting coils 63 and 64 and between the superconducting coils 64 and 65.

[0058] After the superconducting coil 60 is assembled, the current flowing through the superconducting coils 63 to 65 is controlled by the processing circuit 51 of the MRI apparatus 1 (or a control device, not shown, outside the MRI apparatus 1). Here, the relationship between the superconducting coils 64 and 65 will be described as an example. By controlling the current flowing through the superconducting coils 64 and 65 and separating the superconducting coil 65 from the superconducting coil 64, the tough body 74C is deformed and fixed. Even after the current supply to the superconducting coils 64 and 65 is stopped, the superconducting coil 65 remains fixed to the superconducting coil 64 with the tough body 74C deformed.

[0059] Meanwhile, by controlling the current flowing through superconducting coils 64, 65 and attracting superconducting coil 65 to superconducting coil 64, tough body 74C is deformed and fixed in place. Even after the passage of current through superconducting coils 64, 65 is stopped, superconducting coil 65 remains fixed to superconducting coil 64 with tough body 74C in a deformed state. By calculating the relationship between the value for evaluating toughness (fracture toughness value) and the electromagnetic force, superconducting coils 63 to 65 can be slid in the Z-axis direction to any position.

[0060] In addition, after fixing any one of the multiple superconducting coils 60 (for example, the superconducting coil 64) to the helium container 80 (not slidable), only the positions of the superconducting coils 63 and 65 may be slid relative to the superconducting coil 61, or the positions of the superconducting coils 63 to 65 may be slid relative to each other. Since the uniformity of the static magnetic field can be adjusted while changing the relative positional relationship of the superconducting coils 63 to 65, the uniformity of the static magnetic field can be improved without using iron shims. In addition, once the relative positional relationship of the superconducting coils 63 to 65 is determined, the positions of the superconducting coils 63 to 65 after sliding in the Z-axis direction can be maintained by the function of the tough bodies 73C and 74C.

[0061] Fig. 8 is an enlarged view of the upper configuration in the left diagram of Fig. 4. As shown in Fig. 8, the static magnetic field magnet 11 includes, in addition to the members 63-65, 73, and 74, a winding frame F3 of the superconducting coil 63, a winding frame F4 of the superconducting coil 64, a winding frame F5 of the superconducting coil 65, and a frame F35 that connects between the winding frames F3 and F5 that are not adjacent to each other. The winding frames F3-F5 are each connected to a coil support portion 90 (shown in Fig. 4), and wire, arrange, and fix the superconducting coils 63-65.

[0062] The position adjustment unit 70, for example, the position adjustment unit 73, includes a tough body 73D connected between the winding frames F4 and F5. The position adjustment unit 74 includes a tough body 74D connected between the winding frames F4 and F5. That is, the static magnetic field magnet 11 has a structure in which the position adjustment unit 73 connects the winding frames F3 and F4 with the tough body 73D, and the position adjustment unit 74 connects the winding frames F4 and F5 with the tough body 74D. The static magnetic field magnet 11 also has a structure in which the superconducting coils 63 and 65, which are located symmetrically with respect to the central superconducting coil 64, are integrated with the frame 35, and the winding frames that are not integrated are connected with the tough bodies 73D and 74D.

[0063] By passing current through the superconducting coils 63 to 65, it is possible to generate attractive and repulsive forces of any magnitude between the superconducting coils 63 and 64 and between the superconducting coils 64 and 65. Note that Fig. 8 illustrates an example in which an attractive force is generated between the superconducting coils 63 and 64 and an attractive force is generated between the superconducting coils 64 and 65.

[0064] After assembling the superconducting coil 60, the processing circuit 51 of the MRI apparatus 1 (or a control device, not shown, outside the MRI apparatus 1) controls the current flowing through the superconducting coils 63-65 to move the central superconducting coil 64 away from the superconducting coil 63 while attracting the central superconducting coil 64 to the superconducting coil 65, thereby deforming and fixing the tough bodies 73D, 74D. Even after the current supply to the superconducting coils 63-65 is stopped, the central superconducting coil 64 remains fixed to the superconducting coils 63, 65 with the tough bodies 73D, 74D deformed.

[0065] Meanwhile, the current flowing through the superconducting coils 63-65 is controlled to attract the central superconducting coil 64 to the superconducting coil 6 while separating the central superconducting coil 64 from the superconducting coil 65, whereby the tough bodies 73D, 74D are deformed and fixed. Even after the passage of current through the superconducting coils 63-65 is stopped, the central superconducting coil 64 remains fixed to the superconducting coils 63, 65 with the tough bodies 73D, 74D in a deformed state. By calculating the relationship between the value for evaluating the toughness (fracture toughness value) and the electromagnetic force, the superconducting coil 64 can be slid in the Z-axis direction to any position.

[0066] When superconducting coils are normally used, the same magnitude of current flows through all the superconducting coils, generating symmetrical electromagnetic forces. The superconducting coils 63 and 65, which are positioned symmetrically with respect to the central superconducting coil 64, automatically move to positions symmetrical with respect to the central superconducting coil 64 due to the balance of electromagnetic forces. Compared to the above-mentioned sliding movement configuration, it is not possible to slide the multiple superconducting coils 63 to 65 to any position, but the magnetic field uniformity is improved by the coils being symmetrical. Therefore, compared to the above-mentioned sliding movement configuration, it is expected that the magnetic field uniformity can be improved by a simpler method.

[0067] Fig. 9 is an enlarged view of the upper configuration in the left diagram of Fig. 4. As shown in Fig. 9, the static magnetic field magnet 11 includes, in addition to members 63-65, 73, and 74, a winding form F3 for the superconducting coil 63, a winding form F4 for the superconducting coil 64, and a winding form F5 for the superconducting coil 65. The winding forms F3-F5 are each connected to a coil support portion 90 (shown in Fig. 4), and wire, arrange, and fix the superconducting coils 63-65.

[0068] The position adjustment unit 70, for example, the position adjustment unit 73, includes a thermal insulator 73E, a thermal expansion material (a material with a high thermal expansion coefficient, for example, aluminum) 73F, a low melting point material (a material with a low melting point, for example, gallium) 73G, and a heater 73H built into the thermal expansion material 73F and the low melting point material 73G between the winding frames F4 and F5. The position adjustment unit 74 includes a thermal insulator 74E, a thermal expansion material 74F, a low melting point material 74G, and a heater 74H built into the thermal expansion material 74F and the low melting point material 74G between the winding frames F4 and F5. In other words, the static magnetic field magnet 11 has a structure in which the winding frames F3 and F4 are connected by the members 73E to 73G of the position adjustment unit 73, and the winding frames F4 and F5 are connected by the members 74E to 74G of the position adjustment unit 74.

[0069] By heating the thermal expansion material 73F (74F) or the low melting point material 73G (74G) between the multiple superconducting coils 63-65, it is possible to generate thermal expansion and melting of any magnitude between the superconducting coils 63, 64 and between the superconducting coils 64, 65.

[0070] After assembling the superconducting coil 60, the processing circuit 51 of the MRI apparatus 1 (or a control device, not shown, outside the MRI apparatus 1) controls the heating of the eight heaters 73H, 74H along the circumference. Here, the relationship between the superconducting coils 64, 65 will be described as an example. When it is desired to widen the gap between the superconducting coils 64, 65, heat is applied from the heater 74H built in the thermal expansion material 74F to the thermal expansion material 74F to expand the thermal expansion material 74F. On the other hand, when it is desired to narrow the gap between the superconducting coils 64, 65, heat is applied from the heater 74H built in the low melting point material 74G to the low melting point material 74G to melt the portion of the low melting point material 74G around the heater 74H, thereby reducing the volume of the entire low melting point material 74G. After changing the position of the superconducting coils 64, 65, for example, the heating of the heater 74H is continuously controlled even during imaging, thereby fixing the relative position between the superconducting coils 64, 65.

[0071] As described above, according to the static magnetic field magnet 11, it is possible to improve the uniformity of the static magnetic field without using iron shims by adjusting the relative positional relationship in the Z-axis direction of the superconducting coils 61 to 63. As a result, the weight of the static magnetic field magnet can be reduced by not using iron shims, the demagnetization work can be reduced, and the consumption of liquid helium can be reduced.

[0072] According to at least one of the embodiments described above, it is possible to improve the uniformity of the static magnetic field without using iron shims, while reducing the weight of the static magnetic field magnet by not using iron shims, reducing demagnetization work, and reducing liquid helium consumption.

[0073] 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]

[0074] 1...Magnetic resonance imaging (MRI) device 10...Magnetic stand 11...Static magnetic field magnet 12...Gradient magnetic field coil 50…Console 60, 61-65: Superconducting coil 70,71,72...Position adjustment section 80…Helium container 90...Coil support part

Claims

1. A cylindrical static magnetic field magnet that generates a static magnetic field, A plurality of superconducting coils divided by a cross section of the cylindrical shape; a position adjustment unit for changing and fixing a relative positional relationship of the plurality of superconducting coils; A static magnetic field magnet equipped with

2. The position adjustment unit slides all or a part of the plurality of superconducting coils along a height direction of the cylindrical shape.

2. A static magnetic field magnet as claimed in claim 1.

3. the position adjustment unit includes an ultrasonic motor between the plurality of superconducting coils and changes and fixes a relative positional relationship between the plurality of superconducting coils.

3. A static magnetic field magnet as claimed in claim 2.

4. the position adjustment unit includes wedges between the plurality of superconducting coils, and fixes the plurality of superconducting coils by the wedges after the relative positional relationship is changed.

3. A static magnetic field magnet as claimed in claim 2.

5. the position adjustment unit includes a ductile member between the plurality of superconducting coils, and fixes the plurality of superconducting coils by the ductile member after the relative positional relationship is changed.

3. A static magnetic field magnet as claimed in claim 2.

6. Among the plurality of superconducting coils, two superconducting coils spaced apart from each other with a predetermined superconducting coil interposed therebetween are integrated together, the position adjustment unit includes a toughening body between the predetermined superconducting coil and one of the two superconducting coils, and between the predetermined superconducting coil and the other of the two superconducting coils, and fixes the plurality of superconducting coils whose relative positional relationship has been changed by the toughening bodies.

6. A static magnetic field magnet according to claim 5.

7. the position adjustment unit includes a thermal expansion body and a low melting point material between the plurality of superconducting coils, and heaters respectively built into the thermal expansion body and the low melting point material, and fixes the plurality of superconducting coils after the relative positional relationship has been changed by the thermal expansion body and the low melting point material.

3. A static magnetic field magnet as claimed in claim 2.

8. The static magnetic field magnet according to any one of claims 1 to 7, A cylindrical gradient coil is disposed inside the static magnetic field magnet and generates a gradient magnetic field; A transmitting coil for transmitting high frequency pulses; A receiving coil for receiving an MR signal; an image processor that generates an image based on the MR signal from the receiving coil; A magnetic resonance imaging apparatus comprising:

9. A method for adjusting a static magnetic field generated by a static magnetic field magnet having a plurality of superconducting coils divided by a cylindrical cross section, comprising the steps of: A step of changing a relative positional relationship between the plurality of superconducting coils by controlling currents flowing through the plurality of superconducting coils; fixing the plurality of superconducting coils after the relative positional relationship has been changed; A static magnetic field adjustment method comprising:

Images