JP6651593B2 - Manufacturing method of gradient magnetic field coil - Google Patents

Description

  Embodiments of the present invention relate to a method of manufacturing a gradient coil.

  The magnetic resonance imaging apparatus has a gradient magnetic field coil that generates a gradient magnetic field. The gradient magnetic field coil is manufactured by arranging a plurality of conducting wires, cooling tubes, and the like on a cylindrical frame called a winding frame, and solidifying these with a thermosetting resin. When curing the thermosetting resin, it is necessary to heat the entire gradient coil to the curing temperature of the resin and hold it for several hours. At this time, since heat applied to the resin causes thermal expansion of the resin, the fixing of the conductive wire by the resin becomes incomplete.

Japanese Unexamined Patent Publication No. 2007-510452 Patent No. 4795679 Patent No. 2714503 Patent No. 3786460 JP 2007-329959 A Patent No. 2666773

  The problem to be solved by the present invention is to prevent the accuracy of magnetic resonance imaging from deteriorating due to the fluctuation of the position of a conducting wire.

  The manufacturing method of the gradient magnetic field coil of the embodiment includes a step of forming a conductive part of the gradient magnetic field coil, impregnating the conductive part with a thermosetting resin, and winding a tape around the conductive part impregnated with the thermosetting resin. including.

FIG. 2 is a diagram illustrating a configuration of a magnetic resonance imaging apparatus according to the present embodiment. The figure which shows typically the gradient magnetic field coil of FIG. The figure which shows an example of the manufacturing process of the gradient magnetic field coil when using a fiber tape according to this embodiment. The figure which shows an example of the manufacturing process of the gradient magnetic field coil when using a metal tape according to this embodiment. 4 is a graph illustrating the amount of phase change of the gradient coil according to the present embodiment over time. Graph showing the amount of phase change with time of a gradient magnetic field coil according to a conventional example

  Hereinafter, a gradient coil and a magnetic resonance imaging apparatus according to the present embodiment will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a configuration of a magnetic resonance imaging apparatus 1 according to the present embodiment. As shown in FIG. 1, the magnetic resonance imaging apparatus 1 has a gantry 3, a console 5, and a bed 7. The gantry 3, the console 5, and the bed 7 are communicably connected by wire or wirelessly. The gantry 3 and the bed 7 are installed in an examination room, for example. The console 5 is installed in a control room adjacent to the examination room.

  The gantry 3 includes a static magnetic field magnet 11, a gradient magnetic field coil 13, a gradient magnetic field power supply 15, an RF coil 17, a transmission unit 21, and a reception unit 23. The console 5 has an imaging control unit 31, a reconfiguration unit 33, an image processing unit 35, a display unit 37, an input unit 39, a storage unit 41, and a system control unit 43. Note that some of the components of the gantry 3 and the console 5 may be physically mounted on another device.

  The static magnetic field magnet 11 has a hollow, substantially cylindrical shape, and generates a static magnetic field inside the substantially cylindrical portion. A spatial region where the uniformity of the generated magnetic field is good is used for imaging. As the static magnetic field magnet 11, for example, a permanent magnet or a superconducting magnet is used. Here, the central axis of the static magnetic field magnet 11 is defined as the Z axis, an axis perpendicular to the Z axis is called a Y axis, and an axis horizontally orthogonal to the Z axis is called an X axis. The X axis, the Y axis, and the Z axis form an orthogonal three-dimensional coordinate system.

  The gradient magnetic field coil 13 is a coil unit attached to the inside of the static magnetic field magnet 11 and formed in a hollow substantially cylindrical shape. The gradient magnetic field coil 13 receives a current supplied from the gradient magnetic field power supply 15 and generates a gradient magnetic field.

  The gradient magnetic field power supply 15 supplies a current to the gradient magnetic field coil 13 under the control of the imaging control unit 31. The gradient magnetic field power supply 15 supplies a current to the gradient magnetic field coil 13 to generate a gradient magnetic field in the gradient magnetic field coil 13.

  The RF coil 17 is arranged inside the gradient magnetic field coil 15 and receives a supply of an RF pulse from the transmission unit 21 to generate a high-frequency magnetic field. Further, the RF coil 17 receives a magnetic resonance signal (hereinafter, referred to as an MR (Magnetic Resonance) signal) emitted from a target nucleus existing in the subject S under the action of a high-frequency magnetic field. The received MR signal is supplied to the receiving unit 23. Although the above-described RF coil 17 is a coil having a transmitting / receiving function, the present embodiment is not limited to this, and a transmitting RF coil and a receiving RF coil may be separately provided.

  The transmitting unit 21 transmits a high-frequency magnetic field for exciting a target nucleus existing in the subject S to the subject S via the RF coil 17. A proton is typically used as the target nucleus. Specifically, the transmission unit 21 supplies a high-frequency signal (RF signal) for exciting the target nucleus to the RF coil 17 under the control of the imaging control unit 31. The high-frequency magnetic field generated from the RF coil 17 vibrates at a resonance frequency specific to the target nucleus, and excites the target nucleus. An MR signal is generated from the excited target nucleus and detected by the RF coil 17. The detected MR signal is supplied to the receiving unit 23.

  The receiving unit 23 receives the MR signal generated from the excited target nucleus via the RF coil 17. The receiving unit 23 performs signal processing on the received MR signal to generate a digital MR signal.

  The bed 7 is set adjacent to the gradient coil 13. The subject S is placed on the top of the bed 7. The couch top is positioned by the bed 7 so that the imaging region of the subject S is included in the imaging region set in the opening (bore) of the gradient coil 13.

  The imaging control unit 31 includes, as hardware resources, an arithmetic unit of a unique CPU (Central Processing Unit) or MPU (Micro Processing Unit) and a storage device such as a ROM (Read Only Memory) and a RAM (Random Access Memory). . The imaging control unit 31 synchronously controls the gradient magnetic field power supply 15, the transmission unit 21, and the reception unit 23 based on the pulse sequence information supplied from the system control unit 43, and performs a pulse sequence according to the pulse sequence information. Images the subject S. The pulse sequence information defines an imaging procedure according to the pulse sequence. For example, the pulse sequence information includes the intensity and supply timing of the current pulse supplied from the gradient power supply 15 to the gradient coil 13, the intensity and supply timing of the RF pulse supplied from the transmission unit 21 to the RF coil 17, and the reception unit 23 The timing for detecting a signal is defined.

  The reconfiguration unit 33 has, as hardware resources, an arithmetic unit of a unique CPU (Central Processing Unit) or MPU (Micro Processing Unit) and a storage device such as a ROM (Read Only Memory) and a RAM (Random Access Memory). . The reconstructing unit 33 reconstructs an MR image of the subject S based on the MR signal from the receiving unit 23. For example, the reconstruction unit 33 performs a Fourier transform on the MR signals arranged in the k space or the frequency space to generate an MR image defined in the real space. The reconfiguration unit 33 is realized by an integrated circuit such as an ASIC and an FPGA, and an electronic circuit such as a CPU and an MPU.

  The image processing unit 35 has, as hardware resources, an arithmetic unit of a unique CPU (Central Processing Unit) or MPU (Micro Processing Unit) and a storage device such as a ROM (Read Only Memory) and a RAM (Random Access Memory). . The image processing unit 35 performs various image processing on the MR image reconstructed by the reconstruction unit 33. The image processing unit 35 is realized by the above electronic circuit.

  The display unit 37 displays various information on a display device. For example, the display unit 37 displays an MR image reconstructed by the reconstruction unit 33 or an MR image subjected to image processing by the image processing unit 35. The display unit 37 may display a scan plan screen. As the display device, for example, a CRT display, a liquid crystal display, an organic EL display, a plasma display, or the like can be appropriately used.

  The input unit 39 receives various commands and information input from the user via the input device. For example, the input unit 39 receives an imaging start instruction from a user via an input device. As an input device, a keyboard, a mouse, a switch, and the like can be used.

  The storage unit 41 is a large-capacity storage device such as a hard disk drive (HDD) that stores various information. For example, the storage unit 41 stores an MR image, a control program for a magnetic resonance imaging apparatus, and the like.

  The system control unit 43 has, as hardware resources, an arithmetic unit of a unique CPU (Central Processing Unit) or MPU (Micro Processing Unit) and a storage device such as a ROM (Read Only Memory) and a RAM (Random Access Memory). . The system control unit 43 functions as a center of the magnetic resonance imaging apparatus 1. Specifically, the system control unit 43 reads out the control program stored in the storage unit 41 and loads it on the memory, and controls each unit of the magnetic resonance imaging apparatus 1 according to the loaded control program. The system control unit 43 is realized by the above electronic circuit.

  Next, the gradient coil 13 according to the present embodiment will be described in detail.

  FIG. 2 is a diagram schematically illustrating the gradient coil 13 according to the present embodiment. As shown in FIG. 2, the gradient magnetic field coil 13 according to the present embodiment is, for example, an ASGC (Actively Shielded Gradient Coil). Specifically, the gradient magnetic field coil 13 has a conductor 130 and a fixture 140. The conductor 130 is a unit that applies a gradient magnetic field to the imaging region set in the opening, and is formed in a cylindrical shape. The conductor 130 according to the present embodiment is configured such that a conductor for generating a gradient magnetic field is fixed with resin.

  Specifically, the conductor 130 has a main coil 131, an intermediate layer 133, and a shield coil 135 in order from the central axis Z of the cylinder.

  The main coil 131 is a conductor that generates a gradient magnetic field. Specifically, the main coil 131 applies an X coil for applying a gradient magnetic field along the X axis, a Y coil for applying a gradient magnetic field along the Y axis, and applies a gradient magnetic field along the Z axis. For the Z coil. The types of the X coil, the Y coil, and the Z coil can be individually selected from arbitrary coils such as a circular coil, a solenoid coil, a saddle coil, and a birdcage coil. Each coil is formed of a metal having good electric conductivity such as copper or aluminum.

  The intermediate layer 133 has a cooling pipe through which a coolant for cooling the gradient magnetic field coil 13 that has generated heat when a magnetic field is applied, and a shim tray on which an iron shim for adjusting the spatial distribution of the magnetic field is arranged.

  The shield coil 135 generates a magnetic field (shielding magnetic field) for canceling out a magnetic field (leakage magnetic field) that has leaked out of the gradient magnetic field generated from the main coil 131. Specifically, the shield coil 135 applies an X coil for applying a shielding magnetic field along the X axis, a Y coil for applying a shielding magnetic field along the Y axis, and applies a shielding magnetic field along the Z axis. For the Z coil. Each coil is formed of a metal having good electric conductivity such as copper or aluminum.

  The laminate of the main coil 131, the intermediate layer 133, and the shield coil 135 is fixed with resin. For example, a thermosetting resin having a property of curing at a thermosetting temperature is used as the resin. For example, the laminated body of the main coil 131, the intermediate layer 133, and the shield coil 135 is impregnated with a resin and cured by applying heat. Thereby, the laminated body of the main coil 131, the intermediate layer 133, and the shield coil 135 is fixed with the resin.

  The outer periphery of the conductive wire portion 130 fixed with resin is wound around a fixing device 140. Specifically, it is wound around the outer circumference of the shield coil 135 arranged at the outermost circumference of the conductor section 130. By winding the fixture 140, the main coil 131 and the shield coil 135 can be firmly fixed, and the vibration of the main coil 131 and the shield coil 135 in the radial direction when a magnetic field is applied can be suppressed. Specific examples of the fixing device 140 include a tape or ribbon made of fiber (hereinafter, fiber tape), a tape or ribbon made of metal (hereinafter, metal tape), a rope, a string, a rope, and a belt. Flexible elongated devices are preferred. Hereinafter, it is assumed that the fixing device 140 is a fiber tape for a specific description. As the fiber tape, those woven with synthetic fibers having high strength are preferable. Examples of such a fiber tape include a tape woven with Zylon (registered trademark) and Kevlar (registered trademark).

  FIG. 3 is a diagram illustrating an example of a manufacturing process of the gradient coil 13 according to the present embodiment. As shown in FIG. 3, first, the conductive wire portion 130, which is a laminate of the main coil 131, the intermediate layer 133, and the shield coil 135, is formed (step SA1). For example, the conductor portion 130 can be formed by stacking the main coil 131, the intermediate layer 133, and the shield coil 135 on a frame having a cylindrical shape called a winding frame.

  When step SA1 is performed, the conductor 130 is impregnated with a thermosetting resin (step SA2). More specifically, the entire conductor 130 is impregnated with the thermosetting resin injected into the mold, heated to the curing temperature of the resin, and held for several hours. Thereby, the thermosetting resin is cured. After the curing, the conductor 130 impregnated with the thermosetting resin is cooled.

  In addition, the main coil 131, the shield coil 135, and the like thermally expand due to heat generated when the thermosetting resin is cured. Therefore, a gap is created between the thermosetting resin cooled after curing and the main coil 131 or the shield coil 135, and the fixing force of the thermosetting resin to the main coil 131 or the shield coil 135 is reduced. When the main coil 131 and the shield coil 135 are energized and a magnetic field is applied in this state, the main coil 131 and the shield coil 135 vibrate violently due to Lorentz force. Due to the vibration, the positions of the main coil 131 and the shield coil 135 change toward the outside of the gradient coil 13. Variations in the position of the main coil 131 and the shield coil 135 cause distortion in the image due to, for example, disturbing the specification of the gradient magnetic field, and adversely affect imaging.

  When step SA2 is performed, as shown in FIG. 2, the fiber tape 140 is wound around the conductor 130 impregnated with the thermosetting resin (step SA3). Specifically, the fiber tape 140 is wound so as to cover the outermost periphery of the conductor 130. By winding the conductive wire portion 130 with the fiber tape 140, vibration of the main coil 131 and the shield coil 135 due to Lorentz force generated when a magnetic field is applied can be suppressed. In other words, it is preferable that the fiber tape 140 be wound so that a force that does not cause the main coil 131 and the shield coil 135 to vibrate due to Lorentz force acts in the central axis Z direction.

  The method of winding the fiber tape 140 may be arbitrary. For example, the fiber tape 140 may be spirally wound along the central axis Z, or may be wound in parallel along the central axis Z. The fiber tape 140 may be wound so as to overlap with each other in order to further fix the main coil 131 and the shield coil 135, or may save the fiber tape 140, reduce the size of the gradient magnetic field coil 13, and the like. Therefore, they may be wound separately. Further, the fiber tape 140 may be wound so as to cover the entire outermost periphery of the conductive wire portion 130 in order to further firmly fix the main coil 131 and the shield coil 135. Alternatively, in order to reduce the size of the gradient magnetic field coil 13 in order to save the fiber tape 140 or the like, the fiber tape 140 may be wound around only a part of the outermost periphery of the conductor 130. For example, winding may be limited to both ends of the conductor portion 130 about the center axis Z where vibration is particularly severe. Further, the fiber tape 140 may be wound in layers.

  As described above, the tension (tension) at the time of winding the fiber tape 140 is determined according to the pressure necessary to counter the Lorentz force applied to the main coil 131 and the shield coil 135 when applying a magnetic field.

  Next, a manufacturing process of the gradient coil 13 in the case of using a metal tape as the fixture 140 will be described.

  FIG. 4 is a diagram illustrating an example of a manufacturing process of the gradient coil 13 when the metal tape 140 is used. The same reference numerals are given to the same manufacturing steps among the manufacturing steps included in FIGS. 4 and 3, and the description will be simplified.

  As shown in FIG. 4, similarly to FIG. 3, the conductor 130 is formed (step SA1), and the conductor 130 is impregnated with a thermosetting resin (step SA2).

  When step SA2 is performed, the metal tape 140 is wound around the conductor 130 impregnated with the thermosetting resin. The metal tape 140 has better resistance to external force than the fiber tape, and does not deteriorate due to ultraviolet rays.

  On the other hand, unlike the fiber tape, the metal tape 140 has conductivity. Therefore, when the metal tape 140 forms a closed loop by winding the metal tape 140 around the conductor portion 130, the magnetic field is disturbed. Therefore, as the material of the metal tape, it is preferable to use a metal having low electric conductivity as much as possible. An example of such a metal material is steel. In addition, it is preferable that the metal tape 140 be wound around the conductor 130 so that the metal tape 140 does not form a closed loop. In other words, the metal tapes 140 are wound so as not to overlap each other. Specifically, the metal tapes 140 may be spirally wound along the central axis Z or may be wound in parallel along the central axis Z so as not to overlap each other.

  Next, effects according to the present embodiment will be described.

  FIG. 5 shows a phase change amount of the gradient magnetic field coil 130 according to the present embodiment over time, and FIG. 6 is a graph showing a phase change amount of the conventional gradient magnetic field coil over time. 5 and 6, the vertical axis is defined as the amount of phase change, and the horizontal axis is defined as the number of elapsed days. As the gradient magnetic field coil 13 according to the present embodiment, a conductor portion 130 impregnated with a thermosetting resin and having a fiber tape or a metal tape 140 wound around the outermost periphery is used. As the gradient magnetic field coil according to the conventional example, a conductive wire portion impregnated with a thermosetting resin without a fiber tape wound on the outermost periphery is used. The phase change amount is an amount generated by a relative position change between the main coil and the shield coil in each of the X axis, the Y axis, and the Z axis. 5 and 6, X indicates the X channel, Y indicates the Y channel, and Z indicates the Z channel. The phase change amount indicates a change amount of the phase of each coil at the time of measurement from the initial phase of each coil. The amount of phase change is normalized such that the upper limit of the amount of phase change that does not affect imaging is 1.

  As shown in FIG. 6, in the gradient magnetic field coil according to the conventional example, it can be seen that the amount of phase change greatly exceeds 1 in a short period of time. On the other hand, in the gradient coil according to the present embodiment, the phase change amount is suppressed to 1 or less over a long period of time.

  From the comparison results of the phase change amounts shown in FIG. 5 and FIG. 6, the outermost periphery of the conductive wire portion 130 impregnated with the thermosetting resin is wrapped with the fiber tape or the metal tape, and as compared with the case where the wrap is not wrapped, the gradient magnetic field is increased. It can be seen that the position fluctuation of the coil in the coil 13 can be suppressed to a level that does not adversely affect the imaging.

  Thus, according to the present embodiment, it is possible to prevent the accuracy of the magnetic resonance imaging from deteriorating due to the position fluctuation of the conductor.

  In the above-described embodiment, the method of impregnating the conductive wire portion with a thermosetting resin has been described as a method of fixing the conductive wire portion. However, the embodiment is not limited to this. A method of applying a curable resin may be applied.

  Although several embodiments of the present invention have been described, these embodiments are provided by way of example and are not intended to limit the scope of the invention. These new embodiments can be implemented in other various forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Magnetic resonance imaging apparatus, 3 ... Stand, 5 ... Console, 7 ... Bed, 11 ... Static magnetic field magnet, 13 ... Gradient magnetic field coil, 15 ... Gradient magnetic field power supply, 17 ... RF coil, 21 ... Transmission part, 23 ... Reception Unit, 31: imaging control unit, 33: reconstructing unit, 35: image processing unit, 37: display unit, 39: input unit, 41: storage unit, 43: system control unit, 130: conductor unit, 131: gradient magnetic field Coil, 133: middle layer, 135: shield coil, 140: fixture.

Claims (5)

The conductor of the gradient magnetic field coil is formed as a laminate of a main coil, an intermediate layer, and a shield coil ,
Impregnating the conductive wire portion with a thermosetting resin,
Winding a tape around the conductive wire portion impregnated with the thermosetting resin,
A method for manufacturing a gradient magnetic field coil, comprising:   The method for manufacturing a gradient magnetic field coil according to claim 1, wherein the winding of the tape is performed after the thermosetting resin is cured.   The method for manufacturing a gradient magnetic field coil according to claim 2, wherein the winding of the tape is performed after the thermosetting resin is cured and after the conductive wire portion is further cooled.   The method for manufacturing a gradient magnetic field coil according to claim 1, wherein a fiber tape is used as the tape.   The method for manufacturing a gradient magnetic field coil according to claim 1, wherein a metal tape is used as the tape.