Coil element, local coil device, and magnetic resonance imaging device

Abstract

An embodiment of the present invention relates to a coil element, a local coil device, and a magnetic resonance imaging device, in which, in a receiving coil having a retractable coil element, a change in resonance frequency caused by the extension and contraction of the coil element is suppressed. The coil element of the embodiment includes a retractable coil and a capacitor. The capacitor is connected to the coil, and the electrostatic capacitance changes according to a physical change corresponding to the extension and contraction of the coil.

Description

[0001] Citation of related applications such as basis of priority

[0002] This application is based on Japanese Patent Application No. 2019-198867 (filing date: October 31, 2019) and benefits from priority from that application. This application incorporates the entire contents of that application by reference. Technical Field

[0003] Embodiments of the present invention relate to a coil element, a local coil apparatus, and a magnetic resonance imaging apparatus. Background Art

[0004] In a magnetic resonance imaging apparatus, a local coil device that is mounted on an imaging site of a subject is sometimes used as a receiving coil for detecting MR signals. Such a local coil device has a coil element that can be extended and retracted. The coil element is composed of a hollow tube that can be extended and retracted and a liquid metal filled in the tube. When the coil element is extended and retracted due to the movement of the imaging site of the subject, the inductance changes with the extension and retraction of the coil element, and the resonance frequency of the receiving coil changes. Summary of the invention

[0005] The technical problem to be solved by the present invention is to suppress the change in resonance frequency caused by the expansion and contraction of the coil element in a receiving coil having an expandable and contractible coil element.

[0006] A coil component according to an embodiment includes a coil that can expand and contract and a capacitor. The capacitor is connected to the coil, and the electrostatic capacitance of the capacitor changes according to a physical change corresponding to the expansion and contraction of the coil.

[0007] According to the above configuration, in the receiving coil including the expandable and contractible coil element, it is possible to suppress the change in the resonance frequency due to the expansion and contraction of the coil element. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a diagram showing the configuration of a magnetic resonance imaging apparatus according to the first embodiment.

[0009] Figure 2 This is a schematic diagram showing a state where the local coil device according to the first embodiment is mounted on a subject.

[0010] Figure 3 This is a schematic diagram showing a state where the local coil device according to the first embodiment is mounted on a subject.

[0011] Figure 4 It is a diagram showing a circuit configuration of a local coil device according to the first embodiment.

[0012] Figure 5 It is a schematic diagram showing the structure of the coil component according to the first embodiment.

[0013] Figure 6 It is a diagram showing an example of the structure of the capacitor according to the first embodiment.

[0014] Figure 7 It is a diagram showing an example of the structure of the capacitor according to the first embodiment.

[0015] Figure 8 This is a diagram showing an example of the structure of a capacitor according to a first modification of the first embodiment.

[0016] Fig. 9 This is a diagram showing an example of the structure of a capacitor according to a first modification of the first embodiment.

[0017] Fig.10 It is a diagram showing an example of the structure of a capacitor according to the second embodiment.

[0018] Fig.11 It is a diagram showing an example of the structure of a capacitor according to the second embodiment.

[0019] Fig.12 It is a diagram showing an example of the structure of a capacitor according to a first modification of the second embodiment.

[0020] Fig.13 It is a diagram showing an example of the structure of a capacitor according to a first modification of the second embodiment.

[0021] Fig.14 It is a diagram showing an example of the structure of a capacitor according to a second modification of the second embodiment.

[0022] Fig.15 It is a diagram showing an example of the structure of a capacitor according to a second modification of the second embodiment.

[0023] Fig.16 It is a diagram showing a circuit configuration of a local coil device according to a third embodiment.

[0024] Fig.17 It is a schematic diagram showing the structure of a coil component according to a third embodiment.

[0025] Fig.18 It is a diagram showing an example of the structure of a capacitor according to the third embodiment.

[0026] Fig.19 It is a diagram showing an example of the structure of a capacitor according to the third embodiment. DETAILED DESCRIPTION

[0027] Hereinafter, embodiments of a coil element, a local coil device having the coil element, and a magnetic resonance imaging (MRI) device having the local coil device will be described in detail with reference to the accompanying drawings. In the following description, components having substantially the same function and structure are denoted by the same reference numerals, and repeated descriptions are given only when necessary. In addition, in the following description, a "magnetic resonance imaging device" may also be referred to as an "MRI device".

[0028] (First Embodiment)

[0029] Figure 1 1 is a diagram showing the structure of a magnetic resonance imaging apparatus 1 according to this embodiment. Figure 1 As shown, the magnetic resonance imaging apparatus 1 includes a gantry 11, a bed 13, a gradient magnetic field power supply 21, a transmission circuit 23, a reception circuit 25, a bed driving device 27, a sequence control circuit 29, and a host computer 50. The host computer is an example of a data processing device.

[0030] The gantry 11 has a static magnetic field magnet 41 and a gradient magnetic field coil 43. The static magnetic field magnet 41 and the gradient magnetic field coil 43 are accommodated in a housing of the gantry 11. A hollow hole is formed in the housing of the gantry 11. The transmission coil 45 and the local coil device 100 are arranged in the hole of the gantry 11.

[0031] The static magnetic field magnet 41 has a hollow cylindrical shape and generates a static magnetic field inside the cylindrical shape. As the static magnetic field magnet 41, for example, a permanent magnet, a superconducting magnet, or a normal conductive magnet is used. Here, the central axis of the static magnetic field magnet 41 is defined as the Z axis, the axis perpendicular to the Z axis is defined as the Y axis, and the axis perpendicular to the Z axis is defined as the X axis. The X axis, the Y axis, and the Z axis constitute an orthogonal three-dimensional coordinate system.

[0032] The gradient magnetic field coil 43 is a coil unit that is mounted on the inner side of the static magnetic field magnet 41 and is formed into a hollow, roughly cylindrical shape. The gradient magnetic field coil 43 receives the supply of current from the gradient magnetic field power supply 21 to generate a gradient magnetic field. In more detail, the gradient magnetic field coil 43 has three coils corresponding to the mutually orthogonal X-axis, Y-axis, and Z-axis. The three coils form a gradient magnetic field whose magnetic field strength varies along each axis of the X-axis, Y-axis, and Z-axis. The gradient magnetic fields along each axis of the X-axis, Y-axis, and Z-axis are synthesized to form mutually orthogonal slice selection gradient magnetic fields Gs, phase encoding gradient magnetic fields Gp, and frequency encoding gradient magnetic fields Gr in the desired direction. The slice selection gradient magnetic field Gs is used to arbitrarily determine the imaging section (slice). The phase encoding gradient magnetic field Gp is ​​used to change the phase of the magnetic resonance signal (hereinafter referred to as the MR signal) according to the spatial position. The frequency encoding gradient magnetic field Gr is used to change the frequency of the MR signal according to the spatial position. In the following description, it is assumed that the tilt direction of the slice selection gradient magnetic field Gs is the Z axis, the tilt direction of the phase encoding gradient magnetic field Gp is ​​the Y axis, and the tilt direction of the frequency encoding gradient magnetic field Gr is the X axis.

[0033] The gradient magnetic field power supply 21 supplies current to the gradient magnetic field coil 43 according to the sequence control signal from the sequence control circuit 29. The gradient magnetic field power supply 21 supplies current to the gradient magnetic field coil 43, thereby generating a gradient magnetic field along each axis of the X axis, the Y axis, and the Z axis through the gradient magnetic field coil 43. The gradient magnetic field is superimposed on the static magnetic field formed by the static magnetic field magnet 41 and applied to the subject P.

[0034] The transmission coil 45 is disposed, for example, inside the gradient magnetic field coil 43 , and generates a high-frequency pulse (hereinafter referred to as an RF pulse) by receiving a supply of current from the transmission circuit 23 .

[0035] The transmission circuit 23 supplies current to the transmission coil 45 to apply an RF pulse for exciting target protons present in the subject P via the transmission coil 45 to the subject P. The RF pulse vibrates at a resonance frequency inherent to the target protons to excite the target protons. MR signals are generated by the excited target protons, and the MR signals are detected by the local coil device 100. The transmission coil 45 is, for example, a whole body coil (WB coil). The whole body coil can also be used as a transceiver coil.

[0036] The local coil device 100 is a support-type coil mounted on the imaging part of the subject P. When mounted on the imaging part of the subject P, the local coil device 100 is in close contact with the imaging part of the subject P without any gap. The imaging part is, for example, an elbow, a knee, an ankle, etc. The local coil device 100 receives MR signals emitted from object protons existing inside the imaging part under the action of RF pulses. The received MR signals are supplied to the receiving circuit 25 via wire or wirelessly. The local coil device 100 may also be referred to as a receiving coil. The details of the local coil device 100 will be described later.

[0037] The receiving circuit 25 receives the Figure 2 or Figure 3 The coil elements 102 shown in the figure respectively output MR signals. MR signals generated from the excited object protons are received via the local coil device 100. The receiving circuit 25 performs signal processing on the received MR signals to generate digital MR signals. The digital MR signals can be expressed by the k-space defined by the spatial frequency. Therefore, the digital MR signals are referred to as k-space data hereinafter. K-space data is a kind of raw data for image reconstruction. The k-space data is supplied to the host computer 50 via wired or wireless.

[0038] The above-mentioned transmission coil 45 and local coil device 100 are merely examples, and the local coil device 100 may be a transmission / reception coil having the transmission function of the transmission coil 45 in addition to the reception function.

[0039] A diagnostic bed 13 is provided adjacent to the gantry 11. The diagnostic bed 13 includes a top plate 131 and a base 133. A subject P is placed on the top plate 131. The base 133 supports the top plate 131 so as to be able to slide along the X-axis, the Y-axis, and the Z-axis. The base 133 accommodates a diagnostic bed driving device 27. The diagnostic bed driving device 27 receives control from a sequence control circuit 29 to move the top plate 131. The diagnostic bed driving device 27 may include, for example, any motor such as a servo motor or a stepping motor.

[0040] The sequence control circuit 29 has a processor such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory) and other memories as hardware resources. The sequence control circuit 29 synchronously controls the gradient magnetic field power supply 21, the transmission circuit 23 and the reception circuit 25 based on the imaging protocol determined by the imaging protocol setting function 511 of the processing circuit 51, performs magnetic resonance imaging on the subject P according to the pulse sequence corresponding to the imaging protocol, and collects k-space data related to the subject P.

[0041] like Figure 1 As shown, the host computer 50 is a computer having a processing circuit 51 , a memory 52 , a display 53 , an input interface 54 , and a communication interface 55 .

[0042] The processing circuit 51 has a processor such as a CPU as a hardware resource. The processing circuit 51 functions as the core of the magnetic resonance imaging device 1. For example, the processing circuit 51 has an imaging protocol setting function 511, a data acquisition function 512, an image generation function 513, an image processing function 514, and a display control function 515 by executing various programs.

[0043] In the imaging protocol setting function 511, the processing circuit 51 sets an imaging protocol related to magnetic resonance imaging according to a user instruction or automatically via the input interface 54. An imaging protocol is a collection of various imaging parameters related to one magnetic resonance imaging. As imaging parameters, various parameters directly or indirectly set for performing magnetic resonance imaging, such as the type of pulse sequence, the type of k-space filling method, imaging time, repetition time (TR), echo time (TE), etc., can be applied.

[0044] In the data acquisition function 512, the processing circuit 51 acquires MR data related to the processing object such as the subject P. MR data is a general term for k-space data, MR image data, and mixed data. The k-space data can be the original k-space data, or it can be data after any data processing such as data compression processing, resolution decomposition processing, data interpolation processing, resolution synthesis processing, etc. is performed on the original k-space data. Mixed data is data after Fourier transform or inverse Fourier transform is performed along at least one axis of the k-space data.

[0045] In the image generation function 513, the processing circuit 51 reconstructs an MR image related to the subject P based on the MR data obtained from the receiving circuit 25. The processing circuit 51 performs Fourier transform on the MR data arranged in the k-space or frequency space, and generates an MR image defined in the real space. Instead of Fourier transform or in combination with Fourier transform, a reconstruction method using an iterative approximate reconstruction method or a machine learning model may also be performed. The processing circuit 51 that realizes the image generation function 513 is an example of a reconstruction unit.

[0046] In the image processing function 514, the processing circuit 51 performs various image processing on the MR image. For example, the processing circuit 51 performs image processing such as volume rendering, surface rendering, pixel value projection processing, MPR (Multi-Planer Reconstruction) processing, and CPR (Curved MPR) processing.

[0047] In the display control function 515 , the processing circuit 51 displays various information on the display 53 . For example, the processing circuit 51 displays the MR image generated by the image generation function 513 , the MR image generated by the image processing function 514 , and the setting screen of the imaging protocol on the display 53 .

[0048] The memory 52 is a storage device such as a HDD (Hard Disk Drive), an SSD (Solid State Drive), or an integrated circuit storage device that stores various information. In addition, the memory 52 may also be a drive device that reads and writes various information between a removable storage medium such as a CD-ROM drive, a DVD drive, or a flash memory. For example, the memory 52 stores a learned model, k-space data, MR image data, a control program, and the like.

[0049] The display 53 displays various information through the display control function 515. For example, the display 53 displays the MR image generated by the image generation function 513, the MR image generated by the image processing function 514, the setting screen of the imaging protocol, etc. As the display 53, for example, a CRT display, a liquid crystal display, an organic EL display, an LED display, a plasma display, or any other display known in the technical field can be appropriately used.

[0050] The input interface 54 includes an input device for receiving various instructions from the user. As the input device, a keyboard, a mouse, various switches, a touch screen, a touch pad, etc. can be used. In addition, the input device is not limited to a device having physical operating parts such as a mouse and a keyboard. For example, a processing circuit for receiving an electrical signal corresponding to an input operation from an external input device provided separately from the magnetic resonance imaging apparatus 1 and outputting the received electrical signal to various circuits is also included in the example of the input interface 54.

[0051] The communication interface 55 is an interface for connecting the magnetic resonance imaging apparatus 1 to a workstation, PACS (Picture Archiving and Communication System), HIS (Hospital Information System), RIS (Radiology Information System), etc. via a LAN (Local Area Network) etc. The communication interface 55 transmits and receives various information to and from the workstation, PACS, HIS, and RIS of the connection destination.

[0052] The above-mentioned structure is an example and is not limited thereto. For example, the sequence control circuit 29 may be incorporated in the host computer 50. In addition, the sequence control circuit 29 and the processing circuit 51 may be mounted on the same substrate.

[0053] The following describes the structure of the local coil device 100. Here, as an example, the structure of the local coil device 100 mounted on the knee of the subject P is described. The local coil device 100 may be mounted on the elbow, ankle, or the like of the subject P.

[0054] Figure 2 and Figure 3 1 is a schematic diagram showing a state where the local coil device 100 is mounted on the knee of a subject P. FIG. Figure 4 1 is a diagram showing a circuit configuration of a local coil device 100. The local coil device 100 includes a mounting portion 101 and a plurality of receiving paths installed in parallel. The mounting portion 101 is formed, for example, by overlapping a plurality of stretchable cloth materials. The mounting portion 101 is formed in a shape corresponding to the shape of the imaging part, and the local coil device 100 is attached to the knee of the subject P from the outside when mounted on the knee of the subject P. A plurality of receiving paths are accommodated inside the mounting portion 101. The mounting portion 101 is stretched and contracted by the knee of the subject P extending or bending.

[0055] The receiving paths each have a coil element 102 capable of receiving an MR signal emitted from a proton of a subject and an amplifier 115 for amplifying an output signal of the coil element 102. The coil element 102 detects MR signals. The coil element 102 is formed in a ring shape (wheel shape). In addition, the coil element 102 can have a quadrilateral shape such as a rectangle, or can be formed in a polygonal shape such as a dodecagon. The MR signal obtained by each receiving path in the receiving path is outputted by the amplifier 115 according to each receiving path, and is supplied to the receiving circuit 25 via wired or wireless communication. The total number of receiving paths and the total number of coil elements 102 can be the same or different. In addition, the coil element 102 has an inductor 113 and a capacitor 114. A parallel resonant circuit (hereinafter referred to as an LC circuit) is formed in the coil element 102 by the inductor 113 and the capacitor 114. The capacitor 114 can also be referred to as a capacitor.

[0056] The local coil device 100 expands and contracts due to the movement of the imaging part of the subject P. For example, Figure 2 As shown in FIG. 1 , when the knee of the subject P is extended, the coil element 102 is in a state where the conductor portion 111 described later is not extended from its natural length (hereinafter referred to as a reference state). The reference state may also be referred to as a stable state. In the reference state, the various elements of the coil element 102 are adjusted so that the electrostatic capacitance C, inductance L, and resonance frequency of the LC circuit are within a predetermined range. On the other hand, Figure 3 As shown, the coil element 102 is in a state of being extended from its natural length (hereinafter referred to as an extended state) when the knee of the subject P is bent. In the extended state, the inductance L of the inductor 113 is larger than that in the reference state.

[0057] Figure 5 1 is a schematic diagram showing the structure of the coil element 102. Figure 5 As shown, the coil component 102 includes a conductor portion 111 and a case 112 .

[0058] The conductor part 111 is formed of a tube bent into a ring shape. Both ends of the conductor part 111 are inserted into the inside of the box body 112 from opposite sides.

[0059] In addition, the conductor part 111 has flexibility and has a retractable tube. The tube is formed of, for example, silicon. The inside of the tube is filled with liquid metal. The liquid metal is, for example, gallium indium, but is not limited thereto. The conductor part 111 functions as an inductor 113 of the LC circuit. The conductor part 111 is an example of a coil.

[0060] The conductor part 111 expands and contracts in accordance with the expansion and contraction of the tube. For example, when the local coil device 100 expands from the reference state, the tube expands, thereby expanding the conductor part 111. On the other hand, for example, when the local coil device 100 contracts from the extended state, the tube contracts, thereby contracting the conductor part 111.

[0061] In the coil element 102, the inductance L of the inductor 113 changes in accordance with the expansion and contraction of the conductor portion 111. For example, when the local coil device 100 is extended, the conductor portion 111 is extended, and the cross-sectional area of ​​the circular loop formed by the coil element 102 is expanded, so the inductance L of the inductor 113 becomes larger. On the other hand, when the local coil device 100 is contracted, the conductor portion 111 is contracted, and the cross-sectional area of ​​the aforementioned circular loop is narrowed, so the inductance L of the inductor 113 becomes smaller.

[0062] The housing 112 is a metal, resin or plastic housing. The first electrode 120, the second electrode 130 and the amplifier 115 are arranged inside the housing 112. A circuit that performs an AD conversion function as part of the function of the receiving circuit 25 may also be arranged inside the housing 112.

[0063] The first electrode 120 and the second electrode 130 serve as a pair of electrodes of the capacitor 114. The capacitor 114 is connected to the conductor portion 111, and the electrostatic capacitance C changes due to the physical change of the capacitor 114 corresponding to the expansion and contraction of the conductor portion 111. For example, when the local coil device 100 is extended and the inductance L of the inductor 113 increases, the electrostatic capacitance C of the capacitor 114 decreases. On the other hand, when the local coil device 100 is contracted and the inductance L of the inductor 113 decreases, the electrostatic capacitance C of the capacitor 114 increases. Such a change in the electrostatic capacitance C corresponds to, for example, a situation in which the area of ​​the capacitor 114 changes due to the liquid metal flowing out or flowing in from the first electrode 120 corresponding to the expansion and contraction of the conductor portion 111. The electrostatic capacitance C may also be referred to as capacitance.

[0064] The amplifier 115 is connected to the conductor 111 and the receiving circuit 25 . The amplifier 115 amplifies the MR signal received by the conductor 111 and outputs the amplified MR signal to the receiving circuit 25 .

[0065] Hereinafter, the structures of the first electrode 120 and the second electrode 130 constituting the capacitor 114 will be described in detail.

[0066] Figure 6 and Figure 7 This is a diagram showing an example of the structure of the capacitor 114. Figure 6 Corresponding to the case where the coil element 102 is in the reference state, Figure 7 This corresponds to the case where the coil element 102 is in an extended state.

[0067] The capacitor 114 is composed of a first electrode 120 and a second electrode 130 . The first electrode 120 and the second electrode 130 are fixed inside the case 112 .

[0068] The first electrode 120 is connected to one end of the tube of the conductor part 111 inside the box body 112. The second electrode 130 is connected to the other end of the tube of the conductor part 111 inside the box body 112. The first electrode 120 and the second electrode 130 are at least partially opposed to each other.

[0069] The second electrode 130 is, for example, a conductive metal plate and is fixed substantially parallel to the first electrode 120 .

[0070] The first electrode 120 has at least a portion that is conductive. The first electrode 120 has a hollow outer package connected to the tube of the conductor portion 111. The interior of the outer package is filled with liquid metal. The outer package is formed of a material with a lower conductivity than the liquid metal. The outer package is, for example, a bag-shaped component made of silicon with electrical insulation, and has a flat plate shape that maintains a comb-shaped outline and allows the plurality of comb teeth to expand / contract individually.

[0071] The inside of the outer package of the first electrode 120 is connected to the inside of the tube of the conductor part 111. Therefore, the inside of the first electrode 120 is connected to the inside of the conductor part 111. Therefore, the liquid metal can flow between the inside of the first electrode 120 and the inside of the conductor part 111. In addition, the conductor part 111 and the first electrode 120 are configured so that the liquid metal does not flow out to the outside. That is, the inside of the first electrode 120 and the inside of the conductor part 111 are sealed. Therefore, when the conductor part 111 is extended, a negative pressure acts on the inside of the first electrode 120.

[0072] In addition, the outer package of the first electrode 120 is formed to have a lower strength against the negative pressure applied by the extension of the conductor part 111 than the tube of the conductor part 111. For example, the outer package of the first electrode 120 is formed to be thinner than the tube of the conductor part 111. Therefore, the outer package of the first electrode 120 is more easily deformed against the negative pressure applied by the extension of the conductor part 111 than the tube of the conductor part 111.

[0073] In addition, without limitation to this, the strength of the outer package of the first electrode 120 may be appropriately adjusted in accordance with various design values ​​of the capacitor 114. For example, in the case where the facing area between the first electrode 120 and the second electrode 130 is small, the liquid metal in the first electrode 120 is small, so if the outer package is not formed to have a strength that is difficult to deform, there is a possibility that the change in electrostatic capacitance corresponding to the change in the facing area accompanying the change in the outer package becomes too large. Therefore, in the case where the facing area is small, the strength of the outer package of the first electrode 120 may be formed to be greater than the tube of the conductor part 111 with respect to the negative pressure acting due to the elongation of the conductor part 111. In this case, the outer package of the first electrode 120 is formed to be thicker than the tube of the conductor part 111, and the outer package of the first electrode 120 is difficult to deform with respect to the negative pressure acting due to the elongation of the conductor part 111.

[0074] According to the above structure, the tube of the conductor part 111 is deformed, thereby generating pressure changes in the tube and the inside of the outer package, and the liquid metal moves between the inside of the outer package and the inside of the tube. For example, when the tube of the conductor part 111 is extended and a negative pressure of a predetermined magnitude or more acts on the inside of the first electrode 120, a part of the outer package of the first electrode 120 contracts, and the liquid metal filled in the area where the outer package contracts flows out to the inside of the conductor part 111. On the other hand, if the tube of the conductor part 111 contracts and the negative pressure acting on the inside of the first electrode 120 is smaller than the predetermined magnitude, the liquid metal that has flowed out to the inside of the conductor part 111 moves back to the inside of the first electrode 120, and the area of ​​the first electrode 120 where the outer package contracts returns to the original state. That is, the first electrode 120 physically changes according to the expansion and contraction of the conductor part 111. In the first electrode 120, the area where the liquid metal flows out from the inside of the outer package does not function as an electrode of the capacitor 114. That is, in the first electrode 120, only the part of the inner part of the outer package filled with liquid metal functions as an electrode of the capacitor 114.

[0075] The first electrode 120 is formed in a comb shape and includes a support portion 121, a first extension portion 122, a second extension portion 123, a third extension portion 124, and a fourth extension portion 125. The support portion 121 and the first to fourth extension portions 122 to 125 are examples of a plurality of opposing portions facing the second electrode 130.

[0076] The support part 121 is connected to one end of the tube of the conductor part 111. The support part 121 has an opposing surface 1211 opposing the second electrode 130. In addition, the support part 121 has a connection part 1212 with the conductor part 111. The inside of the support part 121 is connected to the inside of the tube. Therefore, liquid metal can flow between the inside of the support part 121 and the inside of the tube of the conductor part 111.

[0077] The first extension portion 122 to the fourth extension portion 125 extend from the support portion 121, respectively. The first extension portion 122 includes an opposing surface 1221 that is opposed to the second electrode 130. The second extension portion 123 is located at a position farther from the connection portion 1212 than the first extension portion 122. The second extension portion 123 includes an opposing surface 1231 that is opposed to the second electrode 130. The third extension portion 124 is located at a position farther from the connection portion 1212 than the second extension portion 123. The third extension portion 124 includes an opposing surface 1241 that is opposed to the second electrode 130. The fourth extension portion 125 is located at a position farther from the connection portion 1212 than the third extension portion 124. The fourth extension portion 125 includes an opposing surface 1251 that is opposed to the second electrode 130.

[0078] In addition, the interior of each of the first to fourth extension parts 122 to 125 is connected to the interior of the support part 121. Liquid metal can flow between the interior of each of the first to fourth extension parts 122 to 125 and the interior of the support part 121. In each of the first to fourth extension parts 122 to 125, by applying a negative pressure of a predetermined magnitude or more, the liquid metal flows into the interior of the support part 121, and the outer package shrinks.

[0079] Each of the support portion 121 and the first to fourth extension portions 122 to 125 functions as a part of the electrode of the capacitor 114 when the inside of the outer package is filled with liquid metal. In addition, each of the opposing surfaces 1221 to 1251 functions as a part of the surface (hereinafter referred to as the opposing electrode surface) opposing the second electrode 130 in the region of the first electrode 120 that functions as the electrode of the capacitor 114 when it functions as the electrode of the capacitor 114. In addition, the electrostatic capacitance C of the capacitor 114 changes according to the change of the total area S of all the opposing electrode surfaces (hereinafter referred to as the opposing electrode area).

[0080] The first extension part 122 to the fourth extension part 125 have different outer packaging thicknesses. The first extension part 122 to the fourth extension part 125 have different outer packaging thicknesses, and therefore, have different strengths with respect to the negative pressure generated by the extension of the conductor part 111. In other words, the first extension part 122 to the fourth extension part 125 have different magnitudes of negative pressures that act when the liquid metal flows out from a state fully filled with liquid metal and does not function as an electrode.

[0081] Specifically, the outer packaging of the second extension part 123 is formed thicker than the outer packaging of the first extension part 122, the outer packaging of the third extension part 124 is formed thicker than the outer packaging of the second extension part 123, and the outer packaging of the fourth extension part 125 is formed thicker than the outer packaging of the third extension part 124. Therefore, the strength of the outer packaging of the second extension part 123 is higher than the strength of the outer packaging of the first extension part 122, the strength of the outer packaging of the third extension part 124 is higher than the strength of the outer packaging of the second extension part 123, and the strength of the outer packaging of the fourth extension part 125 is higher than the strength of the outer packaging of the third extension part 124.

[0082] According to the above structure, as the negative pressure acting on the inside of the first electrode 120 increases with the extension of the conductor part 111, the number of parts where the outer cover shrinks in the first extension part 122 to the fourth extension part 125 increases. Therefore, as the area deformed in the first electrode 120 increases, the amount of liquid metal flowing out from the inside of the first electrode 120 to the inside of the conductor part 111 increases. At this time, as the conductor part 111 extends, the outer cover shrinks sequentially from the part of the first electrode 120 where the strength of the outer cover is low relative to the negative pressure. Therefore, as the conductor part 111 extends, the area in the first electrode 120 that functions as an electrode of the capacitor 114 decreases, and the opposing electrode area S of the opposing electrode surface of the capacitor 114 decreases. And as the opposing electrode area S decreases, the electrostatic capacitance C of the capacitor 114 increases.

[0083] Furthermore, the first to fourth extension portions 122 to 125 are formed so that the outer casing becomes thicker as they are farther from the connection portion 1212. Therefore, the first to fourth extension portions 122 to 125 are more resistant to negative pressure caused by the extension of the conductor portion 111 as they are farther from the connection portion 1212.

[0084] In addition, the thickness of the outer package of the support portion 121 is thicker than that of each of the first to fourth extension portions 122 to 125. Therefore, the support portion 121 has a higher strength against the negative pressure generated inside due to the elongation of the conductor portion 111 than that of each of the first to fourth extension portions 122 to 125. Therefore, the support portion 121 is less likely to be deformed against the negative pressure generated inside due to the elongation of the conductor portion 111 than the first to fourth extension portions 122 to 125.

[0085] In addition, the strength of the outer packaging can be different in the support portion 121 and the first extension portion 122 to the fourth extension portion 125 by changing the composition of the material forming the outer packaging, changing the number of stacked outer packaging sheets, changing the physical structure of the outer packaging, and providing reinforcements to prevent deformation of the outer packaging.

[0086] Next, the operation of the magnetic resonance imaging apparatus 1 will be described.

[0087] like Figure 2 and Figure 6 As shown, when the coil element 102 is in the reference state, the magnitude of the negative pressure caused by the extension of the conductor part 111 in the first electrode 120 is close to 0. Therefore, when the coil element 102 is in the reference state, the outer package of the first electrode 120 does not shrink, and the liquid metal does not flow from the inside of the first electrode 120 to the inside of the conductor part 111. Therefore, in the first electrode 120, the support part 121 and the first extension part 122 to the fourth extension part 125 all function as electrodes of the capacitor 114, and the facing surfaces 1211, 1221 to 1251 all function as facing electrode surfaces of the capacitor 114. Here, the area of ​​the facing surface 1211 is S1, the area of ​​the facing surface 1221 is S2, the area of ​​the facing surface 1231 is S3, the area of ​​the facing surface 1241 is S4, and the area of ​​the facing surface 1251 is S5. The opposing electrode area (hereinafter referred to as the reference electrode area) Sa when the coil element 102 is in the reference state is S1+S2+S3+S4+S5. In addition, the distance between the first electrode 120 and the second electrode 130 is set to d. And the electrostatic capacitance (hereinafter referred to as the reference electrostatic capacitance) Ca of the capacitor 114 when the coil element 102 is in the reference state is ε0·Sa / d. Here, ε0 is the dielectric constant of a vacuum. In addition, the dielectric constant ε0 of a vacuum is substantially the same as the dielectric constant of air, so it can also be used as the dielectric constant of air.

[0088] When the coil element 102 is extended from the reference state, a negative pressure caused by the extension of the conductor part 111 acts on the inside of the first electrode 120, the first electrode 120 contracts, and the liquid metal flows into the inside of the conductor part 111 through the inside of the support part 121 and the inside of the connecting part 1212. Figure 3 and Figure 7As shown in FIG. 1 , the first extension portion 122 and the second extension portion 123 shrink, and the liquid metal filled in the first extension portion 122 and the second extension portion 123 passes through the inside of the support portion 121 and the inside of the connection portion 1212 and flows out of the inside of the conductor portion 111. The first extension portion 122 and the second extension portion 123 no longer function as electrodes of the capacitor 114 due to the outflow of the liquid metal. Therefore, only the support portion 121, the third extension portion 124, and the fourth extension portion 125 function as electrodes of the capacitor 114, and the facing surface 1221, the facing surface 1241, and the facing surface 1251 function as facing electrode surfaces of the capacitor 114. Therefore, the facing electrode area (hereinafter referred to as the extended electrode area) Sb (= S1 + S4 + S5) of the capacitor 114 when the coil element 102 is in the extended state is smaller than the reference electrode area Sa (= S1 + S2 + S3 + S4 + S5). Furthermore, the electrostatic capacitance of the capacitor 114 when the coil element 102 is in the extended state (hereinafter referred to as extended electrostatic capacitance) Cb (=ε0·Sb / d) is smaller than the reference electrostatic capacitance Ca (=ε0·Sa / d).

[0089] In addition, when the coil element 102 contracts from the extended state, a pressure change occurs inside the first electrode 120 and inside the conductor part 111, and a force acts on the conductor part 111 to cause the liquid metal filled inside to flow out into the first electrode 120. Therefore, the conductor part 111 contracts, and the liquid metal inside the conductor part 111 passes through the inside of the support part 121 and the inside of the connecting part 1212 and flows out into the inside of the first electrode 120. As a result, in the first electrode 120, the area filled with liquid metal increases, and the area that functions as an electrode of the capacitor 114 increases. In addition, the area of ​​the opposing electrode of the capacitor 114 increases, and the electrostatic capacitance of the capacitor 114 increases.

[0090] As described above, in coil element 102, when inductance L increases, capacitance C of capacitor 114 decreases as negative pressure due to extension of conductor 111 increases. Also, when inductance L decreases, conductor 111 contracts and capacitance C of capacitor 114 increases.

[0091] Hereinafter, effects of the local coil device 100 including the coil element 102 and the magnetic resonance imaging apparatus 1 according to the present embodiment will be described.

[0092] The coil element 102 of this embodiment includes: a conductor part 111 that can be expanded and contracted; and a capacitor 114 connected to the conductor part 111, and the electrostatic capacitance C changes according to the physical change corresponding to the expansion and contraction of the conductor part 111. The conductor part 111 is equivalent to a coil. As the conductor part 111 is extended, the inductance L of the conductor part 111 increases, and the electrostatic capacitance C of the capacitor 114 decreases.

[0093] That is, according to the local coil device 100 and the magnetic resonance imaging device 1 including the coil element 102 of the present embodiment, through the above-described configuration and operation, when the coil element 102 and the conductor portion 111 are extended, the inductance L of the conductor portion 111 increases, and the electrostatic capacitance C of the capacitor 114 decreases. The relationship among the inductance L, the electrostatic capacitance C, and the resonance frequency f is expressed by f=1 / {2π(LC)^(1 / 2)} (where "^" is a symbol indicating a power). Therefore, the reduction in the electrostatic capacitance C acts to offset the reduction in the resonance frequency f caused by the increase in the inductance L. Therefore, the electrostatic capacitance C of the capacitor 114 changes according to the expansion and contraction of the conductor portion 111, thereby suppressing the change in the resonance frequency f caused by the expansion and contraction of the coil element 102. Furthermore, by suppressing the change in the resonance frequency f, it is possible to suppress the degradation of the image quality of the MR image caused by the expansion and contraction of the coil element 102.

[0094] (First Modification of First Embodiment)

[0095] A first modification of the first embodiment will be described. This modification modifies the structure of the first embodiment as follows. In this modification, the structure of the first electrode 120 is different from that of the first embodiment. The description of the same structure, operation, and effect as the first embodiment will be omitted.

[0096] Figure 8 and Fig. 9 This is a diagram showing an example of the structure of the capacitor 114. Figure 8 Corresponding to the case where the coil element 102 is in the reference state, Fig. 9 This corresponds to the case where the coil element 102 is in an extended state.

[0097] The first electrode 120 includes a support portion 121 and an extending portion 126 .

[0098] The support portion 121 has the same structure as that of the first embodiment.

[0099] The extension portion 126 extends from the support portion 121 . The extension portion 126 includes an opposing surface 1261 that faces the second electrode 130 .

[0100] In addition, the interior of the extension part 126 is connected to the interior of the support part 121. Liquid metal can flow between the interior of the extension part 126 and the interior of the support part 121. A negative pressure of a predetermined magnitude or more acts on the interior of the extension part 126, so that the liquid metal flows from the interior of the extension part 126 to the interior of the support part 121, and the outer package of the extension part 126 shrinks.

[0101] When the outer casing of extension 126 is filled with liquid metal, extension 126 functions as a part of the electrode of capacitor 114. When extension 126 functions as an electrode of capacitor 114, facing surface 1261 functions as a part of the facing electrode surface.

[0102] The thickness of the outer package of the extension part 126 is different depending on the position relative to the second electrode 130. The thickness of the outer package of the extension part 126 is different depending on the position, and therefore, the strength of the negative pressure generated by the extension of the conductor part 111 is different depending on the position. In other words, the magnitude of the negative pressure acting when the extension part 126 does not function as an electrode due to the outflow of liquid metal from the state where the liquid metal is fully filled is different depending on the position. For example, the outer package is formed thicker at a position close to the support part 121 than at a position far from the support part 121. In this case, the strength of the negative pressure at the position close to the support part 121 is higher than the strength of the negative pressure at the position far from the support part 121.

[0103] According to the above structure, as the negative pressure acting on the inside of the first electrode 120 increases with the extension of the conductor part 111, the area of ​​the portion where the outer package shrinks in the extension part 126 increases. Therefore, as the area of ​​deformation in the first electrode 120 increases, the amount of liquid metal flowing out from the inside of the first electrode 120 to the inside of the conductor part 111 increases. At this time, as the conductor part 111 extends, the outer package shrinks sequentially from the portion where the strength of the outer package against the negative pressure in the first electrode 120 is low. Therefore, as the conductor part 111 extends, the area in the first electrode 120 that functions as an electrode of the capacitor 114 decreases, and the opposing electrode area S of the opposing electrode surface of the capacitor 114 decreases. And, as the opposing electrode area S decreases, the electrostatic capacitance C of the capacitor 114 increases.

[0104] Furthermore, by changing the composition of the material forming the outer cover of the extension portion 126 according to the position, etc., the strength of the outer cover of the extension portion 126 may be different according to the position.

[0105] Next, the operation of the magnetic resonance imaging apparatus 1 will be described.

[0106] like Figure 2 and Figure 8As shown, when the coil element 102 is in the reference state, the magnitude of the negative pressure caused by the extension of the conductor part 111 in the first electrode 120 is close to 0. Therefore, when the coil element 102 is in the reference state, the outer package of the first electrode 120 does not shrink, and the liquid metal does not flow from the inside of the first electrode 120 to the inside of the conductor part 111. Therefore, in the first electrode 120, the support part 121 and the extension part 126 all function as electrodes of the capacitor 114, and the opposing surfaces 1221 and 1261 all function as opposing electrode surfaces of the capacitor 114. Therefore, if the area of ​​the opposing surface 1261 is set to S6, the reference electrode area Sa becomes S1+S6. And the reference electrostatic capacitance Ca becomes ε0·Sa / d.

[0107] When the coil element 102 is extended from the reference state, a negative pressure caused by the extension of the conductor part 111 acts on the inside of the first electrode 120, the first electrode 120 contracts, and the liquid metal flows into the inside of the conductor part 111 through the inside of the support part 121 and the inside of the connecting part 1212. Figure 3 as well as Fig. 9 As shown, a part of the extension part 126 shrinks, and a part of the liquid metal filled in the extension part 126 passes through the inside of the support part 121 and the inside of the connection part 1212 and flows out to the inside of the conductor part 111. The area where the liquid metal flows out in the extension part 126 no longer functions as an electrode of the capacitor 114. Therefore, the area of ​​the opposing surface 1261 becomes smaller. In the first electrode 120, only the support part 121 and a part of the extension part 126 function as electrodes of the capacitor 114, and only a part of the opposing surface 1221 and the opposing surface 1261 function as opposing electrode surfaces of the capacitor 114. Therefore, the extension electrode area Sb is smaller than the reference electrode area Sa. Therefore, the extension electrostatic capacitance Cb (=ε0·Sb / d) is smaller than the reference electrostatic capacitance Ca (=ε0·Sa / d).

[0108] In addition, when the coil element 102 contracts from the extended state, a pressure change occurs inside the first electrode 120 and inside the conductor part 111, and a force acts on the conductor part 111 to cause the liquid metal filled inside to flow out to the inside of the first electrode 120. Therefore, the conductor part 111 contracts, and the liquid metal inside the conductor part 111 flows out to the inside of the first electrode 120 through the inside of the support part 121 and the inside of the connecting part 1212. As a result, in the first electrode 120, the area filled with liquid metal increases, and the area that functions as an electrode of the capacitor 114 increases. In addition, the area of ​​the opposing electrode of the capacitor 114 increases, and the electrostatic capacitance of the capacitor 114 increases.

[0109] As described above, in the coil element 102 of the present modification, as the conductor portion 111 is extended, the inductance L of the conductor portion 111 increases, and the electrostatic capacitance C of the capacitor 114 decreases, similarly to the first embodiment. The reduction in the electrostatic capacitance C acts to offset the decrease in the resonance frequency f caused by the increase in the inductance L. Therefore, in the local coil device 100 and the magnetic resonance imaging apparatus 1 including the coil element 102 of the present modification, as well as in the first embodiment, the electrostatic capacitance C of the capacitor 114 changes according to the expansion and contraction of the conductor portion 111, thereby suppressing the change in the resonance frequency f caused by the expansion and contraction of the coil element 102.

[0110] (Second Embodiment)

[0111] The second embodiment will be described. This embodiment modifies the structure of the first embodiment as follows. In this embodiment, the structure of the capacitor 114 is different from that of the first embodiment. The description of the same structure, operation, and effect as those of the first embodiment will be omitted.

[0112] Fig.10 and Fig.11 This is a diagram showing an example of the structure of the capacitor 114. Fig.10 Corresponding to the case where the coil element 102 is in the reference state, Fig.11 This corresponds to the case where the coil element 102 is in an extended state.

[0113] The capacitor 114 includes a first electrode 140 and a second electrode 150 .

[0114] The first electrode 140 is fixed inside the case 112. The first electrode 140 is connected to one end of the tube of the conductor part 111 inside the case 112. The first electrode 140 is formed in a cylindrical shape.

[0115] The second electrode 150 is fixed inside the case 112. The second electrode 150 is connected to the other end of the tube of the conductor part 111 inside the case 112. The second electrode 150 is formed in a bottomed cylindrical shape. The second electrode 150 is formed of metal, for example.

[0116] One end of the first electrode 140 is connected to the tube of the conductor 111, and the opposite end is inserted into the cylindrical interior of the second electrode 150. The outer wall of the first electrode 140 and the inner wall of the second electrode 150 are partially opposite to each other. The first electrode 140 and the second electrode 150 function as a pair of electrodes of the capacitor 114.

[0117] In addition, the shapes of the first electrode 140 and the second electrode 150 are not limited to the above shapes. The shape of the first electrode 140 may be, for example, a prism shape, a rod shape, or the like.

[0118] At least a portion of the first electrode 140 has conductivity. As in the first embodiment, the first electrode 140 includes a hollow outer package filled with liquid metal, and the outer package is connected to the tube of the conductor part 111. Therefore, in this embodiment, if a negative pressure of a predetermined magnitude or more acts on the inside of the first electrode 140, the outer package shrinks in a portion of the first electrode 140, and the liquid metal filled in the area where the outer package shrinks flows out to the inside of the conductor part 111. And, when the negative pressure acting on the inside of the first electrode 140 is less than a predetermined magnitude, the liquid metal flowing out to the inside of the conductor part 111 moves back to the inside of the first electrode 140, and the area where the outer package shrinks in the first electrode 140 returns to the original state. That is, the first electrode 140 physically changes according to the expansion and contraction of the conductor part 111. In the first electrode 140, the area where the liquid metal flows out from the inside of the outer package no longer functions as an electrode of the capacitor 114. That is, in the first electrode 140, only the portion filled with liquid metal in the inside of the outer package functions as an electrode of the capacitor 114.

[0119] The first electrode 140 includes a support portion 141 and an extending portion 142 .

[0120] The support part 141 is connected to one end of the tube of the conductor part 111. The support part 141 has an opposing surface 1411 opposing the second electrode 150. The inside of the support part 141 is connected to the inside of the tube. Therefore, liquid metal can flow between the inside of the support part 141 and the inside of the tube of the conductor part 111.

[0121] The extension portion 142 is located on the front end side of the support portion 141. Therefore, the extension portion 142 is fixed to a position closer to the bottom surface of the second electrode 150 than the support portion 141. The extension portion 142 includes an opposing surface 1421 that opposes the second electrode 150.

[0122] In addition, the interior of the extension part 142 is connected to the interior of the support part 141. Liquid metal can flow between the interior of the extension part 142 and the interior of the support part 141. Since a negative pressure of a predetermined magnitude or more acts on the interior of the extension part 142, the liquid metal flows from the interior of the extension part 142 to the interior of the support part 141, and the outer package of the extension part 142 shrinks.

[0123] When the outer package is filled with liquid metal, support portion 141 and extension portion 142 function as a part of the electrode of capacitor 114. When functioning as the electrode of capacitor 114, facing surfaces 1411 and 1421 function as a part of the facing electrode surface.

[0124] The thickness of the outer package of the support portion 141 is thicker than that of the extension portion 142. Therefore, the support portion 141 is stronger than the extension portion 142 against the negative pressure generated inside due to the extension of the conductor portion 111. Therefore, the support portion 141 is less likely to be deformed against the negative pressure generated inside due to the extension of the conductor portion 111 than the extension portion 142.

[0125] Next, the operation of the magnetic resonance imaging apparatus 1 will be described.

[0126] like Figure 2 and Fig.10 As shown, when the coil element 102 is in the reference state, the magnitude of the negative pressure caused by the extension of the conductor part 111 in the first electrode 140 is close to 0. Therefore, when the coil element 102 is in the reference state, the outer package of the first electrode 140 does not shrink, and the liquid metal does not flow from the inside of the first electrode 140 to the inside of the conductor part 111. Therefore, the distance da between the first electrode 140 and the second electrode 150 (hereinafter referred to as the reference inter-electrode distance) does not change when the coil element 102 is in the reference state. And the reference electrostatic capacitance Ca becomes ε0·S / da.

[0127] When the coil element 102 is extended from the reference state, negative pressure due to the extension of the conductor part 111 acts on the inside of the first electrode 140, the first electrode 140 contracts, and the liquid metal flows through the inside of the support part 141 to the inside of the conductor part 111. And, for example, Figure 3 as well as Fig.11 As shown, a part of the extension part 142 shrinks, and a part of the liquid metal filled in the extension part 142 passes through the inside of the support part 141 and flows out to the inside of the conductor part 111. In addition, the extension part 142 shrinks, thereby increasing the distance between the opposing surface 1421 and the opposing surface 151 between the extension part 142 and the second electrode 150. That is, the distance between the extension part 142 and the second electrode 150 (hereinafter referred to as the elongated electrode distance) db when the coil element 102 is in the elongated state is greater than the reference electrode distance da. Therefore, the elongated electrostatic capacitance Cb (=ε0·S / db) is smaller than the reference electrostatic capacitance Ca (=ε0·S / da).

[0128] In addition, when the coil element 102 contracts from the extended state, the pressure inside the conductor part 111 of the first electrode 140 changes, and a force acts on the conductor part 111 to make the liquid metal filled inside flow out into the first electrode 140. Therefore, the conductor part 111 contracts, and the liquid metal inside the conductor part 111 flows out into the first electrode 140 through the inside of the support part 141, and the area filled with liquid metal in the first electrode 140 increases. As a result, the distance between the facing surface 1421 and the facing surface 151 between the extension part 142 and the second electrode 150 decreases, and the electrostatic capacitance increases.

[0129] As described above, as the conductor part 111 expands, the liquid metal flows out from the inside of the outer casing of the first electrode 140 to the inside of the tube of the conductor part 111, whereby the outer casing of the first electrode 140 contracts and the distance d between the first electrode 140 and the second electrode 150 increases. Therefore, the inductance L of the conductor part 111 increases, and the electrostatic capacitance C of the capacitor 114 decreases. The reduction in the electrostatic capacitance C works to offset the decrease in the resonance frequency f caused by the increase in the inductance L. Therefore, in the local coil device 100 and the magnetic resonance imaging device 1 including the coil element 102 according to the present embodiment, the electrostatic capacitance C of the capacitor 114 changes according to the expansion and contraction of the conductor part 111, and the change in the resonance frequency f caused by the expansion and contraction of the coil element 102 can be suppressed, as in the first embodiment.

[0130] (First Modification of Second Embodiment)

[0131] A first modification of the second embodiment will be described. This modification modifies the structure of the second embodiment as follows. In this modification, the first electrode 140 is movable relative to the second electrode 150. The same structure, operation, and effects as those of the second embodiment will be omitted.

[0132] Fig.12 and Fig.13 This is a diagram showing an example of the structure of the capacitor 114. Fig.12 Corresponding to the case where the coil element 102 is in the reference state, Fig.13 This corresponds to the case where the coil element 102 is in an extended state.

[0133] The first electrode 140 is mounted inside the case 112 on the inner side of the cylindrical shape of the second electrode 150 so as to be movable relative to the second electrode 150 along the extending direction of the cylindrical shape.

[0134] The first electrode 140 moves relative to the second electrode 150 along the extending direction of the second electrode 150 according to the expansion and contraction of the conductor portion 111. For example, when the coil element 102 is extended from the reference state, the conductor portion 111 is extended, and stress that pulls the first electrode 140 in a direction away from the second electrode 150 acts on the first electrode 140 from the conductor portion 111. Thus, the first electrode 140 moves in a direction away from the second electrode 150 as the conductor portion 111 is extended. On the other hand, for example, when the coil element 102 is contracted from the extended state and the conductor portion 111 is contracted, stress that moves the first electrode 140 in a direction approaching the second electrode 150 acts on the first electrode 140 from the conductor portion 111. Thus, the first electrode 140 moves in a direction approaching the second electrode 150 as the conductor portion 111 is contracted.

[0135] In addition, it is preferred that the following structure (hereinafter referred to as a restoring force generating mechanism) is provided inside the box body 112, that is, when the positional relationship between the first electrode 140 and the second electrode 150 changes due to the movement of the first electrode 140, a force for returning the positional relationship between the first electrode 140 and the second electrode 150 to the original state is applied to the first electrode 140.

[0136] Next, the operation of the magnetic resonance imaging apparatus 1 will be described.

[0137] like Figure 2 and Fig.12 As shown, when the coil element 102 is in the reference state, the magnitude of the stress caused by the elongation of the conductor portion 111 in the first electrode 140 is close to 0. Therefore, when the coil element 102 is in the reference state, the first electrode 140 does not move from the position of the first electrode 140 when the coil element 102 is in the reference state (hereinafter referred to as the reference position).

[0138] When the coil element 102 is extended from the reference state, a stress that pulls the first electrode 140 in a direction away from the second electrode 150 acts on the first electrode 140 from the conductor portion 111, and the first electrode 140 moves from the reference position in a direction away from the second electrode 150. Figure 3 as well as Fig.13As shown, the position of the first electrode 140 is offset from the reference position, and the structure of the capacitor 114 is physically deformed. Moreover, by moving the first electrode 140 away from the second electrode 150, the opposing area of ​​the first electrode 140 and the second electrode 150 is reduced, and the distance between the first electrode 140 and the second electrode 150 of the capacitor 114 as a whole is increased. Therefore, the extended electrode area Sb is smaller than the reference electrode area Sa, and the extended electrode distance db is larger than the reference electrode distance da. Therefore, the extended electrostatic capacitance Cb (=ε0·Sb / db) is smaller than the reference electrostatic capacitance Ca (=ε0·Sa / da).

[0139] Furthermore, when the coil element 102 contracts from the extended state, a stress that causes the first electrode 140 to move toward the second electrode 150 acts on the first electrode 140 from the conductor portion 111 inside the first electrode 140, and the first electrode 140 moves toward the second electrode 150. As a result, the facing area of ​​the first electrode 140 and the second electrode 150 increases, and the distance between the first electrode 140 and the second electrode 150 of the capacitor 114 as a whole decreases.

[0140] As described above, in the coil element 102 of the present modification, as the conductor portion 111 is extended, the inductance L of the conductor portion 111 increases, and the electrostatic capacitance C of the capacitor 114 decreases, similarly to the first embodiment. The reduction in electrostatic capacitance C acts to offset the decrease in the resonance frequency f caused by the increase in inductance L. Therefore, in the local coil device 100 and the magnetic resonance imaging apparatus 1 including the coil element 102 of the present modification, as well as in the first embodiment, the electrostatic capacitance C of the capacitor 114 changes according to the expansion and contraction of the conductor portion 111, thereby suppressing the change in the resonance frequency f caused by the expansion and contraction of the coil element 102.

[0141] In addition, in this modification, as an example, the structure in which the second electrode 150 is fixed and the first electrode 140 is movable relative to the second electrode 150 is described, but the present invention is not limited thereto. For example, the first electrode 140 may be fixed inside the case 112 and the second electrode 150 may be movable relative to the first electrode 140. In this case, as the conductor part 111 is extended, the second electrode 150 moves in a direction away from the first electrode 140, and as the conductor part 111 is contracted, the second electrode 150 moves in a direction close to the first electrode 140. In addition, for example, both the first electrode 140 and the second electrode 150 may be movable inside the case 112. In this case, as the conductor part 111 is extended, the first electrode 140 and the second electrode 150 move in a direction away from the other electrode, and as the conductor part 111 is contracted, the first electrode 140 and the second electrode 150 move in a direction close to the other electrode. That is, the structure may be any structure as long as the conductor portion 111 is extended to move at least one of the first electrode 140 and the second electrode 150 functioning as a pair of electrodes of the capacitor 114 and reduce the facing area between the first electrode 140 and the second electrode 150 .

[0142] (Second Modification of Second Embodiment)

[0143] A second variation of the second embodiment is described. This variation is a variation of the structure of the first variation of the second embodiment as follows. In this variation, the amount of dielectric material 160 inserted between the first electrode 140 and the second electrode 150 of the capacitor 114 changes according to the movement of the first electrode 140 relative to the second electrode 150. The description of the same structure, operation, and effect as those of the first variation of the second embodiment is omitted.

[0144] Fig.14 as well as Fig.15 This is a diagram showing an example of the structure of the capacitor 114. Fig.14 Corresponding to the case where the coil element 102 is in the reference state, Fig.15 This corresponds to the case where the coil element 102 is in an extended state.

[0145] A liquid dielectric substance 160 is inserted into the cylindrical interior of the second electrode 150. The dielectric substance 160 is inserted between the first electrode 140 and the second electrode 150, thereby functioning as a dielectric of the capacitor 114. In this case, the electrostatic capacitance C becomes the same value as when the electrostatic capacitance C1 of the first part where air exists between the electrodes and the electrostatic capacitance C2 of the second part where the dielectric exists between the electrodes are connected in parallel. At this time, the dielectric constant ε0 of the vacuum is used as the dielectric constant of the first part, and the dielectric constant ε of the dielectric substance is used as the dielectric constant of the second part.

[0146] The local coil device 100 is further provided with a liquid reservoir. The liquid reservoir stores a liquid dielectric substance 160. The liquid reservoir is arranged, for example, outside the capacitor 114 inside the case 112. The liquid reservoir is connected to the capacitor 114 via a connecting member such as a tube. The dielectric substance 160 can move between the inside of the second electrode 150 and the inside of the liquid reservoir via the connecting member.

[0147] The dielectric substance 160 moves between the inside of the second electrode 150 and the inside of the liquid reservoir according to the expansion and contraction of the conductor 111. For example, as the conductor 111 expands, the first electrode 140 moves in a direction away from the second electrode 150, and the dielectric substance 160 is supplied from the inside of the liquid reservoir to the inside of the second electrode 150. On the other hand, as the conductor 111 contracts, the first electrode 140 moves in a direction approaching the second electrode 150, and the dielectric substance 160 moves from the inside of the second electrode 150 to the inside of the liquid reservoir. That is, the amount of the dielectric substance 160 filled between the first electrode 140 and the second electrode 150 changes due to the movement of at least one of the first electrode 140 and the second electrode 150.

[0148] Next, the operation of the magnetic resonance imaging apparatus 1 will be described.

[0149] like Figure 2 and Fig.14 As shown, for example, when the coil element 102 is in the reference state, the first electrode 140 does not move from the reference position. Therefore, the amount of dielectric material 160 injected into the capacitor 114 does not change relative to the amount when the coil element 102 is in the reference state (hereinafter referred to as the reference injection amount).

[0150] When the coil element 102 is extended from the reference state, the first electrode 140 moves from the reference position in a direction away from the second electrode 150. Furthermore, inside the second electrode 150, the liquid surface of the dielectric substance 160 approaches the bottom surface of the cylindrical shape of the second electrode 150. At this time, as the first electrode 140 moves in a direction away from the second electrode 150, the dielectric substance 160 is supplied from the inside of the liquid storage portion to the inside of the second electrode 150. Furthermore, for example, Figure 3 and Fig.15 As shown, by supplying the dielectric substance 160 to the interior of the second electrode 150, when the coil element 102 is in an extended state, the amount of dielectric substance 160 injected into the capacitor 114 (hereinafter referred to as the extended injection amount) is greater than the reference injection amount, and the liquid level of the dielectric substance 160 that has dropped rises again.

[0151] In addition, when the coil element 102 contracts from the telescopic state, the first electrode 140 moves toward the direction approaching the second electrode 150. Moreover, inside the second electrode 150, the liquid surface of the dielectric substance 160 moves away from the bottom surface of the cylindrical shape of the second electrode 150. At this time, as the first electrode 140 moves toward the direction approaching the second electrode 150, the dielectric substance 160 flows out from the inside of the second electrode 150 to the inside of the liquid storage portion. As a result, the amount of the dielectric substance 160 put into the capacitor 114 becomes smaller.

[0152] Hereinafter, effects of the local coil device 100 including the coil element 102 and the magnetic resonance imaging apparatus 1 according to the present embodiment will be described.

[0153] In the coil component 102 of this modification, as the conductor 111 extends, the first electrode 140 moves, thereby changing the amount of dielectric substance 160 filled between the first electrode 140 and the second electrode 150. Specifically, as the conductor 111 extends, the dielectric substance 160 is supplied into the second electrode 150.

[0154] That is, through the above-mentioned structure and operation, according to the local coil device 100 and the magnetic resonance imaging device 1 including the coil element 102 of this modification, as the coil element 102 and the conductor part 111 are extended, the supply amount of the dielectric substance 160 to the inside of the second electrode 150 increases. The increase in the supply amount of the dielectric substance 160 acts to offset the drop in the liquid level of the dielectric substance 160 caused by the first electrode 140 being away from the second electrode 150. Therefore, the drop in the liquid level of the dielectric substance 160 is suppressed, and thus, even when the positional relationship between the first electrode 140 and the second electrode 150 is offset, by filling an appropriate amount of the dielectric substance 160 between the first electrode 140 and the second electrode 150, it is possible to suppress an unintended change in the electrostatic capacitance C of the capacitor 114. Furthermore, by suppressing an unintended change in the electrostatic capacitance C of the capacitor 114, it is possible to suppress a change in the resonance frequency f.

[0155] (Third Embodiment)

[0156] A third embodiment will be described. This embodiment modifies the structure of the first embodiment as follows. In this embodiment, an LC circuit having a plurality of inductors and a plurality of capacitors is formed in the coil element 102. The description of the same structure, operation, and effect as the first embodiment will be omitted.

[0157] Fig.16 1 is a diagram showing a circuit configuration of the local coil device 100. The coil element 102 includes a first inductor 113A, a second inductor 113B, a first capacitor 114A, and a second capacitor 114B.

[0158] Fig.17 1 is a schematic diagram showing the structure of the coil element 102 .

[0159] The conductor part 111 is formed in a shape in which a flexible tube is bent into a ring shape. A part of the conductor part 111 is inserted into the inside of the case 112. The conductor part 111 is continuous inside the case 112.

[0160] The conductor 111 has flexibility and includes a retractable tube. The inside of the tube is filled with liquid metal. The tube and liquid metal of the conductor 111 are the same as those of the first embodiment, and thus description thereof will be omitted.

[0161] The conductor portion 111 includes a first conductor portion 181, a second conductor portion 182, a first gap portion 183, and a second gap portion 184. In the first conductor portion 181 and the second conductor portion 182, the interior of the tube is filled with liquid metal.

[0162] The first gap 183 and the second gap 184 are respectively provided between the first conductor 181 and the second conductor 182. The first gap 183 is provided at a position 180 degrees opposite to the second gap 184 in the annular ring formed by the conductor 111. In the first gap 183 and the second gap 184, the inside of the tube is filled with air. Air is an example of a fluid different from liquid metal.

[0163] The first conductor portion 181 functions as the first inductor 113A. The second conductor portion 182 functions as the second inductor 113B.

[0164] The first capacitor 114A is formed by the first conductor 181, the second conductor 182, and the first gap 183. The first conductor 181 and the second conductor 182 function as a pair of electrodes of the first capacitor 114A. The first gap 183 functions as a gap between the pair of electrodes in the first capacitor 114A.

[0165] Similarly, the second capacitor 114B is formed by the first conductor 181, the second conductor 182, and the second gap 184. The first conductor 181 and the second conductor 182 function as a pair of electrodes of the second capacitor 114B. The second gap 184 functions as a gap between a pair of electrodes in the second capacitor 114B.

[0166] Fig.18 as well as Fig.19 1 is a diagram showing an example of the structure of the coil element 102 . Fig.18 Corresponding to the case where the coil element 102 is in the reference state, Fig.19 This corresponds to the case where the coil element 102 is in an extended state. Fig.18and Fig.19 The periphery of the first gap portion 183 in the coil element 102 is shown in an enlarged manner.

[0167] The first conductor portion 181 has a boundary surface 1811 with the first gap portion 183. The boundary surface 1811 is a boundary surface of the liquid metal inside the first conductor portion 181 with respect to the air inside the first gap portion 183. In addition, the second conductor portion 182 has a boundary surface 1821 with the first gap portion 183. The boundary surface 1821 is a boundary surface of the liquid metal inside the second conductor portion 182 with respect to the air inside the first gap portion 183. The boundary surface 1811 and the boundary surface 1821 function as a pair of opposing electrode surfaces in the first capacitor 114A. The area of ​​the boundary surface 1811 or the area of ​​the boundary surface 1821 is the opposing electrode area S in the first capacitor 114A.

[0168] Next, the operation of the magnetic resonance imaging apparatus 1 will be described.

[0169] like Figure 2 and Fig.18 As shown, when the coil element 102 is in the reference state, the distance between the boundary surface 1811 and the boundary surface 1821 does not change relative to the distance between the boundary surface 1811 and the boundary surface 1821 (hereinafter referred to as the reference inter-electrode distance) da when the coil element 102 is in the reference state. In addition, the reference electrostatic capacitance Ca becomes ε0·Sa / da.

[0170] As the conductor 111 stretches, an internal pressure acts on the conductor 111 to shrink the conductor 111. Since liquid metal is less deformable than air, the first gap 183 is deformed more than the first conductor 181 and the second conductor 182. Also, as the conductor 111 stretches, the distance between the boundary surface 1811 and the boundary surface 1821 increases, and the area of ​​the boundary surface 1811 and the area of ​​the boundary surface 1821 decrease. Also, for example, Figure 3 and Fig.19 As shown, in the first capacitor 114A, the elongated inter-electrode distance db is greater than the reference inter-electrode distance da, and the elongated electrode area Sb is smaller than the reference electrode area Sa. Therefore, in the first capacitor 114A, the elongated electrostatic capacitance Cb (=ε0·Sb / db) is smaller than the reference electrostatic capacitance Ca (=ε0·Sa / da).

[0171] In addition, when the conductor part 111 contracts from the extended state, the distance between the boundary surface 1811 and the boundary surface 1821 decreases, and the area of ​​the boundary surface 1811 and the area of ​​the boundary surface 1821 increase. As a result, in the first capacitor 114A, the distance between electrodes decreases, and the electrode area increases. In addition, in the first capacitor 114A, the electrostatic capacitance increases.

[0172] In the second capacitor 114B, similarly to the first capacitor 114A, the extension capacitance Cb is smaller than the reference capacitance Ca.

[0173] As described above, in the coil element 102 of the present embodiment, as in the first embodiment, as the conductor portion 111 is extended, the inductance L of the LC circuit increases, and the electrostatic capacitance C decreases. The reduction in the electrostatic capacitance C acts to offset the decrease in the resonance frequency f caused by the increase in the inductance L. Therefore, in the local coil device 100 and the magnetic resonance imaging device 1 including the coil element 102 of the present modification, as in the first embodiment, the electrostatic capacitance C of the capacitor 114 changes according to the expansion and contraction of the conductor portion 111, thereby suppressing the change in the resonance frequency f caused by the expansion and contraction of the coil element 102.

[0174] In addition, the first gap 183 and the second gap 184 may be filled with a liquid dielectric material instead of air. The dielectric material is, for example, silicon. In this case, in the formulas of the reference electrostatic capacitance Ca and the extended electrostatic capacitance Cb, the dielectric constant ε of the dielectric material is used instead of the dielectric constant ε0 of the vacuum.

[0175] Furthermore, in order to ensure the stability of the shape of the gap portion, for example, a separator may be provided at the boundary between the conductor portion and the gap portion.

[0176] According to at least one embodiment described above, in a receiving coil including an expandable and contractible coil element, a change in resonance frequency due to expansion and contraction of the coil element can be suppressed.

[0177] The term "processor" used in the above description refers to circuits such as CPU, GPU, or application-specific integrated circuit (ASIC), programmable logic device (for example, simple programmable logic device (SPLD), complex programmable logic device (CPLD), and field programmable gate array (FPGA)). The processor implements its functions by reading and executing the program stored in the storage circuit. In addition, it is also possible to configure the program to be directly loaded into the circuit of the processor instead of storing it in the storage circuit. In this case, the processor implements its functions by reading and executing the program loaded into the circuit. In addition, it is also possible not to execute the program, but to implement the function corresponding to the program by a combination of logic circuits. In addition, the processors of the present embodiment are not limited to the case where each processor is configured as a single circuit, and multiple independent circuits can be combined to form one processor to implement its functions. Furthermore, it is also possible to Figure 1 Multiple components in a processor are integrated into one processor to realize its functions.

[0178] Several embodiments of the present invention are described above, but these embodiments are presented as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, changes, etc. can be made without departing from the scope of the subject matter of the invention. These embodiments and their variations are included in the scope and subject matter of the invention, and are also included in the invention described in the claims and their equivalents.

Claims

1. A coil element, comprising: a coil including liquid metal and a tube filled with the liquid metal; and A capacitor is connected to the coil, and the liquid metal flows according to the expansion and contraction of the tube, thereby changing the electrostatic capacitance of the capacitor. As the coil is elongated, the inductance of the coil increases, and the electrostatic capacitance of the capacitor decreases.

2. A coil element, comprising: a coil including liquid metal and a tube filled with the liquid metal; and A capacitor is connected to the coil, and the liquid metal flows according to the expansion and contraction of the tube, thereby changing the electrostatic capacitance of the capacitor. The capacitor has a pair of electrodes at least partially facing each other, According to the expansion and contraction of the coil, at least one of the pair of electrodes undergoes a physical change.

3. The coil component according to claim 2, wherein: The coil has a hollow tube that can be expanded and contracted, and expands and contracts according to the expansion and contraction of the tube, wherein the tube has: A first conductor portion having a liquid metal filled therein; A second conductor portion having a liquid metal filled therein; and a gap portion formed between the first conductor portion and the second conductor portion and filled with a fluid different from the liquid metal, The first conductor portion and the second conductor portion function as the pair of electrodes.

4. The coil component according to claim 3, wherein: The fluid is air.

5. The coil component according to claim 3, wherein: As the tube is extended, the area of ​​the boundary surface of the first conductor portion with the gap portion and the area of ​​the boundary surface of the second conductor portion with the gap portion decrease, and the distance between the first conductor portion and the second conductor portion increases.

6. A coil element, comprising: a coil including liquid metal and a tube filled with the liquid metal; and A capacitor is connected to the coil, and the liquid metal flows according to the expansion and contraction of the tube, thereby changing the electrostatic capacitance of the capacitor. The electrostatic capacitance of the capacitor changes in accordance with the expansion and contraction of the coil, thereby suppressing a change in the resonance frequency due to the expansion and contraction of the coil.

7. A coil element, comprising: a coil including liquid metal and a tube filled with the liquid metal; and A capacitor is connected to the coil, and the liquid metal flows according to the expansion and contraction of the tube, thereby changing the electrostatic capacitance of the capacitor. The coil expands and contracts according to the expansion and contraction of the tube. The capacitor comprises a first electrode and a second electrode opposite to the first electrode. The first electrode has a hollow outer package connected to the tube and filled with the liquid metal.

8. The coil component according to claim 7, wherein: The interior of the tube communicates with the interior of the outer package.

9. The coil component according to claim 8, wherein: The tube is deformed, whereby pressure changes occur in the interior of the tube and the interior of the outer package, and the liquid metal moves between the interior of the outer package and the interior of the tube.

10. The coil component according to claim 9, wherein: The outer package is more easily deformed than the tube.

11. The coil component according to claim 10, wherein: The strength of the outer package with respect to negative pressure is smaller than the strength of the tube with respect to negative pressure.

12. The coil component according to claim 10, wherein: The tube stretches, whereby the outer packaging contracts.

13. The coil component according to claim 9, wherein: The electrical conductivity of the outer package is lower than the electrical conductivity of the liquid metal.

14. The coil component according to claim 9, wherein: The first electrode has a plurality of opposing portions facing the second electrode.

15. The coil component according to claim 14, wherein The plurality of opposing portions have different strengths against negative pressure.

16. The coil component according to claim 15, wherein: As the coil stretches, the number of deformed opposing portions increases.

17. The coil component according to claim 9, wherein: The strength of the outer package varies depending on the position relative to the second electrode. As the coil lengthens, the area of ​​deformation in the first electrode increases.

18. The coil component according to claim 9, wherein The second electrode has a cylindrical shape, The first electrode is inserted into the cylindrical shape of the second electrode and has an opposing surface facing an inner wall of the second electrode.

19. The coil component according to claim 18, wherein: The liquid metal flows out from the inside of the outer package to the inside of the tube, whereby the outer package contracts and the distance between the first electrode and the second electrode increases.

20. The coil component according to claim 18, wherein The coil is extended, so that at least one of the first electrode and the second electrode moves, and the facing area between the first electrode and the second electrode decreases.

21. The coil component according to claim 20, wherein: When at least one of the first electrode and the second electrode moves, the amount of the dielectric material filled between the first electrode and the second electrode changes.

22. A local coil device, comprising: The coil element according to any one of claims 1 to 21; and The receiving circuit receives the MR signal output from the coil element.

23. A magnetic resonance imaging apparatus comprising: The local coil device of claim 22; and The reconstruction unit reconstructs an image based on the MR signal acquired from the receiving circuit.

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