WO2013065480A1 - 磁気共鳴イメージング装置およびアンテナ装置 - Google Patents
磁気共鳴イメージング装置およびアンテナ装置 Download PDFInfo
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- WO2013065480A1 WO2013065480A1 PCT/JP2012/076759 JP2012076759W WO2013065480A1 WO 2013065480 A1 WO2013065480 A1 WO 2013065480A1 JP 2012076759 W JP2012076759 W JP 2012076759W WO 2013065480 A1 WO2013065480 A1 WO 2013065480A1
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- electric field
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
- G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
- G01R33/34092—RF coils specially adapted for NMR spectrometers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
- G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
- G01R33/341—Constructional details, e.g. resonators, specially adapted to MR comprising surface coils
- G01R33/3415—Constructional details, e.g. resonators, specially adapted to MR comprising surface coils comprising arrays of sub-coils, i.e. phased-array coils with flexible receiver channels
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
- G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
- G01R33/345—Constructional details, e.g. resonators, specially adapted to MR of waveguide type
- G01R33/3453—Transverse electromagnetic [TEM] coils
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
- G01R33/36—Electrical details, e.g. matching or coupling of the coil to the receiver
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
- G01R33/36—Electrical details, e.g. matching or coupling of the coil to the receiver
- G01R33/3642—Mutual coupling or decoupling of multiple coils, e.g. decoupling of a receive coil from a transmission coil, or intentional coupling of RF coils, e.g. for RF magnetic field amplification
- G01R33/365—Decoupling of multiple RF coils wherein the multiple RF coils have the same function in MR, e.g. decoupling of a receive coil from another receive coil in a receive coil array, decoupling of a transmission coil from another transmission coil in a transmission coil array
Definitions
- the present invention measures nuclear magnetic resonance (Nuclear Magnetic Resonance: hereinafter referred to as NMR) signals from hydrogen, phosphorus, etc. in a subject, and images nuclear density distribution, relaxation time distribution, etc. More particularly, the present invention relates to an antenna device that performs at least one of transmission of a high-frequency signal and reception of an NMR signal.
- NMR Nuclear Magnetic Resonance
- a high-frequency signal which is an electromagnetic wave
- a subject placed in a uniform static magnetic field generated by a static magnetic field magnet to excite nuclear spins in the subject and to generate nuclear spins.
- the subject is imaged by receiving a nuclear magnetic resonance signal and processing the signal.
- High-frequency signal irradiation and nuclear magnetic resonance signal reception are performed by a device called an RF antenna or an RF coil that transmits or receives radio frequency (RF) electromagnetic waves.
- RF radio frequency
- the RF coil classification includes a transmission antenna that performs only transmission, a reception antenna that performs only reception, and a transmission and reception antenna that performs both transmission and reception.
- a transmission antenna that performs only transmission
- a reception antenna that performs only reception
- a transmission and reception antenna that performs both transmission and reception.
- cylindrical transmitting antennas examples include a so-called birdcage type or birdcage type (see, for example, Non-Patent Document 1 and Patent Document 1), and a so-called TEM type (see, for example, Patent Document 2 and Patent Document 3). .)
- these transmission antennas about 16 to 32 bar-shaped conductors, which are generally called rungs (crossbars or ladder bars) and are arranged in parallel with the central axis of the cylinder, are installed along the side of the cylinder.
- Such a cylindrical transmission antenna is used in an MRI apparatus called a tunnel type.
- a tunnel is formed by arranging cylindrical static magnetic field magnets, and the subject enters the tunnel while lying on a bed, and imaging is performed.
- Examples of the receiving antenna include, for example, an example in which a conductor is bent in a loop shape (see, for example, Patent Document 4) and an example in which the conductor is bent in a figure 8 (see, for example, Non-Patent Document 2). . Since such a receiving antenna is arranged closer to the subject than the transmitting antenna, the sensitivity is higher than that of the volume antenna, but the sensitivity region is often partial and narrow.
- the subject is a conductor, such as a human body, so that when an RF magnetic field is irradiated toward the subject, a shielding current called eddy current flows on the subject surface.
- This shielding current prevents the RF magnetic field from penetrating into the subject, and the nuclear spin in the subject is not sufficiently excited.
- the RF magnetic field may not reach the inside of the subject sufficiently.
- the spatial distribution of the RF magnetic field becomes non-uniform, and if it is multi-channeled to prevent this, or if it is multi-channeled to speed up imaging, coupling between channels tends to occur.
- the present invention has been made in view of the above circumstances, and can suppress the coupling and suppress the coupling to a uniform spatial distribution of the RF magnetic field regardless of the magnetic field strength of the MRI apparatus.
- An object is to provide a technique for realizing a good RF coil.
- the present invention includes a pad-shaped electric field conductor having a predetermined area on both outer sides of a rung conductor that forms a loop-shaped circuit and is a part of a configuration for driving as an antenna.
- the present invention includes at least one of a magnet that generates a static magnetic field to form a static magnetic field, a high-frequency signal transmitted to the static magnetic field, and a nuclear magnetic resonance signal generated from a subject placed in the static magnetic field.
- the RF coil includes a sheet-like conductor and an antenna unit, and the antenna unit is disposed at a predetermined distance from the sheet-like conductor.
- a rung conductor, and two electric field conductors disposed at both ends of the rung conductor at a predetermined distance from the sheet conductor, the rung conductor and the sheet conductor are provided by the RF coil.
- a magnetic resonance imaging apparatus comprising a loop circuit that resonates at a frequency of the high-frequency signal to be transmitted or the nuclear magnetic resonance signal to be received.
- the present invention also includes a sheet-like conductor and an antenna portion, and the antenna portion has a rung conductor disposed at a predetermined distance from the sheet-like conductor and a predetermined distance from the sheet-like conductor. And the two electric field conductors disposed at both ends of the rung conductor, wherein the rung conductor and the sheet-like conductor constitute a loop circuit that resonates at a predetermined frequency.
- An antenna device is provided.
- an RF coil that can suppress the coupling and make the spatial distribution of the RF magnetic field uniform, regardless of the magnetic field intensity of the MRI apparatus, and can improve the penetration of the RF magnetic field into the subject.
- Schematic configuration diagram of the MRI apparatus of the first embodiment The perspective view of the antenna apparatus of 1st embodiment (a) is explanatory drawing for demonstrating the magnetic field coupling of the antenna apparatus of 2 channels, (b) is explanatory drawing for demonstrating the electric field coupling of the antenna apparatus of this embodiment.
- FIG. 1 is a schematic configuration diagram of an MRI apparatus 100 of the present embodiment.
- the MRI apparatus 100 transmits a high-frequency signal to the subject 112, a magnet 101 that forms a static magnetic field in the measurement space in which the subject 112 is arranged, a gradient magnetic field coil 102 that gives a magnetic field gradient in a predetermined direction to the static magnetic field, and
- an RF coil 103 that receives a nuclear magnetic resonance signal generated from the subject 112 and a high-frequency signal transmitted from the RF coil 103 are generated and transmitted to the RF coil 103, and the nuclear magnetic resonance signal received by the RF coil 103
- the transmitter / receiver 104 that performs signal processing on the magnetic field, the gradient magnetic field power source 109 that supplies current to the gradient coil 102, the drive of the transceiver 104 and the gradient magnetic field power source 109 are controlled, and various information processing and operations by the operator are performed.
- the data processing unit 105 functions as an imaging unit that images internal information of the subject 112 from a nuclear magnetic resonance signal received by the RF coil 103 and subjected to various signal processing by the transceiver 104.
- the gradient magnetic field power source 109 and the gradient magnetic field coil 102 are connected by a gradient magnetic field control cable 107.
- the RF coil 103 and the transceiver 104 are connected by a transmission / reception cable 106 that transmits and receives signals between the RF coil 103 and the transceiver 104.
- the transceiver 104 includes a synthesizer, a power amplifier, a reception mixer, an analog / digital converter, a transmission / reception changeover switch, and the like.
- the MRI apparatus 100 is classified into a horizontal magnetic field method and a vertical magnetic field method depending on the direction of the static magnetic field formed by the magnet 101.
- the magnet 101 In the case of the horizontal magnetic field method, the magnet 101 generally has a cylindrical bore (central space) and generates a static magnetic field in the horizontal direction in FIG.
- the vertical magnetic field method a pair of magnets are arranged above and below the subject to generate a static magnetic field in the vertical direction in FIG.
- an RF signal 103 and a gradient magnetic field coil 102 irradiate a subject 112 placed in a static magnetic field with intermittent high frequency signals and gradient magnetic fields at intervals of several milliseconds.
- a nuclear magnetic resonance signal emitted from the subject 112 in resonance with the high-frequency signal is received, signal processing is performed, and a magnetic resonance image is acquired.
- the subject 112 is, for example, a predetermined part of the human body.
- the subject 112 lies on the bed 111 and is disposed inside the RF coil 103.
- the high-frequency signal and the gradient magnetic field are transmitted and applied by the RF coil 103 and the gradient magnetic field coil 102, respectively.
- the RF coil 103, the gradient magnetic field coil 102, and the bed 111 are arranged in a static magnetic field space formed by the magnet 101.
- a single RF coil is shown as the RF coil 103 that transmits a high-frequency signal and receives a nuclear magnetic resonance signal.
- the present invention is not limited to this.
- an RF coil composed of a plurality of coils may be used as the RF coil 103, such as combining a wide range imaging RF coil and a local RF coil.
- the high-frequency signal transmitted by the RF coil 103 and the nuclear magnetic resonance signal received by the RF coil 103 are collectively referred to as electromagnetic waves.
- an RF coil 103 that can suppress coupling between channels even when a multi-channel coil is used, and that allows good penetration of an RF magnetic field into the human body.
- details of the RF coil 103 of the present embodiment that realizes this will be described with reference to the drawings.
- the case where the antenna device 200 having a shape close to a planar shape is used as the RF coil 103 will be described as an example.
- FIG. 2 is a perspective view of the antenna device 200 used as the RF coil 103 of the present embodiment.
- the antenna device 200 of the present embodiment includes a sheet-like conductor (hereinafter referred to as a sheet-like conductor) 210 that functions as a ground plane (a ground plane), and an antenna unit 220.
- the antenna unit 220 includes a rung conductor 221, an electric field conductor 222, a frequency adjustment capacitor 223, and a connection terminal 224.
- the sheet-like conductor 210, the rung conductor 221, the frequency adjustment capacitor 223, and the connection terminal 224 realize a function as an antenna that resonates at a predetermined frequency and performs at least one of transmission and reception of electromagnetic waves.
- FIG. 2 illustrates a case where two antenna units 220 are arranged on one sheet-like conductor 210 to form a two-channel antenna device 200.
- the rung conductor 221 is made of one or more elongated flat plates or tapes, or rods or cylinders. In the case of an elongated flat plate, the plate-like surface is disposed substantially parallel to the surface of the sheet-like conductor 210. In the case of the tape shape, if the tape surface is arranged substantially parallel to the surface of the sheet-like conductor 210, there are many cases where the space is effectively used and the performance is good.
- the rung conductor 221 is arranged on the side of the sheet-like conductor 210 where the subject 112 is arranged at a predetermined distance (space) from the sheet-like conductor 210.
- the rung conductor 221 is disposed substantially parallel to the rung conductor 221 of the adjacent antenna unit 220 (channel).
- the electric field conductor 222 is made of a plate-shaped conductor having a predetermined area, and is electrically connected to both ends of the rung conductor 221. At this time, it is desirable to connect so that the electric resistance is almost zero, which is 0.1 ⁇ or less.
- the electric field conductor 222 is separated from the sheet conductor 210 by a predetermined distance (space) on the side of the sheet conductor 210 where the subject 112 is disposed, and the plate-like surface is the sheet conductor. It is arranged substantially parallel to the surface.
- the electric field conductor 222 is disposed so as to be close to the electric field conductor 222 of the adjacent antenna unit (channel) 220.
- the electric field conductor 222 has a plate shape as described above, and a voltage applied to the rung conductor 221 is transmitted to generate an electric field. This electric field suppresses the shielding current flowing on the surface of the subject 112 due to the magnetic field generated by the current flowing in the rung conductor 221.
- the width w 2 of the electric field conductor 222 in the short axis direction of the rung conductor 221 is Width greater than 1 This is to reduce coupling between channels as will be described later.
- the area S 2 of the electric field conductor 222 is preferably larger than the area S 1 of the rung conductor 221. This is to improve the penetration of the RF magnetic field into the deep part of the subject 112, as will be described later.
- the frequency adjusting capacitor 223 is disposed between both end portions of the rung conductor 221 and the sheet-like conductor 210 just below, and connects both end portions of the rung conductor 221 and the sheet-like conductor 210.
- the number of frequency adjustment capacitors 223 is 2N.
- the two end portions of the rung conductor 221 are connected to each other by the frequency adjustment capacitor 223, whereby the two frequency adjustment capacitors 223, the one rung conductor 221 and the sheet-like conductor 210 form a loop-like circuit.
- the value of the frequency adjustment capacitor 223 is adjusted so that the antenna device 200 resonates at the frequency used by the MRI apparatus 100.
- the antenna device 200 transmits and receives an electromagnetic wave having a predetermined frequency as the RF coil 103 of the MRI apparatus 100.
- the frequency adjustment capacitor 223, for example, a capacitor having a value of several pF to several tens of pF is used.
- the electric field conductor 222 has a wide area and faces the sheet-like conductor 210, and therefore has a capacitor component spatially. Therefore, the capacitance of the capacitor that contributes to determining the resonance frequency of the antenna device 200 is the sum of the capacitance of the frequency adjustment capacitor 223 as an element and the capacitance of the capacitor component of the electric field conductor 222 and the sheet-like conductor 210.
- the capacitor component of the electric field conductor 222 and the sheet-like conductor 210 is also taken into consideration.
- the connection terminal 224 is a transmission and / or reception terminal provided on one end of the rung conductor 221 and the sheet-like conductor 210 immediately below.
- the end of the coaxial cable 230 is connected to the connection terminal 224 provided on the rung conductor 221 and the sheet-like conductor 210 immediately below. That is, the inner conductor and the outer conductor of the coaxial cable 230 are connected to the rung conductor 221 side and the sheet-like conductor 210 side of the connection terminal 224, respectively.
- the coaxial cable 230 is used as the transmission / reception cable 106 described above, and connects the antenna apparatus 200 and the MRI apparatus 100 main body (transceiver 104).
- the antenna device 200 transmits and receives electromagnetic waves via the coaxial cable 230.
- the connection terminal 224 is also referred to as a transmission / reception terminal, a port of the antenna device 200, a feeding point, or the like.
- the connection terminal 224 is provided for each channel.
- connection terminal 224 may be configured to have a matching circuit function by using several lumped constant elements such as capacitors and inductors, for example.
- the antenna device 200 includes a conductor support structure for disposing the rung conductor 221 and the electric field conductor 222 while maintaining a predetermined distance from the sheet-like conductor 210.
- the multi-channel (two-channel) antenna device 200 of the present embodiment having the above configuration can reduce the interference (coupling) between channels, and the penetration of the RF magnetic field into the subject 112 is favorable.
- the interference coupling
- the antenna device 200 of the present embodiment can reduce interference (coupling) between channels.
- two rung conductors 221 are arranged adjacent to each other.
- the rung conductors 221a and 221b are used, respectively.
- the electric field conductors 222 connected to the electric field conductors 222a and 222b, respectively, are referred to as antenna parts 220a and 220b, respectively.
- the electric field conductors 222 are connected to both ends of the rung conductor 221, respectively.
- a current 721 flows through one rung conductor 221a
- a charge 724 is generated in the electric field conductor 222a
- a charge 725 having an opposite sign is applied to the electric field conductor 222b of the adjacent channel (antenna unit 220b).
- a voltage is generated in the adjacent antenna unit 220b by the charge 725 having the opposite sign, and a force for causing a reverse current 726 to flow is applied to the other rung conductor 221b.
- a force that causes a reverse current to flow through the rung conductor 221a acts. This is called electric field coupling.
- the electric field conductors 222 of the two adjacent antenna units 220 are arranged close to each other as shown in FIG.
- the force due to the electric field coupling is increased, approaching the force due to the magnetic field coupling, and the interference (coupling) between the channels is reduced.
- the proximity of the electric field conductors 222 of the adjacent antenna units 220 can be realized by making the interval of the electric field conductors 222 of the adjacent antenna units 220 narrower than the interval of the rung conductors 221 of the adjacent antenna units 220.
- the width w 2 of the electric field conductor 222 is made larger than the width w 1 of the rung conductor 221, thereby making the interval between the electric field conductors 222 of adjacent antenna portions 220 smaller than the interval between the rung conductors 221.
- the sheet-like conductor 210 is made of copper foil having a width of 360 mm, a length of 400 mm, and a thickness of 30 microns, and a rung conductor 221 having a width of w 1 20 mm and a length of 200 mm is separated from the distance 20 mm.
- the antenna device 200 of the present embodiment is configured by arranging and connecting the electric field conductor 222 having a width w 2 of 130 mm and a length of 80 mm to both ends thereof.
- the rung conductor 221 and the electric field conductor 222 are made of a conductor such as copper foil, for example. Further, if the interval between the electric field conductors 222 in adjacent channels is 10 mm, the interval between adjacent rung conductors 221 can be made narrower than 120 mm.
- the antenna device 200 of the present embodiment has the electric field conductor 222, thereby suppressing the shielding current generated on the surface of the subject 112 and increasing the penetration of the magnetic field into the subject 112, FIG. This will be described with reference to FIG.
- FIG. 4 and 5 show the current, magnetic field lines, and electric field at predetermined moments when an AC voltage is applied to the antenna device 200.
- FIG. a phantom 113 simulating a living body is used as the subject 112.
- the phantom 113 has a cylindrical shape, in which an aqueous solution composed of water and an electrolyte is enclosed.
- the aqueous solution filled in the phantom 113 has a predetermined electrical conductivity.
- the size of the phantom 113 is, for example, about 20 cm in diameter and about 30 cm in length in the case of simulating a human head.
- FIG. 4 is a diagram for explaining the influence of the magnetic lines of force 702 generated by the alternating current 701 flowing in the rung conductor 221 on the phantom 113.
- FIG. 4 When the current 701 flows, lines of magnetic force (B) 702 are generated so as to surround the current 701 according to Maxwell's equations.
- the magnetic field line (B) 702 passes between the sheet-like conductor 210 and the rung conductor 221 and enters from the cylindrical side surface of the phantom 113 and tries to penetrate.
- an eddy current (surface current) 703 is generated on the surface of the phantom 113 with respect to the magnetic field lines (B) 702 to be penetrated.
- This eddy current (surface current) 703 acts to prevent penetration of the magnetic lines of force 502. Further, the eddy current (surface current) 703 flows in a direction parallel to and opposite to the current flowing through the rung conductor 221 on the cylindrical side surface closest to the rung conductor 221.
- FIG. 5 is a diagram for explaining the influence of the voltage 711 applied to the electric field conductor 222 by the alternating current 701 flowing in the rung conductor 221 on the phantom 113.
- FIG. 5 When the current 701 flows, a positive voltage 711 is applied to one of the electric field conductors 222 at both ends of the rung conductor 221.
- an electric field (E) 712 having a polarity with respect to the cylindrical end portion of the phantom 113 is generated from the electric field conductor 222 to which the positive voltage 711 is applied.
- the electric field (E) 712 generated here is generated up to the other end of the phantom 113, and becomes a positive voltage on the left side of the drawing and a negative voltage on the right side of the drawing.
- the electric field (E) 712 induces a current 713 in a portion near the rung conductor 221 on the surface of the phantom 113.
- the direction of the current 713 is opposite to the eddy current (surface current) 703 shown in FIG.
- the current 713 generated on the surface of the phantom 113 by the electric field (E) 712 cancels the eddy current (surface current) 703 flowing on the surface of the phantom 113. That is, the eddy current 703 on the surface of the phantom 113 can be suppressed by the electric field 712 generated by the voltage 711 applied to the electric field conductor 222. Then, by suppressing the eddy current 703, the number that prevents the magnetic field lines 702 from entering is reduced, and the magnetic field lines 702 penetrate deeper into the phantom 113.
- the electric field conductor 222 In order to effectively apply an electric field to the subject 112 by the electric field conductor 222, it is desirable that the area of the electric field conductor 222 is large.
- the electric field conductor 222 having a large area is realized by making the horizontal width w 2 of the electric field conductor 222 larger than the horizontal width w 1 of the rung conductor 221.
- the electric field can be efficiently applied to the subject 112 as the area of the electric field conductor 222 is increased.
- the electric field conductor 222 only needs to have an area capable of generating an electric field that can suppress the eddy current 703.
- the MRI apparatus of the present embodiment is generated from the magnet 101 that generates a static magnetic field to form the static magnetic field, the transmission of a high-frequency signal to the static magnetic field, and the subject placed in the static magnetic field
- the rung conductor 221 and the sheet-like conductor 210 constitute a loop circuit that resonates at the frequency of the high-frequency signal transmitted by the RF coil 103 or the received nuclear magnetic resonance signal.
- the electric field conductor 222 generates a sufficient electric field as necessary to suppress the shielding current flowing on the subject surface by the magnetic field generated by the current flowing through the rung conductor 221.
- the RF coil 103 is a multi-channel antenna including a plurality of the antenna units 220, and the electric field conductor 222 of each antenna unit 220 suppresses magnetic field coupling between the rung conductors 221 of the adjacent antenna units 220. A voltage to be generated is generated in the electric field conductor 222 of the adjacent antenna unit 220.
- the rung conductor 221 and the electric field conductor 222 are electrically connected.
- the interval between the electric field conductors 222 of the adjacent antenna units 220 may be narrower than the interval between the rung conductors 221 of the adjacent antenna units 220. Further, the area of the electric field conductor 222 may be determined so as to generate the electric field.
- the antenna device 200 used as the RF coil 103 includes electric field conductors 222 having a predetermined area at both ends of a rung conductor 221 that is a component of an antenna that transmits and receives electromagnetic waves.
- the antenna device 200 of the present embodiment can reduce the coupling current between adjacent channels, suppress the shielding current generated on the surface of the subject 112, and reduce the RF magnetic field. Good penetration into the specimen.
- the MRI apparatus 100 of the present embodiment can improve the sensitivity of the RF coil 103 in the deep part of the subject.
- the MRI apparatus of the present embodiment can uniformize the spatial distribution of the RF magnetic field by controlling it with multiple channels without any performance degradation due to magnetic field coupling.
- the imaging speed can be increased by using a multi-channel antenna.
- the width w 2 of the field conductors 222 is greater than the width w 1 of the rung conductor 221, an electric field conductor 222 between the adjacent channels Since they are close to each other, electric field coupling that suppresses magnetic field coupling can be generated more effectively.
- the antenna device 200 of the present embodiment since the area S 2 of the field conductors 222, the size capable of generating an electric field to suppress the shielding current, suppressing effectively shielding current, RF magnetic field Can penetrate deeply into the subject 112.
- An electric field is also generated at the end of the rung conductor of the conventional TEM antenna.
- the width of the conductor does not change between the center portion and the end portion of the rung conductor. Therefore, even when the same voltage as that of the antenna device 200 of the present embodiment is applied, the effective area of the end portion of the rung conductor is small, so that an electric field cannot be effectively applied to the subject.
- some birdcage type antennas have ring conductors connected to both ends of the rung conductor, and the ring conductor part is wider than the rung conductor part.
- the birdcage type ring conductor is connected so as to form a ring around the cylindrical shape, and the voltage does not necessarily increase at the end of the rung conductor. Therefore, the magnitude
- connection terminal 224 is provided for one channel, and the voltage supplied via the connection terminal 224 suppresses the function of the antenna and the shielding current by the electric field conductor 222. And realize.
- the antenna device 200 can configure the RF coil 103 that can arrange a plurality of channels with a simple configuration and has good penetration of the RF magnetic field into the human body. That is, according to the present embodiment, a high-performance RF coil 103 can be realized with a simple configuration.
- the capacitance of the capacitor formed by the electric field conductor 222 and the sheet-like conductor 210 can be changed by changing the area of the electric field conductor 222 or by inserting a dielectric between the electric field conductor 222 and the sheet-like conductor 210. More specifically, the area of the electric field conductor 222 can be increased or decreased by cutting the end portion of the electric field conductor 222 or adding a copper plate to the end portion. Further, by placing a Teflon (registered trademark) plate or the like as a dielectric between the sheet-like conductor 210 and the electric field conductor 222, the capacitance of the capacitor can be increased.
- connection terminal 224 that is the connection point between the end of the coaxial cable 230 and the antenna device 200 is installed near one end of the rung conductor 221 as shown in FIG.
- the installation position of the connection terminal 224 is not limited to this.
- the central portion of the rung conductor 221 may be used.
- a gap is provided at the center of the rung conductor 221 and the coaxial cable 230 is connected to both ends thereof.
- the coaxial cable 230 may be connected to both the end portion of the electric field conductor 222 and the sheet-like conductor 210.
- the antenna device 200 is used as the RF coil 103 that is used for both transmission and reception.
- the antenna device 200 may be used as an RF coil for transmission only or reception only.
- the RF coil 103 (antenna device 200) needs a function called detuning. This is a function of shifting the resonance frequency in order to prevent interference with other antenna devices 200.
- the antenna device 200 is provided with a gap 241 between the rung conductor 221 and one electric field conductor 222, for example, as shown in FIG.
- the gaps 241 are connected by a diode (not shown).
- the antenna device 200 performs a normal operation as an antenna when a current flows through the diode and the rung conductor 221 and the electric field conductor 222 are connected.
- the antenna device 200 resonates with the capacitor component formed between the electric field conductor 222 and the sheet-like conductor 210 on the side where the connection is cut off. Therefore, the resonance frequency is shifted and detuned.
- the coupling is reduced by arranging the electric field conductors 222 between adjacent channels close to each other, but the present invention is not limited to this.
- a capacitor having a capacity of several pF may be connected between two adjacent electric field conductors 222 to suppress coupling.
- a method of cutting off interference between two antennas by connecting the conductors of two adjacent antennas with a capacitor is known as a prior art.
- the antenna unit 220 has been described by taking as an example the case where one rung conductor 221 is provided for the pair of electric field conductors 222, but the number of rung conductors 221 is not limited thereto. .
- the antenna unit 220 may include a plurality of rung conductors 221.
- FIG. 7 illustrates an example in which two antenna portions 220 configured by connecting three rung conductors 221 as a set to a pair of electric field conductors 222 are arranged in a plane.
- the frequency adjustment capacitors 223 are provided at both ends of one rung conductor 221.
- two capacitors 223 are shown for one channel, but a total of six capacitors 223 can be provided at both ends of the three rung conductors 221, respectively.
- the connection terminal 224 is not illustrated. However, one connection terminal 224 is arranged for each channel (antenna unit 220).
- the number of rung conductors 221 connecting the 222 electric field conductors is not limited to this.
- the two-channel antenna device 200 including two antenna units 220 has been described as an example, but the number of antenna units 220 (channels) is not limited thereto. Regardless of the number of antenna portions 220 (channels), as in this embodiment, the rung conductors 221 of each antenna unit 220 are arranged so as to be substantially parallel to the rung conductors 221 of adjacent antenna units. The electric field conductor 222 of 220 is arranged so as to be close to the electric field conductor 222 of the adjacent antenna unit.
- Second Embodiment a second embodiment to which the present invention is applied will be described.
- the rung conductor 221 and the electric field conductor 222 are electrically connected.
- the rung conductor 221 and the electric field conductor 222 are not electrically connected.
- the MRI apparatus 100 of the present embodiment has basically the same configuration as that of the first embodiment. However, as described above, the configuration of the antenna device used as the RF coil 103 is different. Hereinafter, the present embodiment will be described focusing on an antenna device different from the first embodiment.
- FIG. 8 is a diagram for explaining the antenna device 300 of the second embodiment.
- the antenna device 300 of the present embodiment includes a sheet-like conductor 310 and an antenna unit 320.
- the antenna unit 320 includes a rung conductor 321, an electric field conductor 322, a frequency adjustment capacitor 323, and a connection terminal 324.
- Each has the same function as that of the same name in the first embodiment. Further, the configuration and arrangement of each part are basically the same as those in the first embodiment.
- the antenna unit 320 of this embodiment includes a rung conductor 321 and two electric field conductors 322, respectively. That is, in the antenna unit 320 of the present embodiment, as shown in FIG. 8, the rung conductor 321 and the electric field conductor 322 are not electrically connected.
- the rung conductor 321 and the electric field conductor 322 are arranged on the sheet conductor 310 while maintaining a predetermined distance from the sheet conductor 310. Further, the lateral width of the electric field conductor 322 is made larger than the lateral width of the rung conductor 321. Further, it is desirable that the area of the electric field conductor 322 is larger than the area of the rung conductor 321.
- the rung conductors 321 of adjacent antenna units 320 are arranged to be substantially parallel to each other. In addition, the electric field conductors 322 of adjacent antenna portions (channels) are arranged close enough to suppress coupling. Each arrangement is realized by a conductor support structure (not shown) as in the first embodiment.
- the frequency adjustment capacitor 323 is connected to both ends of the rung conductor 321 and connected to the sheet-like conductor 310.
- the rung conductor 321, the frequency adjustment capacitor 323, and the sheet-like conductor 310 form a loop-like circuit.
- the circuit formed by the two frequency adjustment capacitors 323, the rung conductor 321 and the sheet-like conductor 310 functions as a one-channel antenna.
- the frequency adjustment capacitor 323 is adjusted so that the antenna device 300 resonates at a frequency used in the MRI apparatus 100.
- the antenna device 300 of the present embodiment functions as the RF coil 103 of the MRI apparatus 100.
- FIG. 8 illustrates a two-channel antenna device 300 including two antenna units 320 sharing one sheet-like conductor 310.
- connection terminals 324 are arranged in each antenna unit 320 by the total number of the rung conductors 221 and the electric field conductors 222.
- one rung conductor 221 and two electric field conductors 222 are arranged.
- three connection terminals 324 (324a, 324b, 324c) are arranged in one antenna unit 320.
- one connection terminal 324a is provided on one end of the rung conductor 321 and the sheet-like conductor 310 immediately below. That is, the central conductor of the coaxial cable 330a that connects the main body of the MRI apparatus 100 and the antenna device 300 is connected to the rung conductor 321 side of the connection terminal 324a, and the outer conductor of the coaxial cable 330a is connected to the sheet-like conductor 310 side.
- the remaining two connection terminals 324b and 324c are provided on the two electric field conductors 322 and the sheet-like conductor 210, respectively, and are connected to the MRI apparatus 100 by coaxial cables 330b and 330c, respectively.
- the coaxial cables 330a, 330b, and 330c connected to the connection terminals 324a, 324b, and 324c may be gathered along the sheet-like conductor 310.
- the coaxial cable 330c connected to the connection terminal 324c is wired along the sheet-like conductor 310 up to the connection terminal 324a and wired together with the coaxial cable 330a connected to the connection terminal 324a. Is illustrated. With this configuration, wiring to the antenna device 300 is facilitated.
- phase of the voltage applied to each of the three connection terminals 324a, 324b, and 324c when the antenna device 300 of the present embodiment is used as the transmission antenna of the RF coil 103 will be described. Also in this embodiment, as in the first embodiment, an electric field having a polarity is generated in the electric field conductor 322, thereby canceling the shielding current on the surface of the subject 112 by the reverse current flowing on the surface of the subject 112, The penetration of the magnetic field by the current flowing through the rung conductor 321 is improved.
- connection between the connection terminal 324a of the rung conductor 221 and the electric field conductor 222 connected to the side on which the connection terminal 324a of the rung conductor 221 is disposed Power is supplied to the terminal (324b in the example of FIG. 8) in the same phase.
- the connection terminal (324c in the example of FIG. 8) of the electric field conductor 222 connected to the side where the connection terminal 324a of the rung conductor 221 is not disposed is 180 degrees from the phase fed to the connection terminals 324a and 324b. It is desirable to supply power with a different phase (opposite phase).
- the antenna device 300 of the present embodiment also generates an electric field that causes a current to flow in a direction that cancels the shielding current, as in the first embodiment.
- Fig. 9 shows a specific example of the voltage applied to each feeding point (connection terminal 324).
- the horizontal axis represents time and the vertical axis represents voltage.
- the connection terminal 324a and 324b have a solid line sine waveform voltage 801
- the connection terminal 324c has a dotted line sine waveform 180 degrees out of phase with the voltage applied to the connection terminals 324a and 324b.
- a voltage 802 is given.
- connection terminal 324c There are the following methods for changing the waveform of the voltage supplied to the connection terminal 324c by 180 degrees from the waveform of the voltage supplied to the other two connection terminals 324a and 324b.
- the output from one power amplifier is divided into three outputs with the same phase. And it supplies to connection terminal 324a, 324b, 324c, respectively.
- the lengths of the coaxial cables 330a, 330b, and 330c used for feeding are the same as those of 330a and 330b, and 330c is lengthened or shortened by a half wavelength of the frequency used. With this configuration, the phase entering the connection terminal 324c can be shifted by 180 degrees.
- the lateral width w 2 of the electric field conductor 322 is increased by the lateral width w 1 of the rung conductor 321;
- the electric field conductors 222 of adjacent antenna units 220 are arranged so that the distance between them is narrower than the distance between the rung conductors 221.
- the area of the electric field conductor 322 is set to a size that can generate an electric field that can suppress the eddy current generated on the surface of the subject 112.
- the voltage generated in the frequency adjusting capacitor 223 is transmitted to the electric field conductor 222, and the voltage is applied thereto. Therefore, the voltage applied to the electric field conductor 222 is limited, and is adjusted by the area of the electric field conductor 222 in order to generate a necessary electric field.
- the voltage applied to the electric field conductor 322 can be controlled independently of the current applied to the rung conductor 321. Therefore, the electric field to be generated can be adjusted by adjusting the magnitude of the voltage. For this reason, the freedom degree of the area of the electric field conductor 322 is large compared with 1st embodiment.
- the MRI apparatus includes a magnet 101 that generates a static magnetic field to form a static magnetic field, a high-frequency signal transmitted to the static magnetic field, and a subject 112 placed in the static magnetic field.
- An RF coil 103 that performs at least one of reception of the generated nuclear magnetic resonance signal, and the RF coil 103 includes a sheet-like conductor 310 and an antenna part 320, and the antenna part 320 has the sheet-like shape.
- a rung conductor 321 disposed at a predetermined distance from the conductor 310, and two electric field conductors 322 disposed at both ends of the rung conductor 321 at a predetermined distance from the sheet-like conductor 310.
- the rung conductor 321 and the sheet-like conductor 310 constitute a loop circuit that resonates at the frequency of the high-frequency signal transmitted by the RF coil 103 or the received nuclear magnetic resonance signal.
- the electric field conductor 322 generates an electric field that suppresses a shielding current flowing on the surface of the subject 112 by a magnetic field generated by a current flowing in the rung conductor 321.
- the RF coil 103 is a multi-channel antenna including a plurality of the antenna units 320, and the electric field conductor 322 of each antenna unit 320 suppresses magnetic field coupling between the rung conductors 321 of the adjacent antenna units 320.
- a voltage to be generated is generated in the electric field conductor 322 of the adjacent antenna unit 320.
- the rung conductor 321 and the electric field conductor 322 are electrically disconnected, and a voltage is applied to the electric field conductor 322 independently of the rung conductor 321, and the voltage The size to be generated.
- the interval between the electric field conductors 322 of the adjacent antenna units 320 may be narrower than the interval between the rung conductors 321 of the adjacent antenna units 320.
- the electric field conductor 222 having a predetermined area is provided at both ends of the rung conductor 221 that is a component of the antenna that transmits and receives electromagnetic waves.
- the antenna device 200 of the present embodiment can reduce the coupling current between adjacent channels, suppress the shielding current generated on the surface of the subject 112, and reduce the RF magnetic field. Good penetration into the specimen.
- the MRI apparatus 100 of the present embodiment can improve the sensitivity of the RF coil 103 in the deep part of the subject.
- the MRI apparatus of this embodiment makes the spatial distribution of the RF magnetic field uniform by controlling it with multiple channels without any performance degradation due to magnetic field coupling. be able to.
- the rung conductor 321 and the electric field conductor 322 are not electrically connected. Therefore, the voltage applied to the electric field conductor 322 can be controlled independently of the rung conductor 221 that transmits and receives electromagnetic waves, and transmission and reception of electromagnetic waves and suppression of shielding current can be optimally controlled, respectively. it can.
- the size of the electric field conductor 322 is not limited by the generation of an electric field, and the electric field conductor 322 can be formed with a higher degree of freedom.
- connection terminal 324a with respect to the rung conductor 321 does not matter. However, when the position of the connection terminal 324a is different from that in FIG. 8, the relationship of the phase of the voltage waveform applied to each terminal is not a relationship in which the simple 180-degree phase is reversed as shown in FIG. Further, either one of transmission and reception may be realized. In this case, detuning is realized by cutting a part of the rung conductor 321 constituting the loop circuit and connecting it with a diode. In order to reduce coupling, a capacitor having a capacity of several pF may be connected between two adjacent rung conductors 321. Further, the pair of electric field conductors 322 may be configured to include a plurality of rung conductors 321 (not shown) in which both end portions are connected between adjacent rung conductors 321.
- connection terminal is provided for each rung conductor 321 and each of the pair of electric field conductors 322.
- the two-channel antenna device 300 including two antenna units 320 has been described as an example, but the number of channels is not limited thereto.
- the sheet-like conductor is formed in a cylindrical shape or a cylindrical shape of an elliptical cylinder, and a plurality of antenna portions each constituting one channel are arranged inside the sheet-like conductor.
- the MRI apparatus 100 of the present embodiment has basically the same configuration as that of the first embodiment. However, the configuration of the antenna device used as the RF coil 103 is different as described above. As shown in FIG. 10, the antenna device 400 of this embodiment has a cylindrical shape as a whole. Therefore, the MRI apparatus 100 of the present embodiment is of a horizontal magnetic field type having a cylindrical bore.
- the present embodiment will be described with reference to FIGS. 10 and 11, focusing on the antenna device, which is different from the first embodiment.
- FIG. 10 is an external view of the antenna device 400 of the present embodiment.
- four antenna parts 420 are provided in the cylindrical sheet-like conductor 410 on the upper right, lower right, lower left, and upper left when viewed from the opening on one side of the cylinder, and configured as a four-channel antenna. This will be described as an example.
- the antenna device 400 of this embodiment also includes a sheet-like conductor 410 and an antenna unit 420, as in the first embodiment.
- the antenna unit 420 includes a rung conductor 421, an electric field conductor 422, a frequency adjustment capacitor, and a connection terminal.
- the frequency adjustment capacitor and the connection terminal are not shown for simplicity of explanation.
- FIG. 11 is a diagram in which the rung conductor 421 and the electric field conductor 422 are extracted from the antenna unit 420 of the present embodiment.
- the sheet-like conductor 410 of the present embodiment is obtained by deforming the sheet-like conductor that was flat in the first and second embodiments into a cylindrical shape. Inside this cylindrical sheet-like conductor 410, four sets of four antenna portions 420 are arranged. Also in the present embodiment, one antenna unit 420 constitutes one channel.
- each antenna unit 420 includes a pair of electric field conductors 422 and a plurality of rung conductors 421.
- Each rung conductor 421 is disposed in parallel between the pair of electric field conductors 422.
- FIG. 11 illustrates a case where there are ten rung conductors 421.
- a magnetic field can be generated in a wider range in the circumferential direction inside the cylinder, and a wide antenna sensitivity region can be realized.
- the lateral width w 2 of the electric field conductor 422 is made larger than the width w 1 of one rung conductor 421 in the circumferential direction of the antenna device 400.
- the area of the electric field conductor 422 is increased as much as possible to generate an electric field that flows a current that cancels the shielding current.
- the rung conductor 421 and the electric field conductor 422 are arranged at a predetermined distance from the sheet-like conductor 410 as in the first embodiment.
- the sheet-like conductor 410 is cylindrical
- the sheet-like conductor 410 is disposed on a virtual cylinder coaxial with the sheet-like conductor 410.
- the sheet-like conductor 410 has an elliptic cylinder shape
- the sheet-like conductor 410 is disposed on a virtual elliptic cylinder that is coaxial with the sheet-like conductor 410.
- the placement on the virtual cylinder and the virtual elliptic cylinder is realized by a conductor support structure (not shown).
- the sheet-like conductor 410 may be disposed on a virtual elliptic cylinder having a different aspect ratio from that of the sheet-like conductor 410 or on a virtual curved surface having another shape.
- a virtual elliptic cylinder 411 or the virtual curved surface where the distance from the sheet-like conductor 410 becomes shorter as it goes in the major axis radial direction of the ellipse of the section of the sheet-like conductor 410 May be arranged.
- the antenna device 400 that can be photographed with a human being installed inside can be configured. Further, when the diameter of the cylindrical sheet-like conductor 410 is about 270 mm, the antenna device 400 that can be photographed with the human head placed inside can be configured.
- the irradiation RF given to the subject 112 can be optimized by changing the amplitude and phase of the RF waveform transmitted to each channel. Can do.
- This method is called RF shimming or parallel RF irradiation.
- the MRI apparatus includes a magnet 101 that generates a static magnetic field to form a static magnetic field, a high-frequency signal transmitted to the static magnetic field, and a subject 112 placed in the static magnetic field.
- An RF coil 103 that performs at least one of reception of generated nuclear magnetic resonance signals, and the RF coil 103 includes a sheet-like conductor 410 and an antenna portion 420, and the antenna portion 420 is the sheet-like shape.
- a rung conductor 421 disposed at a predetermined distance from the conductor 410, and two electric field conductors 422 disposed at both ends of the rung conductor 421 at a predetermined distance from the sheet-like conductor 410.
- the rung conductor 421 and the sheet-like conductor 410 constitute a loop circuit that resonates at the frequency of the high-frequency signal transmitted by the RF coil 103 or the received nuclear magnetic resonance signal.
- the electric field conductor 422 generates an electric field that suppresses a shielding current flowing on the surface of the subject 112 by a magnetic field generated by a current flowing through the rung conductor 421.
- the RF coil 103 is a multi-channel antenna including a plurality of the antenna units 420, and the electric field conductor 422 of each antenna unit 420 suppresses magnetic field coupling between the rung conductors 421 of the adjacent antenna units 420.
- a voltage to be generated is generated in the electric field conductor 422 of the adjacent antenna unit 420.
- It further includes two frequency adjustment capacitors that connect both end portions of the rung conductor 421 and the sheet-like conductor 410 substantially directly below the rung conductor 421, and the value of the frequency adjustment capacitor is determined by the loop circuit as the high-frequency signal or the It is adjusted to resonate at the frequency of the nuclear magnetic resonance signal.
- the antenna unit 420 includes a plurality of antenna units 420.
- Each antenna unit 420 includes a connection terminal for connecting the RF coil 103 to the MRI apparatus 100.
- the connection terminal is connected to the rung conductor 421 and the sheet-like conductor 410.
- the sheet-like conductor 410 has a cylindrical shape, and the phase and amplitude of the voltage supplied to the antenna units 420 via the connection terminals are optimized by the high-frequency signal transmitted from the RF coil 103. To be controlled independently.
- the sheet-like conductor 410 may be an elliptic cylinder. Further, the antenna unit 420 may be arranged on a virtual curved surface such that the distance from the sheet-like conductor becomes shorter as it goes in the major axis radial direction of the cross section of the elliptic cylinder. In addition, the electric field conductor 422 may be wider than the rung conductor 421 in the short axis direction of the rung conductor 421.
- the antenna device 400 of this embodiment includes electric field conductors 422 having a predetermined area at both ends of a rung conductor 421 that is a component of an antenna that transmits and receives electromagnetic waves.
- the antenna device 400 of the present embodiment can reduce the coupling current between adjacent channels, suppress the shielding current generated on the surface of the subject 112, and reduce the RF magnetic field. Good penetration into the specimen.
- this antenna device 200 As the RF coil 103, the sensitivity of the RF coil 103 in the deep part of the subject can be improved in the MRI apparatus 100 of the present embodiment.
- the MRI apparatus of the present embodiment makes the spatial distribution of the RF magnetic field uniform by controlling it with multiple channels without any performance degradation due to magnetic field coupling. be able to.
- the antenna device 400 of the present embodiment when four antenna portions 420 having a plurality of rung conductors 421 are arranged as a four-channel antenna, the size and shape are In the MRI apparatus 100 of 3 Tesla or more, it is suitable as a transmission / reception antenna for the trunk.
- Each electric field conductor 422 may be provided with a cut (slit) 441 as shown in FIG.
- a cut (slit) 441 By inserting the slit 441, eddy current generated on the surface of the electric field conductor 422 due to the magnetic field generated by the gradient coil 102 can be reduced. Thereby, it is possible to reduce the heat generation and the adverse effect on the image due to the eddy current generated on the surface of the electric field conductor 422.
- FIG. 11 illustrates a case where four slits 441 are provided in one electric field conductor 422 and the electric field conductor 422 is divided into five partial conductors.
- Each partial conductor is connected to an adjacent partial conductor by a slit connection capacitor at both ends of the slit 441.
- As the slit connection capacitor one having several hundred to several thousand pF is used.
- the slit connection capacitor is electrically disconnected in the alternating magnetic field of several kHz used in the gradient magnetic field, and is adjusted to act as one wide electric field conductor 422 in the alternating magnetic field of several tens of MHz used as the RF coil 103.
- the antenna device 400 of the present embodiment may include a bridge conductor 442 that connects between one end of the rung conductor 421 between adjacent channels (antenna section 420). Both ends of the bridge conductor 442 and the end of the rung conductor 421 of the adjacent channel (antenna unit 420) are connected by a coupling reduction capacitor.
- the coupling between channels is further reduced by configuring in this way.
- the bridge conductor 442 is used when the coupling between the channels is large and a slight coupling remains even though the electric field conductor 422 is provided. For example, by using a coupling reduction capacitor of several pF for the connection between the bridge conductor 442 and the rung conductor 421, the coupling between channels can be reduced to about ⁇ 15 dB or less in terms of the S parameter.
- the voltage applied to the electric field conductor 422 may be as high as several kV.
- processing such as rounding corners of the electric field conductor 422 or corona doping coating on the end portions may be performed.
- an air layer may be provided at the end of the electric field conductor 422 in order to prevent creeping discharge. This is intended to reduce the contact surface between the conductor support structure and the electric field conductor 422.
- the configuration in which the electric field conductor and the rung conductor are electrically connected is described as an example, but the present invention is not limited to this.
- the electric field conductor and the rung conductor may be electrically disconnected.
- a connection terminal is provided for each rung conductor and each of the pair of electric field conductors, and the coaxial cable 430 is connected.
- the capacitance of the capacitor by the electric field conductor 422 and the sheet-like conductor 410 may be changed by the same method as in the first embodiment.
- the position of the connection terminal with respect to the rung conductor 421 is not limited. Further, either one of transmission and reception may be realized.
- a gap is provided between the rung conductor 421 and the electric field conductor 422, and the gap is connected with a diode to realize detuning.
- the number of rung conductors 421 between the pair of electric field conductors 422 may be one.
- the configuration in which the slit 441 is provided in the electric field conductor 422 and the configuration in which the bridge conductor 442 is disposed between the adjacent antenna portions 420 (channels) and connected by the coupling reduction capacitor can be applied to other embodiments. is there.
- the four-channel antenna device 400 including the four antenna units 420 has been described as an example, but the number of channels is not limited thereto.
- the antenna device used as the RF coil of the MRI apparatus of the present embodiment makes it possible to adjust the rung conductor to a desired length.
- the MRI apparatus 100 of the present embodiment has basically the same configuration as that of the first embodiment. However, as described above, the configuration of the antenna device used for the RF coil 103 is different. Hereinafter, the present embodiment will be described focusing on the antenna device, which is different from the first embodiment.
- FIG. 13 is an external view of the antenna device 500 of the present embodiment.
- the antenna device 500 of this embodiment also includes a sheet-like conductor 510 and an antenna unit 520, as in the first embodiment.
- the antenna unit 520 includes a rung conductor 521, an electric field conductor 522, a frequency adjustment capacitor, and a connection terminal.
- the frequency adjustment capacitor and the connection terminal are not shown.
- Each configuration has the same function as the configuration of the same name in the first embodiment.
- the frequency adjustment capacitors are connected to both ends of the rung conductor 521 and are connected to the sheet-like conductor 510, respectively.
- the rung conductor 521, the frequency adjustment capacitor, and the sheet-like conductor 510 form a loop-like circuit.
- the circuit formed by the two frequency adjustment capacitors, the rung conductor 521, and the sheet-like conductor 510 functions as a one-channel antenna.
- One connection terminal is provided for each channel.
- the frequency adjustment capacitor is adjusted so that the antenna device 500 resonates at a frequency used in the MRI apparatus 100.
- the antenna device 500 of the present embodiment functions as the RF coil 103 of the MRI apparatus 100.
- FIG. 13 shows, as an example, a 4-channel antenna device 500 including four antenna units 520.
- the sheet-like conductor 510 exemplifies a case where a part of the cylindrical side surface is cut off.
- the rung conductor 521 of this embodiment is connected to a pair of electric field conductors 522 at both ends, respectively, as in the first embodiment.
- the rung conductor 521 of the present embodiment is made of an elongated flat plate, a tape shape, a rod shape, or a cylindrical conductor, as in the first embodiment.
- a folded portion 541 is provided at a part thereof.
- FIG. 13 illustrates a rung conductor 521 having a folded portion 541 that is rotated once so that a tape-shaped conductor forms a ring.
- the rung conductor 521 When the rung conductor 521 is traced from the end, the rung conductor 521 that has progressed in one direction is folded once at the folded portion 541 and then traveled in the opposite direction, and is folded again and proceeds in the same direction as the first, reaching the other end.
- a portion 542 of the folded portion 541 that folds once and advances backward passes through a region closer to the sheet-like conductor 510 than the other portions.
- the rung conductor 521 of the present embodiment is arranged so that the distance from the sheet-like conductor 510 is kept constant at the portion 542 that advances in the opposite direction and the portion parallel to the other sheet-like conductor 510. Further, the sheet-like conductor 510 is arranged so as not to touch it.
- the electric field conductor 522 is arranged at a distance similar to that of the sheet-like conductor 510 and the portion 542 that runs in the opposite direction of the rung conductor 521. The arrangement is realized by a conductor support structure (not shown) as in the first embodiment.
- the shape of the folded portion 541 is also referred to as a spiral shape. Moreover, since it looks like a ring when viewed from the side, it can also be called a loop shape.
- the effective length of the rung conductor 521 is increased by making the rung conductor 521 into a shape having the folded portion 541 shown in FIG. Therefore, in the present embodiment, the voltage generated at both end portions of the rung conductor 521 is higher than that of the rung conductor 521 that does not have the folded portion 541.
- the effective length of the rung conductor 521 of the present embodiment can be adjusted by changing the length of the folded portion 541.
- the capacity of the frequency adjustment capacitor required for resonance can be reduced.
- a frequency adjustment capacitor is not necessary.
- the frequency adjustment capacitor is not required, it is not necessary to solder the frequency adjustment capacitor to the sheet-like conductor 510. Therefore, the antenna unit 520 can be freely moved on the sheet-like conductor 510, and the degree of design freedom is increased. Increase.
- the number of turns (the number of rotations of the spiral) of the turn-back portion 541 is one, but the number of turns is not limited.
- a spiral-shaped rung conductor 521 that rotates a plurality of times such as twice or three times may be configured.
- the other structural features of the rung conductor 521 and the electric field conductor 522 are the same as those of the first embodiment. That is, the lateral width w 2 of the electric field conductor 522 is made larger than the lateral width w 1 of the rung conductor 521.
- the area of the electric field conductor 522 is set to a size that can generate an electric field that suppresses the shielding current. For example, it is desirable to make it larger than the area of the rung conductor 521.
- the rung conductors 521 of the adjacent antenna units 520 are basically arranged substantially parallel to each other. Further, the electric field conductors 522 of adjacent antenna portions (channels) are arranged close enough to suppress coupling.
- the MRI apparatus includes a magnet 101 that generates a static magnetic field to form a static magnetic field, a high-frequency signal transmitted to the static magnetic field, and a subject 112 placed in the static magnetic field.
- An RF coil 103 that performs at least one of reception of the generated nuclear magnetic resonance signal, and the RF coil 103 includes a sheet-like conductor 510 and an antenna part 520, and the antenna part 520 is the sheet-like shape.
- a rung conductor 521 disposed at a predetermined distance from the conductor 510, and two electric field conductors 522 disposed at both ends of the rung conductor 521 at a predetermined distance from the sheet-like conductor 510.
- the rung conductor 521 and the sheet-like conductor 510 constitute a loop circuit that resonates at the frequency of the high-frequency signal transmitted by the RF coil 103 or the received nuclear magnetic resonance signal.
- the electric field conductor 522 generates an electric field that suppresses a shielding current flowing on the surface of the subject 112 by a magnetic field generated by a current flowing in the rung conductor 521.
- the RF coil 103 is a multi-channel antenna including a plurality of the antenna units 520, and the electric field conductor 522 of each antenna unit 520 suppresses magnetic field coupling between the rung conductors 521 of the adjacent antenna units 520.
- a voltage to be generated is generated in the electric field conductor 522 of the adjacent antenna unit 520.
- It further comprises two frequency adjustment capacitors that connect both end portions of the rung conductor 521 and the sheet-like conductor 510 substantially directly below the rung conductor 521, and the value of the frequency adjustment capacitor is determined by the loop circuit as the high-frequency signal or the It is adjusted to resonate at the frequency of the nuclear magnetic resonance signal.
- the rung conductor 521 has a shape capable of adjusting the length of the rung conductor 521, and the length of the rung conductor 521 is such that the loop circuit resonates at the frequency of the high-frequency signal or the nuclear magnetic resonance signal. Adjusted.
- the rung conductor 521 may have a spiral shape.
- the rung conductor 521 and the electric field conductor 522 may be electrically connected. Further, the interval between the electric field conductors 522 of the adjacent antenna units 520 may be narrower than the interval between the rung conductors 521 of the adjacent antenna units 520. Further, the area of the electric field conductor 522 may be determined so as to generate the electric field.
- the antenna device 500 used as the RF coil 103 includes electric field conductors 522 having a predetermined area at both ends of a rung conductor 521 that is a component of an antenna that transmits and receives electromagnetic waves.
- the antenna device 500 of the present embodiment can reduce the coupling current between adjacent channels, suppress the shielding current generated on the surface of the subject 112, and reduce the RF magnetic field. Good penetration into the specimen.
- the MRI apparatus 100 of the present embodiment can improve the sensitivity of the RF coil 103 in the deep part of the subject. Further, by using this antenna device 500 as the RF coil 103, the MRI apparatus of the present embodiment makes the spatial distribution of the RF magnetic field uniform by controlling it with multiple channels without any performance degradation due to magnetic field coupling. be able to.
- the width w 2 of the field conductors 522 is greater than the width w 1 of the rung conductor 521, an electric field conductor 522 between the adjacent channels Since they are close to each other, electric field coupling that suppresses magnetic field coupling can be generated more effectively.
- the antenna device 500 of the present embodiment since the area S 2 of the field conductors 222, the size capable of generating an electric field to suppress the shielding current, suppressing effectively shielding current, RF magnetic field Can penetrate deeply into the subject 112.
- connection terminal is provided for one channel, and the voltage supplied through the connection terminal serves as an antenna and suppresses the shielding current by the electric field conductor 522. Realize.
- the length of the rung conductor 521 can be increased.
- capacitance of a frequency adjustment capacitor can be reduced and said effect can be acquired with a simple structure.
- not only the length of the rung conductor 521 can be increased, but also the desired length can be adjusted. Thereby, a frequency adjustment capacitor can be made unnecessary, and an antenna device having the same effect can be realized with a simpler configuration.
- the antenna device 500 can configure the RF coil 103 that can arrange a plurality of channels with a simple configuration and has good penetration of the RF magnetic field into the human body. That is, according to the present embodiment, a high-performance antenna device can be realized with a simple configuration.
- the antenna device 500 of the present embodiment is useful when it is desired to increase the voltage applied to the electric field conductor 522 and when it is not desired to provide a frequency adjusting capacitor for connecting the sheet-like conductor 510 and the rung conductor 521.
- the method for extending the effective length of the rung conductor 521 is not limited to providing the folded portion 541.
- the conductor constituting the rung conductor 521 may be processed as shown in FIG.
- FIG. 14 is an external view of an antenna device 600 that is a modification of the antenna device 500 of the present embodiment.
- the antenna device 600 of this modification also includes a sheet-like conductor 610 and an antenna unit 620.
- FIG. 14 illustrates a case where three antenna units 620 are arranged inside a cylindrical sheet-like conductor 610 to constitute a three-channel antenna device.
- FIG. 15 shows the antenna unit 620 extracted.
- the antenna unit 620 includes a pair of electric field conductors 622, one or more rung conductors 621 connecting the electric field conductors 622, a frequency adjustment capacitor 623, and a connection terminal 624.
- a coaxial cable 630 that connects to the main body of the MRI apparatus 100 is connected to the connection terminal 624.
- Each unit has the same function as the configuration of the same name in the other embodiments. The arrangement and configuration are basically the same.
- the rung conductor 621 of the present modification is composed of a flat plate or tape-shaped conductor.
- the tape-shaped conductor includes cuts 641 that are alternately formed from the left and right. By providing the notches 641 from the left and right, the effective length of the rung conductor 621 is increased, and a current flows in a zigzag manner on the rung conductor 621.
- the rung conductor 621 of this modification has a meandering shape due to the notches 641.
- the inductance of the rung conductor 621 is increased, and the resonance frequency of the antenna device 600 having the rung conductor 621 as a component can be lowered.
- this modification is useful when it is desired to increase the inductance of the rung conductor 621.
- the antenna device 600 of the present modification includes a thin cylindrical structure 651 as a casing portion that supports the rung conductor 621 and the electric field conductor 622 connected to both ends thereof.
- This thin cylindrical structure 651 is made of a material such as FRP.
- the thin cylindrical structure 651 is connected to and supported by a support member 652 disposed on the sheet-like conductor 610.
- the support member 652 is made of a material such as FRP and has a structure like a wall or a beam.
- the support member 652 is disposed avoiding conductor portions such as the rung conductor 621 and the electric field conductor 622. The reason for disposing the conductor portion is to avoid creeping discharge due to high voltage.
- coaxial cable 630 used for at least one of transmission and reception is disposed between the thin cylindrical structure 651 and the sheet-like conductor 610.
- the thin structure 651 for supporting the rung conductor 621 and the electric field conductor 622 connected to both ends thereof and the support member 652 can be applied to other embodiments as a conductor support structure.
- the shape of the rung conductor in the present embodiment is not only a linear shape, but also a spiral shape, a meandering shape, etc., and functions as an antenna by forming a loop circuit with the sheet-like conductor 510 and the frequency adjustment capacitor. As long as it is done, various shapes are possible.
- the capacitance of the capacitor by the electric field conductor 522 and the sheet-like conductor 510 may be changed by the same method as in the first embodiment.
- the position of the connection terminal with respect to the rung conductor 521 is not limited. Further, either one of transmission and reception may be realized.
- a gap is provided between the rung conductor 521 and one of the electric field conductors 522, and the gap is connected with a diode to realize detuning.
- a capacitor having a capacity of several pF may be connected between two adjacent electric field conductors 522.
- a plurality of rung conductors 321 may be provided for the pair of electric field conductors 522.
- the antenna device 500 or 600 has been described by taking a four-channel antenna including four antenna units 520 or 620 as an example, but the number of antenna units (channels) is limited to this. Absent.
- the antenna device has a plurality of channels.
- a one-channel antenna device including a sheet-like conductor and an antenna unit may be used.
- the antenna device of each of the above embodiments by providing an electric field conductor, the permeability of the magnetic field to the subject An antenna device with high height can be obtained.
- an RF coil that improves the penetration of the RF magnetic field into the subject can be realized in an environment where the spatial distribution of the RF magnetic field is uniform.
- the antenna device of each of the above embodiments can be applied not only as an RF coil of an MRI apparatus but also to any device using an electromagnetic wave having a frequency of several MHz to several GHz.
- MRI apparatus 101 magnet, 102 gradient coil, 103 RF coil, 104 transmitter / receiver, 105 data processor, 106 transmit / receive cable, 107 gradient magnetic field control cable, 108 display device, 109 gradient magnetic field power supply, 111 bed, 112 subject , 113 phantom, 200 antenna device, 210 sheet conductor, 220 antenna section, 221 rung conductor, 222 electric field conductor, 223 frequency adjustment capacitor, 224 connection terminal, 230 coaxial cable, 241 gap, 300 antenna device, 310 sheet conductor, 320 antenna section, 321 rung conductor, 322 electric field conductor, 323 frequency adjustment capacitor, 324 connection terminal, 324a connection terminal, 324b connection terminal, 324c connection terminal, 330a coaxial cable, 330b coaxial cable, 330c coaxial cable, 400 antenna device, 410 Sheet conductor, 411 virtual elliptic cylinder, 420 antenna section, 421 runs Conductor, 422 electric field conductor, 430 coaxial cable, 441 slit,
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Abstract
Description
以下、本発明を適用する第一の実施形態について説明する。
アンテナ部220(チャンネル)数がいくつであっても、本実施形態同様、各アンテナ部220のラング導体221は、隣り合うアンテナ部のラング導体221と略平行になるように配置し、各アンテナ部220の電界導体222は、隣り合うアンテナ部の電界導体222と近接するよう配置する。
次に、本発明を適用する第二の実施形態について説明する。第一の実施形態のRFコイルでは、ラング導体221と電界導体222とは、電気的に接続される。一方、本実施形態では、ラング導体221と電界導体222とは、電気的に非接続とする。
次に、本発明を適用する第三の実施形態を説明する。本実施形態では、シート状導体を円筒または楕円筒の筒状に構成し、その内側に、それぞれ1チャンネルを構成する複数のアンテナ部を配置する。
次に、本発明を適用する第四の実施形態を説明する。本実施形態のMRI装置のRFコイルとして用いるアンテナ装置は、ラング導体を所望の長さに調製可能とする。
左右からの切り込み641を備えることにより、ラング導体621の実効的な長さが長くなるとともに、ラング導体621上で電流がジグザクに流れる。
Claims (20)
- 静磁場を発生し静磁場を形成するマグネットと、前記静磁場への高周波信号の送信および前記静磁場内に置かれた被検体から発生する核磁気共鳴信号の受信の少なくとも一方を行うRFコイルと、を備える磁気共鳴イメージング装置において、
前記RFコイルは、
シート状導体と、
アンテナ部と、を備え、
前記アンテナ部は、
前記シート状導体から所定の距離をおいて配置されるラング導体と、
前記シート状導体から所定の距離をおいて、前記ラング導体の両端部に配置される2つの電界導体と、を備え、
前記ラング導体と前記シート状導体とは、当該RFコイルが送信する前記高周波信号または受信する前記核磁気共鳴信号の周波数で共振するループ回路を構成すること
を特徴とする磁気共鳴イメージング装置。 - 請求項1記載の磁気共鳴イメージング装置であって、
前記電界導体は、前記ラング導体に流れる電流が作る磁場により前記被検体表面に流れる遮蔽電流を抑制する電界を発生させること
を特徴とする磁気共鳴イメージング装置。 - 請求項1または2記載の磁気共鳴イメージング装置であって、
前記RFコイルは、前記アンテナ部を複数備える多チャンネルアンテナであって、
各アンテナ部の前記電界導体は、隣接する前記アンテナ部のラング導体間の磁界カップリングを抑制する電圧を、隣接する前記アンテナ部の前記電界導体に発生させること
を特徴とする磁気共鳴イメージング装置。 - 請求項1記載の磁気共鳴イメージング装置であって、
前記ラング導体の短軸方向において、前記電界導体の幅は、前記ラング導体の幅より広いこと
を特徴とする磁気共鳴イメージング装置。 - 請求項3記載の磁気共鳴イメージング装置であって、
隣接する前記アンテナ部の電界導体の間隔は、当該隣接するアンテナ部のラング導体の間隔より狭いこと
を特徴とする磁気共鳴イメージング装置。 - 請求項1または2記載の磁気共鳴イメージング装置であって、
前記ラング導体の両端部と当該ラング導体の略直下のシート状導体とを接続する2つの周波数調整キャパシタをさらに備え、
前記周波数調整キャパシタの値は、前記ループ回路が前記高周波信号または前記核磁気共鳴信号の周波数で共振するよう調整されること
を特徴とする磁気共鳴イメージング装置。 - 請求項1または2記載の磁気共鳴イメージング装置であって、
前記ラング導体は、当該ラング導体の長さを調整可能な形状を有し、
前記ラング導体の長さは、前記ループ回路が前記高周波信号または前記核磁気共鳴信号の周波数で共振するよう調整されること
を特徴とする磁気共鳴イメージング装置。 - 請求項1または2記載の磁気共鳴イメージング装置であって、
前記アンテナ部は、前記ラング導体を複数備えること
を特徴とする磁気共鳴イメージング装置。 - 請求項1または2記載の磁気共鳴イメージング装置であって、
前記アンテナ部を複数備え、
前記各アンテナ部は、それぞれ、前記RFコイルを当該磁気共鳴イメージング装置に接続する接続端子を備え、
前記接続端子は、前記ラング導体およびシート状導体に接続され、
前記シート状導体は筒状であり、
前記各接続端子を介して前記各アンテナ部に供給される電圧の位相および振幅は、前記RFコイルから送信される前記高周波信号が最適化されるよう、独立して制御されること
を特徴とする磁気共鳴イメージング装置。 - 請求項9記載の磁気共鳴イメージング装置であって、
前記シート状導体は、楕円筒状であること
を特徴とする磁気共鳴イメージング装置。 - 請求項10記載の磁気共鳴イメージング装置であって、
前記アンテナ部は、前記楕円筒の断面の長軸半径方向に行くに従って、前記シート状導体との距離が短くなるような仮想曲面上に配置されること
を特徴とする磁気共鳴イメージング装置。 - 請求項1または2記載の磁気共鳴イメージング装置であって、
前記ラング導体と前記電界導体とは、電気的に接続されること
を特徴とする磁気共鳴イメージング装置。 - 請求項2記載の磁気共鳴イメージング装置であって、
前記電界導体は、前記電界を発生させるよう面積が決定されること
を特徴とする磁気共鳴イメージング装置。 - 請求項2記載の磁気共鳴イメージング装置であって、
前記ラング導体と前記電界導体とは、電気的に非接続であり、
前記電界導体には、前記ラング導体とは独立して電圧が付与され、
当該電圧は、前記電界を発生させる大きさであること
を特徴とする磁気共鳴イメージング装置。 - 請求項1または2記載の磁気共鳴イメージング装置であって、
前記核磁気共鳴信号に位置情報を付与する傾斜磁場を印加する傾斜磁場印加手段をさらに備え、
前記電界導体は、
スリットと、
当該スリットの両側を接続するスリット接続キャパシタと、を備え、
前記スリット接続キャパシタは、前記傾斜磁場で使用する交流磁場の周波数では、前記スリットの両側が電気的に分断されるよう調整されること
を特徴とする磁気共鳴イメージング装置。 - 請求項3記載の磁気共鳴イメージング装置であって、
隣接するチャンネルの前記電気導体間を接続し、前記磁界カップリングを抑制するカップリング低減キャパシタを備えること
を特徴とする磁気共鳴イメージング装置。 - 請求項7記載の磁気共鳴イメージング装置であって、
前記ラング導体は、スパイラル形状を有すること
を特徴とする磁気共鳴イメージング装置。 - 請求項7記載の磁気共鳴イメージング装置であって、
前記ラング導体は、平板形状を有し、左右交互に入れられた切り込みを備えること
を特徴とする磁気共鳴イメージング装置。 - 静磁場を発生し静磁場を形成するマグネットと、前記静磁場への高周波信号の送信および前記静磁場内に置かれた被検体から発生する核磁気共鳴信号の受信のいずれか一方を行うRFコイルと、を備えた磁気共鳴イメージング装置において、
前記RFコイルは、
シート状導体と、
アンテナ部と、を備え、
前記アンテナ部は、
前記シート状導体から所定の距離をおいて配置されるラング導体と、
前記シート状導体から所定の距離をおいて、前記ラング導体の両端部に配置される2つの電界導体と、
前記ラング導体と前記電界導体の一方とを接続するダイオードと、を備え、
前記ラング導体と前記シート状導体とは、当該RFコイルが送信する前記高周波信号または受信する前記核磁気共鳴信号の周波数で共振するループ回路を構成すること
を特徴とする磁気共鳴イメージング装置。 - シート状導体と、
アンテナ部と、を備え、
前記アンテナ部は、
前記シート状導体から所定の距離をおいて配置されるラング導体と、
前記シート状導体から所定の距離をおいて、前記ラング導体の両端部に配置される2つの電界導体と、を備え、
前記ラング導体と前記シート状導体とは、予め定めた周波数で共振するループ回路を構成すること
を特徴とするアンテナ装置。
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JPWO2015056494A1 (ja) * | 2013-10-17 | 2017-03-09 | 株式会社日立製作所 | 磁気共鳴イメージング装置、アンテナ装置およびその製造方法 |
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JP2017153860A (ja) * | 2016-03-04 | 2017-09-07 | 株式会社日立製作所 | 高周波コイル、それを用いた磁気共鳴撮像装置、及び、マルチチャネル高周波コイルの調整方法 |
WO2017150215A1 (ja) * | 2016-03-04 | 2017-09-08 | 株式会社日立製作所 | 高周波コイル、それを用いた磁気共鳴撮像装置、及び、マルチチャネル高周波コイルの調整方法 |
US10761158B2 (en) | 2016-03-04 | 2020-09-01 | Hitachi, Ltd. | Radio frequency coil, magnetic resonance imaging device using same, and method for adjusting multi-channel radio frequency coil |
JP2022115899A (ja) * | 2016-12-22 | 2022-08-09 | コーニンクレッカ フィリップス エヌ ヴェ | 異なるmriモードのためのrfコイル装置及びrf遮蔽装置 |
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JPWO2013065480A1 (ja) | 2015-04-02 |
US20140253126A1 (en) | 2014-09-11 |
US9684044B2 (en) | 2017-06-20 |
JP6087834B2 (ja) | 2017-03-01 |
DE212012000186U1 (de) | 2014-05-28 |
CN204394509U (zh) | 2015-06-17 |
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