JP2004033380A - Radio frequency coil and magnetic resonance imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a radio frequency coil for efficiently radiating heat generated from a decoupling circuit and to realize a magnetic resonance imaging device. <P>SOLUTION: A substrate 202 on which the decoupling circuit is mounted, is formed of ceramics of a fiber reinforced plastic. Both wings of a mounting region of the substrate 202 are enlarged by using the ceramics or the fiber reinforced plastic and used as heat radiating regions. Accordingly, the heat generated from the decoupling circuit and transferred to the substrate 202 is efficiently transferred to the heat radiating regions to radiate the heat over a wide range in the radiating regions each, having a large heat radiating surface. Thus, lowering in the temperatures of the substrate and the decoupling circuit can be realized. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an RF coil including a decoupling circuit and a magnetic resonance imaging apparatus.
[0002]
[Prior art]
In recent years, in a magnetic resonance imaging apparatus, a frequency of a magnetic resonance signal is increased to improve the quality of a captured image. Strong magnetic coupling occurs between the transmitting or receiving RF coils used here. In order to prevent this strong magnetic coupling, a receiving RF coil is provided with a decoupling circuit. By operating this decoupling circuit, when an electromagnetic wave is transmitted from the transmission coil, the impedance of the loop forming the reception coil is made high to reduce magnetic coupling with the transmission coil. Can be.
[0003]
[Problems to be solved by the invention]
However, according to the above conventional technique, the temperature near the decoupling circuit locally became high. Therefore, for safety, it is necessary to prevent the surface of the RF coil from becoming high temperature by covering the decoupling circuit, which is a heat generating portion, with a cover. Further, in order to improve reliability, it is necessary to increase the number of decoupling circuits and to suppress the heat generation in order to prevent deterioration of circuit elements in the decoupling circuits, for example, diodes, due to heat.
[0004]
In particular, where the RF coil is in contact with the subject, strict safety standards are set to prevent the subject from burns, and the high temperature caused by the heat generated by the decoupling circuit also limits the scan conditions. Had become a factor. In addition, increasing the number of decoupling circuits to improve reliability has caused difficulties such as an increase in product cost and difficulty in adjustment.
[0005]
For these reasons, it is extremely important how to realize an RF coil and a magnetic resonance imaging apparatus that efficiently dissipate the heat generated by the decoupling circuit.
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem of the related art, and provides an RF coil and a magnetic resonance imaging apparatus that can efficiently dissipate heat generated by a decoupling circuit. Aim.
[0006]
[Means for Solving the Problems]
In order to solve the above-described problems and achieve the object, an RF coil according to a first aspect of the present invention is an RF coil having a built-in decoupling circuit for preventing magnetic coupling between the coils. Is characterized by comprising a heat radiating means using ceramic or reinforced fiber plastic as a heat transfer material.
[0007]
According to the invention according to the first aspect, since the decoupling circuit uses ceramic or reinforced fiber plastic as the heat transfer material of the heat radiating means, it does not affect the tomographic image of the magnetic resonance imaging apparatus. The heat generated in the decoupling circuit can be radiated using the body.
[0008]
An RF coil according to a second aspect of the invention is characterized in that the RF coil includes a substrate including a mounting area of the decoupling circuit as the heat radiating means.
According to the second aspect of the invention, since the substrate including the mounting area of the decoupling circuit is used as the heat radiating means, the heat generated in the decoupling circuit can be efficiently transmitted and radiated. .
[0009]
Further, an RF coil according to a third aspect of the present invention is characterized in that the substrate is provided with a heat radiation area in which the mounting area is enlarged.
According to the third aspect of the invention, since the heat radiation area is provided on the substrate with the mounting area enlarged, the heat radiation surface can be made large and the heat radiation efficiency can be increased.
[0010]
An RF coil according to a fourth aspect of the present invention is characterized in that the heat dissipation area is a flat substrate orthogonal to the mounting area.
According to the fourth aspect of the invention, since the heat radiation area is a flat substrate orthogonal to the mounting area, the heat radiation surface is enlarged in a direction orthogonal to the substrate surface on which the decoupling circuit is mounted. In addition, the heat radiation effect can be increased.
[0011]
An RF coil according to a fifth aspect of the present invention is characterized in that the substrate is mounted on a case of the RF coil via a rib.
According to the fifth aspect of the invention, since the substrate is mounted on the case of the RF coil via the rib, the heat of the substrate is less likely to be transmitted to the case, and a rise in the temperature of the case can be suppressed. .
[0012]
An RF coil according to a sixth aspect of the present invention is an RF coil including a decoupling circuit for preventing magnetic coupling between the coils, wherein the decoupling circuit is mounted on a substrate on which the decoupling circuit is mounted. The ground pattern portion is enlarged, and the ground pattern portion is provided with a heat radiating means serving as a heat radiating region.
[0013]
According to the invention of the sixth aspect, the decoupling circuit expands the ground pattern portion on the substrate on which the decoupling circuit is mounted by the heat radiating means, and radiates heat at the ground pattern portion. The heat generated in the decoupling circuit can be radiated without affecting the tomographic image of the resonance imaging device.
[0014]
An RF coil according to a seventh aspect of the invention is characterized in that the substrate is mounted on a case of the RF coil via a rib.
According to the seventh aspect of the present invention, since the substrate is mounted on the case of the RF coil via the rib, heat of the substrate is less likely to be transmitted to the case, and a rise in the temperature of the case can be suppressed. it can.
[0015]
Further, a magnetic resonance imaging apparatus according to an eighth aspect of the present invention is a magnetic resonance imaging apparatus, comprising: a static magnetic field forming unit that forms a static magnetic field; a gradient magnetic field forming unit that forms a gradient magnetic field; an RF coil that transmits or receives an RF signal; What is claimed is: 1. A magnetic resonance imaging apparatus comprising: a gradient magnetic field forming unit; and a control unit for controlling the RF coil, wherein the RF coil is a ceramic or reinforced fiber plastic to which a decoupling circuit for preventing magnetic coupling between the coils is mounted. Or a heat radiation means comprising a ground pattern on the substrate on which the decoupling circuit is mounted.
[0016]
According to the invention of the eighth aspect, the RF coil is provided with a ceramic or reinforced fiber plastic substrate or a decoupling circuit on which a decoupling circuit for preventing magnetic coupling between the coils is mounted, as a heat radiating means. Since the ground pattern on the substrate is used, the heat generated by the decoupling circuit can be radiated, and the case of the RF coil can be prevented from being locally heated.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Preferred embodiments of an RF coil and a magnetic resonance imaging apparatus according to the present invention will be described below with reference to the accompanying drawings. Note that the present invention is not limited to this.
(Embodiment 1)
First, the overall configuration of the magnetic resonance imaging apparatus according to the first embodiment will be described. FIG. 1 is a block diagram illustrating the entire configuration of the magnetic resonance imaging apparatus according to the first embodiment of the present invention. In FIG. 1, the magnetic resonance imaging apparatus has a magnet system 100. The magnet system 100 has a main magnetic field coil unit 102, a gradient coil unit 103, a transmission coil unit 108, and a reception coil unit 104. Except for the receiving coil section 104, each of these coil sections has a substantially cylindrical shape and is arranged coaxially with each other. A subject 101 to be imaged is mounted on a cradle 104 in a substantially cylindrical internal space (bore) of the magnet system 100, and is carried in and out by carrying means (not shown).
[0018]
The main magnetic field coil unit 102 forms a static magnetic field in the internal space of the magnet system 100. The direction of the static magnetic field is substantially parallel to the direction of the body axis of the subject 101. That is, a so-called horizontal magnetic field is formed. The main magnetic field coil unit 102 is configured using, for example, a superconducting coil. It should be noted that the present invention is not limited to the superconducting coil, and may be configured using a normal conducting coil or the like.
[0019]
The gradient coil unit 103 generates three gradient magnetic fields for giving a gradient to the static magnetic field strength in directions of three axes perpendicular to each other, that is, a slice axis, a phase axis, and a frequency axis.
[0020]
The receiving coil unit 104 is placed on the cradle 105 and is arranged at the center of the magnet system 100 together with the subject 101. Here, the receiving coil unit 104 forms a rectangular loop coil, and the coil surface and the cradle surface substantially coincide with each other. The transmission coil unit 108 forms a high-frequency magnetic field for exciting nuclear magnetic resonance in the body of the subject 101 in the static magnetic field space. The nuclear magnetic resonance excited by the transmission coil unit 108 is received by the reception coil unit 104 and used for observation.
[0021]
The gradient driving unit 130 is connected to the gradient coil unit 103. The gradient driving section 130 supplies a driving signal to the gradient coil section 103 to generate a gradient magnetic field. The gradient drive unit 130 has three drive circuits (not shown) corresponding to the three gradient coils in the gradient coil unit 103.
[0022]
The data collection unit 150 is connected to the reception coil unit 104. The RF pulse (pulse) generated by the transmission driving unit 140 is transmitted to the transmission coil unit 108, and the transmission coil unit 108 forms an RF magnetic field from the transmitted RF pulse in the center of the magnet system 100, and 101 is set to an excited state of nuclear magnetic resonance.
[0023]
In addition, the data collection unit 150 captures a reception signal received by the reception coil unit 104 by sampling, and collects the received signal as digital data.
[0024]
The bias power supply unit 155 has a function of selectively flowing a bias current to the receiving coil unit 104. Thereby, the loop coil included in the receiving coil unit 104 can be selectively controlled.
[0025]
A scan controller unit 160 is connected to the gradient driving unit 130, the transmission driving unit 140, and the data collection unit 150. The scan controller 160 controls the gradient driving unit 130 to the data collection unit 150 to perform photographing.
[0026]
The data collection unit 150 is connected to the data processing unit 170. The data collected by the data collection unit 150 is input to the data processing unit 170. The data processing unit 170 is configured using, for example, a computer. The data processing unit 170 has a memory (not shown). The memory stores a program for the data processing unit 170 and various data.
[0027]
The data processing section 170 is connected to the scan controller section 160. The data processing unit 170 is above the scan controller unit 160 and controls it. The functions of the present apparatus are realized by the data processing unit 170 executing a program stored in the memory. Further, the data processing unit 170 stores the data collected by the data collection unit 150 in a memory. A data space is formed in the memory. This data space constitutes a two-dimensional Fourier space. The data processing unit 170 reconstructs an image of the subject 101 by performing a two-dimensional inverse Fourier transform on the data in the two-dimensional Fourier space. Note that the data processing unit 170 also performs an image synthesis process after reconstructing an image.
[0028]
The display section 180 and the operation section 190 are connected to the data processing section 170. The display unit 180 is configured by a graphic display or the like. The operation unit 190 is a pointing device (pointing device).
device).
[0029]
The display unit 180 displays the reconstructed image output from the data processing unit 170 and various information. The operation unit 190 is operated by an operator, and inputs various commands and information to the data processing unit 170. The operator operates the present apparatus interactively through the display unit 180 and the operation unit 190.
[0030]
Next, a specific configuration of the receiving coil unit 104 will be described in detail with reference to FIG. FIG. 2 shows a block diagram of the receiving coil unit 104 shown in FIG. The receiving coil unit 104 includes a conductor loop 200 and a substrate 202. A resonance capacitor (condenser) 201, a decoupling circuit, and a power supply line 231 are mounted on the substrate 202. The decoupling circuit includes an inductor 211 and a diode 221. The decoupling circuit controls the diode 221 on-off by a control current from the bias power supply unit 155, so that the decoupling is active. Do.
[0031]
The substrate 202 is formed using ceramics or a reinforced fiber plastic (hereinafter, referred to as FRP) material. Ceramic or FRP materials have higher thermal conductivity than materials such as acrylic and thermoplastic resins. That is, ceramics and the like have a property of easily transmitting heat. Moreover, since ceramic or FRP is a non-magnetic material, it does not affect image information even in the magnetic resonance imaging apparatus.
[0032]
In addition, the substrate 202 has a heat radiation area separately from a mounting area where electronic components are mounted. This heat radiation area is disposed on both wings of the mounting area, and makes the surface area of the substrate 202 large. For example, when the conductor loop 200 is a rectangular loop of approximately Z = 25 cm and Y = 25 cm using a magnetic resonance imaging apparatus having a static magnetic field strength of 1.5 T (Tesla), the substrate 202 is generally Z = 5 cm and Y = 10 cm, and the heat radiation areas are about Z = 5 cm and Y = 2.5 cm on the left and right sides, respectively.
[0033]
Next, a specific configuration of the power supply and decoupling circuit of the reception coil unit 104 will be described with reference to FIG. The conductor loop 200 forms a parallel resonance circuit having a resonance point at a magnetic resonance frequency together with the capacitor 201, and a reception signal is extracted from both ends of the capacitor 201. Here, an inductor 211 is connected in series to a signal line extracted from the capacitor 201, and a diode 221 is connected between the signal line and the ground line in a forward direction. The opening and closing of the diode 221 is controlled by a bias power supply unit 155 connected to a signal line. That is, when the bias power supply unit 155 causes a current to flow in the forward direction, the diode 221 is closed, and the capacitor 201 and the inductor 211 form a parallel resonance circuit. In this case, both ends of the capacitor 201 are in a high impedance state, the conductor loop 200 forms an open loop, and is in a decoupling state in which magnetic coupling with another coil does not occur.
[0034]
When the bias power supply unit 155 causes a current to flow in the reverse direction, the diode 221 is opened, and a reception signal is transmitted to the data collection unit 150 via the power supply line 231 via the signal line and the ground line. .
[0035]
Next, the outline of the operation of the substrate 202 and the related decoupling circuit will be described. As described above, when the bias power supply unit 155 outputs a forward current, the diode 221 is closed, and the capacitor 201 and the inductor 211 form a parallel resonance circuit. At this time, both ends of the capacitor 201 have high impedance. Assuming that a Q value representing the resonance characteristic of the parallel resonance circuit is P, a current P times the current flowing through the conductor loop 200 flows in the parallel resonance circuit. Since the Q value is approximately several hundreds, a large current flows inside the parallel resonance circuit. Here, since the inductor 211 has a high resistance value, it generates heat and has a high temperature.
[0036]
The mounting area of the substrate 202 to which the inductor 211 is connected also has a high temperature due to the heat generated by the inductor 211. Then, since the high-temperature substrate 202 is formed of ceramic or FRP having a high thermal conductivity, heat is released from the mounting region to a low-temperature heat radiation region existing on both wings, and the temperature is lowered. In addition, the heat radiation area that has absorbed the heat in the mounting area has a large surface area in contact with air, and thus efficiently dissipates heat to the surroundings.
[0037]
As described above, in the first embodiment, the substrate 202 on which the decoupling circuit is mounted is formed using ceramic or FRP, and the two wings of the mounting region of the substrate 202 are enlarged and used as heat radiation regions. Therefore, the heat generated in the decoupling circuit and conducted to the substrate 202 can be efficiently transmitted to the heat radiation area and can be radiated through the heat radiation surface of the heat radiation area.
[0038]
In the present embodiment, the horizontal magnetic field type magnetic resonance imaging apparatus is used. However, the same can be performed by using a vertical magnetic field type magnetic resonance imaging apparatus.
Further, in the present embodiment, the case where the power supply unit has the decoupling circuit has been described. However, a decoupling circuit is provided on the conductor loop 200, and the same applies to the substrate of the decoupling circuit. It can be carried out. Further, in addition to the active type decoupling circuit controlled by the bias power supply unit, the same can be applied to a substrate of a passive type decoupling circuit.
[0039]
In this embodiment, an example using a loop coil has been described. However, a decoupling coil used in a coil such as a saddle type coil, a birdcage type coil, a solenoid type solenoid coil, or the like. Exactly the same heat dissipation measures can be taken for the ring circuit.
(Embodiment 2)
By the way, in the first embodiment, the substrate 202 is enlarged to be a heat dissipation region. However, the substrate 202 is not merely enlarged but a heat sink is newly attached. By separating from the case, the heat radiation effect and safety can be improved. Therefore, in the present embodiment, a case where a new heat radiating plate and a new rib are used will be described.
[0040]
FIG. 4 is a substantial wiring diagram illustrating a specific configuration of the receiving coil unit 400 according to the second embodiment. The receiving coil unit 400 corresponds to the receiving coil unit 104 shown in FIG. 1, and the other configuration is the same as that shown in FIG. 1. Description is omitted. Further, the vicinity of the substrate 202 of the receiving coil unit 400, which is different from the receiving coil unit 104, is particularly illustrated.
[0041]
The receiving coil unit 400 includes the conductor loop 200 and the substrate 202 built in the case 420. Here, the decoupling circuit 430 is mounted on the mounting area of the substrate 202, and the heat radiating plates 410 to 413 are mounted on the heat radiating area in a direction orthogonal to the plate surface of the substrate 202. The heat sinks 410 to 413 are made of ceramic or FRP, similar to the substrate 202. The substrate 202 is fixed to the case 420 by ribs 401 to 403 and a rib located on the back surface of the substrate 202 (not shown). The ribs are preferably made of a material such as plastic having a low thermal conductivity.
[0042]
Next, an operation when the decoupling circuit 430 existing in the mounting area of the substrate 202 generates heat will be described. Due to the heat generated by the decoupling circuit 430, the mounting area of the substrate 202 becomes hot. Then, the heat in the mounting region is transmitted to the heat radiation region by heat conduction, and further transmitted to the heat radiation plates 410 to 413. The heat transmitted to the heat radiating plates 410 to 413 is radiated from the surface of the heat radiating plates 410 to 413 into the air.
[0043]
Further, since the substrate 202 is fixed to the case 420 via the rib having low thermal conductivity, heat on the substrate 202 is less likely to be transmitted to the case 420 via the rib. Therefore, even when the decoupling circuit generates heat, the case 420 is less likely to warm up, and the subject 101 does not feel a temperature exceeding the safety standard even when the subject 101 contacts the case.
[0044]
As described above, in the second embodiment, since the heat radiating plate is built in the heat radiating region of the substrate 202 and the substrate 202 and the case 420 are connected via the rib having low thermal conductivity, the case 420 is Local heating due to the heat generated by the decoupling circuit 430 can be prevented, and the heat radiation effect of the substrate 202 can be further improved.
(Embodiment 3)
In the first and second embodiments, the board 202 is used as a heat transfer medium. However, a copper pattern used for connecting electronic components on the board 202 can be used as a heat transfer medium and a heat dissipation medium. Thus, in this embodiment, a case is described in which a copper pattern on the substrate 202 is used as a heat dissipation medium.
[0045]
FIG. 5 is a substantial wiring diagram illustrating a specific configuration of the receiving coil unit 500 according to the third embodiment. The receiving coil section 500 corresponds to the receiving coil section 104 shown in FIG. 1, and the other configuration is the same as that shown in FIG. 1. Description is omitted.
[0046]
The specific configuration of the receiving coil unit 500 will be described with reference to FIG. The receiving coil unit 500 includes the conductor loop 200 and the substrate 202. A resonance capacitor 201, a decoupling circuit, and a power supply line 231 are mounted on the substrate 202. The decoupling circuit includes an inductor 211 and a diode 221, and performs on / off control of the diode 221 by a control current from the bias power supply unit 155 to perform active decoupling.
[0047]
Here, the capacitor 201, the diode 221 and the ground terminal of the power supply line 231 are provided on the common copper pattern 510. Further, the copper pattern 510 forms a solid pattern on the substrate 202 and covers the surface of the substrate 202. The larger the coverage area, the better.
[0048]
Next, the operation when the decoupling circuit existing in the mounting area of the substrate 202 generates heat will be described. Due to the heat generated by the decoupling circuit, the entire copper pattern surface of the copper pattern 510 having a high thermal conductivity becomes high in temperature. Since the copper pattern 510 has a large surface area, it efficiently dissipates heat to the space. Since the heat of the decoupling circuit portion is radiated through the copper pattern 510, the temperature of the decoupling circuit can be reduced.
[0049]
As described above, in the third embodiment, the copper pattern 510 on the substrate 202 is used as a heat dissipation medium, so that the decoupling portion is prevented from being locally heated by heat generation, and The effect can be enhanced.
[0050]
【The invention's effect】
As described above, according to the present invention, the decoupling circuit forms the substrate to be mounted using ceramic or FRP and increases the surface area of this substrate to improve the heat radiation effect. By using a non-magnetic material that does not affect the tomographic image of the magnetic resonance imaging apparatus, heat generated in the decoupling circuit can be efficiently dissipated, and the temperature of the portion where the subject contacts the RF coil is reduced. At the same time, it is possible to suppress the temperature rise of the decoupling circuit itself.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating an overall configuration of a magnetic resonance imaging apparatus.
FIG. 2 is a diagram illustrating a receiving coil unit according to the first embodiment;
FIG. 3 is a diagram illustrating a decoupling circuit according to the first embodiment;
FIG. 4 is a diagram illustrating a receiving coil unit according to a second embodiment.
FIG. 5 is a diagram illustrating a receiving coil unit according to a third embodiment;
[Explanation of symbols]
Reference Signs List 100 magnet system 101 subject 102 main magnetic field coil unit 103 gradient coil unit 104, 400, 500 reception coil unit 105 cradle 108 transmission coil unit 130 gradient drive unit 140 transmission drive unit 150 data collection unit 155 bias power supply unit 160 scan controller unit 170 Data processing unit 180 Display unit 190 Operation unit 200 Conductor loop 201 Capacitor 202 Substrate 211 Inductor 221 Diode 231 Feed line 401 Rib 410 Heat sink 420 Case 430 Decoupling circuit 510 Copper pattern

Claims (8)

An RF coil incorporating a decoupling circuit for preventing magnetic coupling between the coils,
The RF coil according to claim 1, wherein the decoupling circuit includes a heat radiating unit that uses ceramic or reinforced fiber plastic as a heat transfer material. The RF coil according to claim 1, wherein the heat radiating unit includes a substrate including a mounting area of the decoupling circuit. The RF coil according to claim 2, wherein the substrate includes a heat dissipation area in which the mounting area is enlarged. 4. The RF coil according to claim 3, wherein the heat radiation region includes a planar substrate orthogonal to the mounting region. 5. The RF coil according to any one of claims 2 to 4, wherein the substrate is mounted on a case of the RF coil via a rib. An RF coil incorporating a decoupling circuit for preventing magnetic coupling between the coils,
The RF coil according to claim 1, wherein the decoupling circuit includes a heat radiating unit that enlarges a ground pattern portion on a substrate on which the decoupling circuit is mounted, and the ground pattern portion becomes a heat radiating region. The RF coil according to claim 6, wherein the substrate is mounted on a case of the RF coil via a rib. Means for forming a static magnetic field,
Gradient magnetic field forming means for forming a gradient magnetic field,
An RF coil for transmitting or receiving an RF signal,
Control means for controlling the gradient magnetic field forming means and the RF coil;
A magnetic resonance imaging apparatus comprising:
The RF coil may be a heat radiating means made of a ceramic or reinforced fiber plastic substrate on which a decoupling circuit for preventing magnetic coupling between the coils is mounted, or a heat radiating means formed of a ground pattern on the substrate on which the decoupling circuit is mounted. , A magnetic resonance imaging apparatus comprising:

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