JP2004135873A - High-frequency coil and magnetic resonance imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-frequency coil that improves the impedance of a blocking circuit, restrains the calorific value and reduces an irradiation output, and a magnetic resonance imaging device. <P>SOLUTION: A coil element 11 and a coil element 12 forming a receiving coil section are connected by a capacitor 24 and a capacitor 34, and a resonance circuit 20 is formed in the vicinity of the capacitor 24 and a resonance circuit 30 is formed in the vicinity of the capacitor 34. Furthermore, recesses 11a and 12a are provided at the ends of the coil elements 11 and 12 to prevent an interference between the resonance circuit 20 and the resonance circuit 30. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a magnetic resonance imaging apparatus including: an irradiation coil that irradiates an object placed in a static magnetic field with an electromagnetic wave having a predetermined frequency; and a reception coil that receives an electromagnetic wave emitted by the object. In particular, the present invention relates to a magnetic resonance imaging apparatus that reduces interference between an irradiation coil and a reception coil and suppresses heat generation from the reception coil.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a magnetic resonance imaging apparatus (hereinafter, referred to as an “MRI apparatus”) that images an internal structure of an imaging target using a nuclear magnetic resonance phenomenon is known (for example, see Patent Literature 1). Since the nuclear magnetic resonance phenomenon is harmless to a living body, the MRI apparatus is particularly useful for medical use, and is used for diagnosis of brain tumor and the like.
[0003]
This nuclear magnetic resonance phenomenon means that in an object to which a uniform static magnetic field is applied, the spin directions of the nuclei of the atoms constituting the object are aligned and the frequency is proportional to the strength of the static magnetic field (hereinafter referred to as “resonance frequency”). Is the phenomenon of absorbing and emitting electromagnetic waves. The MRI apparatus can image an arbitrary tomographic plane of an imaging target with an arbitrary thickness by using a nuclear magnetic resonance phenomenon for a specific nuclide (mainly, a hydrogen atom).
[0004]
When imaging the internal structure of an imaging target using the nuclear magnetic resonance phenomenon, a spatially and temporally varying gradient magnetic field is applied to the imaging target separately from the static magnetic field in order to check positional information. . By applying the gradient magnetic field, the magnetic field applied to the object to be imaged varies depending on the location, and the resonance frequency of each atom constituting the object to be imaged varies depending on the location. Therefore, by examining the resonance frequency by applying a gradient magnetic field, it is possible to know what atom exists at which position on the imaging target. The above is the mechanism of photographing the internal structure of the object by the MRI apparatus.
[0005]
Specifically, the resonance frequency is measured by irradiating an imaging target to which a gradient magnetic field is applied with an electromagnetic wave to absorb the electromagnetic wave, and then receiving the electromagnetic wave emitted by the imaging target to measure the frequency. Generally, in a magnetic resonance imaging apparatus, an irradiation coil (transmitting coil) for irradiating electromagnetic waves and a receiving coil for receiving electromagnetic waves are provided independently.
[0006]
When the irradiation coil and the receiving coil are separated from each other, the irradiation coil is installed on the magnet assembly so as to irradiate a sufficiently strong electromagnetic wave to the examination area on which the subject is placed. In addition, the receiving coil can be selected in accordance with the inspection site and the inspection content, and is brought as close as possible to the inspection site. As described above, the irradiation coil and the receiving coil are separated from each other, and the receiving coil is brought as close as possible to the inspection site, so that the SNR (Signal to Noise Ratio) of imaging can be improved.
[0007]
On the other hand, when the irradiation coil and the reception coil are independently provided, it is necessary to electrically separate the irradiation coil and the reception coil to prevent mutual interference. Therefore, a configuration in which a transmission coil is formed by connecting a plurality of coil elements and a resonance circuit is provided at a connection portion to electrically separate the irradiation coil and the reception coil from the related art has been used.
[0008]
The resonance circuit adjusts its resonance frequency to the frequency of the electromagnetic wave radiated by the irradiation coil, so that while the irradiation coil irradiates the electromagnetic wave, the resonance circuit resonates and a current flows, thereby increasing the impedance of the circuit. Therefore, while the irradiation coil is irradiating the electromagnetic wave, current is prevented from being generated in the reception coil, and the irradiation coil and the reception coil can be electrically separated. Such a resonance circuit that prevents the generation of a current in the receiving coil during the irradiation of the electromagnetic wave is generally called a blocking circuit.
[0009]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2000-225106
[Problems to be solved by the invention]
However, in the above-described conventional blocking circuit, since the electric resistance and the inductance of the coil element are present, a decrease in impedance and interference with an adjacent circuit occur, causing a shift in the resonance frequency.
[0011]
In addition, as a result, a loss of the irradiation output occurs, so that the required irradiation output increases, and further, the amount of heat generated during the operation of the blocking circuit increases. Since the blocking circuit is arranged near the receiving coil, that is, in the vicinity of the subject, the amount of heat generated in the vicinity of the subject increases, which causes a problem in securing the safety of the subject.
[0012]
That is, in the above-described conventional blocking circuit, there is a problem that the impedance of the blocking circuit decreases, the amount of generated heat increases, and a high irradiation output is required.
[0013]
The present invention has been made in view of the above-described drawbacks of the related art, and provides a high-frequency coil and a magnetic resonance imaging apparatus capable of improving impedance of a blocking circuit, suppressing heat generation, and reducing irradiation output. With the goal.
[0014]
[Means for Solving the Problems]
In order to solve the above-described problems and achieve the object, an invention according to a first aspect is a high-frequency coil formed by connecting a plurality of coil elements, wherein a connection portion of the coil element is a first capacitor. And a second capacitor, comprising: a first resonance circuit disposed near the first capacitor; and a second resonance circuit disposed near the second capacitor. And
[0015]
According to the invention according to the first aspect, the high-frequency coil includes the first capacitor and the second capacitor that connect the coil element in the first resonance circuit and the second capacitor corresponding to the first capacitor. The corresponding second resonance circuits are provided independently of each other.
[0016]
The invention according to a second aspect is the invention according to the first aspect, wherein the coil element has a first protruding end connecting the first capacitor and a second protruding end connecting the second capacitor. And a tip.
[0017]
According to the invention according to the second aspect, the high-frequency coil generates a current from the first capacitor to the second capacitor by connecting the first capacitor and the second capacitor to independent protrusions. To prevent them from doing so.
[0018]
The invention according to a third aspect is characterized in that, in the invention according to the second aspect, the first protrusion and the second protrusion are formed by cutting out the ends of the coil element. .
[0019]
According to the invention according to the third aspect, the high-frequency coil has a first protrusion and a second protrusion formed by cutting off the ends of the coil element, and a capacitor is connected to each of the protrusions.
[0020]
The invention according to a fourth aspect is characterized in that, in the invention according to the third aspect, the notch has a triangular shape.
[0021]
According to the invention according to the fourth aspect, the high-frequency coil forms the first protrusion and the second protrusion by notching the ends of the coil element in a triangular shape.
[0022]
The invention according to a fifth aspect is characterized in that, in the invention according to the third aspect, the notch is rectangular.
[0023]
According to the invention according to the fifth aspect, the high-frequency coil forms the first protrusion and the second protrusion by notching the ends of the coil element in a rectangular shape.
[0024]
The invention according to a sixth aspect is characterized in that, in the invention according to any one of the first to fifth aspects, the coil element is formed by a heat pipe.
[0025]
According to the invention according to the sixth aspect, the high-frequency coil disperses generated heat by using the coil element and the heat pipe together.
[0026]
According to a seventh aspect of the present invention, in the invention according to any one of the first to sixth aspects, a material of the coil element is copper.
[0027]
According to the invention according to the seventh aspect, in the high-frequency coil, the coil element is formed of copper.
[0028]
Further, the invention according to an eighth aspect provides an irradiation coil for irradiating an object placed in a static magnetic field with an electromagnetic wave of a predetermined frequency, and a receiving coil for receiving the electromagnetic wave emitted from the object. A magnetic resonance imaging apparatus, wherein the irradiation coil is a high-frequency coil formed by connecting a plurality of coil elements, and a connection portion of the coil element has a first capacitor and a second capacitor. A first resonance circuit disposed near the first capacitor and resonating at the predetermined frequency; and a second resonance circuit disposed near the second capacitor and resonating at the predetermined frequency. And characterized in that:
[0029]
According to the eighth aspect of the invention, the magnetic resonance imaging apparatus includes a first resonance circuit corresponding to the first capacitor and a second resonance circuit corresponding to the first capacitor and the second capacitor connecting the coil element. The second resonance circuits corresponding to the capacitors are provided independently of each other.
[0030]
The invention according to a ninth aspect is the invention according to the eighth aspect, wherein the coil element has a first protruding end connecting the first capacitor and a second protruding end connecting the second capacitor. And a tip.
[0031]
According to the invention of the ninth aspect, the magnetic resonance imaging apparatus connects the first capacitor and the second capacitor to independent protruding ends to thereby control a current flowing from the first capacitor to the second capacitor. Is prevented from occurring.
[0032]
The invention according to a tenth aspect is characterized in that, in the invention according to the ninth aspect, the first protrusion and the second protrusion are formed by cutting out ends of the coil element. .
[0033]
According to the invention of the tenth aspect, in the magnetic resonance imaging apparatus, the first and second protrusions are formed by cutting out the ends of the coil element, and capacitors are respectively connected to the protrusions. I have.
[0034]
The invention according to an eleventh aspect is characterized in that, in the invention according to the tenth aspect, the notch has a triangular shape.
[0035]
According to the invention of the eleventh aspect, in the magnetic resonance imaging apparatus, the first protrusion and the second protrusion are formed by notching the ends of the coil element in a triangular shape.
[0036]
The invention according to a twelfth aspect is characterized in that, in the invention according to the tenth aspect, the notch is rectangular.
[0037]
According to the invention of the twelfth aspect, in the magnetic resonance imaging apparatus, the first protrusion and the second protrusion are formed by notching the ends of the coil element in a rectangular shape.
[0038]
According to a thirteenth aspect, in the invention according to any one of the eighth to twelfth aspects, the coil element is formed by a heat pipe.
[0039]
According to the invention of the thirteenth aspect, the magnetic resonance imaging apparatus disperses generated heat by using both the coil element and the heat pipe.
[0040]
The invention according to a fourteenth aspect is characterized in that, in the invention according to any one of the eighth to thirteenth aspects, the material of the coil element is copper.
[0041]
According to the fourteenth aspect, in the magnetic resonance imaging apparatus, the coil element is formed of copper.
[0042]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a magnetic resonance imaging apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.
[0043]
FIG. 1 is a diagram illustrating a connection portion of a coil element in a reception coil of the MRI apparatus according to the present embodiment. FIG. 2A is a diagram illustrating a usage example of a receiving coil, and FIG. 2B is a diagram illustrating a schematic configuration of a coil unit of the receiving coil. FIG. 3 shows an MRI apparatus using the receiving coil unit.
[0044]
As shown in FIG. 2A, in this embodiment, a head coil 43 to be placed on the head of the subject is used as a receiving coil. Therefore, when imaging a magnetic resonance image, the subject 42 is placed on the cradle 41 and the head coil 43 is put on the head of the subject 42.
[0045]
Thereafter, as shown in FIG. 3, the cradle 41 is inserted into the irradiation coil 63. Around the irradiation coil 64, a gradient magnetic field generating coil 63 and static magnetic field generating magnets 61 and 62 are provided. The static magnetic field generating magnets 61 and 62 and the gradient magnetic field generating coil 63 are connected to a magnetic control unit 65c inside the MRI apparatus 65, and generate a predetermined magnetic field in the examination region. The RF transmitter b irradiates an electromagnetic wave of a predetermined frequency from the irradiation coil 43. On the other hand, the receiving coil unit 43 receives the electromagnetic wave emitted by the subject due to the nuclear magnetic resonance phenomenon and transmits the electromagnetic wave to the RF receiving unit 65a. The image processor 65d creates a nuclear magnetic resonance image from the electromagnetic waves received by the RF receiver 65a.
[0046]
Here, the receiving coil section 44 provided in the head coil 43 is formed by connecting a plurality of coil elements 11 to 18 as shown in FIG. FIG. 1 illustrates the configuration of the connection between the coil element 11 and the coil element 12 among the coil elements 11 to 18, but the same configuration is used for the connection of the other coil elements.
[0047]
As shown in FIG. 1, at the connection between the coil element 11 and the coil element 12, the capacitors 24 and 34 connect the coil element 11 and the coil element 12. More specifically, the capacitor 24 is connected to the coil element 11 by a terminal 23, and is further connected to the coil element 12 by a terminal 25. The capacitor 34 is connected to the coil element 11 by a terminal 35, and is connected to the coil element 12 by a terminal 33.
[0048]
A terminal 22 is provided near the terminal 23 of the coin element 11, and a terminal 26 is provided near the terminal 25 of the coil element 12. The coil 21 and the diodes 27 and 28 are connected between the terminals 22 and 26. The coil 21, the capacitor 24, and the diodes 27 and 28 form a resonance circuit 20.
[0049]
Further, a terminal 36 is provided near the terminal 35 of the coin element 11, and a terminal 32 is provided near the terminal 33 of the coil element 12. The coil 31, the diode 37 and the diode 38 are connected between the terminal 36 and the terminal 32. The coil 31, the capacitor 34, and the diodes 37 and 38 form the resonance circuit 30.
[0050]
Here, the shapes of the ends of the coil elements 11 and 12 and the arrangement of the terminals will be described. The coil element 11 has a triangular notch at its end, and a concave portion 11a is formed. Due to the recess 11a, the end of the coil element 11 has two protruding ends, and the terminals 22 and 23 are formed on one of the protruding ends, and the terminals 35 and 36 are formed on the other protruding end.
[0051]
Similarly, the coil element 12 has a triangular notch at its end, and a recess 12a. Due to the recess 12a, the end of the coil element 12 has two protruding ends, and the terminals 24 and 26 are formed on one of the protruding ends, and the terminals 32 and 33 are formed on the other protruding end.
[0052]
As described above, by forming the resonance circuit 20 and the resonance circuit 30 for the capacitor 24 and the capacitor 34, heat generated at the connection portion between the coil element 11 and the coil element 12 is distributed to the resonance circuit 20 and the resonance circuit 30. Can be. This heat is mainly generated in the diodes, and the amount of heat generated in each diode is approximately proportional to the square of the current. Therefore, the amount of heat generated can be reduced to about 1/4 by using two resonant circuits and reducing the current generated in each circuit, that is, the current flowing into each diode to about half.
[0053]
Furthermore, by providing the coil element 11 with the concave portion 11a, the resistance and inductance between the terminals 22 and 23 included in the resonance circuit 20 and the terminals 35 and 36 included in the resonance circuit 30 are increased. Similarly, by providing the coil element 12 with the concave portion 12a, the resistance and the inductance between the terminals 25 and 26 included in the resonance circuit 20 and the terminals 32 and 33 included in the resonance circuit 30 are increased. As described above, by increasing the resistance and inductance between the terminal included in the resonance circuit 20 and the terminal included in the resonance circuit 30, interference between the resonance circuits 20 and 30 is prevented, and an independent blocking circuit is provided. Can work.
[0054]
By forming the resonance circuit 20 and the resonance circuit 30 as independent blocking circuits, the influence of the resistance and inductance of the coil elements 11 and 12 can be eliminated, and the impedance of the resonance circuits 20 and 30 can be improved. As a result, the electrical separation between the receiving coil unit 44 and the irradiation coil can be improved. In addition, by improving the impedance of the resonance circuits 20 and 30, it is possible to suppress the loss of the irradiation output, so that the necessary irradiation output can be reduced.
[0055]
Note that the value of the resistance and the inductance between the terminal included in the resonance circuit 20 and the terminal included in the resonance circuit 30 is such that the impedance Zp obtained from the value is L when the inductance of the capacitor 24 or the capacitor 34 is L. , Zp >> ωL. Therefore, the concave portion 11a and the concave portion 12a need to be formed so as to satisfy this relationship.
[0056]
On the other hand, the shape of the concave portions provided in the coil elements 11 and 12 is not necessarily required to be triangular as long as the shape satisfies this relationship, and may be any shape. FIG. 4 shows a connection portion between the coil element 11 and the coil element 12 when a rectangular recess is formed. In FIG. 4, the coil elements 11 and 12 have square notches at their ends to form square recesses 11b and 12b. As described above, even when the rectangular notch is provided, the terminal included in the resonance circuit 20 is provided on one of the protruding ends, and the terminal included in the resonance circuit 30 is provided on the other protruding end. 20 and the resonance circuit 30 can be electrically separated.
[0057]
Next, the coil elements 11 to 18 will be further described. Generally, copper is used as a material for the coil element. By using the coil element also as a heat pipe, heat generated from the blocking circuit can be easily diffused.
[0058]
FIG. 5 is a diagram illustrating the receiving coil unit 51 using the hollow coil elements 51 to 58. In FIG. 5, each of the hollow coil elements 51 to 58 is formed by a copper pipe, and a predetermined solution is put into the inside thereof so as to function as a heat pipe. As this solution, a liquid that does not cause nuclear magnetic resonance is used. More specifically, the solution desirably has a value of electric conductivity close to 0, a value of relative magnetic permeability close to 1, and a value of relative dielectric constant close to 1.
[0059]
Note that a resonance circuit having the same configuration as the resonance circuits 20 and 30 is provided at the connection portions of the hollow coil elements 51 to 58. By forming the coil element by the heat pipe in this way, the heat generated in the resonance circuit is diffused by the solution inside the heat pipe and can be easily radiated.
[0060]
As described above, in this embodiment, by providing two resonance circuits and providing a concave portion for preventing interference of the resonance circuit, the impedance of the resonance circuit is improved, the irradiation output is reduced, and the heat generation source is reduced. Can be dispersed.
[0061]
Further, by forming the coil element by a heat pipe, heat generated from the resonance circuit can be diffused. Therefore, according to the present embodiment, the amount of heat generated from the resonance circuit can be reduced and the heat can be easily discharged, so that a magnetic resonance image can be taken without danger to the subject.
[0062]
In the present embodiment, the case where the receiving coil unit 44 is provided in the head coil has been described. However, the use of the present invention is not limited to this, and the body coil for imaging the body and the arm may be used. It can be used for any receiving coil such as an arm coil for imaging.
[0063]
Further, in the present embodiment, the magnetic resonance imaging apparatus in which the heat generation amount of the receiving coil unit is reduced for ensuring the safety of the subject has been described, but the use of the present invention is not limited to this. It can also be used to reduce the amount of heat generated by the coil, and can be widely applied to other devices to reduce the amount of heat generated by the high-frequency coil.
[0064]
Further, in the present embodiment, the coil elements are connected by two capacitors, and two resonance circuits corresponding to the respective capacitors are formed. However, the number of capacitors and the number of resonance circuits are not limited to two. , Can be increased as needed.
[0065]
Furthermore, by combining the existing heat dissipation technology with the connection part of the coil element according to the present invention, heat dissipation can be performed more effectively. For example, a heat sink may be provided near the coil element, or a heat insulating material may be provided between the receiving coil and the subject to control the direction of heat conduction.
[0066]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a high-frequency coil and a magnetic resonance imaging apparatus capable of improving the impedance of the blocking circuit, suppressing the heat generation, and reducing the irradiation output.
[0067]
Further, by configuring the coil element with a heat pipe, there is an effect that the heat of the high-frequency coil and the magnetic resonance imaging apparatus can be efficiently exhausted.
[Brief description of the drawings]
FIG.
It is a figure showing the connection part of the coil element concerning this embodiment.
FIG. 2
FIG. 2 is a diagram illustrating a receiving coil of the MRI apparatus according to the present embodiment.
FIG. 3
FIG. 1 is a diagram illustrating a schematic configuration of an MRI apparatus according to an embodiment.
FIG. 4
It is a figure which shows the connection part of a coil element at the time of forming a square-shaped recessed part.
FIG. 5
It is a figure explaining a receiving coil part at the time of using a hollow coil element.
[Explanation of symbols]
11-18 Coil elements 11a, 12a Recesses 20, 30 Resonant circuits 21, 31 Coils 22, 23, 25, 26, 32, 33, 35, 36 Terminals 24, 34 Capacitors 27, 28, 37, 38 Diode 41 Cradle 42 Sample 43 Head coil 44 Receiving coil units 51 to 58 Hollow coil elements 61, 62 Static magnetic field generating magnet 63 Gradient magnetic field generating coil 64 Irradiation coil 65 MRI device 65a RF receiving unit 65b RF transmitting unit 65c Magnetic control unit 65d Image processing unit

Claims (14)

A high-frequency coil formed by connecting a plurality of coil elements,
The connection portion of the coil element has a first capacitor and a second capacitor,
A first resonance circuit disposed near the first capacitor;
A second resonance circuit arranged near the second capacitor;
A high frequency coil comprising: 2. The high-frequency coil according to claim 1, wherein the coil element includes a first protrusion connecting the first capacitor, and a second protrusion connecting the second capacitor. 3. The high frequency coil according to claim 2, wherein the first protrusion and the second protrusion are formed by cutting out ends of the coil element. 4. The high frequency coil according to claim 3, wherein the notch has a triangular shape. The high frequency coil according to claim 3, wherein the notch has a rectangular shape. The high frequency coil according to any one of claims 1 to 5, wherein the coil element is formed by a heat pipe. The high frequency coil according to any one of claims 1 to 6, wherein a material of the coil element is copper. An irradiation coil that irradiates an electromagnetic wave of a predetermined frequency to a subject placed in a static magnetic field, and a magnetic resonance imaging apparatus including a receiving coil that receives an electromagnetic wave emitted by the subject,
The irradiation coil includes:
A high-frequency coil formed by connecting a plurality of coil elements,
The connection portion of the coil element has a first capacitor and a second capacitor,
A first resonance circuit disposed near the first capacitor and resonating at the predetermined frequency;
A second resonance circuit arranged near the second capacitor and resonating at the predetermined frequency;
A magnetic resonance imaging apparatus comprising: 9. The magnetic resonance imaging apparatus according to claim 8, wherein the coil element includes a first protrusion connecting the first capacitor and a second protrusion connecting the second capacitor. . The magnetic resonance imaging apparatus according to claim 9, wherein the first protrusion and the second protrusion are formed by cutting out ends of the coil element. The magnetic resonance imaging apparatus according to claim 10, wherein the notch has a triangular shape. 11. The magnetic resonance imaging apparatus according to claim 10, wherein the notch has a rectangular shape. 13. The magnetic resonance imaging apparatus according to claim 8, wherein the coil element is formed by a heat pipe. The magnetic resonance imaging apparatus according to any one of claims 8 to 13, wherein a material of the coil element is copper.

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