JPH0980140A - Rf coil device for magnetic resonance device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an efficient RF coil device for magnetic resonance device by connecting a balance-unbalance conversion circuit corresponding to at least one resonance frequency which a multiple tuning RF coil has in a power feed part and reducing, loss and deterioration, etc. SOLUTION: A balance-unbalance conversion circuit 2 comprising inductance element L and a capacitance element C is provided between a coaxial line 4 and a multiplex tuning RF coil 1. A relationship of ω<2> LC=1 is established for the elements L and C, where ωis the resonance frequency of the nuclides of a balanceunbalance conversion circuit. An impedance Z1 of a circuit which is comprised of the elements L and C is found to be equal to ωL/(ω2 LC-1). By substituting the conditions in the previous expression for the expression, it is found that Z1 =∞ and the current does not flow to a coating conductor, and hence preventing discharge loss from occurring by the circuit 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a magnetic resonance apparatus, and is an RF for performing at least one of application of a high-frequency magnetic field to a subject placed in a static magnetic field and detection of a magnetic field resonance signal from the subject. (High frequency) related to coil device,
In particular, the present invention relates to an RF coil device for a magnetic resonance apparatus capable of performing efficient power feeding and detuning / tuning.

[0002]

2. Description of the Related Art A magnetic resonance apparatus is a system in which a group of nuclei having a unique magnetic moment is placed in a uniform static magnetic field.
It is a device for visualizing chemical and physical microscopic information on a substance or observing a chemical shift spectrum by utilizing the phenomenon of resonating the energy of a high frequency magnetic field rotating at a specific frequency. In such a magnetic resonance apparatus, an RF coil apparatus for irradiating a region of interest of a subject with a high-frequency magnetic field and detecting a magnetic resonance signal generated thereby is indispensable.

A magnetic resonance system allows ³¹ P (phosphorus) and ¹³
When obtaining chemical shift spectra of C (carbon) or both at the same time, ¹ H (proton) images are acquired for positioning and magnetic field uniform correction. In such a case, as an RF coil device for generating a high frequency magnetic field and collecting a magnetic resonance signal, a coil tuned to each magnetic resonance frequency such as ³¹ P, ¹³ C and ¹ H is required.

An RF coil device that tunes to a plurality of frequencies in this way is called a multi-tuned RF coil device. Multiple tuning R
FIG. 7 shows an example of a circuit diagram of the F coil device. The example in FIG.
FIG. 3 is a circuit diagram of an n-fold tuned RF coil device in which n-1 resonance circuits are connected in series to one resonance circuit and have n resonance frequencies.

The RF coil device used in the magnetic resonance device comprises a resonance circuit 7 consisting of an inductance and a capacitance, and an impedance matching (usually 50Ω) circuit. Although FIG. 7 shows the case where the input / output ends of the coils are 1 for all of them, some of them have a plurality of input / output ends as shown in FIG. If an impedance-matched coil and a coaxial line that is an unbalanced input / output impedance are connected to feed power to this RF coil device, a current also flows in the outer conductor of the coaxial line, and radiation by the current is caused. Loss may occur, or the sensitivity distribution of the static magnetic field may deteriorate due to the imbalance of the high frequency current.

A balanced-unbalanced conversion circuit is provided in order to prevent transmission loss such as unnecessary radiation and deterioration of sensitivity distribution of static magnetic field.
It is well known to make a connection between a coil and a coaxial line that connects to the coil. The connection point between this coil and the balanced-unbalanced conversion circuit or the coaxial line is called a power feeding section. The balanced-unbalanced conversion circuit in this case is adjusted so as to perform impedance matching at a resonance frequency that matches the resonance frequency of the coil. In the above, usually 50
Although it is described that the impedance is matched with Ω, the impedance may be matched with 75Ω or another value in accordance with the coaxial line.

In the case of a multi-tuned coil device, conventionally, as shown in FIG. 9, the balanced-to-unbalanced conversion circuits 2a, 2 corresponding to the resonance frequency of each feeding portion corresponding to the resonance frequency of the coil.
b ... 2k ... 2n and duplexers 3a, 3b ... 3k ...
3n is connected to the multi-tuned RF coil 1. But,
In the case of feeding the multi-tuning RF coil device described above, due to the coupling existing between the resonance frequencies of the multi-tuning RF coil device, frequency components other than the resonance frequency are mixed in the feeding portion of each resonance frequency and the coaxial line. However, as a result, deterioration of the sensitivity distribution of the static magnetic field and transmission loss occur. If not only the balanced-unbalanced conversion circuit connected by the power feeding unit corresponding to the resonance frequency but also a plurality of balanced-unbalanced conversion circuits corresponding to the resonance frequency of the multi-tuned RF coil device are connected to each power feeding unit. , It is considered that power supply with less transmission loss can be realized, but such a thing has not been proposed.

In FIG. 9, one feeding point corresponding to each frequency is described, but in the case of a QD coil, there is one feeding point for each resonance frequency. Not exclusively.

On the other hand, the RF coil device should uniformly generate a high-frequency magnetic field and a receiving coil to be used as closely as possible to the subject in order to improve the efficiency of high-frequency power and the detection sensitivity of image and chemical shift spectrum data. The transmission coils that can be used are separately configured and used. In the case of the above configuration, the receiving coil is detuned from the resonance frequency of the coil so as not to deteriorate the uniformity of the magnetic field generated by the transmitting coil at the time of transmission, and means for tuning to the resonance frequency at the time of reception is added. In addition, the transmitting coil needs to be detuned from the resonance frequency of the receiving coil so as not to reduce the detection sensitivity of the receiving coil at the time of reception, and it is necessary to add means for tuning to the resonance frequency at the time of transmission. .

In the case of a multi-tuning RF coil device, as shown in FIG. 15, conventionally, a trap diode 13a, 13b corresponding to the resonance frequency of the coil is connected to a pin diode or variable capacitance diode 11 as each detuning and tuning means. ing. However, in the case of the detuning and tuning of the above-mentioned multi-tuning RF coil device, the detuning and tuning means of each resonance frequency and the coaxial line are provided by the coupling existing between the resonance frequencies of the multi-tuning RF coil device. Frequency components other than the resonance frequency are mixed, and as a result, the distribution of the high frequency magnetic field is deteriorated. A multi-tuning R as well as a high-impedance element or a trap circuit corresponding to the resonance frequency is provided in a power supply line for transmitting power for driving the detuning and tuning means
It is considered that by inserting a trap circuit corresponding to the resonance frequency of the F-coil device, it is possible to realize detuning and tuning means without further deterioration of the high-frequency magnetic field distribution, but the latter is not proposed.

[0011]

As described above, in the conventional RF coil device for the magnetic resonance apparatus, the leakage of the current of the resonance frequency component of the nuclide to be fed or the current of the resonance frequency component of the nuclide to be tuned and detuned is prevented. However, there is a problem in that it is not possible to prevent deterioration of the sensitivity distribution of the static magnetic field and transmission loss due to the current of the resonance frequency component of the nuclide other than the resonance frequency flowing due to the coupling between the resonance frequencies of the RF coil device. It was An object of the present invention is to provide an efficient RF coil device for a magnetic resonance apparatus with less loss and deterioration.

[0012]

In order to solve the above problems, the present invention provides an RF coil device such as a multituned RF coil device in which at least two balanced-to-unbalanced conversion circuits are provided in a power feeding portion of the multituned RF coil. It is characterized by connecting a balanced-unbalanced conversion circuit corresponding to one resonance frequency.

In order to solve the above-mentioned problems, the present invention is an RF coil device such as a multituned RF coil used for transmission or reception, and at least the multituned RF coil is provided in a power feed line of the detuning and tuning means. It is characterized in that a trap circuit corresponding to two resonance frequencies is connected.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a multiple tuning R according to the present invention.
An RF coil device such as an F coil (n-fold tuned RF in FIG. 1)
Shows a coil. ) Shows an example of the state of power feeding. As shown in FIG. 9, which is a state of conventional power feeding, a balanced-unbalanced conversion circuit 2k corresponding to the resonance frequency of the nuclide k to be fed is provided between the multi-tuning RF coil 1 and the coaxial line connected to the coil. In addition to connecting, a plurality of balanced-unbalanced conversion circuits 2a, 2b, ... 2k ... 2n corresponding to the resonance frequency of a nuclide different from the nuclide are connected between the multi-tuning RF coil 1 and a coaxial line connecting to the coil. It shows an example of the case of connecting to. Here, a balanced-unbalanced conversion circuit 2 connected between the multituned RF coil 1 and the coaxial line.
2n may be less than n, and the order of the circuits to be connected may be different from that in FIG.

In FIG. 1, the multi-tuning RF coil 1 is shown as a coil for both transmission and reception, but it may be used when the coil is a reception coil or a transmission coil. In the case of receiving or transmitting coils, duplexers 3a, 3b, ... 3
k ... 3n is unnecessary.

FIG. 2 shows an example of a balanced-unbalanced conversion circuit, in which an inductance element L and a capacitance element C are provided between the coaxial line 4 and the multituned RF coil 1.
A balanced-to-unbalanced conversion circuit 2 is provided. The following relationship is established between the inductance element L and the capacitance element C in the figure.

Ω ² LC = 1 (1) Here, ω is the resonance frequency of the nuclide of the balanced-unbalanced conversion circuit. Further, the impedance Z ₁ of the circuit constituted by the inductance element L and the capacitance element C is obtained by: Z ₁ = ωL / (ω ² LC-1) (2) The condition of the formula (1) is changed to the formula (2). Substituting, Z ₁ = ∞, and no current flows in the outer conductor. Therefore, the balanced-unbalanced conversion circuit 2 shown in FIG. 2 can prevent radiation loss.

FIG. 3 is a diagram showing a state in which the balanced-unbalanced conversion circuit 2 (2 ') shown in FIG. 2 is actually used for the coaxial line 4. The inductance element L in FIG. 2 actually corresponds to the outer conductor of the coaxial line 4.

FIG. 4 shows a plurality of balanced-to-unbalanced conversion circuits 2a, 2 which are composed of the inductance element L and the capacitance element C shown in FIG. 2 and resonate at a desired frequency.
2b ... 2k ... 2n are shown as an example in which the coils 1 and the coaxial line 4 are actually connected in series. In the multi-tuned RF coil 1 having a plurality of resonance frequencies, since there is coupling between the resonance frequencies, a frequency component other than the resonance frequency in the power feeding section is mixed in the coaxial line or the like connected to each power feeding section. I will end up. The mixed frequency component also causes a current to flow through the outer conductor of the coaxial line, leading to radiation loss and deterioration of the sensitivity distribution of the static magnetic field.
It is necessary to connect a, 2b, ... 2k ... 2n. You may connect to an outer conductor like FIG.

FIG. 5 shows another example of the balanced-unbalanced conversion circuit 2 shown in FIG. 4, which is an inductance element L and a capacitance element C.
A plurality of balanced-unbalanced conversion circuits 5a in parallel with the capacitance elements of the balanced-unbalanced conversion circuit 5a.
An example is shown in which b is connected to obtain a desired frequency as a whole. You may connect to an outer conductor like FIG.

FIG. 6 shows another example of the balanced-unbalanced conversion circuit. The balanced-unbalanced conversion circuit 2 covers a specific conductor cylinder 6 on the outer side of the coaxial line, and forms a conductor on the outer side of the coaxial line. Another coaxial circuit is formed. One end insulates the outer conductor cylinder from the outer sheath of the coaxial line, and the other end connects the outer conductor cylinder to the outer sheath conductor of the coaxial line.
At this time, the length of the conductor cylinder is approximately λ / 4 + (n, where λ is a wavelength corresponding to the desired frequency.
−1) λ / 2 (n = 1, 2, 3 ...). The impedance of the outer conductor of the coaxial line with respect to the ground as seen from the power feeding portion is expressed by λ (1/4 + (n-1) / 2) (n) in the well-known equation of the impedance Z at the transmission end of the high-frequency transmission line. =
1, 2, 3 ...) may be substituted. The impedance Z _{2 at the} transmission end of the transmission line is expressed by the following equation (3).

Z ₂ = Z ₀ (Z _r cos (β1) + jZ ₀ sin (β1)) ⁻¹ / (Z ₀ cos (β1) + jZ _r sin (β1)) (3) Z _r = 0, β1 = π / 2 Therefore, Z ₂ = ∞. Therefore, no current flows in the outer conductor. When the whole length is long, it may be used by folding so that the whole length is shortened.

As the balanced-unbalanced conversion circuit 2, L of FIG.
Two examples of the C resonance circuit and the bazooka balun (shbel top) shown in FIG. 6 are given as examples, but a balanced-unbalanced conversion circuit or the like known as a branched conductor or a split coaxial line may also be used. Good.

FIG. 10 is an example showing how to detune the multi-tuning RF coil (n-fold tuning coil in FIG. 10) according to the present invention and supply drive power to the tuning means. As shown in FIG. 115 of the related art, not only is the trap circuit 11, 13a, 13b corresponding to the resonance frequency of the nuclide for driving the detuning and tuning means connected to the power supply line, but also a multiple tuning RF coil different from the resonance frequency is used. It shows an example in which all the trap circuits 8a to 8n corresponding to one resonance frequency are connected. The trap circuits 8a to 8n to be connected are
It may be less than n, or the order of connecting the trap circuits 8a to 8n may be different from that in FIG. In FIG.
A pin diode 9 was used as the detuning and tuning means.

FIG. 11 shows another example of FIG. 10 according to the present invention, in which the variable capacitance diode 10 is used as the detuning and tuning means. FIG. 12 shows an example of the trap circuit. The following relationship is established between the inductance element L _I and the capacitance element C _I in the figure.

Ω ₂ L _I C _I = 1 (4) From the calculation of the impedance of the parallel circuit composed of the inductance L _I and the capacitance element C _{I in the} figure, the driving power of the tuning and detuning means is obtained for the same reason as in FIG. Can be fed without degrading the high frequency magnetic field.

FIG. 13 shows an example of the trap circuit, which is different from the example shown in FIG. In this case, assuming that λ is a wavelength corresponding to a desired high frequency, the length is approximately (λ / 4 + (n-
1) It is configured by short-circuiting one end of the coaxial line 4 of λ / 2).

In FIG. 14, a plurality of parallel circuits each including an inductance element and a capacitance element are connected in parallel to the capacitance element Ca of the trap circuit including the parallel circuit shown in FIG. It is the figure which showed an example of the trap circuit which it has.

In each of the above-mentioned embodiments, R
Although the F coil has been described by taking the multi-tuning RF coil as an example, the F coil is not limited to this and may be a coil composed of a plurality of coils.

[0030]

As described above, according to the present invention, the leakage of high frequency current due to the coupling between the resonance frequencies of the coil is prevented, and it has excellent characteristics in terms of transmission efficiency, stability, etc. Can provide an extremely useful RF coil device for a magnetic resonance apparatus.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a multi-tuning RF coil according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a balanced-unbalanced conversion circuit.

FIG. 3 is a diagram showing a specific configuration of the balanced-unbalanced conversion circuit shown in FIG.

FIG. 4 is a diagram showing an example in which a plurality of balanced-unbalanced conversion circuits in the case of FIG. 2 are connected.

5 is a diagram of another example of FIG. 4 in which the connection method is different from that in FIG.

FIG. 6 is a diagram showing another example of the balanced-unbalanced conversion circuit different from FIG.

FIG. 7 is a circuit diagram of a multi-tuned RF coil.

FIG. 8 is a diagram showing another example of FIG. 7.

FIG. 9 is a diagram showing a configuration of a conventional multituned RF coil.

FIG. 10 is a diagram showing a trap circuit connected to a feed line of a detuning and tuning means of a multi-tuning RF coil according to another embodiment of the present invention.

FIG. 11 is a diagram showing a case where detuning and tuning means is different from FIG. 10 according to another embodiment of the present invention.

12 is a diagram showing an example of the trap circuit shown in FIGS. 10 and 11. FIG.

FIG. 13 is a diagram showing another example of FIG. 12.

FIG. 14 is a diagram showing an example in which a plurality of trap circuits in the case of FIG. 12 are connected.

FIG. 15 is a diagram showing a trap circuit connected to a power feed line of a detuning and tuning means of a conventional multiple tuning coil.

[Explanation of symbols]

 1 ... Multiple tuning coil 2 ... Balanced-unbalanced conversion circuit (balun) 3 ... Duplexer 4 ... Coaxial line 5 ... Resonance circuit 6 ... Conductor cylinder 7 ... Matching circuit 8 ... Trap circuit 9 ... Pin diode 10 ... Variable capacitance diode 11 ... pin diode or variable capacitance diode 12 ... trap circuit 13 ... trap circuit

Claims (12)

[Claims] 1. An RF coil device having at least two resonance frequencies, at least one of applying a high-frequency magnetic field to a subject placed in a static magnetic field and detecting a magnetic field resonance signal from the subject, wherein: An RF for a magnetic resonance apparatus, comprising: a coil; and at least two balanced-unbalanced conversion circuits whose frequencies correspond to the plurality of resonance frequencies between at least one coaxial line connected to the RF coil. Coil device. 2. The balanced-unbalanced conversion circuit is configured to connect a jacket conductor of a coaxial cable and a capacitance element in parallel to form a resonance circuit having a desired frequency. 1. An RF coil device for a magnetic resonance device according to 1. 3. The balanced-unbalanced conversion circuit is configured such that at least one parallel circuit including an inductance element and a capacitance element is connected in series to the capacitance element, and a resonance circuit having a plurality of desired frequencies is formed as a whole. It is comprised, The RF coil apparatus for magnetic resonance devices of Claim 2 characterized by the above-mentioned. 4. The balanced-to-unbalanced conversion circuit has a wavelength λ corresponding to a desired frequency, and is approximately λ outside the coaxial line.
2. A conductor cylinder having a length of / 4 + (n-1) [lambda] / 2 is covered and one end is short-circuited to form a coaxial circuit with the conductor cylinder and the outer conductor of the coaxial line. RF coil device for magnetic resonance apparatus. 5. The RF coil device for a magnetic resonance apparatus according to claim 1, wherein the balanced-unbalanced conversion circuit uses a branched conductor or a split coaxial line. 6. An RF coil device for a magnetic resonance apparatus having at least one resonance frequency, comprising means for detuning or tuning, wherein at least one feed line for supplying power to said means has a frequency An RF coil device for a magnetic resonance apparatus comprising a trap circuit corresponding to at least two resonance frequencies of the plurality of resonance frequencies. 7. The RF coil device for a magnetic resonance apparatus according to claim 6, wherein the detuning or tuning means uses a pin diode or a variable capacitance diode. 8. The RF coil for a magnetic resonance apparatus according to claim 6, wherein the trap circuit comprises a resonance circuit formed by an inductance element and a capacitance element so as to correspond to the plurality of resonance frequencies. apparatus. 9. The trap circuit comprises at least one parallel circuit composed of an inductance element and a capacitance element connected in series to the capacitance element, and is made up of a resonance circuit having a plurality of desired frequencies as a whole. The RF coil device for a magnetic resonance apparatus according to claim 8. 10. The trap circuit has a length of approximately λ / 4 + (n−, where λ is a wavelength corresponding to a desired frequency.
1) A magnetic resonance apparatus R according to claim 6, wherein the coaxial cable is λ / 2 and has one end short-circuited.
F coil device. 11. The multi-tuning RF coil device for a magnetic resonance apparatus according to claim 1, wherein the RF coil comprises a plurality of coils. 12. The multi-tuning RF coil device for a magnetic resonance apparatus according to claim 1, wherein the RF coil is a multi-tuning RF coil having a plurality of coils.