JP2001327477A - Rf coil and magnetic resonance imaging instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an RF coil performing blocking effectively and a magnetic resonance imaging instrument equipped with such an RF coil. SOLUTION: The RF coil comprises a coil loop having a capacitor 302 in which input circuits of low input impedance amplifiers 306 are connected in parallel through a inductor 308. The resonance frequencies of the input circuit of the low input impedance amplifier and a closed circuit consisting of an inductor and a capacitor are shifted to a region lower than the resonance frequency of the coil group.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an RF coil (ra
The present invention relates to a dio frequency coil and a magnetic resonance imaging apparatus, and more particularly, to blocking (blo) for preventing coupling with another coil.
cking) circuit and a magnetic resonance imaging apparatus comprising such an RF coil.

[0002]

2. Description of the Related Art Magnetic resonance imaging (MRI: Magneti)
c Resonance Imaging) device
An object to be imaged is carried into an internal space of a magnet system, that is, a space in which a static magnetic field is formed, a gradient magnetic field and a high-frequency magnetic field are applied to generate a magnetic resonance signal in the object, and a tomographic image is generated based on the received signal. Generate (reconstruct) an image.

An RF coil is used for receiving a magnetic resonance signal. A so-called phased array coil comprising a plurality of coil loops as a receiving RF coil.
Is used, blocking between the coil loops is prevented by a blocking circuit provided in each coil loop, and the SNR (signal-to-nois) of the received signal is used.
eratio) is prevented from lowering.

A blocking circuit is an amplifier having a low input impedance (impedance) (preamplifier: p
The input circuit of the amplifier is connected to a coil loop (coil loop) via an inductor.
loop) in parallel with a capacitor.

The resonance frequency of a closed circuit composed of an input circuit, an inductor, and a capacitor of a preamplifier is tuned to the magnetic resonance frequency, and individual coil loops are blocked by utilizing high impedance due to parallel resonance, and mutual decoupling ( (decoupling).

[0006]

Although the parallel resonance impedance of a closed circuit should theoretically be infinite, the real part of the input impedance of the preamplifier (real part:
(real part), the copper wire resistance of the inductor, the equivalent resistance due to the loss of the capacitor, and the like, the parallel resonance impedance becomes much smaller than the theoretical value, and a sufficient blocking effect cannot always be obtained.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an RF coil that effectively performs blocking and a magnetic resonance imaging apparatus including such an RF coil.

[0008]

Means for Solving the Problems (1) According to one aspect of the invention for solving the above-described problems, an input circuit is connected in parallel to the capacitor via a closed loop having a series capacitor and an inductor. And a low input impedance amplifier, wherein the input circuit of the low input impedance amplifier, the resonance frequency of a closed circuit including the inductor and the capacitor is lower than the resonance frequency of the closed loop, An RF coil characterized in that:

In the invention according to this aspect, the resonance frequency of the closed circuit including the input circuit, the inductor, and the capacitor of the low input impedance amplifier is shifted to a lower frequency side than the resonance frequency of the coil loop. The impedance of the closed circuit viewed from the loop side is
The resonance frequency of the closed circuit can be made higher than that when the resonance frequency of the coil loop is matched. by this,
Decoupling with other coil loops can be made more reliable.

(2) According to another aspect of the present invention, there is provided a closed loop having a series capacitor.
A low input impedance amplifier having an input circuit connected in parallel to the capacitor via an inductor, and an RF coil having a plurality of sets, the closed circuit including the input circuit of the low input impedance amplifier, the inductor and the capacitor. An RF coil, wherein a resonance frequency is lower than a resonance frequency of the closed loop.

In the invention according to this aspect, the resonance frequency of the closed circuit including the input circuit, the inductor, and the capacitor of the low input impedance amplifier is shifted to a lower frequency side than the resonance frequency of the coil loop. With regard to the above, the impedance of the closed circuit viewed from the coil loop side at the time of resonance of the coil loop can be made higher than when the resonance frequency of the closed circuit matches the resonance frequency of the coil loop. Thereby, decoupling between the plurality of coil loops can be further ensured.

(3) According to another aspect of the invention for solving the above-described problem, the imaginary part of the impedance of the input circuit of the low-input impedance amplifier under the closed-loop resonance frequency is positive. The RF coil according to (1) or (2), characterized in that:

In the invention according to this aspect, since the imaginary part of the impedance of the input circuit of the low input impedance amplifier under the resonance frequency of the coil loop is positive, the closed circuit viewed from the coil loop side at the time of resonance of the coil loop. Can be made higher than when the resonance frequency of the closed circuit is made to match the resonance frequency of the coil loop.

(4) According to another aspect of the invention for solving the above-mentioned problem, the inductance of the inductor is larger than a value when the resonance frequency of the closed circuit is made to match the resonance frequency of the closed loop. The RF according to any one of (1) to (3),
Coil.

In the invention according to this aspect, the inductance of the inductor is made larger than the value when the resonance frequency of the closed circuit is made to match the resonance frequency of the coil loop.
The impedance of the closed circuit viewed from the coil loop side at the time of resonance of the coil loop can be made higher than the case where the resonance frequency of the closed circuit matches the resonance frequency of the coil loop.

(5) According to another aspect of the invention for solving the above problem, the capacitance of the capacitor is larger than a value when the resonance frequency of the closed circuit is made to match the resonance frequency of the closed loop. The RF according to any one of (1) to (4), characterized in that:
Coil.

In the invention according to this aspect, the capacitance of the capacitor is made larger than the value when the resonance frequency of the closed circuit is matched with the resonance frequency of the coil loop.
The impedance of the closed circuit viewed from the coil loop side at the time of resonance of the coil loop can be made higher than the case where the resonance frequency of the closed circuit matches the resonance frequency of the coil loop.

(6) According to another aspect of the invention for solving the above-described problem, an image is formed based on a magnetic resonance signal generated inside a target using a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field. A magnetic resonance imaging apparatus, comprising: a closed loop having a series capacitor as an RF coil receiving the magnetic resonance signal; and a low input impedance amplifier having an input circuit connected in parallel to the capacitor via an inductor. An RF coil, comprising: an input circuit of the low input impedance amplifier, an RF coil in which a resonance frequency of a closed circuit including the inductor and the capacitor is lower than a resonance frequency of the closed loop. Magnetic resonance imaging apparatus.

According to the invention from this viewpoint, in the receiving RF coil, the input circuit of the low input impedance amplifier,
The resonance frequency of the closed circuit consisting of the inductor and the capacitor has been shifted to a lower frequency side than the resonance frequency of the coil loop. This can be higher than the case where the resonance frequency is matched with the loop resonance frequency. As a result, decoupling with other coils can be effectively performed, reception with good SNR can be performed, and imaging with good quality can be performed.

(7) According to another aspect of the invention for solving the above problems, an image is formed based on a magnetic resonance signal generated inside a target using a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field. A magnetic resonance imaging apparatus, comprising a plurality of closed loops having a series capacitor as an RF coil for receiving the magnetic resonance signal, and a low input impedance amplifier having an input circuit connected in parallel to the capacitor via an inductor. An RF coil comprising: an input circuit of the low input impedance amplifier, an RF coil in which a resonance frequency of a closed circuit including the inductor and the capacitor is lower than a resonance frequency of the closed loop. This is a magnetic resonance imaging apparatus.

According to the invention from this viewpoint, in the receiving RF coil, the input circuit of the low input impedance amplifier,
Since the resonance frequency of the closed circuit composed of the inductor and the capacitor has been shifted to a lower frequency side than the resonance frequency of the coil loop, the impedance of the closed circuit as viewed from the coil loop side when the coil loop resonates for each of the plurality of coil loops. , The resonance frequency of the closed circuit can be made higher than that in the case where the resonance frequency of the coil loop is matched. Thereby, decoupling between a plurality of coil loops can be effectively performed, and reception with good SNR can be performed.
High quality shooting can be performed.

(8) According to another aspect of the invention for solving the above-mentioned problem, the imaginary part of the impedance of the input circuit of the low-input impedance amplifier under the closed-loop resonance frequency is positive. The magnetic resonance imaging apparatus according to (6) or (7), wherein

In the invention according to this aspect, since the imaginary part of the impedance of the input circuit of the low input impedance amplifier under the resonance frequency of the coil loop is positive, the closed circuit viewed from the coil loop side at the time of resonance of the coil loop. Can be made higher than when the resonance frequency of the closed circuit is made to match the resonance frequency of the coil loop.

(9) According to another aspect of the invention for solving the above-mentioned problem, the inductance of the inductor is larger than a value when the resonance frequency of the closed circuit is matched with the resonance frequency of the closed loop. The magnetic resonance imaging apparatus according to any one of (6) to (8), wherein:

In the invention according to this aspect, the inductance of the inductor is set to be larger than the value when the resonance frequency of the closed circuit is made to match the resonance frequency of the coil loop.
The impedance of the closed circuit viewed from the coil loop side at the time of resonance of the coil loop can be made higher than the case where the resonance frequency of the closed circuit matches the resonance frequency of the coil loop.

(10) According to another aspect of the invention for solving the above-mentioned problems, the capacitance of the capacitor is as follows:
The magnetic resonance imaging apparatus according to any one of (6) to (9), wherein the resonance frequency of the closed circuit is larger than a value when the resonance frequency of the closed circuit is matched with the resonance frequency of the closed loop. .

In the invention according to this aspect, the capacitance of the capacitor is made larger than the value when the resonance frequency of the closed circuit is made to match the resonance frequency of the coil loop.
The impedance of the closed circuit viewed from the coil loop side at the time of resonance of the coil loop can be made higher than the case where the resonance frequency of the closed circuit matches the resonance frequency of the coil loop.

[0028]

Embodiments of the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiment. FIG. 1 shows a block diagram of the magnetic resonance imaging apparatus. This device is an example of an embodiment of the present invention. The configuration of the present apparatus shows an example of an embodiment relating to the apparatus of the present invention.

As shown in FIG. 1, the present apparatus has a magnet system 100. The magnet system 100 includes the main magnetic field magnet unit 1
02, a gradient coil unit 106 and an RF coil unit 108. Each of the main magnetic field magnet section 102 and each coil section is composed of a pair facing each other across a space. In addition, each has a substantially disk-shaped outer shape and is arranged so as to share a central axis. Magnet system 1
The object 300 is mounted on the cradle 500 in the internal space of 00, and is carried in and out by carrying means (not shown).

The cradle 500 has a receiving coil unit 110
Is provided. The receiving coil unit 110 has a substantially cylindrical shape, and is installed on the upper surface of the cradle 500. The target 300 is mounted on the cradle 500 in a posture in which the head is put into the cylinder of the receiving coil unit 110 and the patient 300 is in a supine position.

Hereinafter, in the receiving coil unit 110, the target 3
The parietal side of 00 is called up and the neck side is called down. Object 3
The face side of 00 is called the front and the back of the head is called the back. Also,
The left and right when the object 300 is viewed from below is the receiving coil unit 11
They are called left and right of 0.

The receiving coil section 110 is an example of an embodiment of the RF coil of the present invention. An example of an embodiment relating to the RF coil of the present invention is shown by the configuration of the present coil. The receiving coil unit 110 will be described later.

The main magnetic field magnet section 102 forms a static magnetic field in the internal space of the magnet system 100. The direction of the static magnetic field is orthogonal to the body axis direction of the object 300. That is, a so-called vertical magnetic field is formed. The main magnetic field magnet unit 102 is configured using, for example, a permanent magnet. It is needless to say that the present invention is not limited to the permanent magnet and may be configured using a superconducting electromagnet or a normal conducting electromagnet.

The gradient coil section 106 generates a gradient magnetic field for giving a gradient to the static magnetic field strength. The generated gradient magnetic fields are a slice gradient magnetic field, a readout gradient magnetic field, and a phase encode gradient magnetic field. The gradient coil unit 1 corresponds to these three types of gradient magnetic fields.
Reference numeral 06 has three gradient coils (not shown).

The RF coil unit 108 controls the object 3 in the static magnetic field space.
The RF excitation signal for exciting the spins in the body of 00 is transmitted. The receiving coil unit 110 receives a magnetic resonance signal generated by the excited spin.

The gradient coil unit 106 includes a gradient driving unit 130
Is connected. The gradient driving unit 130 is a gradient coil unit 1
A drive signal is given to 06 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 106.

The RF coil unit 108 includes an RF driving unit 140
Is connected. The RF driving unit 140 is the RF coil unit 1
08, a drive signal is given, an RF excitation signal is transmitted, and the target 3
Excite the spins in the body of 00.

The receiving coil unit 110 includes the data collecting unit 15
0 is connected. The data collection unit 150 captures a reception signal received by the reception coil unit 110 and collects the received signal as digital data.

A control unit 160 is connected to the gradient drive unit 130, the RF drive unit 140, and the data collection unit 150. The control unit 160 controls the gradient driving unit 130 to the data collection unit 150, respectively.

The data processing unit 170 includes the data collection unit 15
The data taken from 0 is stored in the memory. A data space is formed in the memory. The data space is two-dimensional
It constitutes a Fourier space. The data processing unit 170 performs two-dimensional inverse Fourier transform on the data in the two-dimensional Fourier space to generate an image of the target 300 (reconstruction).
I do. Two-dimensional Fourier space is converted to k-space (k-spac
Also referred to as e).

The data processing section 170 is connected to the control section 160. The data processing unit 170 is at a higher level than the control unit 160 and controls it. The display section 180 and the operation section 190 are connected to the data processing section 170. The display unit 180 includes a graphic display (graphic).
display). The operation unit 190 is a pointing device.
e) is composed of a keyboard provided with e).

The display section 180 displays the reconstructed image output from the data processing section 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.

FIG. 2 shows an example of a pulse sequence used for magnetic resonance imaging. This pulse sequence is a pulse sequence based on a gradient echo (GRE) method.

That is, (1) is the RF in the GRE method.
A sequence of α ° pulses for excitation, (2)
(3), (4) and (5) are the sequences of the slice gradient Gs, readout gradient Gr, phase encode gradient Gp and gradient echo MR, respectively. The α ° pulse is represented by the center signal.
The pulse sequence proceeds from left to right along the time axis t.

As shown in the figure, α ° excitation of spin is performed by an α ° pulse. Flip angle (flip
angle) α ° is 90 ° or less. At this time, a slice gradient Gs is applied, and selective excitation for a predetermined slice is performed.

After α ° excitation, the phase encode gradient Gp
Performs phase encoding of the spin. next,
The spin is first dephased by the readout gradient Gr, and then the spin is rephased (r
ephase) to generate a gradient echo MR. The signal strength of the gradient echo MR is α °
It becomes maximum at the time point after the echo time (echo time) TE from the excitation. The gradient echo MR is collected by the data collection unit 150 as view data.

Such a pulse sequence has a period TR
(Repetition time) is repeated 64 to 512 times. The phase encoding gradient Gp is changed for each repetition, and a different phase encoding is performed each time. As a result, view data of 64 to 512 views filling the k space is obtained.

FIG. 3 shows another example of the pulse sequence for magnetic resonance imaging. This pulse sequence is a pulse sequence of a spin echo (SE: Spin Echo) method.

That is, (1) is a sequence of 90 ° and 180 ° pulses for RF excitation in the SE method, and (2), (3), (4) and (5) are slice gradients, respectively. Gs, readout gradient G
r, phase encoding gradient Gp and spin echo M
This is a sequence of R. Note that a 90 ° pulse and 18
Each 0 ° pulse is represented by a center signal. The pulse sequence proceeds from left to right along the time axis t.

As shown in the figure, 90 ° excitation of spin is performed by a 90 ° pulse. At this time, the slice gradient G
s is applied to perform selective excitation for a predetermined slice. After a predetermined time from the 90 ° excitation, 180 ° excitation by a 180 ° pulse, that is, spin inversion is performed. Also at this time, the slice gradient Gs is applied, and selective inversion is performed for the same slice.

During the period between the 90 ° excitation and the spin inversion, the readout gradient Gr and the phase encode gradient Gp
Is applied. The spin dephase is performed by the readout gradient Gr. The phase encoding of the spin is performed by the phase encoding gradient Gp.

After the spin inversion, the spin is rephased with the readout gradient Gr to generate a spin echo MR.
The signal intensity of the spin echo MR becomes maximum at a point after TE from the 90 ° excitation. The spin echo MR is collected by the data collection unit 150 as view data. Such a pulse sequence is repeated 64 to 512 times in the period TR. Phase encoding gradient Gp for each iteration
And perform different phase encoding each time. As a result, view data of 64 to 512 views filling the k space is obtained.

The pulse sequence used for photographing is G
The method is not limited to the RE method or the SE method.
E (Fast Spin Echo) method, Fast Recovery FSE (Fast Recovery Fast)
Spin Echo method, Echo Planar Imaging (EPI: Echo Planar Imaging)
g) or any other suitable technique.

The data processing unit 170 reconstructs a tomographic image of the object 300 by performing two-dimensional inverse Fourier transform on the view data in the k space. The reconstructed image is stored in the memory and displayed on the display unit 180.

As will be described later, since the receiving coil section 110 is a phased array coil having an effective blocking circuit, it can receive a magnetic resonance signal with a good SNR, and based on such a received signal. A high quality reconstructed image can be obtained.

FIG. 4 is a perspective view showing a schematic configuration and arrangement of a coil loop included in the receiving coil unit 110. In the figure, x, y, and z are the left-right direction, the front-back direction, and the up-down direction of the object 300, respectively.

As shown in FIG.
Has upper coils 802, 804, 806 and lower coils 902, 904, 906, 908. Upper coils 802, 804, 806 and lower coils 902, 9
04, 906 and 908 are, for example, one turn (tu)
rn) and are arranged at predetermined intervals in the z direction. It should be noted that the coil loop is not limited to one turn, but may be an appropriate plurality of turns.

The main sensitivity direction of these coils is the z direction. These coils each have a blocking circuit to be described later, and perform electromagnetic coupling (coupling).
So-called phased array coil (phase
d array coil).

The upper coils 802, 804, and 806 are provided at positions substantially surrounding the head of the object 300 in the forehead. Although the upper coils 802, 804, and 806 are shown as three coil loops, the number is not limited thereto, and may be an appropriate number of coil loops. Upper coil 802,
The loop length of 804, 806 is 300
Slightly longer than the circumference of the head.

Lower coils 902, 904, 906, 90
Reference numeral 8 is provided at a position surrounding the head of the subject 300 in a portion below the nose. Lower coil 902, 904, 9
Although 06 and 908 are shown as four coil loops, the number is not limited thereto and may be an appropriate number of coil loops. The lower coils 902, 904, 906, and 908 form a loop partially projecting in the y-direction corresponding to the ridge of the nose. The length of the loop is slightly longer than the circumference of the head of the subject 300 at the nose.

FIG. 5 shows an electric circuit of a unit coil constituting a phased array coil. As shown in the figure, the unit coil is formed by connecting a capacitor 302 and a conductor 304 in series. Note that one or more other capacitors may be provided in the middle of the conductor 304 as necessary.

An input circuit of a preamplifier 306 for amplifying a magnetic resonance signal received by a unit coil is connected to both ends of the capacitor 302 through an inductor 308.
The capacitance of the capacitor 302 (capasita)
nce) and the inductance of the inductor 308 (ind)
tune) is tuned to the magnetic resonance frequency. As the preamplifier 306, an amplifier whose input circuit has sufficiently low impedance, that is, a low input impedance amplifier is used.

The preamplifier 306 is an embodiment of the low input impedance amplifier according to the present invention. The inductor 308 is an example of an embodiment of the inductor according to the present invention. The capacitor 302 is an example of the embodiment of the capacitor according to the present invention.

FIG. 6 shows an electrical connection diagram of the input circuit portion of the preamplifier 306. As shown in the drawing, an FET (Field E), which is an amplifying element at the first stage of the preamplifier 306, is used.
An input signal is supplied through an inductor 364 to a gate of an FFT (transistor) 362. The connection point between the inductor 364 and the gate is grounded through a variable capacitor 366.
d).

Here, since the input impedance of the gate of the FET 362 is extremely high, the input impedance Zin of the preamplifier 306 is given by the series impedance of the LC circuit including the inductor 364 and the capacitor 366. Such a series circuit of the input impedance Zin and the inductor 308 forms the capacitor 30 of the coil loop.
2 are connected in parallel to form a blocking circuit.

FIG. 7 shows an equivalent circuit of the blocking circuit. As shown in FIG.
, The inductance L of the inductor 308 and its resistance R, and the input impedance Zin of the preamplifier 306 are connected in series.

Assuming that a current having a frequency corresponding to the magnetic resonance frequency flows through this closed circuit, the impedance of the closed circuit viewed from the coil loop side is expressed by the following equation.

[0068]

(Equation 1)

Here, ω: angular frequency of current flowing through the closed circuit Zin (Re): real part of Zin (real part: real
l part) Zin (Im): Imaginary part of Zin (imaginary part: i
FIG. 8 shows a change in Z1 with respect to a change in Zin (Im) by a solid line. Note that the broken line is a change in Z1 in an ideal case where the resistance R and Zin (Re) are 0, and is shown for comparison.

In an actual circuit, resistors R and Zin (R
Since e) is not 0, as shown in the figure, Z1 does not become maximum when Zin (Im) = 0 as in the ideal case, but becomes maximum when Zin = a. a is a positive value.

That is, when the imaginary part of the input impedance of the preamplifier 306 takes a positive value, in other words, the imaginary part of the input impedance becomes inductive (inductive) of the blocking circuit.
It is maximum when e).

Therefore, the capacitor 366 of the input circuit of the preamplifier 306 is adjusted so that the condition of Zin (Im) = a is satisfied. As a result, the maximum value of Z1 is obtained, and the blocking circuit exhibits the highest blocking performance possible in the circuit configuration.

By making Zin (Im) of the preamplifier 306 inductive, the resonance frequency of the blocking circuit is shifted from the resonance frequency of the coil loop to the lower side. Therefore, the above adjustment corresponds to shifting the resonance frequency of the blocking circuit from the resonance frequency of the coil loop to the lower frequency side.

The same effect can be obtained by replacing or in addition to adjusting Zin (Im).
May be achieved by increasing the inductance of.

Further, instead of or in addition to the adjustment of Zin (Im), the capacitor 302 of the coil loop
May be realized by increasing the capacitance of. However, in that case, it is necessary to adjust another capacitor in the coil loop in order to prevent a change in the resonance frequency of the coil loop. Furthermore, Zin (I
m), the adjustment of the inductor 308 and the capacitor 302 may all be performed.

By configuring each of the upper coils 802, 804, 806 and the lower coils 902, 904, 906, 908 as such, they are not coupled to each other, and are equivalent to being independently provided. . That is, it is possible to obtain a receiving coil unit that effectively operates as a phased array coil. Also, R
Decoupling with the F coil unit 108 is also effectively performed. Thereby, a magnetic resonance signal can be received with a good SNR.

The phased array coils are not limited to those arranged coaxially as described above. For example, as shown in FIG.
02 to 710 may be arranged with the main sensitivity direction facing upward.

This is a surface coil for a magnetic resonance imaging apparatus using a so-called horizontal magnetic field in which the direction of the static magnetic field is parallel to the body axis of the object 300.
It is suitable as 1). The shape of the coil loop may be a rectangle as shown, a circle as described above, an ellipse, an ellipse, or an appropriate polygon.

It goes without saying that the coil loop may be used as a single coil without forming a phased array. In this case, it becomes a receiving coil that effectively decouples the RF coil unit 108 and other coils.

[0080]

As described above in detail, according to the present invention, it is possible to realize an RF coil that effectively performs blocking and a magnetic resonance imaging apparatus including such an RF coil.

[Brief description of the drawings]

FIG. 1 is a block diagram of a device according to an example of an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a pulse sequence executed by the device shown in FIG.

FIG. 3 is a diagram illustrating an example of a pulse sequence executed by the device illustrated in FIG. 1;

FIG. 4 is a schematic diagram showing a coil arrangement of a receiving coil unit in the device shown in FIG.

FIG. 5 is a circuit diagram of the coil shown in FIG. 4;

6 is a diagram showing an input circuit portion of the preamplifier shown in FIG.

FIG. 7 is a diagram showing an equivalent circuit of a blocking circuit.

FIG. 8 is a graph showing impedance characteristics of a blocking circuit.

FIG. 9 is a diagram showing a schematic configuration of a phased array coil.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 magnet system 102 main magnetic field magnet unit 106 gradient coil unit 108 RF coil unit 110 reception coil unit 130 gradient drive unit 140 RF drive unit 150 data collection unit 160 control unit 170 data processing unit 180 display unit 190 operation unit 300 target 302 capacitor 304 Conductor 306 Preamplifier 308 Inductor 362 FET 366 Capacitor 364 Inductor 500 Cradle 802,804,806 Upper coil 902,904,906,908 Lower coil

Claims (10)

[Claims] An R comprising: a closed loop having a series capacitor; and a low input impedance amplifier having an input circuit connected in parallel to the capacitor via an inductor.
An RF coil, comprising: an F coil, wherein a resonance frequency of a closed circuit including the input circuit of the low input impedance amplifier, the inductor, and the capacitor is lower than a resonance frequency of the closed loop. 2. An RF coil having a plurality of sets of a closed loop having a series capacitor and a low input impedance amplifier having an input circuit connected in parallel to the capacitor via an inductor, wherein the low input impedance amplifier comprises: An RF coil, wherein a resonance frequency of a closed circuit including an input circuit, the inductor, and the capacitor is lower than a resonance frequency of the closed loop. 3. The RF coil according to claim 1, wherein an imaginary part of an impedance of an input circuit of the low input impedance amplifier under the closed loop resonance frequency is positive. 4. The inductor according to claim 1, wherein an inductance of the inductor is larger than a value when the resonance frequency of the closed circuit is made to coincide with the resonance frequency of the closed loop. RF described in one
coil. 5. The capacitance of the capacitor according to claim 1, wherein the capacitance of the capacitor is larger than a value when the resonance frequency of the closed circuit is made to match the resonance frequency of the closed loop. RF described in one
coil. 6. A magnetic resonance imaging apparatus for forming an image based on a magnetic resonance signal generated inside a subject using a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field, wherein the RF coil receives the magnetic resonance signal R having a closed loop having a series capacitor, and a low input impedance amplifier having an input circuit connected in parallel to the capacitor via an inductor.
An RF coil, wherein a resonance frequency of a closed circuit including the input circuit of the low input impedance amplifier, the inductor, and the capacitor is lower than a resonance frequency of the closed loop.
A magnetic resonance imaging apparatus comprising a coil. 7. A magnetic resonance imaging apparatus for forming an image based on a magnetic resonance signal generated inside a subject using a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field, wherein the RF coil receives the magnetic resonance signal An RF coil having a plurality of sets of a closed loop having a series capacitor, and a low input impedance amplifier having an input circuit connected in parallel to the capacitor via an inductor, wherein an input circuit of the low input impedance amplifier, RF in which the resonance frequency of the closed circuit including the inductor and the capacitor is lower than the resonance frequency of the closed loop.
A magnetic resonance imaging apparatus comprising a coil. 8. The magnetic resonance imaging according to claim 6, wherein the imaginary part of the impedance of the input circuit of the low input impedance amplifier under the closed loop resonance frequency is positive. apparatus. 9. The method according to claim 6, wherein the inductance of the inductor is larger than a value when the resonance frequency of the closed circuit is made to match the resonance frequency of the closed loop. A magnetic resonance imaging apparatus according to any one of claims 1 to 3. 10. The capacitance of the capacitor is:
The magnetic resonance imaging apparatus according to any one of claims 6 to 9, wherein the resonance frequency of the closed circuit is larger than a value when the resonance frequency is made to match the resonance frequency of the closed loop.