JPH0686769A - Magnetic resonance video system - Google Patents

Abstract

PURPOSE:To prevent coupling to a transmitting coil and a gradient magnetic field coil, and to obtain a reconstitution image whose picture quality is not deteriorated by connecting electrical middle points of each coil electrically or like a high-frequency through a cutting-off circuit, in the case a bridge circuit is used for decoupling between adjacent surface coils. CONSTITUTION:This system is provided with a means 1 for applying a static magnetic field to an examinee 3, a means 4 for applying a prescribed gradient magnetic field to the examinee, a uniform coil 10 which is arranged in the outside of the examinee and applies a high-frequency magnetic field to the examinee, plural pieces of surface coils 11 which are arranged in the inside of the uniform coil, based on the examines as a reference, provided with a pair of floating capacities of equal capacitance connected in series, and detect a magnetic resonance signal generated from the examinee, and an electronic computer 14 for executing an imaging processing, based on the detected magnetic resonance signal. Also, plural pieces of surface coils 11 set a connecting middle point of the pair of floating capacities as a high-frequency-like ground point, and each high-frequency-like ground point is connected through an electrical or high-frequency-like shielding part 29.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging apparatus, and more particularly to a magnetic resonance imaging apparatus capable of obtaining an image with a high S / N ratio by using a surface coil.

[0002]

2. Description of the Related Art A magnetic resonance imaging apparatus resonantly absorbs the energy of a high frequency magnetic field rotating at a specific frequency when a group of nuclei having a unique magnetic moment is placed in a uniform static magnetic field. It is a method of visualizing chemical and physical microscopic information of a substance by utilizing a phenomenon. Regarding ¹ H, for imaging a stationary or slow-moving part,
It also provides clinically good images.

However, recently moving parts (heart, etc.)
For high-speed imaging (imaging time ~ 50 ms) and nuclides other than ¹ H ( ³¹ P, ¹⁹ F, ¹³ C,
There is an increasing demand for imaging (eg, ²³ N). Improvement of the S / N ratio is an important issue in these imaging techniques. For example, in the case of high speed imaging, S /
The decrease in S / N ratio due to the decrease in N ratio and the increase in gradient magnetic field can be mentioned. With regard to the imaging of ³¹ P, the S / N ratio due to the extremely small amount of abundance in the body, such as 10 ^{−4 of 1} H. There is a decrease in the ratio.

As one means for improving the S / N ratio,
Imaging using a surface coil as a receiving coil has been conventionally performed. The surface coil is installed in close contact with a region of interest of the subject and detects signals around the close region with a high S / N ratio. However, there is a defect that only an image around the close contact portion can be obtained, and an image with a high S / N ratio cannot be obtained over the entire desired region of the subject. There is also a method of sequentially changing the arrangement of a single surface coil and synthesizing the obtained images to obtain an image of the entire desired region of the subject, but each time the surface coil is changed. There is a drawback in that adjustment of the device is required, which makes the work complicated and takes time.

Therefore, for example, in US Pat. No. 4,825,162, a plurality of surface coils are arranged in a desired region of a subject to be imaged, and magnetic resonance from the subject is detected through the plurality of surface coils. After each signal is detected and each detected magnetic resonance signal is imaged to generate multiple series of image data, pixel data corresponding to the same spatial position is generated by the high frequency generated by each surface coil. Data of each pixel is created by multiplying and adding a predetermined weighting function based on the distribution of the magnetic field, and by combining them, an image with a high S / N ratio of the entire desired region of the subject is obtained. Is disclosed. In order to avoid the influence of the coupling between the surface coils adjacent to each other, the surface coils adjacent to each other are overlapped to perform decoupling of the two.

However, in this decoupling method, as compared with the case where an image of a desired region of the subject is obtained without overlapping, the correlation between the noises becomes large because the distance between the coils is close, and the decoupling is performed. Noise is increased in the reconstructed image. Therefore, if superposition is used for decoupling between adjacent surface coils in this way, S / N
There is a problem that the ratio deteriorates. Moreover, a large number of coils are required to cover the desired area of the subject.

Therefore, as a method of decoupling without adjoining the adjacent surface coils, FIG.
A method using a bridge circuit as shown in (a), (b) or FIGS. 11 (a), (b) is known. This method solves the above problem, but in order to achieve accurate decoupling and adjustment between the surface coils, the connecting midpoints of the series-connected stray capacitance pairs of equal capacitance of each surface coil ( Hereinafter, the "electrical midpoint") is used as a high-frequency ground point provided at one point of the surface coil, and it is necessary to connect each of them with a conductor such as a copper plate or a conductor.

In FIG. 21, a differential coil is used as the surface coil 111, and an outer conductor 117 'of a coaxial cable 117 that guides a signal to the preamplifier 118 is connected by a conductor 119, and the electrical midpoint of each surface coil 111 is connected. This is the case when connected. In addition, the code | symbol 120 has shown the decoupling device. However, in this case, as shown by the broken line a,
A high-frequency loop connecting the electrical midpoints is created, which causes the subject to be coupled with a uniform coil outside the surface coil and deteriorate the reconstructed image.

Further, when the surface coil 111 is arranged on the circumference as shown in FIG. 22, in addition to the above-mentioned high frequency loop, a DC loop shown by a broken line b is also formed on the circumference. , Causing coupling with gradient field coils,
Eddy current is generated in the loop of the broken line b, and the reconstructed image is deteriorated.

[0010]

As described above, when the bridge circuit is used for decoupling between the adjacent surface coils, the electrical midpoint of each surface coil is used for accurate decoupling and adjustment. Must be connected, and the loop formed by this connection causes coupling with the uniform coil and the gradient magnetic field coil, which deteriorates the reconstructed image.

In view of the above points, in the present invention, when a bridge circuit is used for decoupling between adjacent surface coils, coupling with a uniform coil or a gradient magnetic field coil can be prevented, and image quality is not deteriorated. An object of the present invention is to provide a magnetic resonance imaging apparatus capable of obtaining a reconstructed image.

[0012]

In order to solve the above-mentioned problems, the present invention provides a means for applying a static magnetic field to a subject, a means for applying a gradient magnetic field pulse to the subject, and an imaging of the subject. A uniform coil for applying a substantially uniform high-frequency magnetic field in a desired region to be desired, and the gradient in the static magnetic field applied by means for applying the static magnetic field, the gradient being arranged inside the uniform coil for generating the high-frequency magnetic field The magnetic resonance signal generated from the subject is detected by applying a magnetic field pulse and the high-frequency magnetic field, and a plurality of surface coils having a stray capacitance pair of equal capacitances connected in series, and the stray capacitance element pair. Is the high frequency ground point of the surface coil, and the high frequency ground points of the respective surface coils are connected via an electrical or high frequency cut-off portion. And the step, there is provided a magnetic resonance imaging apparatus and means for performing image processing on the basis of magnetic resonance signals detected by the surface coils.

[0013]

[Operation] When a bridge circuit is used for decoupling between adjacent surface coils as described above, by connecting the electrical midpoint of each coil through an electrical or high frequency cutoff circuit, Coupling with the gradient magnetic field coil can be prevented, and a reconstructed image without image quality deterioration can be obtained.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the magnetic resonance imaging apparatus of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a magnetic resonance imaging apparatus according to an embodiment of the present invention.

In FIG. 1, the static magnetic field magnet 1 is excited by the excitation power source 2 and applies a uniform static magnetic field to the subject 3. The gradient magnetic field coil 4 is driven by the drive circuit 6 controlled by the system controller 5, and the magnetic field strength of the subject 3 on the bed 7 changes linearly in the X, Y, and Z directions orthogonal to each other. Gradient magnetic field Gx, G
Apply y and Gz. Under the control of the system controller 5, the subject 3 is further applied with a high-frequency magnetic field generated by applying a high-frequency signal from the transmitter 8 through the duplexer 9 to the uniform coil 10, which is a coil for both transmission and reception. It

As shown in FIG. 2, a surface coil 11 serving as a signal detecting coil is arranged inside the uniform coil 10 in the vicinity of the subject 3. Then, the uniform coil 10 and the surface coil 11 receive the magnetic resonance signal from the subject 3. The signal received by the uniform coil 10 is guided to the receiving unit 12 via the duplexer 9. On the other hand, the signal received by the surface coil 11 is directly guided to the receiving unit 12. The duplexer 9 is for switching the uniform coil 10 between transmission and reception, transmits a high-frequency signal from the transmission unit 8 to the uniform coil 10 at the time of transmission, and receives a reception signal from the uniform coil 10 at the time of reception. It serves to lead to the receiving unit 12. The magnetic resonance signal guided to the receiving unit 12 is amplified and detected, and then under the control of the system controller 5,
It is sent to the data collection unit 13. The data collection unit 13 collects the magnetic resonance signals input under the control of the system controller 5, performs A / D conversion, and then sends the signals to the electronic computer 14. The computer 14 is controlled by the console 15,
Image reconstruction processing of the magnetic resonance signal input from the data acquisition unit 13 is performed, the image data obtained from each of the surface coils 11 is weighted and added, and one image data is combined. It also reconstructs the image of the uniform coil 10 and controls the system controller 5. The image data obtained by the electronic computer 14 is transmitted to the display 16 and the image is displayed.

FIG. 3 shows details of the receiving section 12 and the data collecting section 13 in FIG.

A preamplifier 18 and a detection circuit (DET) 21 corresponding to the uniform coil 10 and the surface coil 11, respectively.
Further, a signal detecting means including a low pass filter (LPF) 22 is provided. In the data collecting unit 13, the receiving unit 1
The detected signal of the magnetic resonance signal inputted from 2 is converted into a digital signal by the A / D converter 23, and then is taken into the electronic computer 14 through the interface 24.

FIG. 4 is a schematic view showing the structure and arrangement of the surface coil 11. The surface coils 11 are each connected to a preamplifier 18 via a signal cable 17 such as a coaxial cable,
Further, it is connected to the receiving unit 12 via the preamplifier 18. The outer conductor 17 'of each signal cable 17 is connected via a trap circuit 29 at a high frequency by a conductor 19 such as a copper plate. A detailed view of the trap circuit 29 is shown in FIG.

In FIG. 5,

[Equation 1] The values of L and C are determined so as to satisfy. By turning off the PIN diode 27 at the time of receiving the signal of the surface coil, the electrical midpoint of each surface coil is connected in a high frequency manner. When tuning and transmitting the uniform coil 10 that does not receive a signal, the PIN diode 27 is turned on. At this time, since the circuit of L-C resonates, both ends of C are in a high impedance state, and as a result, it becomes difficult for a high-frequency current to flow in the loop of the broken line a in FIG. The coupling with can be prevented. Although FIG. 4 shows the case where the electric midpoint of each surface coil is connected by the outer conductor of the signal cable, the case where the preamplifier 18 is connected by the conductive frame is also connected through the trap circuit 29 of FIG. . Further, when the electric midpoint of each surface coil is directly connected by the conductor 19 as shown in FIG. 6,
With respect to the loop indicated by the broken line a as shown in FIG. 4, the number of interlinkages of the high frequency magnetic field generated by the uniform coil 10 is almost negligible. However, only when the surface coils 11 are circumferentially arranged, it is necessary to use the following connection method of the second embodiment.

Next, a second embodiment according to the present invention will be described. This embodiment is an embodiment in which the surface coils 11 are circumferentially arranged.

FIG. 7 shows a structure in which six surface coils 11 are arranged in a circumferential shape. In this case, in addition to the loop of the broken line a, a loop of the circular broken line b is formed by the conductor 19 connecting the electrical midpoints of the surface coils 11. Since the loop of the broken line b is perpendicular to the magnetic field generated by the gradient magnetic field coil 4, it causes coupling with the gradient magnetic field coil 4. However, in this case as well, the electric midpoint of each surface coil 11 is connected via the trap circuit 29 as shown in FIG. Can prevent the coupling. Further, since the loop of the broken line b is always cut off in terms of direct current, it is decoupled from the gradient magnetic field coil 4 and no eddy current is generated.

When the electrical midpoint of each surface coil 11 is directly connected, the coupling with the uniform coil can be almost ignored. Therefore, instead of the trap circuit 29 as shown in FIG. 5, a capacitor as shown in FIG. It suffices that the electric midpoint of each surface coil 11 is connected via the, and the loop of the broken line b is cut off in terms of direct current.

Since the uniform coil 10 and the surface coil 11 are arranged close to each other, decoupling between both coils is required. FIG. 9 is a principle diagram for decoupling both the uniform coil 10 during transmission and the surface coil 11 during reception. The surface coil 11 is composed of a differential type coil in which a pair of coils 11a and 11b of the same type are provided so as to face each other and are electrically connected so that currents in opposite directions flow. Therefore, uniform coil 1
When a spatially uniform high-frequency magnetic field H generated by 0 interlinks, equal electromotive forces tend to be generated in the coils 11a and 11b that are placed opposite to each other, but they cancel each other out and no high-frequency current flows in the surface coil 11. . Therefore, if the uniform coil 10 generates a spatially uniform high-frequency magnetic field H in the space in which the surface coil 11 of the differential coil is arranged, the coupling between the uniform coil 10 and the surface coil 11 does not occur.

The decoupling between the adjacent surface coils 11 is performed between the surface coils 11 as described above.
This is performed by adding a decoupling circuit (bridge circuit) as shown in (a), (b) or FIGS. 11 (a), (b).

Next, a decoupling method between surface coils that are not adjacent to each other will be described. The coupling between the non-adjacent surface coils 11, 11 is such that the adjacent surface coils 1
Since it is less than the coupling between 1 and 11, decoupling is sufficient focusing on the fact that the effect of coupling can be suppressed by lowering the apparent Q without using a precise decoupling method. . Specifically, a Q dump circuit described below may be added to each of the surface coils 11. FIG. 12 shows an equivalent circuit when the Q dump circuit is used. In FIG. 12, the surface coil 11 is assumed to resonate at a specific frequency f ₀ with the inductance L and the capacitance C. The parallel resistance Rp represents the impedance of the surface coil 11 in the resonance state, and is expressed as follows using the Q value.

[0028]

[Equation 2] The inverting input terminal and the non-inverting input terminal of the amplifier 25 having a gain of K are connected to both ends of the surface coil 11, and the feedback resistor 26 is provided between the output terminal and the inverting input terminal of the amplifier 25.
(Resistance value Rf) is connected, and the output terminal and the non-inverting input terminal of the amplifier 25 are used as external connection terminals. As the amplifier 25, for example, the preamplifier 18 shown in FIG. 3 is used. The surface coil 11 of FIG. 12, the amplifier 25, and the feedback resistance (resistance value = R
The Q dump circuit consisting of f) 26 is represented by the equivalent circuit shown in FIG.

The resistor Rd in FIG. 13 is

[Equation 3] Given in. Therefore, if the gain K of the amplifier 25 is made sufficiently large, Rp >> Rd and the impedance at both ends becomes low. This reduces the apparent Q and enables decoupling.

Next, the image forming procedure in this embodiment will be specifically described. Imaging methods using surface coils are disclosed in U.S. Pat. No. 4,825,162 and JP-A-2-47814. FIG. 14 shows an imaging sequence for obtaining a two-dimensional image as an example. This imaging sequence is a pulse sequence for obtaining a two-dimensional image by a known spin echo method using a 90 ° pulse-180 ° pulse as a high frequency magnetic field (high frequency pulse).
s represents a gradient magnetic field in the slice direction, Gr represents a gradient magnetic field in the read direction, and Ge represents an application timing of the gradient magnetic field in the encode direction. As shown in FIG. 14, magnetic resonance signals are collected while changing the amplitude of the encoding gradient magnetic field Ge. The uniform coil 10 is used to apply the high-frequency pulse, and the uniform coil 10 and all the surface coils 11 are used to receive the magnetic resonance signals. The magnetic resonance signal detected by the receiving unit 12 via the uniform coil 10 and the surface coil 11 is taken into the electronic computer 14 as image reconstruction data via the data collecting unit 13, and the two-dimensional image is stored in the electronic computer 14. The image is reconstructed by the Fourier transform. In the present embodiment, the surface coil 11 simultaneously detects magnetic resonance signals in the process of image reconstruction and imaging processing is performed. Unlike the present embodiment, when the number of circuits forming the receiving unit is limited and the number of surface coils is less than the number of surface coils, the surface coils are switched by a control signal from the system controller 5 to perform imaging processing a plurality of times. Such a method may be used. By this image reconstruction, 1-channel image data obtained through the uniform coil 10 and multi-channel image data obtained through each surface coil 11 are obtained. Then, the image data of a plurality of channels obtained via the surface coil 11 is
Image data of one image is combined by weighting with a predetermined weighting function so that the S / N ratio becomes maximum. Since the weighting function is represented by the function of the high frequency magnetic field distribution of each surface coil as shown in the above-mentioned known technique, it is necessary to obtain the high frequency magnetic field distribution of each surface coil 11. Hereinafter, how to obtain it will be described.

First, the uniform coil 10 and the surface coil 11
The phase correction of the image data respectively obtained through is performed. Here, it is assumed that an image as shown in FIG. 15 is obtained using the uniform coil 10. The thick line in FIG. 15 is the uniform coil 10.
And the broken line indicate the position of the surface coil 11.
The histogram of the image on the line A is shown in FIG. 16 (a), and the histogram corresponding to the same position in the image obtained by the surface coil 11a is shown in FIG. 16 (b). FIG.
In (a) and (b), the horizontal axis represents the position and the vertical axis represents the signal intensities St and Ss in the respective images.
According to FIG. 16 (b), it can be seen that the image obtained by the surface coil 11 becomes less sensitive as it moves away from the surface coil 11. When the S / N ratio of the image is poor, it is desirable to appropriately perform smoothing processing such as moving average.

Next, the signal intensity ratio ha of the part of the subject 3 is measured.
(= Ss / St) is calculated. FIG. 16C shows the result of calculating the signal intensity ratio ha from the histogram of the image on the line A shown in FIGS. 16A and 16B. Since there is data missing at the point where there is no signal source or the point where no signal is output due to the effect of relaxation time or the like, processing such as interpolation is performed. Since the high frequency magnetic field distribution generated by the surface coil 11 can be expanded by an orthogonal function, a method of determining the coefficient of each term of the orthogonal function system by the least square method or the like using the obtained image data may be used. With these methods, it is possible to obtain a high frequency magnetic field distribution as a histogram shown in FIG. 16D over the entire imaging region of the surface coil 11a. It should be noted that the high frequency magnetic field distribution is simply represented as the histogram of FIG.
The signal intensity ratio ha (= Ss / St) of the part may be used.

On the other hand, in the image obtained through the uniform coil 10, when the high frequency magnetic field distribution of the uniform coil 10 becomes non-uniform due to the influence of the subject 3, the uniform coil 1 is obtained in advance.
It is necessary to obtain a high-frequency magnetic field distribution of 0.

Next, a third embodiment according to this embodiment will be described. This embodiment is an embodiment in which a one-turn coil as shown in FIG. 17 is used as the surface coil 11. Figure 1
FIG. 7 is a diagram showing a configuration of the surface coil 11 when a one-turn coil is used as the surface coil 11. In FIG. 17, the outer conductor corresponding to the ground of the signal cable is connected to the conductive frame of the preamplifier 18, and this frame is connected by the conductor 19 via the trap circuit 29.

When the surface coil 11 in this embodiment is a one-turn coil, it is difficult to structurally decouple it from a uniform coil like a differential coil. Therefore, in order to decouple both the uniform coil 10 at the time of transmitting and the surface coil 11 at the time of receiving, decoupling circuits as shown below are added to the uniform coil 10 and the surface coil 11, respectively. It

For the surface coil 11, a tuning / matching circuit to which a decoupling circuit as shown in FIGS. 18 and 19 is added is used. 18 and 19 are equivalent circuits of a tuning / matching portion when a trap circuit is used.

The principle is the same as in FIG.

[Equation 4] The values of L ₂ , C ₁ and C ₂ are determined so as to satisfy the above. L ₁ is the inductance of the surface coil. 18, when the signal is received, the PIN diode 27 is turned off to resonate in the circuit of L ₁ -C ₁ -C ₂ . When transmitting the uniform coil 10 that does not receive a signal, the PIN diode 27 is turned on. At this time, the circuit of L ₂ -C ₂ also resonates, so both ends of C ₂ are in a high impedance state,
As a result, the high frequency current is less likely to flow in the L ₁ -C ₁ -C ₂ circuit and is in a decoupled state. Figure 1
9 is an example in which a cross diode 28 is used instead of the PIN diode 27 of FIG. 18, and when a large current flows during the transmission of the uniform coil 10, the cross diode 28 is turned on, and the decoupling is performed by the same principle as in FIG. To be ringed.

On the other hand, the uniform coil 10 is added with the decoupling circuit shown in FIGS. 20 (a) and 20 (b). 20A and 20B show a case where a saddle type coil is used as the uniform coil 10. In FIG. 20A, the PIN diode 2 is used when transmitting the uniform coil 10.
7 is turned on, and the PIN diode 27 is turned off when the surface coils 11a and 11b are received. Figure 20
In FIG. 19B, decoupling is performed according to the same principle as in FIG.

[0039]

According to the present invention, when a bridge circuit is used for decoupling between adjacent surface coils and the electrical midpoint of each surface coil is connected, a loop and a uniform coil / gradient magnetic field formed by the connection are formed. Coupling with the coil can be prevented. Therefore, the magnetic resonance imaging apparatus can obtain a reconstructed image without deterioration in image quality due to coupling.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a magnetic resonance imaging apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic view showing the arrangement of uniform coils and surface coils in the example.

FIG. 3 is a diagram showing details of a receiving unit of the magnetic resonance imaging apparatus in the embodiment.

FIG. 4 is a schematic view showing the arrangement and configuration of surface coils in the embodiment.

FIG. 5 is a diagram showing an example of a decoupling circuit of a surface coil and a uniform coil / gradient magnetic field coil in the embodiment.

FIG. 6 is an arrangement of other surface coils in the embodiment.
The figure which shows a structure.

FIG. 7 is a schematic view showing the arrangement and configuration of a surface coil according to another embodiment of the present invention.

FIG. 8: Arrangement of other surface coils in the embodiment
Schematic which shows a structure.

FIG. 9 is a diagram showing the principle of a differential coil.

FIG. 10 is a diagram showing an example of decoupling between one-turn coils using a capacitor element and an inductance element.

FIG. 11 is a diagram showing an example of decoupling between differential coils using a capacitor element and an inductance element.

FIG. 12 is a diagram showing an example of a Q dump circuit for decoupling.

13 is a diagram showing an equivalent circuit of FIG.

FIG. 14 is a diagram showing an example of a pulse sequence for imaging.

FIG. 15 is a diagram showing an example of an image obtained through a uniform coil.

FIG. 16 is a diagram for explaining how to obtain a high-frequency magnetic field distribution generated by a surface coil.

FIG. 17 is a diagram showing another embodiment.

FIG. 18 is a diagram showing an example of a decoupling circuit between a uniform coil and a surface coil.

FIG. 19 is a diagram showing another example of a decoupling circuit between a uniform coil and a surface coil.

FIG. 20 is a diagram showing still another example of the decoupling circuit between the uniform coil and the surface coil.

FIG. 21 is a schematic view showing the arrangement and configuration of a conventional surface coil.

FIG. 22 is a schematic view showing the arrangement and configuration of another conventional surface coil.

[Explanation of symbols]

 1 ... Static magnetic field magnet 2 ... Excitation power supply 3 ... Subject 4 ... Gradient magnetic field generating coil 5 ... System controller 6 ... Drive circuit 7 ... Bed 8 ... Transmitter 9 ... Duplexer 10 ... Uniform coil 11 …… Surface coil (1 turn coil) 12 …… Reception unit 13 …… Data collection unit 14 …… Computer 15 …… Console 16 …… Image display 17 …… Signal cable 17 ′ …… Outer conductor 18 ...... Preamplifier 19 ...... Conductor 20 ...... Decoupling device 21 ...... Detection circuit 22 ...... Low pass filter 23 ...... A / D converter 24 ...... Interface 25 ...... Amplifier 26 ...... Feedback resistor 27 ...... Pin diode 28: Cross diode 29: Trap circuit (decoupling device)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location 8203-2G G01R 33/22 Y

Claims (1)

[Claims] 1. A means for applying a static magnetic field to a subject, a means for applying a predetermined gradient magnetic field to the subject, and a unit arranged outside the subject for applying a high-frequency magnetic field to the subject. A plurality of surfaces for detecting magnetic resonance signals generated from the subject, which have a coil and a stray capacitance pair that are arranged inside the uniform coil with respect to the subject and are connected in series and have the same capacitance. In a magnetic resonance imaging apparatus comprising a coil and a means for performing an imaging process based on the detected magnetic resonance signal, a connection midpoint of the stray capacitance pairs of the plurality of surface coils is a high frequency ground point, A magnetic resonance imaging apparatus characterized in that the high-frequency ground point of is connected via an electric or high-frequency cutoff means.