JPH04212330A - Magnetic resonance video device - Google Patents

Abstract

PURPOSE:To provide the magnetic resonance video device which can obtain the data for determining a weight function within the time when magnetic resonance signals are detected via a multisurface coil in the case of obtaining high S/N images by simultaneously detecting the magnetic resonance signals of plural channels by the multisurface coil. CONSTITUTION:This magnetic resonance signal video device detects the magnetic resonance signals via a uniform coil 9 within the same time to detect the magnetic resonance signals via the multisurface coil 10 and obtains the data necessary for determining the weight function to be used for forming images by using the image data of plural channel obtd. by subjecting the magnetic resonance signal obtd. via the multisurface coil 10 and the uniform coil 9 to imaging processing including Fourier transform.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to a magnetic resonance imaging system, and particularly to a magnetic resonance imaging system using a uniform coil and a surface coil.
The present invention relates to a magnetic resonance imaging apparatus that acquires N images.

0002

BACKGROUND OF THE INVENTION Magnetic resonance imaging apparatuses are considered to be almost complete in terms of 1H imaging, even though the imaging time takes several minutes. Clinically, it provides images of such high quality that there are almost no practical problems when imaging areas that are stationary or that move slowly.

However, in recent years, high-speed imaging (imaging time ~
50ms), 31P, 19F, 13 other than 1H
There is a growing demand for imaging of nuclides such as C and 23N. In these cases, technically speaking, improving the S/N ratio is a major issue. For example, in high-speed imaging, there is a deterioration of S/N due to shortening of imaging time;
Regarding 1P, the S/N is insufficient due to the fact that the amount present in the body is extremely small, about 10-4 of 1H.

In order to improve the S/N ratio, surface coils have been conventionally used for receiving magnetic resonance signals. Surface coils are placed in close contact with the area of interest of the subject and can detect signals around the area of close contact with a high S/N ratio, but they have the disadvantage that only images around the area of close contact can be obtained, and It is not possible to image a predetermined cross section with high S/N over the entire area.

On the other hand, so-called uniform coils (for example, saddle-shaped coils, slotted tuple coils) that generate a substantially uniform high-frequency magnetic field in a plane perpendicular to the static magnetic field in a desired region of the subject
When a resonator, birdcage coil, etc.) is used to receive magnetic resonance signals, an image of the entire desired cross section of the object can be obtained. If this uniform coil is used in a quadrature reception system, the S/N ratio for the entire image can be improved by 21/2 times. However, the S/N of a magnetic resonance signal obtained using a uniform coil cannot be as high as that around the close contact area when a surface coil is used.

[0006] In order to solve the above problems, for example, US Pat. Each magnetic resonance signal from the subject is detected via a surface coil, and each detected magnetic resonance signal is subjected to imaging processing to generate multiple series of image data. After that, pixel data corresponding to the same spatial position ( Create data for each pixel by multiplying a single complex signal or one-dimensional complex signal (spectral signal) by a predetermined weighting function based on the distribution of the high-frequency magnetic field generated by each surface coil, By combining one image of the desired area, high S
A technique for obtaining /N images is disclosed.

Furthermore, in this known technique, since magnetic resonance signals are observed simultaneously by a plurality of surface coils within the time required to obtain one image, it is necessary to prevent the surface coils from constantly interfering with each other. Decoupling means is provided to prevent mutual coupling of the coils so that even if a high frequency current of a predetermined frequency is passed through one surface coil, the high frequency current will not flow through other surface coils.

However, in this known technique, in order to determine the weighting function, it is necessary to obtain the high-frequency magnetic field distribution generated by each surface coil in advance. If this high-frequency magnetic field distribution were to be determined by computer simulation, it would be virtually impossible to do so because it would be necessary to know the structure, electrical conductivity, and permittivity of the object to be examined. Additionally, in order to experimentally determine the high-frequency magnetic field distribution, it is necessary to obtain a uniform image of the entire desired area to be imaged using a uniform coil used for transmission, which requires extra time. shall be. Furthermore, in this case, it is necessary to actively make each surface coil insensitive to a predetermined frequency using a decoupling circuit using a pin diode or the like, which makes the circuit complicated.

[0009] Furthermore, when a plurality of surface coils are arranged to cover the region of interest of the subject, the S/N of the obtained magnetic resonance signal is the same as when uniform coils are used near the coils in a quadrature reception method. However, there is no theoretical certainty that the S/N at the center of the object, that is, the point farthest from any surface coil, is equal to or better than that when a uniform coil is used in the quadrature reception method. Haven't gotten it yet.

0010

[Problems to be Solved by the Invention] As described above, the conventional technology obtains a high S/N image by simultaneously collecting magnetic resonance signals using a plurality of surface coils and weighting and adding the obtained image data. In this method, the weighting function must be determined in advance based on the high-frequency magnetic field distribution generated by each surface coil, which poses the problem of requiring extra time and complicated circuitry. Ta.

[0011] Furthermore, if a surface coil is used, it is possible to image with a high S/N around the close contact area of the subject, but the S/N rapidly decreases as the distance from the close contact area increases.

On the other hand, when a uniform coil using a quadrature reception method is used, an image of the entire desired cross section can be obtained, but when a surface coil is used, the S
/N is not as good as that.

An object of the present invention is to find a weighting function when obtaining a high S/N image by simultaneously detecting magnetic resonance signals via a plurality of surface coils and weighting and adding the obtained image data. The object of the present invention is to provide a magnetic resonance imaging apparatus capable of acquiring data for detecting magnetic resonance signals through a surface coil within a time period of detecting magnetic resonance signals.

Another object of the present invention is to achieve high S/N near the surface of the subject, equivalent to that achieved when using a surface coil.
It is an object of the present invention to provide a magnetic resonance imaging apparatus which can achieve the same S/N ratio as that achieved when a quadrature reception method is applied to at least uniform coils even in the deep part of a subject.

[0015]

SUMMARY OF THE INVENTION The present invention provides a method for detecting magnetic resonance signals via a uniform coil, which was conventionally used exclusively for transmission, in the same time as detecting magnetic resonance signals via a plurality of surface coils. Image generation is performed using multiple channels of image data obtained by detecting magnetic resonance signals and performing imaging processing including Fourier transform on the magnetic resonance signals obtained through these surface coils and uniform coils. The data necessary to determine the weighting function used for the calculation, for example, the high-frequency magnetic field distribution of the surface coil, is obtained.

Further, the present invention arranges inductance elements and capacitance elements in a ladder shape to constitute a uniform coil, and arranges a plurality of surface coils in a space surrounded by these inductance elements and capacitance elements. , a means for preventing mutual coupling between the uniform coil and the surface coil, and a signal detection means for detecting magnetic resonance signals of multiple channels from the subject through the uniform coil and the plurality of surface coils, respectively. It is something.

[0017]

[Operation] By receiving magnetic resonance signals through a uniform coil within the same time as detecting magnetic resonance signals through multiple surface coils, the surface coil can achieve high S/N. Along with the image, uniform image data of the entire desired region of the subject to be imaged is obtained, and the high-frequency magnetic field distribution of each surface coil is determined using these image data.

Therefore, after multiplying the magnetic resonance signal of each channel by a weighting function according to the high-frequency magnetic field distribution, the data is added for each pixel, or the results of inverse Fourier transform of the magnetic resonance signals of multiple channels and the weighting function are calculated. A high S/N image of a desired region can be obtained by Fourier transforming the summation result of the convolution integral results of a plurality of channels.

Furthermore, a plurality of surface coils are arranged in a space surrounded by the inductance element and the capacitance element constituting the uniform coil in a manner that prevents mutual coupling with the uniform coil, and these coils are used to By detecting magnetic resonance signals, a high S/N ratio equivalent to that achieved when using a surface coil near the surface of the object can be achieved, and even deep inside the object, at least a uniform coil using the quadrature reception method can be used. An S/N ratio equivalent to that achieved can be obtained.

[0020]

Embodiments Hereinafter, embodiments of the present invention will be described 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, a static magnetic field magnet 1 is excited by an excitation power source 2, and applies a uniform static magnetic field to a subject 5. The gradient magnetic field coil 3 is driven by a drive circuit (drive amplifier) 4 controlled by a system controller 16, and is directed to a subject 5 (for example, a human body) on a bed 6 by an X, which is perpendicular to a desired tomographic plane of interest. Gradient magnetic field G whose magnetic field strength changes linearly in the Y direction and the Z direction perpendicular to these
Apply x, Gy, and Gz. Further, under the control of the system controller 16, the subject 5 is applied with a high-frequency magnetic field generated by applying a high-frequency signal from the transmitting section 7 via the duplexer 8 to the uniform coil 9, which is a coil for both transmitting and receiving purposes. Ru.

Inside the uniform coil 9, a multi-surface coil 1, which is a signal detection coil, is located close to the subject 5.
0 is placed. Magnetic resonance signals from the subject 5 are then received by the uniform coil 9 and the multi-surface coil 10. The magnetic resonance signal received by the uniform coil 9 is guided to the receiving section 11 via the duplexer 8, and the magnetic resonance signal received by the multi-surface coil 10 is directly guided to the receiving section 11. The duplexer 8 is used to switch the uniform coil 9 between transmission and reception, and transmits the high frequency signal from the transmitter 7 to the uniform coil 9 during transmission, and transmits the high frequency signal from the uniform coil 9 during reception. It functions to guide the received signal to the receiving section 11.

The magnetic resonance signal input to the receiving section 11 is amplified and detected, and then sent to the data collecting section 12 under the control of the system controller 16. The data collection section 12 collects the magnetic resonance signals inputted through the reception section 11 under the control of the system controller 16, performs A/D conversion, and then sends the signals to the computer 13 as image reconstruction data.

The computer 13 is controlled by the console 14 and performs image reconstruction processing including two-dimensional Fourier transformation on the image reconstruction data input from the data collection section 12. Through this image reconstruction, image data of a channel number equal to the number of coils of the multi-surface coil 10 is obtained, and then these image data are weighted and added to synthesize image data corresponding to one image. Further, the electronic computer 13 also controls the system controller 16. Image data obtained by the electronic computer 13 is supplied to an image display 15, and the image is displayed.

FIG. 2 is a schematic cross-sectional view showing the structure and arrangement of the uniform coil 9 and the multi-surface coil 10. The uniform coil 9 applies a high-frequency magnetic field to the entire region of the subject 5 to be imaged, and also receives and detects magnetic resonance signals from the subject 5, and is arranged to cover the subject 5. ing. The uniform coil 9 is a coil that can apply a uniform high-frequency magnetic field to the region to be imaged of the subject 5, and specifically, for example, a saddle-shaped coil, a distributed constant coil, or a configuration using these coils. A quadrature transmitter/receiver coil is used. The multi-surface coil 10 is provided inside the uniform coil 9,
It consists of a plurality of (six in this example) surface coils 10a to 10f arranged close to the subject 5 so as to surround a desired region of the subject 5 to be imaged.

FIG. 3 shows details of the receiving section 11 in FIG. 1. A first signal detection means consisting of a preamplifier 21, a detection circuit (DET) 22, and a low-pass filter (LPF) is provided corresponding to the uniform coil 9, and a preamplifier 31a is provided corresponding to each surface coil 10a to 10f.
-31f, detection circuits 32a-32f, and low-pass filters 33a-33f, respectively. That is, the magnetic resonance signals received by the uniform coil 9 and the surface coils 10a to 10f, respectively, are transmitted to the preamplifiers 21 and 31a to 31f.
and further amplified by the detection circuits 22 and 32a to 32f.
After being detected by the low-pass filters 23 and 33
After unnecessary components are removed in steps a to 33f, the data is input to the data collection unit 12.

The data acquisition section 12 samples and holds the detection output of the magnetic resonance signal input from the reception section 11 and digitizes it using an A/D converter.
Collect data for image reconstruction. This digitized image reconstruction data is taken into the electronic computer 13 in FIG. The data collection method in the data collection unit 12 is to sample and hold all the low-pass filter outputs in the reception unit 11 at every sampling time (denoted as Δt) determined by the band of the image to be acquired, and hold each sample during Δt. A method of scanning and digitizing the output, and Δt
There is a method in which the outputs of each low-pass filter are sequentially sampled and held in between and digitized, and any of these methods may be used.

Uniform coil 9 and surface coil 10a
10f, decoupling between both coils is required. For this decoupling, for example, a differential coil 40 shown in FIG. 4 is used as a surface coil. As shown in FIG. 5, two ring-shaped coils 41 and 42 of the same shape are arranged coaxially and in parallel, and are connected so that currents flow in spatially opposite directions. It is similar to the one used as a differential type coil in a SQUID magnetometer. One surface coil is constituted by this differential coil 40 and a tuning/matching circuit consisting of capacitance elements 43 to 45 connected to both ends thereof. tuning·
The matching circuit is connected to a preamplifier in the receiving section 11.

In the surface coil composed of the differential type coil constructed in this way, when the spatially uniform high-frequency magnetic field B1 generated by the uniform coil 9 interlinks, an induced electromotive force equal to that in both the coils 41 and 42 is generated. However, since the coils 41 and 42 are connected as described above, the electromotive forces induced in both the coils 41 and 42 cancel each other out, and no high-frequency current flows. Therefore, this surface coil is always decoupled from the uniform coil 9 disposed outside. However, in this case, as a property of the uniform coil 9, it is necessary to generate a spatially sufficiently uniform high frequency magnetic field in the area where the surface coil made of the differential type coil is arranged.

Regarding the S/N when a differential coil is used as a surface coil, see the document: Magn. Re
son. Med. 3, 590-603 (1986). In other words, if the noise component from the subject is dominant, the S/N of a surface coil made of this differential type coil is equivalent to the S/N of a normal surface coil made of a one-turn coil, but In situations where its own high frequency loss cannot be ignored, the S/N is inferior to that of a normal surface coil. Therefore, when manufacturing and arranging the actual coil, the distance between the surface coil and the subject and the distance between the two coils 41 and 42 must be adjusted. It is necessary to carefully consider the interval between

Next, surface coils 10a to 10f
A decoupling method between adjacent surface coils when a differential type coil is used will be described with reference to FIGS. 6 to 9. 6 and 7 show surface coils (10a, 10a in the figure) consisting of adjacent differential coils.
b) shows a decoupling method when the surface coils 10a, 10
b shows a decoupling method when arranged on the circumference.

In the case of FIG. 6, decoupling is performed by overlapping two differential type surface coils 10a and 10b in a plane by an area S determined by the area surrounding the coils. A similar decoupling method for a single turn coil is described, for example, in US Pat. No. 4,825,162. In FIG. 7, decoupling is performed by shifting the coils 10a and 10b in the axial direction (direction perpendicular to the plane surrounded by the coils). FIG. 8 shows a modification of the method of FIG. That is, when the differential coil type surface coils 10a and 10b are curved and arranged on the circumference, the area S' of the overlapping part of the outer coil 41 and the area S of the overlapping part of the inner coil 42 are '' is different, but decoupling is possible by arranging the coils 10a and 10b at specific positions that satisfy the condition S''>S>S'. FIG. 9 is a modification of FIG. 7, in which the coil 41 and the coil 42 are arranged at an angle θ. In this case, decoupling can be achieved by adjusting one differential type surface coil 10b in the x and y directions in the figure.

All of these decoupling methods reduce the magnetic field generated when current flows through one differential coil.
This is a state in which the sum of the magnetic fields interlinking with the other differential coil is zero. Another feature of the surface coil using a differential coil is that decoupling is possible in various arrangements.

Next, a method of decoupling between non-adjacent surface coils will be explained. The coupling between non-adjacent surface coils is less than the coupling between adjacent surface coils. Therefore, it is sufficient to perform decoupling without using a precise decoupling method between non-adjacent surface coils, focusing on the fact that the influence of coupling can be suppressed by lowering the apparent Q. Specifically, a Q-dump circuit may be added to each differential type surface coil.

FIG. 10 shows a specific example of a Q-dump circuit, and it is assumed that the coil 50 resonates at a specific frequency fo with an inductance L and a capacitance element C. The parallel resistance Rp indicates the impedance of the coil 50 in a resonant state, and is expressed as Rp = 2πfo LQ using the Q value.

An inverting input terminal and a non-inverting input terminal of an amplifier 51 with a gain of K times are connected to both ends of this coil 50,
Further, a feedback resistor 52 (resistance value Rf) is connected between the output terminal of the amplifier 51 and the inverting input terminal, and the output terminal and the non-inverting input terminal of the amplifier 51 are used as external connection terminals. The amplifier 51 is actually the preamplifier 31a in FIG.
~31f is used.

The Q-dump circuit consisting of the coil 50, amplifier 51 and feedback resistor 52 shown in FIG. 10 is represented by the equivalent circuit shown in FIG. The resistance Rd in FIG. 11 is Rd = Rf
/(K+1).

Therefore, if the gain K of the amplifier 51 is made sufficiently large, Rp>>Rd, and the impedance at both ends becomes low, resulting in a reduction in the apparent Q.

Depending on the actual arrangement of the differential type surface coils, the coupling between non-adjacent surface coils may be sufficiently small, in which case such a Q-dump circuit is unnecessary.

If sufficient decoupling is not possible between the uniform coil 9 and each of the surface coils 10a to 10f, or between adjacent surface coils due to the coil shape or arrangement, the surface coils 10a to 10f
It is better to use a Q dump circuit for 0f.

Next, the procedure for high S/N imaging in this embodiment will be specifically explained. As an example, an imaging sequence for obtaining a two-dimensional image is shown in FIG. This imaging sequence is applied as a 90° radiofrequency magnetic field (radiofrequency pulse).
This is a pulse sequence for obtaining a two-dimensional image by the known spin echo method using a -180° pulse, where Gs is a gradient magnetic field in the slice direction, Gr is a gradient magnetic field in the read direction, and Ge is a gradient magnetic field in the encode direction. The application timing is shown respectively.

As shown in FIG. 12, the encoding gradient magnetic field Ge
Collect magnetic resonance signals while changing the amplitude of the Application of high-frequency pulses is performed using uniform coil 9, and reception of magnetic resonance signals is performed using uniform coil 9 and all surface coils 10a to 10f (multi-surface coil 10). The magnetic resonance signals detected by the receiving unit 11 via the coils 9, 10a to 10f are taken into the computer 13 as image reconstruction data via the data acquisition unit 12, and are processed using two-dimensional Fourier analysis within the computer 13. Image reconstruction is performed by the conversion. Through this image reconstruction, one channel of image data obtained via the uniform coil 9 and a plurality of channels (6 channels in this example) of image data obtained via each of the surface coils 10a to 10f are obtained. And surface coil 10
A total of 7 channels of image data, including 6 channels of image data obtained via a to 10 and 1 channel obtained via the uniform coil 9, are predetermined so that the S/N is maximized. The image data of one image is synthesized by weighted addition using the weighting function.

Generally, considering that most of the noise detected by the coil is inductive noise from the subject 5,
The above weighting functions are given by [Equation 1] to [Equation 3].

[0044] However, R is a position vector indicating the position on the image (pixel position), r is a vector indicating the position of the subject in space, and ki (R) is the vector for the image data obtained with the i-th surface coil. The weighting function, hi (R), is the high-frequency magnetic field distribution generated by the i-th surface coil, and λ (R) is a correction function that corrects the sensitivity unevenness of the image data after weighted addition, which is caused by the high-frequency magnetic field distribution of the surface coil. Ei (r) is an electric field generated when a unit high-frequency current is passed through the i-th surface coil. Note that the integration of Hij is performed over the entire subject.

Coil noise includes high-frequency resistance noise caused by the coil itself, and dielectric or inductive noise caused by the test object, but when the coil is attached to the test object, noise from the test object is generated. It is thought that this accounts for the majority. If the noise caused by the coil itself cannot be ignored, this influence can be taken into consideration by changing the diagonal elements of the matrix [Hij]. However, in practice [Hij
Since the diagonal elements of ] are smaller than the off-diagonal elements, a weighting function in which the off-diagonal elements of [Hij] are set to 0 may be used for simplicity.

To determine the weighting function k(R), the high frequency magnetic field distribution h(R) of each surface coil 10a to 10f is determined.
) is necessary. This will be explained below. h(R) can be approximately substituted for h(r). First, uniform coil 9 and surface coil 10a
Phase correction is performed on the image data obtained through ~10f. Here, it is assumed that an image as shown in FIG. 13 is obtained using the uniform coil 9. In FIG. 13, the thick line indicates the position of the uniform coil 9, and the broken line indicates the position of the surface coil 10a.

FIG. 14(a) shows a histogram of an image on the dashed line A in FIG. 13, and FIG. 14(b) shows a histogram corresponding to the same position of the image obtained by the surface coil 10a. Figure 14(a)(b)
, the horizontal axis represents the position, and the vertical axis represents the signal strength ST, SS in each image. Figure 14(b)
), it can be seen that the sensitivity of the image obtained by the surface coil 10a decreases as the distance from the surface coil 10a increases. Note that if the S/N of the image is poor, it is desirable to perform smoothing processing such as moving average as appropriate.

Next, the signal intensity ratio ha of each part of the subject 5
(=SS/ST) is calculated. From the histogram of the image on the dashed line A shown in FIGS. 14(a) and (b),
The result of calculating this signal strength ratio ha is shown in FIG. 14(c). Since image data is missing at points where there is no signal source or where no signal appears due to relaxation time, etc., processing such as interpolation is performed. Since the high-frequency magnetic field distribution generated by the surface coil can be expanded by orthogonal functions, a method may be used in which the obtained image data is used to determine the coefficients of each term of the orthogonal function system by the method of least squares or the like. By these methods, it is possible to obtain the high-frequency magnetic field distribution ha(R) as shown in the histogram in FIG. 14(d) over the entire imaging region of the surface coil 10a.

[0049] Furthermore, as the high frequency magnetic field distribution ha(R),
A histogram obtained by simply calculating the signal intensity ratio ha (=SS/ST) of the region of the subject 5 may be used, as in the histogram shown in FIG. 14(c).

On the other hand, in the image obtained through the uniform coil 9, if the high frequency magnetic field distribution of the uniform coil 9 becomes non-uniform due to the influence of the subject 5, etc., the uniform coil 9
It is necessary to obtain the high-frequency magnetic field distribution.

In the above explanation, the raw data of the magnetic resonance signals obtained from each surface coil is used as the data for image reconstruction, and the image data obtained by Fourier transform is weighted and added to obtain a high S/N ratio in the desired area. The following method can also be used. That is, the raw data of the magnetic resonance signal from each surface coil before Fourier transformation is convolved with the inverse Fourier transform results of the weighting functions corresponding to these, and the obtained convolution integral results of multiple channels are summed and synthesized. After that, a high S/N image of a desired area can be similarly obtained by Fourier transform.

For example, in the case of a two-dimensional image, the raw data of the magnetic resonance signal obtained by the i-th surface coil is Ifi (Kx, Ky), the image data after Fourier transformation is Ii (X, Y), and the i-th image is The weighting function of ki (X, Y), the inverse Fourier transform of this weighting function ki (X, Y) is kfi (Kx, Ky), and the high S/N image finally obtained is I (X, Y). Then, [Math. 4]
The relationship shown in is established.

As shown in [Equation 4], the raw data Ifi (Kx, Ky) of the magnetic resonance signal and the weighting function ki
The inverse Fourier transform of (X, Y) The sum of the convolution integral results with kfi (Kx, Ky) for each surface coil corresponds to the inverse Fourier transform of the finally obtained image I(X, Y). I understand. Therefore, if this is Fourier transformed, the image I(X,Y) will be obtained.

In the above embodiment, the surface coils 10a to 10f were decoupled by using differential coils as the surface coils and devising their arrangement, but various other decoupling methods were considered. It will be done. For example, decoupling circuits as shown in FIGS. 15 to 17 may be used. FIG. 15(a) shows a decoupling circuit consisting of a bridge circuit using reactance elements Z1 and Z2 of two types of values, and an equivalent circuit thereof is shown in FIG. 15(b). Terminals a, b and terminals c, d are respectively connected to both ends of two surface coils 10a, 10b to be decoupled. As reactance elements Z1 and Z2, the coupling effect can be improved by using capacitance elements C1 and C2 as shown in FIG. 16 or by using inductance elements L1 and L2 as shown in FIG. 17 and adjusting their values. can be canceled out.

FIG. 18 shows an example in which a decoupling circuit using such a bridge circuit is applied to decoupling between surface coils 10a and 10b consisting of one-turn coils, and FIG. An example in which a coil is applied to decoupling between surface coils 10a and 10b is shown.

FIGS. 20 to 22 also show decoupling coils 43 to 4 made of figure-8 or loop-shaped coils.
An example using 5 is shown below. In FIG. 20, a decoupling coil 43 is coupled to surface coils 10a and 10b each consisting of a one-turn coil. This allows coil 1
The magnetic flux interlinking to one of 0a and 10b can be set to 0, making decoupling possible. Figures 21 and 22
is a surface coil 10a, 1 consisting of a differential type coil.
Decoupling coils 44 and 45 are coupled to 0b, and decoupling is performed in the same manner.

[0057] The decoupling coil 43 shown here,
44 is a butterfly type coil, which itself can achieve a decoupled state with the uniform coil 9. However, Figure 2
In example 2, the decoupling coil 45 couples with the uniform coil 9 depending on the direction of the high-frequency magnetic field generated by the uniform coil 9, so it is desirable to consider the arrangement or to separate it from the subject when applying the decoupling coil 45.

In the previous embodiment, a differential coil was used as the surface coil in order to decouple between the uniform coil 9 and the surface coils 10a to 10f. However, when a normal coil is used, the uniform coil For decoupling with 9, a decoupling circuit as shown in FIGS. 15 to 17 may be used.

Next, another embodiment of the high frequency coil section consisting of a uniform coil and a surface coil will be described. FIG. 23 shows an example in which a birdcage type coil 61 is used as a uniform coil, and a differential type coil 64 is used as a surface coil. The birdcage-shaped coil 61 shown here is called a high-pass type, and includes inductance elements 63 arranged parallel to the axial direction and at predetermined intervals in the circumferential direction, and a capacitance element 62 connecting the adjacent inductance elements 63. It is composed of. That is, the birdcage-shaped coil 61 is configured by arranging the inductance element 63 and the capstan element 62 in a ladder shape.

On the other hand, the differential coil 64 has a birdcage-shaped coil 61 in a space surrounded by an inductance element 63 and a capacitance element 62 that constitute the birdcage-shaped coil 61.
The upper and lower conductor loops are connected by a capacitance element 65 so that currents flow in opposite directions. In this way, if the respective magnetic fluxes interlinking with the two conductor loops are equal, no induced electromotive force is generated in response to changes in the magnetic fluxes. Therefore, decoupling between the birdcage coil 61 and the differential coil 64 is possible.

It is desirable to consider decoupling between the differential coils 64 as well. Regarding the differential coil 64, coupling magnetic flux can be blocked by arranging a conductive plate 66 between adjacent coils as shown in FIGS. 24 and 25. This conductive plate 66 is desirably arranged at a position such that the coils on both sides of the conductive plate 66 are symmetrical, and the larger the area, the greater the decoupling effect.

Next, FIGS. 26 to 28 show examples in which the decoupling method explained in FIGS. 24 and 25 is actually applied. In FIG. 26, an axially parallel inductance element (corresponding to the inductance element 63 in FIG. 23) in a high-pass type birdcage coil 61 is configured with a conductive plate 67, so that the conductive plate 67 is connected to the differential coil 64. It also serves as a decoupling role.

Both FIGS. 27 and 28 are examples in which a low-pass birdcage coil 71 is used. Figure 2
7, inductance elements parallel to the axial direction are constructed of conductive plates 72, and capacitance elements composed of electrode plates 73 and dielectric plates 74 are inserted in the middle of these conductive plates 72, respectively. . In this case, the dielectric plate 7
It is desirable to bend the end of the electrode plate 73 so as to cover a part of the dielectric plate 74 so that magnetic flux does not leak even from a small portion corresponding to the thickness of the electrode plate 74. In FIG. 28, two conductive plates 7 each have an inductance element parallel to the axis.
5 and 76, with the tip portions facing each other with a dielectric plate 74 in between.

FIG. 29 shows an example in which the decoupling circuit described in FIG. 16 is applied to decoupling between adjacent differential coils 64 in FIG. 23.

It should be noted that if the above method does not provide sufficient decoupling between adjacent differential coils (for example, if the width of the conductive plate 66 in FIG. 26 cannot be made very large), or if the decoupling between adjacent differential coils is If there is a coupling between
It is desirable to use a dump circuit in combination to lower the apparent Q.

FIGS. 30 to 33 show other configuration examples of the high frequency coil section consisting of a birdcage coil and a differential coil. FIG. 30 shows a high-pass type birdcage coil 61 in which an inductance element parallel to the axial direction is constituted by a conductive plate 67, and a conductive plate 68 extends between the center portions of adjacent conductive plates 67 along the circumferential direction. The space surrounded by the inductance element (conductive plate 67) and the capacitance element 62 of the birdcage coil 61 is divided into two spaces in the axial direction, and a differential coil 64 is connected to each of these divided spaces. are arranged respectively. In this case, the conductive plates 67 and 68 perform decoupling between adjacent differential coils 64.

FIG. 31 shows a low-pass type birdcage coil 7.
This is an example in which a configuration similar to that shown in FIG. 30 is applied to No. 1, and the inductance element (conductive plate 72) and the capacitance element 78 is divided into two spaces in the axial direction, and a differential coil 64 is disposed in each divided space.

FIG. 32 shows that in order to arrange three or more differential coils 64 in the axial direction, decoupling between the differential coils 64 adjacent to each other in the axial direction is achieved by overlapping a portion of each coil. This is done by reducing the intersecting magnetic flux to zero. Note that three or more differential coils can be arranged in the axial direction even if the decoupling method as described in FIGS. 15 and 16 is used.

FIG. 33 shows an example in which a differential coil 64 and a figure-eight coil 69 are used together as the surface coil. Both the differential coil 64 and the figure-of-eight coil 69 can be decoupled with the birdcage coil 61. Further, since the coils 64 and 69 can be arranged so that the sum of magnetic fluxes interlinking with each other becomes zero, by arranging the coils 64 and 69 alternately in the circumferential direction as shown in FIG. Decoupling between adjacent surface coils can be easily achieved, and there is no need to make the inductance element 63 parallel to the axial direction of the birdcage-shaped coil 61 into a plate-like shape that also serves as decoupling.

In the above embodiment, a birdcage type coil was used as the uniform coil, but since the slotted tube resonator also has four gaps, these gaps can be used to uniformly connect the surface coil made of the differential type coil, etc. It is possible to place the coil in close proximity to the other coils.

FIG. 34 shows that, as explained using FIGS. 23 to 29, a birdcage-shaped coil is used as the uniform coil 9,
It is a diagram showing the arrangement of a high-frequency coil section using differential coils as surface coils 10a to 19h, in which a sampling coil 10a is placed in a space surrounded by an inductance element and a capacitance element in a birdcage-shaped coil that constitutes a uniform coil 9. ~10h are arranged. In this way, both the uniform coil 9 and the sampling coils 10a to 10h can be placed close to the subject 5,
Images with a high S/N ratio can be obtained both on the surface and deep parts of the subject 5.

[0072]

[Effects of the Invention] According to the present invention, magnetic resonance signals can be simultaneously detected using a plurality of surface coils and data for imaging can be collected within the same time period, which was conventionally used only for transmitting high-frequency magnetic fields. By collecting data for imaging by detecting magnetic resonance signals even with uniform coils, it is possible to collect data for imaging using high S/N image data from each surface coil. Image data is obtained, and using these image data it is possible to determine the high frequency magnetic field distribution of each surface coil.

[0073] Then, using a weighting function determined based on this high-frequency magnetic field distribution, the high S/N images obtained from each surface coil are weighted and summed, or the magnetic resonance images from each surface coil before Fourier transformation are Convolution integration is performed on the raw signal data and the inverse Fourier transform results of the weighting functions corresponding to these, and the obtained convolution integration results of multiple channels are added and synthesized, and then Fourier transform is performed to create a single high-resolution image. S/images can be synthesized.

Furthermore, if the image data obtained simply by weighted addition is non-uniform, it can be made uniform by performing sensitivity correction using the high-frequency magnetic field distribution obtained by each surface coil.

Further, according to the present invention, a plurality of miniaturized surface coils are arranged in a space surrounded by an inductance element and a capacitance element constituting a uniform coil, and a plurality of surface coils are arranged between the two coils or between the surface coils. With decoupling, both these coils can be used to detect magnetic resonance signals. As a result, near the surface of the object, it is possible to achieve a high S/N ratio equivalent to that achieved when using a surface coil, and even deep inside the object, it is possible to achieve at least the same high S/N ratio as when using a uniform coil using the quadrature reception method. It becomes possible to realize an S/N ratio equivalent to that of .

[0076]

[Math 1]

[0077]

[Math 2]

[0078]

[Math 3]

[0079]

[Math 4]

[Brief explanation of the drawing]

[Fig. 1] Block diagram of a magnetic resonance imaging apparatus according to an embodiment of the present invention

[Figure 2] A schematic cross-sectional view showing an example of the arrangement of uniform coils and multi-surface coils for the subject in Figure 1.

[Figure 3] Block diagram showing details of the receiving section in Figure 1

[Figure 4] Diagram showing a specific example of the surface coil in Figure 3

[Figure 5] Diagram for explaining the principle of the differential coil used in the surface coil in Figure 4

[Figure 6] Diagram showing the decoupling method between each surface coil when using the surface coil in Figure 4

[
Figure 7: A diagram showing an example of the decoupling method between each surface coil when using the surface coils in Figure 4.

[Figure 8] Diagram showing an example of a decoupling method between each surface coil when the surface coils in Figure 4 are used.

[Figure 9] A diagram showing an example of a decoupling method between each surface coil when using the surface coils in Figure 4.

[Figure 10] Diagram showing an example of a Q dump circuit for decoupling

[Figure 11] Diagram showing an equivalent circuit of the circuit in Figure 10

[Figure 1
2] Diagram showing the pulse sequence for imaging in the same example

[Fig. 13] A diagram showing an image obtained through a uniform coil in the same example.

[Figure 14] Diagram for explaining how to obtain the high-frequency magnetic field distribution generated by the surface coil in the same example

[
Figure 15: Diagram showing an example of a decoupling method between surface coils using a capacitance element and an inductance element

[Figure 16] Diagram showing an example of a decoupling method between surface coils using a capacitance element and an inductance element

[Figure 17] Diagram showing an example of a decoupling method between surface coils using a capacitance element and an inductance element

[Figure 18] Diagram showing an example of a decoupling method between surface coils using a capacitance element and an inductance element

[Figure 19] Diagram showing an example of a decoupling method between surface coils using a capacitance element and an inductance element

[Figure 20] Diagram showing an example of a decoupling method between surface coils using a decoupling coil

[Figure 2
1] Diagram showing an example of a decoupling method between surface coils using a decoupling coil

[Fig. 22] A diagram showing an example of a decoupling method between surface coils using a decoupling coil.

[Figure 23] A perspective view of a high-frequency coil section using a high-pass birdcage coil and a differential coil.

[Figure 24] Diagram for explaining the decoupling method between adjacent differential coils in Figure 23

[Figure 25] Diagram for explaining the decoupling principle in Figure 24

[Figure 26] A perspective view of the high frequency coil section to which the decoupling method of Figure 23 is applied

[Figure 27] Diagram showing part of a low-pass birdcage coil

[Figure 28] Diagram showing part of a low-pass type birdcage coil

29 is a diagram showing an example in which the decoupling circuit in FIG. 16 is applied to decoupling between the differential coils in FIG. 23;

[Figure 30] A diagram showing another example of the configuration of the high frequency coil section consisting of a birdcage coil and a differential coil.

[Fig. 31] A diagram showing another example of the configuration of a high-frequency coil section consisting of a birdcage coil and a differential coil.

[Figure 32] A diagram showing another example of the configuration of the high frequency coil section consisting of a birdcage type coil and a differential type coil.

[Figure 33] A diagram showing another example of the configuration of the high frequency coil section consisting of a birdcage type coil and a differential type coil.

FIG. 34 is a diagram showing the arrangement of a high-frequency coil section using a birdcage-type coil as a uniform coil and a differential-type coil as a multi-surface coil.

[Explanation of symbols]

1...Static magnetic field magnet
3... Gradient magnetic field generating coil 5... Subject
7... Transmission unit 8... Duplexer
9...Uniform coil 10a~
10f...Surface coil 11...Receiving section 12...Data collection section 13
...Electronic computer 40...Differential coil
43-45...Decoupling coil 51...Q dump amplifier
61, 71...Birdcage coil 62...Capacitance element 6
3...Inductance element 64...Differential coil
65, 78... Capacitance elements 66-68, 72, 77... Conductive plate 69... Figure-of-eight coil

Claims (8)

[Claims] 1. A means for applying a static magnetic field and a gradient magnetic field pulse to a subject, and generating a substantially uniform high-frequency magnetic field in a plane perpendicular to the static magnetic field in a desired region of the subject to be imaged. a plurality of surface coils disposed close to the subject; and a plurality of channels of magnetic resonance signals from the subject through the uniform coil and the plurality of surface coils, respectively. A signal detection means for detecting, an image data generation means for performing imaging processing including Fourier transform on each of the plurality of channels of magnetic resonance signals to generate plurality of channels of image data, and using the plurality of channels of image data, weighting function determining means for determining a weighting function defined as a function of pixel position for at least each of the plurality of surface coils; and image data obtained via at least the plurality of surface coils using the weighting function. 1. A magnetic resonance imaging apparatus comprising: image generating means for obtaining an image of the desired region by weighting and adding together pixel data corresponding to the same spatial position. 2. Means for applying a static magnetic field and a gradient magnetic field pulse to a subject, and generating a substantially uniform high-frequency magnetic field in a plane perpendicular to the static magnetic field in a desired region of the subject to be imaged. a plurality of surface coils disposed close to the subject; and a plurality of channels of magnetic resonance signals from the subject through the uniform coil and the plurality of surface coils, respectively. A signal detection means for detecting, an image data generation means for performing imaging processing including Fourier transform on each of the plurality of channels of magnetic resonance signals to generate plurality of channels of image data, and using the plurality of channels of image data, weighting function determining means for determining a weighting function defined as a function of pixel position for at least each of the plurality of surface coils; a convolution integrating means for performing convolution integration and obtaining convolution integral results for a plurality of channels; an additive synthesizing means for adding and synthesizing the convolution integral results for the plurality of channels; and Fourier transforming the additive synthesis results obtained by the additive synthesizing means. A magnetic resonance imaging apparatus comprising: image generation means for generating an image of the desired region. 3. The weighting function determining means determines a high-frequency magnetic field distribution of at least the plurality of surface coils using the image data of the plurality of channels, and determines the weighting function depending on the high-frequency magnetic field distribution. The magnetic resonance imaging apparatus according to claim 1 or 2, characterized in that: 4. At least one of mutual coupling between at least adjacent coils among the plurality of surface coils and mutual coupling between at least a part of the plurality of surface coils and the uniform coil is prevented. The magnetic resonance imaging apparatus according to claim 1 or 2, further comprising means. 5. At least some of the plurality of surface coils include a pair of coils having the same shape arranged substantially coaxially and substantially parallel, and connected so that current flows in opposite directions to each other. 5. The magnetic resonance imaging apparatus according to claim 1, 2, 3, or 4. 6. A method comprising: means for applying a static magnetic field to a subject; and a plurality of surface coils disposed in a desired area of the subject, and detecting magnetic resonance signals from the subject via these surface coils. It comprises a signal detection means, and a coupling prevention means for preventing mutual coupling between at least adjacent coils among the plurality of surface coils, and the coupling prevention means includes a figure-eight coil or a loop-shaped coil adjacent to each other. A magnetic resonance imaging device characterized in that the magnetic resonance imaging device is placed overlapping the . 7. A method comprising means for applying a static magnetic field and a high-frequency magnetic field to the subject, and a plurality of surface coils disposed in a desired area of the subject, through which the magnetic field is transmitted from the subject. It comprises a signal detection means for detecting a magnetic resonance signal, and a coupling prevention means for preventing mutual coupling between at least adjacent coils among the plurality of surface coils, the surface coils being arranged on the same axis and having the same shape. The coils are connected so that current flows in opposite directions, and the coupling prevention means is configured so that the sum of mutually interlinking magnetic fields among the high-frequency magnetic fields generated by the adjacent surface coils becomes zero. A magnetic resonance imaging device characterized by: 8. Means for applying a static magnetic field and a gradient magnetic field pulse to a subject, and generating a substantially uniform high-frequency magnetic field in a plane perpendicular to the static magnetic field in a desired region of the subject to be imaged. a uniform coil consisting of an inductance element and a capacitance element, and a plurality of surface coils disposed in a space surrounded by the inductance element and capacitance element of the uniform coil close to the subject; A coupling prevention means for preventing mutual coupling between the uniform coil and the surface coil, and a signal detection means for detecting magnetic resonance signals from the subject through the uniform coil and the plurality of surface coils, respectively. A magnetic resonance imaging device characterized by: