JPH0779948A - Magnetic resonance imaging apparatus - Google Patents

Abstract

PURPOSE:To provide a magnetic resonance imaging apparatus which can image in a high S/N ratio a whole area which is desired to image in a high S/N ratio imaging method using a plurality of surface coils. CONSTITUTION:Either one of size, number, and arrangement of a plurality of surface coils 9 is determined by means for obtaining an SNR (signal-to-noise ratio) distribution of at least a desired area to be imaged. According to the method, in case of arranging the surface coils 9 so as to isotropically surround a subject 5, the coil width is reduced so that there are spaces between adjacent coils and an influence due to a coupling between the coils is eliminated just by reducing a Q value of coil without using means for eliminating an interaction even between the adjacent coils.

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 technique for improving the SNR (signal to noise ratio) of an image.

[0002]

2. Description of the Related Art In recent years, a magnetic resonance imaging apparatus (also referred to as an MRI apparatus) has been widely used as medical diagnostic apparatuses have been developed.

As is well known, a magnetic resonance imaging apparatus is an energy of a high frequency magnetic field rotating at a specific frequency when a group of nuclei having an intrinsic magnetic moment is placed in a uniform static magnetic field. Is a method of visualizing chemical and physical microscopic information of a substance by utilizing the phenomenon of resonance absorption, and 1H is clinically used for imaging a static or slow-moving part. Also provides good quality images.

However, recently moving parts (heart, etc.)
High-speed imaging (imaging time ~ 50ms) and radionuclides other than 1H (31P, 19F, 1)
Improvement of SNR (signal-to-noise ratio) is an important issue in 3C, 23N, etc. imaging. For example, in the case of high-speed imaging, there is a decrease in SNR with a decrease in flip angle during real-time scanning and a decrease in SNR with an increase in gradient magnetic field. For 31P imaging, the abundance in the body is about 10-4 at 1H. The decrease in SNR due to the extremely small amount can be mentioned.

As one means for improving the SNR, for example, Japanese Patent Publication No. 4-42937 (hereinafter referred to as "conventional example 1") discloses a plurality of surface coils in a desired region of an object to be imaged (this conventional example). 1 turn coil) is arranged, the magnetic resonance signals from the subject are respectively detected via the plurality of surface coils, and the detected magnetic resonance signals are subjected to imaging processing to obtain a plurality of series of image data. After generating, the pixel data corresponding to the same spatial position are multiplied by a weighting function determined in advance based on the distribution of the high-frequency magnetic field generated by each surface coil and added to create the data of each pixel. , A technique for obtaining a high S / N image of the entire desired region of a subject by combining them is disclosed.

However, the contents disclosed in the prior art example 1 do not refer to the optimum number of coils, size and arrangement for a desired imaging region.

Conventionally, a plurality of surface coils have at least zero coupling between adjacent coils.
A method of overlapping a certain area is used. But,
This overlapping area depends on the shape of the coil and whether the plurality of coils are arranged in a plane or a curved surface, and cannot be flexibly dealt with. Further, when the surroundings of the subject are isotropically surrounded and imaged, a large coil diameter is required due to the overlapping between adjacent coils, and the SNR improving effect near the surface coil, which is a feature of this method, is diminished.

Considering that a human head is surrounded by six surface coils under the condition of a constant number of coils, even if a cylinder having a radius of 25 cm is simply divided into six equal parts, a width of 12 to 13 cm is obtained. A coil is required, and a larger width is required for decoupling by superposition. The surface coil width used for the purpose of improving SNR is usually 8 to 10 with respect to the head.
cm is 8 to 10 to obtain a similar SNR improving effect.
This is not realistic because it requires individual surface coils.

Further, there is a method of using a bridge circuit as a method of reducing the coupling to 0, but it is very complicated to adjust it along the circumferential direction.

In recent years, the head is a part of the region of interest that has a higher utilization rate of MRI diagnosis than other regions, and there is a demand for high-speed imaging and high resolution, so that the use of a surface coil is desired. Is. However, in the one-turn type such as the conventional surface coil, a high SNR can be expected in the vicinity of the coil, but the sensitivity region is limited due to its shape and size. Was an unsuitable coil. In MRI, high SNR cannot be expected unless the direction of the high frequency magnetic field generated by the high frequency coil is perpendicular to the direction of the static magnetic field. For this reason, it cannot be used in parts such as the parietal region where the generated high-frequency magnetic field direction is parallel to the static magnetic field (except for permanent magnet type MRI where the static magnetic field is generated vertically), and conventionally there are restrictions such as facial undulations and respiration. From the conditions, a cylindrical Birdcca with a spatial gap
Ge type coils and saddle type coils have been used.

On the other hand, as one means for improving the SNR in recent years, US Pat. No. 4,825,162 and Japanese Patent Application No.
As disclosed in Japanese Patent No. 047814 (hereinafter referred to as Conventional Example 2), a plurality of surface coils are arranged in a desired region of a subject to be imaged, and a magnetic resonance signal from the subject is passed through the plurality of surface coils. Respectively, and each of the detected magnetic resonance signals is subjected to imaging processing to generate a plurality of series of image data, and then pixel data corresponding to the same spatial position (single complex signal or one-dimensional complex signal = spectrum signal ), Each pixel data is synthesized by multiplying each other by a predetermined weighting function based on the distribution of the high-frequency magnetic field generated by each surface coil, and adding, to generate one image of the desired area. It is being appreciated. This is called a multi-surface coil. As a result, an image synthesizing means for obtaining a high SNR image of a desired region with a plurality of coils has been clarified.

[0012]

As described above, in the conventional magnetic resonance imaging apparatus, the optimum number and size of the plurality of surface coils for the desired imaging region are
No mention was made of how to determine placement.

Further, in the conventional probe coil for high frequency reception, since its direction must be always arranged perpendicular to the static magnetic field, there is a drawback that it is difficult to adjust the direction in the head coil. there were.

The present invention has been made in order to solve such a conventional problem, and a first object thereof is a magnetic resonance image capable of high SNR imaging for the entire desired imaging region. It is to provide a device.

A second object is to provide a magnetic resonance imaging apparatus capable of high SNR imaging without adjusting the direction of the probe when capturing an image of the subject's head.

[0016]

In order to achieve the above object, the first invention of the present application applies a high frequency magnetic field and a gradient magnetic field in a predetermined sequence to a subject placed under a uniform static magnetic field. In a magnetic resonance imaging apparatus for reconstructing a magnetic resonance image by receiving a magnetic resonance signal generated by a plurality of surface coils arranged close to the subject, the plurality of surface coils are arranged without overlapping each other. In addition, it is characterized by having means for reducing mutual joining with other surface coils.

In the second invention of the present application, a high frequency magnetic field and a gradient magnetic field are applied in a predetermined sequence to a subject placed under a uniform static magnetic field, and a magnetic resonance signal generated thereby is applied to the subject. In a magnetic resonance imaging apparatus for reconstructing a magnetic resonance image by receiving by a plurality of surface coils arranged in close proximity, the surface coils are three coils capable of collecting the magnetic resonance signals in three axial directions orthogonal to each other. And each coil is arranged on the same plane or the same curved surface.

[0018]

According to the first invention of the present application configured as described above, any one of the size, the number, and the arrangement of the plurality of surface coils can be obtained by determining at least the SNR (signal-to-noise ratio) distribution of a desired imaging region. Determine from the means of seeking. The means for obtaining the SNR distribution is based on experiments and computer simulations. S
(Signal) is proportional to the high frequency magnetic field distribution generated by the surface coil, and N (noise) is the inductive loss derived from the subject due to the high frequency magnetic field, the dielectric loss derived from the subject due to the electric field generated in the coil, and the coil itself. It is calculated as the sum of the losses (loss related to the resistivity of the coil wire, loss of the capacitor, and radiation loss), so it is obtained experimentally or by computer simulation.

With this method, when the surface coil is arranged so as to surround the subject isotropically, for example, the number of coils is maximized so that ∫v (SNR (r)) dV is maximized in the desired imaging region. It has been found that when the coil width is optimized under certain conditions, it is necessary to reduce the coil width so that a gap is opened between adjacent coils. Therefore, it is possible to obtain a high SNR image by reducing the Q value of the coil without using a means for making the interaction between adjacent coils zero. This is because the mutual coupling between adjacent coils is reduced by opening the coil gap, and it is not necessary to set the mutual coupling to 0 due to the superposition of the coils and the bridge circuit. This is because the image with less interference can be obtained.

The second invention of the present application comprises a plurality of coils orthogonal to the head-only contact-type probe, and the signals obtained from the coils are summed after applying the phase and amplitude weights. The coil having a high-frequency magnetic field that is orthogonal to the static magnetic field is received so that an image with a high SNR can always be obtained without adjusting the angle of the probe. As a result, the complexity of adjusting the direction of the probe coil is released, and high SNR imaging is performed even for a portion where the direction of the head-only contact probe coil can only be oriented in the direction perpendicular to the static magnetic field. Is possible.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a magnetic resonance imaging apparatus according to the present invention.

In the figure, the static magnetic field magnet 1 is excited by the excitation power source 2 and applies a uniform static magnetic field to the subject 5. The gradient magnetic field generating coil 3 is a sequence controller 1
The magnetic field strength is X, Y, Z with respect to the subject 5 on the bed 6 driven by the drive circuit 4 controlled by 1.
A gradient magnetic field Cx, Gy, Gz that linearly changes in the direction is applied. The subject 5 further includes a sequence controller 1
Under the control of 1, the high frequency magnetic field generated by applying the high frequency pulse from the transmission unit 7 to the transmission coil 8 is applied.

Inside the transmission coil 8, a multi-surface coil 9 serving as a signal detection coil is arranged close to the subject 5. The magnetic resonance signal received from the subject 5 by the multi-surface coil 9 is directly guided to the receiving unit 10.
The magnetic resonance signal guided to the receiver 10 is amplified and detected, and then sent to the data collector 12 under the control of the sequence controller 11. The data collection unit 12 collects the magnetic resonance signals input under the control of the sequence controller 11, performs A / D conversion, and then sends the signals to the electronic computer 13. The electronic computer 13 is controlled by the console 14,
Image reconstruction processing of the magnetic resonance signal input from the data acquisition unit 12 is performed, and the image data obtained from each of the multi-surface coils 9 are weighted and added to be combined into a high SNR image. It also controls the sequence controller 11. The image data obtained by the electronic computer 13 is transmitted to the image display 15 and the image is displayed.

FIG. 2 relates to the first embodiment of the present invention, and is composed of the transmitting coil 8 and the multi-surface coil 9 shown in FIG.
It is a schematic diagram showing arrangement. The transmitting coil 8 applies a uniform high frequency magnetic field to a desired region of the subject 5 to be imaged. The multi-surface coils 9a to 9f are arranged so as to surround the subject as illustrated. Then, as will be described later, the conditions for the size, the number, and the arrangement of each of the multi-surface coils 9a to 9f are obtained from the basic optimization formula.

FIG. 3 shows the multi-surface coil 9 shown in FIG.
Details of the receiving unit 10 and the data collecting unit 12 are shown. The multi-surface coil 9 is composed of six surface coils 9a to 9f,
, 21f, detection circuits (DET) 22a, ..., 22f, and low-pass filters (LPF) 23a ,. In the data collecting unit 12 shown in FIG. 1, the detection signal of the magnetic resonance signal input from the receiving unit 10 is
After being converted into a digital signal by the D converter, it is taken into the electronic calculator 13.

Next, the means for obtaining the SNR (signal-to-noise ratio) distribution of the desired imaging area will be described.

Since the S (signal) is proportional to the high frequency magnetic field distribution generated by the surface coil 9, a unit current is simply passed through the surface coil 9 to obtain the high frequency magnetic field distribution according to the Biot-Savart law. In order to consider the effects of the permittivity and the electrical conductivity of the subject, a typical size of the subject is determined and calculated using analytical or antenna electromagnetic field analysis techniques. The method of moment and the method of spatial network are known as the method of electromagnetic field analysis of an antenna. Of course, the subject can be imaged and experimentally obtained.

N (noise) is divided into a component of each coil and a component representing the correlation of noise between the coils. First, the components of each coil are the inductive loss from the subject due to the high frequency magnetic field, the dielectric loss from the subject due to the electric field generated in the coil, the loss of the coil itself (loss related to the resistivity of the coil wire, loss of the capacitor). , Radiation loss). Here, the noise of the coil itself can be calculated from the following equation (1) from the Q value of the coil when there is no object, the inductance L, and the resonance frequency ω ₀ .

R = Lω ₀ / Q (1) Of the losses originating from the subject, the dielectric loss due to the electric field generated in the coil is electrolysis in the case where the surface coil is divided by a large number of capacitors. Since it concentrates on the capacitor part of the coil, the subject generally does not suffer a large loss. Therefore, it is not necessary to consider it. The induced loss can be calculated using the Coulomb gauge according to the following equation (2).

[0030]

[Equation 1] ★ Assuming that the loss due to the electric field generated in the coil is ignored, the Qload value when the object is inserted in the coil and the Qunload value when it is not measured are measured and calculated by the following equation (3). You can also

R = Lω ₀ × (1 / Qload−1 / Qunload) (3) On the other hand, in the component showing the correlation of the noise between the coils, first, regarding the noise of the coils themselves, the mutual coupling between coils (mutual inductance). Is obtained by experiment or computer simulation. The component representing the noise correlation for the induced loss derived from the subject can be calculated by the following equation (4).

[0032]

[Equation 2] * Experimentally, for example, the conventional example 1 (Japanese Patent Publication No. 4-42937)
It can be measured by the method disclosed in Japanese Patent No.

Then, by summarizing the above results, the following equation (1) is calculated.

[0034]

SNR ² = {ΣΣ k _i k _j B _1xyi B _1xyj } / {ΣΣ k _i k _j R _ij COS (Δθ _ij )} (5) where ki is the weighting function of the i-th surface coil image. This is represented by the following equation (6).

[0035]

## EQU4 ## [k _i ] ^t ∝ [R _ij cos (Δθ _ij )] ^-1 [B _1xyi ] ^t (6) Rij represents a noise matrix element and is expressed by the following equation (7).

[0036]

[Equation 5] * Here, B shows the high frequency magnetic field strength. The noise of the coil itself is incorporated in the diagonal elements of the noise matrix because the correlation of noise does not occur between different coils unless mutual coupling between the coils occurs.

In addition, various concrete methods for obtaining the image SNR can be used, which are realized by a known method for obtaining one high SNR image from images obtained simultaneously by a plurality of surface coils.

Next, the optimum coil size, number, and arrangement will be specifically determined using the equation (5). here,
The number of surface coils is fixed to six, and the arrangement of the subject 5 and the surface coils 9 as shown in FIG.
The image SNR of the desired area XY cross section was calculated for the coil / phantom shape as shown in FIG.

[0039]

[Table 1] ★ In addition, the symbol S is the high frequency magnetic field distribution obtained from Biot-Savart's law, and N is the assumption that the high frequency wavelength is sufficiently long in equations (2) and (4) for the induced loss compared to the size of the coil. And the noise of the coil itself was obtained from the measured Q value and the like. Note that the coupling between the coils was completely absent. FIG. 5 shows the result of calculation of the value [∫ _v {SNR (r)} ² dv] ^1/2 (8) representing the magnitude of SNR while changing the coil width. As is clear from the figure, the value of equation (8) increases from a coil width of 130 mm (a state where adjacent coils are arranged adjacent to each other) to about 50 mm.

Further, FIG. 6A shows S on the Y axis shown in FIG.
FIG. 6B is a diagram in which the SNR of the NR maximum point (the surface coil closest contact of the subject) is plotted against the coil width, and FIG. 6B shows the SN of the SNR maximum point (the surface coil closest contact of the subject) on the X-ray.
The figure which plotted R with respect to the coil width, and FIG.
(C) is a diagram in which the SNR at the image center (coil center) is plotted against the coil width. From FIG. 6C, the center SNR is the largest when it is 130 mm, but even if the coil width is reduced to about half, the SNR is reduced by only about 10%. On the other hand, it can be seen that the SNR near the coil on the Y-axis is almost inversely proportional to the coil width, as shown in FIG. Of course, the S between the open coils as shown in FIG.
NR is slightly lowered. However, considering the S / N improvement effect of the entire desired area XY cross section, particularly the SNR improvement effect in the vicinity of the surface, considering the S / N uniformity of the entire image, the coil width is set between 50 and 90 mm. It can be seen that it is better to reduce the coil width so that a gap is opened between the coils.

In this way, the optimum value of the coil width can be obtained based on the equation (5). Although the number of coils is calculated here under a fixed condition, other parameters may be fixed.

On the other hand, when it is not necessary to arrange the surface coils close to each other, mutual coupling between the coils is reduced, and various techniques for completely decoupling between adjacent coils, which have been conventionally required, are not required, and the coil An image with less interference can be obtained by reducing the Q value. That is,
Conventionally, in order to prevent magnetic coupling between the surface coils adjacent to each other, measures have been taken such as stacking adjacent coils or forming a bridge circuit between the coils, but in this embodiment, This is not necessary. For example, in the case of the surface coil, the conventional example 1 (Japanese Patent Publication No.
Japanese Patent Application Laid-Open No. 2-47 and a method using a preamplifier having a low input impedance as described in Japanese Patent Publication No.
The method using a feedback amplifier as described in 814) may be used to reduce the Q value.

As for the imaging procedure in this embodiment, as described in Conventional Example 1 and Conventional Example 2, a function proportional to the high frequency magnetic field distribution of each surface coil is used as a weighting function, and weighted addition is performed. As a result, a high SNR image can be obtained. In the present embodiment, for example, one high SNR image can be synthesized using the data of the surface coils of the surface coils 9a, ..., 9f in FIG.

The high-frequency magnetic field distribution can be approximately obtained in advance by computer simulation, but it is better to use the ratio of the image obtained by using the transmitting coil 8 and each surface coil image as a weighting function. . FIG. 7 shows a block diagram in that case. In this example, a duplexer 31 that switches the flow of signals at the time of transmission and reception is installed so that the transmission coil 8 can also receive, and a signal at the time of reception is supplied to the receiving unit 10. Particularly, when the transmission coil image and each surface coil image are obtained at the same time, the method described in Conventional Example 2 may be used.

Next, a second embodiment of this embodiment will be described. In this embodiment, a head-contact type multi-coil is used in place of the multi-surface coil shown in FIG. 1, and this multi-coil has three coils 41 as shown in FIG.
It is composed of x, 41y and 41z. 9 (a)-
(C) is a diagram showing a state where the coils 41x, 41y, 41z are separated. As shown in the figure, the coil 41z has a circular shape, and the coils 41y and 42x each have an 8-shape. As shown in FIG. 8, the coils 41y and 41x are arranged in the coil 41z with their longitudinal directions orthogonal to each other. There is.

As a result, the coils 41x, 41y, 4
1z can detect high-frequency magnetic fields in the x-axis, y-axis, and z-axis directions, respectively. FIG. 10 is a schematic diagram showing how the high-frequency magnetic fields in the three directions detected by the head-contact type multi-coils 41x, 41y, 41z are orthogonal to each other.

FIG. 11 is a detailed block diagram of the receiving section 10. The signals from the coils 41x, 41y, 41z are amplified by the preamplifiers 42x, 42y, 42z, respectively, and the phase varying sections 43x, 43y, 43z and the gain adjustment are performed. Part 4
The phase and gain are adjusted by 4x, 44y, and 44z according to the direction of each coil. The adjusted signal is the adder 4
8 is added, detected by the detector 45, and filtered by the filter 46.
Then, unnecessary signals are removed and sent to the data collection unit 47.

Since the head-contact type multi-coils 41x to 41z configured as shown in FIG. 8 are mounted and used at arbitrary positions on the subject's head, they are optimal as the coil mounting position moves. It is desirable to image the sliced surface. For that purpose, it is necessary to determine the receiving condition (amplitude / phase) of each coil of the receiving system. One of the methods to set the amplitude and phase according to the coil direction is to input the coil position information (direction / inclination) and select the appropriate slice plane on the computer when setting the coil on the subject. After the phase is calculated and set, imaging is performed, or after the coil is fixed to the head surface of the subject with a stage arm that can be set freely, this stage arm has the shape after the coil is set in advance. There is a method in which the position information is obtained from the above, the appropriate slice plane is selected from the obtained position information in the computer, and imaging is performed in the same manner as above.

Alternatively, as shown in FIG. 12, switches 49x to 49z may be attached in front of the adder 48, signals may be received from a single coil, and the amplitude and phase of each signal may be examined. Imaging may be performed using the transmitting coil 8 for transmission and reception. However, in that case, it is necessary to use the uniform transmission / reception coil 50 as shown in FIG. 13 and separate the transmission / reception signals by the duplexer 31. Further, at the time of reception, active decoupling between the head-contact type multi-coil 41 and the uniform coil 50 using a pin diode or the like should be performed.

The method of calculating the amplitude and phase from the angle is, for example, when the relationship between the static magnetic field vector B ₀ and the directions of the coils 41x to 41z is as shown in FIG. 14, the projection angle θx to each axis. , Θy, and θz are amplitudes, and an angle deviation from each axis is a phase deviation.

The data collecting section 12 collects image reconstruction data by sample-holding the detected output of the input magnetic resonance signal and digitizing it by the A / D converter.

Here, the received analog signals are weighted and added as they are and the signals from the respective coils are processed. However, as shown in FIG. 15, the signals from the respective coils 41x to 41z are amplified, detected and filtered, Data collection unit 1
2, A / D conversion is performed, and as shown in Conventional Example 2, the image is reconstructed for each image by the computer 13, and weighted addition is performed for each pixel, or a weighting function is obtained in advance and convolution is performed. A higher SNR image can be obtained by performing image reconstruction after integration. In the case of weighted addition for each pixel, various addition methods can be considered as described in Conventional Example 2. As the simplest example of the addition, there is also a method of taking the square root of the sum of the squares (power) of the absolute value of each pixel corresponding to the same position in each image data.

In such a case, the data collection unit 12
The detection output of the magnetic resonance signal input from each coil is sampled and held, digitized by the A / D converter, and image reconstruction data corresponding to each coil is collected.

When the magnetic field direction of one coil becomes parallel to the static magnetic field direction, the signal strength from the coil is extremely small or no signal is received. In such a case, if it is added as it is, a lot of noise will be included.
On the other hand, a threshold value may be set for the signal strength or the image data before addition, and a signal weaker than a certain value may be regarded as noise and removed.

The equivalent circuit of each coil may be provided with a trap circuit as shown in FIG. In this case, when the signal is received, the cross diode D1 in the trap circuit is OF
Since it is in the F state, the trap circuit is turned off. During transmission, the cross diode D1 is turned on, causing resonance in the trap circuit and high impedance at both ends, so that the coil is artificially opened and protects the receiving system from excessive input during transmission. FIG. 17 shows an example in which the capacitor C2 is adjusted to tune the resonance frequency and the capacitor C3 matches the output impedance of the coil to 50Ω. In addition, FIG.
A preamplifier may be arranged immediately after the coil as shown in.
Further, such fine adjustment may use a variable capacitance diode or the like.

Further, although the coils are arranged so as to be orthogonal to each other, residual coupling is also conceivable. In order to prevent this, decoupling may be performed by using Q dump as shown in Conventional Example 2.

FIG. 19 is an explanatory view showing a state in which the probe 51 equipped with the head-contact type multi-coils 41x to 41z of this embodiment is actually mounted on the head of the subject 5, and FIG. The front part of the head (cerebrum / frontal lobe), the central part of the head (cerebrum, midbrain, brain stem), etc. in the same figure (b), the rear part of the head (cerebellar, medulla oblongata), etc. This is the case when the region of interest is set.

As described above, in the second embodiment of the present invention, since data is collected at the subject's head by using the multi-coils arranged on one plane or curved surface,
High SNR even when the probe 51 is attached from any direction
The magnetic resonance image of can be obtained.

[0059]

As described above, according to the first invention of the present application, it is possible to determine the optimum number of coils, size, and arrangement for a desired imaging region, and in particular, a plurality of surfaces so as to surround the subject. When placing the coils, high SNR imaging is possible without the need for complete decoupling between adjacent coils.

Further, according to the second invention of the present application, a high SNR is always maintained without adjusting the direction of the head-contact coil with respect to the static magnetic field so as to improve the SNR.
The head can be imaged with.

[Brief description of drawings]

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

FIG. 2 is a schematic diagram showing the configuration and arrangement of a transmitting coil and a plurality of surface coils according to the first embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a plurality of surface coils and a receiving unit.

FIG. 4 is a diagram showing an example of arrangement of a subject and a multi-surface coil.

FIG. 5 is a characteristic diagram showing the relationship between the square root of the SNR sum of squares of the desired cross section of the subject and the width of the coil.

FIG. 6 is an SNR at each point on the Y axis, the X axis, and the coil center.
It is a characteristic view which shows the relationship between and a coil width.

FIG. 7 is a block diagram showing a configuration of a magnetic resonance imaging apparatus according to a modified example of the first embodiment.

FIG. 8 is a configuration diagram showing a head-contact type multi-coil according to a second embodiment of the present invention.

FIG. 9 is an individual configuration diagram of a head-contact type multi-coil.

FIG. 10 is an explanatory diagram showing a high-frequency magnetic field in three axis directions.

FIG. 11 is a block diagram showing a configuration of a receiving unit.

FIG. 12 is a block diagram showing another configuration of the receiving unit.

FIG. 13 is a block diagram showing a configuration of a transmission / reception unit when transmitting and receiving a high frequency signal with a uniform coil.

FIG. 14 is an explanatory diagram showing the relationship between the direction axes x, y, z of the probe coil and the static magnetic field direction.

FIG. 15 is a block diagram showing still another configuration of the receiving unit.

FIG. 16 is an explanatory diagram showing an example of a trap circuit.

FIG. 17 is an explanatory diagram showing an equivalent circuit of each coil.

FIG. 18 is an explanatory diagram showing another equivalent circuit of each coil.

FIG. 19 is an explanatory diagram showing a state in which the head-contact type multi-coil is attached to the subject.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Static magnetic field magnet 2 Excitation power supply 3 Gradient magnetic field generation coil 4 Driving circuit 5 Subject 6 Bed 7 Transmitter 8 Transmitter coil 9 Multi-surface coil 10 Receiver 11 Sequence controller 12 Data collector 13 Electronic calculator 14 Console 15 Image display 21a to 21f Preamplifier 22a to 22f Detector 23a to 23f Low-pass filter 31 Duplexer 41x, 41y, 41z Head-contact type surface coil 51 Probe

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location 8105-2J G01N 24/04 520 A

Claims (2)

[Claims] 1. A plurality of surfaces arranged in proximity to the subject by applying a high-frequency magnetic field and a gradient magnetic field in a predetermined sequence to the subject placed under a uniform static magnetic field and generating magnetic resonance signals thereby. In a magnetic resonance imaging apparatus that receives a coil and reconstructs a magnetic resonance image, the plurality of surface coils are arranged so as not to overlap each other, and have means for reducing mutual bonding with other surface coils. Magnetic resonance imaging apparatus characterized by. 2. A plurality of surfaces arranged in proximity to the subject by applying a high-frequency magnetic field and a gradient magnetic field in a predetermined sequence to the subject placed under a uniform static magnetic field and generating magnetic resonance signals thereby. In a magnetic resonance imaging apparatus for receiving a magnetic resonance image by a coil and reconstructing a magnetic resonance image, the surface coils are three coils capable of collecting the magnetic resonance signals in directions of three axes orthogonal to each other, and each coil is the same. A magnetic resonance imaging apparatus characterized by being arranged on a plane or on the same curved surface.