JPH0332645A - Magnetic resonance image device - Google Patents

Abstract

PURPOSE:To allow the subject device to have sensitivity in the sufficient depth direction even in the case photographing is executed by using a partial unit coil and to photograph a distinct tomographic image by placing a detecting means so that a high sensitivity area of a sub-coil is positioned in an area in which sensitivity of a unit coil of a main coil is deteriorated. CONSTITUTION:A device 1 is provided with an inclined magnetic field generating coil, and a high frequency coil for radiating a rotational high frequency magnetic field, and also, detecting an induced magnetic resonance signal. Also, the high frequency coil has a surface coil 10 of a composite type for detecting the induced magnetic resonance signal, and the surface coil consists of a main coil 11 consisting of four unit coils 11a, 11b, 11c and 11d placed adjacently to each other in the Z axis direction and three sub-coils 12a, 12b and 12c placed in parallel to its unit coil array direction. In such a way, the sub-coils are placed so that a high sensitivity area of the sub-coils is positioned in an area in which sensitivity of a unit coil of the main coil is deteriorated, an in the case photographing is executed by using a partial unit coil, sensitivity in the depth direction in a boundary of the unit coil is secured.

Description

[Detailed description of the invention] [Object of the invention] (Industrial application field) The present invention is directed to nuclear magnetic resonance (NMR).
The present invention relates to a magnetic resonance imaging apparatus that applies the agnetic resonance phenomenon, and particularly relates to a magnetic resonance imaging apparatus that has an improved detection means.

(Prior Art) Nuclear magnetic resonance is a phenomenon in which atomic nuclei placed in a magnetic field resonate and absorb electromagnetic wave energy of a specific wavelength, and then emit this energy as electromagnetic waves. Devices that utilize this phenomenon to diagnose living organisms use the above-mentioned atomic nuclei, especially
A test subject that detects electromagnetic waves emitted from protons and processes the detected signals to reflect information such as nuclear (proton) density, longitudinal relaxation time T1, transverse relaxation time T2, flow, chemical shift, etc. Diagnostic information such as tomographic images can be obtained.

By the way, a magnetic resonance imaging apparatus that can obtain a tomographic image of a subject using such a nuclear magnetic resonance phenomenon includes a coil called a surface coil for detecting an induced magnetic resonance signal. When taking a tomographic image using this surface coil, a large surface coil is used when taking a tomographic image of a wide area, while a small surface coil is used selectively when taking a tomographic image of a narrow area. It was used and replaced. However, replacing the coil at the time of imaging is complicated, such as adjusting the imaging conditions again.

Therefore, in order to save the trouble of replacing such coils, it has recently been proposed to use a shape-switchable surface coil [for example, Siemens, Work-in Progress, Switched Array Coil: A New Multi-Purpose Tool In MIR (Siea+cn)
s, Work in Progress.

5w1tched Array Co11s:
A Now Multi-PurposeTool I
n MRI, August 1987)]. This shape-switchable surface coil is a unit that has a desired size of area by arranging coil elements that divide the area within the rectangular surface coil into small areas, and electrically connecting the selected coil elements. A coil is formed, a signal is detected by this surface coil, and a desired imaging area can be photographed. By using this shape-switchable surface coil, it is possible to save the effort of replacing the coil when taking tomographic images.

In addition to this shape-switchable surface coil, a composite surface coil in which a plurality of unit coils having a predetermined size are arranged close to each other has also been proposed for the same purpose (Japanese Patent Application Laid-Open No. 1983-83-1). (See Publication No. 234957). With this surface coil, by electrically appropriately selecting a predetermined unit coil, a photographing area of a desired size can be obtained. This surface coil also eliminates the trouble of replacing the coil as in the conventional case.

However, in the above-mentioned shape-switching type and composite type surface coils, small unit coils are arranged adjacent to each other in order to make the sensitivity distribution in the imaging depth direction of the subject uniform. When imaging a region located at the boundary of , using a partial unit coil such as one, the sensitivity in the depth direction at the boundary of the unit coil decreases, making it difficult to obtain a good tomographic image. .

Therefore, when photographing the boundary area of a unit coil, it is conceivable to image the boundary area using two unit coils that sandwich the boundary area. However, by using two unit coils, the combined sensitivity in the boundary region can be prevented from decreasing. However, the strength of the signal obtained is one 11
While the signal strength does not increase much compared to the signal strength obtained when the first coil is used, the noise increases in proportion to the square root of the number of unit coils used. As a result, there is a problem in that the S/N ratio of the signal decreases and a clear image cannot be obtained.

In addition, in order to solve the problem of decreased sensitivity in the boundary area of unit coils, it is possible to further reduce the size of the unit coils and form a composite surface coil using a large number of unit coils. . However, reducing the size of the unit coil increases the number of switching circuits and amplifiers, which is undesirable because it becomes complicated.

(Problems to be Solved by the Invention) As described above, with shape-switching type and composite type surface coils, when imaging is performed using some unit coils, the sensitivity in the depth direction at the boundaries of the unit coils decreases. There is an inconvenience in doing so.

An object of the present invention is to provide a magnetic sensor I! that has a detection means that has sufficient sensitivity in the depth direction even when imaging is performed using a part of the 111th coil, and is capable of imaging clear tomographic images. An object of the present invention is to provide an rt imaging device.

[Structure of the Invention] (Means for Solving the Problem) The present invention provides a static magnetic field generating means for generating a static magnetic field to be applied to a subject, and a method for obtaining positional information of a site where a magnetic resonance signal is induced. gradient magnetic field generating means for generating a gradient magnetic field;
A magnetic resonance imaging apparatus comprising a detection means for emitting a rotating high-frequency magnetic field for inducing a magnetic resonance signal and detecting the induced magnetic resonance signal, wherein a plurality of the detection means are arranged close to each other. The main coil has a main coil consisting of unit coils, and a sub coil arranged in parallel with the main coil, and the sub coil has a high sensitivity of the sub coil in a region where the sensitivity of the heavy duty coil of the main coil decreases. The magnetic resonance imaging apparatus is characterized in that the magnetic resonance imaging apparatus is arranged such that the regions are located.

(Function) In the magnetic resonance imaging apparatus of the present invention, the detection means includes:
A sub-coil is placed in parallel with a main coil consisting of several vehicle-colored coils arranged close to each other, and the high-sensitivity region of the sub-coil is located in an area where the sensitivity of the unit coil of the main coil decreases. Therefore, when imaging is performed using partial unit coils, sensitivity in the depth direction at the sub-coil boundary at the li position is ensured.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
The figure is a schematic diagram showing the configuration of a nuclear magnetic resonance imaging apparatus used in an example of the present invention. As shown in Figure 1, this device (1) consists of a gradient magnetic field generating coil (2) that generates a gradient magnetic field to obtain positional information of a region where a magnetic resonance signal is generated, and a rotating high-frequency magnetic field that emits a magnetic field. It also has a high frequency coil (3) for detecting the induced magnetic resonance signal.This gradient magnetic field generating coil (2) has an axis in the height direction of the subject (P) as the Z axis, and a high frequency coil (3) for detecting the induced magnetic resonance signal. Assuming that the axes orthogonal to
2a>, a Y-axis gradient magnetic field generation coil (2b), and a Z-axis gradient magnetic field generation coil (2c). Each gradient magnetic field generating coil (2a>, (2b), (2C) is connected to an X-axis gradient magnetic field power supply (4a), a Y-axis gradient magnetic field power supply (4b), and a Z-axis gradient magnetic field power supply (4c), respectively. In addition, the high frequency coil (3) is connected to the transmitting circuit system (5) for generating a rotating high frequency magnetic field (not shown) and the receiving circuit system (6) to generate a rotating high frequency magnetic field. It consists of a surface coil (not shown) for detecting magnetic resonance signals.

This surface coil will be explained in detail later.

Furthermore, this device (1) includes a sequencer (7) that disables the pulse sequence, and each power source <4a>, (4b).
, (4c) includes a computer system (8) that controls all of the transmitting circuit system (5), the receiving circuit system (6), and the sequencer (7) and performs signal processing of the detection signal.

The signals processed by this computer system (8) are displayed on a display (9). This device (1) includes a static magnetic field coil (not shown) that generates a static magnetic field in the Z-axis direction toward the subject (P), and a power source (not shown) that supplies current to this static magnetic field coil. Also equipped.

As shown in FIG. 2, the high frequency coil (3) of the above embodiment has a composite surface coil (10) for detecting the induced magnetic resonance signal. As shown in FIG. 2, this surface coil (10) consists of four rectangular unit coils (lla) and (l) arranged close to each other in the Z-axis direction.
A main coil (11) consisting of lb), (llc), (lid) and a unit coil (l) of this main coil (11)
Three sub coils (12a) arranged parallel to the arrangement direction of la), (llb), (lie), and (lid)
, (12b), and (12c). These sub-coils (12a), (12b), (12c) are unit coils (lLa), (llb), (llc), (lld
), and has a rectangular shape approximately the same as the sub coil (12a), (
The centers of each of +2b) and (12c) are the 711th coils (lla), (llb), (llc), (lid
) is located on the border of These sub coils (12a), (12b), and (12e) are provided to improve the sensitivity of the surface coil within the area surrounded by the main coil (11), so the unit coil ( lla) , (llb) , (llc) , (l
Since there is only one less than id), it is sufficient to provide only one.

These main coil (11) and sub coil (12a),
(12b) and (12c) are respectively switching amplifier circuits (1
3〉, 04) through the receiving circuit (1) shown in FIG.
5> is connected. This switching amplifier circuit (13〉, (
14), each unit coil (lla), (llb), (lie), (lid) is controlled by a sequencer (7) under the control of a computer system.
) and sub coils (12a), (12b), (12
c) selective switching is performed automatically; Note that the shape of the sub coil is preferably approximately the same as that of the main coil (11) from the viewpoint of setting the operating conditions of the switching amplifier circuit.

By the way, as shown above, the main coil (11) and the sub coil (12)
The surface coil (10) composed of a) , (12b) and (12c) has all the unit coils (lla) and (
llb), (Llc), and (lid) to capture a wide imaging area, some of the main coils 01), for example, 1
Sufficient sensitivity of the surface coil can be ensured even when imaging a narrow area using one unit coil. That is, as shown in FIG. 3, each unit coil (lla), (l
lb), (lie), (lid) and sub coil (1
2a), (12b), and (12c) are each curve (A
) , (B) , (C) , (D), (E) , (F)
, (G) shows a mountain-shaped sensitivity profile with a sensitivity peak near the center of each coil. When capturing an image in a wide imaging area using such a surface coil (lO), a uniform sensitivity distribution can be obtained over a wide area by adding up the outputs of a plurality of unit coils. For example, unit coils (lla), (llb)
, (lie), and (lld), a uniform sensitivity distribution can be obtained over a wide area, as shown by curve (11) in FIG.

In addition, when obtaining an image of a narrow imaging area such as the boundary area of unit coils (lla) and (llb), unit coil (l
If the image is taken by selectively using both la) and (llb), the uniform sensitivity obtained by combining the curves (A) and (B) representing the sensitivity will be obtained using a surface coil that calculates 11 and q. It turns out. However, these unit coils (lla)
, (llb) does not increase appreciably compared to using a single medium coil, whereas the noise increases by 1 in proportion to the square root of the number of unit coils used. As a result, the S/N decreases. Therefore, when photographing this boundary area, it is preferable to use one of the unit coils. However, in this boundary region, the unit coil (ll
The sensitivities of a) and (llb) are shown in Figure 3 by curves (A) and (llb).
As shown in B), both of them are decreased, and the S/N is also decreased due to the noise from the subject.

On the other hand, in the surface coil (lO) of this embodiment, 1
The secondary coil (12a) is arranged so that its high sensitivity area is located in the boundary area between the 11th position coils (lla) and (llb), that is, the area where the ilt position secondary coil degree decreases. A good image can be obtained by photographing this boundary region using the sub-coil (12a) having high sensitivity.

In an imaging apparatus having such a configuration, a sequencer is used to detect magnetic resonance signals using a predetermined gradient magnetic field, spin echo method, etc. under the control of a computer while a subject is lying in a static magnetic field. A pulse sequence is executed to detect a magnetic signal (signal) from the surface coil, which is then displayed on a display or the like to obtain a tomographic image.

In the above embodiment, a rectangular coil was explained, but
A similar effect can be achieved with solid or rectangular coils.

Furthermore, in the above embodiments, a cross method is described which includes a surface coil for receiving signals and a transmitting coil for generating a high frequency magnetic field. can also be applied.

[Effects of the Invention] As described above, according to the present invention, even when imaging is performed using a part of the 111th coil, a detection means having sufficient sensitivity in the depth direction is provided, and a clear tomographic image can be obtained. A magnetic resonance imaging device capable of taking images can be provided.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the configuration of a magnetic resonance imaging apparatus according to an embodiment of the present invention, FIG. 2 is a plan view showing a surface coil according to an embodiment of the present invention, and FIG. 3 is a diagram showing the surface coil of the embodiment of the present invention. Y
It is a graph showing the sensitivity characteristics in the axial direction, and the curve (A)
, (B) , (C) , (D), (E) , (P) ,
(G) are unit coils (lla), (Ilb), (ll
c) , (lld) and sub-coil (12a), (1
2b), (12G), and curve (II) shows the sensitivity characteristics of unit coils (lla), (llb), (lie).
, (lid), FIG. 4 is a circuit diagram showing the receiving circuit system of the embodiment. DESCRIPTION OF SYMBOLS 1... Magnetic resonance imaging device, 2... Gradient magnetic field generation coil, 3... High frequency coil, 5... Transmission circuit system, 6... Receiving circuit system, 10... Surface coil, 11. ...Main coil, 11a 5llb, llc %lid -...Unit coil, 12a 1 12b. 2c... Sub-coil, 13. 14...Switching amplifier circuit.

Claims (1)

[Claims] A static magnetic field generating means for generating a static magnetic field to be applied to a subject, a gradient magnetic field generating means for generating a gradient magnetic field for obtaining positional information of a region where a magnetic resonance signal is induced, and a gradient magnetic field generating means for inducing a magnetic resonance signal. In the magnetic resonance imaging apparatus, the detection means includes a plurality of unit coils disposed close to each other. The sub coil has a main coil and a sub coil arranged in parallel with the main coil, and the sub coil has a high sensitivity region located in a region where the sensitivity of a unit coil of the main coil is reduced. A magnetic resonance imaging device characterized in that: