JPH06254070A - Magnetic resonance imaging device - Google Patents

Abstract

PURPOSE:To obtain high S/N by adopting the constitution to selectively use plural first coil segments for detecting the magnetic resonance signal correspond ing to a high-frequency magnetic field in a first direction and a second coil segment for detecting the magnetic resonance signal corresponding to a high-fre quency magnetic field in a second direction. CONSTITUTION:The signal transmission and reception coil 3 of the MRI device contg. X-axis to Z-axis gradient magnetic field coils and the signal transmission and reception coil 3 in a gantry is composed of the plural coil segments 15 (15a to 15e) and the coil segment 16. The coil segments 15 are formed respectively as rectangular plane coils which are constituted as a so-called multiview coil having sensitivity with the high-frequency magnetic field in the first direction as a whole. On the other hand, the coil segment 16 is formed as the rectangular plane coil of about the size to cover one surface of the multiview coil and is so provided as to have sensitivity with the high-frequency magnetic field approximately orthogonal with the first direction. The respective coil segments 15, 16 are selectively used according to the various sizes of a photographing region.

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 for detecting a magnetic resonance signal by applying a high frequency magnetic field to a subject.

[0002]

2. Description of the Related Art Conventionally, one of the RF coils of this type is a multi-view coil as shown in FIG. This multi-view coil includes a plurality of relatively small-sized coils 30 arranged in parallel in a one-dimensional direction, and by selecting the number of coils 30 to be driven simultaneously, it is possible to cope with various sized imaging regions. It is like this. When actually imaging an examination site, for example, a part of the spine using this multi-view coil, first, all or a large number of coils 30 are simultaneously driven to image the entire spine, and the imaging image is used. Confirm the location of the examination site and select one or a few coils. Then, this time, only the selected coil is driven to detect the magnetic resonance signal from the examination site. This allows the inspection site to be imaged with a high S / N ratio. Thus, the multi-view coil is a very convenient coil. However, when all or a large number of coils are driven at the same time, it becomes equivalent to a commonly used integrally formed surface type coil, and the S / N ratio is lower than that in the case of a coil having a relatively small size. There's a problem.

As another conventional example, there is a surface quadrature (QD) coil as shown in FIG. 5 (b).
The orthogonal coil includes a coil 31 sensitive to a high frequency magnetic field in the first direction and a coil 32 sensitive to a high frequency magnetic field in a second direction substantially orthogonal to the first direction,
There is an advantage that the S / N ratio is improved as compared with the case of a normal surface coil. However, this quadrature coil has a problem that the S / N ratio becomes extremely low when the examination site is relatively small, such as a part of the spine, as compared with the case where the multi-view coil or a small coil is used for imaging. ing. In this way, the multi-view coil and quadrature coil have advantages and disadvantages,
The current situation is that they are used properly according to the object to be photographed.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to address the above-mentioned circumstances, and its purpose is to provide a magnetic resonance device capable of always capturing an image with a high S / N ratio regardless of the size of the target area. An imaging device is provided.

[0005]

A magnetic resonance imaging apparatus according to the present invention comprises a plurality of magnetic resonance imaging devices which are sensitive to a high frequency magnetic field in a first direction and detect a magnetic resonance signal corresponding to the high frequency magnetic field in a predetermined region of a subject. A first coil segment of

A second coil which is sensitive to a high frequency magnetic field in a second direction substantially orthogonal to the first direction at a predetermined portion of the subject and detects a magnetic resonance signal corresponding to the high frequency magnetic field in the second direction. A segment and a first selection unit that selects any one of the plurality of first coil segments and generates a reception signal based on an output signal of the selected first coil segment;

Second selecting means for generating a reception signal based on the output signal of the second coil segment and the output signal of the first coil segment selected by the first selecting means, and the first and second selecting means. And a means for obtaining a magnetic resonance image based on a reception signal generated by any one of the above.

[0008]

According to the present invention, when the photographing area is relatively small, an image having a high S / N ratio can be photographed by selecting and using one of the plurality of first coil segments, and the photographing area Is relatively large, an orthogonal coil is formed by using the first coil segment and the second coil segment together, so that an image with a high S / N ratio can be captured.

[0009]

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

FIG. 1 is a block diagram showing the overall configuration of a magnetic resonance imaging apparatus using this RF coil. Inside the gantry 20, a static magnetic field magnet 1, an X-axis / Y-axis / Z-axis gradient magnetic field coil 2, and a transmission / reception coil (hereinafter referred to as “RF coil”).
3) is provided. The RF coil 3 may be directly attached to the subject or may be placed on the bed 13 instead of being embedded in the gantry. The static magnetic field magnet 1 as the static magnetic field generator is configured by using, for example, a superconducting coil, a normal conducting coil or a permanent magnet. X axis
The Y-axis / Z-axis gradient magnetic field coil 2 is a coil for generating an X-axis gradient magnetic field Gx, a Y-axis gradient magnetic field Gy, and a Z-axis gradient magnetic field Gz. The RF coil 3 is one of the characteristic components of the present invention, and has a high frequency (RF).
The coil is used both as a transmitter and a receiver for generating a pulse to excite a target site and detecting a magnetic resonance signal (MR signal) generated by magnetic resonance. The structure of the RF coil 3 will be described later. The subject P placed on the bed 13 is inserted into an imageable area (a spherical area where an imaging magnetic field is formed and data can be collected only in this area) in the gantry 20.

The static magnetic field magnet 1 is driven by the static magnetic field controller 4. The RF coil 3 is connected to the transmitter 5 during excitation (transmission) and to the receiver 6 during detection of magnetic resonance signals (reception). The receiver 6 includes a coil selecting means in addition to the receiving system. The configuration of this coil selection means will be described later. In addition to the transmitting system, the transmitter 5 also includes coil selecting means similar to the coil selecting means of the receiver 6. X-axis / Y-axis / Z-axis gradient magnetic field coil 2
Are driven by an X-axis gradient magnetic field power source 7, a Y-axis gradient magnetic field power source 8 and a Z-axis gradient magnetic field power source 9.

The X-axis gradient magnetic field power source 7, the Y-axis gradient magnetic field power source 8, the Z-axis gradient magnetic field power source 9, and the transmitter 5 are driven by a sequencer 10 according to a predetermined sequence, and an X-axis gradient magnetic field Gx, a Y-axis gradient magnetic field Gy, A Z-axis gradient magnetic field Gz and a radio frequency (RF) pulse are generated in a predetermined pulse sequence.
In this case, the X-axis gradient magnetic field Gx, the Y-axis gradient magnetic field Gy, and the Z-axis gradient magnetic field Gz are mainly used as the phase encoding gradient magnetic field Ge, the reading gradient magnetic field Gr, and the slice gradient magnetic field Gs, respectively. The computer system 11 drives and controls the sequencer 10, captures the magnetic resonance signal received by the receiver 6 and performs predetermined signal processing to generate a tomographic image of the subject, and displays it on the display unit 12.

The structure of the RF coil 3 will be described with reference to FIG. FIG. 2 is a plan view of the RF coil 3. RF
The coil 3 includes a plurality of coil segments 15a to 15e.
And another coil segment 16. Each of the coil segments 15a to 15e is a rectangular planar coil, and they are one-dimensionally arranged in parallel to form a so-called multi-view coil. This multi-view coil
It is sensitive to a high frequency magnetic field in a predetermined direction (hereinafter referred to as the first direction). The coil segment 16 is a rectangular planar coil having a size that covers one surface of the multi-view coil, and is superposed on the multi-view coil. Further, the coil segment 16 is sensitive to a high frequency magnetic field that is substantially orthogonal to the first direction.

The structure of the coil selecting means provided in the receiver 6 will be described with reference to FIG. Since the coil selecting means provided in the transmitter 5 has the same configuration as the coil selecting means provided in the receiver 6, the description thereof will be omitted. The coil segments 15a to 15e of the multi-view coil (MVC) 17 are coil segments 15a to 15e.
e Preamplifiers 18a to 1 provided corresponding to each
8e and switches 19a to 19e are connected in order to the adder 21. Adder 21 is coil segment 1
The inputs from 5a to 15e are added in an analog manner. The output side of the adder 21 is connected to the receiver 6 and the QD (quadrature) adder 2 according to the switching operation of the changeover switch 22.
3 is selectively connected. The QD adder 23 is connected to the coil segment (QC) 16 via the preamplifier 24, and the output side thereof is connected to the receiving system of the receiver 6.

Next, the operation of the apparatus of this embodiment constructed as described above will be described with reference to FIGS. 4 (a) and 4 (b). FIG. 4A is a coil selection provided in the receiver 6 when a relatively large area such as the whole spine is imaged, and FIG. 4B is a case where a relatively small area such as a part of the spine is imaged. It is a figure showing operation of means.

When photographing a relatively large area such as the entire spine, as shown in FIG.
e are all set to the closed state, and the changeover switch 22 is QD
Is connected to the adder 23 side. At this time, the coil segments 15a to 15e become equivalent to a single relatively large coil as a whole, and form the QD coil together with the other coil segment 16.

The reception signals of the coils 15a to 15e are amplified by the preamplifiers 18a to 18e, added by the adder 21, and then supplied to the QD adder 23 via the changeover switch 22. On the other hand, the reception signal of the coil segment 16 is amplified by the preamplifier 24, and Q
It is supplied to the D adder 23. In the QD adder 23,
Both signals having different phases by 90 ° are input, one of the signals is shifted by 90 ° to align the phases of both signals, and the two signals are added, and the result is output to the receiver 6. The output of the receiver 6 is sent to the computer system 11. The computer system 11 generates a tomographic image based on the input from the receiver 6 and visualizes it on the display unit 12.

Next, when photographing a relatively small area such as a part of the spine, as shown in FIG. 4B, one of the coil segments 15a to 15e facing the concerned photographing area or A small number of coils, here coil segment 15c
Only the switch 19c corresponding to is set to the closed state, and the others are set to the open state. The changeover switch 22 is connected to the receiver 6 side. At this time, QD adder 2
3 is set to a non-operating state.

The received signal of the coil segment 15c is amplified by the preamplifier 18c, then passes through the adder 21 and the changeover switch 22 in order, is supplied to the receiver 6, and is formed into a tomographic image by the computer system 11. , Is visualized on the display unit 12.

As described above, according to this embodiment, when the photographing area is relatively small, the plurality of coil segments 15a ...
A high S / N can be achieved by selecting and using one or a few coil segments from 15e, and a plurality of coil segments 15e can be used when the imaging area is relatively large.
Since the orthogonal coils are formed by using a to 15e and other coil segments 16, it is possible to take an image with a high S / N.

The present invention is not limited to the above-mentioned embodiments, but can be modified in various ways. For example, although the RF coil is a planar coil in the above description, it may be formed in a curved shape or a concave shape. In this case, adhesion to the back surface of the subject is improved, which is suitable for imaging the spine. is there. Further, the RF coil may be formed in a cylindrical shape or an ellipsoidal shape so as to cover the circumference of the body or the head of the subject. In this case, the cross section of the body or the head of the subject is entirely covered. You can take good pictures. Further, in the above description, the coil segment 15a
.About.15e are arranged in a one-dimensional array, but the coil segments 15a to 15e may be arranged in a two-dimensional array, for example, along a predetermined circumference on a plane.

[0022]

As described above, the magnetic resonance imaging apparatus according to the present invention is designed so that the first part of the subject is located at a predetermined position.
A plurality of first coil segments having sensitivity to a high frequency magnetic field in the direction and detecting magnetic resonance signals corresponding to the high frequency magnetic field;

A plurality of first portions having sensitivity to a high frequency magnetic field in a second direction substantially orthogonal to the first direction at a predetermined portion of the subject and detecting magnetic resonance signals corresponding to the high frequency magnetic field in the second direction. A two-coil segment and a first selection unit that selects one of the plurality of first coil segments and generates a reception signal based on an output signal of the selected first coil segment;

Second selection means for generating a reception signal based on the output signal of the second coil segment and the output signal of the first coil segment selected by the first selection means, and the first and second selection means. And a means for obtaining a magnetic resonance image based on a reception signal generated by any one of the above.

Therefore, according to the present invention, when the photographing area is relatively small, it is possible to photograph an image with a high S / N ratio by selecting and using any one of the plurality of first coil segments. First when the shooting area is relatively large
Since the orthogonal coil is formed by using the coil segment and the second coil segment together, an image with a high S / N ratio can be captured.

[Brief description of drawings]

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

FIG. 2 is a plan view of the RF coil shown in FIG.

FIG. 3 is a block diagram of coil selection means included in the receiver shown in FIG.

FIG. 4 is a diagram for explaining the operation of the coil selection means shown in FIG.

FIG. 5 is a plan view of a conventional RF coil.

[Explanation of symbols]

1 ... Static magnetic field magnet, 2 ... X-axis / Y-axis / Z-axis gradient magnetic field coil, 3 ... RF coil, 4 ... Static magnetic field control device, 5 ... Transmitter, 6 ... Receiver, 7 ... X-axis gradient magnetic field amplifier, 8 ... Y-axis gradient magnetic field amplifier, 9 ... Z-axis gradient magnetic field amplifier, 10 ... Sequencer, 11 ... Computer system, 12 ... Display unit, 1
3 ... Sleeper, 20 ... Gantry.

Claims (1)

[Claims] 1. A magnetic resonance imaging apparatus that applies a high-frequency magnetic field to a subject to detect a magnetic resonance signal, has a sensitivity to a high-frequency magnetic field in a first direction at a predetermined portion of the subject, and is compatible with the high-frequency magnetic field. A plurality of first coil segments for detecting magnetic resonance signals, the second coil segment having a high sensitivity to a high frequency magnetic field in a second direction substantially orthogonal to the first direction at a predetermined portion of the subject,
A second coil segment for detecting a magnetic resonance signal corresponding to a high-frequency magnetic field in a direction, and selecting one of the plurality of first coil segments,
First selecting means for generating a reception signal based on the output signal of the selected first coil segment, and based on the output signal of the second coil segment and the output signal of the first coil segment selected by the first selecting means Magnetic resonance imaging, comprising: second selection means for generating a reception signal by means of the above-mentioned method; and means for obtaining a magnetic resonance image based on the reception signal generated by either the first or second selection means. apparatus.