JP3342909B2 - Magnetic resonance imaging equipment - Google Patents

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 applying a high-frequency magnetic field to a subject and detecting a magnetic resonance signal.

[0002]

2. Description of the Related Art Conventionally, as one type of this type of RF coil, there is a multi-view coil as shown in FIG. The multi-view coil includes a plurality of relatively small-sized coils 30 arranged in a one-dimensional direction, and by selecting the number of simultaneously driven coils 30, it is possible to cope with imaging areas of various sizes. It has become. When actually photographing a part to be examined, for example, a spine, using the multi-view coil, first, all or a large number of coils 30 are simultaneously driven to photograph the entire spine, and the photographed image is used to perform imaging. Check the position of the inspection site and select one or a few coils. Then, only the selected coil is driven to detect a magnetic resonance signal from the inspection site. As a result, the inspection site can 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 simultaneously, it is equivalent to a commonly used integrally formed surface type coil, and the S / N ratio is reduced as compared with a case of a coil having a relatively small size. There's a problem.

As another conventional example, there is a quadrature (QD) coil as shown in FIG.
The orthogonal coil includes a coil 31 having sensitivity to a high-frequency magnetic field in a first direction and a coil 32 having sensitivity 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 orthogonal coil has a problem that the S / N ratio is very low when the examination site is relatively small, such as a part of the spine, as compared with the case of imaging with a multi-view coil or a small coil. ing. Thus, multi-view coils and orthogonal coils have their advantages and disadvantages,
At present, they are properly used depending on the shooting target.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in order to address the above-described circumstances, and has as its object to provide a magnetic resonance apparatus capable of always taking an image having a high S / N ratio regardless of the size of a target area. It is to provide an imaging device.

[0005]

According to the present invention, there is provided a magnetic resonance imaging apparatus for detecting a magnetic resonance signal by applying a high frequency magnetic field to a subject.
A plurality of first coil segments having a sensitivity to a high-frequency magnetic field in a direction and detecting a magnetic resonance signal corresponding to the high-frequency magnetic field; and a second direction substantially orthogonal to the first direction in a predetermined portion of the subject. A second coil segment having a sensitivity to a high-frequency magnetic field including a region obtained by combining the respective sensitivity regions of the plurality of first coil segments, and detecting a magnetic resonance signal corresponding to the high-frequency magnetic field in the second direction A plurality of switches individually provided for the plurality of first coil segments; an adder connected to the plurality of first coil segments via the plurality of switches; Q for adding the output signal and the output signal of the second coil segment in phase.
An adder for D, a changeover switch for selectively outputting an output signal of the adder and an output signal of the adder for QD, and an output signal of the adder selectively output by the changeover switch or Means for generating a magnetic resonance image based on the output signal of the QD adder.

[0006]

[0007]

[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. 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 taken.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the 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. In 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, "RF coil")
3) is provided. The RF coil 3 may not be embedded in the gantry, but may be directly mounted on the subject, or may be mounted on the bed 13. The static magnetic field magnet 1 as a static magnetic field generator is configured 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 includes a radio frequency (RF).
This is a coil for both transmission and reception 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 in the gantry 20 (a spherical area where an imaging magnetic field is formed, and data can be collected only in this area).

The static magnetic field magnet 1 is driven by a static magnetic field control device 4. The RF coil 3 is connected to the transmitter 5 at the time of excitation (at the time of transmission), and is connected to the receiver 6 at the time of detection (at the time of reception) of a magnetic resonance signal. 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. The transmitter 5 also includes the same coil selection means as the coil selection means of the receiver 6 in addition to the transmission system. X-axis / Y-axis / Z-axis gradient magnetic field coil 2
Are driven by an X-axis gradient magnetic field power supply 7, a Y-axis gradient magnetic field power supply 8, and a Z-axis gradient magnetic field power supply 9.

An X-axis gradient magnetic field power supply 7, a Y-axis gradient magnetic field power supply 8, a Z-axis gradient magnetic field power supply 9, and a 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 high 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, for example, the phase encoding gradient magnetic field Ge, the readout gradient magnetic field Gr, and the slice gradient magnetic field Gs. The computer system 11 controls the drive of the sequencer 10, acquires a magnetic resonance signal received by the receiver 6, and performs predetermined signal processing to generate a tomographic image of the subject, and displays the tomographic image 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 arranged one-dimensionally in parallel to form a so-called multi-view coil as a whole. This multi-view coil is
It has sensitivity to a high-frequency magnetic field in a predetermined direction (hereinafter, referred to as a first direction). The coil segment 16 is a rectangular planar coil having a size enough to cover one surface of the multi-view coil, and is superimposed on the multi-view coil. The coil segment 16 has sensitivity to a high-frequency magnetic field that is substantially orthogonal to the first direction.

The configuration of the coil selecting means provided in the receiver 6 will be described with reference to FIG. Note that the coil selecting means provided in the transmitter 5 has the same configuration as the coil selecting means provided in the receiver 6, and therefore the description is omitted. The coil segments 15a to 15e of the multi-view coil (MVC) 17 include the coil segments 15a to 15e.
e, preamplifiers 18a-1 provided corresponding to each
8e and the switches 19a to 19e are connected to the adder 21 in order. 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 in accordance with 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 a preamplifier 24, and the output side is connected to the receiving system of the receiver 6.

Next, the operation of the apparatus having the above-described structure according to the present embodiment will be described with reference to FIGS. 4 (a) and 4 (b). FIG. 4A shows a case where a relatively large region such as the entire spine is photographed, and FIG. 4B shows a case where a coil selected in the receiver 6 is photographed when a relatively small region such as a part of the spine is photographed. It is a figure showing operation of a 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 set to the QD
Connected to the adder 23 side. At this time, the coil segments 15a to 15e as a whole are equivalent to a single relatively large coil, and together with the other coil segment 16, form a QD coil.

The received signals of the coils 15a to 15e are amplified by preamplifiers 18a to 18e, respectively, added by an adder 21, and then supplied to a QD adder 23 via a changeover switch 22. On the other hand, the received signal of the coil segment 16 is amplified by the preamplifier 24 and
It is supplied to the adder 23 for D. In the adder for QD 23,
The two signals having phases different from each other by 90 ° are input, one of the phases is shifted by 90 °, the phases of both signals are aligned, the two are added, and the result is output to the receiver 6. The output of the receiver 6 is sent to a 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 region such as a part of the spine, as shown in FIG. 4B, one or the other of the coil segments 15a to 15e facing the photographing region. A small number of coils, here coil segment 15c
Are set to the closed state, and the other switches are set to the open state. The changeover switch 22 is connected to the receiver 6 side. At this time, the QD adder 2
3 is set to a non-operation state.

After the signal received by the coil segment 15c is amplified by the preamplifier 18c, it 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. , Are displayed 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 to 15a
By selecting and using one or a small number of coil segments from among the coil segments 15e, a high S / N ratio can be achieved.
Since the orthogonal coils are formed by using the a to 15e and the other coil segments 16, an image can be captured with a high S / N.

The present invention is not limited to the above-described embodiment, but can be implemented with various modifications. For example, in the above description, the RF coil is described as a planar coil. However, the RF coil may be formed in a curved or concave shape. In this case, the adhesion to the back surface of the subject is improved, so that the RF coil is suitable for imaging the spine. is there. Further, the RF coil may be formed in a cylindrical shape or an elliptical shape so as to cover the periphery of the torso and the head of the subject. In this case, the cross section of the torso and the head of the subject is entirely formed. We can photograph well. Further, in the above description, the coil segment 15a
Although the coil segments 15a to 15e are arranged one-dimensionally, these coil segments 15a to 15e may be dispersedly arranged two-dimensionally, for example, along a predetermined circumference on a plane.

[0022]

According to the present invention, when the photographing area is relatively small, a plurality of switches are arbitrarily turned on to selectively use one or some of a plurality of first coil segments. , An image having a high S / N ratio can be taken, and when the imaging region is relatively large, a quadrature coil is formed by using a plurality of first coil segments and second coil segments in combination, so that a high S / N ratio is obtained. You can take images of the ratio.

[0023]

[0024]

[0025]

[Brief description of the 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. 1;

FIG. 3 is a block diagram of a coil selecting unit included in the receiver shown in FIG.

FIG. 4 is a view for explaining the operation of the coil selection means shown in FIG. 3;

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

[Explanation of symbols]

DESCRIPTION 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 ... Bed, 20 ... Gantry.

Claims (1)

(57) [Claims] 1. A magnetic resonance imaging apparatus for applying a high-frequency magnetic field to a subject and detecting a magnetic resonance signal, wherein the magnetic resonance imaging apparatus has a sensitivity to a high-frequency magnetic field in a first direction at a predetermined portion of the subject and responds to the high-frequency magnetic field. A plurality of first coil segments for detecting a magnetic resonance signal to be applied, and a high frequency magnetic field in a second direction substantially orthogonal to the first direction at a predetermined portion of the subject, for each of the plurality of first coil segments. A second coil segment having a sensitivity of a region including a region in which the sensitivity regions are combined and detecting a magnetic resonance signal corresponding to the high-frequency magnetic field in the second direction; and a second coil segment provided for each of the plurality of first coil segments. A plurality of switches, an adder connected to the plurality of first coil segments via the plurality of switches, and an output signal of the adder. A QD adder for adding the output signal of the second coil segment with the same phase, and a changeover switch for selectively outputting an output signal of the adder and an output signal of the QD adder; Means for generating a magnetic resonance image based on the output signal of the adder or the output signal of the QD adder selectively output by a switch.