JPH1156806A - Magnetic resonance signal receiving method and magnetic resonance imaging - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic resonance signal receiving method for receiving a magnetic resonance signal from under a subject in a vertical magnetic field by receiving the magnetic resonance signal through a dipole antenna and to provide a magnetic resonance image pickup device equipped with such a receiving means. SOLUTION: The reagent is laid on dipole antennas 102-10n covered with a covering member or the like. Then, the direction of the rotary shaft of a spin in a subject is coincident with the direction of a magnetostatic field so that a magnetic moment to occur with the excitation of the spin can be rotated within a plane parallel to the surface of arranging the dipole antennas 102-10n. With the components of a high frequency magnetic field generating this magnetic moment in the arranging direction of the dipole antennas 102-10n, the high frequency current of the dipole antennas 102-10n is respectively induced and the magnetic resonance signal is received as an electric signal. Namely, the magnetic resonance signal in the vertical magnetic field can be received from under the subject.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance signal receiving method and a magnetic resonance imaging apparatus, and more particularly, to a magnetic resonance signal receiving method for receiving a magnetic resonance signal at a position close to the body surface of a subject and such reception The present invention relates to a magnetic resonance imaging apparatus provided with means.

[0002]

2. Description of the Related Art Magnetic resonance imaging (MRI)
In a nance imaging device, a gradient magnetic field and a high-frequency magnetic field are applied to an imaging target (subject) housed in a static magnetic field space, and a magnetic resonance signal in which spins of atoms in the subject are generated is received and received. An image of the subject is generated (reconstructed) based on the signal.

[0003] RF coils for receiving magnetic resonance signals
(radio frequency coil) is used. In order to receive a magnetic resonance signal at a position close to the body surface of the subject, a surface coil is used. The surface coil is, for example, a one-turn solenoid coil (solenoi
d coil). A plurality of one-turn solenoid coils are arranged to form a multi-coil type surface coil. The multi-coil type surface coil is used, for example, for laying under a subject to image a spine or the like.

[0004]

The surface coil as described above has a structure in which a spin (magnetic moment) rotating in a plane parallel to a plane (coil plane) formed by a coil loop is used. Has no sensitivity. Therefore, for example, in a so-called vertical magnetic field type magnetic resonance imaging apparatus in which the direction of the static magnetic field is perpendicular to the body axis of the subject, when a surface coil is laid under the subject, the magnetic moment is parallel to the coil surface. Since it will rotate in the plane,
Unable to receive magnetic resonance signals.

An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to provide a magnetic resonance signal receiving method for receiving a magnetic resonance signal from under a subject in a vertical magnetic field, and a receiving means of such a method. To realize a magnetic resonance imaging apparatus having the above.

[0006]

[Means for Solving the Problems]

(1) A first invention for solving the above-mentioned problem is characterized in that a magnetic resonance signal is received by a dipole antenna.

(2) According to a second aspect of the present invention, there is provided a static magnetic field forming means for forming a static magnetic field in a predetermined space,
A gradient magnetic field forming means for forming a gradient magnetic field in the predetermined space, a high frequency magnetic field forming means for forming a high frequency magnetic field in the predetermined space, a dipole antenna for receiving a magnetic resonance signal generated in the predetermined space, Image generating means for generating an image based on a received signal of the dipole antenna.

In the first invention or the second invention, it is preferable that the dipole antenna is a plurality of dipole antennas arranged in parallel with each other in terms of expanding an imaging range.

(3) According to a third aspect of the present invention, there is provided a static magnetic field forming means for forming a static magnetic field in a predetermined space,
A gradient magnetic field forming means for forming a gradient magnetic field in the predetermined space; a high frequency magnetic field forming means for forming a high frequency magnetic field in the predetermined space; and a magnetic resonance signal generated in the predetermined space, arranged perpendicular to each other. And a pair of dipole antennas, respectively, and image generating means for generating an image based on the reception signals of the pair of dipole antennas.

In a third aspect, one of the pair of dipole antennas is a first group of a plurality of dipole antennas arranged in a first direction in parallel with each other.
The other of the pair of dipole antennas may be a second group of a plurality of dipole antennas arranged parallel to each other and along a length direction of the first group of dipole antennas. Is preferable in that the imaging range of the image is widened.

In any one of the first to third inventions, it is preferable that the dipole antenna has a loading coil in that the length of the dipole antenna is equivalently extended.

(Operation) In the present invention, a magnetic resonance signal based on a magnetic moment that changes in a direction crossing the longitudinal direction of the dipole antenna is received by the dipole antenna.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiment.

FIG. 1 shows a block (bloc) of a magnetic resonance imaging apparatus.
k) Show the figure. This device is an example of an embodiment of the present invention. The configuration of the present apparatus shows an example of an embodiment relating to the apparatus of the present invention. Further, an example of an embodiment relating to the method of the present invention is shown by the operation of the present apparatus.

(Construction) In the present apparatus, as shown in FIG. 1, the static magnetic field generating section 2 forms a uniform static magnetic field in its internal space. The static magnetic field generation unit 2 is an example of an embodiment of a static magnetic field forming unit according to the present invention. The static magnetic field generation unit 2 includes a pair of magnetic generators such as permanent magnets (not shown), which are opposed to each other in the vertical direction with a space therebetween, and form a static magnetic field (vertical magnetic field) in the opposed space. I have. The magnetic generator is not limited to a permanent magnet, and may be a normal conductive magnet, a superconductive magnet, or the like.

The transmission coil units 4, 4 'are provided in the static magnetic field generation unit 2.
And gradient coil portions 6 and 6 ′ are provided, respectively, and are opposed to each other in the vertical direction with a similar interval. In the static magnetic field space between the transmission coil units 4 and 4 ′, the subject 12
And loaded by loading means (not shown). The body axis of the subject 12 is perpendicular to the direction of the static magnetic field.

The top plate 14 has a receiving antenna (antenn
a) The part 10 is placed, and the subject 12 is connected to the receiving antenna 1
0 is placed on the top plate 14 so as to lie on the top plate 0. The receiving antenna unit 10 will be described later.

A transmitting section 16 is connected to the transmitting coil sections 4 and 4 '. The transmitting coil units 4, 4 'and the transmitting unit 16
It is an example of embodiment of the high frequency magnetic field formation means in this invention. The transmitting unit 16 supplies a driving signal to the transmitting coil units 4 and 4 ′ to generate an RF magnetic field, thereby
2 to excite the spin of a specific atom (for example, a hydrogen atom) in the body.

A gradient driving unit 18 is provided in the gradient coil units 6 and 6 '.
Is connected. The gradient coil units 6, 6 'and the gradient driving unit 18 are an example of the embodiment of the gradient magnetic field forming means in the present invention. The gradient driving unit 18 includes gradient coil units 6 and 6 ′.
To generate a gradient magnetic field. The generated gradient magnetic fields are of three types: a slice gradient magnetic field, a readout gradient magnetic field, and a phase encode gradient magnetic field.

The receiving antenna unit 10 receives a magnetic resonance signal generated by excited spins in the subject 12. The receiving unit 20 is connected to the receiving antenna unit 10. The reception signal of the reception antenna unit 10 is input to the reception unit 20.

The receiving section 20 has an analog / digital (ana
log-to-digital) converter 22 is connected. The analog-to-digital converter 22 converts an output signal of the receiver 20 into a digital signal. analog·
The digital converter 22 is connected to a computer 22.

The computer 24 receives a digital signal from the analog-to-digital converter 22 and stores it in a memory (not shown). A data space is formed in the memory. This data space constitutes a two-dimensional Fourier space. The computer 24 performs a two-dimensional inverse Fourier transform on the data in the two-dimensional Fourier space to perform the subject 12
Is generated (reconstructed). The computer 24 is an example of an embodiment of an image generating unit according to the present invention.

The computer 24 also has a control unit 30
Is connected. The control unit 30 is connected to the transmission unit 16, the gradient driving unit 18, the reception unit 20, and the analog / digital conversion unit 22.

The control unit 30 receives a command from the computer 24 and, based on the command, transmits the transmission unit 16 and the gradient drive unit 1.
8, receiving unit 20 and analog / digital conversion unit 22
, Respectively.

The computer 24 also has a display unit 32
And the operation unit 34 are connected. The display unit 32 displays various information including a reconstructed image output from the computer 24. The operation unit 34 is operated by an operator, and inputs various commands and information to the computer 24.

FIG. 2 shows a schematic configuration of the receiving antenna unit 10. As shown in FIG. 1, the receiving antenna unit 10 includes a plurality of dipole antennas 102,
, 10n. The dipole antennas 102 to 10n are an example of the embodiment of the dipole antenna in the present invention.

Each of the dipole antennas 102 to 10n has signal extraction portions 112 to 11n at the center and loading coils 122, 122 'to 12n at both ends.
12n '. Note that the signal extraction units 112 to 11n
Corresponds to a so-called feeding point of the antenna.

Loading coils 122, 122'-1
2n and 12n 'are also called extension coils, and their inductances correspond to the lengths of the dipole antennas 102 to 10n, respectively, equivalently to a half wavelength of a magnetic resonance signal (RF signal). The value has been chosen to extend to the length.

FIG. 3 conceptually shows an effect of extending the dipole antenna by the loading coil. This allows
In reality, the length of a dipole antenna of about several tens of cm is equivalently extended to, for example, about 17 m corresponding to a half wavelength of an RF signal of 8.52 MHz.

The dipole antennas 102 to 10n are arranged on the support member 200 along the longitudinal direction thereof at regular intervals in parallel with each other. The longitudinal direction of the support member 200 matches the body axis direction of the subject 12. The upper surface of the support member 200 on which the dipole antennas 102 to 10n are arranged is covered with a cover member (not shown) or the like. The subject 12 lies on the dipole antennas 102 to 10n covered by the covering member or the like.

Since the direction of the rotation axis of the spin in the subject 12 coincides with the direction of the static magnetic field, the magnetic moment generated by the excitation of the spin has dipole antennas 102 to 10n arranged as shown in FIG. Rotate in a plane parallel to the plane. Of the high-frequency magnetic field where this magnetic moment occurs,
High-frequency currents are induced in the dipole antennas 102 to 10n by the components in the arrangement direction of the dipole antennas 102 to 10n, and the magnetic resonance signals are received as electric signals. That is, it is possible to receive a magnetic resonance signal generated from the subject 12 in the vertical magnetic field from below the subject 12.

FIG. 4 shows the receiving antenna unit 10 and the receiving unit 20.
FIG. 3 is a block diagram showing a connection state with the STA. In FIG. 4, FIG.
The same parts as those in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted. As shown in FIG.
(preamplifier) 202 to 20n. The preamplifiers 202 to 20n are RF amplifiers. Preamplifier 20
The dipole antennas 102-
10n are respectively connected. Preamplifier 202 ~
As 20n, one having sufficiently low input impedance is used.

The output signals of the preamplifiers 202 to 20n are
The full addition is performed by the adder 210, and after passing through a main amplifier and a phase detection circuit (not shown), the analog / digital conversion unit 2
2 is supplied to an analog / digital converter (not shown).

FIG. 5 shows another example of the configuration of the receiving antenna unit 10. In this figure, dipole antennas 102 to 10n arranged on a support member 200 are the same as those shown in FIG. In contrast, the support member 20
Dipole antennas 102 'to 10' arranged on 0 '
n ′ indicates the direction of their arrangement by the dipole antenna 102.
It is different from the arrangement direction of 10 to 10 n by 90 °. And
Support members 200 and 20 having such an antenna arrangement
The receiving antenna unit 10 is configured by overlapping 0 '. Further, preamplifiers 202 'to 20n' (not shown) are provided corresponding to the dipole antennas 102 'to 10n'.

When the receiving antenna unit 10 having such a configuration is used, the dipole antennas 102 to 10n and the dipole antennas 102 ′ to 10n ′ are sensitive to the magnetic field components in the antenna arrangement direction, respectively. And the magnetic resonance signals received by the systems of the dipole antennas 102 ′ to 10n ′ have a phase difference of 90 °.

For this reason, by adding the received signals of both systems, the signal level can be increased about 1.4 times, and the signals of one system are shifted by 90 ° and added. As a result, the signal level can be doubled, and so-called quadrature reception can be performed.

For quadrature reception, it is conceivable that one of the systems is a loop antenna, that is, a one-turn solenoid coil. Fig. 6 shows an example.
Shown in In the figure, a loop antenna 130 is superimposed on dipole antennas 102 to 10n. The arrangement direction of the dipole antennas 102 to 10n is a direction perpendicular to the body axis.

In the case of a so-called horizontal magnetic field in which the direction of the static magnetic field coincides with the body axis direction, the magnetic moment due to the spin excitation is perpendicular to the plane of the loop antenna 130 and the arrangement plane of the dipole antennas 102 to 10n, as shown in the figure. Since it rotates in the plane, the magnetic resonance signal caused by the rotation is received by the loop antenna 130 and the dipole antennas 102 to 10n, respectively.

At this time, the loop antenna 130 is sensitive to a magnetic field component that changes in a direction perpendicular to the loop plane, and the dipole antennas 102 to 10n are sensitive to a magnetic field component that changes in a direction parallel to their arrangement plane. Received signal of antenna 130 and dipole antennas 102 to 10n
Have a phase difference of 90 °. That is, quadrature reception is performed. According to this configuration, a receiving antenna for quadrature reception applicable to a horizontal magnetic field can be obtained.

(Operation) The operation of the present apparatus will be described. As one specific example of magnetic resonance imaging, spin echo (spin ech)
o) A case where imaging is performed by the method will be described. In the spin echo method, for example, a pulse sequence as shown in FIG. 7 is used.

FIG. 7 is a schematic diagram of a pulse sequence when collecting magnetic resonance signals (spin echo signals) for one view. Such a pulse sequence is repeated, for example, 256 times to acquire a spin echo signal of 256 views.

The execution of the pulse sequence and the collection of the spin echo signal are controlled by the control unit 30. In addition,
This apparatus can perform magnetic resonance imaging by not only the spin echo method but also various other techniques.

As shown in FIG. 7 (6), the pulse sequence is divided into four periods (a) to (d) along the time axis. First, in the period (a), RF excitation is performed by the 90 ° pulse P90 as shown in (1).
The RF excitation is performed by the transmission coil units 4 and 4 ′ driven by the transmission unit 16.

At this time, a slice gradient magnetic field Gs is applied as shown in (2). The application of the slice gradient magnetic field Gs is performed by the gradient coil units 6 and 6 ′ driven by the gradient driving unit 18. Thereby, the spin of a predetermined slice in the body of the subject 12 is excited (selective excitation).

Next, in the period (b), a phase encoding gradient magnetic field Gp is applied as shown in (3). The application of the phase encoding gradient magnetic field Gp is also performed by the gradient coil units 6 and 6 ′ driven by the gradient driving unit 18. As a result, spin phase encoding is performed.

During the phase encoding period, spin rephase is performed by the slice gradient magnetic field Gs as shown in (2).
(rephase) is performed. Further, as shown in (4), a read gradient magnetic field Gr is applied, and the spin dephase (d
ephase) is performed. The application of the read-out gradient magnetic field Gr is also performed by the gradient coil units 6 and 6 ′ driven by the gradient driving unit 18.
It is performed by

Next, in the period (c), a 180 ° pulse P180 is applied as shown in (1), whereby the spin is inverted. The spin reversal is performed by the transmitter 1
This is performed by the transmission coil units 4 and 4 ′ that are RF-driven in 6.

Next, in the period (d), a read gradient magnetic field Gr is applied as shown in (4). As a result, as shown in (5), the spin echo signal is
From 2

The spin echo signal is transmitted to the receiving antenna 10
, Respectively. Alternatively, when quadrature reception is performed, the signals are further received by dipole antennas 102 to 10n '. The received signals are respectively connected to preamplifiers 202 to 20n (and preamplifiers 202 ′ to 202 ′).
20n '), and are fully added by the adder 210. The output signal of the adder 210 is further amplified and phase-detected, and input to the analog / digital converter 22.

The analog / digital converter 22 converts the received signal into a digital signal and inputs the digital signal to the computer COM. The computer COM stores the input signal in a memory as measurement data. by this,
One view of spin echo data is collected in the memory.

The above operation is performed at a predetermined cycle, for example, 256 times.
Repeated times. Each time the operation is repeated, the phase encoding gradient magnetic field Gp is changed, and a different phase encoding is performed each time. This is indicated by a plurality of broken lines attached to the waveform of (3) in FIG.

The computer COM performs image reconstruction based on the spin echo data of all views collected in the memory, and generates an image of the subject 12. The generated image is displayed on the display unit 32 as a visible image.

In the above embodiment, an example in which a plurality of dipole antennas are used has been described.
When V (field of view) is narrow, a single dipole antenna may be used to receive a magnetic resonance signal.

[0054]

As described above in detail, according to the present invention, the magnetic resonance signal is received by the dipole antenna, so that the magnetic resonance signal is received from under the subject in the vertical magnetic field. A method and a magnetic resonance imaging device comprising such a receiving means can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of a device according to an example of an embodiment of the present invention.

FIG. 2 is a diagram illustrating a schematic configuration of a receiving antenna unit in the device according to an example of the embodiment of the present invention;

FIG. 3 is a conceptual diagram illustrating an effect of a loading coil of a dipole antenna.

FIG. 4 is a block diagram of a receiving antenna unit and a receiving unit in the device according to the embodiment of the present invention;

FIG. 5 is a diagram illustrating a schematic configuration of a receiving antenna unit in the device according to an example of the embodiment of the present invention;

FIG. 6 is a diagram illustrating a schematic configuration of an application example of the receiving antenna unit.

FIG. 7 is a schematic diagram showing an example of a pulse sequence executed by the device according to the embodiment of the present invention;

[Explanation of symbols]

Reference Signs List 2 static magnetic field generating section 4, 4 'transmitting coil section 6, 6' gradient coil section 10 receiving antenna section 12 subject 14 top plate 16 gradient driving section 18 transmitting section 20 receiving section 22 analog / digital converting section 24 computer 30 control section 32 display unit 34 operation unit 102 to 10n dipole antenna 112 to 11n signal extraction unit 122, 122 'to 12n, 12n' loading coil 202 to 20n preamplifier 210 adder

Claims (3)

[Claims] 1. A method for receiving a magnetic resonance signal, comprising: receiving a magnetic resonance signal with a dipole antenna. 2. A static magnetic field forming means for forming a static magnetic field in a predetermined space; a gradient magnetic field forming means for forming a gradient magnetic field in the predetermined space; and a high frequency magnetic field forming means for forming a high frequency magnetic field in the predetermined space. A magnetic resonance imaging apparatus, comprising: a dipole antenna that receives a magnetic resonance signal generated in the predetermined space; and an image generation unit that generates an image based on a reception signal of the dipole antenna. 3. A static magnetic field forming means for forming a static magnetic field in a predetermined space; a gradient magnetic field forming means for forming a gradient magnetic field in the predetermined space; and a high frequency magnetic field forming means for forming a high frequency magnetic field in the predetermined space. A pair of dipole antennas arranged so as to be perpendicular to each other and respectively receiving magnetic resonance signals generated in the predetermined space; and an image generation means for generating an image based on the reception signals of the pair of dipole antennas And a magnetic resonance imaging apparatus comprising: