JP2002010991A - Vibration imparting device and magnetic resonance photographing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vibration imparting device for not influencing a magnetic environment and a magnetic resonance photographing device provided with such a vibration imparting device. SOLUTION: This vibration imparting device is constituted of a vibration member 112 composed of a piezoelectric vibrator, a supporting member 114 for supporting one end of the vibration member, a vibration transmitting member 116 attached to the other end of the vibration member for transmitting the vibration of the vibration member to an object 300 and a driving means for electrically driving the vibration member.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vibration applying apparatus and a magnetic resonance imaging apparatus, and more particularly to an MR elastography (Magnetic Resonance Elas).
The present invention relates to a vibration imparting device that imparts vibration to an object for performing a graph, and a magnetic resonance imaging apparatus including such a vibration imparting device.

[0002]

2. Description of the Related Art Magnetic resonance imaging (MRI: Magneti)
c Resonance Imaging) device
A subject to be imaged is carried into an internal space of a magnet system, that is, a space in which a static magnetic field is formed, a gradient magnetic field and a high-frequency magnetic field are applied, a magnetic resonance signal is generated in the subject, and based on the received signal To generate (reconstruct) a tomographic image.

In MR elastography, magnetic resonance imaging is performed while applying a predetermined vibration to an object to obtain an image representing the propagation of a wave inside the object. This image corresponds to a visualization of a ripple in the body of the applied vibration, and the degree of hardness of the tissue in the body can be known from the pattern. As a result, it is possible to perform a so-called palpation of a deep tissue that cannot be touched from the outside.

[0004] Vibration is given by vibrating a contact element in contact with the body surface at a constant amplitude and a constant frequency. For example, U.S. Pat.
As described in the specification, a moving coil installed in a static magnetic field of a magnet system is used.
il) is used. An alternating current is passed through the movable coil, and a vibration is generated using a force acting on the alternating current in the static magnetic field.

[0005]

The moving coil generates a magnetic field due to the current flowing therethrough, which adversely affects the magnetic field environment in the magnet system and degrades the quality of a magnetic resonance image.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a vibration imparting device which does not affect the magnetic environment and a magnetic resonance imaging apparatus provided with such a vibration imparting device.

[0007]

(1) According to one aspect of the present invention, there is provided a vibration member comprising a piezoelectric vibrator, and a support member for supporting one end of the vibration member in a vibration direction. A vibration transmission member attached to the other end of the vibration member in the vibration direction for transmitting vibration of the vibration member to a target, and a driving unit for electrically driving the vibration member. It is a vibration imparting device.

In the invention according to this aspect, since the vibrating member is made of the piezoelectric vibrator, no magnetic field is generated with its driving, and the magnetic field environment is not affected. (2) According to another aspect of the invention for solving the above-described problem, the vibration transmitting member transmits to the object a vibration whose vibration direction is perpendicular to the traveling direction of the wave. The vibration imparting device according to (1).

In the invention according to this aspect, since the vibration whose vibration direction is perpendicular to the traveling direction of the wave is transmitted from the vibration transmitting member to the object, a transverse wave suitable for MR elastography can be propagated inside the object. it can.

(3) The invention according to another aspect for solving the above-mentioned problem is characterized in that the vibration transmitting member is non-magnetic and non-conductive. Is a vibration imparting device.

In the invention according to this aspect, since the vibration transmitting member is non-magnetic and non-conductive, its movement does not affect the magnetic field environment. (4) According to another aspect of the invention for solving the above-described problem, the support member is non-magnetic and non-conductive, and the support member is one of (1) to (3). The vibration applying device according to any one of the first to third aspects.

In the invention according to this aspect, since the support member is non-magnetic and non-conductive, it does not affect the magnetic field environment. (5) According to another aspect of the invention for solving the above-described problem, there is provided a magnetic resonance imaging apparatus that forms an image based on a magnetic resonance signal generated inside a target using a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field. A vibrating member comprising a piezoelectric vibrator, a support member for supporting one end of the vibrating member in the vibration direction, and a device attached to the other end of the vibrating member in the vibration direction. A magnetic resonance imaging apparatus comprising: a vibration imparting device having a vibration transmission member that transmits vibration of the vibration member to the object, and a driving unit that electrically drives the vibration member. .

In the invention according to this aspect, since the vibrating member is formed of the piezoelectric vibrator, no magnetic field is generated with its driving, and the magnetic field environment is not affected. Therefore, high quality magnetic resonance imaging can be performed.

(6) According to another aspect of the present invention for solving the above-mentioned problems, the vibration transmitting member transmits a vibration whose vibration direction is perpendicular to a traveling direction of a wave to the object.
(5) The magnetic resonance imaging apparatus according to (5).

In the invention according to this aspect, since the vibration whose vibration direction is perpendicular to the traveling direction of the wave is transmitted from the vibration transmitting member to the object, the transverse wave can be propagated inside the object. Thereby, MR elastography can be performed effectively.

(7) According to another aspect of the invention for solving the above-mentioned problem, the vibration transmitting member is non-magnetic and non-conductive, and is described in (5) or (6). Is a magnetic resonance imaging apparatus.

In the invention according to this aspect, since the vibration transmitting member is non-magnetic and non-conductive, its movement does not affect the magnetic field environment. Therefore, high quality magnetic resonance imaging can be performed.

(8) According to another aspect of the invention for solving the above-mentioned problem, the support member is non-magnetic and non-conductive. A magnetic resonance imaging apparatus according to any one of the above.

In the invention according to this aspect, since the supporting member is non-magnetic and non-conductive, it does not affect the magnetic field environment. Therefore, high quality magnetic resonance imaging can be performed.

[0020]

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 diagram of the magnetic resonance imaging apparatus. 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.

As shown in FIG. 1, the present apparatus has a magnet system 100. The magnet system 100 includes a main magnetic field coil unit 102 and a gradient coil unit 106
And an RF (radio frequency) coil unit 108. Each of these coil portions has a substantially cylindrical shape and is arranged coaxially with each other. A generally cylindrical internal space of the magnet system 100 (bore: bor)
e), the subject 300 to be photographed is a cradle
e) loaded and unloaded by transport means (not shown) mounted on the 500; The target 300 is, for example, a patient or the like.

The object 300 is provided with a vibration applying unit 110. The vibration applying unit 110 applies vibration to the object 300. The vibration applying unit 110 will be described later.

The main magnetic field coil unit 102 forms a static magnetic field in the internal space of the magnet system 100. The direction of the static magnetic field is substantially parallel to the direction of the body axis of the object 300. That is, a so-called horizontal magnetic field is formed. The main magnetic field coil unit 102 is configured using, for example, a superconducting coil. It is needless to say that not only the superconducting coil but also a normal conducting coil may be used.

The gradient coil unit 106 generates a gradient magnetic field for giving a gradient to the static magnetic field strength. The generated gradient magnetic fields are a slice gradient magnetic field, a readout gradient magnetic field, and a phase encode gradient magnetic field. The gradient coil unit 1 corresponds to these three types of gradient magnetic fields.
Reference numeral 06 has three gradient coils (not shown).

The RF coil unit 108 controls the object 3 in the static magnetic field space.
A high-frequency magnetic field for exciting spins in the body of 00 is formed. Hereinafter, forming a high-frequency magnetic field is also referred to as transmitting an RF excitation signal. The RF coil unit 108
Further, it receives an electromagnetic wave generated by the excited spin, that is, a magnetic resonance signal.

The RF coil unit 108 has a transmitting coil and a receiving coil (not shown). The same coil is used for the transmitting coil and the receiving coil, or a dedicated coil is used for each.

The vibration applying section 110 includes a vibration applying drive section 12.
Connected to 0. The vibration applying drive section 120 supplies a drive signal to the vibration applying section 110. The portion including the vibration imparting unit 110 and the vibration imparting drive unit 120 is an example of an embodiment of the vibration imparting device of the present invention. The configuration of the present apparatus shows an example of an embodiment relating to the apparatus of the present invention.

The gradient coil unit 106 includes a gradient driving unit 130
Is connected. The gradient driving unit 130 is a gradient coil unit 1
A drive signal is given to 06 to generate a gradient magnetic field. The gradient drive unit 130 has three drive circuits (not shown) corresponding to the three gradient coils in the gradient coil unit 106.

The RF coil unit 108 includes an RF driving unit 140
Is connected. The RF driving unit 140 is the RF coil unit 1
08, a drive signal is given, an RF excitation signal is transmitted, and the target 3
Excite the spins in the body of 00.

The RF coil unit 108 includes a data collection unit 15
0 is connected. The data collection unit 150 captures a received signal received by the RF coil unit 108 and collects the received signal as view data.

The vibration applying drive unit 120 and the gradient drive unit 13
The control unit 160 is connected to the RF drive unit 140 and the data collection unit 150. The control unit 160 controls the vibration applying drive unit 120 to the data collection unit 150 to perform photographing. The control unit 160 performs imaging in synchronization with the application of the vibration to the target 300.

The output side of the data collection unit 150 is connected to the data processing unit 170. The data processing unit 170 is configured using, for example, a computer. The data processing unit 170 includes a memory (me
(money). The memory stores a program for the data processing unit 170 and various data. The function of the present apparatus is realized by the data processing unit 170 executing a program stored in the memory.

The data processing unit 170 is provided with the data collection unit 15
The data taken from 0 is stored in the memory. A data space is formed in the memory. The data space is two-dimensional
It constitutes a Fourier space. The data processing unit 170 performs two-dimensional inverse Fourier transform on the data in the two-dimensional Fourier space to generate an image of the target 300 (reconstruction).
I do. Hereinafter, the two-dimensional Fourier space is referred to as a k-space (k-s
space).

The data processing section 170 is connected to the control section 160. The data processing unit 170 is at a higher level than the control unit 160 and controls it. The display section 180 and the operation section 190 are connected to the data processing section 170. The display unit 180 includes a graphic display (graphic).
display). The operation unit 190 is a pointing device.
e) is composed of a keyboard provided with e).

The display section 180 displays the reconstructed image output from the data processing section 170 and various information. The operation unit 190 is operated by an operator, and inputs various commands and information to the data processing unit 170. The operator operates the present apparatus interactively through the display unit 180 and the operation unit 190.

FIG. 2 shows a block diagram of another type of magnetic resonance imaging apparatus. 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.

The apparatus shown in FIG. 2 has a magnet system 100 'which is different from the apparatus shown in FIG.
Except for the magnet system 100 ', the configuration is the same as that of the apparatus shown in FIG. 1, and the same parts are denoted by the same reference numerals and description thereof will be omitted.

The magnet system 100 'has a main magnetic field magnet unit 102', a gradient coil unit 106 ', and an RF coil unit 108'. These main magnetic field magnet units 1
02 ′ and each of the coil portions are formed of a pair of coils opposing each other across a space. Each of them has a substantially disk shape and is arranged so as to share a central axis. The object 300 is mounted on the cradle 500 and is carried in and out of the internal space (bore) of the magnet system 100 ′ by carrying means (not shown).

The main magnetic field magnet unit 102 'forms a static magnetic field in the internal space of the magnet system 100'. The direction of the static magnetic field is substantially perpendicular to the body axis direction of the object 300. That is, a so-called vertical magnetic field is formed. The main magnetic field magnet unit 102 'is configured using, for example, a permanent magnet. It is needless to say that the present invention is not limited to the permanent magnet and may be configured using a superconducting electromagnet or a normal conducting electromagnet.

The gradient coil section 106 'generates a gradient magnetic field for giving a gradient to the intensity of the static magnetic field. The generated gradient magnetic fields are a slice gradient magnetic field, a readout gradient magnetic field, and a phase encode gradient magnetic field, and the gradient coil unit 106 'has three types of gradient coils (not shown) corresponding to these three types of gradient magnetic fields. .

The RF coil unit 108 'transmits an RF excitation signal for exciting spins in the body of the subject 300 to the static magnetic field space. The RF coil unit 108 'also receives a magnetic resonance signal generated by the excited spin. The RF coil unit 108 'has a transmitting coil and a receiving coil (not shown). The same coil is used for the transmitting coil and the receiving coil, or a dedicated coil is used for each.

FIG. 3 shows a schematic configuration of a main part of the vibration imparting unit 110 in relation to the object 300. FIG. 4 and FIG. 5 show schematic configurations of main parts of the vibration applying unit 110 as perspective views viewed from different viewpoints.

As shown in the figure, the vibration applying section 110 has a vibrator 112. The vibrator 112 is constituted by a piezoelectric vibrator. As the piezoelectric vibrator, for example, PZT (lead zirconate titanate (Ti) (Zr) (Pb)) or the like is used. The vibrator 112 is an example of an embodiment of the vibration member according to the present invention.

The vibrator 112 has one end attached to one end of a support rod 114. The other end of the support bar 114 is attached to a column 142. The height of the column 142 can be adjusted by a vertical mechanism 144.

A stress sensor is attached to an end of the support bar 114 on the support column 142 side. The stress sensor 146 senses the stress at the root of the support bar 114.

The support bar 114 is made of a non-conductive and non-magnetic material. Such materials include, for example, plastics and ceramics (c).
eramics) are used. The support bar 114 is an example of an embodiment of the support member in the present invention.

A vibrating plate 116 is attached to the other end of the vibrator 112. Diaphragm 116 has a generally L-shaped shape and has a vertical portion 162 and a horizontal portion 164.
The diaphragm 116 has a vertical portion 162 attached to the vibrator 112 and a horizontal portion 164 in contact with the body surface of the subject 300.

The diaphragm 116 is made of a non-conductive and non-magnetic material. As such a material, for example, plastics or ceramics is used. Diaphragm 1
16 is an example of an embodiment of the vibration transmitting member according to the present invention.

The vibrator 112 includes a vibration applying drive unit 120.
Provides a drive signal. The vibration applying drive unit 120 includes:
As shown in FIG. 6, an oscillator 122 and an amplifier 124 are provided, and an output signal of the oscillator 122 is amplified by the amplifier 124 and provided to the vibrator 112. Thereby, the vibrator 112
Vibrates at the same frequency as the frequency of the output signal of the oscillator 122. The vibrator 112 is a so-called vertical effect type piezoelectric vibrator that vibrates in a direction in which an electric field is applied. As shown in FIG. 7, the vibrator 112 may be a so-called transverse effect type piezoelectric vibrator that vibrates in a direction perpendicular to the direction in which the electric field is applied. The portion including the oscillator 122 and the amplifier 124 is an example of the embodiment of the driving means in the present invention.

The vibrating direction of the vibrator 112 is the axial direction of the support rod 114 regardless of whether the vertical effect type or the horizontal effect type is used. Thereby, the vibrator 112 vibrates the diaphragm 116 in a direction parallel to the plate surface of the horizontal portion 164.

When the diaphragm 116 that is in contact with the body surface vibrates in a direction parallel to the plate surface, the object 300 is subjected to shearing at the portion where the diaphragm 116 is in contact, as indicated by the arrow 302. (Shear) vibration is applied. Hereinafter, this vibration is also referred to as lateral vibration. Waves generated by the applied vibrations travel from the body surface toward the body. The traveling direction of the wave is perpendicular to the direction of the vibration.

In order to effectively apply vibration, it is preferable to appropriately adjust the pressing force of the diaphragm 116 against the object 300. Therefore, the column 14 is moved by the vertical mechanism 144.
The pressing force of the diaphragm 116 is adjusted by adjusting the height of 2.
The stress generated in the support bar 114 at the time of pressing is the stress sensor 146.
The pressing force can be known based on the detection signal.

Since the vibrator 112 is composed of a piezoelectric vibrator, the vibration applying section 110 does not generate a magnetic field when driven. Therefore, the magnet system 1
It does not disturb the magnetic field environment within 00 (100 '). Further, since the diaphragm 116 is made of a non-conductive and non-magnetic material, even if it vibrates, it does not affect the magnetic field environment at all.

Further, since the support rod 114 is also made of a non-conductive and non-magnetic material, no eddy current flows due to the gradient magnetic field. Therefore, no disturbing magnetic field is generated by the eddy current. The vibrator 112 and the support rod 1
It is preferable to cover the portion consisting of 14 with an electromagnetic shield from the viewpoint of shielding electromagnetic waves that may be generated when the vibrator 112 is driven.

FIGS. 8 and 9 show an example of a pulse sequence used for magnetic resonance imaging. This pulse sequence is obtained by using MR (Gradient Echo).
This is a pulse sequence for performing elastography.

In the figure, (1) is α ° for RF excitation.
(2), (3), (4), and (5) are sequences of slice gradient Gs, phase encode gradient Gp, readout gradient Gr, and gradient echo MR, respectively. Note that α °
The pulse is represented by the center signal. The pulse sequence proceeds from left to right along the time axis t.

These pulse sequences correspond to the object 300
The process is executed in a state where the lateral vibration is applied by the vibration applying unit 110. First, the pulse sequence of FIG. 8 is executed, and then the pulse sequence of FIG. 9 is executed. The order may be reversed.

As shown in FIG. 8, α ° excitation of spin is performed by an α ° pulse. Flip angle (flip a
ngle) α ° is 90 ° or less. At this time, a slice gradient Gs is applied, and selective excitation for a predetermined slice is performed.

After the α ° excitation, for example, using the phase encoding gradient Gp, a contrast is applied to the spin phase in accordance with the spin displacement speed.
The gradient for imparting contrast to the spin phase is an AC gradient, and its frequency is made equal to the frequency of the transverse vibration applied to the object 300. The phase contrast is
A slice gradient or a readout gradient may be used instead of the phase encoding gradient.

After applying the phase contrast gradient over a predetermined period, the phase of the spin is encoded by the phase encode gradient Gp. Then, the spin is first dephased by the readout gradient Gr (d
ephase) and then spin the phase (rep)
hase) to generate a gradient echo MR. The signal intensity of the gradient echo MR becomes maximum at a time point after an echo time TE after the α ° excitation. The gradient echo MR is collected by the data collection unit 150 as view data.

Such a pulse sequence has a period TR
(Repetition time) is repeated 64 to 512 times. The amount of phase encoding is changed for each repetition, and different phase encoding is performed each time. As a result, one set of view data of 64 to 512 views filling the k space is obtained.

Next, the pulse sequence shown in FIG.
While changing the amount of phase encoding, 64 to 5 in the period TR
Repeat 12 times. This fills the k space 6
Another set of view data of 4 to 512 views is obtained. In the pulse sequence of FIG. 9, the phase of the gradient of the alternating current for performing phase contrast is different from that of the pulse sequence of FIG.

The data processing section 170 obtains a difference between two sets of view data in the k-space, and performs a two-dimensional inverse Fourier transform on the difference to reconstruct a tomographic image of the object 300. The reconstructed tomographic image is an image obtained by visualizing ripples of the transverse vibration applied to the object 300, that is, an MR elastography image. The operation of the vibration applying unit 110 is performed by the magnet system 10.
0 (100 ') does not adversely affect the magnetic field environment.
The R elastography image is of high quality. The reconstructed image is stored in the memory and displayed on the display unit 180.

[0064]

As described above in detail, according to the present invention, it is possible to realize a vibration imparting apparatus which does not affect the magnetic environment and a magnetic resonance imaging apparatus having such a vibration imparting apparatus. it can.

[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 block diagram of an apparatus according to an embodiment of the present invention.

FIG. 3 is a diagram showing a schematic configuration of a main part of a vibration applying unit in the apparatus shown in FIG. 1 or FIG.

FIG. 4 is a diagram showing a schematic configuration of a main part of a vibration applying unit in the apparatus shown in FIG. 1 or FIG.

FIG. 5 is a diagram showing a schematic configuration of a main part of a vibration imparting unit in the apparatus shown in FIG. 1 or FIG.

FIG. 6 is a block diagram of an electrical configuration of a vibration applying unit and a vibration applying drive unit in the apparatus shown in FIG. 1 or FIG.

FIG. 7 is a block diagram of an electrical configuration of a vibration applying unit and a vibration applying drive unit in the device shown in FIG. 1 or FIG.

FIG. 8 is a diagram showing an example of a pulse sequence executed by the device shown in FIG. 1 or FIG.

FIG. 9 is a diagram showing an example of a pulse sequence executed by the device shown in FIG. 1 or 2;

[Explanation of symbols]

 100, 100 'Magnet system 102 Main magnetic field coil unit 102' Main magnetic field magnet unit 106, 106 'Gradient coil unit 108, 108' RF coil unit 110 Vibration applying unit 112 Vibrator 114 Support rod 116 Vibration plate 120 Vibration applying drive unit 122 Oscillator 124 Amplifier 130 Gradient drive unit 140 RF drive unit 150 Data collection unit 160 Control unit 170 Data processing unit 180 Display unit 190 Operation unit 300 Target 500 cradle

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G01N 24/02 510Y

Claims (8)

[Claims] A vibration member formed of a piezoelectric vibrator; a support member supporting one end of the vibration member in a vibration direction; and a vibration member attached to the other end of the vibration member in the vibration direction and transmitting vibration of the vibration member to a subject. A vibration transmission member, and a driving unit for electrically driving the vibration member. 2. The vibration imparting device according to claim 1, wherein the vibration transmission member transmits a vibration whose vibration direction is perpendicular to a traveling direction of the wave to the object. 3. The vibration imparting device according to claim 1, wherein the vibration transmission member is non-magnetic and non-conductive. 4. The vibration imparting device according to claim 1, wherein the support member is non-magnetic and non-conductive. 5. A magnetic resonance imaging apparatus for forming an image based on a magnetic resonance signal generated inside a subject using a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field, wherein the apparatus applies vibration to the subject. A vibration member including a piezoelectric vibrator; a support member that supports one end of the vibration member in the vibration direction; and a vibration transmission that is attached to the other end of the vibration member in the vibration direction and transmits the vibration of the vibration member to the object. A magnetic resonance imaging apparatus comprising: a member; and a driving unit that electrically drives the vibration member. 6. The vibration transmitting member transmits a vibration whose vibration direction is perpendicular to a traveling direction of a wave to the object.
The magnetic resonance imaging apparatus according to claim 5, wherein: 7. The magnetic resonance imaging apparatus according to claim 5, wherein the vibration transmitting member is non-magnetic and non-conductive. 8. The magnetic resonance imaging apparatus according to claim 5, wherein the support member is non-magnetic and non-conductive.