JP2004275380A - Magnetic resonance imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic resonance imaging (MRI) apparatus highly precisely creating tomographic image of a subject under a respiratory movement using a nuclear magnetic resonance. <P>SOLUTION: For detecting a detection signal originating from the nuclear magnetic resonance, this MRI apparatus 1000 is provided with a static magnetic field coil 100 for impressing a magnetic field to the subject 10, a gradient magnetic field 102, an RF coil 104 and a tomographic imaging control part 200 providing the RF coil 104 with a vibrating magnetic field and creating the tomographic image from the detection signal by the RF coil 106. A trigger generation part 230 in the tomographic imaging control part 200 controls the starting timing of the imaging operation of the MRI apparatus and gives a stimulating sound to the subject 10 synchronously with the starting timing via a speaker 232. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a configuration of a magnetic resonance imaging (MRI) apparatus for performing tomography of a living body, and particularly to a configuration for measurement synchronized with a respiratory motion of a subject.
[0002]
[Prior art]
2. Description of the Related Art As a method of imaging a cross section of the brain or whole body of a living body, a magnetic resonance imaging method using a nuclear magnetic resonance phenomenon for an atom in a living body, particularly a hydrogen atom nucleus, is used for a clinical image diagnosis of a human. .
[0003]
When applied to the human body, the magnetic resonance imaging has, for example, the following characteristics as compared with “X-ray CT” which is a similar tomography in the human body.
[0004]
(1) An image having a concentration corresponding to the distribution of hydrogen atoms and the signal relaxation time (reflecting the strength of atomic bonding) can be obtained. For this reason, light and shade according to the difference in the properties of the tissue are exhibited, and the difference in the tissue is easily observed.
[0005]
(2) The magnetic field has no absorption by bone. Therefore, it is easy to observe a region surrounded by the bone (intracranial, spinal cord, etc.).
[0006]
(3) Since it does not harm the human body unlike X-rays, it can be widely used.
[0007]
Such magnetic resonance imaging uses the magnetic properties of hydrogen nuclei (protons) which are most contained in each cell of the human body and have the greatest magnetism.
[0008]
The motion of a spin angular momentum, which is responsible for the magnetism of hydrogen nuclei, in a magnetic field can be classically compared to the precession of a coma. The direction of the spin angular momentum of hydrogen nuclei as described above (the direction of the axis of rotation of the coma) is random in an environment without a magnetic field, but is oriented in the direction of the line of magnetic force when a static magnetic field is applied.
[0009]
When an oscillating magnetic field is further superimposed in this state, if the frequency of the oscillating magnetic field is a resonance frequency f ₀ = γB ₀ / 2π (γ: coefficient specific to a substance) determined by the strength of the static magnetic field, the nucleus is generated by resonance. The energy moves to the side, and the direction of the magnetization vector changes (precession increases). When the oscillating magnetic field is turned off in this state, the precession returns to the direction in the static magnetic field while returning the inclination angle. By detecting this process from outside using an antenna coil, an NMR (nuclear magnetic resonance) signal can be obtained.
[0010]
Further, when observing such nuclear magnetic resonance, a modulation is applied to the applied magnetic field (encoding) so that the spatial position of the source of the generated NMR signal can be specified (encoding). If the position of the NMR signal source in the two-dimensional section of the object to be measured (for example, a person) is specified by performing a Fourier transform on the two-dimensional section of the object to be measured reflecting the amount of water contained in the tissue and the like. Images can be obtained. Such an imaging method is referred to as "magnetic resonance imaging (MRI)."
[0011]
For example, MRI is suitable for measuring a three-dimensional shape including the internal structure of a speech organ. However, imaging an MRI requires several seconds to several minutes of imaging time. In particular, the larynx related to the generation of the sound source is small in size, and the image resolution and the S / N ratio cannot be sufficiently obtained. Therefore, the imaging time tends to be long in order to obtain a high-quality image. In spite of the above situation, the larynx moves up and down with the opening and closing movements of the vocal cords and breathing. Artifact).
[0012]
On the other hand, there has been proposed a method of capturing a moving image synchronized with a trigger by using an external trigger in a magnetic resonance image (for example, see Non-Patent Document 1). By applying this method to still image shooting, in order to suppress the above-mentioned artifacts and avoid problems due to respiratory movement, conventionally, body movements due to respiration are monitored by bellows attached to the abdomen, and exhalation stability Occasionally, a “respiratory-gated imaging method”, which is a method of driving MRI, has been used.
[0013]
FIG. 6 is a diagram showing a sequence of a conventional MRI imaging.
FIG. 6A shows a sequence in which, for example, a subject repeatedly spontaneously utters “A to” and drives the MRI apparatus to perform imaging continuously during the operation of the subject. When such an imaging sequence is used, as described above, a clear cross-sectional image cannot be obtained due to an artifact accompanying the breathing of the subject.
[0014]
On the other hand, FIG. 6B shows an imaging sequence by the “respiratory synchronization imaging method”.
Monitoring the signal from the above-mentioned bellows, and when the signal fluctuates from a state larger than a predetermined threshold value to a smaller value, driving the MRI for a predetermined time triggered by a point of time when the signal crosses the threshold value It is.
[0015]
[Non-patent document 1]
Masaki, S.M. , Tiede, M .; , Honda, K .; Authors, "MRI-based speech production using a synchronized sampling method." Acoustic. Soc. Jpn. (E). , 20 (5). p. 375-379.
[0016]
[Problems to be solved by the invention]
However, in order to detect when the breathing is stable, the threshold value is set based on the vertical movement of the abdomen accompanying the respiratory movement. Therefore, (1) the threshold value must be set based on the experience of the examiner. 2) Individual differences in subject are large in respiratory motion, (3) respiratory motion varies even within the same subject, (4) setting by threshold value, imaging is included even at the start of inhalation, etc. is there. (5) If the threshold value is narrowed, a clear image can be captured, but the imaging time is prolonged. Conversely, if the threshold value is widened, the image is disturbed.
[0017]
The present invention has been made in order to solve the above-described problems, and an object thereof is to perform tomographic imaging of a subject with high accuracy using nuclear magnetic resonance even when the subject has respiratory motion. It is to provide a magnetic resonance imaging device that can be performed.
[0018]
[Means for Solving the Problems]
In order to achieve such an object, a magnetic resonance imaging apparatus of the present invention detects a detection signal resulting from nuclear magnetic resonance from a subject, and generates a tomographic image of the subject by using a magnetic resonance imaging apparatus. And a static magnetic field applying means for applying a static magnetic field to the subject, and applying a magnetic field modulated to the subject in such a manner that the detection signal has position information of a nucleus emitting a detection signal in a selected cross section of the subject. Gradient magnetic field applying means for applying a fluctuating magnetic field to a subject, a fluctuating magnetic field transmitting / receiving means for detecting a detection signal from the subject, and providing the fluctuating magnetic field to the fluctuating magnetic field transmitting / receiving means, and receiving the detection signal. Tomography control means for generating a tomographic image, wherein the tomography control means controls the start timing of the imaging operation of the magnetic resonance imaging apparatus and receives the tomographic image in synchronization with the start timing. Including the synchronization control means for providing a stimulus sound in person.
[0019]
Preferably, the synchronization control means repeats the start timing at a predetermined cycle, and the tomography control means performs the imaging operation for a predetermined period from the start timing.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0021]
[Configuration and Operation of Magnetic Resonance Imaging Apparatus]
FIG. 1 is a functional block diagram showing a configuration of a magnetic resonance imaging apparatus (hereinafter, referred to as “MRI apparatus”) 1000 according to the present invention.
[0022]
Referring to FIG. 1, an MRI apparatus 1000 includes a platform 12 for supporting a subject 10, a static magnetic field coil 100 for generating a static magnetic field, and an observation section (slice) of the subject as described later. A gradient magnetic field coil 102 for giving information of a position and a position in a slice to an observation signal, an RF coil 104 for outputting an electromagnetic wave to apply a fluctuating magnetic field to an atomic nucleus to be observed, and an atomic nucleus to be observed And a tomography control unit 200 for controlling the coils 100 to 104 and generating a tomographic image based on the signal received by the RF coil 106.
[0023]
Further, the tomography control unit 200 includes an input unit 210 for inputting an instruction or the like from a user, a control unit 220 for controlling a measurement operation, and a trigger serving as a reference for the utterance timing of the subject 10. The trigger generation unit 230 outputs a stimulus sound of a predetermined rhythm through the speaker 232 to notify the subject 10 of the utterance timing while providing a signal to the control unit 220, and the RF coil 104 controlled by the control unit 220. RF pulse transmitting section 240 for applying an RF pulse thereto, signal amplifying section 250 for amplifying a signal from RF coil 106, and performing Fourier transform processing based on a detection signal from signal amplifying section 250. Thus, an image reconstruction unit 260 for reconstructing a cross-sectional image to be observed, and a reconstruction based on information from the image reconstruction unit 260 And a display unit 270 for displaying the cross-sectional image.
[0024]
Note that the trigger generation unit 230 may be a computer external to the MRI apparatus 1000, and may be configured to provide a trigger signal to the control unit 220 via a predetermined interface and provide a stimulus sound to the speaker 232.
[0025]
The speaker 232 may be any type that can output a sound of a predetermined rhythm to notify the subject of the above-mentioned utterance timing, and may be, for example, headphones.
[0026]
Here, more specifically, the static magnetic field coil 100 is composed of, for example, four air-core coils, and generates a uniform magnetic field inside by combining the four air-core coils to give orientation to spins of hydrogen nuclei in the body of the subject 10. .
[0027]
The RF coil 104 emits high frequency to excite atomic nuclei in the body of the subject 10, and the RF coil 106 detects a detection signal (echo signal) caused by the generated nuclear magnetic resonance.
[0028]
The gradient magnetic field coil 102 includes three sets of gradient coils, not shown, of X, Y, and Z. The Z coil, when excited, inclines the magnetic field strength in the Z direction to limit the resonance surface. Immediately after the application of the magnetic field, a short-time gradient is applied to apply a phase modulation proportional to the Y coordinate to the detection signal (phase encoding). The X coil then applies a gradient at the time of data collection to make the detection signal proportional to the X coordinate. Gives a modulated frequency (frequency encoding).
[0029]
That is, when a high-frequency electromagnetic field having a resonance frequency is applied to the subject 10 in a state where a Z-axis gradient magnetic field is applied to a static magnetic field through the RF coil 104, hydrogen nuclei in a portion where the magnetic field strength is in a resonance condition are generated. , Are selectively excited and begin to resonate. Hydrogen nuclei in a portion that satisfies the resonance condition (for example, a slice of the subject 10 having a predetermined thickness) are excited, and the spins rotate together. When the excitation pulse is stopped, an electromagnetic wave emitted from the spinning spin induces a signal in the RF coil 106, and this signal is detected for a while. With this signal, the tissue containing water in the body of the subject 10 is observed. Then, in order to know the signal transmission position, a signal is detected by applying a gradient magnetic field of X and Y.
[0030]
The control unit 220 measures the detection signal while repeatedly providing the excitation signal, and the image reconstruction unit 260 reduces the resonance frequency to the X coordinate by the first Fourier transform calculation, and performs the Y coordinate by the second Fourier transform. Is restored to obtain an image, and the corresponding image is displayed on the display unit 270.
[0031]
FIG. 2 is a diagram for describing in detail the configuration of the RF coil 106 shown in FIG.
[0032]
FIG. 2A is a side view of the RF coil 106, and FIG. 2B is a top view of the RF coil 106.
[0033]
The RF coil 106 is for detecting an NMR signal from the larynx by being placed on the larynx of the subject 10 in the supine position. As shown in FIG. 2, in the RF coil 106, an elliptical antenna 106.2 obtained by transforming a circular surface coil antenna into an elliptical shape (long axis 140 mm, short axis 75 mm) is used to convert a measured induced current into a signal. Is attached to a housing 106.4 in which the circuit of FIG.
[0034]
The measurement signal is sent from the housing 106.4 to the signal amplifier 250 via the cable 106.6.
[0035]
Here, as shown in FIG. 2A, the elliptical antenna 106.2 has a bent shape when viewed from the side, and has a shape that can be easily installed on the larynx of the subject 10.
[0036]
By using such an RF coil 106, the subject 10 can utter naturally in the supine position even after the coil is mounted.
[0037]
FIG. 3 is a diagram for explaining a cartilage organ of a larynx to be measured. FIG. 3A is a sagittal cross-sectional view of a human body, and FIG. 3B is a diagram showing a cartilage organ of the larynx extracted.
[0038]
In the following description, an example of observing cricoid cartilage in a cartilage organ of the larynx will be described as an example.
[0039]
Referring to FIG. 3, thyroid cartilage 300 is a shield-shaped cartilage formed by two plates below the hyoid bone. The vocal cords are attached to the medial surface of the thyroid cartilage. In the upper and lower rear portions are characteristic upper and lower corners 302 and 304.
[0040]
The cricoid cartilage 306 is located immediately below the thyroid cartilage 300, and is a ring-shaped cartilage that is high posteriorly and short in front. A thyroid joint is formed inside the lower corner of the thyroid cartilage 300 and outside the posterior part of the cricoid cartilage.
[0041]
FIG. 4 is a diagram showing a sequence for performing cross-sectional imaging of the larynx when the subject 10 utters voice by the MRI apparatus 1000 shown in FIG. In FIG. 4, the horizontal axis represents time, and the vertical axis represents the intensity of each signal.
[0042]
Referring to FIG. 4, trigger generation unit 230 outputs a trigger signal to control unit 220 and an appropriate stimulus sound to subject 10 in synchronization with each other at predetermined timings. The trigger signal is an electric pulse for driving the imaging operation of the MRI apparatus 1000.
[0043]
On the other hand, the stimulus sound is a sound having a rhythm such as two beats, three beats, or four beats within the repetition interval, and the subject 10 periodically repeats the imaging task such as vocalization in accordance with this.
[0044]
The “imaging task” is a periodic operation (vocalization, exhalation, inspiration) that the subject 10 repeats in accordance with the stimulus sound.
[0045]
Here, in order to make it easier for the subject 10 to take the utterance timing, it is desirable that the stimulus sound or the rhythm that defines the start timing is repeated at regular time intervals.
[0046]
When the patient repeats the utterance in accordance with the stimulus sound based on the trigger signal, a stable still image can be captured in a short time. That is, since the MRI apparatus 1000 performs the imaging operation only for a predetermined period after the control unit 220 receives the trigger signal, the MRI apparatus 1000 captures only the stable part of the movement of the subject 10 and obtains an image with less artifact described above. Can be done.
[0047]
FIG. 5 is a diagram showing a cross-sectional image of the II ′ cross-section in FIG. 3 taken by MRI.
[0048]
FIG. 5A shows an image captured in the sequence shown in FIG. 6A, and FIG. 5B shows a case captured in the sequence described in FIG.
[0049]
In FIG. 5A, the image is clearly degraded due to the artifact, whereas in the sequence of the present invention shown in FIG. 5B, the disturbance of the image is greatly improved.
[0050]
In the above description, the case where the cross section of the larynx is imaged has been described as an example. However, in the present invention, in the MRI imaging, other parts where movement due to respiration is likely to occur, particularly the chest, abdomen, etc. effective.
[0051]
The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
[0052]
【The invention's effect】
As described above, according to the magnetic resonance imaging apparatus of the present invention, even when there is a subject's respiratory motion, a nuclear magnetic resonance image can be selectively captured in a stable period of the respiratory motion, so that a stable and highly accurate Measurement of magnetic resonance images is possible.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing a configuration of an MRI apparatus 1000 according to the present invention.
FIG. 2 is a diagram for describing in detail a configuration of an RF coil shown in FIG. 1;
FIG. 3 is a diagram for explaining a cartilage organ of a larynx to be measured.
FIG. 4 is a diagram showing a sequence for performing cross-sectional imaging of the larynx when the subject 10 utters, by the MRI apparatus 1000 shown in FIG.
FIG. 5 is a diagram showing a cross-sectional image of the II ′ cross-section in FIG. 3 taken by MRI.
FIG. 6 is a diagram showing a conventional MRI imaging sequence.
[Explanation of symbols]
10 subjects, 12 units, 100 static magnetic field coil, 102 gradient magnetic field coil, 104, 106 RF coil, 200 tomography control unit, 210 input unit, 220 control unit, 230 trigger generation unit, 240 RF pulse transmission unit, 250 signals Amplifying unit, 260 image reconstructing unit, 270 display unit, 1000 MRI apparatus.

Claims (2)

A magnetic resonance imaging apparatus for detecting a detection signal caused by nuclear magnetic resonance from a subject and generating a tomographic image of the subject,
Static magnetic field applying means for applying a static magnetic field to the subject,
Within the selected cross section of the subject, gradient magnetic field applying means for applying to the subject a magnetic field modulated so that the detection signal has the position information of the nucleus emitting the detection signal,
Applying a fluctuating magnetic field to the subject, fluctuating magnetic field transmitting and receiving means for detecting the detection signal from the subject,
The tomography control means for providing the fluctuating magnetic field to the fluctuating magnetic field transmitting / receiving means, receiving the detection signal and generating the tomographic image,
The tomographic control means,
A magnetic resonance imaging apparatus, comprising: a synchronization control unit for controlling a start timing of an imaging operation of the magnetic resonance imaging apparatus and giving a stimulus sound to the subject in synchronization with the start timing. The synchronization control means repeats the start timing at a predetermined cycle,
The magnetic resonance imaging apparatus according to claim 1, wherein the tomography control unit performs the imaging operation for a predetermined period from the start timing.

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