JP2000175881A - Magnetic resonance imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To start imaging action while a will of a subject to be examined is esteemed by providing a magnetic resonance imaging apparatus being suitable for performing imaging of narrow blood vessels and blood streams in a stomach region of the subject to be examined. SOLUTION: In a magnetic resonance imaging apparatus, a signal generator 34 for generating a signal indicating that preparation to imaging has been completed by a subject himself and a timing generator 31 for starting imaging following to a specified sequence as a trigger by using the output from the signal generator 34 are provided. It is possible thereby to start the imaging at a timing where mind of the subject side is stabilized and preparation to the imaging such as stopping of respiration is completed without enforcing stopping of the respiration by convenience of the imaging apparatus side.

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 suitable for imaging a cross section of a thin blood vessel or blood flow in an abdominal region of a subject.

[0002]

2. Description of the Related Art When a group of nuclear spins having a specific magnetic moment is placed in a uniform static magnetic field, a phenomenon of resonantly absorbing the energy of a high-frequency magnetic field rotating at a specific frequency (this is referred to as a nuclear phenomenon). Utilizing the magnetic resonance phenomenon)
2. Description of the Related Art A technique for visualizing chemical and physical microscopic information of a substance is known. As an application of this technology to medical care,
Magnetic resonance imaging devices that measure the density distribution and relaxation time distribution of nuclear spins at a desired examination site in a subject, and visualize and display a cross section of the examination site of the subject based on the measured data are widely used. I have.

As shown in FIG. 3, a schematic configuration of a magnetic resonance imaging apparatus includes a magnet system 1, a gradient magnetic field system 2, an RF system 3, a pulse sequencer 4, a computer system 5, and the like. Magnet system 1
Is composed of a permanent magnet or a superconducting electromagnet for generating a uniform static magnetic field, and the gradient magnetic field system 2 is composed of a gradient magnetic field coil 6 and a gradient magnetic field power supply 7 for supplying a current thereto. Further, the RF system 3 supplies an RF pulse 10 to the RF coil 8 via the RF amplifier 9 or an echo signal 11 (NMR signal) obtained from the RF coil 8.
) For receiving and detecting signals. Therefore, the subject is placed in a static magnetic field generated by the magnet system 1, and a gradient magnetic field pulse 13 from the gradient magnetic field system 2 and an RF system 3 are supplied to the subject according to a specific timing controlled by the pulse sequencer 4.
, An RF pulse 10 is applied. As a result, a nuclear magnetic resonance phenomenon occurs, and an echo signal 11 is emitted from the subject after an echo time (TE). This echo signal 11 is represented by R
F system 3 receives and detects, and computer system 5
Performs image reconstruction processing, displays a tomographic image on a display (not shown), and records the image on an external storage device such as a magnetic disk or a magnetic tape. The gradient magnetic field pulse 1
The pulse sequencer 4 defines the shape and application timing of the RF signal 3 and the RF pulse 10 and the collection timing of the echo signal 11, and the pulse sequencer 4 controls the pulse sequence based on the pulse sequence.

One of the most basic pulse sequences used in a magnetic resonance imaging apparatus is a spin echo method (SE method). In this SE method, as shown in FIG. 4, when an echo time is TE, an RF pulse 10 is applied to an RF coil 8 to form an echo signal 11.
First, a 90-degree pulse 10a is applied, and then TE
After a lapse of / 2 hours, a 180-degree pulse 10b is applied. By applying the 90-degree pulse 10a, each spin starts to rotate in the XY plane at a unique speed.
And a phase difference occurs between each spin with the passage of time,
When a 180-degree pulse 10b is applied thereto, each spin is inverted symmetrically to the X 'axis, and continues to rotate at the same speed thereafter. At time TE, the spin converges again and the echo signal 11
To form Since only one echo signal 11 can be acquired at a time, the acquisition must be repeated a plurality of times to obtain all the data necessary for the image reconstruction processing. At this time, since the spatial distribution of the signal has to be obtained, the gradient magnetic field pulse 13 is applied to the gradient magnetic field coil 6, and the gradient magnetic field is superimposed on the uniform static magnetic field. In order to obtain an image of a required number of times, that is, for example, a resolution of, for example, 256 × 256, for each fixed repetition time TR equal to or longer than the echo time TE while changing the intensity of the gradient magnetic field every time, 256 times
Times (256 shots). The basic pulse sequence has been described above. However, there is a strong demand for high-speed imaging in a magnetic resonance imaging apparatus, and a pulse sequence capable of imaging with a single shot (one shot) has been put into practical use with recent technological innovation. Have been.

[0005]

By the way, when a magnetic resonance imaging apparatus performs cross-sectional imaging of various parts such as a cross-section of a thin blood vessel or a blood flow in an abdominal region of a human (subject), it is necessary to perform respiratory and In order to prevent the image from being disturbed due to body movement, it is common to take an image with the subject temporarily stopping breathing. Therefore, it is necessary for the operator to give an instruction to the subject about stopping and releasing breathing every time an image is taken, which burdens the operator, and the subject also takes time to breathe properly when receiving the instruction. Was sometimes painful. As a solution to such a problem, a respiratory sensor is used to detect inspiration and expiration of the subject, and a timing is measured from the voice generation circuit so that the breathing is stopped when switching from inspiration to expiration. There is known an apparatus in which an instruction to stop breathing is issued (Japanese Patent Laid-Open No. 5-103770). However, the physical strength of the subject is not limited to healthy subjects, and it is possible that the patient's physical strength is weakened. There is a problem that the burden on the subject increases, and it is difficult to obtain a clear image. Also, besides disturbed breathing, body movement is also a factor that deteriorates image quality, so it is necessary to have the body not move with respiratory arrest during shooting, and if breathing is disturbed or the body moves, Once the imaging was stopped and the subject calmed down, the imaging was restarted from the beginning. As described above, once the photographing is stopped, the photographing is restarted from the beginning, so that there is a problem that the energy loss including the time loss is increased. The present invention has been made to solve such a problem.

[0006]

According to a first aspect of the present invention, there is provided a magnetic resonance imaging apparatus for generating a signal indicating that a subject is ready for imaging. Means, and timing generating means for starting photographing in accordance with a predetermined sequence by using an output from the signal generating means as a trigger. Accordingly, the subject does not force the subject to stop breathing at the timing of the imaging device, but the subject's feelings are stabilized and the shooting is started at a timing ready for the shooting such as respiratory arrest. Thus, a magnetic resonance imaging apparatus that is easy to use is provided. According to a second aspect of the present invention, in the magnetic resonance imaging apparatus, a signal generating means for generating a signal indicating that the subject is ready for imaging, and a predetermined signal triggered by an output from the signal generating means. Timing generating means for starting the imaging according to the sequence, interrupting the sequence during the imaging, and restarting the interrupted imaging from the interrupted time point triggered by a signal indicating that the subject is ready for the imaging to be newly performed. And characterized in that: In this way, if the shooting is interrupted once due to a disorder of breathing or movement of the body, the shooting is resumed from the point at which the shooting was interrupted, so that the waste of restarting the shooting from the beginning is eliminated. . The invention described in claim 3 is:
In the magnetic resonance imaging apparatus, a signal generating means for generating a signal indicating that the subject is ready for imaging, and starting an imaging according to a predetermined sequence with an output from the signal generating means as a trigger, Timing generating means for interrupting the sequence and restarting the interrupted imaging retroactively for a predetermined time from the interrupted time point by using a signal indicating that the subject is ready for an imaging operation to be newly performed by the subject as a trigger. It is assumed that. As a result, if imaging is interrupted once due to respiratory disturbances or body movements, the time retroactive by the time that the respiratory disturbances or body movements occurred before the interruption was taken Since the photographing is restarted from the beginning, wastefulness of retaking the photographing from the beginning can be eliminated, and an image free from the influence of disordered breathing and body movement can be obtained. According to a fourth aspect of the present invention, in the magnetic resonance imaging apparatus according to any one of the first to third aspects, a voice generating means for generating a voice message according to an operation of the timing generating means. It is characterized by having. Thus, an appropriate instruction can be given to the subject, the anxiety of the subject can be eliminated, and the burden on the operator can be reduced.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a system diagram showing one embodiment of a magnetic resonance imaging apparatus according to the present invention. FIG. 1 shows the RF system 3 shown in FIG.
The RF unit 12 is shown in a slightly expanded form, and the RF coil 8 shown once is divided into a transmitting RF coil 8a and a receiving RF coil 8b. Further, a display 21 and an external storage device 22, which are not shown, are shown. In FIG. 1, the same parts as those in FIG. 3 are denoted by the same reference numerals. Therefore, a specially provided embodiment of the present invention is a timing generator 31 that takes timings such as start of shooting, interruption of shooting, and restart of shooting, and a necessary message is selected based on an instruction from the timing generator 31. Sound generator 3
2. A speaker 33 for notifying a message from the timing generator 31 by voice, a signal generator 34 for sending a signal for notifying that the subject 20 is ready for imaging such as stopping breathing, and the like. Others are handled by software. Note that the signal generator 34 is
For example, it is provided at a hand position where the subject 20 is placed in the magnet system 1.

[0008] When the subject 20 (patient) is placed in the magnet system 1 for generating a static magnetic field and is ready to start imaging, an operator (such as an imaging technician) presses the start button of the timing generator 31. Make a shooting start request. In response to the photographing start request, the timing generator 31 instructs the sound generator 32 to generate a message at the start of photographing, and the sound generator 32 reads, for example, "Start photographing now" from among the prepared messages. Please calm down and stop breathing, do not move. Press the button after stopping breathing. "And give it to the subject as audio output from the speaker 33. When the subject hears this message and presses the button of the signal generator 34 after adjusting the respiration and inhaling sufficiently, the subject triggers the timing generator 31 to send the signal to the computer system 5.
, A shooting start signal is sent to the camera to start shooting according to a predetermined sequence. That is, the computer system 5 executes the pulse sequencer 4 and the R according to a predetermined program.
The pulse sequencer 4, which controls the F system 3 and the like and operates based on a control command from the computer system 5, sends a command necessary for collecting tomographic image data of the subject 20 to the modulator 23. The modulator 23 amplitude-modulates the high-frequency pulse from the high-frequency oscillator 24 in accordance with this command, and supplies the amplitude-modulated high-frequency pulse to the transmission RF coil 8 a via the RF amplifier 9, thereby obtaining a predetermined pulsed electromagnetic wave. Is irradiated on the subject 20. On the other hand, the NMR signal (echo signal 11) from the subject 20 is detected by the receiving coil 8b, and the signal is converted into a digital amount via the amplifier 25, the phase converter 26, and the A / D converter 27, and , Is converted into collected data sampled at a timing according to a command from the pulse sequencer 4 and sent to the computer system 5. The computer system 5 performs signal processing and image reconstruction processing on the collected data, and displays the resulting cross-sectional image of a desired portion of the subject 20 on the display 21 or stores it in the external storage device 22. .

When the photographing is completed as described above, an end signal is issued from the computer system 5 to the timing generator 31, and the timing generator 31, which has received the end signal, sends to the audio generator 32 a message indicating the end of the photographing. Is generated, and the voice generator 32 selects a message such as “please make it easy” and gives it to the subject 20 via the speaker 33. By the way, the operator observes the state of the subject during imaging, and if the subject 20 moves or cannot stop breathing on the way, the operator presses the pause button of the timing generator 31. Make a shooting suspension request. Then, in response to the photographing interruption request, the timing generator 31 instructs the computer system 5 to suspend the photographing by ending the processing of the smallest unit of the photographing processing, and waits for the end of the minimum unit of the photographing processing to wait for the sound generator From 32, a message such as "please make it easy" is given to the subject as a message at the time of interruption of imaging. Thereafter, when the operator has determined that the state of the subject has settled down and is in a state in which imaging is possible, the operator presses the pause release button of the timing generator 31 to request imaging restart. In response to the photographing restart request, the timing generator 31 instructs the sound generator 32 to generate a message at the time of restarting photographing, and the sound generator 32 reads, for example, “Restart photographing” from among the prepared messages. Please calm down and hold your breath and do not move. Press the button when you stop breathing. "And give it to the subject as audio output. When the subject presses the button of the signal generator 34 after adjusting the respiration and insufficiently inhaling in the same manner as at the start of imaging, the timing generator 31 sends an imaging restart signal from the timing generator 31 to the computer system 5 by using this as a trigger, and the previous imaging is performed. The photographing according to the predetermined sequence is resumed from the point where the operation was interrupted. Normally, several seconds are required from when the subject 20 recognizes that the subject 20 cannot move or stop breathing until the imaging is interrupted. For this reason, data during this period is collected, and an image reconstructed by the collected data may be unclear. Therefore, when resuming the photographing, the photographing is started backward by a predetermined amount of data before the time when the photographing was interrupted. The time going back before this depends on the judgment of the operator.
This is realized by setting in the timing generator 31 the time required from when the subject 20 cannot move or stop breathing until the imaging is interrupted. By performing image reconstruction based on the data collected in this manner, a clear image free from the influence of body motion can be obtained.

The above operation will be supplementarily described with reference to FIG. FIG. 2 shows a temporal change of collected data obtained by one photographing. That is, it is assumed that data is collected from [t1, 0] to [tp, n] in one shooting, and the minimum unit of the shooting process (that is, data collected in each phase encoding) is T (for example, t1,
0 to t1, n). Here, shooting is started based on the shooting start request, and data collection starts from [t1, 0]. However, if the operator notices that the subject has begun to move around [tm, l] and issues a request to interrupt the imaging by pressing the pause button at [tn, m], the computer system 5 executes the imaging processing. [T
[n, n], and then stop photographing. Then, after the subject has settled down, the operator issues an imaging restart request, and when the subject presses the button of the signal generator 34, the imaging is restarted from the next [tn + 1,0].
At this time, the operator sets the time going back from the time when the photographing was interrupted to the timing generator 31 so that
For example, photographing is resumed back to [tl, 0], and the previously collected data from [tl, 0] to [tn, m] is canceled.

[00011]

As described above in detail, according to the first aspect of the present invention, the subject's feelings are stabilized rather than forcing the subject to stop breathing at the timing of the imaging apparatus. Since the imaging is started at the timing when the preparation for the imaging such as the respiratory arrest is completed, a magnetic resonance imaging apparatus which is extremely kind to the subject is provided. According to the second aspect of the present invention, if the imaging is temporarily interrupted due to a disorder in breathing or movement of the body of the subject, the imaging is restarted from the point at which the imaging was interrupted. The uselessness of re-shooting from is eliminated. According to the third aspect of the present invention, when imaging is interrupted once due to respiratory disturbance or body movement in the subject, respiratory disturbance or body movement occurs. The camera resumes shooting from the time before the point where it was interrupted by the amount of time that was interrupted, eliminating the need to restart shooting from the beginning and eliminating the effects of breathing disturbances and body movements. Image can be obtained. Claim 4
According to the invention described in the above, it is possible to give an appropriate instruction to the subject, and also eliminate the anxiety of the subject,
Further, the burden on the operator can be reduced.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram showing a time change of collected data obtained by one photographing.

FIG. 3 is an explanatory diagram for explaining a schematic configuration of a magnetic resonance imaging apparatus.

FIG. 4 is a timing chart shown for explaining a pulse sequence of the SE method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnet system 2 Gradient magnetic field system 3 RF system 4 Pulse sequencer 5 Computer system 6 Gradient magnetic field coil 8a RF coil for transmission 8b RF coil for reception 20 Subject 31 Timing generation circuit 32 Sound generator 34 Signal generator

Claims (4)

[Claims] 1. A signal generating means for generating a signal indicating that a subject is ready for radiography, and a timing generating means for starting radiography according to a predetermined sequence triggered by an output from the signal generating means. A magnetic resonance imaging apparatus. 2. A signal generating means for generating a signal indicating that a subject is ready for imaging, and an image from the signal generating means is used as a trigger to start an imaging according to a predetermined sequence, and a sequence during the imaging. Magnetic resonance imaging, comprising: timing generation means for interrupting the imaging, and restarting the interrupted imaging from the time of the interruption with a signal indicating that the subject is ready for the imaging to be newly performed as a trigger. apparatus. 3. A signal generating means for generating a signal indicating that the subject is ready for imaging, an image output according to the signal generating means being used as a trigger to start an imaging according to a predetermined sequence, and a sequence during the imaging. And a timing generating means for restarting the interrupted imaging retroactively for a predetermined time from the interrupted time point by using a signal indicating that the subject is ready for the imaging to be newly performed by the subject as a trigger. Magnetic resonance imaging equipment. 4. The magnetic resonance imaging apparatus according to claim 1, further comprising a voice generating unit that generates a voice message in accordance with an operation of the timing generating unit. .