JP4117533B2 - Magnetic resonance imaging device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic resonance imaging apparatus, and more specifically to display of a captured image.
[0002]
[Prior art]
A magnetic resonance imaging (hereinafter referred to as MRI) apparatus uses a nuclear magnetic resonance phenomenon of protons, ie, hydrogen nuclei, which is a main constituent material of a subject, and generates a nuclear magnetic resonance signal generated from the subject by the nuclear magnetic resonance phenomenon. By detecting and imaging the spatial distribution of proton density and relaxation phenomenon based on the detected nuclear magnetic resonance signals, the shape and function of the human head, abdomen, extremities, etc. can be converted into a two-dimensional or three-dimensional image. Known as a display device.
[0003]
Such an MRI apparatus irradiates a subject with a radio frequency (RF) pulse while applying a static magnetic field and a gradient magnetic field to cause the subject to cause a nuclear magnetic resonance phenomenon. A nuclear magnetic resonance signal generated by the induced nuclear magnetic resonance phenomenon is detected by an RF detection coil, the detected signal is converted into an image signal by a signal processing unit, and the converted image signal is converted into a space of 256 to 1024, for example. It is displayed on the monitor with resolution.
[0004]
By the way, in cardiac imaging by MRI, puncture monitoring at the time of surgery, and the like, operations for arbitrarily determining the position of a cross section to be imaged next on an image displayed on a monitor are performed. For example, a part of the coronary artery of the heart (for example, 10 cm square) is displayed on the screen, and for example, a desired orientation or position of the artery is determined based on the displayed image, and the image is displayed based on the determined sectional position. A myocardial infarction or the like is discovered at an early stage by taking an image and observing, for example, a stenosis from the taken image.
[0005]
As operations for determining the position of the imaging section, the following two operations have been proposed. First, for example, still images of the heart are acquired in order, the acquired still images are stored, the stored still images are sequentially read, and the position of the cross section to be imaged based on the read still images is determined. Decide. Second, for example, the heart is imaged in real time (for example, at a rate of 5 to 20 frames / second (fps)), and the captured real-time image is displayed on a monitor using a graphical user interface technique, and the displayed screen is displayed. Click the button to determine the cross-sectional position to be imaged in real time. The operation to determine the cross-sectional position on this second real-time image is described in “Magnetic Resonance in Medicine: Real-time interactive MRI on a conventional scanner; AB. Kerr et al., 38, pp. 355-367 (1997)”. It has been reported.
[0006]
[Problems to be solved by the invention]
However, in the operation of determining the position of the imaging section using a still image, the stored images are read in order and positioned sequentially with respect to the read image. It is difficult to carry out in a short time.
[0007]
In addition, in the operation of determining a cross section immediately using a real-time image, for example, when imaging the heart, the position of the diaphragm varies with breathing, and the position of the heart periodically varies due to the varied diaphragm. Since the shape and position of the heart periodically change with the heartbeat, when the heart whose position and shape change periodically is imaged in real time, the heart of the captured image is displayed with its position changed one after another. It is difficult to accurately determine a desired cross-sectional position on the displayed image.
[0008]
An object of the present invention is to facilitate an operation for positioning an imaging section of a subject.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, an MRI apparatus of the present invention includes a static magnetic field generating means for generating a static magnetic field to be applied to a subject and a gradient magnetic field generating means for generating three different gradient magnetic fields to be applied to the subject. A high frequency magnetic field pulse generating means for generating a high frequency magnetic field pulse to be applied to the subject, a signal detecting means for detecting a nuclear magnetic resonance signal generated from the subject, and a nuclear magnetic resonance obtained by the signal detecting means A signal processing means for reconstructing an image based on a signal, a storage means for an image reconstructed by the signal processing means, and an image reconstructed by the signal processing means or an image stored in the storage means are displayed. Display means, input means, and control means for controlling each of the means to execute an imaging sequence, the control means captures a dynamic signal of the imaging region, and A plurality of time periods having an appropriate period are allocated, the imaging sequence is executed in association with each time phase, and the time phase information is associated with the captured image and stored in the storage unit, and input by the input unit An image corresponding to a specific time phase is read out and displayed on the display means.
[0010]
In this way, the dynamic signal of the imaging region, that is, the signal representing the motion state of the imaging region is captured, and a plurality of periodic time phases are appropriately assigned to the captured dynamic signal. For example, an electrocardiogram waveform of the heart is captured, and the time from when the electrocardiogram R wave is sensed to the captured electrocardiogram waveform until the next electrocardiogram R wave is sensed is divided at regular intervals, and time phases are assigned respectively. Then, the captured cardiac image is associated with the time phase by executing imaging of the heart in correspondence with each assigned time phase. As a result, the heart of the image corresponding to the specific time phase set by the input means among the related time phases is always in substantially the same position, shape or form. Therefore, by continuously displaying only the images corresponding to a specific time phase, when the heart is imaged in real time, the heart image at the desired time phase to be observed is displayed on the display means as if it has stopped moving. Is done. Therefore, since the position and orientation of the imaging section are determined based on the displayed image of the heart that has stopped moving, compared to the case where the heart is determined on the image displayed by changing the position one after another, The position and orientation of the imaging section can be easily determined.
[0011]
Here, an electrocardiogram waveform has been described as an example of a dynamic signal. However, the dynamic signal is not limited to this, and a different dynamic signal is used depending on the imaging region, such as a signal representing movement of the imaging region due to respiration. For example, when using respiratory motion information as a dynamic signal, the control unit can associate a time phase set based on the respiratory motion information with the captured image. In addition, by correcting the display position of the imaging part in real time using the dynamic signal relating to the other part, it is possible to reduce the shift of the display position according to the movement of the imaging part. An image of the part can be displayed. As for the control means, when the imaging sequence is executed in real time, an image corresponding to the same time phase among the images taken in real time can be displayed on the display means to update the display image of the imaging region. it can. Moreover, about a display means, the captured image, the time phase linked | related with the captured image, and the position and direction of the imaging surface of the captured image can be simultaneously displayed on the same screen.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration example of an MRI apparatus to which the present invention is applied. As shown in the figure, a static magnetic field magnet 12 for generating a static magnetic field to be applied to the subject 10 and a gradient magnetic field coil 14 for generating different three-direction gradient magnetic fields to be applied to the subject 10 are provided. An RF coil 16 that generates a high frequency magnetic field (RF) pulse to be applied to the subject 10 and an RF probe 18 that detects a nuclear magnetic resonance signal generated from the subject 10 are provided. A signal processing unit 20 for reconstructing an image based on a nuclear magnetic resonance signal obtained by the RF probe 18, a storage unit 36 for an image reconstructed by the signal processing unit 20, and a reconstruction by the signal processing unit 20 A display unit 22 for displaying an image or an image stored in the storage unit 36 and an input unit 34 are provided. And the control means 24 which performs an imaging sequence is provided, the RF transmission part 28 which sends a signal to the RF coil 16 by the control means 24, the signal detection part 30 which sends a signal to the RF probe 18, and the gradient magnetic field coil 14, the gradient magnetic field power supply 26 for sending a signal, the signal processing unit 20, the display unit 22, the input unit 34, and the storage unit 36 are controlled.
[0013]
The MRI apparatus configured as described above applies a static magnetic field to the subject 10 by the static magnetic field magnet 12 and applies gradient magnetic fields in three directions different from each other by the gradient coil 14 to the subject 10 to which the static magnetic field is applied. While applying, an RF pulse is applied by the RF coil 16 to cause a nuclear magnetic resonance phenomenon in the subject 10. The nuclear magnetic resonance signal generated by the nuclear magnetic resonance phenomenon is detected by the RF probe 18, the detected nuclear magnetic resonance signal is reconstructed by the signal processing unit 20, and the reconstructed image is displayed on the display unit 22. The Further, the image can be stored in the storage unit 36. In this case, the image in the storage unit 36 can be appropriately displayed on the display unit 22.
[0014]
In such an MRI apparatus, for example, when the heart is imaged in real time (for example, at a rate of 20 images / second (fps)) and the image is displayed on the display unit 22, the shape of the heart on the image and The position changes one after another. Therefore, even if an attempt is made to input and set the position of a desired imaging section, it is difficult to accurately determine the position. Therefore, in the present embodiment, the direction and position of the cross section of the heart to be observed on the displayed image can be easily determined by displaying an image of the heart that has stopped moving on the display unit 22 while updating in real time. .
[0015]
Here, the positioning operation of the imaging section on the real-time imaging image according to the present invention will be described with reference to FIG. FIG. 2 is a flowchart illustrating an example of a processing procedure for determining the position of the imaging cross section of the heart.
Step 100: The control means 24 captures a dynamic signal, for example, an electrocardiographic waveform of the heart, and sets the time from when the R wave is sensed based on the taken electrocardiogram waveform to when the next R wave is sensed at regular intervals. Assign multiple time phases by separating them. Then, a real-time imaging sequence is executed in association with each time phase. Thereby, the real-time captured image and the time phase are associated with each other and stored in the storage unit 36.
Step 101: It is confirmed whether or not a desired time phase to be observed, that is, a specific time phase is input through the input unit 34. If the specific time phase is set, the process of step 102 is performed. On the other hand, when the specific time phase is not set, the process of step 103 is performed.
Step 102: The time phase associated with the image in Step 100 is compared with the specific time phase confirmed in Step 101, and if the compared time phases coincide with each other, a real-time captured image corresponding to the time phase is stored in the storage unit The data is read from 36 and displayed on the display unit 22. On the other hand, when the compared time phases are different, an image corresponding to the time phases is not displayed.
Step 103: A straight line is drawn on the heart on the screen on the image displayed on the display unit 22 by, for example, a pointing device (not shown), and the position and orientation of a desired imaging cross section are determined by the drawn straight line. When the position and orientation are not input on the display image, the process returns to step 100 and the process is repeated.
Step 104: Calculate imaging plane data relating to the position and orientation of the determined imaging section.
Step 105: The position of the imaging surface to be imaged is updated based on the calculated imaging surface data, and the processing shown in Step 100 is performed again based on the updated position, and a real-time captured image of the cross section to be observed is acquired. The
[0016]
In such a processing procedure, the heart of the real-time captured image corresponding to the specific time phase among the time phases associated by the processing in step 100 is always in substantially the same position and form. Therefore, the processing shown in Step 100, Step 101, and Step 102 is sequentially repeated, and only the image corresponding to the specific time phase is continuously displayed on the display unit 22, so that the heart of the image in the time phase to be observed moves. It is displayed in the state where is stopped. Therefore, since the position and orientation of the imaging cross section to be observed on the stationary image are determined, the position and orientation of the imaging cross section are determined as compared with the case where the heart is sequentially changed on the displayed image. Can be easily determined.
[0017]
In this case, as a time phase associated with an image in the processing shown in step 100, a phase (p) in which the time from when an R wave is sensed based on an electrocardiogram waveform until the next R wave is sensed is divided at regular intervals. ) That is, the cardiac phase is used. These phases (p) are defined as p = first phase, second phase, etc., and real-time captured images acquired in the respective phases are associated with each other. At this time, for example, the image associated with the first phase indicates the first image after the R wave, and the image associated with the second phase indicates the second image after the R wave. Further, the accumulated time T from the R wave may be managed and used as a time phase. At this time, if the image capturing time for one sheet is t, the time T is T = t · p.
[0018]
Further, the respiratory motion may be monitored in real time, and the monitored respiratory motion may be attached to each real-time captured image as time phase information instead of the cardiac time phase. At this time, as the respiratory motion, a signal obtained by converting the motion of the respiratory sensor attached to the subject into an electrical signal, or a navigation echo, that is, a signal added to the RF pulse in order to read the dynamics of the subject from the change in the echo signal. The signal extracted from can be used. Furthermore, if both the cardiac phase and respiratory motion are managed in association with the real-time captured image, the heart display position can be corrected based on the respiratory motion even if the subject does not hold his / her breath. By displaying the real-time captured image related to the time phase, the heart in the same position and the same form can be displayed more accurately.
[0019]
In addition, as the specific time phase confirmed in step 101, a numerical value of a value input and set via the input unit 34 can be used. Further, instead of this numerical value input, for example, a plurality of images relating to one heartbeat may be acquired, a desired image may be specified from the acquired images, and a time phase associated with the specified image may be used. .
[0020]
FIG. 3 is a conceptual diagram in which position data and time phase data are managed in association with a real-time captured image. As shown in A of FIG. 3, for each captured image acquired in real time, time phase data associated with the captured image and imaging surface data representing the position and orientation of the imaging surface are attached respectively. Yes.
[0021]
In this way, by managing the captured image with the imaging plane data and the time phase data, as shown in FIG. 3B, the captured image, the time phase at the time of image acquisition, and the position and orientation of the imaging plane are displayed. Can be displayed on the display unit 22 at the same time, and while observing the imaging surface, the position and orientation of the imaging surface and the time phase at the time of image acquisition of the imaging surface can be always grasped.
[0022]
Further, as shown in FIG. 3C, the imaging surface data and time phase data attached to the image are stored in the storage unit 36 as a database, so that the imaging surface data and time phase data in the database can be obtained at a desired time. Since it can be read out, a captured image captured in the past can be re-displayed on the same imaging surface with the same time phase.
[0023]
In addition, by displaying the imaging surface data on the display unit 22 in a three-dimensional form including the X axis, the Y axis, and the Z axis, the tomographic position of the imaging surface currently displayed can be grasped visually and intuitively. .
[0024]
Further, simultaneously with imaging the heart in real time, the electrocardiographic waveform related to the heart is attached to the captured image, and the attached electrocardiographic waveform is displayed on the display unit 22 simultaneously with the captured image, whereby the displayed captured image is displayed. The ECG waveform can also be confirmed while observing. Thereby, when the image quality is deteriorated due to an arrhythmia or the like, the electrocardiogram waveform corresponding to the deteriorated image can be referred to immediately, so that the judgment regarding the treatment can be made quickly.
[0025]
As described above, the present invention has been described based on the embodiments. However, the object that can be imaged by the MRI apparatus according to the present invention is not limited to the heart, but can be applied to the liver, kidney, lung, blood vessel, and the like.
[0026]
【The invention's effect】
As described above, according to the present invention, the positioning operation of the imaging section of the subject can be facilitated.
[Brief description of the drawings]
FIG. 1 is a configuration example of an MRI apparatus to which the present invention is applied.
FIG. 2 is a flowchart showing an example of a processing procedure for determining the position of the imaging cross section of the heart.
FIG. 3 is a conceptual diagram in which position data and time phase data are attached to a real-time captured image.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Subject 12 Static magnetic field magnet 14 Gradient magnetic field coil 16 RF coil 18 RF probe 34 Input part 36 Memory | storage part

Claims (4)

A static magnetic field generating means for generating a static magnetic field to be applied to the subject, a gradient magnetic field generating means for generating gradient magnetic fields in three different directions to be applied to the subject, and a high-frequency magnetic field pulse to be applied to the subject are generated. High-frequency magnetic field pulse generation means, signal detection means for detecting a nuclear magnetic resonance signal generated from the subject, signal processing means for reconstructing an image based on the nuclear magnetic resonance signal obtained by the signal detection means, Storage means for the image reconstructed by the signal processing means, display means for displaying the image reconstructed by the signal processing means or the image stored in the storage means, input means, and control each means In the magnetic resonance imaging apparatus including the control means for executing the imaging sequence,
The control means captures a periodic dynamic signal of the imaging region, assigns a plurality of periodic time phases by dividing one period of the dynamic signal, and associates the dynamic signal with each time phase within the period of the dynamic signal. The imaging sequence is executed in real time, the time phase information is associated with the captured image and stored in the storage unit, and an image corresponding to a specific time phase input by the input unit is read and displayed on the display unit A magnetic resonance imaging apparatus.   In the case where an electrocardiogram waveform is used as the dynamic signal, the control means sets the time phase by dividing the time from when the electrocardiogram R wave is sensed to when the next electrocardiogram R wave is sensed into every predetermined time. The magnetic resonance imaging apparatus according to claim 1.   In the case where the imaging sequence is executed in real time, the control means displays an image corresponding to the same time phase among images taken in real time on the display means and updates the display image of the imaging part. The magnetic resonance imaging apparatus according to claim 1 or 2.   4. The magnetic resonance according to claim 1, wherein when using respiratory motion information as the dynamic signal, the control unit associates the time phase set based on the respiratory motion information with a captured image. Imaging device.

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