JP2761912B2 - Magnetic resonance imaging equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a magnetic resonance which obtains a tomographic image of a desired part of a subject (human body) using a nuclear magnetic resonance (hereinafter abbreviated as “NMR”) phenomenon. The present invention relates to an imaging apparatus, and more particularly to a magnetic resonance imaging apparatus capable of obtaining a plurality of images having different cardiac phases in a plurality of heartbeats in ECG-gated measurement.

[Conventional technology]

A magnetic resonance imaging device measures the density distribution, relaxation time distribution, etc. of nuclear spins at a desired test site in a subject using the NMR phenomenon, and displays an image of an arbitrary cross section of the subject based on the measured data. It is. And the conventional magnetic resonance imaging apparatus, each magnetic field generating means for applying a static magnetic field and a high-frequency magnetic field and a gradient magnetic field to the subject,
A control device for driving each of these magnetic field generating means to generate the respective magnetic fields to cause nuclear magnetic resonance in the nuclei of the atoms constituting the living tissue of the subject, and a high-frequency signal emitted by the nuclear magnetic resonance And a signal receiving unit for detecting an R-wave trigger signal from an electrocardiograph attached to the subject, sending out a command for generating each magnetic field to the control device, and a high-frequency signal detected by the signal receiving unit. The image processing apparatus includes a central processing unit that performs image reconstruction by performing calculations, and an image display device that displays the reconstructed image.

In the electrocardiographic synchronous measurement in such a conventional apparatus, an R-wave trigger signal of one heartbeat from an electrocardiograph attached to the subject is input, and at this timing, a command for generating each magnetic field is transmitted, and the The measurement of a plurality of images of the required cardiac phase or slice position in one heartbeat was performed. Also,
In some cases, a plurality of heartbeats of the subject may be used, but also in this case, the second and subsequent heartbeats are measured in the same cardiac phase as the first heartbeat, which is completely the same as the measurement within one heartbeat. .

[Problems to be solved by the invention]

In such a conventional magnetic resonance imaging apparatus, a command for generating each magnetic field is transmitted at the same timing from the R-wave trigger signal for each heartbeat to measure the signals, so that a plurality of images obtained within one heartbeat are obtained. Were the same in each cardiac phase. Since the time for measuring one image data in one heartbeat is a fixed time, the number of images that can be measured in one heartbeat is determined, for example, to be ten in one heartbeat (one second). Was something.
Therefore, the number of images of different cardiac phases obtained by one scanning operation is limited by the length of the cardiac cycle of the subject, and particularly when the heart rate is high, that is, when the cardiac cycle is short. And the number of measurement images obtained is reduced. For this reason, many images required for displaying moving images may not be obtained.

On the other hand, in order to measure image data at a different cardiac phase from a cardiac phase within a certain heartbeat at another heartbeat, the setting conditions of the apparatus are changed at the end of the previous scanning operation, and the electrocardiograph is used. In response to the input of the R-wave trigger signal, the timing at which each magnetic field generation command is sent must be shifted by a predetermined time and remeasured. In this case, it is necessary to change the setting conditions of the apparatus halfway and start again, which complicates the scanning operation. Also,
The overhead time becomes long, and the subject may be restrained for a long time, causing pain. Furthermore, the subject may move during a long measurement time, and an artifact may be generated in displaying a moving image, making it difficult to view the image.

Therefore, an object of the present invention is to provide a magnetic resonance imaging apparatus that can solve such a problem.

[Means for solving the problem]

In order to achieve the above object, a magnetic resonance imaging apparatus according to the present invention includes a magnetic field generating means for applying a static magnetic field, a high-frequency magnetic field, and a gradient magnetic field to a subject, and the magnetic field generating means for driving each of these magnetic field generating means. A control device that generates nuclear magnetic resonance in the nuclei of the atoms constituting the living tissue of the subject, a signal receiving unit that detects a high-frequency signal emitted by the nuclear magnetic resonance, and is attached to the subject. A central processing unit that inputs an R-wave trigger signal from the electrocardiograph, sends commands for generating each magnetic field to the control device, and calculates an RF signal detected by the signal receiving unit to perform image reconstruction; and A magnetic resonance imaging apparatus comprising: an image display device configured to display a reconstructed image. The time until the transmission of each magnetic field generation command after the reception of the force is sequentially changed for each heartbeat, and the control is performed so as to obtain a plurality of images whose heart phases are different from each other in a plurality of heartbeats. is there.

[Action]

The magnetic resonance imaging apparatus configured as described above,
Under the control of the central processing unit, R of multiple heartbeats from the electrocardiograph
In response to the input of the wave trigger signal, after receiving the signal, the time until each magnetic field generation command is transmitted is sequentially changed for each heartbeat,
This is to obtain a plurality of images in which cardiac phases are different from each other in a plurality of heartbeats. Thus, a large number of images having different cardiac phases can be obtained in a short time by one scanning operation.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of a magnetic resonance imaging apparatus according to the present invention. This magnetic resonance imaging apparatus uses a nuclear magnetic resonance (NMR) phenomenon and obtains a tomographic image of a subject by electrocardiographic synchronous measurement. As shown in FIG. 1, a static magnetic field generator 1 and a high-frequency magnetic field Generator 2
, A gradient magnetic field generator 3, a controller 4, and a signal receiver 5
, An electrocardiograph 6, a central processing unit (hereinafter abbreviated as "CPU") 7, and an image display device 8.

The static magnetic field generation unit 1 generates a strong and uniform static magnetic field around the subject 9 in the body axis direction or a direction perpendicular to the body axis, and has a certain space around the subject 9. A magnetic field generating means of a normal conduction type, a superconductivity type, or a permanent magnet type is disposed in the apparatus. Although not shown, the gradient magnetic field generating unit 3 includes a gradient magnetic field coil wound in three axes of X, Y, and Z and a gradient magnetic field power supply for driving each coil. By driving the gradient magnetic field power supply of each coil according to
X-, Y-, and Z-axis gradient magnetic fields are applied to the subject 9. And depending on how to add this gradient magnetic field,
A slice plane for the subject 9 can be set.
The control device 4 operates under the control of the CPU 7, and controls each of the above-described magnetic field generation units.
The magnetic field is generated by driving 1, 2, and 3 to cause nuclear magnetic resonance in the nuclei of the atoms constituting the living tissue of the subject 9. The signal receiving unit 5 detects a high-frequency signal emitted from the subject 9 by the above-described nuclear magnetic resonance, and although not shown, a high-frequency coil, an amplifier, a quadrature detector, and an A / D converter on the receiving side. Consisting of The electrocardiograph 6 takes an electrocardiogram of the subject 9 and extracts the R-wave trigger signal from the heartbeat.
The detector is attached to the pulsating part of. Also, CPU7
Receives the heartbeat R-wave trigger signal output from the electrocardiograph 6 attached to the subject 9 and sends commands for generating each magnetic field to the control device 4;
The image reconstruction is performed by calculating the data of the high-frequency signal detected in step (1). The image display device 8 is connected to the CPU 7
The data of the image reconstructed by the above is input, converted into an analog signal, and displayed as an image on a CRT or the like.

Here, in the present invention, the CPU 7 receives the input of the R-wave trigger signal of a plurality of heartbeats from the electrocardiograph 6 and after receiving the R-wave trigger signal, the static magnetic field generating unit 1, the high-frequency magnetic field generating unit 2 and the gradient magnetic field generating unit 3 The time until each magnetic field generation command is transmitted is sequentially changed for each heartbeat, and control is performed so as to obtain a plurality of images in which a plurality of heartbeats have different cardiac phases.

Next, an operation of measuring an image in the magnetic resonance imaging apparatus thus configured will be described with reference to FIG. 2 and FIG. First, the electrocardiograph 6 shown in FIG. 1 outputs a signal of a heart radio wave of the subject 9 as shown in FIG. At this time, the CPU 7
Immediately after receiving the R-wave trigger signal using the R-wave 11 as a trigger signal in the first heartbeat, a command for generating each magnetic field is sent to the control device 4 in order to perform image measurement of one cross section at time t. Then, the control device 4 sends a drive signal to each of the magnetic field generators 1, 2, and 3, and drives each of the magnetic field generators 1, 2, and 3. As a result, the respective magnetic fields are generated from the magnetic field generators 1, 2, and 3 and applied to the subject 9 to cause nuclear magnetic resonance in the nuclei of the atoms constituting the living tissue of the subject 9. Then, the high frequency signal emitted from the subject 9 by the nuclear magnetic resonance is detected by the signal receiving unit 5. Thereby, as shown in FIG. 2 (b), image measurement is performed for each cross section at time t immediately after the reception of the first R-wave trigger signal. Here, since the time t is shorter than the heartbeat period T of the first heartbeat, the data D ₁ ,
Measurement of D ₂ , D ₃ , D ₄ is performed.

Next, in the second heartbeat, the CPU 7 receives the R-wave trigger signal using the R-wave 12 of the second heartbeat as a trigger signal and, for example, after a lapse of time t / 2, similarly to the first heartbeat. In order to perform image measurement of one cross section at time t, a command for generating each magnetic field is sent to the control device 4. Thereafter, by the same operation as that in the first heartbeat, as shown in FIG. 2 (b), after the time t / 2 has elapsed after the reception of the second R-wave trigger signal, the time t and one section The image measurement is performed every time. Then, data d ₁ , d ₂ , d ₃ , d _{4 of} a plurality of sections are continuously obtained.
Is measured.

In this way, by repeating the image measurement at the timing shown in FIG. 2 a required number of times, measurement data required for image reconstruction can be collected. Here, since the measurement data of the first heartbeat and the second heartbeat collected in this manner are both measurement data within one heartbeat of the heartbeat period T, they are measured within the same heartbeat as shown in FIG. The image data can be synthesized as image data. In each case, the image measurement of one section is performed during time t, and the second heartbeat is R
Since the measurement is started after a wait time of t / 2 from the wave trigger signal, the cardiac phases of each data are all shifted by t / 2. The order is as follows: at time 0, data D ₁ starts to be collected,
From there, data d ₁ is collected by sending t / 2, and then D ₂ → d
_This is similar to the case where image data is sequentially collected in the order of ₂ → D ₃ → d ₃ → D ₄ → d ₄ . From this, a large amount of image data can be collected within one heartbeat.

In FIG. 2, the number of sections measured in one heartbeat is shown as, for example, four, but the present invention is not limited to this.
The heartbeat period T can be the maximum number of cross sections that can be divided by the time t. Further, in FIGS. 2 and 3, the image data is collected using two heartbeats at different timings of measurement, but the measurement may be performed using three heartbeats, for example. In this case, the first heartbeat starts measurement from time 0, the second heartbeat is delayed by time t / 3,
At the third heartbeat, measurement may be started with a delay of 2t / 3.
Generally, when measuring using N heartbeats as a whole, n
The waiting time after receiving the R-wave trigger signal at the heartbeat is:
(N-1) t / N may be set. Furthermore, by inputting the waiting time at each heartbeat by the operator using the CPU 7, an image at an arbitrary cardiac time phase can be measured.

〔The invention's effect〕

Since the present invention is configured as described above, under the control of the CPU 7, it is possible to set the time required for transmitting the command for generating each magnetic field after receiving the input of the R-wave trigger signal of a plurality of heartbeats from the electrocardiograph 6 after receiving the signal. A plurality of images can be obtained which are sequentially changed for each heartbeat and in which the cardiac phases are different from each other in a plurality of heartbeats. By appropriately setting the time until receiving the command for generating each magnetic field after receiving the R-wave trigger signal, one scan operation can be performed without being limited by the length of the cardiac cycle T of the subject 9. Thus, many images having different cardiac phases can be measured in a short time. Therefore, the scanning operation is simplified, and the operability of the apparatus can be improved. Also,
Since images having different cardiac phases can be obtained for a plurality of heartbeats, a large number of images required for displaying a moving image can be easily obtained. Further, since a large number of necessary images can be obtained by one scanning operation, the overhead time can be shortened, and the pain can be reduced without restraining the subject 9 for a long time. Accordingly, the influence of body movement during the measurement time of the subject 9 is reduced, and the occurrence of artifacts in moving image display is reduced, making it easier to view the image. Therefore, the diagnostic capability of the device can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a magnetic resonance imaging apparatus according to the present invention, FIG. 2 is a timing diagram for explaining an image measuring operation in the present invention, and FIG. FIG. 4 is an explanatory diagram showing a relationship with the above. 1 ... Static magnetic field generator, 2 ... High frequency magnetic field generator, 3 ...
Gradient magnetic field generating section, 4 ... control device, 5 ... signal receiving section,
6: electrocardiograph, 7: CPU, 8: image display device, 9:
... subject.

Claims (1)

(57) [Claims] 1. A magnetic field generating means for applying a static magnetic field, a high-frequency magnetic field, and a gradient magnetic field to a subject, and the respective magnetic field generating means are driven to generate the respective magnetic fields to constitute a living tissue of the subject. A control device for causing nuclear magnetic resonance in atomic nuclei, a signal receiving unit for detecting a high-frequency signal emitted by the nuclear magnetic resonance, and an R-wave trigger signal from an electrocardiograph attached to the subject are input. And a central processing unit that sends out a command for generating each magnetic field to the control device and calculates the high-frequency signal detected by the signal receiving unit to perform image reconstruction, and an image display device that displays the reconstructed image. In the magnetic resonance imaging apparatus comprising: the central processing unit is configured to receive an R-wave trigger signal of a plurality of heartbeats from the electrocardiograph and, after receiving the R-wave trigger signal, transmit an instruction for generating each magnetic field after the reception. During sequentially varied for each heart beat, and magnetic resonance imaging apparatus characterized by cardiac phase is assumed to be controlled to obtain all multiple different images at multiple heartbeats.