JPH06133950A - Magnetic resonance imaging method - Google Patents

Abstract

PURPOSE:To stably describe blood flow and to reduce the time for imaging. CONSTITUTION:A delay time is set by which the timing of starting a sequence from the R wave of a cardiogram is delayed, and at each R-R, a dummy pulse is added before data collection, and data for encoding plural phases are collected at 1R-R.

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 method for imaging a subject using a sequence suitable for imaging blood vessels.

[0002]

2. Description of the Related Art Generally, in a magnetic resonance imaging apparatus (WRI apparatus) to which this type of magnetic resonance imaging method is applied, it is necessary to collect imaging data for all phase encodes for one section while shifting slice positions. By repeating for each cross section of the range, the reconstructed image is obtained with a contrast ratio in which the signal intensity of the blood flow part where blood flow is generated is high and the signal intensity of the static part where blood flow is not generated is low for each cross section. By taking advantage of this, a three-dimensional image in which the blood flow is drawn is displayed on the monitor.

Conventionally, in the case of imaging for drawing blood flow, electrocardiography or pulse wave synchronization is not carried out when collecting imaging data. In the case of heart imaging, 1
Taking one heartbeat or two to three heartbeats as one cycle, data for one phase is collected within this cycle, and data acquisition is completed by repeating the number of times corresponding to all phase encodes of the imaging cross section, so-called synchronized imaging. Was going on.

[0004]

However, in the case where the time phase is not limited as described above in the imaging of blood flow depiction, the blood flow in which the direction, the speed, and the flow rate of the blood flow greatly change depending on the time phase. Could not be rendered stably.

For example, in the coronary arteries, it has been clinically confirmed that the blood flow of the electrocardiogram is from the T wave onward to the P wave before the P wave. Therefore, unless the time phase is limited to the time zone in which the blood flow is flowing, there was no blood flow in the acquisition with one phase encoding and there was no refresh effect, and there was no blood flow in the acquisition with another phase encoding. There is a flow and there is a refreshing effect. Especially in the case of acquisition around the zero phase encoding, there is a problem that the flow of blood flow must be visualized, but this is not guaranteed.

Therefore, even if all phase encodes are collected in one cross section, the blood flow condition becomes unstable for each phase encode, and accordingly, the blood flow condition becomes undefined between the cross sections. Therefore, the blood flow cannot be stably depicted.

The above-mentioned matter generally occurs in pulsatile blood flow like an artery. In the arteries, the flow velocity changes greatly depending on the time phase, and there is also a time phase in which a regurgitation is exhibited.

Further, in the imaging of the heart, if only the imaging data for one phase encoding is collected for each cycle as described above, there is a problem that the imaging time becomes long.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a magnetic resonance imaging method capable of stably depicting a blood flow and shortening an imaging time. To do.

[0010]

In order to achieve the above object, the present invention provides a method for magnetic resonance imaging of a subject using a sequence suitable for drawing a blood vessel, in which a sequence suitable for drawing a blood vessel is electrocardiographically or In addition to performing imaging to visualize the blood vessels of the subject using pulse wave synchronization, set a predetermined delay time until the sequence runs from the peak point of the electrocardiographic waveform or pulse wave and set the timing of data collection to the peak. It is limited to only a specific time between the points, and a sequence for exciting only the same section as the imaging section of the data collection target before the data collection between the peak points is flowed at least once or more, and then a predetermined plurality of phase encoding portions are extracted. Captured image data is collected, and this collection operation is performed only the number of times obtained by dividing the total number of phase encodes by the number of predetermined multiple phase encodes to obtain the total number of phase encodes. Characterized in that it collected the shadow data.

[0011]

With the magnetic resonance imaging method according to the present invention, the imaging data can be collected in a state where the blood flow condition is stable due to the time phase limitation. In addition, the signal strength of the blood flow part is lowered by lowering the signal strength of the stationary part by flowing a sequence of dummy pulses which are not used for data collection before the data collection between the peak points such as the R wave of the electrocardiographic waveform. Since this corresponds to a relatively shorter recovery time, the contrast between the still portion and the blood flow portion becomes more remarkable on the reconstructed image. Furthermore, when collecting imaging data for all phase encodes for one cross section, it is possible to collect imaging data for a plurality of phase encodes for each cycle, so that the imaging time can be significantly shortened compared to the conventional case.

[0012]

1 is a system configuration diagram showing the outline of an MRI apparatus to which a magnetic resonance imaging method according to the present invention is applied.

This MRI apparatus includes a computer system 1 as a control center of the entire system, and under the control of the computer system 1, a sequencer 2 causes a gradient magnetic field power source 3 and a transmitter 4 to operate in sequence. At this time, the RE pulse is applied to the subject P arranged in the static magnetic field space by the main magnet 5 by the transmission coil 6 driven by the transmitter 4, and at the same time, the gradient driven by the gradient magnetic field power supply 3 is applied. The magnetic field coil 7 provides X, Y, and Z gradient magnetic fields (G
E, GR, GS) are applied. As a result, the MR signal excited in the subject P is received and detected by the receiver 9 via the receiving coil 8 and sent to the computer system 1. The computer system 1 collects MR signals,
A three-dimensional image capable of creating a reconstructed image for each cross-section based on the collected MR signals and displaying a blood flow of a blood vessel and a heart using the reconstructed image can be displayed on the monitor 10. Is.

When magnetic resonance imaging of the subject P is performed by the MR1 apparatus as described above, in the first embodiment of the present invention, data acquisition is limited to the diastole in which the movement of the heart is small and the coronary blood flow is large. To do this, the following method was adopted.

That is, in the first embodiment of the present invention, the MRA of the coronary artery of the subject P is imaged by using the pulse sequence of the field echo method as shown in FIG. At the same time, in order to solve the problem of the movement of the heart, a delay time that delays the sequence start timing from the R wave of the electrocardiographic waveform to the start of the sequence is set as shown in FIG. It was limited to a specific time phase of RR of the electrocardiographic waveform. Then, in order to solve the problem of recovery time extension due to electrocardiographic synchronization, a sequence (dummy pulse) that excites only the same cross-section as the imaging cross-section of the data acquisition target is added several times before the data acquisition in RR of the electrocardiographic waveform. Then, in order to solve the problem of a long photographing time, the photographing data of a plurality of predetermined phase encodes (Pe) are Pe: 1, 2,
3,4, Pe: 5,6,7,8 in the second cycle, Pe: 9,10,11,12 in the third cycle, or the first
Pe: 1,33,65,97 in the cycle, Pe: 2,34,66,98 in the second cycle, P in the third cycle
e: 3, 35, 67, 99, and in order to solve the problem of positional displacement due to breathing, this collection operation is performed by dividing the total number of phase encodes by the number of predetermined plural encodes ( This is carried out by breath-hold scan only 32 times, for example, and the imaging data for all phase encodes of one section is collected. As a result of the implementation study, the collection operation according to FIG. 4 has less phase shift than the collection operation according to FIG. 3 and can contribute to the improvement of image quality.

The computer system 1 reconstructs each cross section by repeating the collection operation for all phase encodes of one cross section by the breath-holding scan for the cross section of the range required for blood flow visualization while shifting the slice position. An image is created, and a three-dimensional image showing the blood flow in the coronary artery can be displayed on the monitor 10 based on the image.

The photographing conditions in this embodiment are as follows:
Magnetic field intensity of static magnetic field by: 0, 5 Tesla, field echo method as shown in FIG. 2, repetition time (TR): 25
msec, echo time (TE): 8 msec (with rephase), flip angle: 90 °, 5 mm slice 2 mm overlap, 256 × 128 matrix, addition number of 2 times.

As described above, according to the first embodiment of the present invention, the insertion of the delay time limits the time phase for data collection to the time zone during which stable blood flow occurs, so that the heart beat There is almost no effect of movement, and by applying methods such as presaturation and tagging for the direction of blood flow and tagging for the speed of blood flow, It becomes possible to measure the direction, speed, and flow rate of blood flow. Also,
It is equivalent to the fact that the recovery time of the signal strength of the blood flow section was relatively shortened by lowering the signal strength of the stationary section by adding dummy pulses several times before the data collection between R and R of the electrocardiographic waveform. Therefore, the contrast between the static portion and the blood flow portion on the reconstructed image becomes more remarkable. The number of dummy pulses is the number of times that the signal intensity of the stationary portion can be kept low to some extent, for example, 2 to 4 times in imaging a coronary artery. This is determined by a phantom, which is determined based on the signal value for each phase encoding. If the time for issuing the dummy pulse is too long, the number of phase encodes in one heartbeat of data collection will be small, and the conditions of the blood flow and the stationary portion will be changed. Furthermore, when capturing imaging data for all phase encodes for one cross section, data for multiple phase encodes can be collected within one cycle, so compared with the conventional case in which data for one phase encode is collected within one cycle. The shooting time can be greatly shortened. Furthermore, since the data for all phase encodes of one cross section is collected by the breath-hold scan, the influence of respiratory variation is reduced.
Although only the pulse sequence of the field echo method as shown in FIG. 2 is applied as the pulse sequence in the present embodiment, the pulse sequences as shown in FIG. 5 may be combined for imaging. In this case, a reconstructed image in which blood flow is likely to be obtained is obtained by the pulse sequence shown in FIG.
Since a reconstructed image in which blood flow is less likely to be obtained is obtained by the pulse sequence shown in FIG.
It is possible to obtain a composite image in which blood flow appears more prominently.

As described above, in the first embodiment of the present invention, the coronary artery T
An example of OFMRA imaging has been described, but other applications are possible.

Next, a second embodiment of the present invention will be described. Also in this second embodiment, magnetic resonance imaging can be performed by the MRI apparatus having the system configuration as shown in FIG. 1, and the state of data collection is shown in FIG.

That is, the repetition time (TR) for which the data acquisition for all phase encodes in the phase encode direction (one direction) is sufficiently set within the R-R of the electrocardiographic waveform, and the data acquisition for the number of phase encodes is the timing of zero encode acquisition. The delay time is set so as to arrive at the time, and three-dimensional data of one temporal phase can be obtained in a time of RR × GS as shown in FIG.
In Figure 6, deley 1 is the delay time in one phase, Gigi 1
Is a dummy pulse group in one temporal phase, GS1 is the first slice encode and all GE, and GS2 is the second slice encode and all GE. By performing this several times while changing the delay time, three-dimensional (3D) cine mode imaging data of the heart can be obtained. Therefore, high-speed imaging of the heart can be achieved for a specific time phase.

[0022]

As described above, according to the present invention, the time phase of data acquisition for each phase encode can be limited to a constant value, and moreover, at the time of photographing blood flow visualization,
Exciting only the same section as the imaging section before data collection in each cycle does not reduce the signal strength of the inflowing blood flow, so the direction, speed, and flow rate change significantly depending on the time phase. Such a blood flow can be stably depicted. In addition, since the time phase of data acquisition for each phase encode can be limited to a constant value, high-speed imaging for a specific time phase can be achieved when imaging the heart.

[Brief description of drawings]

FIG. 1 is an M to which a magnetic resonance imaging method according to the present invention is applied.
It is a system configuration diagram showing an outline of an RI apparatus.

FIG. 2 is a timing chart showing a pulse sequence applied in the first embodiment of the present invention.

FIG. 3 is a timing chart showing an example of a data collection operation in the first embodiment of the present invention.

FIG. 4 is a timing chart showing another example of the data collection operation according to the first embodiment of the present invention.

FIG. 5 is a timing chart showing a pal sequence used in combination with the pal sequence of FIG. 2 in a modification of the first embodiment of the present invention.

FIG. 6 is a timing chart showing an example of a data collection operation in the second embodiment of the present invention.

[Explanation of symbols]

 1 Computer System 2 Sequencer 3 Gradient Magnetic Field Power Supply 4 Transmitter 5 Main Magnet 6 Transmitting Coil 7 Gradient Magnetic Field Coil 8 Receiver Coil 9 Receiver 10 Monitor

Claims (4)

[Claims] 1. A method for magnetic resonance imaging a subject using a sequence suitable for blood vessel delineation, wherein a sequence suitable for blood vessel delineation is used for electrocardiography or pulse wave synchronization to perform imaging for object blood vessel delineation. Along with
Set a predetermined delay time from the peak point of the electrocardiographic waveform or pulse wave to run the sequence to limit the timing of data collection to only a specific time between the peak points, and before the data collection between the peak points. At least 1 sequence to excite only the same cross section as the data acquisition target
Shooting data for a predetermined number of phase encodes after flowing more than once, and performing this collecting operation for the number of times obtained by dividing the total number of phase encodes by the number of the predetermined plurality of phase encodes A magnetic resonance method characterized by collecting data. 2. A magnetic resonance imaging method in which a breath-hold scan method is applied to the magnetic resonance imaging method according to claim 1. 3. A method for magnetic resonance imaging of a subject using a sequence suitable for blood vessel delineation, wherein a sequence suitable for blood vessel delineation is used for electrocardiography or pulse wave synchronization to perform imaging for object blood vessel delineation. Along with
A magnetic resonance imaging method characterized in that a sequence for exciting only the same cross section as a data acquisition target cross section is flowed at least once before data collection between peak points of an electrocardiographic waveform or pulse wave. 4. A method for magnetic resonance imaging a subject using a sequence suitable for blood vessel visualization, wherein a sequence suitable for blood vessel visualization is used for electrocardiography or pulse wave synchronization to perform imaging for subject blood vessel visualization. Along with
Imaging data for a predetermined plurality of phase encodes is collected between peak points of the electrocardiographic waveform or pulse wave, and this collection operation is performed only the number of times divided by the number of the predetermined plurality of phase encodes. A magnetic resonance imaging method characterized by collecting imaging data for all phase encodings.