JPH01136648A - Mri blood flow imaging system - Google Patents

Abstract

PURPOSE:To take and display an angiographic image so as to display a concern region most clearly, by measuring the blood flow velocity of the concern region using an imaging sequence preliminarily measuring blood flow velocity quantitatively and subsequently controlling a spot having said velocity so as to have the max. density value on an image to perform imaging. CONSTITUTION:An image is taken by an imaging sequence and the blood flow velocity of a concern region is measured. In the sequency, phase turning is generated only with respect to the flow velocity in a Y-direction and the velocities in Z- and X- directions are not concerned. Therefore, the phase angle theta of rotation of a measuring signal is shown as theta=0.36gammaGy.tPtIVy on the basis of flow velocity Vy and, according to this formula, the flow velocity Vy of the concern region can be calculated. Since Vy is calculated, the parameter of the flow encoding pulse at the imaging time of a angiographic image is determined. The angiographic images are taken with respect to the sequences in a case applying the determined flow encoding pulse and in a case not applying said pulse. When subtraction is performed between two images of the concern region to calculate a difference image, the density concern region to calculate a difference image, the density value at said region becomes max. Therefore, the angiographic image sharply displaying the concern region can be taken.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a diagnostic nuclear magnetic resonance apparatus, and particularly to an imaging method for angiographic images that clearly display a region of interest.

[Conventional technology]

In MRI angiography, conventional methods have been used to capture images using a pulse sequence that observes signals only from moving parts of the human body, or EC.
A subtraction method called "diastolic image minus systolic image" using G-gate has been proposed. These are methods that simply display a perspective image of only a moving part or the direction in which the image was taken, regardless of the flow velocity.

[Problem that the invention seeks to solve]

In the above conventional technology, the relationship between the flow velocity and the resulting phase rotation is fixed by the imaging sequence,
Even if there is a region of interest, there is a problem in that it is not always clearly displayed because the flow velocity in that region is unknown.

A first object of the present invention is to capture and display an angiographic image that most clearly displays a region of interest.

Further, the above-mentioned conventional technology has a problem in that the displayed image is viewed only from one direction and lacks depth information.

A second object of the present invention is to provide an angiographic image that makes it easier to understand the three-dimensional spread of blood vessels, etc., compared to the above-mentioned conventional techniques.

[Means for solving problems]

The first purpose is to measure the blood flow velocity in the area of interest using an imaging sequence that quantitatively measures blood flow velocity in advance, and then set the point with this velocity to have the highest density value on the image. This is achieved by controlling the sequence and taking angiographic images.

In addition, the second purpose is to use an imaging method to obtain fluoroscopic images of blood vessels in the human body, to take two fluoroscopic images that are slightly different in the slice axis direction, and to display these images in stereo on a screen. This is achieved by

[Effect]

(1) In MRI, a pair of reversing gradient magnetic field pulses (flow encode pulses) 301 in FIG. .

302, the flow velocity and the resulting phase rotation are 1:1.
The relationship is shown by the following equation.

a=o, 36γG t p t, rV −(
1) Here, O: Phase rotation angle (degrees) γ: Nuclear gyromagnetic ratio (4, 258 kHz) t,: Gradient magnetic field application time (msec) tl Gradient magnetic field application interval (msec) V: Flow velocity (■/s) G : Gradient magnetic field gradient (Gauss/cx+) Therefore, if the blood flow velocity V of the region of interest is measured in advance, the phase rotation angle can be controlled by changing tp and t during the sequence. Therefore, by skillfully controlling the sequence according to the measured flow velocity in the region of interest, it is possible to give and display the highest concentration value to the region of interest. For example, in FIG. 4, for the velocity V of the region of interest measured in advance, 0.36γtp' t,
t p' + so that r' V= 18 Q''
1, / is determined. Here, when the flow encode pulses 401 and 402 are removed and added, if images are taken for each, the phase rotation angle at the region of interest will be 0° in the former case and 180° in the latter case, so the difference between the two images will be When subtraction is performed and a difference image is calculated, the density value at that part becomes the maximum. Therefore, it is possible to take an angiographic image that clearly displays the region of interest.

(2) The imaging sequence for extracting signals only from moving parts of the human body, ie, blood vessels, is shown in FIG. In this sequence, the 90° pulse 805,1
The 80' pulse 806° and the 90° pulse 807 (neither slice is selected) are applied in this order, but the spins in the stationary part of the human body rotate exactly 360° at the end of these applications and return to the initial state. Since it returns, no signal is generated from this part. On the other hand, when there is movement in the phase encoding direction, the spins fall onto a plane perpendicular to the slice axis, and then a pair of flow encoding pulses 809, 81.0, which corresponds one-to-one to the flow velocity and phase, move. This causes a phase rotation on that surface, and at the end of application of the 90' pulse 807, the signal does not return to the initial state and a signal is generated from that portion. Based on this principle, by applying the imaging sequence as shown in FIG. 6, it is possible to obtain a single fluoroscopic image that displays only moving parts of the human body, that is, blood vessels.

In the present invention, two fluoroscopic images whose slice axis directions are slightly shifted from each other are photographed in the above-described sequence, and these images are displayed in stereo on the same screen. This provides additional information in the depth direction to the observer compared to a single display. Therefore, compared to the conventional method.

It becomes possible to display an angiographic image that makes it easier to understand the two-dimensional spread of blood vessels.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1, 2, and 3. FIG. 2 shows a block configuration of an embodiment of the present invention. MR
A magnetic field control unit 203 that generates a static magnetic field that determines the double signal resonance frequency and a gradient magnetic field whose strength and direction can be arbitrarily controlled, and a receiver 205 that performs measurement after detecting the MR double signal generated from the subject. control and receiver 20
The processing device 206 performs image reconstruction based on the measurement signals taken in from the CRT display 207, and the finally obtained image is displayed on the CRT display 207. The magnetic field drive unit 204 generates a magnetic field necessary for measurement based on the control signal output from the magnetic field control unit 203.

The first embodiment of the present invention with the above configuration is shown in FIG.
This will be explained using FIGS. 3 and 4.

Step 101: Images are taken according to the sequence shown in FIG. 3, and the blood flow velocity in the region of interest is measured. Here, in the gradient magnetic field Gz in the Z direction, 303.304 and 30
5, and in the gradient magnetic field GX in the X direction, 306,3
07, 308, and 309 are flow encode pulses in opposite directions, and phase rotations due to movements in the X direction and Z direction are canceled. Therefore, in this sequence, a phase rotation occurs only for the flow velocity in the Y direction, and 2
It is not sensitive to direction or speed in the X direction. Therefore, the phase rotation angle θ of the measurement signal is 0=0.36yGy- due to the flow velocity Vy.
tptrVy appears, and from this, the flow velocity Vy of the region of interest can be calculated.

Step 102: Since Vy has been calculated, tp in FIG.
', tr', that is, the parameters of the flow encode pulse during angiography imaging are determined.

The decision condition is 0.36Gy-tP'・tX'vy=1
It is 80°.

Step 103: Angiography images are taken for each sequence in which the flow encode pulse determined as described above is not applied and in which it is applied.

In this case, Gz for slice selection is always 0. Also, as in Fig. 3, in Gx, 403, 404 and 405, 406 are reverse flow encode pulses, and the phase rotation is in the X direction.

It is insensitive to movement in two directions.

Step 104: Perform subtraction between the two images and display the obtained difference image.

Next, a second embodiment of the present invention having the configuration shown in FIG. 1 will be described with reference to FIGS. 5 and 6. FIG. 6 shows a sequence of a high-frequency magnetic field and gradient magnetic fields in three directions used for imaging in the present invention. If you apply this sequence,
At the time when the 90'' pulse 8o5°180° pulse 806 and 90° pulse 807 are applied, the spin of the stationary part in the human body rotates exactly 3606 times and returns to the initial state, so no signal is observed.On the other hand, in the phase encoding direction After the spins in the moving part fall onto a plane perpendicular to the slice axis by a 90° pulse 805, a pair of flow encode pulses 80 is applied to make the flow velocity and phase correspond one-to-one.
9 and 810 causes a phase rotation, and when the application of the 90° pulse 807 ends, the spins do not return to the initial state and a signal is generated. After this, the 18
00 pulse 808 is applied, and an observation signal is obtained by spin echo. With such an imaging sequence, one transparent image of a moving part of the human body, that is, a blood vessel, can be obtained. In the present invention, as shown in FIG. 5, in such a photographing sequence, one fluoroscopic image is first photographed (step 501), and then the second image is photographed by shifting the direction of the fluoroscopy by a certain angle. (Step 5o2).

The viewing direction can be arbitrarily selected by electrically controlling the gradient magnetic field strength in the three axial directions. The two fluoroscopic images photographed as described above are displayed in stereo on the CRT display (step 503), and the process ends. In addition,
In FIG. 6, the gradient of the gradient magnetic field in the slice direction is always 0 because slice selection is not selected for fluoroscopic imaging.

Further, according to this embodiment, as shown in FIG.
-180'-90' pulse sequence is used, and unlike the conventionally proposed 90' - (-90°) pulse sequence, the effect of static magnetic field inhomogeneity can be canceled by the action of 1800 pulses. Therefore, you can expect an improvement in image quality.

〔Effect of the invention〕

According to the present invention, there are the following effects.

(1) Useful diagnostic information can be obtained from such an angiographic image since the region of interest can be displayed with maximum density.

(2) Stereo display of angiographic images adds depth information to the observer, making it easier to understand the three-dimensional spread of blood vessels compared to conventional single displays. .

[Brief explanation of the drawing]

Fig. 1 is a diagram showing one implementation procedure of the present invention, Fig. 2 ゛(),
2) is a diagram showing the hardware block configuration of the present invention, FIG. 3 is a diagram showing a pulse sequence for preliminarily measuring the blood flow velocity in the region of interest, and FIG. The figure which shows the pulse sequence of. FIG. 5 is a flowchart showing an approximate processing procedure in the present invention, and FIG. 6 is a diagram showing a pulse sequence for imaging applied in the present invention.

Claims (1)

[Claims] 1. A means for generating a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field, a detecting means for extracting a nuclear magnetic resonance signal from an object to be inspected, and performing various calculations including image reconstruction on the detected signal. MRI blood flow is characterized in that the diagnostic nuclear magnetic resonance apparatus has a means for performing MRI blood flow, which measures the blood flow velocity in a region of interest in the human body in advance, determines an imaging sequence in accordance with this, and then photographs an image. Imaging method. 2. The MRI blood flow imaging method according to item 1, wherein the sequence is controlled so that the point having the blood flow velocity of the measured region has the highest density value on the image. 3. MRI blood according to item 2, characterized in that a sequence is applied to extract signals only from moving parts of the human body, and the sequence is controlled so that the value of the measurement signal with respect to the flow velocity of the region of interest is maximized. Flow imaging method. 4. Take two shots and check the blood flow velocity in the area of interest.
The above sequence is controlled so that the difference in phase rotation between the first and second measurement signals is 180 degrees, subtraction is performed between the two reproduced images, and a difference image is calculated and displayed. MRI blood flow imaging method in Section 2. 5. For diagnosis, which has means for generating a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field, a detecting means for extracting nuclear magnetic resonance signals from an object to be examined, and a means for performing various calculations, including image reconstruction, on the detected signals. An MRI blood flow imaging method that uses a nuclear magnetic resonance apparatus to take a plurality of fluoroscopic images in different directions using an imaging method that obtains fluoroscopic images of blood vessels in a human body. 6. The MRI blood flow imaging method according to item 5, which uses an imaging method that extracts signals only from moving parts of the human body. 7. Select two of the multiple images taken above,
Item 5, M, characterized by stereo display on the screen.
RI blood flow imaging method. 8. The MRI blood flow imaging method according to item 6, characterized in that each of the two captured images is colored and displayed in stereo color. 9. The MRI blood flow imaging method according to item 5, wherein a three-dimensional shape of a blood vessel is extracted and displayed from the plurality of fluoroscopic images taken.