KR101848126B1 - method of obtaining turbulent flow image in blood vessel at MRA - Google Patents

Abstract

The present invention relates to a method for acquiring a vortex image of a blood flow in an MRA that accurately acquires an image of a vortex region in an MRA image, Magnetic Resonance Angiography) blood flow images are obtained; (b) selecting a vortex generation region among the acquired blood flow images; (c) the selected vortex generation region is 2D local excited to obtain an excitation region image; And (d) displaying the acquired excitation region image. The MRA method includes the steps of: (a) detecting a blood vessel stenosis, an aneurysm, an arteriovenous malformation, atherosclerosis, It is possible to detect the vortex phenomenon occurring at the branch point of the blood vessel more sensitively and to be usefully used for the diagnosis of the vascular disease in the future.

Description

[0001] The present invention relates to a method and apparatus for acquiring vortical flow in an MRA,

The present invention relates to an image acquisition method, and more particularly, to a method of acquiring a vortex image of blood flow in an MRA that accurately acquires an image of a vortex region in an MRA image.

3D TOF (time of flight) -MRA (Magnetic Resonance Angiography) is the most frequently used MR imaging method for the diagnosis of vascular disease.

However, the effect is limited in that it can not be clearly shown due to signal attenuation occurring in the region of turbulence in abnormal blood vessels

The severity of the arterial stenosis or aneurysm can be overestimated due to the signal attenuation due to turbulence in the blood vessel region such as arterial stenosis or aneurysm. To compensate for such signal attenuation, a contrast-enhanced, Contrast enhancement) -MRA. PC (phase contrast) -MRA, and the like have been proposed.

In addition, various images can be obtained by exciting a part of the image using the MRA apparatus.

Theoretically, the excitation volume is obtained by using the excitation k-space and the Fourier transform relationship. If the excitation K-space is designed for the purpose, the desired region can be selected and photographed .

Generally, to obtain a basic volume image, a magnetic field is applied to one axis (e.g., the Z axis) and the RF pulse is synchronized to use the resonance phenomenon occurring in the excited volume.

In this regard, Patent Document 1 discloses a method of acquiring a blood flow image with higher resolution by exciting an MRA image using an RF (Radio Frequency) pulse designed through an SLR (Shinnar-Le Roux) algorithm, Non-Patent Document 1 discloses improvement of errors due to intravascular stenosis caused by TOF-MRA test. However, it is applied to 3D imaging technique, Although it is a method to image the walls of blood vessels because it is based on images, there is a disadvantage that the contrast difference between blood vessels and tissues is lower than that of TOF-MRA, and there is a difference in not using local excitation characteristics.

KR 2004-0017027E

 A Study on the Improvement of Measurement Error of Intravascular Stenosis during TOF-MRA Test by 3D-SPACE T2 Technique. Journal of the Institute of Electronics Engineers of Korea. Vol. 51, No. 12, 2014.12, pp 180-188

Accordingly, the present invention has been conceived to solve the problems of the conventional techniques described above, and the conventional local image excitation technique has been applied to local anatomy and localized blood flow imaging by focusing on shortening the imaging time . However, it is an object of the present invention to provide a method of obtaining an MRA image having less image signal attenuation due to a vortex flow of a blood stream, using an image technique using an oblique magnetic field of a helical trajectory.

According to an aspect of the present invention, there is provided a method for acquiring a 3D time-of-flight MRA (Magnetic Resonance Angiography) blood flow image of a target site; (b) selecting a vortex generation region among the acquired blood flow images; (c) the selected vortex generation region is 2D local excited to obtain an excitation region image; And (d) displaying the obtained excitation region image. The present invention provides a method for acquiring a vortex image of blood flow in an MRA.

(C) simultaneously applying a two-dimensional helical gradient magnetic field and an RF (Radio Frequency) pulse to the selected vortex generation region; A step of delay correction of the two-dimensional helix gradient magnetic field by synchronizing an applied K-space and an RF (Radio Frequency) pulse of the two-dimensional helical gradient magnetic field; And acquiring an excitation region image by combining the two-dimensional helical magnetic field and an RF (Radio Frequency) pulse.

As described above, according to the method of acquiring vortical images of blood flow in the MRA according to the present invention, the MRA has the advantage of noninvasive vascular imaging technique, It can be used to diagnose vascular diseases because it can more sensitively detect the vortex phenomenon that occurs in aneurysm, arteriovenous malformation, arteriosclerosis, and bifurcation of blood vessel.

 The proposed method, which is applied to the MRA of the rotating image section of the local imaging technique, is able to prevent signal cancellation due to the random blood flow caused by the vortex that may vary depending on the vascular pathology, The image of the blood vessel region where the phenomenon occurs is very advantageous.

In addition, since the sensitivity to slow blood flow is relatively higher than the sensitivity of fast blood flow, it can be usefully used to accurately acquire the blood vessel shape in blood vessels having various blood flow rates at the same time.

1 and 2 are flowcharts illustrating a method of acquiring vortex images of blood flow in an MRA according to an embodiment of the present invention.
FIG. 3 is a pulse sequence diagram illustrating the temporal operation of the gradient magnetic field coil and the RF coil in the method of acquiring vortex images of blood flow in the MRA according to an embodiment of the present invention.
FIG. 4 is a 2D RF local excitation profile according to an embodiment of the present invention, wherein (a) shows a k-space helical excitation trajectory by vertical slope in two axes (YZ), (b) The time course of the RF pulse is simplified and (c) shows the k-space excitation profile.
FIG. 5 shows a scout (localizer) image (a) obtained using a general image sequence and a local image and an enlarged image (b) obtained using a 2D RF local excitation sequence.
FIG. 6 shows the maximum intensity projection (MIP) of the MRA. The MIP (Maximum Intensity Projection) shows a region of interest (a) and a 2D RF local excitation image sequence in the case of using a general blood vessel image (TOF MRA) Indicates an area of interest and an area of excitation when used.
Fig. 7 is a comparative diagram of a healthy person's conventional TOF-MRA image (a) and 2D RF locally excited MRA image (b).
8 to 9 are comparative views of a conventional TOF-MRA image (a) and a 2D RF locally excited MRA image (b) in a patient with middle cerebral artery (MCA) constriction symptoms.

These and other objects, features and other advantages of the present invention will become more apparent by describing in detail preferred embodiments of the present invention with reference to the accompanying drawings. In this process, the thicknesses of the lines and the sizes of the components shown in the drawings may be exaggerated for clarity and convenience of explanation. In addition, the terms described below are defined in consideration of the functions of the present invention, which may vary depending on the intention or custom of the user, the operator. Therefore, the definitions of these terms should be described based on the contents throughout this specification.

In addition, the described embodiments are provided for illustrative purposes and do not limit the technical scope of the present invention.

Hereinafter, a method for acquiring a vortical flow image of blood flow in an MRA according to an embodiment of the present invention (hereinafter, simply referred to as a 'vortex image acquisition method') will be described with reference to the accompanying drawings.

First, a 3D time-of-flight MRA (Magnetic Resonance Angiography) blood flow image of the target site is acquired (S100).

The 3D TOF MRA blood flow image can be acquired through a known MRI apparatus, and a detailed description thereof will be omitted.

Next, among the obtained blood flow images, a vortex generation region is selected (S200).

Among the 3D TOF MRA blood flow images as described above, a portion where vortices are expected to be generated is selected. Since the vortex generating portion in the blood vessel generally appears dark, this portion is selected.

Next, the selected vortex generation region is subjected to two-dimensional local excitation (2D local excitation) to obtain an excitation region image (S300).

The selected two-dimensional helical magnetic field and RF (Radio Frequency) pulse are simultaneously applied (S310).

As shown in FIGS. 3 to 4, a helical gradient magnetic field in the two-axis (Z, Y) direction is applied to the selected vortex generation region through the sequence as shown in FIG. 3, (See the dotted line in FIG. 3), a desired local excitation image can be obtained, and the applied RF energy is applied to the rotating image section produced by the RF pulses and the biaxial oblique magnetic fields orthogonal to each other. The intensity of the applied magnetic field has an intensity of a high magnetic field to an ultra high magnetic field of 3T to 7T, which can improve the sensitivity.

At this time, when there is no movement or flow of blood in one direction (normal blood flow), the RF cross-section is rotated, and the RF signal is absorbed less and the video signal is relatively decreased. On the other hand, The sensitivity is increased and it can be discriminated.

Next, in order to increase the accuracy, the two-dimensional helical gradient magnetic field can be delay-corrected by synchronizing the K-space and RF (Radio Frequency) pulses of the applied two-dimensional helical gradient magnetic field (S320) An excitation region image by a combination of a two-dimensional helical magnetic field and an RF (Radio Frequency) pulse is acquired (S330).

Next, the obtained excitation region image is displayed by a display unit (not shown) such as a display (S400).

Hereinafter, an actual application process and results of the vortex image acquisition method according to the present invention will be described with reference to FIGS. 5 to 9.

In this experiment, two normal and two patients signed and participated.

As the MRI apparatus, an ultra-high field 7T MRI (Siemens Magnetom, Erlangen, Germany) apparatus using a multi-channel array coil for supporting angiography was used, and the slew rate of the tilt intensity and the tilt system was 4 mT / 200 T / m / s, and the other conditions are shown in Table 1 below.

Conventional MRA Invention TR 15 ms 15 ms TE 4.78 ms 4.86 ms FA 25 ° 20 ° FOV 180 x 135 mm2 180 x 72 mm2 imaging resolution 0.28 x 0.28 x 0.36 mm3 0.4 x 0.4 x 0.4 mm < 3 > slices 104 104 Pixel Bandwidth 90 Hz / Px 235 Hz / Px Partial Fourier 6/8 No Elliptical Scanning Yes No TA 4:10 min 3:07 min

In Table 1, in the present invention, a high pixel bandwidth is applied to reduce time echo (TE), and similarly, in order to improve SNR and low resolution in the conventional MRA, an elliptic scan without partial Fourier transformation Were selected.

The images obtained by performing the above steps are shown in FIGS. 5 to 9.

As shown in Fig. 5, the cylindrical profile image is obtained by FWHM (Fourier transform) generated with a total width of 35 mm in a 72 mm FOX (excitation field, field of excitation) of FOV full width at half maximum).

The image of the existing TOF MRA is compared with the image obtained by the vortex region image acquisition method according to the present invention.

As shown in Fig. 6, in the present invention, although the visual field is substantially reduced as half of the FOV of the conventional TOF MRA (Fig. 6A), the image distortion problem is dominantly visible I did.

In addition, the conventional TOF MRA image can not visualize blood vessels in such a region because the blood flow in the blood vessel flows generally upward, causing a problem of easily causing signal attenuation by the RF pulse (Fig. 6 ) Lower arrow).

On the other hand, it can be seen that the vortex region image acquisition method according to the present invention exhibits uniform signal intensity irrespective of the direction of blood flow in the excitation region (see the lower arrow in FIG. 6 (b)).

In the forked area punctured from the parent vessel, or at the root of the artery, abnormal blood flow generally occurs, which also causes signal distortion or loss.

Perforations such as LSAs (lenticulostriate arteries, perforating arteries) can be visualized with high-field magnetic resonance imaging (MRI), but their roots are difficult to visualize by vortex or abnormal flow.

7, a signal intensity higher than that at the root of the perturbed region is shown in the vortex region image according to the present invention, unlike the conventional MRA image shown in FIG. 7 (a) Black arrows). In the conventional MRA image, signal attenuation due to saturation of a video signal in a curved blood vessel whose blood flow direction is directed downward is seen (see a white arrow in Fig. 7 (a)), I can see clearly the spread.

FIG. 8 is an MRA image of a patient with right MCA (middle cerebral artery) stenosis and FIG. 9 is an MRA image of a patient with severe bilateral MCA stenosis.

Conventional MRA images are. 8 (a) and 9 (a)), but shows a completely occluded image in the MCA stenotic region (Figs. 8 (a) and 9 See the black arrow in a).

On the other hand, in the image according to the present invention, it can be seen that the distortion and attenuation signals in the narrowed region of the conventional MRA image are clearly visualized (refer to the respective arrows in Figs. 8 (b) and 9 (b)).

Although conventional MRA images have the advantage of noninvasive angiographic imaging techniques, there are many limitations in their use due to signal attenuation of the vortex. As described above, the present invention can more sensitively detect a vortex phenomenon occurring in a high magnetic field region, such as stenosis of an artery, an aneurysm, an arteriovenous malformation, arteriosclerosis, a branch point of a blood vessel, .

Although the preferred embodiments of the present invention have been described, the present invention is not limited to the specific embodiments described above. It will be apparent to those skilled in the art that numerous modifications and variations can be made in the present invention without departing from the spirit or scope of the appended claims. And equivalents should also be considered to be within the scope of the present invention.

Claims (2)

(a) obtaining a 3D time-of-flight MRA (Magnetic Resonance Angiography) blood flow image of a target site (S100);
(b) a vortex generation region is selected from among the acquired blood flow images (S200);
(c) a step (S300) in which the selected vortex generation region is subjected to 2D local excitation to acquire an excitation region image; And
(d) displaying the acquired excitation region image (S400)
The step (c)
(c1) simultaneously applying a two-dimensional helical magnetic field and an RF (Radio Frequency) pulse to the selected vortex generation region (S310);
(c2) a step (S320) of performing delay correction of the two-dimensional helical magnetic field by synchronizing the applied K-space of the two-dimensional helical magnetic field with an RF (Radio Frequency) pulse; And
(c3) an excitation region image is obtained by a combination of the two-dimensional helical magnetic field and a radio frequency (RF) pulse (S330).
A Method for Obtaining Vortical Imaging of Blood Flow in MRA.
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