JPH0282946A - Method for taking contrast image of blood vessel - Google Patents

Abstract

PURPOSE:To obtain a blood vessel contrast image of high accuracy by setting a phase to zero with respect to the terms of the flow velocity and acceleration of a proton in a rephase image to be substracted. CONSTITUTION:In order to obtain the data of a rephasing image, slice and read inclined magnetic fields GS, GR of cross-hatching are added and a sequence wherein phase shift is brought to zero with respect to the terms of flow velocity and acceleration is set. The first encoding is executed in the rephase sequence and, after this operation, the first encoding is executed immediately in a dephase sequence. Next, the second encoding is executed in the rephase sequence and the 256-th encoding is executed in the dephase sequence at last to finish imaging. Rephase images and dephase images are collected in the data memory part in a computer system and respectively subjected to two-dimensional Fourier transferm to reconstitute an image. Subsequently, subtraction is executed to form a blood vessel contrast image.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a method of taking magnetic resonance angiographic images by the subtraction method.

(Prior technology) General imaging MRI (Magnetic Re5on
Anse Imaging (Magnetic Resonance Imaging) equipment uses gradient magnetic fields and excitation high-frequency pulses (
A magnetic resonance phenomenon is caused in a specific region of the subject by applying a F pulse), and a magnetic resonance signal (echo signal or l''I D signal) induced thereby is detected, for example, 2 By performing signal processing using a reconstruction method such as a dimensional Fourier transform method, anatomical information and qualitative information of a specific region of the subject are imaged.

An example of this type of MRI apparatus will be described below with reference to FIG. In FIG. 6ζ, in the cylindrical body MA, a superconducting or normal conducting static magnetic field coil r is used as a static magnetic field generator.
SX axis, Y axis, 2-axis gradient magnetic field coil 2, transmitting/receiving coil 3
is provided.

The subject P is introduced into the diagnosable magnetic field generation area within the main body MA.

Also, static magnetic field coil! is driven by a static magnetic field control system 4, the transmitter/receiver coil 3 is driven by a transmitter 5 for excitation and by a receiver 6 for detection (collection); The gradient magnetic field coils 2 are each Xl
11] Gradient magnetic field M, source 7, Y axis I) A gradient magnetic field power source 8, Z
It is driven by an axial gradient magnetic field power supply 9.

Y-axis, Y-axis, Z-axis gradient magnetic field power supply 7°8.
9 and the transmitter 5 are driven by a sequencer IO according to a predetermined image data collection sequence. For example, the seventh
As shown in FIG. 1, a slicing gradient magnetic field G5, a read gradient magnetic field GR1, an encoding gradient magnetic field GE, and a 90°
Pulse, SB (Spie echo) with 180° pulse
The law is carried out.

The data group obtained by executing the above sequence is taken into the receiver 6 each time it is acquired, where it is subjected to quadrature phase detection, converted into a digital signal, and then sent to the computer system II.

The computer system 11 generates a digitized detection output (Red part data, Tmagina#) for each encoding process.
data) and stores it in a disk storage device, etc., and then performs two-dimensional Fourier transform processing to create a two-dimensional image (
A slice image) is created and displayed on the monitor.

Images produced by the above-mentioned M-processing device are different from conventional X-ray images and ultrasound images and present a variety of clinical information, and new clinical applications are being attempted to make effective use of this. One of them is M-Angio. This is a method for obtaining blood vessel and i (blood flow) contrast images using an MRI apparatus, and the conventional method will be explained below.

That is, in angiography using X-rays, for example, an image before contrast medium injection and an image after contrast medium injection are obtained, and by subtracting these images, an image in which only blood vessels are contrasted is obtained. MRI equipment is also implemented using a similar concept. First, in the M-processing device, protons (H
) to distinguish between stationary protons (non-blood) and moving protons (blood). For example, Fig. 7 is a diagram showing a normal SE method sequence, but from this SE method sequence, an image related to stationary protons (dephasing image) (Fig. 9 (b)
))obtain. This image corresponds to the image before contrast agent injection. In addition, as shown in FIG. 8, a sequence (SE method with flow compensation) in which the magnetic field shown in the shaded area (read gradient magnetic field GR) is applied to FIG. An image that does not distinguish between moving protons (refaging image) (Figure 9 (a))
get. Here, flow compensation is a method that aligns the phase of something moving at a constant speed with the phase of something stationary at the echo center.

From the image shown in FIG. 9(a), FIG. 9(b)
By subtracting the image shown in FIG. 9(C) on the image, the image shown in FIG.

(Problem to be Solved by the Invention) In the conventional method described above, the refaging image that is the basis of the subtraxilon is a sequence in which the phase shift is eliminated for the flow velocity term, and
When the blood flow is in a constant velocity state, it is possible to present a highly accurate reaging image and, by extension, an angiographic image with excellent diagnostic ability. However, blood flow generally does not remain at a constant speed, but rather repeats acceleration, constant speed, etc. Therefore, the angiographic image obtained by the conventional method (even if it is rough) is not accurate because it is based on a re-aging image that does not take into account the term of acceleration.

Therefore, an object of the present invention is to provide a method that makes it possible to obtain highly accurate blood vessel (blood flow) contrast images using an MRI apparatus.

[Structure of the invention]

(Means for solving the problem) The present invention is as above! ! ! ! In order to solve the problem and achieve the purpose, the following measures have been taken.

That is, the present invention utilizes the magnetic resonance phenomenon to obtain an image reflecting the spin density and relaxation time constant of a specific atomic nucleus.
A method of taking an angiogram using an RI device, in which a re-aging image is obtained by executing a sequence in which the phase shift is set to zero for terms of flow velocity and acceleration, targeting protons; The present invention is characterized in that a dephasing image is obtained by executing a sequence in which the phase shift does not become zero, and an angiographic image is obtained by subtracting the dephasing image from the refading image.

(Effect) As mentioned above, since the refaging image is obtained with the flow velocity and acceleration terms and the phase shift of appear accurately.

(Example) An example of the angiography imaging method according to the present invention will be described below.
This will be explained with reference to FIGS. 1 to 3.

FIG. 1 shows one encoding sequence for obtaining dephasing image data, and is a sequence of a normal spin echo (SE) method. FIG. 2 shows one encoding sequence for obtaining data of a refaging image, and in contrast to the sequence of FIG. 8, the gradient magnetic field G8. This is a sequence in which GR is added and the phase shift is zero for the flow velocity and acceleration terms.

The above sequence is executed at the timing shown in FIG.

That is, if the acquisition matrix is 256x256, the first encoding is performed using the refage sequence shown in FIG. 2, and immediately after this is completed, the first encoding is performed using the differential needs sequence shown in FIG. Next, the second encoding is performed using the rephase sequence shown in Figure 2, and finally the second encoding is performed using the rephase sequence shown in Figure 1.
56 encoding and finishes shooting. Upon completion of this imaging, in the case of the apparatus shown in FIG. 6, the data storage unit 1 in the computer system II will be able to store the image data group (rephased image) corresponding to FIG. 9(a) and the tg9(b)
A group of image data corresponding to one image (deficiency images) is collected, and each image is reconstructed using a two-dimensional Fourier transform method, etc., and then subtraction is executed to obtain the subtraction image shown in FIG. 9(C). , that is, an angiogram is generated.

Here, the setting of the gradient magnetic fields G, , GR in FIG. 2 will be explained.

Here, a point (X.

y) and the echo signal source ρ(x,y) at the raw data plane (
Point (tx, ty) in Fourier space plane) tx, ty
Consider the relationship with the echo signal 5 (tx, ty). Here, C8,OR,G is G2. Gx, G
, where r is the gyromagnetic ratio and TR is the sequence (1
The repetition interval of the encoding process), T, is the longitudinal relaxation time constant, and T is the transverse relaxation time constant.

The same applies to Z.

Now, if we consider only the direction of X as an example, Using the formula, becomes.

becomes. Vectors representing the phase X (tx), Y (t
y) can be expanded as a function of time, where C0 indicates the phase of the stationary proton, C8 indicates the phase of the flow velocity term, and C1? It shows the phase of the acceleration term of Iff, and C3 shows the phase of a higher-order term.

Then, for the terms of rest, velocity, and acceleration, set the phase to zero,
In other words, C,=C,=C,=Q. O at this time
x (OR) is solved by calculation to determine the application timing and intensity. Similarly, Gz (Gs) is also calculated.

As described above, according to the first embodiment, the refaging image is generated with the phase of the proton flow velocity and acceleration terms being zero, and is subtracted with the defaging image, so it is used as a subtraction image. This method provides an accurate contrast image of blood vessels (blood flow).

Also, when collecting data (photographing), as shown in Figure 3, the rephase sequence and the differential needs sequence are performed alternately 10 times without interruption. Since it is strained,
There is no time difference between the rephase image to be subjected to subtraxion and the differential image, and therefore a highly accurate subtrax image with no temporal difference can be obtained.

Next, other embodiments of the present invention will be described.

In the embodiments described above, both the dephasing sequence and the rephasing sequence are based on the spin echo (SE) method IC, or the field echo (F) method shown in FIG.
B) method is used as a differential sequence, and as shown in Figure 5, a gradient magnetic field (Gs,
The subtraction between the two images may be obtained using a differential sequence to which GE (hatched area in the figure) is added.

In addition, various modifications can be made without departing from the gist of the present invention.

〔Effect of the invention〕

As described above, in the present invention, there is one rephased image to be subtracted, and since the phases of proton flow velocity and acceleration terms are made zero, accurate one blood vessel (blood flow) image can be obtained. You can get the displayed image.

[Brief explanation of the drawing]

1 and 2 show a pulse sequence of an embodiment of the angiographic imaging method according to the present invention, in which FIG. 1 shows a defens sequence, and FIG. 2 shows a rephase sequence. Figure 3 is similar to Figures 1 and 2.
Figure 4 showing the timing of execution of the sequence shown in Figure 4.
5 and 5 show pulse sequences of other embodiments of the present invention, in which FIG. 4 shows a de-phase sequence, FIG. 5 shows a beam-phase sequence, and FIG. 6 shows a beam-phase sequence. The figure is a block diagram of the magnetic resonance imaging device, No. 7
8 and 8 show the pulse sequence of the conventional example, and FIG.
...Gradient magnetic field coil, 3...Transmission/reception coil, 4...
static magnetic field control system, 5... transmitter, 6... receiver, 7,
8.9...Gradient magnetic field power supply, IO...Sequencer, I
I... Computer system. Diagram 1: Agent appearing at the funeral of patent attorney Takehiko Suzue (a) (b) Diagram (c)

Claims (1)

[Claims] In a method of taking an angiogram using an MRI device that uses magnetic resonance phenomena to obtain an image that reflects the spin density and relaxation time constant of a specific atomic nucleus, terms of flow velocity and acceleration for protons are used. A rephasing image is obtained by executing a sequence in which the phase shift is zero for , a dephasing image is obtained by executing a sequence in which the phase shift is not zero, and the dephasing image is subtracted from the rephasing image. An angiographic imaging method characterized by obtaining an angiographic image by.