JPH0578343B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a magnetic resonance imaging apparatus that is capable of obtaining magnetic resonance angiography images using a subtraction method.

(Conventional technology) General medical MRI (Magnetic Resonance
In a magnetic resonance imaging (Magnetic Resonance Imaging) system, a gradient magnetic field and an excitation radio-frequency pulse (RF pulse) are applied to a subject placed in a static magnetic field according to a predetermined excitation/detection procedure. A magnetic resonance phenomenon is caused in a specific part of the examiner, and the magnetic resonance signal (echo signal or FID
Anatomical information and qualitative information of a specific region of the subject are imaged by detecting the signal (signal) and performing signal processing using a reconstruction method such as a two-dimensional Fourier transform method. That's what I do.

An example of this type of MRI apparatus will be described below with reference to FIG. 6. In Figure 6, the cylindrical body
In the MA, a superconducting or normal conducting static magnetic field coil 1, X-axis, Y-axis, and Z-axis gradient magnetic field coils 2, and a transmitting/receiving coil 3 are provided as a static magnetic field generator.
The subject P is introduced into the diagnosable magnetic field generation area within the main body MA.

Further, the static magnetic field coil 1 is driven by a static magnetic field control system 4, and the transmitting/receiving coil 3 is driven by a transmitter 5 for excitation and a receiver 6 for detection (collection). , Y-axis, and Z-axis gradient magnetic field coils 2 are connected to X-axis gradient magnetic field power supply 7 and Y-axis gradient magnetic field coil 2, respectively.
It is designed to be driven by an axial gradient magnetic field power supply 8 and a Z-axis gradient magnetic field power supply 9.

The X-axis, Y-axis, and Z-axis gradient magnetic field power supplies 7, 8, and 9 and the transmitter 5 mentioned above are driven by the sequencer 10 according to a predetermined image data collection sequence. For example, as shown in FIG. 7, an SE (spied echo) method is performed using a slicing gradient magnetic field G _S , a read gradient magnetic field G _R , an encoding gradient magnetic field G _E , and a 90° pulse and a 180° pulse. .

The data group obtained by executing the above-described sequence is taken into the receiver 6 each time it is acquired, where it is generally subjected to quadrature phase detection, converted into a digital signal, and then sent to the computer system 11. The computer system 11 digitizes the detection output (real part data,
Imaginaly part data) is captured and stored in a disk storage device, etc., and then a two-dimensional image (slice image) is created by two-dimensional Fourier transform processing,
I am trying to display it on that monitor.

Images produced by the above-mentioned MRI apparatus 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
There is MR angio. This method obtains blood vessel (blood flow) contrast images using an MRI device, 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 can be obtained. MRI equipment is also implemented using almost the same concept. First,
In an MRI machine, protons ( ^1H ) that make up blood
By focusing on this, we distinguish between stationary protons (non-blood) and moving protons (blood). For example, FIG. 7 is a diagram showing a normal SE method sequence, and by this SE method sequence, an image (a dephasing image) of stationary protons is obtained (FIG. 9b). This image is
This corresponds to the image before contrast agent injection. Also,
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 G _R ) is applied to Fig. 7 is executed, and stationary protons and Images that do not distinguish between moving protons (refaging images)
(Figure 9a) is obtained. Here, flow compensation is to align the phase of something moving at a constant speed with the phase of something stationary at the echo center.

Then, by subtracting the image shown in FIG. 9b from the image shown in FIG. 9a (subtraction), the image shown in FIG. 9c is obtained.
An image in which blood vessels are contrasted (angiography image) is obtained.

(Problem to be Solved by the Invention) In the above-mentioned conventional method, the refaging image that is the basis of subtraction is a sequence in which the phase shift is zero for the flow velocity term, and the When in a constant speed state, highly accurate refaging images, and even
Angiography with excellent diagnostic ability can be presented. However, the fact that blood flow is at a constant speed means that
This is not the case in general, and the behavior is repeated acceleration, constant speed, etc. Therefore, the angiographic images produced by the conventional method are not accurate because they are based on re-aging images that do not take into account the term of acceleration.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a magnetic resonance imaging apparatus that is capable of obtaining highly accurate magnetic resonance angiography images.

[Structure of the invention]

(Means for Solving the Problems) In order to solve the above problems and achieve the objects, the present invention is configured to take the following measures.
That is, the present invention provides: a static magnetic field generating means for generating a static magnetic field to be applied to a subject; a gradient magnetic field generating means for generating a gradient magnetic field to be applied to the subject; a high-frequency pulse generating means for generating a high-frequency pulse related to excitation, and applying the gradient magnetic field and the high-frequency pulse under predetermined conditions to the subject placed in the static magnetic field, the device comprising: a first pulse sequence for generating a first magnetic resonance signal such that a phase shift becomes zero in terms of velocity and acceleration of the proton flow after selectively exciting the protons present in the region; A second method such that the phase shift becomes non-zero in terms of velocity and acceleration of the proton flow after selectively exciting the protons present in a specific region of the specimen.
a second pulse sequence for generating a magnetic resonance signal; and a control means for executing a second pulse sequence for generating a magnetic resonance signal of the first magnetic resonance signal and the second pulse sequence according to the execution of the first pulse sequence and the second pulse sequence. a collecting means for collecting a magnetic resonance signal of the object, and reconstructing a re-aging image based on the first magnetic resonance signal generated from the subject and obtained by the collecting means when the control means is driven. and reconstructing means for reconstructing a dephasing image based on the second magnetic resonance signal; and the dephasing image obtained by the reconstructing means from the rephasing image obtained by the reconstructing means. By subtracting the image,
A magnetic resonance imaging apparatus comprising: means for obtaining an angiographic image in the specific region;

(Function) As mentioned above, since the re-aging image is obtained with zero phase shift in terms of flow velocity and acceleration, the blood flow (vessel) to be contrasted can be accurately identified on the subtraction image. appears in

(Embodiment) An embodiment of the magnetic resonance imaging apparatus according to the present invention will be described below 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.
Figure 2 shows a one-encoding sequence for obtaining refaging image data, in which gradient magnetic fields G _S and _GR shown in the cross-hatching are added to the sequence in Figure 8, and the velocity and acceleration of the flow are This is a sequence with zero phase shift for the terms.

The above sequence is executed at the timing shown in FIG. That is, the collection matrix is 256×256
Then, 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 defage sequence shown in FIG. Next, the refase in Figure 2
The second encode is executed in the sequence, and finally the 256th encode is executed in the defase sequence shown in Fig. 1 to complete the shooting. By the end of this photographing, in the case of the apparatus shown in FIG. 6, the image data group (refuse image) corresponding to FIG.
Image data group corresponding to Figure b (Defais image)
are collected, image reconstruction is performed using a two-dimensional Fourier transform method, etc., and then subtraction is performed to generate a subtraction image, that is, an angiographic image shown in FIG. 9c.

Here, the procedure for setting the gradient magnetic fields G _S and _GR shown in FIG. 2 will be explained.

Here, an echo signal source ρ(x, y) at a point (x, y) in the excitation slice plane XY and an echo signal S at a point (tx, ty) in the raw data plane (Fourier space plane) tx, ty Consider the relationship with (tx, ty). Here, G _S , G _R , G _E are G _Z ,
corresponding to G _X and G _Y , γ is the gyromagnetic ratio, T _R is the repetition interval of the sequence (one encoding process), and _T
is the longitudinal relaxation time constant, and T ₂ is the transverse relaxation time constant.

TE is the echo time.

S (tx, ty) = ∫∫ (x, y)・e ^-j2 〓〓〔 ^G(tx)

Claims (1)

[Scope of Claims] 1. Static magnetic field generating means for generating a static magnetic field to be applied to a subject; gradient magnetic field generating means for generating a gradient magnetic field to be applied to the subject; and protons to be applied to the subject. a high-frequency pulse generation stage for generating a high-frequency pulse related to excitation of the subject; a first pulse sequence for generating a first magnetic resonance signal such that the phase shift becomes zero in terms of velocity and acceleration of the proton flow after selectively exciting the protons present in a specific region; A second method such that a phase shift becomes non-zero in terms of velocity and acceleration of the proton flow after selectively exciting the protons present in a specific region of the subject.
a second pulse sequence for generating a magnetic resonance signal; and a control means for executing a second pulse sequence for generating a magnetic resonance signal of the first magnetic resonance signal and the second pulse sequence according to the execution of the first pulse sequence and the second pulse sequence. a collecting means for collecting a magnetic resonance signal of the object, and reconstructing a re-aging image based on the first magnetic resonance signal generated from the subject and obtained by the collecting means when the control means is driven. and reconstructing means for reconstructing a dephasing image based on the second magnetic resonance signal; and the dephasing image obtained by the reconstructing means from the rephasing image obtained by the reconstructing means. By subtracting the image,
A magnetic resonance imaging apparatus comprising: means for obtaining a blood vessel image in the specific region.