JPH01238851A - Magnetic resonance fluid photographing method - Google Patents

Abstract

PURPOSE:To enable and a blood vessel image and information on the speed and the direction of liquid, e.g., a blood flow in a blood vessel, to be simultaneously formed in a picture, a picture using a pulse sequence by which only a substance in a rest state is formed in a picture and a picture by using a pulse sequence by which both a substance in a rest state and a substance in a moving state are formed in a picture are subtracted. CONSTITUTION:At a stage precedent to a pulse sequence used for MR angiography and a pulse sequence by which the pictures of a substance in a rest state and a substance in a moving state are both formed, namely in a section 1, by applying a selection 90 deg. RF pulse simultaneously with a gradient magnetic field Gx, only a spin in the region of some fluid flowing vertically to a direction Gx in a photograph region is selected excited. Thereafter, after waiting is made for a given delay time td in a section 2, by using a pulse sequence (90 deg. RF pulse 180 deg. RF pulse) by which a spin echo signal displayed in a section 3 is provided, an NMR signal is observed. In this case, the applying patterns of gradient magnetic fields (Gx, Gy, and Gz) where a substance moving at a speed (v) can be also formed in a picture are employed. The so provided NMR signal is collected and its picture is formed by changing the amplitude of Gy 128 or 256 times.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention relates to a magnetic resonance diagnostic apparatus (hereinafter referred to as an MHI apparatus) that creates a tomographic image of a subject using nuclear magnetic resonance (hereinafter referred to as NMR) phenomenon. It is something.

Conventional technology NMR has long been attracting attention as a means of non-invasively obtaining flow information from a subject, and many methods have been proposed in i9.MHI. There are two methods: a method that uses changes in the amplitude of longitudinal magnetization of the NMR signal, and a method that uses changes in the phase of transverse magnetization.A method that uses an MHI device to depict blood vessels similar to angiography (MR angiography) Although both of these methods can be used, the latter method, which takes advantage of the fact that the phase changes due to the flow of blood, is mainly used. Using a pulse sequence in which the phase of the NMR signal changes and the signal disappears, and a pulse sequence that is unaffected by the flow, an image consisting only of "stationary objects" is created with the first pulse sequence, and an image consisting of "only stationary objects" is created with the second pulse sequence. Create an image consisting of "stationary objects + moving objects" with the pulse sequence of
This method attempts to obtain an image of ``only moving objects'' by subtraction.

An example of these pulse sequences is shown in Figure 4 (1, (b)
Shown below.

At the time of measurement, 80 = JG(t)・Vt dt・・・・・・■G
(t)...Gradient magnetic field strength V...N because it receives a phase shift according to the speed V given by the speed of the moving spins
The MR signal disappears and cannot be imaged. On the other hand, the pulse sequence shown in Fig. 4 (Fig. 4) is one in which the method of applying the gradient magnetic field O for frequency encoding and slice selection has been added or changed as shown in the shaded area in the figure. ) It is possible to make the phase shift Δ0 of the spin moving at the velocity given by the above equation 0 zero. By doing this, D, (a)
With this pulse sequence, signals from the moving spins that had disappeared can be obtained, and moving parts can be imaged in the same way as stationary parts.

The MR angiography image obtained by 5 ubtraction of the two images obtained using these two pulse sequences does not require the use of a contrast agent, compared to angiography conventionally used in the radiology field. It has the advantage of being able to obtain blood vessel images.

However, with the above method, although it is possible to selectively image only the area where the flow is, it is impossible to simultaneously obtain information on the speed and direction of the flow, and in order to obtain this information, another pulse sequence is required. Since it was necessary to take the measurements again after the test was completed, the test time was extended.

(c) Problems to be Solved by the Invention As mentioned above, in conventional MR angiography methods, blood vessel images can be obtained without using a contrast medium, but in conventional angiography, the contrast medium moves. In particular, it was impossible to obtain information on the velocity and direction of the flow, which was previously available. In order to obtain such information, it is necessary to perform measurement again using a different pulse sequence, which poses a problem in that the test takes a long time.

The present invention considers the above problems, applies a conventional pulse sequence, and uses a fluid similar to MR angiography ([
The objective is to obtain an f[L-tube] image and to simultaneously image information on the velocity and direction of fluid such as blood flow within the blood vessel.

4) Means for Solving the Problems The present invention is based on a pulse sequence for imaging (a stationary object + a moving object), which is one of the pulse sequences of conventional MR angiography (Fig. (corresponding to b)), a process of applying another RF pulse to selectively saturate the spins existing in a certain region of the subject and differentiate them from other spins before applying the excitation RF pulse. The image obtained by changing to the added pulse sequence and the image obtained by the conventional MR angiography pulse sequence (Fig. 4 (corresponding to ω)) are 5ubtractloned. is expressed as a percentage.

Specifically, after applying a first 90° radio frequency pulse to selectively excite the flow region of the imaging region, a second radio frequency pulse is applied to the imaging region including the flow region after a predetermined delay time has elapsed. A first step in which a resonance signal is extracted in a state in which the flowing region is saturated by applying an electric current, and both the flowing region and the stationary region are imaged based on the obtained resonance signal and the delay time, and information on the flow velocity and flow direction is obtained. 9 for the process and the imaging area
A second process in which a 0' radio frequency pulse is applied to selectively excite all imaged areas to extract resonance signals, and a stationary area is imaged based on the obtained resonance signal, and a flow area obtained in the first process. and obtain a composite image of the static region.

(e) Effect The 5 ubtracti between images that has been proposed in the past
By changing one of the two Norculus sequences of MR angiography using on according to the above method, information on the speed and direction of blood flow can be obtained simultaneously with the blood vessel image obtained by MR angiography. It is something that can be transformed into

(f) Examples The present invention will be explained based on examples. FIG. 3 shows a conceptual diagram of the MR angiography method.

An image using a pulse sequence that images (only a stationary object) obtained with the two different conventional pulse sequences shown in Fig. 4 (a) and (b), and an image (-a stationary object). 5ubtraction
By doing this, it is possible to image a fluid such as blood in a blood vessel. .

This MR angiography method can obtain blood vessel images without using a contrast medium. It is also a useful method because arteries and veins can be selectively visualized by changing the timing of synchronization with the heartbeat. However, although such a method can obtain an image of a region where a flow exists, that is, a blood vessel, it is difficult to obtain information regarding the velocity and direction of the flow.

Therefore, the pulse sequence used in the MR angiography shown in Fig. 4 is changed to the pulse sequence (Fig. 4 (b )) By adding a process of applying 90 RF (radio frequency) pulses to the previous step, it becomes possible to obtain an MR angiography image and at the same time obtain information on the velocity and direction of the flow.

This will be explained in detail using FIGS. 1 and 2.

Figure 1 (a) is (a stationary object + a moving object)
This is a sequence for imaging. In the figure, Gx is a frequency encode, Gy is a phase encode, and Gz is a gradient magnetic field for slice selection. Select 90'R in section 1
By applying the F pulse simultaneously with the gradient magnetic field Qx,
Only spins in a region of the fluid perpendicular to the Gx direction within the image transport region are selectively excited. Next, after waiting for a predetermined delay time td in section 2, a spin echo signal shown in section 3 is obtained using a Luhalus sequence (90IRF) (Luhalus → 1
80RF pulse) to observe the NMR signal. At this time, as shown in Fig. 4, etc., gradient magnetic fields (Gx, Gy, Gz
) is used. NMR obtained in this way
A signal is collected by changing the amplitude of oy 128 or 256 times to create an image. An example of the obtained image is shown in Figure 2(a).
Shown below. In the figure, 41 indicates a blood vessel, and 44 indicates a stationary surrounding tissue. The spins excited in section 1 of Figure 1 (al) and saturated in section 3 are depicted with 1!ow intensity as shown by diagonal lines 42 and 43. However, as shown in 43, the spins in the blood vessel are moving. Therefore, from the time of excitation to the observation time of the signal (time until td signal observation), it moves K and is imaged at a distance given by ΔX from the surrounding area where the position is stationary. The velocity V of the blood flow is given by Δx/(t d +TE)−■ in V.

FIG. 1(b) is the same pulse sequence as in the normal spin knee method and is the same as FIG. 4(a). The results obtained when the same subject site as in FIG. 2(a) was imaged using this pulse sequence are shown in FIG. 2).

In the figure, the stationary surrounding tissue 45 is imaged in the same way as in FIG. 2(a), but blood vessels shown at 46 have a phase shift Δθ given by the equation 0 because blood is flowing through them.I! ow
It is depicted at 1 ntense (medium signal zero). If these two images are subjected to 5ubtraction in the same manner as in general MR angiography, the fourth
As shown in Figure (C), the blood vessels 51 are
In the city, the stationary surrounding tissues are
nsity. Further, information such as the speed and direction of blood flow can be obtained from the positional relationship between the j'ow 1 ntensity portion 54 in the blood vessel and the negative signal portion 53 in the stationary region according to equation 0.

In this way, by adding the process of applying a 90° RF pulse to the pulse sequence for obtaining MR angiography, it is possible to obtain speed and direction information at the same time as obtaining an MR angiography image. becomes possible. In addition, the above method uses the spin echo method shown here.
MR using other methods, not limited to R angiography
It can also be applied to angioguthuphy.

(g) Effects According to the present invention, MR angiography, which in the conventional method only depicts blood vessels, can simultaneously obtain information on the velocity and direction of direct current, and is also clinically useful. Become.

[Brief explanation of the drawing]

FIGS. 1 and 2 show an embodiment of the magnetic resonance fluid imaging method of the present invention, and FIG. , Fig. 1(a) is a diagram showing a pulse sequence for obtaining an image of only a stationary part, and Fig. 2(a) is a diagram showing a pulse sequence for obtaining an image of only a stationary part.
Figure 2 (b) is a diagram showing the image obtained by Figure 1 Φ), Figure 2 (c) is a diagram showing the image obtained by Figure CaJ.
Figure 2 shows an MR angiography image obtained by subtracting the images in (a) and Φ), Figure 3 is a conceptual diagram of MR angiography, and Figure 4 is an example of conventional OMR angiography. FIG. 3A is a diagram showing the pulse sequence thereof, and FIG. 3B is a diagram showing a gradient magnetic field pattern for preventing spin phase shift.

Claims (1)

[Claims] (1) After applying a first 90° radio frequency pulse to selectively excite the fluid region of the imaging region, wait for a predetermined delay time to elapse, and then apply a second 90° radio frequency pulse to the imaging region including the fluid region. A first step, in which a resonance signal is extracted in a state where the flowing region is saturated by applying a voltage, and both the flowing region and the stationary region are imaged based on the obtained resonance signal and the delay time, and information on the flow velocity and the flow direction is obtained. a second step in which a 90° radio frequency pulse is applied to the imaging region to selectively excite all the imaging regions to extract a resonance signal, and a stationary region is imaged based on the obtained resonance signal; Magnetism characterized in that an image of only the flowing region including information on flow velocity and flow direction is obtained by subtracting the image of the stationary region obtained in the second step from the mixed image of the flowing region and the stationary region obtained in the step. Resonant fluid imaging method.