JPH01126955A - Blood flow imaging system - Google Patents

Abstract

PURPOSE:To obtain the image only of a blood flow part only by one imaging, by differentiating the timing of the echo signal from a stationary part from that of the echo signal from the blood flow part. CONSTITUTION:A magnetic field and an RF pulse are generated to the subject placed under a static magnetic field of 5,000G according to the sequence shown by (a)-(f) to measure a signal. That is, an RF pulse 101 bringing down magnetization by 90 deg. under the application of a z-direction inclined magnetic field 102 to excite the spin in a desired slice. A non-linear inclined magnetic field is applied for t1msec and, after t2msec, a non-linear inclined magnetic field 104 is applied for t1msec. Then, a y-direction position encoding magnetic field 105 is applied and, next, an x-direction linear inclined magnetic field 106 is applied. At the same time, an NMR signal S is received. The measuring signal S is subjected to Fourier transform by a processing apparatus and an absolute value is taken to obtain an angiogram.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an in-body tomography apparatus that utilizes nuclear magnetic resonance phenomena, and is used for medical diagnosis.

In particular, it relates to technology for imaging the course of blood vessels within the body.

[Conventional technology]

The typical conventional method is the April/May issue of Radiowag (198
6) Pages 411 to 418 (RadiologyMa
y (1986) pp. 411-418).

This does not affect the signal from the stationary part, but uses a sequence that gives a phase change proportional to the flow velocity to the signal from the blood flow part, so that only the signal from the blood flow part changes. In this method, a blood vessel is extracted from a difference image between two images obtained by performing image capturing twice and reconstructing each image. In other words, since the blood flow speed is different during the diastole and systole of the heart, synchronization is achieved using an electrocardiograph, and the sequence described above is
When imaging is performed during the diastole and systole and image reconstruction is performed for each, images with the same density in the stationary area and different densities in the blood flow area are obtained. Therefore, by taking the difference between these images, only the blood flow portion can be extracted.

[Problem that the invention seeks to solve]

The above-mentioned conventional technology has a problem in that it requires imaging twice and takes a lot of time to eliminate static parts and extract only the direct current parts in the reproduced image.

An object of the present invention is to provide an imaging method that solves the above problem by separating signals from a stationary portion and signals from a blood flow portion in one imaging session.

[Means for solving problems]

The above object is achieved by performing an imaging method as shown below.

(1) As shown in the sequence shown in FIG. 1, (i) Apply an RF pulse for slice selection.

(Hereinafter, as shown in FIG. 3, the slice surface 3 of the subject 31
The x and y directions are defined on 0, and the direction perpendicular to these is defined as 2. ) Simultaneously apply gradient magnetic fields in two directions.

(it) Next, the nonlinear gradient magnetic field H expressed by the following equation is
Leave it on for tz+n5ec.

H=Dx''ez where G is a constant and ez is a unit vector in two directions.

(iii) After t zrasec, a nonlinear gradient magnetic field -H is applied for timsec.

(tv) Then, similarly to the normal sequence, a linear gradient magnetic field in the y direction is applied as a phase encode, and then a linear gradient magnetic field H' expressed by the following equation is applied to measure the signal.

(2) Images are reconstructed from the measured signals excluding the vicinity of the first peak.

[Effect]

The spins excited by the slice selection RF pulse in (1)(i) are applied because the nonlinear gradient magnetic field H in (1)(jt) is applied for tlmsec.

θ1=γGx”tx (y is a constant) The phase of the spin advances by θl determined by H.

If the spin moves and the value of the X coordinate changes from X to X+ΔX by t4msec after that, the nonlinear gradient magnetic field -0 in (1) (■) above is applied for tlmsec.

02=-yG(x+Δx)"t,1 The spin phase advances by O2 determined by (-H).

Therefore, the phase advance O due to H and -X() is θ
= (h+θx= 2yGtt (Δx) x-YG (
x) It becomes 2tt. Therefore, at the time of the timing shift of the echo signal measured by performing (1) (iv) above, since -2y G t 1 (Δx) x = γG' ) will be proportional to

Therefore, as shown in FIG. 1(f), S is the timing deviation time of the echo signal from the stationary part.

τS=0, the echo signal from the stationary part appears as the first peak of the measurement signal, and the timing deviation time τ of the echo signal from the part of the average blood flow velocity V.

becomes G'.Therefore, in the measurement signal, except for the vicinity of the first peak, it is an echo signal from the blood flow part.

Only S(t,c) can be obtained. However, C is the number of phase encodes, and at this time, the flow velocity is Vl ((k=1
．． 2. ..., N), the blood flow density distribution is expressed as ρh(x,
y), and the signal generated from this part is 5k(t, c)
Then, S (tt c) = Σ S k (t e a )
k=1, and the term γG(Δx)''tl of the phase θ is ignored as being extremely small. However, F is a two-dimensional discrete Fourier transform of 256×256 size, and a is a constant.

Therefore, at this time, if the flow velocity can be considered constant in two directions, then the following results.

Therefore, a blood vessel system image can be obtained by 1FSl.

〔Example〕

Hereinafter, the present invention will be described in detail based on Examples.

FIG. 2 is a block diagram of an embodiment of the present invention. A high-frequency pulse transmitter 202 generates high-frequency pulses to resonate a specific nuclide in the subject. Magnetic field control section 2
03 generates a static magnetic field that determines the resonance frequency of the NMR signal and a gradient magnetic field whose strength and direction can be controlled arbitrarily. The receiver 205 detects the NMR signal generated from the subject.

The sequence control unit 201 that performs measurement
Controls the various pulses and magnetic fields generated to detect the R signal, as well as the receiver.

The processing device 206 performs image reconstruction and various calculations based on the measurement signal taken in from the receiver 205, and displays the reconstructed image on the CRT display 207.

The magnetic field drive unit 304 generates a magnetic field necessary for measurement based on the control signal output from the magnetic field control unit 203.

An embodiment of the present invention having the above configuration will be described below with reference to FIG.

Step 301: Generate a magnetic field and RF pulse as follows for the subject placed under a static magnetic field of 5000G according to the sequence shown in Figure 1 (a) to (f), and measure the signal. . Namely.

(i) RF pulse 101 is applied (4
m5ec) to excite spins within the desired slice.

(it) Nonlinear gradient magnetic field 103 (H) expressed by the following formula
is applied for tz+5 seconds.

H=G*
04(-H) is applied for tl@8ee.

(tv) Apply a y-direction position encode magnetic field 105 (H') (4 m5ec).

1(v) Next, an X-direction linear gradient magnetic field 106 (H') is applied (50 seconds).

H' = G' xXaz (G' X:!0.3G/
FIL) (vi) At the same time, NMR signal S (t + c
).

The above steps (i) to (iv) are repeated 256 times while changing C from 127 to 128.

Step 302: The measurement signal S (tt c) excluding the signal at t=o~4 m5ec is Fourier-transformed by the processing device 206, the absolute value is taken, an angiography image is obtained, and the flow velocity v (x+ y) is obtained.

v(Xpy)=λ(Art(F5)(X-y))/
x (where, Art(FS) is the phase of FS, and λ is a constant) [Effects of the Invention] According to the present invention, the timing of the echo signal from the stationary part and the echo signal from the blood flow part can be made different. Therefore, it is possible to obtain an image of only the blood flow part with only - times of imaging.

[Brief explanation of the drawing]

FIG. 1 is a timing chart showing an example of a sequence using the present invention, FIG. 2 is a block diagram showing an apparatus configuration of an example of the present invention, and FIG. 3 is a timing chart showing an example of a sequence on a subject. It is an explanatory diagram. t in FIG. 1 is the elapsed time with the origin at the rising time 105 in FIG. 1(d), and τV is the time at which the echo signal from the blood flow portion appears. τS is the time when the echo signal from the stationary part appears.
The figure is also -ts-〇

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 a subject, and a means for performing various calculations including image reproduction on the detected signal. In a magnetic resonance imaging system that has a magnetic resonance imaging system, by using a gradient magnetic field that is nonlinear with respect to position, the echo signals from the stationary part of the subject and the echo signals from the moving part are output at different times. A blood flow imaging method that separates signals from moving parts and moving parts. 2. The blood flow imaging method according to item 1, characterized in that after the resonance RF pulse, a gradient magnetic field that is nonlinear with respect to position is applied, and then a gradient magnetic field with the polarity of this gradient magnetic field reversed is applied. 3. The blood flow imaging method according to item 1, characterized in that after the resonance RF pulse, a gradient magnetic field that is nonlinear with respect to position is applied, then a 180° pulse is applied, and then the same gradient magnetic field is applied once again. . 4. The blood flow imaging system according to item 2, wherein the nonlinear gradient magnetic field in item 2 has a magnitude in one direction that is proportional to the square of the coordinates with respect to the coordinate axis. 5. The blood flow imaging method according to item 2, wherein the nonlinear gradient magnetic field in item 3 has a magnitude proportional to the square of coordinates with respect to a coordinate axis in one direction. 6. The blood flow imaging method according to item 4, characterized in that, in item 4 above, an angiographic image is reconstructed from the measurement signal and a blood flow velocity at each point in the image is determined. 7. The blood flow imaging method according to item 5, characterized in that, in item 5 above, an angiographic image is reconstructed from the measurement signal and the blood flow velocity at each point in the image is determined.