JPH05253201A - Imaging method of mri device - Google Patents

Abstract

PURPOSE:To generate images having different contrasts efficiently by applying rephase gradient when the second RF pulse is impressed, superposing spin echo over a stimulated echo, and making image separation for the stimulated echo and spin echo from the superposed echo for restructuring. CONSTITUTION:An NMR signal generated by a reception coil of a magnet assembly is fed to a phase detector through a preamplifier and forwarded to a computer via an A/D converter. The computer restructures the image on the basis of the data of NMR signal and displays the result on a display device. Therein a superposed echos E are collected which are formed by the process that a spin echo Sp image formed by RF pulse alpha2 deg., alpha3 deg. is superposed on a stimulated echo St wherein a rephase gradient Rp2 is applied when the RF pulse alpha2 deg. is to be impressed, and restructuring is made by separating the image due to stimulated echo St and the image due to spin echo Sp from the data of this superposed echo E.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an MRI apparatus imaging method, and more particularly to an MRI apparatus imaging method for obtaining images of different contrasts.

[0002]

2. Description of the Related Art MRI systems collect different signals according to various pulse sequences in order to obtain images with different contrasts. FIG. 8 is an exemplary diagram of a pulse sequence for obtaining an image by stimulated echo.

In this stimulated echo pulse sequence B, a first RF pulse α1 ° is applied to generate a first transverse magnetization component. Time τ from application of the RF pulse α1 ° to application of the second RF pulse α2 °
During 1, the first transverse magnetization component is out of phase.

Next, a second RF pulse α2 ° is applied to generate a first longitudinal magnetization component from the first transverse magnetization component. Then, the time τ2 has elapsed since the second RF pulse α2 ° was applied.
After that, a third RF pulse α3 ° is applied to generate a second transverse magnetization component from the first longitudinal magnetization component. The second transverse magnetization component corresponds to an inversion of the first transverse magnetization component, and the phase shift generated during the time τ1 is the same time τ1.
Focus and image in between.

In this way, the stimulated echo St which forms an inverted image after the time τ1 from the application of the third RF pulse α3 ° is collected, and an image by the stimulated echo St is obtained. However, Rp1 is the rephase gradient for the stimulated echo. Further, the gradient amount Dp1 of the lead shaft = the gradient amount R.

The second RF pulse α2 ° and the third RF pulse α2 °
For the spin echo imaged by the pulse α3 °,
In consideration of the adverse effect of the stimulated echo on the image, it is eliminated without rephasing.

[0007]

In the pulse sequence B of the stimulated echo described above, α1 ° -α2 ° -α
Only one stimulated echo St is collected by the 3 ° pulse sequence, and an image with a certain contrast is obtained. Then, the objective of this invention is to provide the imaging method of the MRI apparatus which can obtain the image from which contrast differs.

[0008]

An imaging method for an MRI apparatus according to the present invention collects stimulated echoes formed by a first RF pulse, a second RF pulse and a third RF pulse. In an imaging method of an MRI apparatus for reconstructing an image by a stimulated echo, a rephase gradient is added when a second RF pulse is applied, and an image is formed by the second RF pulse and the third RF pulse. A superposition echo obtained by superimposing a spin echo on a stimulated echo is collected, and the superposition echo collected based on the fact that the influence of the transmission phase for each RF pulse is different between the stimulated echo and the spin echo. The image by the stimulated echo and the image by the spin echo are separated from the data of It is an aspect of the structure that is configured.

In the above configuration, the 2DFT method is applied on the basis that the influence of the transmission phase for each RF pulse is different between the stimulated echo and the spin echo, and the stimulus is collected from the collected superposed echo data. It is preferable to reconstruct the image obtained by the Ted echo and the image obtained by the spin echo separately.

In the above structure, the 3DFT method is applied on the basis that the influence of the transmission phase for each RF pulse is different between the stimulated echo and the spin echo, and the stimulated echo is collected from the collected echo data. It is preferable to reconstruct the image obtained by the Ted echo and the image obtained by the spin echo separately.

In the above structure, the influence of the transmission phase for each RF pulse is different between the stimulated echo and the spin echo, which is based on Hadama
It is preferable that the image by the stimulated echo and the image by the spin echo are separately reconstructed from the collected superimposed echo data by applying the rd) method.

[0012]

In the imaging method of the MRI apparatus of the present invention, a spin echo formed by the second RF pulse and the third RF pulse is stimulated by adding a rephase gradient when applying the second RF pulse. Collect the superimposed echo that is superimposed on the rated echo. Then, the image of the stimulated echo and the image of the spin echo are separately reconstructed from the collected data of the superimposed echo.

In order to reconstruct the two images separately from the collected superimposed echo data, it is noted that the effect of the transmission phase for each RF pulse differs between the stimulated echo and the spin echo.

That is, for example, by adding the transmission phase φ only to the second RF pulse, the signal intensity of the stimulated echo with respect to the collected superimposed echo data is ∝sinα1, sinα2, sinα3, exp { j ・ φ} Spin echo signal strength ∝sin α2 ・ sin {α3 / 2} ・ sin {α3 /
2} · exp {-j · φ}, and the transmission phase φ is inverted by the signal intensity of the stimulated echo and the signal intensity of the spin echo. However, the first RF pulse = α1 ° pulse, the second RF pulse = α2 ° pulse, and the third RF pulse = α3 ° pulse.

Therefore, by using the difference of the influence of the transmission phase φ as a factor, it is possible to reconstruct the image by the stimulated echo and the image by the spin echo separately.

When the transmission phase is not taken into consideration,
Signal strength of stimulated echo for collected echo data ∝sinα1 ・ sinα
2 ・ sinα3 Spin echo signal strength ∝sinα2 ・ sin {α3 / 2} ・ sin {α3 /
2}.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail below with reference to the embodiments shown in the drawings. However, this does not limit the present invention. FIG. 1 is a block diagram of an MRI apparatus 1 for carrying out an imaging method according to an embodiment of the present invention.

The computer 2 controls the entire operation based on the instruction from the console 13. Sequence controller 3
Operates the gradient magnetic field driving circuit 4 based on the stored sequence to generate a static magnetic field and a gradient magnetic field by the static magnetic field coil and the gradient magnetic field coil of the magnet assembly 5. Further, it controls the gate modulation circuit 7 to control the RF oscillation circuit 6
The RF pulse generated in 1 is modulated into a predetermined waveform and applied from the RF power amplifier 8 to the transmission coil of the magnet assembly 5.

The NMR signal obtained by the receiving coil of the magnet assembly 5 is input to the phase detector 10 via the preamplifier 9 and further to the computer 2 via the AD converter 11. The computer 2 reconstructs an image based on the data of the NMR signal obtained from the AD converter 11, and displays it on the display device 12. An imaging method according to an embodiment of the present invention includes a computer 2 and a sequence controller 3.
Is carried out according to the procedure stored in.

FIG. 2 is an exemplary diagram of a pulse sequence according to the imaging method of one embodiment of the present invention. This pulse sequence A gives a transmission phase φ (m) that changes according to the view number m to only the RF pulse α2 °, and a rephase for imaging the spin echo Sp when applying the RF pulse α2 °. The pulse sequence B is where the gradient Rp2 and the dephase gradient Dp2 are added.
(See FIG. 8). Further, the time intervals for applying the respective RF pulses are equal (τ = τ1 = τ2), and the lead shaft gradient amount Dp1 = gradient amount Dp2 = gradient amount R.

Therefore, in this pulse sequence A, α
The stimulated echo St by the 1 ° -α2 ° -α3 ° pulse sequence and the spin echo Sp by the α2 ° -α3 ° pulse sequence are imaged at the same timing, and both echoes St, Sp
Of the superposed echo E (= St + Sp) superposed on each other.

The signal intensity of the stimulated echo St of the collected superposition echo E and the spin echo Sp.
The signal intensity of St is the signal intensity of St ∝ρ ・ sinα1 ・ sinα2 ・ sinα3 ・ exp {j ・ φ
(m)} Sp signal strength ∝ρ ・ sinα2 ・ sin {α3 / 2} ・ sin {α3 / 2} ・ ex
p {-j · φ (m)}.

The transmission phase φ (m) given to the RF pulse α2 ° is inverted by the signal intensity of the stimulated echo St and the signal intensity of the spin echo Sp. In consideration of the influence of the transmission phase φ (m), the image of the stimulated echo and the image of the spin echo are separately reconstructed from the collected data of the superimposed echo E.

FIG. 3 is a flow chart of a method of imaging a superposed echo by collecting the superposed echo E and applying the 2DFT method from the data of the superposed echo E to separately reconstruct the two images. The method of imaging the superimposed echo will be described below with reference to the flowchart.

After setting the subject on the magnet assembly 5, when the user gives an FOV designation and an instruction for imaging the superimposed echo from the console 13, the computer 2 executes the following processing. However, the designation of the FOV is the same as that when collecting only the stimulated echo St (that is, the pulse sequence B).

In step S1, the FO designated by the user
Set the FOV that is doubled from V only in the warp direction. In step S2, the number of views of the pulse sequence B is doubled according to the FOV. In step S3, the warp step is calculated with the pixel size of the pulse sequence B unchanged.

In step S4, the pulse sequence A as shown in FIG. 2 having the calculated warp step is created. However, the transmission phase φ given to the RF pulse α2 °
(M) is, for example, φ (m) = {π / 2} · m, where m is a view number.

In step S5, a scan is executed based on the created pulse sequence A to collect the superimposed echo E. Raw data of the superposed echo E collected (Raw dat
In a), the raw data of the stimulated echo St has a primary phase of {φ (m)} and the spin echo S
The raw data of p will have a primary phase of {-φ (m)}.

In step S6, 2DFT is performed on the raw data of the superimposed echo E by doubling the FFT size only in the warp direction. By this 2DFT, as shown in FIG. 4, the image StG of the stimulated echo is generated.
And the image SpG of the spin echo are separated in the warp direction and reconstructed.

In step S7, the two images reconstructed as shown in FIG. 4 are divided into two in the warp direction, and the stimulated echo image StG and the spin echo image SpG are extracted and stored / displayed. Note that the timing of adding the phase gradient of the pulse sequence A is different from that of the pulse sequence B because the reconstructed image StG and image SpG are aligned in the warp direction in consideration of the influence of the transmission phase φ. Is.

As another embodiment of the present invention, instead of the superimposed echo imaging method as shown in FIG. 3, the superimposed echo E is collected and the 3DFT method is applied from the data of the superimposed echo E to apply the two images. An example is a method of performing an imaging method of a superimposed echo in which StG and SpG are separately reconstructed. However, the configuration of the MRI apparatus is the same as the MR
This is the same as the I-device 1. Hereinafter, the imaging method of the superimposed echo will be described with reference to the flowchart of FIG.

After setting the subject on the magnet assembly 5, when the user gives an FOV designation and a superimposition echo imaging instruction from the console 13, the computer 2 executes the following processing. However, the designation of the FOV is the same as that when collecting only the stimulated echo St (that is, the pulse sequence B).

In step S11, the depth encode number K in the depth direction is set to 2. The number of views, warp steps, and pixel size are set in the same manner as the pulse sequence B.

In step S12, the transmission phase φ (k) that changes according to the depth encode k only for the RF pulse α2 °.
A pulse sequence A as shown in FIG. 2 is created (note that φ (m) in FIG. 2 is replaced by φ (k)). The transmission phase φ (k) is, for example, φ (k) = {π / 2} · k, where depth encoding k = 0,1.

In step S13, the depth encode number K =
2. Perform 3D scan 2 to collect superimposed echo E.
Superposed echo E collected when depth encoding k = 0
Is set to dk0, and the raw data when k = 1 is set to dk1. Then, for the raw data dk0, the signal strength of St ∝ρ ・ sinα1 ・ sinα2 ・ sinα3 ・ exp {j ・
0} Sp signal strength ∝ρ ・ sinα2 ・ sin {α3 / 2} ・ sin {α3 / 2} ・ ex
p {-j · 0}, and for the raw data dk1, the signal strength of St ∝ρ ・ sinα1 ・ sinα2 ・ sinα3 ・ exp {j ・ π
/ 2} Sp signal strength ∝ρ ・ sinα2 ・ sin {α3 / 2} ・ sin {α3 / 2} ・ ex
p {-j · π / 2}.

In step S14, the raw data dk1 is added.
The raw data Dk1 is obtained by multiplying exp {j · π / 2}.
In step S15, an FFT of FFT size 2 is performed in the depth direction on the raw data dk0 and Dk1 to obtain the raw data S of the stimulated echo as shown in FIG.
It is divided into tR and spin echo raw data SpR. At step S16, the raw data StR divided as shown in FIG.
And SPR are subjected to 2DFT respectively to reconstruct a stimulated echo image StG and a spin echo image SpG, and store and display them.

As still another embodiment of the present invention, instead of the superposed echo imaging method as shown in FIG. 5, superposed echoes E are collected and the Hadamard method is applied from the data of the superposed echoes E to obtain the two Image StG, SpG
One example is a method of performing an imaging method of a superimposed echo that reconstructs separately. However, the configuration of the MRI apparatus is the same as that of the MRI apparatus 1. Hereinafter, the imaging method of the superimposed echo will be described with reference to the flowchart of FIG.

After setting the subject on the magnet assembly 5, when the user gives an instruction for FOV and an instruction for imaging the superposed echo from the console 13, the computer 2 executes the following processing. However, the designation of the FOV is the same as that when collecting only the stimulated echo St (that is, the pulse sequence B).

In step S21, the number of views, the warp step, the pixel size, etc. are set in the pulse sequence B.
The pulse sequence A as shown in FIG. 2 is created in the same manner as above. However, the transmission phase φ given to the RF pulse α2 °
(M) shows RF pulse α1 °, R in the first scan
Φ (m) = 0, which is equivalent to the F pulse α3 °, and φ (m) = {π / 2} · m 2 in the second scan.

In step S22, two scans are executed based on the created pulse sequence A to collect the superimposed echo E. The raw data (Raw data) of the superimposed echo E collected in the first scan is d (0), and the raw data in the second scan is d (π / 2). In step S23, raw data d (π / 2) is multiplied by exp {j · π / 2} to obtain raw data D (π / 2).

At step S24, the raw data d (0),
D (π / 2) is subjected to Hadamard transformation as described below to divide into raw data Ha of stimulated echo and raw data Hb of spin echo. Ha = [d (0) -D (π / 2)] / 2 Hb = [d (0) + D (π / 2)] / 2 In step S25, for the raw data Ha and Hb,
2DFT is performed for each to reconstruct the image StG of the stimulated echo and the image SpG of the spin echo, and store / display.

[0042]

According to the imaging method of the MRI apparatus of the present invention, the image by the stimulated echo and the image by the spin echo can be separately reconstructed at the same time, and two types of images having different contrasts can be efficiently obtained. ..

[Brief description of drawings]

FIG. 1 is a block diagram of an MRI apparatus for carrying out an imaging method according to an embodiment of the present invention.

FIG. 2 is an exemplary diagram of a pulse sequence according to an imaging method of an embodiment of the present invention.

FIG. 3 is a flowchart of an imaging method according to an embodiment of the present invention.

FIG. 4 is an exemplary diagram of an image reconstructed by an imaging method according to an embodiment of the present invention.

FIG. 5 is a flow chart of an imaging method of another embodiment of the present invention.

FIG. 6 is an explanatory diagram of raw data according to an imaging method of another embodiment of the present invention.

FIG. 7 is a flow chart of an imaging method of still another embodiment of the present invention.

FIG. 8 is a view showing an example of a pulse sequence of a conventional stimulated echo.

[Explanation of symbols]

 1 MRI device 2 Computer 3 Sequence controller E Superimposed echo St Stimulated echo Sp Spin echo α1 ° First RF pulse α2 ° Second RF pulse α3 ° Third RF pulse φ Transmission phase

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location 9118-2J G01N 24/08 Y

Claims (4)

[Claims] 1. A first RF pulse and a second RF pulse
Stimulation test for imaging with the third RF pulse
Collected echoes by stimulated echo
In an imaging method of an MRI apparatus for reconstructing an image
At the time of applying the second RF pulse, a rephase gradient is added
By the second RF pulse and the third RF pulse.
The spin echo to be imaged is superimposed on the stimulated echo.
The superimposed echoes that are folded are collected and the transmission position for each RF pulse is collected.
The effect of the phase is on the stimulated echo and the spin.
Based on the difference between the
According to the stimulated echo from the data of Kor
Image and the image by the spin echo are separated
Image of MRI device characterized by reconstructing
Method. 2. The imaging method for an MRI apparatus according to claim 1, wherein the 2DFT method is applied on the basis that the influence of the transmission phase for each RF pulse is different between the stimulated echo and the spin echo. An imaging method for an MRI apparatus, characterized in that an image by a stimulated echo and an image by a spin echo are separately reconstructed from the collected superimposed echo data. 3. The imaging method for an MRI apparatus according to claim 1, wherein the 3DFT method is applied based on the fact that the effect of the transmission phase for each RF pulse differs between the stimulated echo and the spin echo. An imaging method for an MRI apparatus, characterized in that an image by a stimulated echo and an image by a spin echo are separately reconstructed from the collected superimposed echo data. 4. The imaging method for an MRI apparatus according to claim 1, wherein the Hadamard method is applied based on the fact that the influence of the transmission phase for each RF pulse differs between the stimulated echo and the spin echo. An imaging method for an MRI apparatus, characterized in that an image by a stimulated echo and an image by a spin echo are separately reconstructed from the collected superimposed echo data.