JP3343392B2 - MR angiography device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a two-dimensional PC (Phase
More specifically, the present invention relates to an MR angiography method and apparatus using the Contrast method, and more particularly, to an MR angiography method using a two-dimensional PC method that can determine the flow direction and reduce residual errors even when the voxel is long in the slice direction. The present invention relates to a method and an apparatus for lithography.

[0002]

2. Description of the Related Art FIG. 6 shows a conventional pulse sequence used in an MR angiography method using a two-dimensional PC method. In this pulse sequence B, the RF pulse α
And applying a slice gradient S to selectively excite the slice, and applying a bipolar gradient pulse G1, a read gradient R, a projection dephase gradient PD, and a phase encode gradient PE shown by a solid line to collect first data. I do. Next, the second data is collected by replacing the bipolar gradient pulse G1 shown by the solid line with the bipolar gradient pulse G2 shown by the dotted line. And the first data and the second data
Image by taking the difference between the data of
The difference between the image based on the data and the image based on the second data is obtained to obtain an image of the flowing portion. In the image of the flowing portion, the flow velocity is represented by luminance.

FIG. 7 shows a voxel V by the two-dimensional PC method. y is the phase encoding direction, x is the frequency encoding direction, and z is the slice direction. In the two-dimensional PC method, there is no spatial resolution in the slice direction (hence, it is projected in the slice direction and becomes two-dimensional), and the voxel V becomes a rectangular parallelepiped long in the slice direction. However, as the length becomes longer in the slice direction, the ratio of the blood flow K to each voxel V decreases, and most of the voxels V become stationary parts. Therefore, a projection dephase gradient PD that changes the phase according to the depth in the slice direction is applied to suppress the signal from the stationary part.

[0004]

The above conventional two-dimensional PC
In the MR angiography method using the method, since the projection dephase gradient PD is applied, the phase is disturbed in the projection direction, and there is a problem that the flow direction cannot be determined. However, if the projection dephase gradient PD is not applied, as described above, when the voxel V is long in the slice direction, the signal from the stationary part becomes dominant, causing a so-called "digit dropout", and causing a residual error. There is a problem that arises. SUMMARY OF THE INVENTION It is an object of the present invention to provide an MR angiography apparatus using a two-dimensional PC method that can determine the flow direction and reduce residual errors even when the voxel V is long in the slice direction.

[0005]

According to the MR angiography method using the two-dimensional PC method of the present invention, a predetermined slice is selectively excited by applying an RF pulse and a slice gradient to generate two different types of bipolar gradient pulses. Apply 2
Two-dimensional P that collects two types of data and obtains an image of the flow section from the difference in the phase components of the two types of data
In the MR angiography method using the C method, R
Immediately before the application of the F-pulse, the magnetization of the stationary portion is saturated by the magnetization transfer method, and the projection dephase gradient is not applied.

In the MR angiography apparatus of the present invention, a predetermined slice is selectively excited by applying an RF pulse and a slice gradient, and two different types of bipolar gradient pulses are applied to collect two types of data. Those two
In an MR angiography apparatus that implements an MR angiography method using a two-dimensional PC method that acquires an image of a flowing portion from a difference in phase component of different types of data, a magnetization transfer method is performed immediately before an RF pulse is applied. Reduces the magnetization intensity of the stationary part,
In addition, the present invention is characterized in that a control means for executing a pulse sequence that does not apply the projection dephase gradient is provided.

[0007]

The MR angiography method and apparatus using the two-dimensional PC method of the present invention have the following features. Magnetization transfer method (Magnetizati
on-Transfer method (hereinafter, referred to as MT method)), reduce the magnetization intensity of the stationary part, and then apply an RF pulse or less,
Collect data.

[0008] No projection dephase gradient is applied.

As described above, it is possible to suppress the signal from the stationary part without applying the projection dephase gradient. As described above, since the phase is not disturbed in the projection direction, the information on the flow direction is not lost. As described above, even when the voxel V is long in the slice direction, the direction of the flow can be recognized and the remaining error can be reduced.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. It should be noted that the present invention is not limited by this. FIG. 1 shows a two-dimensional PC of the present invention.
Practicing MR angiography method using MR method
FIG. 2 is a block diagram of an I device (ie, functioning as an MR angiography device). The computer 2 is a console 1
3 to control the overall operation. The sequence controller 3 operates the gradient magnetic field drive circuit 4 based on the stored sequence to generate a gradient magnetic field with the gradient magnetic field coil of the magnet assembly 5. Further, it controls the gate modulation circuit 7, modulates the RF pulse generated by the RF oscillation circuit 6 into a predetermined waveform, and applies the RF pulse 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 a phase detector 10 via a preamplifier 9 and further input to a computer 2 via an AD converter 11. The computer 2 reconstructs an image based on the NMR signal data obtained from the AD converter 11 and displays the image on the display device 12. The MR angiography method using the two-dimensional PC method according to the present invention is performed by a procedure stored in the computer 2 and the sequence controller 3.

FIG. 2 is a flowchart of one embodiment of the MR angiography method using the two-dimensional PC method of the present invention. After the user sets the subject on the magnet assembly 5 and gives an instruction to execute the MR angiography method using the two-dimensional PC method using the console 13, the computer 2 executes the processing in FIG. .

In step S1, data is collected based on a pulse sequence as shown in FIG. In the pulse sequence A, first, a polynomial pulse (Polynomia pulse) having an RF frequency matched to the Larmor frequency of protons
l Pulse) Apply PP. As a result, a magnetizing transfer effect occurs, and the stationary part (soft tissue) is selectively excited without affecting the blood flow. In addition, the polynomial pulse PP of FIG.
1 pulse, but “1, 2, 1 pulse” or “1,
Then, a spoiler gradient SP is applied to saturate the magnetization of the stationary part excited by the polynomial pulse PP.

Next, data is collected in the same manner as in the conventional pulse sequence B (FIG. 7) except that the projection dephase gradient PD is not applied. That is, the slice is selectively excited by applying the RF pulse α and the slice gradient S, and the first raw data R1 is collected by applying the bipolar gradient pulse G1, the read gradient R, and the phase encode gradient PE shown by the solid line. I do. Next, the bipolar gradient pulse G1 shown by the solid line is replaced with the bipolar gradient pulse G2 shown by the dotted line, and the second Raw data R2
To collect.

In step S2, a complex image f1 (i, j) is obtained from the raw data R1, and a complex image f2 (i, j) is obtained from the raw data R2. Here, i is a pixel number in the phase encoding direction, and j is a pixel number in the frequency encoding direction. In step S3, for the complex images f1 (i, j) and f2 (i, j), the zero-order phase correction for matching the phase of the stationary part to zero and the first-order phase correction for correcting the phase shift due to the eddy current Is applied. The complex image after performing the 0th-order phase correction and the 1st-order phase correction is represented by F1
(I, j) and F2 (i, j).

In step S4, the complex image F1 (i,
j) and the difference D (i, j) between the complex image F2 (i, j). An image of the absolute value | D (i, j) | of the difference D (i, j) corresponds to a blood flow image obtained by an MR angiography method using a conventional two-dimensional PC method.

In step S5, the argument of the difference D (i, j)
arg [D (i, j)] (= arctan [imaginary part / real part])
To determine the direction of the blood flow. For example, when −90 ゜ ≦ arg [D (i, j)] <90 ゜ S
(I, j) = + 1 arg [D (i, j)] <− 90 ゜ S
When (i, j) =-1 90 ゜ ≦ arg [D (i, j)] S
(I, j) = − 1. S (i, j) represents the direction of the blood flow.

In step S6, the luminance I (i, j) of the pixel on the display screen is calculated as follows: I (i, j) = Is + S (i, j) .multidot.D (i, j) | , To display the blood flow image. In the blood flow image, the absolute value | D (i, j) of the difference D (i, j)
The pixel at which | is zero, that is, the pixel corresponding to the stationary part has the luminance Is, the blood flow flowing in one direction has a luminance higher than Is, and the blood flow flowing in the opposite direction has a luminance lower than Is. Also, the degree of the brightness and darkness indicates the flow velocity. In addition, it is also possible to change the color according to the direction of the blood flow and display in color, like the CFM of the ultrasonic diagnostic apparatus.

In the MR angiography method using the two-dimensional PC method described above, the signal from the stationary part is suppressed by the MT method without affecting the blood flow. Therefore, not only the flow velocity of the blood flow but also the direction can be accurately calculated, and the flow velocity and the direction of the blood flow can be appropriately imaged.

FIG. 4 is a flowchart of another embodiment of the MR angiography method using the two-dimensional PC method of the present invention. Steps S1 to S3 are the same as in FIG. In step S14, the difference P (i, j) between the argument of the complex image F1 (i, j) and the argument of the complex image F2 (i, j) is obtained.
In step S15, the direction of the blood flow is determined from the difference P (i, j). For example, when −90 ° ≦ P (i, j) <90 °, S (i, j)
= + 1 P (i, j) <− 90 ゜ S (i, j)
= (− 90) ≦ P (i, j) S (i, j)
= -1. In step S16, the signal strength I ′ (i, j) on the display screen is calculated as follows: I ′ (i, j) = Is + S (i, j) · | F1 (i, j)
| · P (i, j) | and displays a blood flow image masked with the absolute value | F1 (i, j) |. Note that | F1 in the above equation
Instead of (i, j) |, | F2 (i, j) | may be used.

In the above embodiment, the polynomial pulse PP
Was adopted, but the RF frequency with the carrier frequency shifted by several kHz from the Larmor frequency was irradiated for a certain period, or another MT method such as using a pulse whose amplitude was modulated by a sinc function was adopted. Is also good.

The MT method is effective for lowering the signal intensity of muscle and brain parenchyma, but is not effective for fat. For this reason, when the abdomen or the like containing a large amount of fat in the stationary part is used as the diagnostic site, in addition to the MT method, the phase of the signal from water (blood flow) and the phase of the signal from fat are inverted. It is desirable to set an echo time or to use a fat suppression pulse such as the CHESS method. FIG. 5 shows the MT polynomial pulse PP and spoiler gradient SP (solid line).
And a pulse sequence A ′ for alternately applying a fat suppression pulse C such as a CHESS method and a spoiler gradient D (dotted line) for each view scan. As a result, even when a large amount of fat is contained, the signal from the stationary part can be appropriately attenuated.

In step S3 of the above embodiment, when a complex image is obtained from the raw data, all the R data on the k-space are complex-added with the phase angle of the sum of all the R data.
The 0th-order phase correction may be performed by rotating the phase of the aw data. In addition, SGC (Shi) that can correct eddy current
In an MRI apparatus provided with an elded gradient coil, primary phase correction need not be performed.

In step S5 of the above embodiment, the direction of the blood flow is determined based on whether the deviation angle of the difference D (i, j) is within ± 90 °. For example, −45 ° ≦ arg When [D (i, j)] <45 °
S (i, j) = + 1 45 ゜ ≦ arg [D (i, j)] <135 ゜
When S (i, j) = 0 135 ゜ ≦ arg [D (i, j)]
When S (i, j) = − 1−135 ゜ ≦ arg [D (i, j)] <− 45 °
When S (i, j) = 0 arg [D (i, j)] <-135 °
The determination may be made as S (i, j) = − 1, and the blood flow may not be displayed where the argument is large (where the reliability is low).

[0025]

According to the MR angiography method and apparatus using the two-dimensional PC method of the present invention, the signal from the stationary part is suppressed by the MT method without affecting the flowing part. Not only that, but also the direction can be accurately calculated and imaged.

[Brief description of the drawings]

FIG. 1 is a block diagram of an MRI apparatus for performing an MR angiography method using a two-dimensional PC method of the present invention.

FIG. 2 is a flowchart according to an embodiment of an MR angiography method using a two-dimensional PC method of the present invention.

FIG. 3 is a view showing an example of a pulse sequence according to an embodiment of the MR angiography method using the two-dimensional PC method of the present invention.

FIG. 4 is a flowchart according to another embodiment of the MR angiography method using the two-dimensional PC method of the present invention.

FIG. 5 is an illustration of a pulse sequence according to still another embodiment of the MR angiography method using the two-dimensional PC method of the present invention.

FIG. 6 is a view showing an example of a pulse sequence according to a conventional MR angiography method using a two-dimensional PC method.

FIG. 7 is an illustration of a slice selectively excited by a two-dimensional PC method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 MRI apparatus 2 Computer A, B Pulse sequence G1 Bipolar gradient pulse K Blood flow PD Projection dephase gradient PP Polynomial pulse SP Spoiler gradient

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-4-53531 (JP, A) JP-A-3-47236 (JP, A) JP-A-4-129528 (JP, A) JP-A-6-127 154187 (JP, A) JP-A-5-84226 (JP, A) JP-A-4-64343 (JP, A) JP-A-3-149032 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) A61B 5/055 JICST file (JOIS)

Claims (4)

(57) [Claims] 1. An RF pulse and a slice gradient are applied to selectively excite a predetermined slice, two different types of bipolar gradient pulses are applied to collect two types of data, and a phase component of the two types of data. In an MR angiography apparatus that implements an MR angiography method using a two-dimensional PC method that acquires an image of a flowing part from the difference, the magnetization intensity of a stationary part is determined by a magnetization transfer method immediately before an RF pulse is applied. An MR angiography apparatus comprising control means for executing a pulse sequence that reduces and does not apply a projection dephase gradient. 2. The MR angiography apparatus according to claim 1, wherein said magnetization transfer method is performed by applying a polynomial pulse. 3. The method according to claim 1, wherein the control unit acquires two types of complex images from the collected two types of data, and performs zero-order and first-order phase correction on the complex images. 3. The MR angiography apparatus according to 2. 4. The MR angiography apparatus according to claim 1, wherein the control unit adds a method of suppressing a signal intensity from fat, such as a CHESS method, to the pulse sequence. MR angiography apparatus for performing a pulse sequence.