JP2879231B2 - MR imaging device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an MR imaging apparatus, and more specifically, it is possible to measure the absolute value of blood flow even when the slice thickness of MR imaging is larger than the thickness of a blood vessel. Related to a simple MR imaging apparatus.

[Prior Art] FIGS. 5 to 7 show an example of a conventional MR blood vessel imaging method. This method is called phase contrast MR angio.

First, in step Q1, as shown in FIG. 6, an RF signal is output in a steady state where a predetermined magnetic field is formed, and then a flow encode gradient 20, a dephase gradient 21, and a warp gradient 22 are output.
And then applying the readout gradient 23 to obtain the first
And the first complex data | Z1 | ∠Δφ1 is obtained based on the first echo signal.

Next, in step Q2, the flow encode gradient 20
The second echo signal is obtained in the same manner as in the above sequence except that an inverted flow encode gradient 24 obtained by inverting the second echo data is added, and the second complex data | Z2 | ∠
Δφ2 is obtained.

In step Q3, a phase difference (Δφ1−Δφ2) is calculated.

In step Q4, an image is displayed based on the phase difference (Δφ1−Δφ2).

FIG. 7 shows complex data | Z1 | ∠Δφ1 and | Z2 | ∠Δφ
2 and a phase difference (Δφ1−Δφ2).
The phase difference (Δφ1−Δφ2) includes the blood flow velocity information in the size and the flow direction information in the code.

Therefore, the image of the phase difference (Δφ1−Δφ2) is an image representing the blood flow velocity and the blood flow direction.

[Problem to be Solved by the Invention] FIG. 8 shows a blood vessel V and slices LN and LK for performing MR imaging. The slice LN indicates a small slice thickness, and the slice LK indicates a large slice thickness. Any slice LN, LK
In the case of, the data of the region AH of the image corresponding to the blood vessel V is formed only from the spins generated from the blood flow portion, and the relationship shown in FIG. 7 is established. Therefore, a normal blood flow image can be obtained.

Next, FIG. 9 shows that the blood vessel V
Indicates the case of vertical slice. Also in this case, the data of the region AVN of the image corresponding to the blood vessel V is created only by the spins generated from the blood flow portion, and the relationship shown in FIG.
A normal blood flow image can be obtained.

However, as shown in FIG. 10, when the blood vessel V is sliced in the vertical direction by a slice LK having a large slice thickness, the data of the region AVK of the image corresponding to the blood vessel V includes the spin generated from the blood flow portion and the stationary state. Made from both spins arising from the part. FIG. 11 shows this state. The first complex number data | W1 | ∠Δθ1 obtained by the measurement is the complex number data | Z1 | ∠Δφ1, the spin number resulting from the stationary part, resulting from the blood flow part. Data | Z0 | ∠Δφ
It is the sum of 0 complex numbers. The measured second complex number data | W2 | ∠Δθ2 is the complex number sum of the complex number data | Z2 | φΔφ2 due to the spin generated from the blood flow portion and the complex number data | Z0 | ∠Δφ0 due to the spin generated from the stationary portion. Has become. Therefore, the obtained phase difference (Δθ1−Δθ)
2) is a phase difference (Δφ1) having a magnitude proportional to the blood flow velocity.
−Δφ2).

That is, in the conventional MR blood vessel imaging method, when the slice thickness is made larger than the blood vessel thickness, there is a problem that the absolute value of the blood flow cannot be measured.

Therefore, an object of the present invention is to provide an MR imaging apparatus that does not have the above-mentioned problems.

[Means for Solving the Problems] An MR imaging apparatus according to the present invention includes an MR imaging unit that obtains three types of complex data by three measurements while changing the magnitude of a flow encode gradient magnetic field, and three types of complex data. A center calculating means for calculating a center of a circle passing through three points on a corresponding complex number plane; and a blood flow information calculating means for calculating blood flow information based on the complex number data obtained by the measurement and the center. The above features.

In the above configuration, as the MR imaging means, a method using a sequence using gradient inversion or a method using a sequence of spin echo using a 180 ° pulse can be used.

[Operation] In the MR imaging apparatus of the present invention, the MR imaging means changes the magnitude of the flow encode gradient magnetic field to 3
Measurement is performed three times to obtain three types of complex data.

What changes by changing the magnitude of the flow encode gradient magnetic field is the phase of the complex data due to the spin of the blood flow portion. Therefore, in FIG. 11, the complex number data | Z1 | ∠Δφ1 due to the blood flow part rotates.

The center calculating means calculates the center of a circle passing through three points on a complex plane corresponding to the three types of complex number data, and this is the center of the rotation.

If this rotation center is known, complex data generated from spins in the blood flow portion can be correctly calculated, and a phase difference (Δφ1−Δφ2) that correctly reflects the size of the blood flow can be obtained.

That is, the blood flow information calculating means can calculate correct blood flow information based on the calculated rotation center and the complex number data obtained by the measurement.

[Example] Hereinafter, the present invention will be described in more detail based on an example shown in the drawings. It should be noted that the present invention is not limited by this.

FIG. 3 is a block diagram showing an MR imaging apparatus 1 according to one embodiment of the present invention.

The computer 2 controls the entire operation based on instructions from the console 13.

The sequence storage circuit 3 operates the gradient magnetic field drive circuit 4 based on the stored sequence, and generates a static magnetic field and a gradient magnetic field with the static magnetic field coil and the gradient magnetic field coil of the magnet assembly 5. Further, it controls the gate modulation circuit 7 and modulates the RF signal generated by the RF oscillation circuit 6 to generate an RF signal.
The power is applied from the power amplifier 8 to the transmission coil of the magnet assembly 5.

NMR obtained with the receiving coil of the magnet assembly 5
The signal is input to the phase detector 10 via the preamplifier 9 and further input to the computer 2 via the AD converter 11.

The computer 2 calculates image data based on the data of the NMR signal obtained from the AD converter 11 and displays the image on the display device 12.

FIG. 1 shows a main part of the operation of the MR imaging apparatus 1.

In step S1, using a flow encode pulse,
The complex data | W1 | ∠Δθ1 is measured.

In step S2, the flow encode pulse is set to 0, and the complex number data | W0 | ∠Δθ0 is measured.

In step S3, the complex data | W2 | ∠Δθ2 is measured using the inverted flow encode pulse.

The above steps S1, S2 and S3 are the MR imaging means, and FIG. 4 shows a time chart of the operation.

First, an RF signal is output in a steady state where a predetermined magnetic field is formed, and then the flow encode gradient 20 and the dephase gradient are output.
21 and a warp gradient 22 and then a readout gradient 23
To obtain a first echo signal. Based on the first echo signal, Calculator 2 calculates the first complex data | W
1 | ∠Δθ1 is obtained. Next, the flow encode gradient 20
Is set to 0 (25 in FIG. 7), except that the 0th echo signal is obtained in the same manner as the above sequence. Based on the 0th echo signal, Calculator 2 calculates the 0th complex data | W0 | ∠Δθ
Get 0. Next, a second echo signal is obtained in the same manner as in the first sequence except that an inverted flow encode gradient 24 obtained by inverting the flow encode gradient 20 is added. Based on the second echo signal, Calculator 2 obtains the second complex data | W2 | ∠Δθ2.

In step S4, as shown in FIG.
The center C of the circle E passing through three points on the complex plane of the complex number data obtained in S1 to S3 is calculated. This can be easily obtained, for example, as the intersection of a perpendicular bisector of a line connecting two sets of two points arbitrarily selected from three points. This step S4 is the center calculating means.

In step S5, the complex number data | Z1 | ∠Δφ1 based on the spin of the blood flow portion is calculated by the complex number subtraction (W1-C).

In step S6, complex number data | Z2 | ∠Δφ2 based on the spin of the blood flow component is calculated by complex number subtraction (W2-C).

In step S7, a phase difference (Δφ1−Δφ2) is calculated.

In step S8, an image is displayed based on the phase difference (Δφ1−Δφ2).

 Steps S5, S6 and S7 are blood flow information calculation means.

The image of the phase difference (Δφ1−Δφ2) obtained as described above is an image in which the blood flow velocity and the blood flow direction are correctly represented. That is, blood vessel imaging can be performed correctly even when the slice thickness includes a stationary portion.

As a modification, a step of performing a complex number subtraction and calculating an absolute value, that is, a step of calculating | Z1-Z2 |, instead of the above step S7, may be mentioned. In this case, an image representing the spin density information of the blood flow is obtained.

As still another modified example, the phase difference (Δφ1−Δ
φ2) and the absolute value of the complex subtraction | Z1−Z2 |
One that displays an image of the result of the multiplication may be used. In this case, an image including all information of the blood flow velocity, the flow direction, and the spin density is obtained.

In the above description, the embodiment in which the flow encode gradient is applied in the X-axis direction has been described.
It may be applied in the axial direction.

[Effect of the Invention] According to the MR imaging apparatus of the present invention, it becomes possible to measure the absolute value of the flow velocity of blood in a slice plane thicker than a blood vessel, which was impossible in the past.

In addition, since the slice thickness can be increased, the target portion can be measured with a small number of slices,
There is also an effect that the scanning time can be reduced.

[Brief description of the drawings]

FIG. 1 is a flowchart of the operation of an MR imaging apparatus according to one embodiment of the present invention, FIG. 2 is an explanatory diagram showing the relationship between measured complex data, and FIG. 3 is an MR imaging according to one embodiment of the present invention. FIG. 4 is a block diagram of the apparatus, FIG. 4 is a time chart showing a sequence for the MR blood vessel imaging method according to the present invention, FIG. 5 is a flowchart of the conventional MR blood vessel imaging method, and FIG. FIG. 7 is an explanatory diagram showing the relationship between complex number data due to spins of blood flow components and a phase difference, FIGS. 8 to 10 are conceptual diagrams showing the relationship between blood vessels and slices, and FIG.
FIG. 11 is an explanatory diagram showing the relationship between complex data measured when both a blood flow portion and a stationary portion are included. (Explanation of Signs) 1 ... MR Imaging Device 2 ... Computer 12 ... Display Device 20 ... Flow Encoding Gradient 24 ... Inverted Flow Encoding Gradient 25 ... Flow Encoding Gradient with Zero Amplitude | W1 | ∠Δθ1 ... Complex Number Data | W0 | ∠Δθ0 ... complex data | W2 | ∠Δθ2 ... complex data E… circle C… center | Z1 | ∠Δφ1 …… complex data | Z2 | ∠Δφ2 …… complex data Δφ1-Δφ2 ... Phase difference.

Claims (1)

(57) [Claims] 1. An MR imaging means for obtaining three kinds of complex data by three measurements while changing the magnitude of a flow encode gradient magnetic field, and a circle passing through three points on a complex plane corresponding to the three kinds of complex data. An MR imaging apparatus comprising: a center calculating means for calculating a center; and blood flow information calculating means for calculating blood flow information based on complex data obtained by measurement and the center.