JP3152669B2 - MR imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an MR imaging apparatus, and more particularly, to an MR imaging apparatus for tracking the temporal spread of a contrast medium at high speed using MRI.

[0002]

2. Description of the Related Art A contrast agent tracking method using MRI is a method in which after a contrast agent is injected into a blood vessel, an image of a target site is continuously captured by MRI, and the state of the contrast agent spreading over time is tracked. It is. As a result, the function of an organ and the internal structure of a tumor are examined.

[0003]

In order to obtain a good image, high resolution (for example, 256.times.
It is necessary to perform imaging at a resolution of 256 (phase direction × frequency direction) or more. However, continuous imaging at high resolution increases the imaging interval, so that it is possible to track in detail how the contrast agent spreads over time. There is a problem that cannot be done.

On the other hand, if continuous imaging is performed at a low resolution in order to shorten the time interval of continuous imaging, there is a problem that ringing artifacts appear.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an MR imaging apparatus capable of shortening the time interval of continuous imaging and suppressing the appearance of ringing artifacts.

[0006]

According to a first aspect of the present invention, there is provided an initial image capturing step of capturing an image of a target portion with high resolution, a contrast agent injecting step of injecting a contrast agent, and an image of the target portion. A continuous imaging step of continuous imaging at a low resolution, a data synthesis step of synthesizing a high spatial frequency portion of the data obtained in the initial image imaging step and data obtained in the continuous imaging step, and using the synthesized data. And an image reconstruction step of performing image reconstruction by using a contrast agent tracking method using MRI.

According to a second aspect, the present invention provides an initial image capturing step of capturing an image of a target site with high resolution, a contrast agent injecting step of injecting a contrast agent, and a continuous image capturing of the target site with low resolution. A two-dimensional Fourier transform is performed using data consisting of a high spatial frequency part of the data obtained in the initial image capturing step and a low spatial frequency part containing 0, to obtain a first complex image. (2) a two-dimensional Fourier transform is performed using the data obtained in the two-dimensional Fourier transform step (1) and the data obtained in the continuous imaging step and a high spatial frequency part containing 0 to obtain a second complex image; Dimensional Fourier transform step; and an image synthesizing step of synthesizing the first complex image and the second complex image to obtain an image of its absolute value. It was to provide a contrast agent tracking method.

[0008]

In the contrast agent tracking method using MRI according to the first aspect of the present invention, an image of a target site is taken with high resolution before the contrast agent is injected. Next, after the contrast agent is injected, continuous imaging is performed at a low resolution. Since continuous imaging is performed with low resolution, the time interval of imaging can be shortened. However, since high spatial frequency data cannot be obtained, the high spatial frequency portion of the data obtained by imaging with high resolution before injection of the contrast agent is used, and data that is apparently equivalent to the case of imaging with high resolution Are synthesized. Comparing the synthesized data with the data obtained by actually imaging at a high resolution, the portion where the contrast agent is not spread is equal,
There is only a difference in the portion where the contrast agent is spread, because of the contrast agent. Therefore, if an image is reconstructed from the combined data, ringing artifacts will not appear. That is, tracking can be performed at short time intervals, and occurrence of ringing artifacts can be prevented. Although the spatial resolution is lower than that in the case where the image is actually taken at a high resolution, there are few cases in which it is necessary to obtain the spread of the contrast agent at a high spatial resolution on a clinical basis.

In the contrast agent tracking method using MRI according to the second aspect of the present invention, synthesis is performed at the complex image stage instead of at the data stage as in the above method. From the linearity, both are equivalent. Therefore, tracking can be performed at short time intervals, and occurrence of ringing artifacts can be prevented.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. It should be noted that the present invention is not limited by this.

FIG. 8 is a block diagram showing an MR imaging apparatus 1 for executing a contrast agent tracking method using MRI.

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

The sequence controller 3 operates the magnetic field drive circuit 4 based on the stored sequence,
A static magnetic field and a gradient magnetic field are generated by the static magnetic field coil and the gradient magnetic field coil of the magnet assembly 5. The modulation circuit 7
And modulates the RF signal generated by the RF oscillation circuit 6 into a predetermined waveform, and applies the modulated signal 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 contrast agent tracking method using MRI according to the present invention is performed according to the procedure stored in the computer 2 and the sequence controller 3.

FIG. 1 is a flow chart of an embodiment of a contrast agent tracking method using MRI of the present invention. In step S1, an image of a target part to be inspected is, for example, 256 × 2
An image is taken with a high resolution of 56 (phase direction × frequency direction) by taking only one image over time. This image is called an initial image. FIG. 2 shows a conceptual diagram of the data obtained in step S1.

In step S2, a contrast agent is injected into a blood vessel. In step S3, the image of the target part is
Continuous imaging is performed at a low resolution of 28 × 256 (phase direction × frequency direction). The sequence is the same as the sequence in step S1. The imaging time interval is 256 × 256
Compared to a case where continuous imaging is performed at a high resolution in the (phase direction × frequency direction), the ratio is halved. FIG. 3 shows a conceptual diagram of the data obtained in step S3. Data of a high spatial frequency portion indicated by a two-dot chain line cannot be obtained.

In step S4, the data of the high spatial frequency portion of the data of the initial image obtained in step S1 and the data obtained by the continuous imaging in step S3 are combined.
FIG. 4 shows a conceptual diagram of the data synthesized in step S4.

In step S5, an image is reconstructed using the data synthesized in step S4 to obtain an image.

The time interval between the images obtained as described above is one half that in the case of continuous imaging with high resolution. Moreover,
An image in which the appearance of the ringing artifact is suppressed.

At the time of data synthesis in step S4, both data may be weighted and added to smooth the connection of the data. If it is sufficient to know the approximate distribution of the contrast agent, for example, 64 × 256
As the low resolution in the (phase direction × frequency direction), the time interval of imaging may be further shortened. Further, the resolution of the initial image may be further increased. Further, the pulse sequence for capturing the initial image and the pulse sequence for capturing continuous images may be changed to adjust the degree of high-frequency enhancement.

FIG. 5 is a flowchart of another embodiment of the contrast agent tracking method using MRI of the present invention. Steps S1 to S3 are the same processing as steps S1 to S3 in FIG.

In step R4, data is created in which only the high spatial frequency portion of the echo data of the initial image is left and the low spatial frequency portion is zero. Figure 6 shows a conceptual diagram of this data.
Shown in Then, this data is subjected to a two-dimensional Fourier transform,
Obtain a first complex image.

In step R5, 0 is added to the high spatial frequency portion.
To create data in which the data obtained in step S3 is inserted in the low spatial frequency portion. Figure 7 shows a conceptual diagram of this data.
Shown in Then, this data is subjected to a two-dimensional Fourier transform,
Obtain a second complex image.

In step R6, the first complex image obtained in step R4 and the second complex image obtained in step R5 are added to obtain an image of the absolute value of the added complex image.

The time interval between the images obtained as described above is one half that in the case of continuous imaging at high resolution. Moreover,
An image in which the appearance of the ringing artifact is suppressed.

[0027]

According to the MR imaging apparatus of the present invention, continuous imaging is performed at short time intervals after a contrast medium is injected into a target site, so that the spread of the contrast medium can be tracked with high time resolution. In addition, since the tracking image is configured using data captured at a high resolution, a good image free of ringing artifacts can be obtained.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an embodiment of a method for tracking a contrast agent using MRI.

FIG. 2 is a conceptual diagram of data obtained in step S1 of FIG.

FIG. 3 is a conceptual diagram of data obtained in step S3 of FIG.

FIG. 4 is a conceptual diagram of data obtained in step S4 of FIG.

FIG. 5 is a flowchart of another embodiment of a contrast agent tracking method using MRI.

FIG. 6 is a conceptual diagram of data used in step R4 of FIG.

FIG. 7 is a conceptual diagram of data used in step R5 of FIG. 5;

FIG. 8 is an MR that implements a contrast agent tracking method using MRI.
It is a block diagram of an imaging device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 MR imaging apparatus 2 Computer 3 Sequence controller 4 Magnetic field drive circuit 5 Magnet assembly

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-4-246327 (JP, A) JP-A-2-224736 (JP, A) JP-A 1-124447 (JP, A) JP-A-1- 160541 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) A61B 5/055 JICST file (JOIS)

Claims (2)

(57) [Claims] An imaging unit for applying an RF pulse and a gradient magnetic field to a subject in a static magnetic field to acquire data of an NMR signal generated from the subject, and performing an arithmetic operation on the data to generate an image of the subject. An MR imaging apparatus comprising: an image generating unit configured to generate an image of one image of a target portion of the subject with high resolution without first injecting a contrast agent. And performing continuous imaging to continuously image at a low resolution an image of a plurality of images of the target site of the subject into which the contrast agent has been injected, wherein the image generating means includes a high spatial frequency portion of data obtained in the initial image imaging. And an image for a plurality of images generated by synthesizing data of each image obtained by the continuous imaging and reconstructing an image using the synthesized data. 2. An imaging means for applying an RF pulse and a gradient magnetic field to a subject in a static magnetic field to acquire data of an NMR signal generated from the subject, and performing an arithmetic operation on the data to form an image of the subject. An MR imaging apparatus comprising: an image generating unit configured to generate an image of a target portion of the subject at a high resolution. Perform continuous imaging to continuously image the image of the part at a low resolution, the image generating means, using data consisting of a high spatial frequency portion of the data obtained in the initial image imaging and a low spatial frequency portion of 0 put A second two-dimensional Fourier transform for obtaining a first complex image by performing a two-dimensional Fourier transform, and a second order using data obtained in the continuous imaging step and data consisting of a high spatial frequency part with 0 added thereto Performing a second two-dimensional Fourier transform step of performing a Fourier transform to obtain a second complex image, and combining the first complex image and the second complex image to generate an image of the absolute value thereof An imaging device characterized by the above-mentioned.