JPH10192252A - Mr imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the performance of 3D-imaging magnetic resonance(MR) angiography by determining the time when a contrast medium is fully introduced into a region intended for examination. SOLUTION: This MG imaging device is operated to control through a computer 51 so that an initial 2D imaging sequence is repeated when a contrast medium is injected into an examine 61. Further, intensities of signal from the 2D image in ROI(region of interest) obtained through repeating the imaging sequence are sought by an extraction circuit 58 and a peak in the intensities of signal is interpreted by a peak detection circuit 59 based on fluctuations of the intensity of signal over time to connect a trigger signal to the computer 51, which, in turn, switches the operation from the 2D imaging sequence to the 3D imaging sequence in response to the input of the trigger signal.

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 for producing an image by utilizing an MR phenomenon (nuclear magnetic resonance phenomenon), and in particular, to enhance a signal from a blood flow or the like using a contrast agent to perform 3D imaging. The present invention relates to an MR imaging apparatus suitable for the above.

[0002]

2. Description of the Related Art In recent years, a contrast agent such as Gd-DTPA has been intravenously injected, and after an appropriate delay time, a short TR 3
A 3D-contrast MR angiography imaging method for obtaining a blood vessel image of an artery or a vein by a D gradient echo sequence has been reported (Prince MR, Yucel EK, Kaufman JA, H
arrison D. Dynamic gadolinium-enhanced three-dimen
sional abdominal MR arteriography. JMRI 1993; 3:87
7-881). In this method, a blood vessel is made into a high-signal portion by a T1 shortening effect of a contrast agent so as to provide contrast with other tissues.

[0003]

However, in the conventional 3D-contrast MR angiography imaging method, the time required for a blood vessel to be examined to be filled with a contrast agent is not known, and individual differences are large. There is a problem that it is difficult to make the imaging timing appropriate. Therefore, the imaging timing often tends to be inappropriate, and in many cases, an image sufficiently depicting the target blood vessel cannot be obtained.

On the other hand, it is not conceivable to continuously capture images in a wide time zone before and after the timing considered appropriate to cover all the timings. In addition, if all the obtained data is not processed, it is not easy to know at what timing the best imaging was performed.

[0005] In view of the above, it is an object of the present invention to provide an MR imaging apparatus that can easily perform 3D-contrast MR angiography imaging at an appropriate timing.

[0006]

In order to achieve the above object, an MR imaging apparatus according to the present invention comprises:
Means for generating a static magnetic field, means for generating gradient magnetic fields in first, second, and third directions perpendicular to each other so as to be superimposed on the static magnetic field, RF transmitting means, RF receiving means, and controlling these 2D including an RF excitation pulse, a slice selection gradient magnetic field pulse in the first direction, a phase encoding gradient magnetic field pulse in the second direction, and a readout gradient magnetic field pulse in the third direction.
The imaging sequence is sequentially repeated, and the RF excitation pulse, the slice selection gradient magnetic field pulse in the first direction,
Control means for shifting to a 3D imaging sequence including a phase encoding gradient magnetic field pulse in the first direction, a phase encoding gradient magnetic field pulse in the second direction, and a readout gradient magnetic field pulse in the third direction; Means for obtaining a signal intensity from a 2D image obtained by the sequence.

[0007] The 2D imaging sequence is sequentially repeated prior to the 3D imaging sequence, and 2D images are obtained one after another.
Then, when the contrast agent is injected into the subject, the contrast agent appears in the 2D image. Therefore, when the signal intensity is obtained from the 2D image, the degree of filling of the contrast agent can be determined. It is easy to obtain the peak of the signal intensity by observing the temporal variation of the signal intensity by an operator or automatically judging by a computer or the like. If the timing is given manually or automatically at this peak point, the 3D imaging sequence can be performed without missing the point when the contrast agent is most full. Therefore, regardless of individual differences in the time from the injection of the contrast agent to the arrival at the target site, 3D-
Good images can be obtained by performing contrast MR angiography imaging.

[0008]

Next, embodiments of the present invention will be described in detail with reference to the drawings. The MR imaging apparatus according to the present invention is configured as shown in FIG. In FIG. 1, the magnet assembly 11 includes a main magnet for generating a static magnetic field, and a gradient coil for generating gradient magnetic fields Gx, Gy, Gz superimposed on the static magnetic field. A subject 61 placed on an examination table 62 is inserted into the space to which the static magnetic field and the gradient magnetic field are applied. The subject 61 is irradiated with an RF pulse and the NM generated by the subject 61 is emitted.
An RF coil 12 for receiving the R signal is attached. Although not shown, a contrast agent such as Gd-DTPA is injected intravenously into the subject 61 at a predetermined timing.

A magnetic field control circuit 21 is provided as a circuit for supplying a gradient magnetic field current to the gradient coil of the magnet assembly 11. A waveform signal from the waveform generation circuit 53 is sent to the magnetic field control circuit 21. In the waveform generating circuit 53, information on each pulse waveform of the gradient magnetic fields Gx, Gy, Gz is set in advance from the computer 51. At the timing instructed by the sequence controller 52, the gradient magnetic field Gx,
Waveform signals for each of Gy and Gz are generated and sent to the magnetic field control circuit 21, whereby pulsed gradient magnetic fields Gx, Gy and Gz having a predetermined waveform are generated.

R generated by the RF oscillation circuit 31
The F signal is sent to the amplitude modulation circuit 32, which becomes a carrier signal, and is amplitude-modulated according to the RF waveform signal sent from the waveform generation circuit 53. The RF signal after the amplitude modulation is amplified through the RF power amplifier 33 and then applied to the RF coil 12. The oscillation frequency of the RF oscillation circuit 31 is controlled by the computer 51 and the subject 61
Is matched to the resonance frequency of the body tissue. Information on the waveform of the modulation signal is given from the computer 51 to the waveform generation circuit 53 in advance. Waveform generation circuit 53
The timing of the RF oscillation circuit 31 is determined by the sequence controller 52.

NMR received by RF coil 12
The signal is sent to a phase detection circuit 42 via a preamplifier 41 and is subjected to phase detection. An RF signal from the RF oscillation circuit 31 is sent as a reference signal for the phase detection. The signal obtained by the phase detection is sampled at a predetermined sampling timing by the A / D converter 43 controlled by the sequence controller 52, and is converted into digital data. The data obtained from the A / D converter 43 is taken into a computer 51, and the computer 51 performs a two-dimensional or three-dimensional Fourier transform to reproduce image data of each pixel.

The computer 51 includes a display device 54, a keyboard 55, a mouse 56, and a recording device 5.
7 is connected. The display device 54 displays the reconstructed MR image and the like. Keyboard 5
5. Input and setting of an imaging sequence, imaging parameters, a region of interest (ROI), and the like are performed by the mouse 56 and the like. The recording device 57 is composed of a magneto-optical disk device or the like, and records obtained data such as images.

The computer 51 is further connected to an ROI signal strength extraction circuit 58 for detecting the signal strength at the set ROI. The peak detection circuit 59 detects that the signal strength detected by the ROI signal strength extraction circuit 58 has reached a peak, and outputs the signal at that timing.
Send to 1. The computer 51 receives this signal and
Switching from imaging to 3D imaging.

Further description will be made with reference to FIG. In this example, a pulse sequence of the gradient echo method as shown in FIG. 2 is performed. First, as shown in FIG. 2A, a 2D imaging sequence in which only phase encoding in the Y direction is performed, and at the above timing, phase encoding in the Z direction as shown in FIG. The sequence is switched to the 3D imaging sequence.

In the 3D imaging sequence shown in FIG. 2B, a gradient magnetic field pulse (here, a Gz pulse) 72 for slice selection is added at the same time when the RF pulse 71 is applied.
One site (a certain range) in the Z direction is selectively excited. Then Z
Gradient magnetic field pulse for phase encoding of direction (Gy pulse)
73 and a phase-encoding gradient magnetic field pulse (Gy pulse) 74 in the Y direction are applied, and the read-out (and frequency encoding) gradient magnetic field pulse (Gx) is inverted.
(Pulse) 75 to generate a resonance signal 76. 2D
In the imaging sequence, as shown in FIG. 2A, a gradient magnetic field pulse (Gy pulse) 73 for phase encoding in the Z direction.
Are omitted, and others are the same.

In the 3D imaging, as shown in FIG. 3, a slab region having a thickness in the Z direction so as to include the target blood vessel 81 is defined as a rectangular parallelepiped excitation region 82. In the 2D imaging, the slab region includes the blood vessel 81. A region 83 having a very small slice thickness is excited. Such regions 82 and 83 are provided with the excitation RF pulse 71
And the size of the Gz pulse 72.

In the 2D imaging performed earlier, the 2D
An image (an image of the region 83 as viewed from the Z direction) is obtained, which should be as shown in FIG. 4 and a blood vessel image 84 should be displayed. Therefore, as shown in FIG. 5, before the injection of the contrast agent, 2D imaging in which the above-mentioned region 83 is the same slice is started, and as shown in FIG. 5A, the k-space (kx-ky 2) is obtained.
Data to fill the (dimensional space) is collected one after another, and reconstructed images are obtained one after another as shown in FIG. 5B.
In the 2D imaging sequence, for example, TR (repetition time) is repeated 256 times while changing Gy to 256 ×
Collect the data needed to reconstruct a single image of 256 pixels. Then, from this data, 256 × 25
Reconstruct one image of 6 pixels. During this time, about 1
TR is shortened so that the processing is completed in about seconds. The reason why the TR is shortened is also to emphasize the signal of the blood vessel portion. This is because a contrast agent such as Gd-DTPA has a T1 shortening effect. Therefore, when the TR is shortened, signals of other tissues are attenuated, whereas a signal of the contrast agent becomes a high signal.

The first reconstructed image as shown in FIG. 4 is displayed on the display device 54, and an appropriate ROI 85 including the blood vessel image 84 is set by operating the mouse 56 or the like. Then, the signal intensity at the ROI 85 is obtained by the ROI signal intensity extraction circuit 58 from the next reconstructed image. When the ROI 85 is set to a size of about 30 × 30 pixels assuming that the image matrix is 256 × 256 as described above, the current hardware and software can obtain this signal intensity within 0.5 seconds.

This signal intensity is obtained one after another every time an image is reconstructed.
From the time when the first ROI 85 is reached, it gradually increases as shown in FIG. The peak detection circuit 59 generates a signal when the signal intensity reaches the peak or when the signal intensity approaches the peak (immediately before the peak).

The signal generated from the peak detection circuit 59 is taken into the computer 51 and is used as a start trigger signal for a 3D imaging sequence. In this manner, the 3D imaging sequence as shown in FIG. 2B is started. The magnitude of the Gz pulse 73 starts from 0 and is gradually increased, so that the data on the low frequency side changes to the data on the high frequency side. The phase encoding order in the Z direction is determined so that data collection is performed. Further, the Gz pulse 73 is changed to only one polarity, and only half data in the kz direction of the k space is collected as shown in FIG. 5D. From this, a 3D image is obtained by a half Fourier reconstruction method. Reconfigure.

As described above, the 3D imaging sequence can be shifted to the 3D imaging sequence with a delay of about 1.5 seconds from the time when the ROI 85 is actually filled with the contrast agent most, and the optimum timing can be obtained. Moreover, in the 3D imaging sequence, data is collected from the low-frequency components, and when the signal intensity at the ROI 85 of the target blood vessel 81 is maximized, data of the low-frequency components that determines the image quality in the 3D reconstructed image is obtained. 84 good 3D images can be obtained. Since the half Fourier reconstruction method is employed, the acquisition time of all data necessary for 3D image reconstruction is short, and the process can be completed before the contrast agent flows out of the target blood vessel 81.

Note that the slice thickness (2D
The thickness of the excitation region 83 in the Z direction (the thickness in the Z direction) is preferably equal to the slab thickness of the 3D imaging (the thickness of the 3D excitation region 82 in the Z direction) as much as possible. This is to increase the stability of magnetization at the start of the 3D imaging sequence. Therefore, specifically, the parameters of the 3D imaging sequence are set up from the beginning, and in the 2D imaging sequence performed prior thereto, the Gz pulse 73 for Z-direction phase encoding may be simply set to 0. This allows 3D
It becomes possible to shift to the 3D imaging sequence almost in real time (after one TR time) from the input of the trigger signal for switching to the imaging sequence.

In order to capture the temporal change of the signal intensity, the ROI 85 is not set, but a reference image is obtained by a 2D imaging sequence before the injection of the contrast agent, and the reference image is sequentially obtained at the time of injection of the contrast agent. A difference image from the obtained 2D image may be obtained, and the signal intensity thereof may be obtained. Such signal strength extraction and peak detection
In the above description, the processing is performed by dedicated hardware. However, the processing can be automatically performed by processing (as software) by the computer 51.

Further, instead of automatically determining the peak of the signal strength as described above, a graph as shown in FIG.
4, the operator may observe the displayed information, determine the peak (or likely to become a peak), and perform an input operation of the trigger signal.

In addition, it goes without saying that the specific configuration and the like can be variously changed without departing from the spirit of the present invention.

[0026]

As described above, according to the MR imaging apparatus of the present invention, it is easy to determine the timing when the target region is most filled with the contrast agent, and the 3D-contrast MR angiography imaging can be performed at that timing. Data can be collected when the target site has the strongest signal, and a good image can be obtained without being affected by individual differences in the time until the contrast agent arrives. Can be

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a time chart showing a pulse sequence used in the embodiment.

FIG. 3 is a diagram showing a positional relationship between a target blood vessel and an excitation region.

FIG. 4 is a diagram showing a 2D image.

FIG. 5 is a diagram illustrating a relationship between sequentially acquired collected data, sequentially acquired reconstructed images, and temporal changes in signal intensity.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Magnet assembly 12 RF coil 21 Magnetic field control circuit 31 RF oscillation circuit 32 Amplitude modulation circuit 33 RF power amplifier 41 Preamplifier 42 Phase detection circuit 43 A / D converter 51 Computer 52 Sequence controller 53 Waveform generation circuit 54 Display device 55 Keyboard 56 Mouse 57 Recording device 58 ROI signal strength extraction circuit 59 Peak detection circuit 61 Subject 62 Examination table 71 RF excitation pulse 72 Gradient magnetic field pulse for slice selection 73 Gradient magnetic field pulse for Z direction phase encoding 74 Gradient magnetic field for Y direction phase encoding Pulse 75 readout gradient magnetic field pulse 76 resonance signal 81 target blood vessel 82 3D excitation area 83 2D excitation area 84 blood vessel image 85 ROI (region of interest)

Claims (1)

[Claims] 1. A means for generating a static magnetic field, means for generating gradient magnetic fields in first, second, and third directions perpendicular to each other so as to overlap the static magnetic field, RF transmitting means, and RF receiving means By controlling these, a 2D imaging sequence including an RF excitation pulse, a gradient magnetic field pulse for slice selection in the first direction, a gradient magnetic field pulse for phase encoding in the second direction, and a gradient magnetic field pulse for readout in the third direction is sequentially performed. The RF excitation pulse, the gradient pulse for slice selection in the first direction, the gradient magnetic field pulse for phase encoding in the first direction, and the phase encoding pulse in the second direction are repeated from the 2D imaging sequence according to the input timing. Gradient pulse,
MR imaging comprising: control means for shifting to a 3D imaging sequence including a readout gradient magnetic field pulse in a third direction; and means for obtaining a signal intensity from a 2D image obtained in the above-described sequential 2D imaging sequence. apparatus.