JPH0788100A - Magnetic resonance imaging device - Google Patents

Abstract

PURPOSE:To enable tracing of a tagged state of a blood flow portion in a fatty tissue, by equipping a magnetic resonance imaging device with a tagging flow imaging means for inserting a striped pattern in a picture image and a means to control a signal generation from fat ingredients in the position to be photographed. CONSTITUTION:By the subtracting a picture image with a tag and an ordinary picture image, a background portion including fat is eliminated to obtain a tagging picture image of only a vein portion. Here, by realizing a first sequence consisting of a tagging portion and a rephase-type imaging portion which makes a blood flow a high signal and a second sequence consisting of only a dephase- type imaging which makes the blood flow a low signal, a subtraction of picture images Tt, Tn obtained by both the sequences is performed. Otherwise, a subtraction of the sequence consisting of the rephase-type imaging portion and the sequence consisting of the dephase-type imaging of the tagging portion is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging apparatus capable of visualizing or measuring a flow such as a blood flow.

[0002]

2. Description of the Related Art As such a magnetic resonance imaging apparatus, a two-dimensional or three-dimensional TOF (Time of Flight)
MR angiography device that uses the effect or phase shift, or modifies only the spin at a specific position in the imaging region to a state different in phase from other spins, and the phase state of this modified spin is a captured image There is known a labeling method (tagging method) in which a pattern (tag) of light and shade is reflected. In the tagging method, it is possible to observe a movement phenomenon in a living body as a change of a light and shade pattern in an image by giving a tag a role of a tracer.

However, the MR angiography apparatus utilizing the TOF effect has a drawback that the flow velocity and the MR value are not so correlated. Further, in the MR angiography apparatus using the phase shift, although the flow velocity is reflected, it may be difficult to intuitively understand, and the dynamic range of the flow velocity may be narrow and discontinuous.

The tagging method is applied not only to the flow but also to the imaging of heart and muscle movements. In the tagging method, various types have been reported as pre-pulses applied before the pulse sequence of the field echo method or the spin echo method. In the normal tagging method, even with the current single sequence (tagging section + imaging section), the blood flow signal is hidden in a fat-rich tissue, and to grasp the three-dimensional distribution of the entire volume, There was a problem in drawing output because the background signal such as fat became an obstacle.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned circumstances, and an object thereof is to provide a magnetic resonance imaging apparatus capable of well depicting the state of a tag in a blood flow portion even in a fat-rich tissue. That is. Another object of the present invention is to provide a magnetic resonance imaging apparatus which intuitively understands not only anatomical information of blood vessels but also flow information.

[0006]

A magnetic resonance imaging apparatus according to the present invention is a tagging flow imaging means for inserting a stripe pattern in an image of an object to be imaged by utilizing a magnetic resonance phenomenon, and a region to be imaged. And means for suppressing the signal generation from the fat component in the inside.

The magnetic resonance imaging apparatus according to the present invention is characterized by performing tagging flow imaging by using a prepulse of the DANTE method. The magnetic resonance imaging apparatus according to the present invention is characterized by performing tagging flow imaging by using a binomial prepulse.

The magnetic resonance imaging apparatus according to the present invention is characterized by performing tagging flow imaging by using an in-plane saturation prepulse. A magnetic resonance imaging apparatus according to the present invention executes a first imaging sequence in which a blood flow component has a high signal and a second imaging sequence in which a blood flow component has a low signal, and subtracts the images obtained by both sequences. It is characterized in that the fat component is suppressed by processing.

The magnetic resonance imaging apparatus according to the present invention is characterized in that the fat component is suppressed by saturating the fat component and eliminating longitudinal magnetization of the fat component. A magnetic resonance imaging apparatus according to the present invention includes means for generating a tagging image by inserting a striped pattern in an image of a subject using a magnetic resonance phenomenon, and means for three-dimensionally processing a plurality of tagging images. It is characterized by including.

[0010]

According to the magnetic resonance imaging apparatus of the present invention, a pulse sequence in which a fat signal is suppressed is used, or the first image with a tag and the first image without a stripe pattern and the blood flow. A tagging image in which the fat component is suppressed can be obtained by performing subtraction processing with the second image having a different signal intensity of the part and deleting the signal of the still part including the fat component.

Further, in addition to the image of the blood flow portion, the striped pattern shifted according to the velocity of the blood flow is displayed in an overlapping manner, so that not only the anatomical information of the blood flow but also the flow information is intuitively obtained. You can catch it.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a magnetic resonance imaging apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of the first embodiment. Gantry 20
A static magnetic field magnet 1, an X-axis / Y-axis / Z-axis gradient magnetic field coil 2 and a transmission / reception coil 3 are provided therein. Transmit / receive coil 3
Instead of being embedded in the gantry, it may be directly attached to the subject. The static magnetic field magnet 1 as the static magnetic field generator is configured by using, for example, a superconducting coil or a normal conducting coil. The X-axis / Y-axis / Z-axis gradient magnetic field coil 2 is a coil for generating an X-axis gradient magnetic field Gx, a Y-axis gradient magnetic field Gy, and a Z-axis gradient magnetic field Gz. The transmission / reception coil 3 has a high frequency (R) as a selective excitation pulse for selecting a slice.
F) Used to generate pulses and to detect magnetic resonance signals (MR signals) generated by magnetic resonance. The subject P on the bed 13 is inserted into an imageable region (a spherical region where an imaging magnetic field is formed, and diagnosis is possible only in this region) in the gantry 20.

The static magnetic field magnet 1 is driven by the static magnetic field controller 4. The transmission / reception coil 3 is driven by the transmitter 5 when magnetic resonance is excited, and is coupled to the receiver 6 when detecting a magnetic resonance signal. The X-axis / Y-axis / Z-axis gradient magnetic field coil 2 is driven by an X-axis gradient magnetic field power source 7, a Y-axis gradient magnetic field power source 8 and a Z-axis gradient magnetic field power source 9.

The X-axis gradient magnetic field power supply 7, the Y-axis gradient magnetic field power supply 8, the Z-axis gradient magnetic field power supply 9 and the transmitter 5 are driven by a sequencer 10 according to a predetermined sequence, and an X-axis gradient magnetic field Gx, a Y-axis gradient magnetic field Gy, A Z-axis gradient magnetic field Gz and a radio frequency (RF) pulse are generated in a predetermined pulse sequence described later. In this case, the X-axis gradient magnetic field Gx, the Y-axis gradient magnetic field Gy, and the Z-axis gradient magnetic field Gz are mainly used as the phase encoding gradient magnetic field Ge, the reading gradient magnetic field Gr, and the slice gradient magnetic field Gs, respectively. The computer system 11 drives and controls the sequencer 10, captures the magnetic resonance signal received by the receiver 6 and performs predetermined signal processing to generate a tomographic image of the subject, and displays it on the display unit 12.

FIG. 2 shows an outline of the pulse sequence of the first embodiment. In the first embodiment, the background portion (still portion) also including fat is erased by subtracting the tagged image (tagging image) and the normal image, and the tagging image of only the blood vessel portion is obtained. FIG. 3A shows a first sequence consisting of a tagging section and a rephase type imaging section for making blood flow a high signal, and a second sequence consisting of only a dephase type imaging section for making a blood flow a low signal.
, And the subtraction is performed on the images It and In obtained in both sequences. In the same figure, (b) executes a sequence including a rephasing type imaging unit and a sequence including a tagging unit and a dephasing type imaging unit, and subtracts the images In and It obtained in both sequences. Indicate the case. In this case, the subtraction may subtract either image from either image,
After subtraction, the black and white of the image may be reversed if necessary. Further, if some background is to be left, one of the images may be weighted during subtraction.

In the tagging image to be finally obtained by such tagging flow imaging, the tags are not shifted in the stationary portion (background portion) as shown in FIG. Then, the tag shifts according to the flow velocity distribution, and the shift amount reflects the flow velocity at that point. Here, the flow is a steady flow (laminar flow)
In the case of, the tag in the vessel shows a parabola, and the tag shift amount L (see FIG. 4A) is the delay from the center of the RF pulse of the tagging section to the center of the RF pulse of the imaging section (main sequence). The larger the time Td (see FIG. 4B), the larger the time. The relationship between L and Td is as follows.

Vmax = L / Td (1) Here, since Vmax is the maximum flow velocity and the average flow velocity Vave can be obtained as follows, quantitative observation of the blood flow is also possible from L and Td.

Vave = (1/2) Vmax (2) When the flow is an unsteady flow (turbulent flow), the tag has a complicated shape due to the generation of vortices, and quantitative measurement is difficult. However, by observing the pattern, it is found that the flow is turbulent, and it is possible to diagnose an aneurysm or the like.

As described above, the tagging flow imaging is important in the sense that the spatial information of the flow is intuitively grasped as an image, and the quantitative measurement can be performed if necessary.

A concrete sequence of each part in FIG. 2 will be described. FIG. 5 shows an example of the sequence (pre-pulse sequence) of the tagging unit. The figure (a) is a prepulse by the DANTE method, the figure (b) is a binomial type prepulse, and the figure (c) is inplane saturation (in-plane saturation).
2 shows a prepulse of a mold.

FIG. 6 shows an example of the sequence of the imaging unit (main sequence). The figure (a) shows the rephasing type imaging sequence of the field echo method, and the figure (b) shows the dephasing type imaging sequence of the field echo method.

Among these sequences, the pre-pulse by the DANTE method is used as the tagging section, the rephase type sequence of the 2DFT FE method is used as the main sequence section, and the primary GMN (Gradien) in the Gs and Gr directions is used.
FIG. 7 shows the entire sequence when t Moment Nulling) is used. FIG. 7 shows the upper pulse sequence of the two pulse sequences shown in FIG.

The DANTE method is used by Freeman et al. To selectively extract a component of a predetermined frequency in the field of spectroscopy, and is an array of several elongated rectangular RF pulses at equal intervals. When these DANTE pulses are applied while applying a gradient magnetic field in a predetermined direction, here, in the Gr direction, when echoes are collected and imaged in this sequence, a low signal portion in a direction orthogonal to the Gr direction,
That is, a tag (striped pattern) is generated in the stationary portion in parallel with the entire screen.

The relationship between the tag interval Δx (in the Gr direction) on the image shown in FIG. 8 and the interval Ti between each DANTE pulse and the intensity Gd of the gradient magnetic field in the Gr direction is expressed as follows. Δx = 1 / γGdTi (3) where γ is the gyromagnetic ratio.

In order to put the tags uniformly over the entire FOV (Fielf of View), each DANT is added to the FOV band BW.
Make E pulse width Tp narrow enough (1 / Tp >> BW)
This is very important.

The sequence of FIG. 7 obtains an image at a predetermined cross section, and when the blood vessels of the subject are on the same plane, positioning allows obtaining a desired tagging flow image even in two dimensions. However, when blood vessels are distributed three-dimensionally, 2DFT multi-slice or 3D
You can see what was collected by FT method on any cross section,
As shown in (3), projection is performed as volume data, for example, a method of viewing as an image superimposed on a three-dimensional information plane by a maximum intensity projection method (MIP: Maximum Intensity Projection) is used. If the projection direction is made parallel to the tag direction, the tag will be projected as it is without spreading.

However, in the case of the sequence of FIG. 7 alone, the blood flow signal is buried in the fat signal in the background portion, particularly in the portion where there is a lot of fat, and the blood vessel tag can be seen when seen in one section, but the MIP method or the like. If the signal of the blood vessel portion is lower than the surrounding fat, the blood vessel becomes invisible when the projection is performed.

Therefore, the same region is scanned by the dephasing type imaging sequence having no tagging part, which is the lower sequence of the two pulse sequences shown in FIG. 2A, and there is no tag and the blood flow part is low. The signal image In is reconstructed, and the blood flow portion obtained in the sequence shown in FIG. 7 subtracts from the high signal tagging image It. Then, if the fat in the stationary portion has the same TR and TE in the two imaging sequences, the fat component becomes approximately the same in the tagging image It and the normal image In.
Since the tag is attached only to the image, by performing subtraction like It-In, only the blood flow signal without a fat portion has a high signal and an image with a tag is obtained. Note that the subtraction may be In-It, in which case black and white of the image are only inverted. Also, if one image is weighted during subtraction, the background can be left to some extent. Details of the subtraction process are shown in FIG.

In the case of a two-dimensional image, this is the final image, but in the case of 2DFT multi-slice and 3DFT, after performing the same processing for each slice, the line of sight is made parallel to the tag as shown in FIG. To perform MIP processing.

As described above, according to the first embodiment,
First tagged with high (or low) signal in the bloodstream
Image is subtracted from the second image, which has a low signal (or high signal) in the blood flow part and has no tag, so that the fat component is eliminated and the image of the blood flow part with a tag (tagging) is removed. Flow image) can be obtained and the flow can be visualized. In addition, since the tag shifts according to the flow rate, quantitative measurement is possible. In the above description, the projection process is performed and the three-dimensional display is performed, but the two-dimensional display may be used as it is.

Another embodiment will be described below. The configuration of the other examples is the same as that of the first example, and only the pulse sequence is different, so the description of the configuration is omitted. In the first embodiment, since the first sequence in which the blood flow portion has a high signal and the second sequence in which the blood flow portion has a low signal are executed and the subtraction is performed, two scans are required. 1
A second embodiment capable of creating a tagging flow image in which fat is suppressed by one scan will be described with reference to FIG. This embodiment comprises a tagging section, a fat suppress section, and a normal imaging section.

Among the components shown in FIG. 5 described in the first embodiment as the tagging portion, the pre-pulse according to the DANTE method shown in (a) is used for the fat suppress portion for eliminating the longitudinal magnetization of fat and suppressing the fat signal. 1-3 'shown in FIG.
-3-1 'pulse sequence (where each numerical value indicates the amplitude of the pulse, the dash on the right shoulder of the numerical value indicates the inverted pulse), and the imaging unit uses the rephasing type sequence of the field echo method FIG. 13 shows the entire sequence when a first-order GMN is used in the Gs, Gs, and Gr directions.

As described above, according to the second embodiment, since the pulse sequence including the fat suppress portion is used, 1
A single scan results in a fat suppressed tagging image. However, there are some cases where the suppression of fat is not successful because it is weak against the inhomogeneity of the magnetic field. On the other hand, according to the first embodiment, two scans and image processing are required, but the non-uniformity of the magnetic field and the degree of freedom of contrast are large, and the image quality is good. Therefore, it is necessary to utilize the characteristics of each method as appropriate. Note that the tagging unit of the second embodiment can use the various sequences shown in FIG. 5 as in the first embodiment, and the imaging unit of the second embodiment can also use the various sequences shown in FIG. 6 as in the first embodiment. Can be used. Also, the temporal order of the tagging portion and the fat suppress portion may be exchanged. Furthermore, the tagging flow image obtained in the second embodiment may be displayed three-dimensionally or two-dimensionally.

FIG. 14 shows a pulse sequence of the third embodiment according to the 3DFT method, which includes a tagging pre-pulse portion and a rephasing or dephasing type normal imaging portion. This differs from the pulse sequence of the second embodiment shown in FIG. 13 in that the fat suppress part is omitted and instead the imaging part is scanned while changing Gs for each Ge in order to apply the 3DFT method.

The present invention is not limited to the above-described embodiments, but can be implemented with various modifications. For example, in the above description,
The flow is a steady flow, and it can be considered as a steady flow in the peripheral veins, but it cannot be considered as a steady flow because the arteries and trunk veins are pulsatile flows. In this case, attach a sensor to the ECG or the fingertip of the patient. Pulse wave synchronization (PPG: Periphera)
Gating) may be used together to create a tagging flow image for each face in one cycle. Although the normal field echo method is shown as the pulse sequence of the imaging unit, the spin echo method, the fast gradient field echo method, the echo planar imaging method, the turbo-FLASH method or the like may be used. In particular,
The spin echo method is effective in that it is possible to scan multiple cross sections with one excitation because the effect of magnetic field nonuniformity is small even if the entire volume is sliced.

[0036]

As described above, according to the present invention, it is possible to provide a magnetic resonance imaging apparatus capable of clearly showing the state of the tag in the blood flow part even in a fat-rich tissue. Further, it is possible to provide a magnetic resonance imaging apparatus which intuitively understands not only anatomical information of blood vessels but also flow information.

[Brief description of drawings]

FIG. 1 is a first magnetic resonance imaging apparatus according to the present invention.
The block diagram which shows the structure of an Example.

FIG. 2 is a diagram showing an outline of a pulse sequence of the first embodiment.

FIG. 3 is a diagram showing an example of a tagging image.

FIG. 4 is a diagram illustrating a relationship between a tag shift amount in a tagging image, a flow velocity, and a delay time from a center of an RF pulse in a tagging unit to a center of an RF pulse in an imaging unit.

FIG. 5 is a diagram showing an example of a pulse sequence of a tagging unit in the first embodiment.

FIG. 6 is a diagram showing an example of a pulse sequence of the imaging unit in the first embodiment.

FIG. 7 is a diagram showing an entire pulse sequence of the first embodiment when a DANTE pulse is used as a tagging unit and a rephasing sequence of the field echo method is used as an imaging unit.

FIG. 8 is a diagram showing tag intervals of a tagging image.

FIG. 9 is a diagram showing MPI projection processing.

FIG. 10 is a diagram showing a subtraction process.

FIG. 11 is a diagram showing an outline of a pulse sequence of a second embodiment.

FIG. 12 is a diagram showing an example of a pulse sequence of a fat suppress part in the second embodiment.

FIG. 13 is a pulse sequence of the entire second embodiment when a DANTE pulse is used as a tagging unit, a 1-3′-3-1 ′ pulse sequence is used as a fat suppression unit, and a rephasing sequence of the field echo method is used as an imaging unit. FIG.

FIG. 14 is a diagram showing a pulse sequence of a third embodiment of the present invention.

[Explanation of symbols]

1 ... Static magnetic field magnet, 2 ... X-axis / Y-axis / Z-axis gradient magnetic field coil, 3 ... Transmitting / receiving coil, 4 ... Static magnetic field control device, 5 ... Transmitter, 6 ... Receiver, 7 ... X-axis gradient magnetic field amplifier, 8 ... Y-axis gradient magnetic field amplifier, 9 ... Z-axis gradient magnetic field amplifier, 10 ... Sequencer, 11 ... Computer system, 12 ... Display part.

Claims (7)

[Claims] 1. A tagging flow imaging unit that puts a striped pattern in an image of a subject using a magnetic resonance phenomenon, and a unit that suppresses signal generation from a fat component in a region to be imaged. A magnetic resonance imaging apparatus comprising: 2. The tagging flow imaging means
The magnetic resonance imaging apparatus according to claim 1, wherein a prepulse of the DANTE method is used. 3. The tagging flow imaging means
2. A binomial prepulse is used.
The magnetic resonance imaging apparatus according to. 4. The magnetic resonance imaging apparatus according to claim 1, wherein the tagging flow imaging means uses an in-plane saturation prepulse. 5. The fat suppressing means executes a first imaging sequence in which a blood flow component has a high signal and a second imaging sequence in which a blood flow component has a low signal, and images obtained by both sequences are processed. The magnetic resonance imaging apparatus according to claim 1, further comprising means for performing a subtraction process. 6. The magnetic resonance imaging apparatus according to claim 1, wherein the fat suppressing means includes means for saturating the fat component and eliminating longitudinal magnetization of the fat component. 7. A magnetic field comprising means for generating a tagging image by inserting a striped pattern in an image of a subject using a magnetic resonance phenomenon, and means for three-dimensionally processing a plurality of tagging images. Resonance imaging device.