JP3350176B2 - Magnetic resonance imaging equipment - Google Patents

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 and 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) is used.
An 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 that is different in phase from other spins, and the phase state of the modified spin is captured There is known a labeling method (tagging method) that reflects a light and shade pattern (tag) in the image. In the tagging method, it is possible to observe a movement phenomenon in a living body as a change in 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 disadvantage that the flow velocity and the MR value do not correlate very much. Further, in an MR angiography apparatus using a phase shift, although the flow velocity is reflected, it may be difficult to understand intuitively, or the dynamic range of the flow velocity may be narrow and discontinuous.

[0004] The tagging method is applied not only to flow but also to imaging of movement of the heart and muscles. Various tagging methods 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 unit + imaging unit), the blood flow signal is hidden in a tissue with a lot of fat, and in order to grasp the three-dimensional distribution of the whole volume, A background signal such as fat obstructed the drawing output.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a magnetic resonance imaging apparatus capable of well displaying a tag of a blood flow portion even in a tissue having a large amount of fat. That is. It is another object of the present invention to provide a magnetic resonance imaging apparatus in which not only anatomical information of blood vessels but also flow information can be intuitively understood.

[0006]

SUMMARY OF THE INVENTION A magnetic resonance imaging apparatus according to the present invention includes a tagging flow imaging means for forming a stripe pattern in an image of a subject by using a magnetic resonance phenomenon, and a part to be imaged. Means for suppressing the generation of signals from fat components in the inside.

[0007] The magnetic resonance imaging apparatus according to the present invention is characterized in that tagging flow imaging is performed by using a pre-pulse of the DANTE method. The magnetic resonance imaging apparatus according to the present invention performs tagging flow imaging by using binomial pre-pulses.

A magnetic resonance imaging apparatus according to the present invention is characterized in that tagging flow imaging is performed by using an in-plane saturation prepulse. The 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 images obtained in both sequences. It is characterized in that fat components are 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 the longitudinal magnetization of the fat component. A magnetic resonance imaging apparatus according to the present invention includes a means for generating a tagging image by inserting a stripe pattern in an image of a subject using a magnetic resonance phenomenon, and a means for three-dimensionally processing a plurality of tagging images. It is characterized by having.

[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 By subtracting the signal of the stationary part including the fat component by performing the subtraction processing with the second image having the different signal intensity of the part, a tagging image in which the fat component is suppressed can be obtained.

In addition, since a stripe pattern shifted according to the speed of the blood flow is displayed in addition to the image of the blood flow portion, not only the anatomical information of the blood flow but also the flow information is intuitively displayed. Can be caught.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the 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. Transmitter / receiver coil 3
May be mounted directly on the subject instead of being embedded in the gantry. The static magnetic field magnet 1 as a static magnetic field generator is configured 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) It is used to generate a pulse and detect a magnetic resonance signal (MR signal) generated by magnetic resonance. The subject P on the couch 13 is inserted into an imageable area in the gantry 20 (a spherical area where an imaging magnetic field is formed, and diagnosis can be performed only in this area).

The static magnetic field magnet 1 is driven by a static magnetic field control device 4. The transmitting and receiving coil 3 is driven by the transmitter 5 when exciting magnetic resonance, 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 supply 7, a Y-axis gradient magnetic field power supply 8, and a Z-axis gradient magnetic field power supply 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 the X-axis gradient magnetic field Gx, the Y-axis gradient magnetic field Gy, A Z-axis gradient magnetic field Gz and a high 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, for example, the phase encoding gradient magnetic field Ge, the readout gradient magnetic field Gr, and the slice gradient magnetic field Gs. The computer system 11 controls the drive of the sequencer 10, acquires a magnetic resonance signal received by the receiver 6, and performs predetermined signal processing to generate a tomographic image of the subject, and displays the tomographic image on the display unit 12.

FIG. 2 shows an outline of the pulse sequence of the first embodiment. In the first embodiment, a background part (stationary part) including fat is deleted by subtracting an image containing a tag (tagging image) from a normal image, and a tagging image of only a blood vessel part is obtained. FIG. 7A shows a first sequence including a tagging unit and a rephase type imaging unit that makes a blood flow a high signal, and a second sequence that includes only a dephase type imaging unit that makes a blood flow a low signal.
Are performed, and the subtraction with the images It and In obtained in both sequences is performed. FIG. 3B shows the execution of a sequence composed of a rephase type imaging unit and a sequence composed of a tagging unit and a dephase type imaging unit, and subtraction of the images In and It obtained in both sequences. Show the case. In this case, the subtraction may subtract either image from either image,
After the subtraction, the black and white of the image may be inverted as needed. If some background is to be left, one image may be weighted at the time of subtraction.

In the tagging image finally obtained by such tagging flow imaging, the tags are not shifted in the stationary portion (background portion) as shown in FIG. 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 shift amount L of the tag (see FIG. 4A) is the delay from the center of the RF pulse of the tagging unit to the center of the RF pulse of the imaging unit (this sequence). It becomes larger as the time Td (see FIG. 4B) becomes longer. L and Td have the following relationship.

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

Vave = (１ ／) Vmax (2) When the flow is an unsteady flow (turbulent flow), the tag has a complicated shape due to the generation of a vortex, and it is difficult to perform a quantitative measurement. However, observing the pattern indicates that the flow is turbulent, and a diagnosis of an aneurysm or the like can be made.

As described above, tagging flow imaging is important in terms of intuitively grasping spatial information of a flow as an image, and quantitative measurement is also possible if necessary.

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

FIG. 6 shows an example of a sequence (main sequence) of the imaging unit. FIG. 2A shows a rephasing type imaging sequence of the field echo method, and FIG. 2B shows a dephasing type imaging sequence of the field echo method.

Of these sequences, a pre-pulse by the DANTE method is used as the tagging part, a rephase type sequence of the 2DFT FE method is used as the main sequence part, and the primary GMN (Gradien) is used in the Gs and Gr directions.
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, in which several elongated rectangular RF pulses are arranged at equal intervals. When these DANTE pulses are applied while applying a gradient magnetic field in a predetermined direction, here in the Gr direction, then, when echoes are collected and imaged in this sequence, a low signal portion in a direction orthogonal to the Gr direction is obtained.
That is, a tag (striped pattern) is generated parallel to the entire screen in the stationary portion.

The relationship between the tag interval Δx (Gr direction) on the image shown in FIG. 8 and the interval Ti of 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 tags uniformly over the entire FOV (Fielf of View), each DANT
E Make the pulse width Tp sufficiently narrow (1 / Tp >> BW)
This is very important.

The sequence shown in FIG. 7 is an image at a predetermined cross section. If the blood vessel of the subject is located on the same plane, a desired tagging flow image can be obtained even in two dimensions by positioning. However, when blood vessels are distributed three-dimensionally, multi-slice of 2DFT method or 3D
See what was collected by the FT method on any cross section, or
As shown in FIG. 2, a method of projecting as volume data, for example, a method of viewing as an image superimposed on a three-dimensional information plane by maximum intensity projection (MIP) is used. If the projection direction is parallel to the direction of the tag, the tag does not spread and is projected as it is.

However, in the sequence of FIG. 7 alone, the blood flow signal is buried in the fat signal in the background part, particularly in the part with a lot of fat, and when viewed in one cross section, the tag of the blood vessel can be seen, but the MIP method or the like is used. Is projected, if the signal of the blood vessel part is lower than the surrounding fat, the blood vessel becomes invisible.

Therefore, the same region is scanned by a dephasing type imaging sequence having no tagging portion, which is the lower sequence of the two pulse sequences shown in FIG. The signal image In is reconstructed, and the blood flow obtained by the sequence shown in FIG. 7 performs subtraction with the high-signal tagging image It. Then, if the TR and the TE of the two imaging sequences are the same, the fat component in the stationary part is substantially the same between the tagging image It and the normal image In, and the fat component is the same.
Since only a tag is attached, by performing a subtraction like It-In, a high-signal only blood flow signal without a fat portion and a tagged image can be obtained. Note that the subtraction may be In-It, in which case only the black and white of the image is inverted. In addition, when one image is weighted at the time of subtraction, a background can be left slightly. FIG. 10 shows the details of the subtraction process.

In the case of a two-dimensional image, this is the final image. In the case of a 2DFT multi-slice, in the case of a 3DFT, the same processing is performed for each slice, and as shown in FIG. To perform MIP processing.

As described above, according to the first embodiment,
The first with a high blood signal (or low signal) and a tag
Is subtracted from the second image having no tag that makes the blood flow part a low signal (or a high signal) to remove the fat component, and an image of only the blood flow part with a tag (tagging) Flow image) can be obtained, and the flow can be visualized. Further, since the tag shifts according to the flow rate, quantitative measurement is also possible. In the above description, a three-dimensional display is performed by performing the projection process. However, the two-dimensional display may be performed.

Hereinafter, another embodiment will be described. The configuration of the other embodiments is the same as that of the first embodiment, and only the pulse sequence is different. Therefore, the description of the configuration is omitted. In the first embodiment, 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. Therefore, two scans are required. 1
A second embodiment capable of creating a tagging flow image in which fat is suppressed by a single scan will be described with reference to FIG. This embodiment includes a tagging unit, a fat suppressor, and a normal imaging unit.

As the tagging section shown in FIG. 5 described in the first embodiment, a pre-pulse by the DANTE method shown in FIG. 5A is used, and the fat suppression section for eliminating the longitudinal magnetization of fat and suppressing the fat signal is used for the tagging section. 1-3 'shown in FIG.
Use a -3-1 'pulse sequence (where each numerical value indicates the amplitude of a pulse, and the dash on the right shoulder of the number indicates an inverted pulse), and a rephasing type sequence of the field echo method is used for the imaging unit. FIG. 13 shows the entire sequence when the primary GMN is used in the G, Gs, and Gr directions.

As described above, according to the second embodiment, the pulse sequence including the fat suppressor is used.
A tagging image in which fat is suppressed can be obtained in each scan. However, there is a case where it is weak to the non-uniformity of the magnetic field and the fat is not effectively controlled. On the other hand, according to the first embodiment, two scans and image processing are necessary, but the nonuniformity of the magnetic field and the degree of freedom of contrast are large, and the image quality is good. Therefore, it is necessary to appropriately use the characteristics of each method. The tagging section of the second embodiment can use the various sequences shown in FIG. 5 similarly to the first embodiment, and the imaging section of the second embodiment can use the various sequences shown in FIG. 6 similarly to the first embodiment. Can be used. In addition, the temporal order of the tagging unit and the fat suppressing unit may be interchanged. Further, 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 comprises a tagging pre-pulse section and a normal imaging section of the rephase or dephase type. This is different from the pulse sequence of the second embodiment shown in FIG. 13 in that the fat suppressor is omitted, and instead the Gs is changed for each Ge in order to apply the imaging unit to the 3DFT method.

The present invention is not limited to the embodiments described above, but can be implemented with various modifications. For example, in the above description,
The flow is a steady flow, and it can be regarded as almost steady flow in the peripheral vein, but it can not be considered as a steady flow because the artery and the trunk vein are pulsating flow, but in this case, attach a sensor to the ECG or the fingertip of the patient Pulse wave synchronization (PPG: Periphera)
l Gating) may be used together to create a tagging flow image for each face in one cycle. Further, although a normal field echo method has been described as a pulse sequence of the imaging unit, a spin echo method, a high-speed gradient field echo method, an echo planar imaging method, a turbo-FLASH method, or the like may be used. In particular,
The spin echo method is effective because even if the entire volume is thickly cut, the influence of the non-uniformity of the magnetic field is small, so that multiple cross sections can be scanned by one excitation.

[0036]

As described above, according to the present invention, it is possible to provide a magnetic resonance imaging apparatus capable of clearly displaying a tag in a blood flow portion even in a tissue having a large amount of fat. Further, it is possible to provide a magnetic resonance imaging apparatus in which not only anatomical information of blood vessels but also flow information can be intuitively understood.

[Brief description of the drawings]

FIG. 1 shows a first embodiment of a magnetic resonance imaging apparatus according to the present invention.
FIG. 1 is a block diagram illustrating a configuration of an embodiment.

FIG. 2 is a diagram schematically illustrating a pulse sequence according to the first embodiment.

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

FIG. 4 is a view for explaining the relationship between a tag shift amount and a flow velocity in a tagging image, and a delay time from the center of the RF pulse of the tagging section to the center of the RF pulse of the imaging section.

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 illustrating an example of a pulse sequence of an imaging unit according to 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 a field echo method is used as an imaging unit.

FIG. 8 is a diagram showing a tag interval 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 schematically illustrating a pulse sequence according to the second embodiment.

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

FIG. 13 shows 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 suppressor, and a rephasing sequence of a field echo method is used as an imaging unit. FIG.

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

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Static magnetic field magnet, 2 ... X-axis / Y-axis / Z-axis gradient magnetic field coil, 3 ... Transmission / reception 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 unit.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-212014 (JP, A) JP-A-5-115458 (JP, A) JP-A-60-35222 (JP, A) JP-A-3-352 82446 (JP, A) JP-A-64-52447 (JP, A) JP-A-61-88132 (JP, A) JP-A-5-204995 (JP, A) JP-A-62-57539 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) A61B 5/055

Claims (7)

(57) [Claims] 1. A tagging flow imaging means for making a stripe pattern in an image of an object by using a magnetic resonance phenomenon, and a means for suppressing signal generation from a fat component in a part to be imaged. A magnetic resonance imaging apparatus comprising: 2. The tagging flow imaging means
2. The magnetic resonance imaging apparatus according to claim 1, wherein a pre-pulse of a DANTE method is used. 3. The tagging flow imaging means
2. A binomial pre-pulse is used.
7. The magnetic resonance imaging apparatus according to item 1. 4. The magnetic resonance imaging apparatus according to claim 1, wherein said tagging flow imaging means uses an in-plane saturation pre-pulse. 5. The fat suppression unit 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 obtains images obtained by both sequences. 2. The magnetic resonance imaging apparatus according to claim 1, further comprising means for performing subtraction processing. 6. The magnetic resonance imaging apparatus according to claim 1, wherein said fat suppressing means includes means for saturating a fat component and eliminating longitudinal magnetization of the fat component. 7. A magnetic apparatus comprising: means for generating a tagging image by inserting a stripe pattern in an image of an object using a magnetic resonance phenomenon, and means for performing three-dimensional processing on a plurality of tagging images. Resonance imaging device.