JP2001252263A - Method and instrument for magnetic resonance imaging using selectively excited inversion pulse - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an MRA which can upgrade both of time resolving power and space resolving power without the use of any contrast medium. SOLUTION: Immediately after the inversion of the spin of a photographing area CS by the first inversion pulse, the second inversion (IR) pulse with a tag is applied together with a selectively excited gradient magnetic field. As a result, the spin of a tag region RGA1 as selected region is inverted and a tag is attached. Then, after a fixed TI time passes, a scanning is started to receive an echo signal. The altering of the space position of the tag region is ordered to repeat the above series of processing. A plurality of images (IMrec1-, IMint1-, and IMfin1-) are generated from the echo signal collected associated with each scanning. The generation procedure contains a masking processing, a maximum projection processing and the like. A high signal part from a blood stream with a tag is depicted on the plurality of images and the images are shown, for example, by a cine display.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to imaging for imaging a blood vessel image or CSF (cerebrospinal fluid) of a subject using a high-frequency selective inversion (inversion recovery: IR) pulse for magnetic resonance imaging for medical use. In particular, the present invention relates to non-contrast magnetic resonance imaging that does not administer a contrast agent, but can simulate the blood flow and CSF dynamics as if a contrast agent was administered.

[0002]

2. Description of the Related Art In magnetic resonance imaging, nuclear spins of a subject placed in a static magnetic field are magnetically excited by a high frequency signal of a Larmor frequency, and FI generated by the excitation is excited.
This is a method of obtaining an image from a D (free induction attenuation) signal or an echo signal.

As one category of the magnetic resonance imaging, attention has been paid to MR angiography (MRA) for imaging blood dynamics.

[0004] In this MRA, generally, a contrast agent having a property of greatly changing the signal intensity in MRI is administered into a blood vessel, scans are continuously performed under the same conditions, and the state of movement of a blood flow is imaged. , Contrast Dynamic MR Angiography (hereinafter CE-DMRA: con)
trust enhanced dynamic MR
A (for example, “M.Pr.
ince, Radiology 1994; 191: 1
44-164 ".

[0005] Conceptually, the imaging procedure of this CE-DMRA
As shown in FIG. First, a contrast agent is injected into a vein, and the imaging area is
From the time when the contrast agent reaches the blood vessels in the
Perform A curve CB in FIG.
5 shows a time change of signal intensity at a position of a point. Same figure
As shown in (b), the contrast agent injection time t₀From the contrast agent
The point crosses the imaging area and all blood vessels are drawn
Depends on the size of the region and the imaging area, and
No, but it takes about 30 seconds to 2 minutes. Same figure
Period PD of (b)₁, PD₂, ... are the first and second
The scanning period of the eyes,... Also, this scan
Period PD₁, PD₂, ... are the desired, for example, three-dimensional
A loose sequence is executed and occurs in response to this execution
An echo signal is collected. The echo signal is scanned
For example, as shown in FIG.
3D image data D₁, D₂,…. this
Image data D ₁, D₂,…, For example, from a certain point of view
When the maximum value is projected (maximum value projection processing)
As shown conceptually in FIG. 3D, the maximum intensity projected image IM
_{max 1}, IM_max2, ... are displayed.

[0006] The scanning method used in this CE-DMRA is mainly a pulse sequence based on the FE (field echo) method. An example of this is shown in FIG. As shown in the figure, a harmonic excitation pulse P _ext is applied together with a slice selective excitation gradient magnetic field Gs _sel and an echo signal S
_{The echo} is received together with the application of the read-direction gradient magnetic field Gr. In the figure, a gradient magnetic field Gs _rew indicates a rewind gradient magnetic field in the slice direction. This series of excitation and collection is repeated a predetermined number of times at every repetition time TR until the echo data necessary for image reconstruction is completed while changing, for example, the intensity of the phase encoding gradient magnetic field Ge. Repetition time TR
Is typically on the order of 3-10 ms.

Although FIG. 13 illustrates a pulse sequence required for image reconstruction based on the two-dimensional Fourier method, image reconstruction based on the three-dimensional Fourier method may be used depending on the purpose of imaging. In this case, when a series of data is collected by changing the intensity of the phase encoding gradient magnetic field Ge by repeating each excitation, the intensity of the rewind gradient magnetic field Gs _{rew in} the slice direction is changed. Then, an operation of collecting a series of data associated with a change in the intensity of the phase encoding gradient magnetic field Ge is executed for the number of matrices in the slice direction. Thus, all data necessary for image reconstruction based on the three-dimensional Fourier method is collected.

Thus, in CE-DMRA, images D ₁ , D ₂ ,... Along the reconstructed time series, or images IM _max1 , IM maximally projected from the images D ₁ , D ₂ ,.
_By displaying and observing _max2 ,... in time series, the blood vessel B
The dynamic behavior of the blood BD flowing through the V can be grasped. This method is used for moving objects,
For example, when the imaging target is a human body, CSF (cerebrospinal fluid)
And the like, and the behavior can be observed through similar processing. When the CSF is to be imaged, it is called hydrography.

On the other hand, a conventional method of labeling locally moving spins with an inversion (IR) pulse without administering a contrast agent and obtaining a blood vessel image is described in the article "Cons.
indications of Magnetic Re
sonace Angiography by Sel
active Inversion Recover
y ", DG Nishimura et al.,
Magnetic Resonance in Me
dicine, Vol. 7,472-484,198
8 ". FIG. 14 shows an outline of the angiography according to the conventional method. FIG. 2A shows a pulse sequence when an ECG (electrocardiogram) synchronization method is used together, FIG. 2B shows a temporal change in the longitudinal magnetization of spin in each part of the imaging target, and FIG. section and h labeled for showing the positional relationship between the region RG _a excited in (tag) inversion pulse _{P i nv-a.}

[0010] As shown in FIG. 6 (a), after a certain time has elapsed from R-wave of the ECG signal (however, described immediately below in the figure of the R-wave), the flip angle of 180 ° inversion pulse _{P i nv -A} is applied. At this time, as the region RG _A I think that the inflow source to the imaging section CS of the blood vessel of interest is selectively excited, inversion pulse P _in
RF frequency of _v-A is shifted by the offset amount Df from the center frequency, the inversion pulse P
_A selective excitation gradient magnetic field Ge is applied together with _inv-A .
After the inversion pulse P _inv-A is applied, 3
After a certain time interval of about 00～1000Ms, the pulse sequence _{P se q} for collecting echo signals is executed. This sequence is, for example, SE (spin echo)
Composed of law. This series of operations is repeated until all the echo data necessary for reconstructing one screen can be collected. The echo data is subjected to a reconstruction process to generate a blood vessel image. The pulse sequence that can be used for this angiography is not limited to the SE method, but may be the segmented FE method. As an example, this segmented FE method is described in the paper “Fast Angiography Us”.
ing SelectiveInversion Re
coverage ", Samuel J. Wanget
al. , Magnetic Resonance i
n Medicine, Vol. 23,109-12
1, 1992 ".

Note that "DG Nishimurae"
t al. “The paper includes the inversion pulse P
Collect a plurality of images by changing the position and width of the partial region RG _A excited in _inv-A, method of generating a difference image from each image is described. By this difference calculation, the signal of the portion other than the blood vessel is suppressed, and the drawing ability of the blood vessel is improved.

Further, as another example of an angiography that does not use a contrast agent, a method described in FIGS. 15A to 15C is also known. The technique shown in the figure is based on the technique shown in FIG. 14 described above and the paper "D. Chien et al.,
“High Speed black blood i
magic of vessel stenosis
in the presence of pulsat
ile flow ", J. Magn. Reson. Im
aging, Vol. 2 (4), 437-441, 1
992 "or" Simonetti OPe "
t al. , Radiology, 199, 49, 19
96 ". As a scanning pulse sequence P _seq for obtaining an echo signal, for example, a fast SE (FSE) method is used. The method shown in FIG. 15 is the same as that shown in FIG. 14, but differs in the application of the inversion pulse. That is, the inversion pulse P _inv-A that excites the entire cross section CS to be imaged is first selectively applied, and immediately thereafter (for example, after 2 to 10 ms), it is considered that the blood vessel of interest is the inflow source similarly to FIG. 14. _A second inversion pulse P _inv-B is applied so that the partial region RGA is selectively excited. Since the time between the first and second inversion pulses P _inv-A and P _inv-B is extremely short as compared with the blood flow velocity, it is considered that they are almost the same when viewed from the nuclear spin of the blood vessel. be able to. Therefore, the nuclear spin of the blood vessel of interest is 1 in a very short time.
Since receiving twice application of 80 ° pulse, as shown in FIG. (B), from flowing into an imaging section CS from some region RG _A state longitudinal magnetization is returned to substantially the initial state, higher than the tissue Rendered as part of the signal. Note that FIG.
The technique of 4 is symmetrical in that the blood vessel signal is imaged as a lower value than that of the tissue.

[0013]

However, in the conventional CE-DMRA method using the above-described contrast agent, the contrast agent can be injected only once (or about twice) during one examination. All scans must be completed within a limited time of about 30 seconds to 2 minutes when the signal strength changes due to the injected contrast agent. In principle, one scan time must be as short as possible to ensure sufficient time resolution. On the other hand, since the S / N of an image is proportional to the square root of the scan time, the shorter the scan time, the lower the S / N. For this reason, according to the conventional method, there is a trade-off relationship between the time resolution of scanning and the spatial resolution, and it is not possible to significantly increase both of them.

On the other hand, in the case of the MR angiography without administration of the contrast agent, the difference between a plurality of blood vessel images obtained through the execution of the pulse sequence shown in FIG. 14 or FIG. Suppressing partial signals is stated. As a result, the ability to visualize blood vessels can be improved, but there is no display or observation method for dynamically capturing the dynamics of blood flow. In the case of blood flow, information on how it behaves over time is extremely important as well as its visualization ability.

The present invention has been made in view of the above-mentioned situation in the related art, and breaks the trade-off relationship between the time resolution and the spatial resolution due to the conventional scanning.
It is an object to provide images with both temporal and spatial resolution raised to very high levels without the administration of contrast agents.

Another object of the present invention is to provide an image capable of raising both the temporal resolution and the spatial resolution to a very high level without administering a contrast agent and enabling dynamic observation of a moving object. I do.

[0017]

According to the principle of the present invention, a high-frequency inversion (IR) pulse is locally applied to at least a part of an area of an object to be imaged, and at least a part of the area is applied to the area. Tag (labeling) by inverting and exciting the longitudinal magnetization of the spins located in. Of those regions, the tagged stationary spins remain in place, while the tagged spins of, for example, blood as moving objects continue to flow along the blood vessels thereafter. As a scan, after a predetermined time has elapsed after the application of the above-described inversion pulse, a scan of the imaging region according to a desired pulse sequence is started, and echo signals are collected. An image of the imaging area is obtained based on the echo signal. In this image,
Signals such as blood flowing to the imaging region while being tagged are reflected with contrast different from that of other parts, so that dynamic information such as blood can be provided.

As will be described in the structure of the present invention, as an example, the time from tagging to collection of an echo signal or the position of a partial area to be tagged is gradually set in the imaging area. The echo signal is collected and generated into an image while changing to By sequentially observing a plurality of images generated in response to such a change in time or position, it is possible to simulate the dynamics of a moving object such as blood.

As a specific configuration, in the magnetic resonance imaging method according to the present invention, a tagging inversion (IR) pulse is applied to an imaging region of an object together with a selective excitation gradient magnetic field, and at least a part of the imaging region is applied. A process including tagging for inverting the spin of the region is performed, and thereafter, after a certain period of time, a pulse sequence is started to receive an echo signal of the spin, and from the echo signal, there is movement in the imaging region. In the magnetic resonance imaging method for imaging an imaging target, the spatial position of the partial region is changed to apply the selective excitation gradient magnetic field and the inversion pulse a plurality of times. And executing the pulse sequence.

For example, the processing includes a step of first applying another inversion pulse to the entire imaging region, and immediately thereafter applying the tagging inversion pulse.

Preferably, a plurality of images are generated from echo signals generated in response to the pulse sequence executed a plurality of times in accordance with a change in the spatial position of the partial area. Images can be displayed continuously in a predetermined order. For example, the plurality of images are continuously displayed according to the change order of the spatial position of the partial area.

Further, for example, a plurality of images are generated from echo signals generated in response to the pulse sequence executed a plurality of times in accordance with a change in the spatial position of the partial area, and a plurality of images are generated from the plurality of images. A plurality of projection images obtained by projecting the pixels of the value can be created, and the plurality of projection images can be displayed continuously in a predetermined order.

Further, as one example, a plurality of images are generated from echo signals generated in response to the pulse sequence executed a plurality of times in accordance with a change in the spatial position of the partial area, and the plurality of images are generated. Above, a position on the image corresponding to the partial area is obtained, a masking process is performed on the position, and one or a plurality of projected images obtained by projecting pixels of a fixed value from the plurality of images after the masking process are obtained. It may be created and displayed on this projected image. In this case, for example, a plurality of the projection images are created, and the plurality of projection images are continuously displayed in a predetermined order.

Further, preferably, the process of projecting a pixel having a constant value is a process of projecting a maximum value or a minimum value of a pixel value.

Further, as another example, a plurality of images are generated from echo signals generated in response to the pulse sequence executed a plurality of times in accordance with a change in the spatial position of the partial area, and the plurality of images are generated. In each of the images, only one of the divided areas divided by the partial area may be continuously displayed.

Further, as another example, a plurality of images are generated from echo signals generated in response to the pulse sequence executed a plurality of times in accordance with a change in the spatial position of the partial area, and the plurality of images are generated. It is also possible to apply a masking process to only one of the two divided areas by the partial area in each of the images. At this time, preferably, a plurality of images subjected to the masking processing are displayed continuously. In addition, one or more projection images may be created by projecting a pixel of a fixed value from at least a part of each of the plurality of images subjected to the masking process, and the projection images may be displayed. For example, the masking process is performed on a divided area on the upstream side in the direction of movement of the imaging target.

Further, as another example, the tagging inversion pulse is composed of a plurality of inversion pulses that are continuously applied at every minute time that can be regarded as simultaneous as compared with the movement of the imaging object, Thereby, a plurality of the at least some areas are set for each scan. As a preferable example at this time, the application condition of the plurality of inversion pulses and the selective excitation gradient magnetic field applied simultaneously with the pulses is such that the at least a part of the regions is spatially arranged at a constant interval on the imaging region. In addition, they are set so that they are shifted from each other for each scan.

In the magnetic resonance imaging method of the present invention, the gradient magnetic field and the pulse are applied to the imaging region of the subject while changing the conditions of the tagging inversion (IR) pulse together with the selective excitation gradient magnetic field. The process of inverting the spin of a partial region of the region and thereafter starting a pulse sequence after a certain time has elapsed and receiving the echo signal of the spin is repeated a plurality of times. It is also possible to adopt an aspect including a pre-process for deciding the optimum position and size of the partial area from the specifics of the display of the imaging target on the plurality of images from the imaging of the imaging target having the movement every time. . For example, the preceding step includes a process of continuously displaying the plurality of images in the order of the size of the partial area to be changed.

Further, according to the magnetic resonance imaging method of the present invention, one inversion (IR) pulse is applied to an imaging region of a subject together with a selective excitation gradient magnetic field to invert the spin of the entire imaging region. Alternatively, a pulse sequence may be started after a lapse of a predetermined time to receive an echo signal of the spin, and an image of a moving imaging target in the imaging region may be formed from the echo signal.

Still further, in the magnetic resonance imaging method of the present invention, a tagging method in which an inversion (IR) pulse is applied to an imaging region of a subject together with a selective excitation gradient magnetic field to invert at least a part of spins in the imaging region. May be performed to detect a change in the echo signal of the imaging region due to the tagging, and to image a moving imaging target in the imaging region based on the signal change.

For example, the imaging target is a blood flow passing through the imaging region.

On the other hand, according to the magnetic resonance imaging apparatus of the present invention, a tagging inversion (IR) pulse is applied to the imaging region of the subject together with the selective excitation gradient magnetic field, and at least a part of the imaging region is obtained. Means for performing processing including tagging for inverting spins, means for starting a pulse sequence after a certain period of time has elapsed after application of the tagging inversion pulse, and means for receiving an echo signal of the spin; and Means for imaging a moving imaging target in the imaging region, wherein the selective excitation gradient magnetic field and the inversion pulse are applied a plurality of times by changing the spatial position of the partial region. And a means for executing the pulse sequence after the elapse of the predetermined time for each application. And it features.

Specific configurations and features according to other aspects of the present invention will become apparent from the following embodiments of the present invention and the accompanying drawings.

[0034]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) An MRI (magnetic resonance imaging) apparatus according to a first embodiment will be described with reference to FIGS.

This MRI apparatus is characterized in that a pseudo dynamic image representing, for example, the dynamics of a blood flow as a moving object in a subject is displayed as a cine mode image without using a contrast agent. It has a function of executing contrast MR angiography (MRA). This non-contrast M
A pulse sequence for performing RA uses a harmonic inversion recovery (IR) pulse of selective excitation.

FIG. 1 shows a schematic configuration of the MRI apparatus.
This device configuration can be commonly used in each embodiment described later.

This MRI apparatus uses a patient P as a subject.
Bed, a static magnetic field generator for generating a static magnetic field, a gradient magnetic field generator for adding positional information to the static magnetic field, a transmitter / receiver for transmitting and receiving high-frequency signals, control of the entire system and image reconstruction A control / arithmetic unit responsible for
The apparatus includes an electrocardiogram measurement unit that measures an ECG signal as a signal representing a cardiac phase of the subject P, and a breath-holding command unit that commands the patient P to hold his / her breath.

The static magnetic field generating section includes, for example, a superconducting magnet 1 and a static magnetic field power supply 2 for supplying a current to the magnet 1, and has a cylindrical opening (diagnostic space) into which the subject P is loosely inserted. the axial direction (Z axis direction) to generate a static magnetic field H _0. Note that a shim coil 14 is provided in this magnet portion. The shim coil 14 is supplied with a current for homogenizing a static magnetic field from a shim coil power supply 15 under the control of a host computer described later. The couch part can retreatably insert the top plate on which the subject P is placed into the opening of the magnet 1.

The gradient magnetic field generator has a gradient coil unit 3 incorporated in the magnet 1. The gradient magnetic field coil unit 3 includes three sets (types) of x, y, and z for generating gradient magnetic fields in X, Y, and Z axis directions orthogonal to each other.
The coils 3x to 3z are provided. The gradient magnetic field section also has x,
A gradient magnetic field power supply 4 for supplying a current to the y, z coils 3x to 3z is provided. The gradient magnetic field power supply 4 supplies a pulse current for generating a gradient magnetic field to the x, y, and z coils 3x to 3z under the control of a sequencer 5 described later.

An x, y, z coil 3x from the gradient magnetic field power supply 4
By controlling the pulse current supplied to ~ 3z,
The gradient magnetic fields in the three axes X, Y, and Z directions, which are physical axes, are synthesized, and the respective logics of a slice-direction gradient magnetic field Gs, a phase encoding direction gradient magnetic field Ge, and a readout direction (frequency encoding direction) gradient magnetic field Gr that are orthogonal to each other. The axial direction can be set and changed arbitrarily. Slice direction, phase encoding direction, and gradient magnetic fields in the readout direction are superimposed on the static magnetic field H _0.

The transmitting / receiving section includes an RF coil 7 disposed near the subject P in the imaging space in the magnet 1,
And a transmitter 8T and a receiver 8R, which are connected to each other. The transmitter 8T and the receiver 8R are connected to a sequencer 5 described later.
It operates under the control of. The transmitter 8T supplies the RF coil 7 with an RF current pulse having a Larmor frequency for causing nuclear magnetic resonance (NMR). The receiver 8R has R
The echo signal (high-frequency signal) received by the F coil 7 is fetched, subjected to various signal processing such as preamplification, intermediate frequency conversion, phase detection, low frequency amplification, and filtering, and then A / D converted. A digital amount of echo data (original data) corresponding to the echo signal is generated.

The control / arithmetic unit includes a sequencer (also called a sequence controller) 5, a host computer 6, an arithmetic unit 10, a storage unit 11, and a display unit 1.
2, an input device 13 and a sound generator 16. Among them, the host computer 6 has a function of instructing the sequencer 5 with pulse sequence information and controlling the operation of the entire apparatus by the stored software procedure.

The host computer 6 performs an imaging scan based on the pulse sequence shown in FIG. 2, following a preparation operation such as a positioning scan. This imaging scan is a scan for collecting a set of echo data necessary for image reconstruction, and is set to a two-dimensional scan here. Imaging scan is EC
This is performed using the ECG gate method based on the G signal. The ECG gate method may not be used in some cases.

The pulse sequence is a three-dimensional (3D) scan or a two-dimensional (2D) scan. As the form of the pulse train, there are an SE (spin echo) method, an FSE (fast SE) method, and a FASE (fast As)
ymmetric SE) method (that is, an imaging method in which the half Fourier method is combined with the fast SE method), E
A PI (echo planar imaging) method or the like is used.

The sequencer 5 has a CPU and a memory, stores pulse sequence information sent from the host computer 6, and controls the operations of the gradient magnetic field power supply 4, the transmitter 8T, and the receiver 8R according to the information. And simultaneously input the echo data output by the receiver 8R,
This is configured to be transferred to the arithmetic unit 10. Here, the pulse sequence information is all information necessary to operate the gradient magnetic field power supply 4, the transmitter 8T, and the receiver 8R in accordance with a series of pulse sequences, for example, x, y, z coils 3x to 3z. And information on the intensity of the pulse current to be applied to the device, the application time, the application timing, and the like.

The arithmetic unit 10 receives the echo data (original data or raw data) output from the receiver 8R through the sequencer 5 and echoes the echo data to a Fourier space (also called k-space or frequency space) on its internal memory. The data is arranged, and this echo data is subjected to two-dimensional or three-dimensional Fourier transform for each group to reconstruct image data in a real space. Further, the arithmetic unit can perform a process of synthesizing data relating to the image, a difference operation process, and the like as necessary.

In the synthesizing process, an adding process of adding image data of a plurality of two-dimensional frames for each corresponding pixel, 3
Maximum value projection (MIP) or minimum value (MIP) projection processing for selecting the maximum value or the minimum value in the line-of-sight direction for the dimensional data is included. Further, as another example of the combining process, the axes of a plurality of frames may be matched in Fourier space, and the echo data may be combined with the echo data of one frame as it is. Note that the addition processing includes simple addition processing, averaging processing, weighted addition processing, and the like.

The storage unit 11 can store not only the reconstructed image data but also the image data on which the above-described synthesizing processing and differential processing have been performed. The display 12 displays an image. In addition, the operator can input, to the host computer 6, imaging conditions desired by the operator, pulse sequences, and information regarding image synthesis and difference calculation.

A voice generator 16 is provided as an element of the breath-hold command section. The voice generator 16 can emit a breath-hold start and a breath-hold end message as voice when instructed by the host computer 6.

Further, the electrocardiogram measuring section comprises an ECG sensor 17 which is attached to the body surface of the subject and detects an ECG signal as an electric signal. 6 and an ECG unit 18 for outputting to the sequencer 5. The measurement signal from the electrocardiograph is used by the sequencer 5 when performing an imaging scan. This gives E
Synchronization timing by the CG gate method (cardiac synchronization method) can be set appropriately, and data can be collected by performing an imaging scan of the ECG gate method based on the synchronization timing.

Next, the operation of the MRI apparatus according to this embodiment will be described with reference to FIGS.

FIG. 2 shows a pulse sequence used in non-contrast MR angiography according to the present embodiment, and FIG. 3 shows a process for explaining a process from scanning to generation of a display image. In order to facilitate understanding, non-contrast MR angiography performed in this embodiment involves performing three two-dimensional scans to obtain three continuous final images and displaying them in a cine form. And

In an actual image, a pixel having a lower signal value is displayed darker, but in FIGS. 2B to 2D, a portion which is rendered as a high signal is represented by darker hatching, and a region in which a low signal is rendered is represented. It shall be represented by a thin housing.

First, the pulse sequence will be described. FIG.
The pulse sequences shown in (a) to (c) are pulse trains based on the above-described method of FIG. 15 in which two inversion pulses are applied during a very short time (2 to 10 ms). More specifically, the first inversion pulse P _inv-A includes an area CS to be imaged (see FIG. 3A) in synchronization with the R wave of the ECG signal (the delay time for the R wave is arbitrary). It is applied non-selectively.

Thereafter, when viewed from the blood flow velocity, a second inversion pulse P _inv-B is applied together with the selective excitation gradient magnetic field Ge after a very short period of time, which can be regarded as simultaneous. Is done. After this, when a predetermined TI time (for example, 600 ms) elapses,
For example, an imaging scan based on a pulse sequence based on the FSE method is performed on the imaging region CS.

Each of the pulse sequences shown in FIGS. 2A to 2C corresponds to the second inversion pulse P _inv-B
To depend selective excitation position, namely that it is configured to change the spatial position of the tag area RG A _(spin inversion region) are different from each other with respect to the imaging region CS. Specifically, the offset amount Df of the carrier frequency of the inversion pulse P _inv-B is changed from each other.

Therefore, the second inversion pulse P
_inv-B by selectively excited the tag area RG _A
(: RG _{A1 to} RG _A3 ) are first adjusted by adjusting the selective excitation gradient magnetic field Ge and the frequency offset amount Df in the patient (subject) to be imaged as indicated by the dotted line in the left column of FIG. Is set at an upstream portion of the blood BD flowing into a region CS (for example, a cross section) to be imaged.

[0059] During imaging, the host computer 6 sends the pulse sequence information includes information for setting the position of such tag area RG _A sequencer 5. In response, sequencer 5
Drives the gradient power supply 4 and the transmitter 8T according to the given pulse sequence information. This allows
The pulses constituting the pulse train of the pulse sequence of FIG. 2A are applied in a time series.

[0060] Thus, as described in FIG. 15 described above, the spin of the entire imaging region CS by the initial inversion pulse _{P i nv-A} 180 degrees it is reversed. But then the immediately second inversion pulse P _inv-B to be applied, only spins in the selected tag area RG _A is again rotated 180 degrees (tagging), returned to substantially the initial state (FIG. 15 (B)). Based on the return of the flip angle of the spin, that is, tagging, as schematically shown in FIG. 15C described above, the blood of the portion excited by both the inversion pulses P _inv-A and P _inv-B is obtained. The echo signal is generated with the highest intensity.

The whole echo signal including the echo signal from the blood is received by the receiver 8 R via the RF coil 7 and sent to the arithmetic unit 10 via the sequencer 5 as echo data.

The arithmetic unit 10 performs appropriate processing on the echo data and arranges the echo data in a two-dimensional k-space. When the entire k space is filled with the echo data, the arithmetic unit 10
Performs a two-dimensional Fourier transform of the echo data, and FIG.
(B) Two-dimensional reconstructed image IM as shown in the left column
_Rec1 is obtained.

[0063] As can be seen from the reconstructed image _{IM rec1,} blood BD that were in the tag area RG _A when applying a second inversion pulse _{P inv-B} is reversed magnetization spin almost initial state It has been
After the second inversion pulse P _inv-B is applied on the imaging region CS, a portion of the signal that has flowed out of the tag region until the application of the imaging pulse sequence P _seq is partially drawn as a high signal. You. Also, among the tag area RG _A, part of the free tissue motion as a background, since almost become a spin in the initial state by receiving a second inversion pulse P _inv-B, the first inversion pulse P _{The image} is drawn with a contrast different from that of a portion having no motion where only _inv-A is applied.

When this reconstruction is completed, the operation unit 10
As a result, the masking process is performed on a portion having a different contrast in the reconstructed image IM _rec1 . In the figure, the cross-hatched portion MG ₁ shows the masking area. The masking process is a process of rewriting a certain range of image values on an image to a certain pixel value. By the masking process, the intermediate image I represented as shown in the left column of FIG.
M _int1 is obtained.

The second and third scans are performed in the same manner as the first scan described above. Then, the echo signals obtained by these scans are processed in the same manner, and as shown in the middle column and right column of FIG. _3C, intermediate images IM _int2 and IM _int3 that have been subjected to the masking process are obtained.

However, in the case of the second and third scans, the application position of the inversion pulse P _inv-B selectively applied at the second time is shown in the middle column of FIGS. 3 (a) to 3 (c). As shown in the right column, the offset amount of the carrier frequency (high frequency) of the selective excitation gradient magnetic field Ge and the inversion pulse P _inv-B is changed so as to move the blood little by little along the blood flow direction. A pulse sequence is executed.

The timing of the process of generating an intermediate image by image reconstruction and masking performed in the arithmetic unit 10 may be arbitrary.

Thus, the intermediate image IM _int1 , I
When M _int2 and IM _int3 are obtained, the arithmetic unit 1
0 performs the maximum value projection process by appropriately combining the images, and outputs a plurality of final images IM _fin1 and I _fin1
M _fin2 and IM _fin3 are generated. At the time of this maximum intensity projection processing, for the first intermediate image IM _int1 ,
1st final image IM without masking area
_fin1 , and the first and second intermediate images IM _int1 and IM _int2 are compared with each other by comparing corresponding two pixels between the images, and the larger one is taken to obtain the second final image IM _fin2 Is generated, and the first, second, and third intermediate images IM _{i
Regarding nt1} , IM _int2 , and IM _int3 , a third collected image IM _fin3 is generated by comparing their corresponding three pixels with each other and taking the maximum value.

The three final images IM _fin1 , IM
_{The fin2} and the IM _fin3 are continuously displayed on the display unit 12 in a cine mode in a moving image. Thereby, the inflow state (dynamics) of the blood flowing into the region of interest can be dynamically observed and grasped.

In particular, the same dynamic observation can be performed even when the dynamics of blood is shorter in time. In this case, the total scan time becomes longer, to reduce the amount of movement of the spatial position of the tag area RG _A for applying the inversion pulse P _inv-B, may be collected more images. Furthermore, if it is desired to further improve the spatial resolution of each image, without changing the spatial position of the tag area RG _A for applying the inversion pulse P _inv-B, it may be scanned repeatedly. Thereby, an image having a large number of matrices, that is, an image having a high spatial resolution can be obtained. Further, when an image having a high S / N is desired, similarly,
Scanning may be repeated without changing the spatial position to which the inversion pulse P _inv-B is applied, and scanning with a large number of additions may be performed.

That is, in the case of the above-mentioned conventional CE-DMRA (see FIG. 12), since the time during which a signal change occurs in the region of interest due to the contrast agent is constant, the imaging conditions such as the number of scan repetitions must be changed. Although there is a problem that the time resolution is reduced when the change is made, according to the present embodiment, the inversion excitation by the inversion pulse can be repeatedly executed, so that there is no restriction as in the related art. Therefore, the spatial resolution and the temporal resolution can be freely changed within the allowable time, and both can be improved.

This embodiment can be variously modified as follows.

For example, as another example of the above-described dynamic display method, three final images IM _fin1 ,
IM _fin2 and IM _fin3 may be simply displayed at the same time, and the image _reader may visually compare the images with each other. This allows visual observation of hemodynamics.

In this embodiment, an MR for imaging blood is used.
Although A has been described, other moving objects such as CSF can be imaged in the same manner as the imaging target. In the case of this CSF, the time width from the application of the inversion pulse to the imaging scan may be appropriately changed.

In the pulse sequence shown in FIG. 2, if necessary, the second inversion pulse P
_{Between the inv-B} and the imaging scan P _seq , a fat suppression pulse for suppressing a signal from fat present in a section to be imaged may be applied.

Further, in the present embodiment, the embodiment based on the method using two inversion pulses in the same manner as the above-described method of FIG. 15 has been described. Instead, as shown in FIG. The above embodiment may be performed based on a technique using only one inversion pulse. In the post-processing in this case, a minimum value projection process may be performed instead of the above-described maximum value Toei process.

The pulse sequence that can be used in the present embodiment is not limited to the example using the FSE method as described above, and employs various methods such as the FE method, the segmented FE method, the SE method, and the echo planar method. it can. Further, the data acquisition and the image reconstruction are not limited to the two-dimensional scan and the two-dimensional reconstruction described above, but may be performed in three dimensions.

[0078] Further, in the embodiment described above has been to generate a final image _IM fin1 _{to IM FIN3} by performing maximum value projection processing from the intermediate image _IM int1 _{to IM int3,} which will can be various modifications is there.
For example, the dynamics of the blood flow can be observed even if only a plurality of intermediate images are sequentially displayed in the cine mode without executing the maximum intensity projection processing. Further, a masking process for creating an intermediate image may be omitted.

(Second Embodiment) An MRI apparatus according to a second embodiment will be described with reference to FIGS. In the following embodiments, the same or equivalent components as those in the above-described first embodiment are denoted by the same reference numerals, and description thereof will be omitted or simplified.

The MRI apparatus of this embodiment is the same as that of FIG.
The MRA based on the method described in 5 is performed.
In particular, the method is characterized in that a blood vessel image or a cine image representing blood flow dynamics in a wider range than the distance traveled by blood within a period from application of an inversion pulse to scanning, that is, a time period until a scan for imaging is performed, is acquired. Having.

The hardware configuration of this MRI apparatus is the same as that of the first embodiment.

FIG. 4 shows a pulse sequence used in non-contrast MR angiography imaging according to this embodiment.
FIG. 2 shows a diagram for explaining a process from scanning to generation of a display image. In the non-contrast MR angiography performed in this embodiment, three two-dimensional scans are performed to obtain a single wide area final blood vessel image.

In FIGS. 5B to 5D, the magnitude of the pixel value is represented by the density of the hatching, and the higher the signal is, the darker the hatching is.

First, the pulse sequence will be described. FIG.
In the pulse sequences shown in (a) to (c), four inversion pulses are applied at very short time intervals (2 to 10 ms). Specifically, in synchronization with the R wave of the ECG signal (the delay time with respect to the R wave is arbitrary), the region CS where the first inversion pulse P _inv-A is to be imaged (FIG. 5)
(See (a)). Thereafter, at very short time intervals, the second to fourth inversion pulses P _{inv-B to} P _inv-D can be regarded as simultaneous when viewed from the blood flow velocity,
It is applied together with the selective excitation gradient magnetic field Ge. Applied position of the inversion pulse _{P inv-B ~P inv- D,} as shown in FIGS. 5 (a) the left column, as arranged at regular intervals from the upstream portion of the blood flowing into the imaging region CS in the downstream direction In addition, an offset amount Df of the frequency of the selective excitation gradient magnetic field Ge and those pulses is set. Unlike the first embodiment, the spatial interval between the tag regions in the blood flow traveling direction is slightly longer than the distance traveled by the blood from the application of the inversion pulse to the start of the scan. It is set to be. Since the time interval between inversion pulses is very short, these four inversion pulses can be regarded as simultaneous from the viewpoint of blood flow.

After the application of a series of inversion pulses, when a predetermined time TI (for example, 600 ms) elapses, an imaging scan based on a pulse sequence based on, for example, the FSE method is executed on the imaging region CS. .

In each of the pulse sequences shown in FIGS. 4A to 4C, the frequency offset amount Df is adjusted for each sequence. Thus, three selective excitation position due to to 4 th second inversion pulse _{P inv-B ~P inv-D} , i.e. the spatial location of the tag area _RG A _{~RG C} with respect to the imaging region CS is 5 ( a) ~
As shown in the left column, the middle column, and the right column of FIG.

When the imaging is started, the pulse sequence shown in FIG. 4A is executed by the sequencer 5 according to the given pulse sequence information, as in the first embodiment. As a result, as described above, the echo signal of the blood excited by any one of the first inversion pulse P _inv-A and the second to fourth inversion pulses P _{inv-B to} P _inv-D is _reduced to one. In turn, it occurs with high strength. This echo signal is sent to the arithmetic unit 10 as echo data. The arithmetic unit 10 subjects the echo data to appropriate processing, arranges the echo data in a two-dimensional k-space, and performs a two-dimensional Fourier transform on the data. As a result, FIG.
(B) Two-dimensional reconstructed image IM as shown in the left column
_Rec1 is obtained.

This reconstructed image IM_rec1You can see from
Sea urchin 2nd to 4th inversion pulse P
_inv-B~ P_inv-DIs applied to the tag region R
G_A~ RG _CThe blood BD that was inside has its magnetization spin
Since it is almost returned to the initial state,
In the second to fourth inversion pulse P
_{inv -B}~ P_inv-DAfter applying
Pulse sequence P_seqT before applying
Signal is partially drawn to a high signal
You. Also, the tag area RG_A~ RG_COut of the background movement
The part of the organization without the mark is the second to fourth inversion
Pulse P_inv-B~ P_inv-DAlmost any
Because the spin is in the initial state, the first invar
John pulse P_{in vA}No movement just by applying
The image is rendered with a different contrast from the uncolored part.

When this reconstruction is completed, the operation unit 10
As a result, the masking process is performed on a portion having a different contrast in the reconstructed image IM _rec1 . In the figure, the cross-hatched portion _MG 11 _{~MG 21} denotes a masking area. By this masking process, FIG.
(C) An intermediate image IM _int1 represented as shown in the left column is obtained.

The second and third scans are performed in the same manner as the first scan described above. Then, the echo signals obtained by these scans are processed in the same manner, and as shown in the middle column and the right column of FIG. _5C, intermediate images IM _int2 and IM _int3 subjected to the masking process are obtained.

However, the second and third scans
In the case of (2), the
Version pulse P_inv-B~ P_inv-DApplication position
Are blood as shown in the middle and right columns of FIGS.
Move it little by little along the liquid flow direction
In addition, the selective excitation gradient magnetic field Ge and the inversion pulse P
_inv-B~ P_inv-DFrequency offset amount Df
The pulse sequence described above is changed.

The timing of the process of generating an intermediate image by image reconstruction and masking performed in the arithmetic unit 10 may be arbitrary.

The intermediate image I thus obtained
M _int1 , IM _int2 , and IM _int3 are subjected to maximum value projection processing by the arithmetic unit 10 to generate one final image IM _fin . This final image IM _fin
Is displayed by the display unit 12. Thereby, the inflow state (dynamics) of the blood flowing into the region of interest can be observed.

[0094] Thus, in each round of scanning a plurality of times, and detects the moving amount of the second to fourth th inversion pulse blood lies at a plurality of tag area RG _A ~RG _C upon application of the same time, A blood vessel image can be obtained over a wider range than the distance that the blood flow moves between the application of the inversion pulse and the scan. As a result, conditions such as the number of tag regions to be set in one scan (that is, the number of applied inversions after the second scan), the width thereof (selective excitation width), and the number of scans as a whole are appropriately selected. Thus, even when the blood flow velocity is low, a fine blood vessel image can be provided with a small number of scans over a wide area covering the entire travel path of the blood flow.

This embodiment can be modified as follows.

From the plurality of intermediate images IMint1 to IMint3 obtained in the above embodiment, the remaining images R1 to R9 that have not been subjected to the masking process may be cut out and displayed, for example, in this order.

Further, as shown in FIG.
While increasing the number of original images (here, intermediate images) to be subjected to the maximum value projection processing, a plurality of maximum value projection images may be created and displayed in an appropriate order. Thereby, a dynamic image of the blood flow dynamics can be provided in a pseudo manner, and the behavior of the blood flow can be easily grasped.

Further, in the present embodiment, M is used to image blood.
Although RA has been described, other moving objects, such as CSF, can be similarly imaged as imaging targets. In the case of this CSF, the time width from the application of the inversion pulse to the imaging scan may be appropriately changed.

In the pulse sequence shown in FIG. 4, if necessary, the fourth inversion pulse P
_A fat suppression pulse may be applied between _inv-D and the imaging scan _Pseq .

Further, in the present embodiment, the embodiment based on the method shown in FIG. 15 has been described. Alternatively, the above-described embodiment may be performed based on the method shown in FIG. In this case, a minimum value projection process may be performed instead of the maximum value Toei process described above.

On the other hand, in the present embodiment, the pulse sequence for imaging uses the FE method, the segmented FE method,
Various methods such as the SE method and the echo planar method can be adopted. Further, data collection and image reconstruction may be performed in three dimensions.

(Third Embodiment) Next, a third embodiment of the present invention will be described with reference to FIGS. The MRI apparatus according to this embodiment is characterized by a function of displaying a blood vessel image that separately represents a flow direction.

FIG. 6 shows a pulse sequence used in this MRA, FIG. 7 shows a method for drawing a blood flow (for example, vein BD _V ) flowing above the paper surface, and FIG. 8 shows a blood flow flowing below the paper surface. Each of the techniques for drawing an artery (for example, artery BD _A ) will be described.

[0104] The pulse sequence shown in FIG. 6, except for setting the frequency offset amount Df of inversion pulse P _{i nv-B} to be applied to the second time, is set in the same manner as in FIG. 2 described above. That is, the offset amount Df of the second inversion pulse P _inv-B applied in a total of three scans as an example is set to a predetermined value of + polarity, zero, and a predetermined value of-polarity. Accordingly, the spatial positions of the tag regions RG _{A1 to} RG _A3 selectively excited by the three scans are shown in FIG.
As shown in FIG. 8 (a), they are symmetrically located in the upper, middle, and lower predetermined portions of the imaging area CS in the blood flow direction, and are set to be separated from each other by a predetermined distance.

Now, as shown in FIGS. 7 and 8, an MR image obtained by separating the artery and vein of an imaging site CS including two blood vessels flowing in opposite directions in the vertical direction one by one on the left and right is assumed. I do.

[0106] First, based on FIGS explaining a case of imaging a vein BD _V. The pulse sequences shown in FIGS. 6A to 6C are respectively executed. As a result, as shown in the left column, the center column, and the right of FIG. _7A , the selective excitation based on the second inversion pulse P _{inv- B} causes the symmetrical positions to be separated by an equal distance in the blood flow traveling direction. The existing tag regions RG _{A1 to} RG _A3 are excited (tagged), and echo signals reflecting the selected excitation are collected.

The echo signal is processed into a digital amount of echo data and reconstructed by the arithmetic unit 10 as described above. This reconstructed image is represented by an image I in FIG.
M _{r ec1,} shown as _{IM rec2, IM rec3.}

This reconstructed image IM _rec1 , IM
_rec2, as can be seen from the _{IM rec3,} arterial BD _A and veins BD _V that was in tag area _{RG A} 1 _{~RG A3} when applying a second inversion pulse _{P inv-B} is the magnetic spins most since it was returned to the initial state, on the imaging area CS, after applying a second inversion pulse P _inv-B, from the tag area until applying a pulse sequence P _{s eq} for imaging The amount that has flowed out (signs A1 to A3 and V1
... V3) is partially rendered as a high signal. At this time, the distance flowing out differs depending on the flow velocity of the artery and the vein.

In the tag regions RG _{A1 to} RG _A3 , the portion of the tissue with no background movement has been almost in the initial state of spins after receiving the second inversion pulse P _inv-B, and therefore has a first spin. Inversion pulse P
_{The image} is drawn with a contrast different from that of a portion having no motion where only _inv-A is applied.

When this reconstruction is completed, the operation unit 10
Thus, the reconstructed images IM _rec1 , IM _rec2 , IM
_A masking process is performed on a part of _rec3 in which the contrast of the background is different. That is, FIG.
As shown in the figure, a tag area RG _A1 that bisects the imaging area CS
~ RG _A3 , each tag region RG
The portions on the upstream side of the vein including _A1 (（RG _A3 ) are respectively masked. In the figure, a cross-hatched portion MG
_{1 to} MG ₃ indicate masking regions. By this masking process, intermediate images IM _{int1 to} IM _int3 shown in the left column, the center column, and the right column of FIG. _7C are obtained.

The thus obtained intermediate image I
M _int1 , IM _int2 , and IM _int3 are subjected to maximum intensity projection processing by the arithmetic unit 10 to generate one final image IM _{fin -V} as shown in FIG. 7D. This final image IM _fin-V is displayed on the display 12. Thereby, the vein BD _V flowing through the region of interest
Can be obtained.

On the other hand, the artery BD_AFig.
A description will be given based on FIGS. Also at this time, FIG.
Each of the pulse sequences shown in (c) is executed.
Thereby, the vein BD_VThe reconstructed image
IM_rec1, IM_rec2, IM _rec3Is obtained
(FIG. 8 (b)), followed by a masking process. This
The masking process in the case of
As shown in FIG. 8C, a tag area that bisects the imaging area CS
RG_A1~ RG_A3Each of these tags
Region RG_A1(~ RG_A3) Including the upstream part of the artery
Each is masked.

The intermediate image IM created by this
_{int1, IM int2, IM int3} is then subjected to the maximum value projection processing, it is possible to display the MRA image only arterial BD _A appeared.

As described above, according to the present embodiment, in the post-processing after the echo signal collection, the MRA in which the artery and vein are separated by a simple method only by changing the position of the masking processing is performed.
Images can be provided easily. Further, by using the MRA image, the traveling direction of the artery and vein can be simply checked.

In this embodiment, the remaining images R1, R2, R3 for the arteries and veins formed by masking are also provided.
May be displayed continuously in order, or the reconstructed image I
M _rec1 , IM _rec2 , and IM _rec3 may be sequentially displayed in order. Thereby, a pseudo dynamic image of an artery and a vein can be observed.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described with reference to FIGS. The MRI apparatus according to this embodiment sets the thickness (slice thickness or slab thickness) to be excited more selectively than inversion (IR) used in a pulse sequence when performing an imaging scan (main scan) to an optimum value. Scan (pre-scan).

4 and 5 according to the second embodiment described above.
Alternatively, when the MR angiography according to FIGS. 14 and 14 described above is performed, the inflow velocity of the blood flow changes depending on the cross section to be imaged and the blood vessel whose dynamics are to be observed.
When the distance of the part where the signal is increased by the inversion pulse is short, or on the contrary, it is too long and the high signal part remains in the tag area excited by another inversion, which is not suitable for image synthesis or cine image display It is possible. In the present embodiment, a pre-scan method that can surely eliminate such a situation is taught.

In this prescan, scanning is performed continuously while changing the excitation thickness by the inversion pulse stepwise, and the optimum excitation thickness and excitation position are obtained.

FIG. 9 shows an example of a pulse sequence used for the prescan, and FIG. 10 schematically shows the procedure of the prescan.

FIGS. 9A to 9C show the first to third times.
Pulse sequences used for three scans in
Is represented. In these pulse sequences,
Every inversion, the second inversion pulse P
_inv-BCarrier frequency offset amount Df and selective excitation
At least one of the strengths of the gradient magnetic field Ge is adjusted.
ing. As a result, the left column, the center column, and the left column in FIG.
As shown in the right column and the area CS to be imaged
Tag area RG_A(RG_A1~ RG_A3) The thickness gradually
As it gets thicker, in any of the first to third scans
Even if there is a belt-like tag region RG_A1~ RG_A3Under the bloodstream
The position is selected so that the boundary position on the downstream side is the same.
You. In other words, as the number of scans increases, the tag area
RG_A1~ RG _A3Only the boundary position on the upstream side of blood flow
The excitation position is set so that is changed and becomes thicker.
In the pulse sequences shown in FIGS.
The other pulse trains are the same as described above.

Conditions such as the number of scans in the pre-scan and the fluctuation range of the boundary position on the upstream side of the blood flow are as follows.
The determination is made in consideration of conditions including the blood flow velocity of the imaging site and the desired value of the change width.

By sequentially executing these pulse sequences as a pre-scan, the pulse sequence shown in FIGS.
As shown in (c), the reconstructed image IM for each sequence
_{rec1 to} IM _rec3 are obtained.

[0123] Therefore, for example, the operator, the series of image _IM rec1 _{to IM rec3} by visual observation, seems to be ideal for imaging sites of interest, determines the excitation thickness and spatial position by inversion pulse . At this time, in order to facilitate such a determination, a series of images IM _rec1 to IM _rec1 to
IM _rec3 may be displayed continuously in the order of the thickness of the tag area. Note that the above-described determination may be automatically performed using an appropriate algorithm such as a method for extracting blood flow activity, in addition to a method based on artificial judgment by an operator.

The information of the excitation thickness and the spatial position obtained by the above pre-scan is based on the second inversion pulse P applied in the pulse sequence of the main scan.
carrier frequency and _{in v-B} which to be reflected in the example the intensity of the selective excitation gradient magnetic field applied at the same time. As a result,
In the MRA image obtained by the main scan, the relationship between the imaging length of the blood flow portion tagged with the inversion pulse P _inv-B and the blood flow velocity becomes appropriate, and accurate image synthesis and cine image display are performed. Can be.

Although the above embodiment has described MRA for imaging blood, other moving objects, such as CSF, can be similarly imaged as imaging targets. In the case of this CSF, the time width from the application of the tagging inversion pulse to the imaging scan may be appropriately changed.

In the pulse sequence shown in FIG. 9, if necessary, the second inversion pulse P
_A fat suppression pulse may be applied between _inv-B and the imaging scan _Pseq .

Further, in the present embodiment, the embodiment based on the method shown in FIG. 15 has been described. Alternatively, the above embodiment may be performed based on the method shown in FIG. In this case, the minimum value projection processing may be performed as post-processing instead of the maximum value Toei processing described above.

On the other hand, in the present embodiment, the imaging pulse sequence is not limited to the FSE method, but may employ various methods such as the FE method, the segmented FE method, the SE method, and the echo planar method. Further, data collection and image reconstruction may be performed in three dimensions.

(Fifth Embodiment) An MRI apparatus according to a fifth embodiment of the present invention will be described. This embodiment relates to another example of a tagging region based on selective excitation.

FIG. 11A shows an example of a pulse sequence used in this MRI apparatus, and FIG.
4 shows an example of a reconstructed image.

According to this pulse sequence, the inversion pulse uses only one pulse P _{in v-O} . The carrier frequency of this pulse and the selective excitation gradient magnetic field Ge
, The region RG _A excited by an inversion pulse _{P inv-O} is as shown in FIG. 11 (b), it is set to be the same as the area CS for capturing. In other words, the inversion pulse P _inv-O has a function of tagging by inverting the spin by 180 degrees, but this tagging adds a contrast to a high signal due to a new blood flow flowing in at the time of scanning. comprising the spin region RG _a reversed tagging function for low signaling. FIG. 11 (a)
As shown in (2), as the inversion pulse, only the tagging pulse P _inv-O alone is applied. Other pulse trains are the same as those in the above-described embodiments.

The pulse sequence is executed to collect an echo signal, and a reconstructed image IM _rec exemplified in FIG. 11B is obtained from the echo signal.

Therefore, the inversion pulse P
The _inv-O is the same area RG _A the imaging region CS is reversed tagged, then after the inversion time TI, scan is performed.

For this reason, at the time of scanning, for example, the artery BD _A and the vein BD _V flow from the region not selectively excited by the inversion pulse P _inv-O into the imaging region CS as an unsaturated spin. Therefore, high signals can be obtained from the artery BD _A and the vein BD _V , and they can be reliably drawn.

In particular, since there is a speed difference in the flow velocity in arteries and veins, the length of the portion flowing into the imaging area CS during scanning is usually different. For this reason, an image displaying only the artery BD _A is presented by, for example, setting to selectively excite an area that has entered the vein upstream from the imaging area CS by the inflow length L of the vein BD _V. Can be.

As a modified example common to all the embodiments described above, there is a synchronous method. That is, although the above embodiments have described the MR imaging based on the electrocardiographic synchronization method, an electroencephalogram synchronization method, a respiration synchronization method, or the like may be used instead of the synchronization method. Further, even with the same electrocardiographic synchronization method, a pulse wave synchronization method (PPG) can be used.

Further, in each of the above-described embodiments, the technique of displaying the dynamics of blood and CSF by changing the excitation position by the inversion pulse for tagging has been taught, but from the generation of the trigger used in the synchronous method. Scanning may be performed while appropriately changing the time width (delay time) until the application of a series of inversion pulses.
By displaying the images obtained in this manner in an appropriate order, or by creating and displaying a plurality of maximum intensity projection images, it is possible to observe the periodic movement of the imaging target synchronized with the heartbeat and respiration.

Further, each of the above embodiments can be developed in various forms. First, the transposition of the blood flow portion that is imaged with the application of the tagging inversion pulse varies depending on the flow velocity of the blood flow, so that the flow velocity of the blood flow can be measured based on this correspondence. .

Secondly, by appropriately changing the offset amount of the carrier frequency of the tagging inversion pulse and the intensity of the selective excitation gradient magnetic field, the tag region can be set at any slice position (slab position) and slice thickness (slab thickness). ) Or at the oblique excitation position.

Third, by changing the slice thickness (slab thickness) by the tagging inversion pulse, a blood vessel having an arbitrary slice thickness (slab thickness) can be drawn.

Fourth, a preferred example of the flip angle of the tagging inversion pulse is 180 degrees, but the flip angle is not necessarily limited to this. This angle is 18
By setting the value to an appropriate value less than 0 degrees, it is possible to collect the signals in the signal-reduced area in a shorter TI time and shorten the entire scan time.

It should be noted that the present invention is not limited to the above-described exemplary embodiments and modifications, and those skilled in the art will not depart from the gist of the claims based on the contents of the claims. Modifications and changes can be made to various embodiments within the scope, and these also belong to the scope of the present invention.

[0143]

As described above, according to the MR imaging of the present invention, a problem has arisen in the conventional MRA.
Both time resolution and spatial resolution can be achieved, both can be maintained at a high level, and detailed information on the dynamics of fluids such as blood and CSF can be obtained.

Furthermore, the MR imaging technique of the present invention eliminates the necessity of administering a contrast agent, which is essential in conventional CE-DMRA, so that it is non-invasive,
The physical burden can be significantly reduced. In addition, there is no need for troublesomeness in recognizing the imaging timing such as when a contrast agent is administered, and preparation and labor for examination are greatly reduced. Moreover, since no contrast agent is used, it is possible to easily cope with the re-examination.

Further, according to the MR imaging method of the present invention, the position of the region to be tagged with the inversion pulse can be freely set, so that the inspection can be performed with a limited inflow blood vessel, and the accuracy and reliability can be improved. High inspection becomes possible.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an MRI apparatus according to an embodiment of the present invention.

FIG. 2 is a pulse sequence used in the first embodiment, which includes one tag inversion pulse.

FIG. 3 is a diagram illustrating a positional relationship between an imaging region and a tag region and a procedure for generating an MRA image according to the first embodiment.

FIG. 4 shows a pulse sequence having a plurality of tag inversion pulses used in the second embodiment.

FIG. 5 is a view for explaining a positional relationship between an imaging region and a tag region and a procedure for generating an MRA image in the second embodiment.

FIG. 6 shows a pulse sequence used in the third embodiment.

FIG. 7 relates to arteriovenous separation in the third embodiment.
FIG. 4 is a diagram for explaining a positional relationship between an imaging region and a tag region and a procedure for generating an MRA image.

FIG. 8 relates to arteriovenous separation in the third embodiment.
FIG. 4 is a diagram for explaining a positional relationship between an imaging region and a tag region and a procedure for generating an MRA image.

FIG. 9 is a pulse sequence including one tag inversion pulse used in prescan according to the fourth embodiment.

FIG. 10 is a view for explaining a positional relationship between an imaging region and a tag region and a procedure for generating an MRA image in a pudding scan according to the fourth embodiment.

FIG. 11 is a view showing a pulse sequence and an image example according to a fifth embodiment.

FIG. 12 is a view for explaining CE-DMRA as a conventional technique.

FIG. 13 is a diagram illustrating a pulse sequence used for CE-DMRA.

FIG. 14 is a diagram illustrating an example of a conventional MRA together with a pulse sequence.

FIG. 15 is a view for explaining another example of the conventional MRA together with a pulse sequence.

[Explanation of symbols]

 Reference Signs List 1 magnet 2 static magnetic field power supply 3 gradient magnetic field coil unit 4 gradient magnetic field power supply 5 sequencer 6 host computer 7 RF coil 8T transmitter 8R receiver 10 arithmetic unit 11 storage unit 12 display 13 input unit

Claims (21)

[Claims] A process including applying a tagging inversion (IR) pulse together with a selective excitation gradient magnetic field to an imaging region of a subject to invert spin of at least a part of the imaging region; Thereafter, a pulse sequence is started after a lapse of a predetermined time to receive an echo signal of the spin, and a magnetic resonance imaging method for imaging a moving object in the imaging region from the echo signal. Magnetic field characterized by changing the spatial position of the region of the part and applying the selective excitation gradient magnetic field and the inversion pulse a plurality of times, each time applying the pulse sequence after the elapse of the certain time. Resonance imaging method. 2. The magnetic resonance imaging method according to claim 1, wherein the processing includes a step of first applying another inversion pulse to the entire imaging region and immediately applying the tagging inversion pulse. A magnetic resonance imaging method comprising: 3. The magnetic resonance imaging method according to claim 1, wherein a plurality of echo signals generated in response to the pulse sequence executed a plurality of times in response to a change in the spatial position of the partial region are obtained. A magnetic resonance imaging method for generating an image and displaying the images successively in a predetermined order. 4. The magnetic resonance imaging method according to claim 3, wherein the plurality of images are continuously displayed according to a change order of a spatial position of the partial area. 5. The magnetic resonance imaging method according to claim 1, wherein a plurality of echo signals generated in response to the pulse sequence executed a plurality of times in response to a change in the spatial position of the partial area are obtained. A magnetic resonance imaging method of generating a plurality of images, generating a plurality of projection images by projecting pixels of a fixed value from the plurality of images, and continuously displaying the plurality of projection images in a predetermined order. 6. The magnetic resonance imaging method according to claim 1, wherein a plurality of echo signals generated in response to the pulse sequence executed a plurality of times in accordance with a change in a spatial position of the partial region are obtained. Is generated, a position on the image corresponding to the partial area is obtained on the plurality of images, and a masking process is performed on the position, and a pixel having a fixed value is obtained from the plurality of images after the masking process. A magnetic resonance imaging method in which one or more projected images are created and displayed on the projected images. 7. The magnetic resonance imaging method according to claim 6, wherein a plurality of the projection images are created, and the plurality of projection images are sequentially displayed in a predetermined order. 8. The magnetic resonance imaging method according to claim 2, wherein the processing of projecting the pixel having the fixed value is a processing of projecting a maximum value or a minimum value of the pixel value. Imaging method. 9. The magnetic resonance imaging method according to claim 1, wherein a plurality of echo signals generated in response to the pulse sequence executed a plurality of times in response to a change in a spatial position of the partial region are obtained. A magnetic resonance imaging method of generating an image and continuously displaying only one of two divided regions by the partial region in each of the plurality of images. 10. The magnetic resonance imaging method according to claim 1, wherein a plurality of echo signals generated in response to the pulse sequence executed a plurality of times in accordance with a change in a spatial position of the partial region are obtained. A magnetic resonance imaging method for generating an image and performing a masking process on only one of two divided regions by the partial region in each of the plurality of images. 11. The magnetic resonance imaging method according to claim 10, wherein a plurality of images subjected to the masking processing are displayed continuously. 12. The magnetic resonance imaging method according to claim 10, wherein at least a part of each of the plurality of images subjected to the masking process is used to generate one or a plurality of projected images obtained by projecting pixels of a fixed value. A magnetic resonance imaging method for displaying a projection image. 13. The magnetic resonance imaging method according to claim 10, wherein the masking process is performed on a divided region on an upstream side in a direction of movement of the imaging target. 14. The magnetic resonance imaging method according to claim 1, wherein the tagging inversion pulse is applied continuously at every minute time that can be regarded as simultaneous as compared with the movement of the imaging target. A magnetic resonance imaging method comprising a plurality of inversion pulses, whereby a plurality of the at least some regions are set for each scan. 15. The magnetic resonance imaging method according to claim 14, wherein the application conditions of the plurality of inversion pulses and the selective excitation gradient magnetic field applied simultaneously with the plurality of inversion pulses are such that at least a part of the region is on the imaging region. A magnetic resonance imaging method which is arranged so as to be spatially arranged at regular intervals and to be shifted from each other at each scan. 16. A method of applying a gradient magnetic field and a pulse to an imaging region of a subject while changing conditions of a tagging inversion (IR) pulse together with a selective excitation gradient magnetic field to reduce a spin of a partial region of the imaging region. After that, after a certain period of time, a pulse sequence is started and a process of receiving the echo signal of the spin is repeated a plurality of times. A magnetic resonance imaging method including a pre-process for determining an optimum position and a size of the partial region from the display specifics of the imaging target on the plurality of images. 17. The magnetic resonance imaging method according to claim 16, wherein the previous step includes a process of displaying the plurality of images successively in the order of the size of the partial region to be changed. 18. An inversion (IR) pulse together with a selective excitation gradient magnetic field is applied to an imaging region of a subject to invert the spin of the entire imaging region. And receiving a spin echo signal, and imaging a moving imaging target in the imaging region from the echo signal. 19. A process including tagging for applying an inversion (IR) pulse together with a selective excitation gradient magnetic field to an imaging region of a subject to invert spin of at least a part of the imaging region, and performing the tagging. A magnetic resonance imaging method for detecting a change in an echo signal in the imaging region, and imaging a moving imaging target in the imaging region based on the signal change. 20. The magnetic resonance imaging method or the magnetic resonance imaging method according to claim 1, wherein the imaging target is a blood flow passing through the imaging region. Method. 21. A means for performing processing including tagging for applying a tagging inversion (IR) pulse together with a selective excitation gradient magnetic field to an imaging region of a subject to invert spin of at least a part of the imaging region. Means for starting a pulse sequence after a certain period of time has elapsed after the application of the tagging inversion pulse and receiving an echo signal of the spin, and an image of a moving imaging object in the imaging region from the echo signal. A magnetic resonance imaging apparatus comprising: means for changing a spatial position of the partial region to apply the selective excitation gradient magnetic field and the inversion pulse a plurality of times; Means for executing the pulse sequence after a lapse of time.