JP4594482B2 - Magnetic resonance imaging method and magnetic resonance imaging apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an imaging method for imaging a blood vessel image or CSF (cerebrospinal fluid) of a subject using an inversion (inversion recovery: IR) pulse for selective excitation of high frequency in medical magnetic resonance imaging, and in particular, contrast enhancement. The present invention relates to non-contrast-enhanced magnetic resonance imaging in which blood flow and CSF dynamics can be displayed in a pseudo manner as if a contrast agent was administered, although no agent was administered.
[0002]
[Prior art]
In magnetic resonance imaging, the nuclear spin of a subject placed in a static magnetic field is magnetically excited with a high-frequency signal of Larmor frequency, and an image is generated from an FID (free induction decay) signal or echo signal generated by this excitation. It is a technique to obtain.
[0003]
As one category of this magnetic resonance imaging, MR angiography (MRA) for imaging blood dynamics has attracted attention.
[0004]
In this MRA, in general, a contrast medium having the property of greatly changing the signal intensity in MRI is administered inside the blood vessel, scanning under the same conditions is continuously performed, and the movement of blood flow is imaged. MR angiography (hereinafter referred to as “CE-DMRA”) is employed (for example, “M. Prince, Radiology 1994; 191: 144-164”).
[0005]
  This CE-DMRA imaging procedure is conceptually shown in FIG. First, a contrast medium is injected into a vein, and scanning is continuously performed from the time when the contrast medium reaches a blood vessel in the imaging region. A curve CB in FIG. 5A shows a time change of the signal intensity at the position of one point in the imaging target. As shown in FIG. 6B, the arrival point of the contrast agent crosses the imaging region from the contrast agent injection time t0, and all blood vessels are drawn depending on the size of the region and the imaging region. Although it cannot be defined, it is about 30 seconds to 2 minutes. In FIG. 7B, periods PD1, PD2,... Represent first, second,. In the scan periods PD1, PD2,..., A desired, for example, three-dimensional pulse sequence is executed, and echo signals generated in response to the execution are collected. The echo signal is reconstructed for each scan and is conceptually shown in FIG.As shown inFor example, it is generated into three-dimensional image data D1, D2,. This image data D1, D2,... Is attached to, for example, a process of projecting the maximum value when viewed from a certain viewpoint (maximum value projection process), and is conceptually shown in FIG.As shown in, Maximum value projection images IMmax1, IMmax2,... Are processed and displayed.
[0006]
The scan method used in the CE-DMRA is a pulse sequence mainly based on the FE (field echo) method. An example of this is shown in FIG. As shown in the figure, the harmonic excitation pulse P_extIs slice selective excitation gradient magnetic field Gs_selApplied with the echo signal S_echoAre received together with the application of the read direction gradient magnetic field Gr. In the figure, gradient magnetic field Gs_rewIndicates a rewind gradient magnetic field in the slice direction. This series of excitation and acquisition is repeated a predetermined number of times for each repetition time TR until echo data necessary for image reconstruction is completed while changing, for example, the intensity of the phase encoding gradient magnetic field Ge. The repetition time TR is usually about 3-10 ms.
[0007]
Note that FIG. 13 illustrates the pulse sequence necessary for image reconstruction based on the two-dimensional Fourier method, but image reconstruction based on the three-dimensional Fourier method may be used depending on the imaging purpose. In that case, when a series of data is collected by changing the intensity of the phase encoding gradient magnetic field Ge by repeating each excitation, this time the rewind gradient magnetic field Gs in the slice direction is collected._rewVary the intensity. Then, the operation of collecting a series of data associated with the intensity change of the phase encoding gradient magnetic field Ge is performed again for the number of matrices in the slice direction. As a result, all data necessary for image reconstruction based on the three-dimensional Fourier method is collected.
[0008]
Thus, in CE-DMRA, the image D along the reconstructed time series₁, D₂, ..., or an image IM obtained by projecting the maximum value_max1, IM_max2,... Are displayed and observed in time series to grasp the dynamic behavior of the blood BD flowing through the blood vessel BV. This method can be applied to imaging of a moving object in the imaging target, for example, a CSF (cerebrospinal fluid) when the imaging target is a human body, and the behavior can be observed through similar processing. In addition, when CSF is taken as an imaging target, it is called hydrography.
[0009]
  On the other hand, a conventional method for labeling a spin that is locally moved by an inversion (IR) pulse and obtaining a blood vessel image without administration of a contrast agent is described in the paper “Considations of Magnetic Resonance by Selective Inversion Recovery”, DG Nishimura et al., Magnetic Resonance in Medicine, Vol. 7, 472-484, 1988 ". An outline of the angiography according to this conventional method is shown in FIG. FIG. 6A shows a pulse sequence when the ECG (electrocardiogram) synchronization method is used together, FIG. 6B shows a time change state of longitudinal magnetization of spins in each part to be imaged, and FIG.Section and labelingInversion pulse P for (tag)_inv-AExcited region RG_AThe positional relationship is shown.
[0010]
As shown in FIG. 5A, after an elapse of a certain time from the R wave of the ECG signal (however, shown immediately after the R wave in the same figure), the inversion pulse P having a flip angle of 180 degrees._inv-AIs applied. At this time, a region RG that seems to be an inflow source to the imaging section CS of the blood vessel of interest_AInversion pulse P so that is selectively excited_inv-AThe RF frequency of the inversion pulse P is shifted from the center frequency by the offset amount Df._inv-AAt the same time, a selective excitation gradient magnetic field Ge is applied. Inversion pulse P_inv-APulse sequence P for collecting echo signals after a certain time of about 300 to 1000 ms is applied._seqIs executed. This sequence is constituted by, for example, the SE (spin echo) method. This series of operations is repeated until all echo data necessary for reconstruction of one screen can be collected. The echo data is reconstructed and generated into a blood vessel image. The pulse sequence that can be used for this angiography is not limited to the SE method, but may be a segmented FE method. As an example, this segmented FE method is described in the paper “Fast Angiography Using Selective Inversion Recovery”, Samuel J. et al. Wang et al. , Magnetic Resonance in Medicine, Vol. 23, 109-121, 1992 ".
[0011]
In addition, the paper “DG Nishimura et al.” Includes an inversion pulse P_inv-ARegion RG excited by_AA method is described in which a plurality of images with different positions and widths are collected and a difference image is created from each image. By this difference calculation, signals other than the blood vessel are suppressed, and the blood vessel rendering ability is improved.
[0012]
Further, as another example of angiography that does not use a contrast agent, a technique described in FIGS. 15A to 15C is also known. 14 and the paper “D. Chien et al.,“ High Speed black blood imaging of vessellensis the presence of pulsatile flow ”, J. Ming. 2 (4), 437-441, 1992 "or" Simonetti OP, et al., Radiology, 199, 49, 1996 ". Scanning pulse sequence P to obtain an echo signal_seqFor 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 an inversion pulse. That is, the inversion pulse P that excites the entire cross section CS to be imaged._inv-AIs selectively applied first, and immediately after this (for example, after 2 to 10 ms), as in FIG._ASecond inversion pulse P so that is selectively excited_inv-BIs applied. The first and second inversion pulses P_inv-AAnd P_inv-BSince the time between is extremely short compared to the blood flow velocity, it can be regarded as almost the same when viewed from the nuclear spin of the blood vessel. Therefore, since the nuclear spin of the blood vessel of interest receives the application of the 180-degree pulse twice within a very short time, as shown in FIG. 5B, the longitudinal magnetization is partially returned to the initial state. Region RG_ASince it flows out from the imaging section CS to the imaging section CS, it is rendered as a portion having a higher signal than the tissue. Note that the above-described method of FIG. 14 is symmetric to that the blood vessel signal is imaged as a value lower than that of the tissue.
[0013]
[Problems to be solved by the invention]
However, in the case of the conventional CE-DMRA method using the above-described contrast agent, since the contrast agent can be injected only once (or twice) during one examination, the signal intensity depends on the injected contrast agent. All scans must be completed within a limited time of 30 seconds to 2 minutes, where the change is. In principle, in order to ensure a sufficient time resolution, it is necessary to shorten a scan time as much as possible. On the other hand, since the S / N of the image is proportional to the square root of the scanning time, the shorter the scanning time, the lower the S / N. For this reason, according to the conventional method, the temporal resolution and the spatial resolution of the scan are in a trade-off relationship, and both cannot be increased dramatically.
[0014]
On the other hand, in the case of 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 is stated. Thereby, the ability to depict blood vessels can be improved, but no display or observation technique for dynamically capturing the dynamics of blood flow has been presented. In the case of blood flow, in addition to its ability to depict, information on how it behaves over time is extremely important.
[0015]
The present invention has been made in view of the situation of the above-described conventional technology, and breaks the trade-off relationship between the temporal resolution and the spatial resolution due to the scanning of the conventional method. One object is to provide an image in which both resolution and spatial resolution are raised to a very high level.
[0016]
Another object of the present invention is to provide an image that allows both temporal and spatial resolutions to be very high without administering a contrast agent and enables dynamic observation of a moving object.
[0017]
[Means for Solving the Problems]
The principle of the present invention is that a high-frequency inversion (IR) pulse is locally applied to at least a part of a region to be imaged of a subject, and the longitudinal magnetization of spins in the at least part of the region is reversed. Tag (label) by excitation (also called labeling). Of the partial area, the tagged spin of the stationary part remains in the same position, but the tagged spin of blood as a moving object continues to flow along the blood vessel thereafter. As a scan, after a certain time has elapsed after applying the above-described inversion pulse, a scan based on a desired pulse sequence is started with respect to the imaging region, and an echo signal is collected. An image of the imaging region is obtained based on this echo signal. In this image, a signal such as blood flowing out to the imaging region while being tagged is reflected with a contrast different from that of other parts, so that dynamic information such as blood can be provided.
[0018]
As described in the configuration of the invention below, as an example, the time from tagging to collecting echo signals or the position of a partial area for tagging is gradually changed in the imaging area. However, echo signals are collected and generated into an image. By observing a plurality of images generated in response to such time and position changes in order, it is possible to artificially grasp the dynamics of a moving object such as blood.
[0019]
  As a specific configuration, in the magnetic resonance imaging method according to the present invention, the control means of the magnetic resonance imaging apparatus is configured so that each part of the apparatusBy controllingTagging inversion with a selective excitation gradient to tag at least some of the imaging area of the subject to invert the spin.DamperAfter that, after a predetermined time has elapsed, a pulse sequence is started and the echo signal of the spin is received. From this echo signal, a moving imaging target in the imaging area is imaged.WhoAnd changing the spatial position of the partial region to change the selective excitation gradient magnetic field andTaggingAn inversion pulse is transmitted several times, each timeInThe predetermined timeButProgressafterExecute the pulse sequenceAnd generating a plurality of images based on the echo signals respectively generated in response to the pulse sequence performed at each transmission, projecting the plurality of images to create a plurality of projection images, Dynamically display projected images ofIt is characterized by that.
[0020]
  For example, theAs a process for taggingIncludes first transmitting another inversion pulse to be applied to the entire imaging region, and then immediately transmitting the tagged inversion pulse.
[0021]
  Also preferably,SaidpluralprojectionImages can be continuously displayed in a predetermined order. For example, the plurality ofprojectionThe images are continuously displayed according to the change order of the spatial positions of the partial areas.
[0022]
  Further, for example,By simultaneously displaying a plurality of projection images, the plurality of projection images can be moved.Can be displayed automatically.
[0023]
  As an example,For the plurality of images,After obtaining the position on the image corresponding to the partial area, the position is masked, and after this masking processIn the aboveProject pixels of a certain value from multiple imagesToCreate multiple projected imagesdo itAlso good. In this case, for example, beforeWritingA number of projected images are continuously displayed in a predetermined order.
[0024]
Further preferably, the process of projecting the pixels having the constant value is a process of projecting the maximum value or the minimum value of the pixel values.
[0025]
  Furthermore, as another example,WritingNumberprojectionimageofIn each,Only one of the divided areas divided into two by the partial area may be continuously displayed.
[0026]
  Furthermore, as another example,In order to create a plurality of projection images,In each of multiple images,Masking processing may be performed only on one of the divided areas divided into two by the partial area. At this time, preferably, the masking processGenerated by applyingpluralprojectionDisplay images continuously. In addition, the masking process was performedSaidMultiple imagesofProjected pixels of a certain value from at least a part of eachSaidCreate multiple projected images,theseA projection image may be displayed. For example, the masking process is performed on the upstream divided area in the direction of movement of the imaging target.
[0027]
  Furthermore, as another example, the tagging inversion pulse is composed of a plurality of inversion pulses that are continuously transmitted every minute time that can be regarded as simultaneous compared to the movement of the imaging target, Each timeThe pulse sequenceEach time, a plurality of the at least some areas are set. As a preferred example at this time, the plurality of inversion pulsesSending conditions,as well asThe plurality of inversionsThe transmission condition of the selective excitation gradient magnetic field transmitted simultaneously with a pulse is that the at least a part of the region is spatially arranged at a constant interval on the imaging region.,and,Each timeThe pulse sequenceEach position is set to be shifted from each other.
[0032]
  On the other hand, the magnetic resonance imaging apparatus according to the present inventionIs, SubjectofTagging to reverse the spin of at least a part of the imaging areaTo do this, send a tagged inversion pulse with a selective excitation gradient,After a certain time has elapsed, a pulse sequence is started to receive the echo signal of the spinShiThis echo signalOn the basis of theImaging a moving imaging target in the imaging areaMagneticIn the gas resonance imaging apparatus, the selective excitation gradient magnetic field andTaggingMultiple inversion pulsesA means for transmitting, a means for executing the pulse sequence after elapse of the predetermined time each time the transmission is performed, and a plurality of images based on echo signals respectively generated in response to the pulse sequence performed for each transmission Generating means, means for projecting the plurality of images to create a plurality of projection images, and dynamically displaying the plurality of projection imagesAnd means for performing.
[0033]
Specific configurations and features according to other aspects of the present invention will become apparent from the embodiments of the present invention described below and the accompanying drawings.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0035]
(First embodiment)
An MRI (magnetic resonance imaging) apparatus according to the first embodiment will be described with reference to FIGS.
[0036]
Characteristically, this MRI apparatus is a non-contrast-enhanced MR angio that presents, for example, a cine-mode image as a pseudo dynamic image representing the dynamics of blood flow as a moving object in a subject without using a contrast agent. It has a function of executing the graphic (MRA). The pulse sequence for performing this non-contrast MRA uses a harmonic inversion recovery (IR) pulse of selective excitation.
[0037]
A schematic configuration of this MRI apparatus is shown in FIG. This apparatus configuration can be used in common in each embodiment described later.
[0038]
This MRI apparatus includes a bed unit on which a patient P as a subject is placed, a static magnetic field generating unit for generating a static magnetic field, a gradient magnetic field generating unit for adding position information to the static magnetic field, and transmission and reception for transmitting and receiving high-frequency signals. Unit, a control / arithmetic unit responsible for overall system control and image reconstruction, an electrocardiogram measurement unit that measures an ECG signal as a signal representing the cardiac time phase of the subject P, and commands the patient P to hold his / her breath And a breath-hold command unit.
[0039]
The static magnetic field generation unit includes, for example, a superconducting magnet 1 and a static magnetic field power supply 2 that supplies current to the magnet 1, and an axial direction of a cylindrical opening (diagnostic space) into which the subject P is loosely inserted. Static magnetic field H in the Z-axis direction₀Is generated. In addition, the shim coil 14 is provided in this magnet part. 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 to be described later. The couch portion can removably insert the top plate on which the subject P is placed into the opening of the magnet 1.
[0040]
The gradient magnetic field generator includes a gradient magnetic field coil unit 3 incorporated in the magnet 1. The gradient coil unit 3 includes three sets (types) of x, y, and z coils 3x to 3z for generating gradient magnetic fields in the X, Y, and Z axis directions orthogonal to each other. The gradient magnetic field unit also includes a gradient magnetic field power supply 4 that supplies current to the x, y, and z coils 3x to 3z. The gradient magnetic field power supply 4 supplies a pulse current for generating a gradient magnetic field to the x, y, z coils 3x to 3z under the control of a sequencer 5 described later.
[0041]
By controlling the pulse current supplied from the gradient magnetic field power source 4 to the x, y, z coils 3x to 3z, the gradient magnetic fields in the three axes X, Y, and Z, which are physical axes, are synthesized and slices orthogonal to each other. The logical axis directions of the direction gradient magnetic field Gs, the phase encode direction gradient magnetic field Ge, and the readout direction (frequency encode direction) gradient magnetic field Gr can be arbitrarily set and changed. Each gradient magnetic field in the slice direction, the phase encoding direction, and the readout direction is represented by a static magnetic field H.₀Is superimposed on.
[0042]
The transmission / reception unit includes an RF coil 7 disposed in the vicinity of the subject P in the imaging space in the magnet 1, and a transmitter 8T and a receiver 8R connected to the coil 7. The transmitter 8T and the receiver 8R operate under the control of the sequencer 5 described later. 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 takes in an echo signal (high frequency signal) received by the RF coil 7, and performs various signal processing such as preamplification, intermediate frequency conversion, phase detection, low frequency amplification, filtering, etc. A digital amount of echo data (original data) corresponding to the echo signal is generated by / D conversion.
[0043]
The control / arithmetic unit further includes a sequencer (also referred to as a sequence controller) 5, a host computer 6, an arithmetic unit 10, a storage unit 11, a display device 12, an input device 13, and a sound generator 16. Among these, the host computer 6 has a function of commanding the pulse sequence information to the sequencer 5 according to the stored software procedure and overseeing the operation of the entire apparatus.
[0044]
The host computer 6 performs an imaging scan based on the pulse sequence shown in FIG. 2 following a preparatory operation such as a positioning scan. This imaging scan is a scan that collects a set of echo data necessary for image reconstruction, and is set to a two-dimensional scan here. The imaging scan is performed using an ECG gate method based on an ECG signal. This ECG gate method may not be used in some cases.
[0045]
This pulse sequence is a three-dimensional (3D) scan or a two-dimensional (2D) scan. The pulse trains include SE (spin echo) method, FSE (fast SE) method, FASE (fast asymmetric SE) method (that is, imaging method combining the fast SE method with the half Fourier method), EPI (echo planar imaging). ) Method, etc. are used.
[0046]
The sequencer 5 includes a CPU and a memory, stores pulse sequence information sent from the host computer 6, controls the operations of the gradient magnetic field power source 4, the transmitter 8T, and the receiver 8R according to this information, The echo data output from the receiver 8R is once input and transferred to the arithmetic unit 10. Here, the pulse sequence information is all information necessary for operating the gradient magnetic field power source 4, the transmitter 8T, and the receiver 8R according to a series of pulse sequences, for example, x, y, z coils 3x to 3z. Includes information on the intensity, application time, application timing, and the like of the pulse current applied to.
[0047]
The arithmetic unit 10 inputs echo data (original data or raw data) output from the receiver 8R through the sequencer 5, and places the echo data in the Fourier space (also referred to as k space or frequency space) in the internal memory. Then, the echo data is subjected to two-dimensional or three-dimensional Fourier transform for each group to reconstruct the image data in real space. Further, the arithmetic unit can perform a data synthesizing process, a difference arithmetic process, and the like as necessary.
[0048]
In this synthesis process, two-dimensional image data of a plurality of frames are added for each corresponding pixel, and maximum value projection (MIP) or minimum for selecting the maximum value or minimum value in the line-of-sight direction for three-dimensional data Value (MIP) projection processing and the like are included. As another example of the synthesis process, the axes of a plurality of frames may be matched in the Fourier space and synthesized into one frame of echo data as it is. The addition processing includes simple addition processing, addition averaging processing, weighted addition processing, and the like.
[0049]
The storage unit 11 can store not only the reconstructed image data but also the image data that has been subjected to the above-described combining process and difference process. The display device 12 displays an image. In addition, information relating to imaging conditions, pulse sequences, image synthesis, and difference calculation desired by the operator can be input to the host computer 6 via the input unit 13.
[0050]
Moreover, the sound generator 16 is provided as an element of the breath-hold command unit. The voice generator 16 can emit a breath holding start message and a breath holding end message as voice when instructed by the host computer 6.
[0051]
Further, the electrocardiogram measurement unit attaches to the body surface of the subject and detects an ECG signal as an electrical signal, and performs various processing including digitization processing on the sensor signal to perform the host computer 6 and the sequencer. And an ECG unit 18 for outputting to the PC. The measurement signal from the electrocardiogram measurement unit is used by the sequencer 5 when executing an imaging scan. Thereby, the synchronization timing by the ECG gate method (electrocardiogram synchronization method) can be set appropriately, and the ECG gate method imaging scan based on this synchronization timing can be performed to collect data.
[0052]
Next, the operation of the MRI apparatus according to the present embodiment will be described with reference to FIGS.
[0053]
FIG. 2 shows a pulse sequence used in non-contrast-enhanced MR angiography according to this embodiment, and FIG. 3 shows a diagram for explaining a processing process from scanning to display image generation. In order to facilitate understanding, the non-contrast MR angiography performed in this embodiment performs three two-dimensional scans to obtain three consecutive final images and displays them in cine display. And
[0054]
In an actual image, pixels with lower signal values are displayed darker. However, in FIGS. 2B to 2D, the portion rendered as a high signal is represented by darker hatching, and the rendering region of the low signal is a thin housing. It shall represent.
[0055]
First, the pulse sequence will be described. The pulse sequence shown in FIGS. 2A to 2C is a pulse train based on the method of FIG. 15 described above in which two inversion pulses are applied in a very short time (2 to 10 ms). Specifically, the first inversion pulse P is synchronized with the R wave of the ECG signal (the delay time for the R wave is arbitrary)._inv-AIs applied non-selectively so as to include a region CS (see FIG. 3A) to be imaged.
[0056]
After that, when viewed from the blood flow velocity, the second inversion pulse P can be regarded as simultaneous, after a very short time has elapsed._inv-BIs applied together with a selective excitation gradient magnetic field Ge. Thereafter, when a predetermined TI time (for example, 600 ms) elapses, an imaging scan based on a pulse sequence based on, for example, the FSE method is performed on the imaging region CS.
[0057]
Each of the pulse sequences in FIGS. 2A to 2C is the second inversion pulse P._inv-BSelected excitation position based on the tag region RG for the imaging region CS_AThey are different from each other in that they are configured to change the spatial position of (spin inversion region). Specifically, the inversion pulse P_inv-BThe carrier frequency offset amounts Df are mutually changed.
[0058]
Therefore, the second inversion pulse P_inv-BRegion RG selectively excited by_A(: RG_A1~ RG_A3), By adjusting the selective excitation gradient magnetic field Ge and the frequency offset amount Df, first, as indicated by the dotted line in the left column of FIG. 3A, the imaging region CS (for example, the subject CS) (for example, the subject) Set in the upstream portion of the blood BD flowing into the cross section).
[0059]
At the time of imaging, the host computer 6 uses the tag area RG._AIs sent to the sequencer 5. In response to this, the sequencer 5 drives the gradient magnetic field power supply 4 and the transmitter 8T according to the given pulse sequence information. Thereby, the pulse which comprises the pulse sequence of the pulse sequence of Fig.2 (a) is applied in time series.
[0060]
As a result, as described with reference to FIG._inv-AAs a result, the spin of the entire imaging region CS is inverted by 180 degrees. However, the second inversion pulse P applied immediately thereafter_inv-BThe selected tag region RG_AOnly the spins are inverted 180 degrees again (tagging) and returned to the initial state (see FIG. 15B). Depending on the return of the flip angle of the spin, that is, the tagging, both inversion pulses P are schematically shown in FIG._inv-AAnd P_inv-BThe echo signal of blood in the portion excited by is generated with the highest intensity.
[0061]
The entire echo signal including the echo signal from the blood is received by the receiver 8R via the RF coil 7 and sent to the arithmetic unit 10 via the sequencer 5 as echo data.
[0062]
  The arithmetic unit 10 applies this echo data to appropriate processing and places it in a two-dimensional k-space. This k skyEverything is echodeWhen filled with the data, the arithmetic unit 10 performs a two-dimensional Fourier transform on the echo data to obtain a two-dimensional reconstructed image IMrec1 as shown in the left column of FIG.
[0063]
This reconstructed image IM_rec1As can be seen, the second inversion pulse P_inv-BTag region RG when applying_AThe blood BD contained in the blood has its magnetization spin almost restored to the initial state, and therefore, the second inversion pulse P on the imaging region CS._inv-BPulse sequence P for imaging_seqA portion corresponding to the flow out of the tag area before applying is partially rendered as a high signal. In addition, tag region RG_AAmong these, the part of the tissue that does not move as the background is the second inversion pulse P_inv-BIn response to the initial spin, the first inversion pulse P_inv-AThe image is drawn with a different contrast from the non-moving part to which is applied.
[0064]
When this reconstruction is finished, the reconstructed image IM is obtained by the arithmetic unit 10._rec1Among these, the masking process is executed for portions having different contrasts. In the figure, cross-hatched part MG₁Indicates a masking region. The masking process is a process of rewriting a certain range of image values on the image to a certain pixel value. Intermediate image IM represented as shown in the left column of FIG._int1Is obtained.
[0065]
Similarly to the first scan described above, the second and third scans are also performed. The echo signals obtained by these scans are processed in the same manner, and the intermediate image IM subjected to the masking process as shown in the middle column and the right column in FIG._int2And IM_int3Is obtained.
[0066]
However, in the case of the second and third scans, the inversion pulse P that is selectively applied the second time._inv-BAs shown in the middle column and the right column in FIGS. 3A to 3C, the application position of the selective excitation gradient magnetic field Ge and the inversion pulse P are moved little by little along the blood flow direction._inv-BThe offset amount of the carrier frequency (high frequency) is changed, and the above-described pulse sequence is executed.
[0067]
Note that the timing of the intermediate image generation processing by the image reconstruction and masking processing executed in the arithmetic unit 10 may be arbitrary.
[0068]
In this way, the intermediate image IM_int1, IM_int2, IM_int3Is obtained, the arithmetic unit 10 performs a maximum value projection process by appropriately combining the images, and obtains a plurality of final images IM._fin1, IM_fin2, IM_fin3Is generated. During this maximum value projection process, the first intermediate image IM_int1For the first final image IM, the masking area is removed as it is._fin1As the first and second intermediate images IM_int1, IM_int2For the second final image IM by taking the larger of the two corresponding pixels between the images_fin2Are generated, and the first, second, and third intermediate images IM_int1, IM_int2, IM_int3For the third collected image IM by comparing the corresponding three pixels with each other and taking the maximum value._fin3Is generated.
[0069]
These three final images IM_fin1, IM_fin2, IM_fin3Are continuously displayed on the display 12 under the cine mode. Thereby, the inflow situation (dynamics) of the blood flowing into the region of interest can be dynamically observed and grasped.
[0070]
In particular, even when the dynamics of blood are shorter in time, the same dynamic observation can be performed. In this case, the entire scan time becomes long, but the inversion pulse P_inv-BTag region RG to apply_AIt is only necessary to reduce the amount of movement of the spatial position and collect more images. Furthermore, in order to further improve the spatial resolution of each image, the inversion pulse P_inv-BTag region RG to apply_AIt is sufficient to scan repeatedly without changing the spatial position. As a result, an image having a large number of matrices, that is, a high spatial resolution can be obtained. Furthermore, when it is desired to obtain an image with a high S / N, the inversion pulse P is similarly applied._inv-BThe scan may be repeated without changing the spatial position to apply, and a scan with a large number of additions may be performed.
[0071]
That is, in the case of the above-described conventional CE-DMRA (see FIG. 12), since the signal change time in the region of interest due to the contrast agent is constant, changing the imaging conditions such as the number of scan repetitions, There is a problem that the time resolution is lowered. However, according to the present embodiment, the inversion excitation by the inversion pulse can be repeatedly executed, and thus there is no restriction as in the prior art. Therefore, the spatial resolution and the temporal resolution can be freely changed within the allowable time, and both can be improved.
[0072]
This embodiment can be variously modified as follows.
[0073]
For example, as another example of the dynamic display method described above, three final images IM are displayed on the display 12._fin1, IM_fin2, IM_fin3May be displayed simultaneously, and the image reader may visually compare the images with each other. Thereby, observation of hemodynamics by visual observation becomes possible.
[0074]
Moreover, although this embodiment demonstrated MRA which images the blood, it can image similarly about the object which has another motion as an imaging target, for example, CSF. In the case of this CSF, the time width from the application of the inversion pulse to the imaging scan may be changed as appropriate.
[0075]
Further, in the pulse sequence shown in FIG._inv-BAnd imaging scan P_seqA fat suppression pulse that suppresses signals from fat in the cross section to be imaged may be applied between the two.
[0076]
  Furthermore, in the present embodiment, an embodiment based on a technique using two inversion pulses as in the technique of FIG. 15 described above has been described, but instead of this, as shown in FIG. The above-described embodiment may be performed based on a method using only one. The post-processing in this case is the maximum value mentioned aboveprojectionInstead of processing, minimum value projection processing may be performed.
[0077]
Further, the pulse sequence usable in the present embodiment is not limited to the example using the FSE method as described above, and various methods such as the FE method, the segmented FE method, the SE method, and the echo planar method can be adopted. Further, data collection and image reconstruction are not limited to the above-described two-dimensional scan and two-dimensional reconstruction, and they may be performed in three dimensions.
[0078]
Furthermore, in the above-described embodiment, the intermediate image IM_int1~ IM_int3To the final image IM_fin1~ IM_fin3However, various modifications can be made for this. For example, blood flow dynamics can be observed even if a plurality of intermediate images are displayed in order in the cine mode without executing the maximum value projection processing. Further, the masking process for creating the intermediate image may be omitted.
[0079]
(Second Embodiment)
An MRI apparatus according to the second embodiment will be described with reference to FIGS. In the following embodiments, the same or equivalent components as those in the first embodiment described above are denoted by the same reference numerals, and the description thereof is omitted or simplified.
[0080]
The MRI apparatus according to this embodiment performs MRA based on the technique shown in FIG. 15 described above, and in particular, within the time from the application of the inversion pulse to the scan, that is, the time until the scan for imaging is executed. It is characterized by collecting vascular images or cine images representing blood flow dynamics in a wider range than the distance traveled by blood.
[0081]
The hardware configuration of this MRI apparatus is the same as that of the first embodiment.
[0082]
FIG. 4 shows a pulse sequence used in non-contrast-enhanced MR angiography according to the present embodiment, and FIG. 5 shows a diagram for explaining a processing process from scanning to display image generation. In the non-contrast MR angiography performed in this embodiment, three final two-dimensional scans are performed to obtain a single wide-range final blood vessel image.
[0083]
Note that in FIGS. 5B to 5D, the magnitude of the pixel value is represented by the hatching density, and the portion rendered as a high signal is represented by the darker hatching.
[0084]
First, the pulse sequence will be described. The pulse sequence shown in FIGS. 4A to 4C applies four inversion pulses at very short time intervals (2 to 10 ms). Specifically, the first inversion pulse P is synchronized with the R wave of the ECG signal (the delay time for the R wave is arbitrary)._inv-AIs applied non-selectively so as to include a region CS (see FIG. 5A) to be imaged. Thereafter, when viewed from the blood flow velocity, the second to fourth inversion pulses P can be considered to be the same at very short time intervals._inv-B~ P_inv-DAre sequentially applied together with the selective excitation gradient magnetic field Ge. This inversion pulse P_inv-B~ P_inv-DAs shown in the left column of FIG. 5A, the application positions of the selective excitation gradient magnetic field Ge and the frequency of these pulses are arranged at regular intervals from the upstream part of the blood flowing into the imaging region CS toward the downstream direction. Offset amount Df is set. Unlike the case of the first embodiment, the space interval between the tag regions in the direction of blood flow is slightly longer than the distance traveled by blood after the inversion pulse is applied until the scan is started. It is set to be. In addition, since the time interval between inversion pulses is very short, these four inversion pulses can be regarded as simultaneous when viewed from the blood flow.
[0085]
When a predetermined fixed TI time (for example, 600 ms) elapses after the application of the series of inversion pulses, an imaging scan based on a pulse sequence based on, for example, the FSE method is performed on the imaging region CS.
[0086]
  4A to 4C.In each pulse sequenceThe frequency offset amount Df is adjusted for each sequence. Thereby, three selective excitation positions based on the second to fourth inversion pulses Pinv-B to Pinv-D, that is, the spatial positions of the tag areas RGA to RGC with respect to the imaging area CS are shown in FIGS. As shown in the left column, middle column, and right column of c), they are mutually changed.
[0087]
When 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 first inversion pulse P_inv-AAnd the second to fourth inversion pulse P_inv-B~ P_inv-DThe echo signal of the blood excited in any of the above occurs most intensely. This echo signal is sent to the arithmetic unit 10 as echo data. The arithmetic unit 10 subjects this echo data to appropriate processing and places it in a two-dimensional k-space, and performs two-dimensional Fourier transform on this data. As a result, a two-dimensional reconstructed image IM as shown in the left column of FIG._rec1Get.
[0088]
This reconstructed image IM_rec1As can be seen from the second to fourth inversion pulse P_inv-B~ P_inv-DTag region RG when applying_A~ RG_CThe blood BD that was inside has almost returned to its initial state, so that the second to fourth inversion pulses P on the imaging region CS._inv-B~ P_inv-DPulse sequence P for imaging_seqA portion corresponding to the flow out of the tag area before applying is partially rendered as a high signal. In addition, tag region RG_A~ RG_CAmong them, the tissue part with no background movement is the second to fourth inversion pulse P._inv-B~ P_inv-DIn response to any of the above, the spin is almost in the initial state, so the first inversion pulse P_inv-AThe image is drawn with a different contrast from the non-moving part to which is applied.
[0089]
When this reconstruction is finished, the reconstructed image IM is obtained by the arithmetic unit 10._rec1Among these, the masking process is executed for portions having different contrasts. In the figure, cross-hatched part MG₁₁~ MG₂₁Indicates a masking region. By this masking process, the intermediate image IM represented as shown in the left column of FIG._int1Is obtained.
[0090]
Similarly to the first scan described above, the second and third scans are also performed. The echo signals obtained by these scans are processed in the same manner, and the intermediate image IM subjected to the masking process IM as shown in the middle column and the right column in FIG. 5C._int2And IM_int3Is obtained.
[0091]
However, in the case of the second and third scans, the inversion pulse P that is selectively applied at the second to fourth times._inv-B~ P_inv-DAs shown in the middle column and the right column in FIGS. 5A to 5C, the selective excitation gradient magnetic field Ge and the inversion pulse P are applied so as to move gradually along the blood flow direction._inv-B~ P_inv-DThe frequency offset amount Df is changed, and the above-described pulse sequence is executed.
[0092]
Note that the timing of the intermediate image generation processing by the image reconstruction and masking processing executed in the arithmetic unit 10 may be arbitrary.
[0093]
Intermediate image IM obtained in this way_int1, IM_int2, IM_int3Is subjected to the maximum value projection processing by the arithmetic unit 10, and one final image IM_finIs generated. This final image IM_finIs displayed by the display 12. Thereby, the inflow situation (dynamics) of the blood flowing into the region of interest can be observed.
[0094]
In this way, in each scan performed a plurality of times, a plurality of tag regions RG are applied when the second to fourth inversion pulses are applied._A~ RG_CAt this time, blood movements in the blood vessel are detected at the same time, and a blood vessel image having a wider range than the distance in which the blood flow moves between the inversion pulse application and the scan is obtained. Accordingly, conditions such as the number of a plurality of tag areas set in one scan (that is, the number of inversion applied after the second time), its width (selective excitation width), and the total number of scans are appropriately selected. As a result, even when the blood flow velocity is low, a fine blood vessel image can be provided over a wide area covering the entire blood flow traveling path with a small number of scans.
[0095]
This embodiment can be modified as follows.
[0096]
From the plurality of intermediate images IMint1 to IMint3 obtained in the above-described embodiment, the remaining portions of the images R1 to R9 that are not subjected to the masking process may be cut out and displayed, for example, in this order.
[0097]
Further, as shown in FIG. 3D described above, while increasing the original image (here, the intermediate image) to be subjected to the maximum value projection processing, a plurality of maximum value projection images are created and displayed in an appropriate order. You may make it do. Thereby, a dynamic image of blood flow dynamics can be provided in a pseudo manner, and blood flow behavior can be easily grasped.
[0098]
Furthermore, although the present embodiment has been described with respect to 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 inversion pulse to the imaging scan may be appropriately changed.
[0099]
In addition, in the pulse sequence shown in FIG._inv-DAnd imaging scan P_seqYou may make it apply a fat suppression pulse between.
[0100]
  Furthermore, although this embodiment demonstrated embodiment based on the method of FIG. 15 mentioned above, it may replace with this and may perform above-mentioned embodiment based on the method shown in FIG. 14 mentioned above. In this case, the maximum value mentioned aboveprojectionInstead of processing, minimum value projection processing may be performed.
[0101]
On the other hand, in the present embodiment, various methods such as the FE method, the segmented FE method, the SE method, and the echo planar method can be employed for the imaging pulse sequence. Furthermore, data collection and image reconstruction may be performed in three dimensions.
[0102]
(Third embodiment)
Next, the 3rd Embodiment of this invention is described based on FIGS. The MRI apparatus according to this embodiment is characterized by the function of displaying a blood vessel image representing the flow direction separately.
[0103]
FIG. 6 shows a pulse sequence used in this MRA, and FIG. 7 shows a blood flow (for example, vein BD) flowing above the paper surface._V), And FIG. 8 shows a blood flow (for example, arterial BD) flowing downward on the paper surface._A) Are shown respectively.
[0104]
The pulse sequence shown in FIG. 6 is the inversion pulse P applied for the second time._inv-B2 except for the setting of the frequency offset amount Df. That is, the second inversion pulse P applied in a total of three scans as an example_inv-BThe offset amount Df is set to a predetermined value of + polarity, zero, and a predetermined value of -polarity. Thereby, the tag region RG selectively excited by these three scans._A1~ RG_A37 (a) and FIG. 8 (a), the spatial positions are symmetrically positioned in the upper, middle, and lower predetermined portions in the blood flow direction on the imaging region CS, and They are set apart from each other by a predetermined distance.
[0105]
Now, as shown in FIGS. 7 and 8, it is assumed that MR images obtained by performing arterial and vein separation of the imaging region CS including two blood vessels flowing in the opposite directions in the vertical direction one by one on the left and right are obtained.
[0106]
First, vein BD_VThe case of imaging is described with reference to FIGS. Each of the pulse sequences shown in FIGS. 6A to 6C is executed. As a result, as shown in the left column, the central column, and the right in FIG._inv-BTag region RG located at symmetrical positions at equal distances in the direction of blood flow by selective excitation based on_A1~ RG_A3Are excited (tagged), echo signals reflecting this selective excitation are collected respectively.
[0107]
This echo signal is processed into digital amount of echo data and reconstructed by the arithmetic unit 10 as described above. This reconstructed image is designated as an image IM in FIG._rec1, IM_rec2, IM_rec3As shown.
[0108]
This reconstructed image IM_rec1, IM_rec2, IM_rec3As can be seen, the second inversion pulse P_inv-BTag region RG when applying_A1~ RG_A3Artery BD that was inside_AAnd vein BD_VSince the magnetization spin is almost returned to the initial state, the second inversion pulse P is captured on the imaging region CS._inv-BPulse sequence P for imaging_seqA portion corresponding to the flow from the tag area before application of (see reference signs A1 to A3 and V1 to V3) is partially rendered as a high signal. At this time, the flow-out distance varies depending on the flow velocity of the artery and vein.
[0109]
In addition, tag region RG_A1~ RG_A3Of the tissue with no background movement, the second inversion pulse P_inv-BIn response to the initial spin, the first inversion pulse P_inv-AThe image is drawn with a different contrast from the non-moving part to which is applied.
[0110]
When this reconstruction is finished, the reconstructed image IM is obtained by the arithmetic unit 10._rec1, IM_rec2, IM_rec3Among these, the masking process is executed for the portions having different background contrasts. That is, as shown in FIG. 7C, the tag area RG that bisects the imaging area CS._A1~ RG_A3Each of these tag regions RG_A1(~ RG_A3The portions upstream of the vein including) are masked. In the figure, cross-hatched part MG₁~ MG₃Indicates a masking region. By this masking processing, the intermediate image IM shown in the left column, the central column, and the right column in FIG._int1~ IM_int3Is obtained.
[0111]
Intermediate image IM obtained in this way_int1, IM_int2, IM_int3Is subjected to the maximum value projection processing by the arithmetic unit 10, and one final image IM_fin-VIs generated as shown in FIG. This final image IM_fin-VIs displayed by the display 12. Thereby, the vein BD flowing through the region of interest_VMRA images can be obtained.
[0112]
On the other hand, artery BD_AThe case of imaging the image will be described with reference to FIGS. Also at this time, the pulse sequences shown in FIGS. 6A to 6C are executed. As a result, vein BD_VReconstructed image image IM_rec1, IM_rec2, IM_rec3Is obtained (FIG. 8 (b)) and then subjected to a masking process. In the masking process in this case, the tag region RG that bisects the imaging region CS as shown in FIG._A1~ RG_A3Each of these tag regions RG_A1(~ RG_A3The portion upstream of the artery including) is masked.
[0113]
Intermediate image IM created by this_int1, IM_int2, IM_int3Is then subjected to a maximum projection process and the artery BD_AAn MRA image in which only appears can be displayed.
[0114]
As described above, according to the present embodiment, an MRA image obtained by separating the arteriovenous vein can be easily provided by a simple method of changing the position of the masking process in the post-processing after collecting the echo signals. In addition, by using this MRA image, it is possible to simply check the running direction of the arteriovenous vein.
[0115]
Even in this embodiment, the remaining arteriovenous images R1, R2, and R3 that have been masked may be sequentially displayed in sequence or the reconstructed image IM_rec1, IM_rec2, IM_rec3May be displayed in sequence. Thereby, a pseudo dynamic image of the arterial vein can be observed.
[0116]
(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) that is selectively excited from the inversion (IR) used for the pulse sequence when performing an imaging scan (main scan) to an optimum value. This relates to scanning (pre-scan).
[0117]
4 and 5 according to the second embodiment described above, or the MR angiography according to FIGS. Since the inflow speed changes, the distance of the high signal portion due to the inversion pulse is short, or on the contrary, the high signal portion remains in the tag region that is too long and excited by another inversion. It may not be suitable for cine image display. The present embodiment teaches a pre-scan technique that can surely eliminate such a situation.
[0118]
In this pre-scan, the optimum excitation thickness and excitation position are obtained by continuously scanning while changing the excitation thickness by the inversion pulse stepwise.
[0119]
FIG. 9 schematically shows an example of a pulse sequence used for this prescan, and FIG. 10 schematically shows a prescan procedure.
[0120]
9A to 9C show pulse sequences used for three scans from the first to the third time, respectively. In these pulse sequences, the second inversion pulse P is used for each scan._inv-BAt least one of the carrier frequency offset amount Df and the intensity of the selective excitation gradient magnetic field Ge is adjusted. As a result, as shown in the left column, the central column, and the right column in FIG._A(RG_A1~ RG_A3) Gradually increases, and in any of the first to third scans, the strip-shaped tag region RG_A1~ RG_A3The positions are selected so that the boundary positions on the downstream side of the blood flow are the same. That is, as the number of scans increases, the tag region RG_A1~ RG_A3The excitation position is set so that only the boundary position on the upstream side of blood flow changes and becomes thicker. In the pulse sequences of FIGS. 9A to 9C, the other pulse trains are the same as described above.
[0121]
Note that conditions such as the number of scans in this pre-scan and the fluctuation range of the boundary position on the upstream side of the blood flow are determined in consideration of conditions including the blood flow velocity at the imaging region and the desired value of the change width.
[0122]
By sequentially executing these pulse sequences as pre-scanning, as shown in FIGS._rec1~ IM_rec3Is obtained.
[0123]
Therefore, for example, the operator can make this series of images IM._rec1~ IM_rec3Are visually observed to determine the excitation thickness and spatial position by the inversion pulse, which seems to be optimal for the target imaging region. At this time, in order to facilitate such a determination, a series of images IM_rec1~ IM_rec3May be continuously displayed in the order of the thickness of the tag area. The above-described determination may be automatically performed using an appropriate algorithm such as a blood flow extraction method in addition to a method based on an artificial judgment by an operator.
[0124]
The information on the excitation thickness and the spatial position obtained by the above pre-scan is obtained from the second inversion pulse P applied in the pulse sequence of the main scan._{in v-B}For example, the intensity of the selective excitation gradient magnetic field applied simultaneously with the carrier frequency. As a result, in the inversion pulse P in the MRA image obtained by the main scan._inv-BThus, the relationship between the imaging length of the blood flow part tagged with the blood flow velocity and the blood flow velocity becomes appropriate, and accurate image synthesis and cine image display can be performed.
[0125]
In the above-described embodiment, MRA that images blood is described. However, other moving objects such as CSF can be similarly imaged as an imaging target. In the case of this CSF, the time width from the application of the inversion pulse for tagging to the imaging scan may be appropriately changed.
[0126]
Further, in the pulse sequence shown in FIG._inv-BAnd imaging scan P_seqYou may make it apply a fat suppression pulse between.
[0127]
  Furthermore, although this embodiment demonstrated embodiment based on the method of FIG. 15 mentioned above, it may replace with this and may perform above-mentioned embodiment based on the method shown in FIG. 14 mentioned above. In this case, the maximum value mentioned aboveprojectionInstead of processing, minimum value projection processing may be performed as post-processing.
[0128]
On the other hand, in the present embodiment, the imaging pulse sequence is not limited to the FSE method, and various methods such as the FE method, the segmented FE method, the SE method, and the echo planar method can be employed. Furthermore, data collection and image reconstruction may be performed in three dimensions.
[0129]
(Fifth embodiment)
An MRI apparatus according to the fifth embodiment of the present invention will be described. This embodiment relates to another example of a tagging region that relies on selective excitation.
[0130]
FIG. 11A shows an example of a pulse sequence used in the MRI apparatus, and FIG. 11B shows an example of a reconstructed image.
[0131]
According to this pulse sequence, the inversion pulse is one pulse P_inv-OUse only. The carrier frequency of this pulse and the selective excitation gradient magnetic field Ge are the inversion pulse P_inv-ORegion RG excited by_AIs set to be the same as the area CS to be imaged as shown in FIG. That is, this inversion pulse P_inv-OHas the function of reversing the spin 180 degrees and tagging, but this tagging contrasts the high signal due to the new blood flow that flows during the scan, so the region RG_AThis is a reverse tagging function that lowers the spin of the signal. As shown in FIG. 11 (a), the inversion pulse is the tagging pulse P._inv-OOnly is applied alone. Other pulse trains are the same as those of the above-described embodiments.
[0132]
An echo signal is collected by executing this pulse sequence, and the reconstructed image IM illustrated in FIG._recIs obtained.
[0133]
Therefore, the inversion pulse P_inv-ODue to the same area RG as the imaging area CS_AAre reverse-tagged and then a scan is performed after the inversion time TI.
[0134]
For this reason, during scanning, the inversion pulse P_inv-OFrom the region not selectively excited by, for example, arterial BD_AAnd vein BD_VFlows into the imaging region CS as unsaturated spins. Therefore, artery BD_AAnd vein BD_VYou can get a high signal from and reliably depict them.
[0135]
In particular, since there is a speed difference in the flow velocity in the arteriovenous vein, the length of the portion that flows into the imaging region CS during scanning is usually different. For this reason, for example, vein BD_VIs set so as to selectively excite the region that has entered the venous upstream side of the imaging region CS by the inflow length L of the artery BD._AIt is possible to present an image displaying only the image.
[0136]
As a modification common to all the embodiments described above, there is a synchronization method. In other words, each of the above-described embodiments has described MR imaging based on the electrocardiogram synchronization method, but instead of this synchronization method, an electroencephalogram synchronization method, a respiratory synchronization method, or the like may be used. Further, even with the same electrocardiographic synchronization method, the pulse wave synchronization method (PPG) can also be used.
[0137]
  Further, in each of the above-described embodiments, a method for displaying the dynamics of blood or CSF by changing the excitation position by the inversion pulse for tagging has been taught. However, a series of inversions are generated from generation of a trigger used in the synchronization method. Scanning may be performed while appropriately changing the time width (delay time) until the application of the version pulse. Display the images obtained in this order in an appropriate order, or create multiple maximum-value projection images.DisplayAccordingly, it is possible to observe the periodic movement of the imaging target synchronized with the heartbeat and the respiration.
[0138]
Furthermore, each embodiment described above can be developed in various forms. First, the transposition of the blood flow portion imaged with the application of the tagged inversion pulse varies depending on the blood flow velocity, so that the blood flow velocity can be measured based on this correspondence. .
[0139]
Second, by appropriately varying 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 arbitrarily sliced (slab position), slice thickness (slab thickness), or The oblique excitation position can be set.
[0140]
Third, by varying the slice thickness (slab thickness) by the tagging inversion pulse, a blood vessel having an arbitrary slice thickness (slab thickness) can be depicted.
[0141]
Fourth, a suitable example of the flip angle of the tagged inversion pulse is 180 degrees, but the flip angle is not necessarily limited thereto. By setting this angle to an appropriate value of less than 180 degrees, it is possible to collect the signal of the signal-reduced region in a shorter TI time and shorten the entire scan time.
[0142]
It should be noted that the present invention is not limited to the above-described exemplary embodiments and modifications, which are representatively exemplified, and those skilled in the art will be within the scope of the gist of the present invention based on the content of the claims. Various modifications and changes can be made and these are also within the scope of the present invention.
[0143]
【The invention's effect】
As described above, according to the MR imaging of the present invention, it is possible to achieve both time resolution and spatial resolution, both of which are problems in the conventional MRA, and can be maintained at a high level, such as blood and CSF. Detailed information on fluid dynamics can be obtained.
[0144]
Furthermore, the MR imaging method of the present invention eliminates the need for contrast medium administration, which is essential in conventional CE-DMRA, and is therefore non-invasive and significantly reduces the mental and physical burden on the subject. be able to. Moreover, the troublesomeness associated with the recognition of the imaging timing, such as when a contrast agent is administered, is unnecessary, and the preparation and labor of the examination are greatly reduced.
In addition, since no contrast agent is used, it is possible to easily cope with re-inspection.
[0145]
Furthermore, according to the MR imaging method of the present invention, the position of the region to be tagged with the inversion pulse can be set freely, so that the inflowing blood vessel can be limited and the inspection can be performed with high accuracy and certainty. It 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 having one tag inversion pulse used in the first embodiment.
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 in the first embodiment.
FIG. 4 is a pulse sequence having a plurality of tag inversion pulses used in the second embodiment.
FIG. 5 is a diagram 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 is a diagram illustrating a positional relationship between an imaging region and a tag region and a procedure for generating an MRA image regarding arteriovenous separation in the third embodiment.
FIG. 8 is a diagram illustrating a positional relationship between an imaging region and a tag region and a procedure for generating an MRA image regarding arteriovenous separation according to the third embodiment.
FIG. 9 is a pulse sequence having one tag inversion pulse used in pre-scanning according to the fourth embodiment.
FIG. 10 is a view for explaining a positional relationship between an imaging region and a tag region and an MRA image generation procedure in a pudding scan according to a fourth embodiment.
FIG. 11 is a view showing a pulse sequence and an image example according to the fifth embodiment.
FIG. 12 is a diagram for explaining CE-DMRA as a prior art.
FIG. 13 is a diagram exemplifying a pulse sequence used for CE-DMRA.
FIG. 14 is a diagram for explaining an example of a conventional MRA together with a pulse sequence.
FIG. 15 is a diagram for explaining another example of a conventional MRA together with a pulse sequence.
[Explanation of symbols]
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 device

Claims (30)

By controlling means of the magnetic resonance imaging apparatus to control the respective units of the apparatus, the tagging Inbajo damper with selective excitation gradient magnetic field for tagging to invert the spins of at least a partial region of the imaging region of the object It originated the pulse, after this, a magnetic resonance imaging for imaging an imaging object to start a pulse sequence received echo signals of the spins, which from the echo signal motion of the imaging area after a predetermined time has elapsed In the method
Together with the said selective excitation gradient magnetic field and said tagged inversion pulse by changing the spatial position of the partial region originated multiple times, to execute the pulse sequence from the predetermined time has elapsed each time the outgoing Generating a plurality of images based on the echo signals respectively generated in response to the pulse sequence performed at each transmission, projecting the plurality of images to create a plurality of projection images, A magnetic resonance imaging method characterized by dynamically displaying a projected image . The magnetic resonance imaging method according to claim 1.
In order to perform the tagging magnetic resonance imaging method characterized in that said another inversion pulse to be applied to the entire imaging area is first originated transmits the tagged inversion pulse immediately thereafter. The magnetic resonance imaging method according to claim 1 or 2,
A magnetic resonance imaging method , wherein the plurality of projection images are dynamically displayed by continuously displaying the plurality of projection images in a predetermined order . The magnetic resonance imaging method according to claim 3.
Wherein the plurality of projection images, magnetic resonance imaging method characterized in that it is continuously displayed in accordance with the change order of the spatial position of the partial region. The magnetic resonance imaging method according to claim 1 or 2,
A magnetic resonance imaging method , wherein the plurality of projection images are dynamically displayed by simultaneously displaying the plurality of projection images . The magnetic resonance imaging method according to claim 1 or 2,
For the plurality of images, with determining the position on the image corresponding to the partial region, the masking processing to the obtained position, to project the pixels of the predetermined value from the plurality of images after the masking process Thus , the magnetic resonance imaging method , wherein the plurality of projection images are created. The magnetic resonance imaging method according to claim 6.
A magnetic resonance imaging method , wherein the plurality of projection images are dynamically displayed by continuously displaying the plurality of projection images in a predetermined order. The magnetic resonance imaging method according to any one of claims 1 to 7,
Process, magnetic resonance imaging method, which is a maximum value projection processing or the minimum value projection processing of generating the plurality of projection images. The magnetic resonance imaging method according to claim 1 or 2,
In each of the plurality of projection images, only one of the divided regions which are divided into two by the partial region by continuously displayed, and characterized by dynamically displaying the plurality of projection images magnetic resonance imaging method for. The magnetic resonance imaging method according to claim 1 or 2,
To create a plurality of projection images, magnetic resonance imaging method characterized in that in each of the plurality of images, one only masking of the divided regions which are divided into two by the partial region subjected . The magnetic resonance imaging method according to claim 10.
A magnetic resonance imaging method , wherein the plurality of projection images generated by performing the masking process are continuously displayed. The magnetic resonance imaging method according to claim 10.
Magnetic resonance imaging method characterized by creating each of the plurality of projection images by projecting the pixels of a predetermined value from at least a portion of said plurality of images subjected to the masking process. The magnetic resonance imaging method according to any one of claims 10 to 12,
The magnetic resonance imaging method according to claim 1, wherein the masking process is performed on a divided region upstream in the direction of movement of the imaging target. The magnetic resonance imaging method according to claim 1 or 2,
The tagged inversion pulse is composed of a plurality of inversion pulses that are continuously transmitted every minute time that can be regarded as simultaneous as compared to the movement of the imaging target, and thus, for each pulse sequence of each time A magnetic resonance imaging method, wherein a plurality of at least some of the regions are set. The magnetic resonance imaging method according to claim 14.
The conditions for transmitting the plurality of inversion pulses and the conditions for transmitting the selective excitation gradient magnetic field transmitted simultaneously with the plurality of inversion pulses are such that the at least a part of the region is spatially spaced on the imaging region. arrangement, and a magnetic resonance imaging method comprising Rukoto is set to be at a position deviated from each other each time the pulse sequence. In order to perform the tagging to invert the spin of at least a part of the imaging region of the subject, a pulse sequence is started together with a selective excitation gradient magnetic field, a pulse sequence is started after a certain time, and the spin In the magnetic resonance imaging apparatus that receives the echo signal of the image and images the imaging object having movement in the imaging area based on the echo signal,
Means for changing the spatial position of the partial area and transmitting the selective excitation gradient magnetic field and the tagging inversion pulse a plurality of times;
Means for executing the pulse sequence after elapse of the predetermined time each time the transmission;
Means for generating a plurality of images based on echo signals respectively generated in response to the pulse sequence performed at each transmission;
Means for projecting the plurality of images to create a plurality of projection images;
Means for dynamically displaying the plurality of projected images;
A magnetic resonance imaging apparatus comprising: The magnetic resonance imaging apparatus according to claim 16.
The magnetic resonance imaging apparatus further comprising means for transmitting another inversion pulse to be applied to the entire imaging region immediately before transmitting the tagging inversion pulse . The magnetic resonance imaging apparatus according to claim 16 or 17,
The magnetic resonance imaging apparatus characterized in that the display means displays the plurality of projection images continuously in a predetermined order . The magnetic resonance imaging apparatus according to claim 18.
The magnetic resonance imaging apparatus characterized in that the display means continuously displays the plurality of projection images in accordance with a change order of a spatial position of the partial area . The magnetic resonance imaging apparatus according to claim 16 or 17,
The magnetic resonance imaging apparatus, wherein the display means displays the plurality of projection images simultaneously . The magnetic resonance imaging apparatus according to claim 16 or 17,
The means for creating the plurality of projection images obtains a position on the image corresponding to the partial area for the plurality of images, performs a masking process on the obtained position, and performs the masking process after the masking process. A magnetic resonance imaging apparatus characterized in that a plurality of projected images are created by projecting pixels having a constant value from a plurality of images . The magnetic resonance imaging apparatus according to claim 21, wherein
The magnetic resonance imaging apparatus, wherein the display means continuously displays the plurality of projection images in a predetermined order . The magnetic resonance imaging apparatus according to any one of claims 16 to 22,
The magnetic resonance imaging apparatus characterized in that the means for creating the plurality of projection images includes a maximum value projection process or a minimum value projection process . The magnetic resonance imaging apparatus according to claim 16 or 17,
The magnetic resonance imaging apparatus characterized in that the display means continuously displays only one of the divided areas divided into two by the partial area in each of the plurality of projection images . The magnetic resonance imaging apparatus according to claim 16 or 17,
The means for creating a plurality of projection images applies a masking process to only one of the divided regions divided into two by the partial region in each of the plurality of images. . The magnetic resonance imaging apparatus according to claim 25.
The magnetic resonance imaging apparatus, wherein the display means continuously displays the plurality of projection images generated by the masking process . The magnetic resonance imaging apparatus according to claim 25.
The means for creating a plurality of projection images creates the plurality of projection images by projecting pixels having a constant value from at least a part of each of the plurality of images subjected to the masking process. Magnetic resonance imaging device. The magnetic resonance imaging apparatus according to any one of claims 25 to 27,
  The magnetic resonance imaging apparatus according to claim 1, wherein the masking process is performed on a divided region upstream in the direction of movement of the imaging target. The magnetic resonance imaging apparatus according to claim 16 or 17,
  The tagged inversion pulse is composed of a plurality of inversion pulses that are continuously transmitted every minute time that can be regarded as simultaneous as compared with the movement of the imaging target, and thereby, for each pulse sequence of each time A magnetic resonance imaging apparatus characterized in that a plurality of the at least some regions are set. 30. The magnetic resonance imaging apparatus of claim 29.
  The conditions for transmitting the plurality of inversion pulses and the conditions for transmitting the selective excitation gradient magnetic field transmitted simultaneously with the plurality of inversion pulses are such that the at least a part of the region is spatially spaced on the imaging region. A magnetic resonance imaging apparatus, wherein the magnetic resonance imaging apparatus is set so that the positions are aligned and shifted from each other for each pulse sequence.

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