WO2019009487A1 - Appareil d'imagerie par résonance magnétique et procédé de reconstruction d'image du flux sanguin l'employant - Google Patents

Appareil d'imagerie par résonance magnétique et procédé de reconstruction d'image du flux sanguin l'employant Download PDF

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WO2019009487A1
WO2019009487A1 PCT/KR2018/001496 KR2018001496W WO2019009487A1 WO 2019009487 A1 WO2019009487 A1 WO 2019009487A1 KR 2018001496 W KR2018001496 W KR 2018001496W WO 2019009487 A1 WO2019009487 A1 WO 2019009487A1
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image
blood flow
magnetic resonance
imaging apparatus
signals
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PCT/KR2018/001496
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English (en)
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Jae Seok Park
Hahn Sung Kim
Jun Sik Park
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Research & Business Foundation Sungkyunkwan University
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    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/563—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution of moving material, e.g. flow contrast angiography
    • G01R33/5635—Angiography, e.g. contrast-enhanced angiography [CE-MRA] or time-of-flight angiography [TOF-MRA]
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    • A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/026—Measuring blood flow
    • A61B5/0263—Measuring blood flow using NMR
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    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
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    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
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    • G01R33/561—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
    • G01R33/5615—Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE]
    • G01R33/5617—Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE] using RF refocusing, e.g. RARE
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    • G16H30/00—ICT specially adapted for the handling or processing of medical images
    • G16H30/40—ICT specially adapted for the handling or processing of medical images for processing medical images, e.g. editing

Definitions

  • the present disclosure relates to a magnetic resonance imaging apparatus and a blood flow image reconstructing method using the same, and more particularly to a method of reconstructing a blood flow image on the basis of non-contrast magnetic resonance angiography (MRA) and a magnetic resonance imaging apparatus therefor.
  • MRA non-contrast magnetic resonance angiography
  • MRI magnetic resonance imaging
  • MRA magnetic resonance angiography
  • the MRA has been mainly used to examine an ischemia region or an infarction region of the brain or heart.
  • the conventional MRA has been performed by administering a contrast medium and thus has a problem such as side effects or dangers of the contrast medium.
  • a non-contrast MRA which does not use the contrast medium is being actively researched.
  • a fresh blood imaging (FBI) method of imaging a blood flow by capturing a high-velocity blood flow according to beats of the heart using electro cardiogram has some difficulties such as a need to image a volume for each of two cardiac phases, systole and diastole, and a need to acquire a MR signal by capturing a specific cardiac phase. Further, the FBI method has a problem of being unsuitable for application to cardiac arrhythmia patients with irregular heartbeats.
  • Japanese Patent No. 4632535 discloses MR imaging using ECG-prep scan.
  • the present disclosure has been conceived to solve the above-described problems of the conventional technology, and some exemplary embodiments of the present disclosure provides a non-contrast MRA-based blood flow image reconstructing method capable of scanning an object regardless of a specific cardiac activity state of the object. Further, the present disclosure is provided to reconstruct a blood flow image robust to cardiac phases and noises.
  • a first aspect of the present disclosure provides a non-contrast MRA-based blood flow image reconstructing method including: acquiring MR signals including blood flow information by applying a flow sensitive pulse sequence to an object; differentiating the MR signals depending on cardiac phases of the object; mapping MR signals corresponding to cardiac phases different from each other into respective k-spaces different from each other; and reconstructing a blood flow image using data of the k-spaces different from each other.
  • a second aspect of the present disclosure includes a memory in which a program configured to process a magnetic resonance image is stored and a processor configured to execute the program.
  • the processor acquires MR signals including blood flow information by applying a flow sensitive pulse sequence to an object, differentiates the MR signals depending on a cardiac phase of the object, maps MR signals corresponding to cardiac phases different from each other into respective k-spaces different from each other, and reconstructs a blood flow image using data of the k-spaces different from each other.
  • a third aspect of the present disclosure provides a computer-readable storage medium in which a program configured to implement the first aspect is recorded.
  • a magnetic resonance imaging apparatus retrospectively synchronizes MR signals acquired according to a flow sensitive pulse sequence with multiple cardiac phases and thus can scan an object regardless of a cardiac activity state of the object. Further, the magnetic resonance imaging apparatus retrospectively maps MR signals for cardiac phases different from each other into respective k-spaces different from each other and then reconstructs a blood flow image using a residual image between them and thus can acquire a blood flow image robust to artifacts and noises and naturally remove signals generated from surrounding tissues except a blood flow.
  • FIG. 1 is a block diagram illustrating an overall configuration of a magnetic resonance imaging apparatus according to an exemplary embodiment of the present disclosure.
  • FIG. 2 is a block diagram illustrating a magnetic resonance imaging apparatus according to another exemplary embodiment of the present disclosure.
  • FIG. 3 is a flowchart illustrating a method of reconstructing a blood flow image based on non-contrast MRA by a magnetic resonance imaging apparatus according to an exemplary embodiment of the present disclosure.
  • FIG. 4 illustrates an example where a magnetic resonance imaging apparatus records time stamps in MR signals depending on a cardiac phase according to another exemplary embodiment of the present disclosure.
  • FIG. 5 is a diagram illustrating an example of time stamps according to an exemplary embodiment of the present disclosure.
  • FIG. 6 is a diagram illustrating an example where a magnetic resonance imaging apparatus maps MR signals into multiple k-spaces according to an exemplary embodiment of the present disclosure.
  • FIG. 7 is a diagram illustrating an example where a magnetic resonance imaging apparatus directly reconstructs a blood flow image from k-spaces in which non-acquired data are present according to an exemplary embodiment of the present disclosure.
  • FIG. 8 are diagrams illustrating blood flow images reconstructed by maximum intensity projection of a residual image between k-spaces acquired by the method illustrated in FIG. 7 by time series
  • 'k' of FIG. 8 is a diagram illustrating a blood flow image reconstructed by maximum intensity projection of the blood flow images illustrated by time series in a time direction.
  • FIG. 9 illustrates an example where a blood flow image reconstructed according to an exemplary embodiment of the present disclosure is compared with blood flow images reconstructed according to conventional methods.
  • FIG. 10 illustrates another example where blood flow images reconstructed according to an exemplary embodiment of the present disclosure are compared with a blood flow image reconstructed according to a conventional method.
  • connection or coupling that is used to designate a connection or coupling of one element to another element includes both a case that an element is “directly connected or coupled to” another element and a case that an element is “electronically connected or coupled to” another element via still another element.
  • the term “comprises or includes” and/or “comprising or including” used in the document means that one or more other components, steps, operation and/or existence or addition of elements are not excluded in addition to the described components, steps, operation and/or elements unless context dictates otherwise.
  • magnetic resonance imaging (MRI) apparatus refers to an apparatus configured to apply a magnetic field and non-ionizing radiation (radio high frequency) to an object in order to acquire an image based on a physical principle known as nuclear magnetic resonance (NMR).
  • NMR nuclear magnetic resonance
  • image refers to multi-dimensional data composed of discrete elements and may include multiple pixels for 2-dimensinal image and multiple voxels for 3-dimensional image.
  • the term "object” refers to a target to be taken by the MRI apparatus and may include a person or animal or a part thereof. Also, the object may include various organs such as the heart, brain, or blood vessels or a variety of phantoms.
  • the term "user” refers to a medical expert such as a doctor, a nurse, a medical imaging expert, and the like or an engineer repairing a medical apparatus, but is not limited thereto.
  • pulse sequence refers to a signal repeatedly applied from the MRI apparatus.
  • the pulse sequence is a time parameter for a RF pulse and may include Time of Repetition (TR) or Time to Echo (TE).
  • TR Time of Repetition
  • TE Time to Echo
  • FIG. 1 is a block diagram illustrating an overall configuration of a magnetic resonance imaging apparatus in accordance with an exemplary embodiment of the present disclosure.
  • a magnetic resonance imaging apparatus 1 may include a MRI scanner 10, a signal processing unit 20, an interface unit 30, a control unit 40, and a monitoring unit 50.
  • the MRI scanner 10 generates a magnetic field and generates a resonance with respect to an atomic nucleus, and a magnetic resonance image is taken while an object is present inside the MRI scanner 10.
  • the MRI scanner 10 includes a main magnet 12, a gradient coil 14, a RF coil 16, and the like and thus generates a static magnetic field and a gradient magnetic field and irradiates a RF signal toward the object.
  • the main magnet 12, the gradient coil 14, and the RF coil 16 are arranged within the MRI scanner 10 along a predetermined direction.
  • the object may be positioned on a table which can be inserted into a cylinder along a horizontal axis of the cylinder, and as the table moves, the object can be positioned within a bore of the MRI scanner 10.
  • the main magnet 12 generates a static magnetic field that aligns for aligning magnetic dipole moments of atomic nucleuses included in the object in a certain direction.
  • the gradient coil 14 includes X, Y, and Z coils that respectively generate gradient magnetic fields in X-axis, Y-axis, and Z-axis directions orthogonal to each other.
  • the gradient coil 14 may induce different resonance frequencies for respective parts of the object and provide position information of each part of the object.
  • the RF coil 16 may irradiate a RF signal to the object and receive a magnetic resonance image signal emitted from the object.
  • the RF coil 16 may output a RF signal having the same frequency as a precessional motion toward an atomic nucleus performing the precessional motion and then receive a magnetic resonance image signal emitted from the object.
  • the RF coil 16 may generate a RF signal having a frequency corresponding to the atomic nucleus and apply the RF signal to the object. Then, when the RF coil 16 stops the transmission of the RF signal, the atomic nucleus to which the electromagnetic wave was applied may transition from the high energy level to the low energy level and emit an electromagnetic wave having a Larmor frequency, and the RF coil 16 receives a signal of the electromagnetic wave.
  • the RF coil 16 includes a RF transmission coil that transmits a RF signal having a radio frequency corresponding to the kind of an atomic nucleus and a RF reception coil that receives an electromagnetic wave emitted from an atomic nucleus.
  • the RF coil 16 may be fixed to the MRI scanner 10 or may be detachably attached to the MRI scanner 10.
  • the detachable RF coil 16 may be implemented as a head RF coil, a chest RF coil, a leg RF coil, a neck RF coil, a shoulder RF coil, a wrist RF coil, and an ankle RF coil which can be coupled to a part of the object.
  • the MRI scanner 10 may provide various kinds of information to a user or the object through a display and may include a display 18 provided outside the MRI scanner 10 and a display (not illustrated) provided inside the MRI scanner 10.
  • the signal processing unit 20 may control a gradient magnetic field which is formed inside the MRI scanner 10 and control transmission and reception of a RF signal and a magnetic resonance image signal according to a predetermined MR pulse sequence (i.e., pulse train).
  • a predetermined MR pulse sequence i.e., pulse train
  • the signal processing unit 20 may include a gradient amplifier 22, a switching unit 24, a RF transmitter 26, and a RF receiver 28.
  • the gradient amplifier 22 drives the gradient coil 14 included in the MRI scanner 10 and supplies the gradient coil 14 with a pulse signal that generates a gradient magnetic field under the control of a gradient magnetic field controller 44.
  • Gradient magnetic fields in the X-axis, Y-axis, and Z-axis directions may be synthesized by controlling the pulse signal supplied from the gradient amplifier 22 to the gradient coil 14.
  • the RF transmitter 26 drives the RF coil 16 by supplying a RF pulse to the RF coil 16.
  • the RF receiver 28 receives a magnetic resonance image signal received and then transferred by the RF coil 16.
  • the switching unit 24 may adjust a transmission/reception direction of each of a RF signal and a magnetic resonance image signal. For example, in a transmission mode, the switching unit 24 may irradiate a RF signal to the object through the RF coil 16, and in a reception mode, the switching unit 24 may receive a magnetic resonance image signal from the object through the RF coil 16. The switching unit 24 is controlled by a control signal from a RF controller 46.
  • the interface unit 30 may give pulse sequence information to the control unit 40 and transfer a command to control an operation of the entire MRI system at the same time by manipulation of the user.
  • the interface unit 30 may include an image processing unit 36 configured to process a magnetic resonance image signal received by the RF receiver 28, an output unit 34, and an input unit 32.
  • the image processing unit 36 may process a magnetic resonance image signal received by the RF receiver 28 and generate MR image data for the object.
  • the image processing unit 36 may perform various signal processing operations, such as amplification, frequency conversion, phase detection, low-frequency amplification, and filtering, to the magnetic resonance image signal received by the RF receiver 28.
  • the image processing unit 36 may arrange digital data in a k-space and perform a 2-dimensioanl or 3-dimensional Fourier transform to the digital data to reconfigure the digital data into image data.
  • the image processing unit 36 may parallelly perform the signal processing operations to the magnetic resonance image signal.
  • the image processing unit 36 may parallelly perform a signal processing operation to multiple magnetic resonance image signals received by a multi-channel RF coil to reconfigure the multiple magnetic resonance image signals into image data.
  • the output unit 34 may output the image data generated or reconfigured by the image processing unit 36 to the user. Further, the output unit 34 may output information, which is necessary for the user to manipulate the MRI system, such as a user interface (UI), user information, or object information.
  • the output unit 34 may include a speaker, a printer, or various image display devices.
  • the input unit 32 enables the user to input object information, parameter information, a scanning condition, a pulse sequence, information on image synthesis or differential operation, and the like.
  • the input unit 32 may include a keyboard, a mouse, a trackball, a voice recognizer, a gesture recognizer, a touch screen, etc., and include various input devices within a scope obvious to those skilled in the art.
  • the control unit 40 may include a sequence controller 42 configured to control a sequence of signals generated within the MRI scanner 10 and a scanner controller 48 configured to control the MRI scanner 10 and devices provided in the MRI scanner 10.
  • the sequence controller 42 includes the gradient magnetic field controller 44 configured to control the gradient amplifier 22 and the RF controller 46 configured to control the RF transmitter 26, the RF receiver 28, and the switching unit 24.
  • the sequence controller 42 may control the gradient amplifier 22, the RF transmitter 26, the RF receiver 28, and the switching unit 24 according to a pulse sequence received from the interface unit 30.
  • the pulse sequence may include all information required to control the gradient amplifier 22, the F transmitter 26, the RF receiver 28, and the switching unit 24, and may include, for example, information on an intensity of a pulse signal applied to the gradient coil 14, an application time, an application timing, and the like.
  • the monitoring unit 50 may monitor or control the MRI scanner 10 or the devices provided in the MRI scanner 10.
  • the monitoring unit 50 may include a system monitor 52, an object monitor 54, a table controller 56, and a display controller 58.
  • the system monitor 52 may monitor and control a state of a static magnetic field, a state of a gradient magnetic field, a state of a RF signal, a state of a RF coil, a state of a table, a state of a device that measures body information of the object, a power supply state, a state of a heat exchanger, a state of a compressor, and the like.
  • the object monitor 54 monitors a state of the object, and may include a camera for taking a picture of a movement or position of the object, a breath measurer for measuring a breath of the object, an electrocardiogram (ECG) measurer for measuring an ECG of the object, or a body temperature measurer for measuring a body temperature of the object.
  • a camera for taking a picture of a movement or position of the object
  • a breath measurer for measuring a breath of the object
  • ECG electrocardiogram
  • body temperature measurer for measuring a body temperature of the object.
  • the table controller 56 controls a movement of the table on which the object is positioned.
  • the table controller 56 may control the movement of the table according to a sequence control signal output by the sequence controller 42. For example, during moving imaging of the object, the table controller 56 may move the table according to the sequence control and thus take a picture of the object in a field of view (FOV) greater than that of the MRI scanner.
  • FOV field of view
  • the display controller 58 controls an on/off operation of the displays respectively positioned outside and inside the MRI scanner 10 or screen images output on the displays. Also, in the case where a speaker is positioned inside or outside the MRI scanner 10, the display controller 58 may control the speaker to be turned on or off or may control sound to be output through the speaker.
  • the MRI scanner 10, the RF coil 16, the signal processing unit 20, the monitoring unit 50, the control unit 40, and the interface unit 30 may be connected to each other in a wireless or wired manner, and when they are connected in a wireless manner, the magnetic resonance imaging apparatus 1 may further include an apparatus (not illustrated) for synchronizing clocks therebetween.
  • Communication between the MRI scanner 10, the RF coil 16, the signal processing unit 20, the monitoring unit 50, the control unit 40, and the interface unit 30 may be performed by using a high-speed digital interface such as low voltage differential signaling (LVDS), asynchronous serial communication such as a universal asynchronous receiver transmitter (UART), a low-delay network protocol such as error synchronous serial communication or a controller area network (CAN), optical communication, or any of other various communication methods within a scope obvious to those skilled in the art.
  • LVDS low voltage differential signaling
  • UART universal asynchronous receiver transmitter
  • CAN controller area network
  • optical communication or any of other various communication methods within a scope obvious to those skilled in the art.
  • the magnetic resonance imaging apparatus 1 is characterized by a configuration of the image processing unit 36.
  • the image processing unit 36 or the interface unit 30 including the image processing unit 36 may be implemented as a magnetic resonance imaging apparatus 100 in the form of a separate computing system as illustrated in FIG. 2, and a non-contrast magnetic resonance angiography (MRA)-based blood flow image reconstruction to be described later is performed using a memory 110 and a processor 120 installed in the computing system.
  • MRA non-contrast magnetic resonance angiography
  • the memory 110 stores a program configured to reconstruct a blood flow image.
  • the memory may collectively refer to a non-volatile storage device that retains information stored therein even when power is not supplied and a volatile storage device that requires power to retain information stored therein.
  • the processor 120 Upon execution of the program stored in the memory 110, the processor 120 reconstructs a blood flow image on the basis of a MR signal supplied from the signal processing unit 20.
  • the MR signal includes blood flow information of the object.
  • the processor 120 may acquire a MR signal including blood flow information by supplying a flow sensitive pulse sequence to the control unit 40 (or the signal processing unit 20) illustrated in FIG. 1.
  • the processor 120 monitors the object's cardiac activity state which affects a blood flow and retrospectively differentiates MR signals depending on a cardiac phase and maps the differentiated MR signals into respective k-spaces different from each other. That is, the processor 120 rearranges MR signals corresponding to the identical or similar cardiac phase into the same k-space.
  • the processor 120 reconstructs a blood flow image using data of the k-spaces different from each other, and, thus, it is possible to reconstruct an image robust to heartbeats and noise as compared with the conventional non-contrast MRA.
  • the MRI scanner 10 connected to the signal processing unit 20 (or the control unit 40) illustrated in FIG. 1 may excite a spin system by adjusting a magnetic field with an electromagnetic pulse while fixing another magnetic field as described above with reference to FIG. 1. Further, the MRI scanner 10 may generate a magnetic field on the basis of multiple gradient coils 14 to acquire a MR signal for a spatio-temporal area. As such, the processor 120 of the magnetic resonance imaging apparatus 1 may generate a blood flow image using MR signals generated by the MRI scanner 10.
  • FIG. 3 is a flowchart illustrating a method of reconstructing a blood flow image based on non-contrast MRA by the magnetic resonance imaging apparatus 100 according to an exemplary embodiment of the present disclosure.
  • the magnetic resonance imaging apparatus 100 applies a flow sensitive pulse sequence to the object to acquire a MR signal (S110).
  • the flow sensitive pulse sequence may include various pulse sequences for acquiring a MR signal including blood flow information and may be based on, for example, a fast spin echo (FSE) sequence.
  • FSE fast spin echo
  • the flow sensitive pulse sequence may include various pulse sequences within a scope obvious to those skilled in the art.
  • the magnetic resonance imaging apparatus 100 may apply the flow sensitive pulse sequence to the object and monitor a cardiac activity state of the object at the same time. For example, the magnetic resonance imaging apparatus 100 may acquire a projection echo (or a navigator echo) indicative of a cardiac phase by adding a navigator pulse sequence to the flow sensitive pulse sequence of the object. In this case, the navigator pulse sequence may be added to the inside or outside of the flow sensitive pulse sequence.
  • the magnetic resonance imaging apparatus 100 may monitor a cardiac activity state of the object using data received from an external heartbeat monitoring apparatus.
  • the heartbeat monitoring apparatus may include, for example, a pulse oximeter, an ECG apparatus, and the like, and the data received from these apparatuses may include, for example, pulse oximeter waveform data, ECG data, and the like.
  • the magnetic resonance imaging apparatus 100 may differentiate MR signals depending on a cardiac phase of the object (S120). For example, the magnetic resonance imaging apparatus 100 may record a time stamp during a cardiac activity corresponding to the time when a MR signal is acquired.
  • FIG. 4 illustrates an example where the magnetic resonance imaging apparatus 100 records time stamps in MR signals during the cardiac activity according to another exemplary embodiment of the present disclosure.
  • a flow sensitive pulse sequence is illustrated as a FSE having a variable flip angle (VFA), but may employ various flow sensitive pulse sequences as described above.
  • VFA variable flip angle
  • the magnetic resonance imaging apparatus 100 applies a flow sensitive pulse sequence 402 to the object regardless of a cardiac activity (i.e., heartbeat) of the object to acquire MR signals and also monitors a cardiac activity state 401 of the object.
  • the magnetic resonance imaging apparatus 100 may record time stamps at the time when MR signals are acquired (illustrated as shaded in each TR of FIG. 4) in order to differentiate the MR signals depending on a cardiac phase.
  • the time stamp may be shown as relative time information in each cardiac activity cycle (e.g., R-R interval in ECG data) of the object.
  • the time stamp may be recorded as a delay time from a starting point of a cardiac activity cycle.
  • a time stamp 500 may include delay times of respective MR signals in an average cardiac activity cycle 501.
  • the time stamp 500 may function as a criterion for retrospectively synchronizing cardiac phases of the object with MR signals.
  • the magnetic resonance imaging apparatus 100 may acquire first to eighth MR signals corresponding to cardiac phases different from each other in first to eighth TRs and then, the first to eighth MR signals may be differentiated on the basis of the respective delay times different from each other.
  • the magnetic resonance imaging apparatus 100 may retrospectively differentiate MR signals corresponding to identical or similar cardiac phases using the time stamp 500.
  • FIG. 4 and FIG. 5 illustrate that a time stamp is recorded on the basis of TR, and this is because a single echo train is generated from a single TR. Therefore, in the case where two or more echo trains are generated from a single TR and a MR signal is acquired at different times, two or more time stamps may be recorded in a single TR.
  • the magnetic resonance imaging apparatus 100 maps the MR signals (i.e., MR signals in which different times stamps are recorded) corresponding to the cardiac phases different from each other into respective k-spaces (hereinafter, referred to as "bins") different from each other (S130).
  • the magnetic resonance imaging apparatus 100 can rearrange MR signals corresponding to the same cardiac phase into the same bin.
  • each bin may be a 3-dimensional k-space. Therefore, MR signals may be under-sampled by a Cartesian method in a ky-kz space such as a radial trajectory or a spiral trajectory in a 3-dimensional space.
  • the magnetic resonance imaging apparatus 100 may enable MR signals to be sampled at a relatively high density in a low-frequency region (i.e., central region) in each k-space.
  • the present disclosure is not limited thereto, and MR signals may be under-sampled by a Non- Cartesian method in a 3-dimensional space.
  • FIG. 6 is a diagram illustrating an example where the magnetic resonance imaging apparatus 100 maps MR signals into multiple bins according to an exemplary embodiment of the present disclosure.
  • the magnetic resonance imaging apparatus 100 may set N number of k-spaces and then under-sample MR signals in which the same time stamp is recorded into the same k-space.
  • the MR signals are sampled at a relatively high rate in a low-frequency region in the k-space.
  • the low-frequency region in the k-space determines the overall signal intensity of a reconstructed image, and, thus, the above-described method can improve the resolution of the reconstructed image.
  • the magnetic resonance imaging apparatus 100 reconstructs a blood flow image using multiple k-spaces (i.e., multiple bins) (S140).
  • the magnetic resonance imaging apparatus 100 may directly reconstruct a blood flow image from each k-space (or image) in which non-acquired data are present.
  • the magnetic resonance imaging apparatus 100 generates a reference image on the basis of k-space data averaged in a time direction (i.e., bin direction) and then images a residual image between data of the k-space in which non-acquired data are present and the reference image.
  • the magnetic resonance imaging apparatus 100 may reconstruct an image by applying a constrained optimized image reconstruction method to a residual image.
  • the magnetic resonance imaging apparatus 100 may image a residual based on data of identical or similar intensities of multiple k-spaces to remove a signal generated from a non-flowing tissue except a blood flow and thus can reconstruct a clearer blood flow image.
  • the magnetic resonance imaging apparatus 100 may interpolate non-acquired data of each k-space first and then reconstruct an image using data of the k-space into which non-acquired data are interpolated.
  • the magnetic resonance imaging apparatus 100 may reconstruct a blood flow image by using a multi-coil convolution interpolation method or a compressed sensing method.
  • a MR signal including blood flow information can be expressed by the following Equation 1.
  • Equation 1 the MR image including a blood flow image to be reconstructed can be expressed by a Casorati matrix as shown in the following Equation 2. If Equation 2 is applied to Equation 1, Equation 1 can be expressed as the following Equation 3.
  • the sensitivity encoding operator represents a sensitivity encoding operator including coil sensitivity and Fourier transform.
  • the sensitivity encoding operator may further include an under-sampling pattern.
  • the MR image X including blood information can be expressed by the following Equation 4.
  • the magnetic resonance imaging apparatus 100 may perform modeling to a blood flow image which is changed depending on a cardiac phase as shown in the following Equation 5.
  • FIG. 7 is a diagram illustrating an example where the magnetic resonance imaging apparatus 100 directly reconstructs a blood flow image from k-spaces in which non-acquired data are present on the basis of the above description.
  • STEP 1 The magnetic resonance imaging apparatus 100 performs modeling to a residual image by subtracting a reference image from an image in a time direction (i.e., bin direction). The residual image is input into STEP 2.
  • STEP 2 The magnetic resonance imaging apparatus 100 acquires an optimized residual image on the basis of the constrained optimized image reconstruction method which can be expressed by the following Equation 6.
  • the magnetic resonance imaging apparatus 100 may find the value of Equation 6 on the basis of a sparsity prior of a residual image as expressed by the following Equation 7 and a low rank prior (property caused by a non-flowing tissue) between k-space data as expressed by the following Equation 8.
  • the magnetic resonance imaging apparatus 100 may optimize a residual image by repeatedly performing STEP 2. In this case, for operation optimization, the magnetic resonance imaging apparatus 100 may adjust the number of iterations of Equation 7 and Equation 8.
  • STEP 3 The magnetic resonance imaging apparatus 100 reconstructs a blood flow image on the basis of the optimized residual image and outputs the blood flow image.
  • FIG. 8 are diagrams illustrating blood flow images reconstructed by maximum intensity projection of a residual image between k-spaces (i.e., bins) acquired by the method illustrated in FIG. 7 by time series
  • 'k' of FIG. 8 is a diagram illustrating a blood flow image reconstructed by maximum intensity projection of the blood flow images illustrated by time series in a time direction.
  • k-space data ('a' to 'j' of FIG. 8) include blood flow information (indicated by arrows) which are not shown in other k-space data. Therefore, a blood flow image ('k' of FIG. 8) reconstructed by maximum intensity projection in a time direction (e.g., bin direction) includes all blood flow information included in k-space data acquired at different times, and, thus, it is possible to show more accurate blood flow information.
  • the magnetic resonance imaging apparatus 100 can minimize an artifact generated when a cardiac phase of the object is not synchronized. Further, the magnetic resonance imaging apparatus 100 does not have a need to acquire a MR signal corresponding to a specific cardiac phase (e.g., systole, diastole, etc.).
  • the magnetic resonance imaging apparatus 100 since the magnetic resonance imaging apparatus 100 differentiates blood flow information of various cardiac phases as separate k-space data, the magnetic resonance imaging apparatus 100 can selectively reconstruct a blood flow image at the time of a cardiac activity as required by the user.
  • FIG. 9 illustrates an example where a blood flow image reconstructed according to an exemplary embodiment of the present disclosure is compared with blood flow images reconstructed according to conventional methods. In this case, it is assumed that cardiac activities of the object are regular.
  • FIG. 9 illustrates an example of an image reconstructed by using a difference in blood flow rate between systole and diastole on the basis of a free blood imaging (FBI) method which is a non-contrast MRA method of TOSHIBA?
  • FBI free blood imaging
  • FIG. 9 illustrates an example of fat suppression (FS) in the above-described method.
  • (c) of FIG. 9 illustrates an example of an image reconstructed by using MR signals retrospectively differentiated depending on multiple cardiac phases according to an exemplary embodiment of the present disclosure.
  • a method of reconstructing a blood flow image requires the total amount of time similar to that of the conventional methods and reconstructed an image with few artifacts and noises. Further, it can suppress the signals generated from surrounding tissues.
  • FIG. 10 illustrates another example where blood flow images reconstructed according to an exemplary embodiment of the present disclosure are compared with a blood flow image reconstructed according to a conventional method. In this case, it is assumed that cardiac activities of the object are irregular.
  • FIG. 10 illustrates an example of images reconstructed on the basis of the FBI method of TOSHIBATM in the same manner as shown in FIG. 9, and (c) of FIG. 10 illustrates an example of an image reconstructed according to an exemplary embodiment of the present disclosure.
  • the method of reconstructing a blood flow image retrospectively synchronizes cardiac phases with MR signals and thus requires the same scan time regardless of cardiac activities. Further, it can be seen that even if cardiac activities are irregular, MR signals for identical or similar cardiac phases are differentiated and sampled into respective spaces different from each other and then reconstructed, and, thus, a clear image of (c) of FIG. 10 remarkably distinctive from (a) and (b) of FIG. 10 can be reconstructed. Furthermore, it can suppress the signals generated from surrounding tissues except a blood flow. That is, according to the present disclosure, a residual image of MR signals having the same intensity is imaged using a time stamp, and, thus, signals generated from surrounding tissues except a blood flow can be naturally removed.
  • the exemplary embodiments of the present disclosure have an advantage of being able to scan the object regardless of a cardiac activity state by retrospectively synchronizing MR signals acquired from the object with multiple cardiac phases of the object. Further, the exemplary embodiments of the present disclosure can acquire a blood flow image robust to artifacts and noises by sampling MR signals into k-spaces differentiated depending on a cardiac phase and then directly reconstructing a blood flow image.
  • the above-described magnetic resonance imaging apparatus and method of reconstructing a blood flow image by the magnetic resonance imaging apparatus can be embodied in a storage medium including instruction codes executable by a computer such as a program module executed by the computer.
  • a computer-readable medium can be any usable medium which can be accessed by the computer and includes all volatile/non-volatile and removable/non-removable media. Further, the computer-readable medium may include all computer storage.
  • the computer storage medium includes all volatile/non-volatile and removable/non-removable media embodied by a certain method or technology for storing information such as computer-readable instruction code, a data structure, a program module or other data.

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Abstract

La présente invention concerne un procédé de reconstruction d'une image de flux sanguin sur la base d'une angiographie par résonance magnétique (ARM) sans contraste et un appareil d'imagerie par résonance magnétique associé. En particulier, le procédé de reconstruction d'image de flux sanguin selon un exemple de mode de réalisation de la présente invention comprend : l'acquisition de signaux RM comprenant des informations sur le flux sanguin par application d'une séquence d'impulsions sensibles au flux à un objet ; la différenciation des signaux RM en fonction d'une phase cardiaque de l'objet ; la cartographie des signaux RM correspondant à des phases cardiaques différentes les unes des autres dans des espaces k respectifs différents les uns des autres ; et la reconstruction d'une image du flux sanguin à l'aide de données des espaces k différents les uns des autres.
PCT/KR2018/001496 2017-07-06 2018-02-05 Appareil d'imagerie par résonance magnétique et procédé de reconstruction d'image du flux sanguin l'employant WO2019009487A1 (fr)

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WO2014185521A1 (fr) * 2013-05-17 2014-11-20 学校法人北里研究所 Dispositif d'imagerie par resonance magnetique (irm), dispositif de traitement d'image, dispositif de diagnostic d'image, dispositif d'analyse d'image et procede et programme de creation d'image d'irm
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KR101826702B1 (ko) * 2015-11-10 2018-03-22 삼성전자주식회사 자기 공명 영상 장치 및 그 방법

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US20130121550A1 (en) * 2010-11-10 2013-05-16 Siemens Corporation Non-Contrast-Enhanced 4D MRA Using Compressed Sensing Reconstruction
WO2014185521A1 (fr) * 2013-05-17 2014-11-20 学校法人北里研究所 Dispositif d'imagerie par resonance magnetique (irm), dispositif de traitement d'image, dispositif de diagnostic d'image, dispositif d'analyse d'image et procede et programme de creation d'image d'irm
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