WO2018186578A1 - Magnetic resonance imaging device and control method therefor - Google Patents

Abstract

Provided are: a magnetic resonance imaging device for receiving an RF echo signal including image information and motion information of a subject for each period and generating magnetic resonance imaging in which the motion information has been removed from the received RF echo signal; and a control method therefor. The magnetic resonance imaging device according to one embodiment can comprise: an RF coil part for emitting a first RF pulse at a first cross-section of a subject and a second RF pulse at a second cross-section of the subject for each period, and receiving an RF echo signal including an image echo component generated in correspondence to the first RF pulse and a tracking echo component generated in correspondence to the second RF pulse; an image processing part for acquiring k-space data on the basis of the received RF echo signal, synchronizing the k-space data with the motion information acquired from the tracking echo component, removing the tracking echo component from the synchronized k-space data, and generating magnetic resonance imaging by using the k-space data from which the tracking echo component has been removed; and an output part for displaying the generated magnetic resonance imaging.

Description

Magnetic Resonance Imaging Device and Control Method

A magnetic resonance imaging apparatus for obtaining a cross-sectional image of an object based on a magnetic resonance signal, and a control method thereof.

In general, a medical imaging apparatus is an apparatus that provides an image by acquiring patient information. Medical imaging apparatuses include X-ray apparatus, ultrasound diagnostic apparatus, computed tomography apparatus, magnetic resonance imaging apparatus, and the like.

Among these, magnetic resonance imaging apparatuses occupy an important position in the field of diagnosis using medical imaging because imaging conditions are relatively free, and excellent contrast in soft tissue and various diagnostic information images are provided.

Magnetic Resonance Imaging (MRI) is an image of the density and physicochemical characteristics of nuclear nuclei by using nuclear magnetic field and non-electromagnetic radiation, RF, which is harmless to the human body, causing nuclear magnetic resonance.

In principle, magnetic resonance imaging needs to be performed on patients who do not breathe. If the patient breathes during the magnetic resonance imaging, since the data acquired during the breathing constitutes one k-space, there is a possibility that artifacts may occur in the magnetic resonance images generated based on this.

According to an embodiment of the present invention, a magnetic resonance imaging apparatus for receiving an RF echo signal including image information and motion information of an object at each cycle, and generating a magnetic resonance image from which the motion information is removed from the received RF echo signal; It provides a control method.

The magnetic resonance imaging apparatus according to an embodiment irradiates a first RF pulse with respect to a first cross section of the object and a second RF pulse with respect to a second cross section of the object at intervals, and generates the first RF pulse in response to the first RF pulse. An RF coil unit configured to receive an RF echo signal including a captured image echo component and a tracking echo component generated in response to the second RF pulse; Construct a k-space based on the received RF echo signal, synchronize the data of the k-space with motion information obtained from the tracking echo component, and use an eigenvector of the tracking echo component An image processor which removes the tracking echo component from the synchronized k-spatial data and generates a magnetic resonance image using the k-spatial data from which the tracking echo component is removed; And an output unit displaying the generated magnetic resonance image. It may include.

The RF coil unit may be operated such that the second RF pulse phases of the adjacent periods are opposite to each other.

In addition, after the first RF pulse irradiation, before the second RF pulse irradiation, the gradient magnetic field forming unit for applying a gradient magnetic field for phase encoding (Phase Encoding) to the object; It may further include.

The image processor may acquire the motion information of the object by using the center of gravity for each frequency component of the tracking echo component.

The image processor may extract the synchronized k-spatial data that falls within the valid range determined by the motion information, and may remove the tracking echo component from the extracted k-spatial data.

The image processing unit may further include k-spaces extracted from the plurality of k-spaces when a plurality of k-spaces are configured by the first RF pulse and the second RF pulses irradiated repeatedly for each period. Data obtained in the same phase among the data may be accumulated to reconstruct one k-space, and the tracking echo component may be removed from the reconstructed one k-space data.

The image processor may acquire the eigenvector of the tracking echo component using a frequency component equal to or greater than a predetermined reference frequency among the synchronized k-spatial data.

The image processor may remove the tracking echo component from the synchronized k-spatial data by projecting the synchronized k-spatial data to the eigenvector of the tracking echo component.

The image processor may restore the k-spatial data from which the tracking echo component has been removed through a parallel imaging method, and generate the magnetic resonance image using the restored k-spatial data. have.

In another embodiment, a method of controlling a magnetic resonance imaging apparatus includes irradiating a first RF pulse with respect to a first cross section of an object and a second RF pulse with respect to a second cross section of an object at each cycle; Receiving an RF echo signal comprising an image echo component generated in response to the first RF pulse and a tracking echo component generated in response to the second RF pulse; Constructing k-space based on the received RF echo signal; Synchronizing the k-space data with motion information obtained from the tracking echo component; Removing the tracking echo component from the synchronized k-spatial data using an eigenvector of the tracking echo component; Generating a magnetic resonance image using the k-spatial data from which the tracking echo component has been removed; And displaying the generated magnetic resonance image. It may include.

In the irradiating of the first RF pulse and the second RF pulse, the second RF pulse may be irradiated such that the second RF pulse phases of the adjacent periods are opposite to each other.

The method may further include applying a gradient magnetic field for phase encoding to the object after the first RF pulse irradiation and before the second RF pulse irradiation for each period; It may further include.

The synchronizing of the k-spatial data with the motion information may include obtaining motion information of the object by using a center of gravity for each frequency component of the tracking echo component, and obtaining the k-spatial data from the obtained motion information. Can be synchronized.

In addition, removing the tracking echo component from the synchronized k-spatial data includes: extracting the synchronized k-spatial data that falls within an effective range determined by the motion information; And removing the tracking echo component from the extracted k-spatial data; It may include.

The removing of the tracking echo component from the extracted k-space data may include: when a plurality of k-spaces are configured by the first RF pulse and the second RF pulse irradiated repeatedly for each period, Reconstructing one k-space by accumulating data acquired in the same phase among the k-space data extracted from the plurality of k-spaces; And removing the tracking echo component from the reconstructed one k-space data; It may include.

In addition, removing the tracking echo component from the synchronized k-spatial data may include obtaining the eigenvector of the tracking echo component using a frequency component equal to or greater than a predetermined reference frequency among the synchronized k-spatial data, The tracked echo component may be removed from the synchronized k-spatial data using the obtained eigenvectors.

In addition, removing the tracking echo component from the synchronized k-spatial data may include projecting the synchronized k-spatial data to the eigenvector of the tracking echo component to generate the synchronized k-spatial data. The tracking echo component can be removed from the system.

The generating of the magnetic resonance image may include restoring the k-spatial data from which the tracking echo component has been removed through a parallel imaging method, and using the restored k-spatial data. An image can be generated.

According to a magnetic resonance imaging apparatus and a control method thereof according to an aspect, since an RF echo pulse including both image information and motion information is received by RF pulses irradiated every cycle, the magnetic resonance image acquisition time may be shortened. . In addition, since image information and motion information are not separately obtained, a steady state of the image information may be maintained.

1 is a schematic diagram of an MRI system.

2 is a sequence diagram of a magnetic resonance imaging apparatus according to an exemplary embodiment.

3 is an image of a k-space taken by a magnetic resonance imaging apparatus according to an exemplary embodiment.

4 is a magnetic resonance image taken by the magnetic resonance imaging apparatus according to an embodiment.

5 is a diagram for describing a method of searching for a weighting coefficient by a magnetic resonance imaging apparatus according to an exemplary embodiment.

6A illustrates a 1D Fourier transform image of k-spatial data in a kx direction of a magnetic resonance imaging apparatus, and FIG. 6B illustrates an estimated tracking echo of k-spatial data of the magnetic resonance imaging apparatus, according to an exemplary embodiment. It is a 1D Fourier transform image in the kx direction of the component.

7 to 9 are diagrams for describing a method of removing a tracking echo component of a magnetic resonance imaging apparatus, according to an exemplary embodiment.

10 to 12 are diagrams for describing a method of removing a tracking echo component of a magnetic resonance imaging apparatus according to another exemplary embodiment. 13 is a flowchart of a method of controlling a magnetic resonance imaging apparatus, according to an exemplary embodiment.

The present specification clarifies the scope of the present invention, describes the principles of the present invention, and discloses embodiments so that those skilled in the art can carry out the present invention. The disclosed embodiments can be implemented in various forms.

Like reference numerals refer to like elements throughout. The present specification does not describe all elements of the embodiments, and overlaps between general contents or embodiments in the technical field to which the present invention belongs. As used herein, the term 'part' may be implemented in software or hardware. Depending on the embodiments, a plurality of 'parts' may be embodied as one unit or one' It is also possible for a subsection to include a plurality of elements.

In the present specification, an 'object' is an object to be photographed, and may include a person, an animal, or a part thereof. For example, the subject may comprise part of the body (organ or organ; organ) or phantom or the like.

Hereinafter, the working principle and the embodiments of the present invention will be described with reference to the accompanying drawings.

1 is a schematic diagram of an MRI system.

The MRI system may acquire a magnetic resonance (MR) signal and reconstruct the acquired magnetic resonance signal into an image. The magnetic resonance signal may refer to an RF signal radiated from the object.

In an MRI system, a main magnet forms a static magnetic field, and the magnetic dipole moment direction of a specific atomic nucleus of an object located in the static field may be aligned in the direction of the static field. The gradient magnetic field coil may apply an inclination signal to the static magnetic field to form a gradient magnetic field to induce a resonance frequency for each part of the object.

The RF coil unit may radiate an RF pulse according to a resonance frequency of a portion of which an image is to be acquired. In addition, as the gradient coil is formed, the RF coil unit may receive magnetic resonance signals of different resonance frequencies (hereinafter referred to as RF echo signals) emitted from various parts of the object. In this step, the MRI system acquires an image from the RF echo signal using an image reconstruction technique.

To this end, referring to FIG. 1, the MRI system 1 may include an operating unit 10, a controller 30, and a scanner 50. Here, the controller 30 may be independently implemented as shown in FIG. 1. Alternatively, the controller 30 may be divided into a plurality of components and included in each component of the MRI system 1. Hereinafter, each component will be described in detail.

The scanner 50 may be embodied in a shape (eg, a bore shape) in which an object may be inserted, so that the internal space is empty. Static and gradient magnetic fields are formed in the internal space of the scanner 50, and RF signals may be irradiated.

The scanner 50 may include a static magnetic field forming unit 51, a gradient magnetic field forming unit 52, an RF coil unit 53, a table unit 55, and a display unit 56. The static field forming unit 51 may form a static field for aligning the directions of the magnetic dipole moments of the nuclei included in the object in the direction of the static field. The static field forming unit 51 may be implemented as a permanent magnet or a superconducting magnet using a cooling coil.

The gradient magnetic field forming unit 52 may be connected to the control unit 30. Inclination is applied to the static magnetic field according to the control signal received from the controller 30 to form a gradient magnetic field. The gradient magnetic field forming unit 52 includes X, Y, and Z coils that form gradient magnetic fields in the X-, Y-, and Z-axis directions that are orthogonal to each other, and photographed to induce resonance frequencies differently for each part of the object. The tilt signal can be generated according to the position.

The RF coil unit 53 may be connected to the controller 30 to irradiate an RF pulse to the object according to a control signal received from the controller 30 and receive an RF echo pulse emitted from the object. The RF coil unit 53 may transmit an RF signal having a frequency equal to the frequency of the precession toward the atomic nucleus during the precession to the object, stop transmitting the RF pulse, and receive the RF echo pulse emitted from the object. .

The RF coil unit 53 is implemented as a transmitting RF coil for generating electromagnetic waves having a radio frequency corresponding to the type of atomic nucleus and a receiving RF coil for receiving electromagnetic waves radiated from the atomic nucleus, respectively, or having a transmission / reception function together. May be implemented as an RF transmit / receive coil. In addition, in addition to the RF coil unit 53, a separate coil may be mounted on the object. For example, a head coil, a spine coil, a torso coil, a knee coil, or the like may be used as a separate coil according to a photographing part or a mounting part.

The display unit 56 may be provided outside and / or inside the scanner 50. The display unit 56 may be controlled by the controller 30 to provide information related to medical image capturing to a user or an object.

In addition, the scanner 50 may be provided with an object monitoring information acquisition unit for obtaining and delivering monitoring information on the state of the object. For example, the object monitoring information acquisition unit (not shown) may include a camera (not shown) for photographing the movement and position of the object, a respiratory meter (not shown) for measuring breathing of the object, and an electrocardiogram for measuring the object. The monitoring information about the object may be obtained from the ECG measuring device (not shown) or the body temperature measuring device (not shown) for measuring the body temperature of the object and transferred to the controller 30. Accordingly, the controller 30 may control the operation of the scanner 50 by using the monitoring information about the object. Hereinafter, the controller 30 will be described.

The controller 30 may control the overall operation of the scanner 50.

The controller 30 may control a sequence of signals formed in the scanner 50. The controller 30 may control the gradient magnetic field forming unit 52 and the RF coil unit 53 according to a pulse sequence received from the operating unit 10 or a designed pulse sequence.

The pulse sequence includes all the information necessary for controlling the gradient magnetic field forming unit 52 and the RF coil unit 53, for example, the intensity of a pulse signal applied to the gradient magnetic field forming unit 52. , Application duration, application timing, and the like.

The controller 30 may include a waveform generator (not shown) for generating a gradient waveform, that is, a current pulse according to a pulse sequence, and a gradient amplifier (not shown) for amplifying the generated current pulse and transferring the gradient to the gradient magnetic field forming unit 52. By controlling, the gradient magnetic field formation of the gradient magnetic field forming unit 52 can be controlled.

The controller 30 may control the operation of the RF coil unit 53. For example, the controller 30 may irradiate an RF pulse having a resonance frequency by the RF coil unit 53, and receive an RF echo signal received by the RF coil unit 53. In this case, the controller 30 may control the operation of a switch (for example, a T / R switch) capable of adjusting a transmission / reception direction through a control signal, and may adjust the irradiation of the RF pulse and the reception of the magnetic resonance signal according to the operation mode. .

The controller 30 may control the movement of the table unit 55 in which the object is located. Before the photographing is performed, the controller 30 may move the table 55 in advance in accordance with the photographed portion of the object.

The controller 30 may control the display 56. For example, the controller 30 may control on / off of the display 56 or a screen displayed through the display 56 through a control signal.

The controller 30 may include an algorithm for controlling the operation of components in the MRI system 1, a memory for storing data in a program form (not shown), and a processor for performing the above-described operations using data stored in the memory ( Not shown). In this case, the memory and the processor may be implemented as separate chips. Alternatively, the memory and the processor may be implemented in a single chip.

The operating unit 10 may control the overall operation of the MRI system 1. The operating unit 10 may include an image processor 11, an input unit 12, and an output unit 13.

The image processor 11 may store the MR signals received from the controller 30 using a memory, and generate image data of the object from the stored MR signals by applying an image reconstruction technique using the image processor. Can be.

For example, the image processor 11 may reconstruct various images through the image processor when the k-space data is completed by filling digital data in k-space (eg, also referred to as Fourier space or frequency space) of the memory. The technique can be applied (eg, by inverse Fourier transform of k-spatial data) to reconstruct k-spatial data into image data.

In addition, various signal processings applied by the image processor 11 to the magnetic resonance signal may be performed in parallel. For example, a plurality of magnetic resonance signals received by the multi-channel RF coil may be signal-processed in parallel to restore the image data. The image processor 11 may store the restored image data in a memory or the controller 30 may store the restored image data in an external server through the communication unit 60.

The input unit 12 may receive a control command regarding the overall operation of the MRI system 1 from the user. For example, the input unit 12 may receive object information, parameter information, scan conditions, information about a pulse sequence, and the like from a user. The input unit 12 may be implemented as a keyboard, a mouse, a trackball, a voice recognition unit, a gesture recognition unit, a touch screen, or the like.

The output unit 13 may output image data generated by the image processor 11. In addition, the output unit 13 may output a user interface (UI) configured to allow a user to receive a control command regarding the MRI system 1. The output unit 13 may be implemented as a speaker, a printer, a display, or the like.

In FIG. 1, the operating unit 10 and the control unit 30 are illustrated as separate objects from each other, but as described above, may be included together in one device. In addition, processes performed by each of the operating unit 10 and the control unit 30 may be performed in another object. For example, the image processor 11 may convert the magnetic resonance signal received by the controller 30 into a digital signal, or the controller 30 may directly convert the magnetic resonance signal.

The MRI system 1 includes a communication unit 60, and through the communication unit 60, an external device (not shown) (eg, a server, a medical device, a portable device (smartphone, tablet PC, wearable device, etc.)). Can be connected with

The communication unit 60 may include one or more components that enable communication with an external device, for example, at least one of a short range communication module (not shown), a wired communication module 61, and a wireless communication module 62. It may include.

On the other hand, magnetic resonance imaging by the above-described magnetic resonance imaging apparatus 1 may take a relatively long time, if the movement of the subject (for example, the heart rate, breathing, etc. of the patient) during this time, finally Artifacts may occur in the acquired MRI signal. Therefore, in the case of an object having a high possibility of motion, it is necessary to additionally acquire information about the motion in addition to the information on the image when the MRI is taken.

If the navigator echo signal is acquired by irradiating an RF pulse for the motion information separately from acquiring the image information, the total photographing time may be increased because the image information and the motion information are obtained by dividing the navigator echo signal. In addition, since a photographing for acquiring motion information is involved in the middle of photographing for acquiring image information, a steady state imaging technique which is frequently used in magnetic resonance imaging of a heart region cannot be applied.

Accordingly, the magnetic resonance imaging apparatus 1 and the control method according to the disclosed embodiment receive an RF echo signal including the image information and the motion information of the object at each cycle and remove the motion information from the received RF echo signal. Resonance images can be generated.

2 is a sequence diagram of a magnetic resonance imaging apparatus according to an embodiment, FIG. 3 is an image of a k-space photographed by the magnetic resonance imaging apparatus according to an embodiment, and FIG. 4 is a magnetic resonance according to an embodiment. Magnetic resonance image taken by the imaging device. In FIG. 2, RF denotes a sequence of RF pulses radiated by the RF coil unit 53, SL denotes a sequence of Z-axis gradient magnetic fields applied by the gradient magnetic field forming unit 52, and RE denotes gradient magnetic field formation. It may mean a sequence of the Y-axis gradient magnetic field applied by the unit 52, RO may mean a sequence of the RF echo signal received by the RF coil unit 53.

Referring to FIG. 2, the RF coil unit 53 may radiate a first RF pulse having a flip angle of α ° and a second RF pulse having a flip angle of β ° every cycle. Here, the first RF pulse may be an RF pulse for obtaining image information, and the second RF pulse may be an RF pulse for obtaining motion information. In particular, the second RF pulse may be reversed in phase every period. That is, if the second RF pulse phase in the first period is 0 degrees, the RF pulse phase in the second period may be 180 degrees, and the RF pulse phase in the third period may be 0 degrees again. This is for easily removing the tracking echo component to be described later, which will be described later.

Therefore, when the first RF pulse is irradiated, the gradient magnetic field forming unit 52 may apply the Z-axis gradient magnetic field to the object so that the cross section S1 of interest is selected. In addition, when the second RF pulse is irradiated, the gradient magnetic field forming unit 52 may apply the Z-axis gradient magnetic field to the object such that the cross-section S2 of which movement is expected to be selected is selected. In this case, the cross-section of interest S2, which is expected to generate a movement, may be set as a plane passing through the heart region and the liver region so that the cross-section of interest S2 may include both heart and respiration movement information.

Meanwhile, in order to obtain image information through the first RF pulse, the gradient magnetic field forming unit 52 may apply a Y-axis gradient magnetic field for phase encoding to the object at a time after the irradiation of the first RF pulse. .

On the other hand, since the second RF pulse has a purpose to obtain motion information, phase coding by the gradient magnetic field forming unit 52 may not be performed after the irradiation of the second RF pulse.

Finally, the RF coil unit 53 includes an image echo component (including image information generated by the first RF pulse) generated in response to the first RF pulse and a tracking echo component (second second generated in response to the second RF pulse). And a single RF echo signal including image information and motion information generated by the RF pulse. That is, in response to the first RF pulse and the second RF pulse irradiated within one period, the RF coil unit 53 may receive one RF echo signal. Therefore, in order to eliminate the artifacts caused by the movement and to acquire the magnetic resonance image composed only of the image information, the magnetic resonance imaging apparatus 1 needs to remove the tracking echo component from the received RF echo signal.

Prior to removing the tracking echo component from the received RF echo signal, the image processor 11 may remove the tracking echo component including motion information from the received RF echo signal. First, the image processor 11 may form a k-space by storing an RF echo signal in a memory. The k-space may be a two-dimensional space consisting of the kx axis and the ky axis, the kx axis may be in the frequency direction, and the ky axis may be in the phase direction.

For example, in the case of obtaining an RF echo signal for 20 different Y-axis gradient fields, the ky-axis may consist of 20 transverse lines, or 20 ky lines, obtained for each Y-axis gradient field. The RF echo signal can fill one ky line. Therefore, if all RF echo signals are obtained for 20 different y-axis gradient fields, one k-space can be completed while all 20 ky lines are filled.

The image processor 11 may generate a magnetic resonance image by using the data of the k-space thus completed. 3 is a k-space image formed by the above-described RF echo signal, and FIG. 4 is a magnetic resonance image generated using k-space data constituting the k-space of FIG. 3. Since the above-described RF echo signal includes an image echo component and a tracking echo component, the magnetic resonance signal generated based on the RF echo signal may include information of each echo component. In FIG. 4, it can be seen that the ROI S1 representing the information of the image echo component generated in response to the first RF pulse and the ROI S2 representing the information of the trace echo component generated in response to the second RF pulse are also displayed.

The magnetic resonance image of FIG. 4 illustrates a case in which the region of interest S2 appears on one side. This is caused by reversing the phase of the second RF pulse for each period. In the process of imaging the tracking echo component of the received RF echo signal, the ROI S2 may be shifted to one side or both sides of the image due to the phase difference. As a result, since the ROIs S1 and S2 are separated from each other and appear on the magnetic resonance image, the tracking echo component can be easily removed from the RF echo signal.

As described above, when the RF echo signal is converted into the magnetic resonance image without removing the tracking echo component from the k-space data stored therein, an unnecessary region of interest S2 may appear on the magnetic resonance image. Therefore, the image processor may first remove the tracking echo component from the k-spatial data and then image the result.

In order to remove the tracking echo component, the image processor 11 may perform steps of estimating the <1> tracking echo component, <2> moving gating, and <3> removing the tracking echo component.

First, the image processor 11 may estimate the <1> tracking echo component. In this step, the image processor 11 may extract the motion information included in the tracking echo component by estimating the tracking echo component in the k-spatial data.

In detail, the image processor 11 may estimate the tracking echo component from the k-spatial data according to the equation of Slice-GRAPPA.

Here, K _{j, S1 + S2} is k-space data configured by the RF echo signal, K _{j, S2} is the tracking echo component of the k-space data, j, l is the Index of the RF coil unit 53 B may mean location information of k-space, N _b may mean total position, and n (j, b, l) may mean a weighting factor.

Since the receiving coil of the RF coil unit 53 has a plurality of channels, Equation 1 may mean that information about the tracking echo component may be estimated by weighting k-space data received by each receiving coil. have.

In order to apply Equation 1, the image processor 11 needs to search the weight coefficient n (j, b, l). To this end, the magnetic resonance imaging apparatus 1 may obtain only k-spatial data by irradiating only the first RF pulse and then irradiate the RF pulse according to the above-described method.

FIG. 5 is a diagram for describing a method of searching a weight coefficient by a magnetic resonance imaging apparatus, and FIG. 6A is a 1D Fourier in kx direction of k-space data of the magnetic resonance imaging apparatus, according to an exemplary embodiment. 6B is a 1D Fourier transform image in the kx direction of an estimated tracking echo component among k-spatial data of the magnetic resonance imaging apparatus according to an exemplary embodiment. In FIG. 5, the graph refers to a motion curve of the object over time, M1 is a weight coefficient search interval (preferably within the first 2 to 3 seconds), and M2 is a data acquisition interval.

As described above, when magnetic resonance imaging is started, an RF echo signal consisting of only trace echo components is obtained by first irradiating only the second RF pulse, and then, an image according to irradiation of the first RF pulse and the second RF pulse. An RF echo signal can be obtained that includes an echo component and a tracking echo component. Accordingly, as shown in FIG. 5, the image processing unit 11 includes k-spatial data according to an RF echo signal composed only of the tracking echo components in the weight coefficient search interval M1, and an image echo component and a tracking echo component in a subsequent period. The weighting coefficient n can be searched by comparing k-spatial data according to the RF echo signal.

FIG. 5 illustrates a case in which the weighting factor n is searched at various positions of the weighting coefficient search section M1 (indicated by X in FIG. 5), that is, in various motion states of the object. Since the receiving coil of the RF coil unit 53 may respond to the change in the magnetic field generated by the movement of the object, it is necessary to search for the weighting coefficient n for each movement state.

When the search for the weighting coefficient n is completed, it may be applied to Equation 1 to estimate the tracking echo component K _S2 in the k-space data. As a result, when the image of FIG. 6A is input to Equation 1, the image of FIG. 6B may be output. For reference, the image of FIG. 6A is an image in which two k-space data are arranged in chronological order, and includes 384 (192 × 2) phase coding lines (PE lines) in total and was acquired for 1.8 seconds.

The estimated tracking echo component K _S2 may have a slight error according to factors such as the sensitivity of the receiving coil and the error of the weight coefficient. Therefore, the image processor 11 can use the estimated tracking echo component K _S2 only to extract motion information.

Referring to the image of FIG. 6B according to the result of Equation 1, it can be seen that the region including the C region representing the heart movement information and the R region representing the movement information of the breath. As such, since the estimated tracking echo component K _S2 includes motion information, the image processor 11 may digitize such motion information.

The image processor 11 may adopt any one of various known methods for digitizing motion information from the estimated tracking echo component K _S2 . For example, the image processor 11 may quantify the motion information from the tracking echo component K _S2 using the Center Of Mass (COM), and the equation for obtaining the center of gravity is shown in Equation (2).

Here, COM may mean a center of gravity, and I _proj (x) may mean a value obtained by performing a 1D Fourier Transform on K _S2 in the kx direction.

After acquiring the COM value, the image processor 11 performs a band pass filter (BW: 50 to 120 bpm or 0.5 Hz to 2 Hz) corresponding to the heart movement and a band pass filter (BW: 0.1 Hz to 0.4 Hz corresponding to the respiratory movement). ) Can be applied to the acquired COM.

In this way, the image processor 11 may digitize the motion information of the object, thereby setting an effective range used for gating to be described later. Here, the effective range may mean a range in which the movement is minimized, such as the end of the exhalation in the breath can be obtained stably image information, and can act as a gating window in the gating to be described later have.

When the setting of the effective range is completed through the motion information, the image processing unit 11 may perform <2> motion gating. Here, gating refers to reconstructing one k-space by synchronizing data constituting each of the plurality of k-spaces with motion information and then accumulating data acquired in the same phase with respect to k-space data belonging to an effective range. Can mean a process. Through the gating process, the image processor 11 may remove the motion information from the k-spatial data.

Hereinafter, k-spatial data gated with motion information is referred to as G _{s1 + S2} .

After acquiring G _{s1 + S2} from the gated k-spatial data, the image processor 11 may remove the tracking echo component. 7 to 9 are diagrams for describing a method of removing a tracking echo component of a magnetic resonance imaging apparatus, according to an exemplary embodiment.

As described above, the tracking echo component may include image information on the cross-section S2 of interest together with the motion information. 7 is a magnetic resonance image generated based on G _{s1 + S2} of gated k-spatial data according to an embodiment, and it can be seen that noise images exist on both sides of the image. This indicates that the image information about the cross section S2 of interest is included in the magnetic resonance image.

Since the tracking echo component includes image information of the cross-section S2 that is not yet necessary even though the motion information is removed through gating, the image processor 11 removes the gated tracking echo component G _S2 from the gated k-spatial data G _{s1 + S2} . Needs to be.

The gated k-spatial data G _{s1 + S2} may be expressed in the form of adding the gated tracking echo component as the same DC component to all phase coding lines of the image echo component, which is expressed by Equation 3 below.

Here, G _{s1 + S2} denotes the gated k-spatial data, G _s1 denotes the image echo component of the gated k-spatial data, and G _S2 denotes the tracking echo component of the gated k-spatial data. Can be.

In this case, the gated tracking echo component G _S2 may have a low rank property because the phase coding components configured in the phase coding direction are the same or very similar. On the other hand, the gated picture echo component G _S1 may not be low rank because the phase coding components are different. In addition, the gated image echo component G _S1 is a tracking echo component G _{S2 in} which the magnitude of the phase coding component is gated in the high frequency region. Very small compared to Accordingly, the image processor 11 may remove G _S2 from G _{s1 + S2} based on such characteristics.

Specifically, first, the image processor 11 may extract a high frequency component of the gated k-spatial data G _{s1 + S2} . As described above, the characteristics of the tracking echo component G _S2 are better revealed in the high frequency region. The image processor 11 may reconstruct the k-space of the k-spatial data G _{s1 + S2} gated based on the extracted high frequency component.

Next, the image processor 11 may perform Principal Component Analysis (PCA) by applying Singular Value Decomposition (SVD) to the gated k-spatial data G _{s1 + S2} . A tracking echo component having a rank close to 1 may be positioned around a principal component, and an image echo component not otherwise may be located in a vector space other than the principal component. Thus, by checking the eigenvector corresponding to the largest eigenvalue λ, the traced echo component G _S2 gated. It is possible to obtain an eigenvector of.

Finally, the image processing unit 11 is gated tracking echo component G _S2 By projecting k-spatial data G _{s1 + S2} gated in the eigenvector space excluding the eigenvector of, only the gated image echo component G _S1 can be separated.

8 is the gated tracking echo component G _S2 removed from the image of FIG. FIG. 9 shows a magnetic resonance image of a gated image echo component G _S1 separated from the image of FIG. 7. In the finally obtained image of FIG. 9, not only the motion information of the object is excluded, but also the image information of the region of interest S2 of the tracking echo component for tracking the motion information may be removed.

On the other hand, K _{s1 + S2} may not be obtained for a sufficient time, and thus data may not be stored in some phase coding lines. In this case, the gated image echo component G _S1 finally obtained by the image processor 11 may also have an under sampling pattern. In this case, the image processor 11 may reconstruct an image by applying a parallel imaging method to an empty phase encoding line.

Finally, the output unit 13 may visually output the magnetic resonance image, for example, the image of FIG. This allows the user to collect more accurate anatomical information of the subject.

So far, the embodiment of removing the tracking echo component using the eigenvector has been described. However, the image processor 11 may remove the gated tracking echo component from the gated k-spatial data according to a different method.

Hereinafter, another embodiment of removing the gated tracking echo component from the gated k-spatial data will be described. The gated k-spatial data is set to S _acq to distinguish it from the above-described embodiment. The component is S _im , and the gated trace echo component is denoted by S _nav .

10 to 12 are diagrams for describing a method of removing a tracking echo component of a magnetic resonance imaging apparatus according to another exemplary embodiment.

FIG. 10 is a diagram illustrating magnetic resonance images I _acq obtained by performing two-dimensional Fourier transform of gated k-spatial data S _acq and S _acq according to another embodiment.

Referring to FIG. 10, the gated k-spatial data S _acq may include image information about a cross-section S2 of interest formed in the ky direction at the top thereof, and as a result, magnetic resonance images obtained by performing two-dimensional Fourier transform of S _acq . I _acq may have noise on both sides.

In order to eliminate this, the image processor 11 may add the gated k-spatial data to two adjacent components in S _acq in the ky direction. In detail, the image processor 11 may process S _acq according to Equation 4 to obtain S _im ^esti obtained by combining two adjacent components in the ky direction.

Here, S _im ^esti may mean an intermediate value for obtaining a gated image echo component S _im . Also, since the gated tracking echo component S _nav is not subjected to phase coding by the gradient magnetic field forming unit 52, ky is zero. In consideration of this, an N value may be set.

As described above, since the phases of the second RF pulse for obtaining the motion information are reversed for each period, the sum of the components adjacent in the ky direction among the gated tracking echo components _Snav may be calculated according to Equation 5 below.

Referring to Equation 5, the gated tracking echo component can be eliminated S _nav by summing adjacent consecutive components in the ky direction.

When the S _im ^esti obtained through the above process, the image processing unit 11 is an image from the echo component gating S S _{im im} ^esti This 2D Fourier Converted I _im Can be obtained. In this case, the image processor 11 may follow Equation 6.

Where I _im ^esti is the result of 2D Fourier transforming the gated image echo component S _im , and I _im Is gated image echo component S _im 2D Fourier It can mean the result of the conversion. In addition, W (y) may mean a Magnitude Window for obtaining S _im from S _im ^esti .

Referring to Equation 6, the image processor 11 divides I _im ^esti by W (y), thereby gating the image echo component S _im. This 2D Fourier Converted I _im Can be obtained. The obtained image I _im may be an image obtained by removing not only the motion information of the object but also the image information of the region of interest S2 of the tracking echo component for tracking the motion information.

FIG. 11 is a diagram illustrating magnetic resonance images I _im ^esti obtained by performing two-dimensional Fourier transformation of S _im ^esti and S _im ^esti according to another embodiment, and FIG. 12 illustrates a magnitude window W (y) according to an embodiment. The illustrated figure.

Referring to FIG. 11, as described above, it may be confirmed that image information about a tracking echo component, specifically, the section S2 of interest is removed from S _im ^esti . As a result, in the obtained two-dimensional Fourier transform to S _im ^esti MRI I _im ^esti can be concluded that the noise is removed, that existed on both sides. Image processing unit 11 can obtain the I _{im im} ^esti from I using the magnitude window W (y) as shown in FIG. 12.

13 is a flowchart of a method of controlling the magnetic resonance imaging apparatus 1 according to an exemplary embodiment.

First, the magnetic resonance imaging apparatus 1 irradiates an RF pulse according to an RF pulse sequence for irradiating a first RF pulse for obtaining image information of a first section and a second RF pulse for obtaining motion information of a second section. In this case, the irradiated second RF pulse may be reversed in phase every period.

The magnetic resonance imaging apparatus 1 may then obtain k-spatial data including an image echo component generated in response to the first RF pulse and a tracking echo component generated in response to the second RF pulse. Specifically, the magnetic resonance imaging apparatus 1 may configure a k-space by receiving an RF echo signal including an image echo component and a tracking echo component, and storing the received RF echo signal in a memory.

When the k-space is configured, the magnetic resonance imaging apparatus 1 may identify motion information from the obtained tracking echo component of the k-space data. (930) For this purpose, the magnetic resonance imaging apparatus 1 may use the above-described math. The tracking echo component can be estimated according to Equation 1, and the motion information can be confirmed using the estimated center of gravity of the tracking echo component. At this time, the magnetic resonance imaging apparatus 1 may also set the effective range according to the motion information.

After confirming the motion information, the magnetic resonance imaging apparatus 1 may perform gating by synchronizing k-spatial data with the identified motion information. (940) Here, gating refers to each of a plurality of k-spaces. After synchronizing the constituent data with motion information, it may mean a process of reconstructing one k-space by accumulating data acquired in the same phase with respect to k-space data belonging to the effective range. Through the gating process, the image processor 11 may remove the motion information from the k-spatial data.

Next, the magnetic resonance imaging apparatus 1 may remove the tracking echo component from the gated k-spatial data.

The magnetic resonance imaging apparatus 1 according to an exemplary embodiment may remove the tracking echo component from the gated k-space data using the eigenvector of the tracking echo component. Specifically, first, the magnetic resonance imaging apparatus 1 may obtain an eigenvector of the tracking echo component from the gated k-spatial data. To this end, the magnetic resonance imaging apparatus 1 may use high frequency components of gated k-spatial data.

After acquiring the eigenvector, the magnetic resonance imaging apparatus 1 may remove the tracking echo component from the k-space data by using the acquired eigenvector of the tracking echo component. Specifically, the magnetic resonance imaging apparatus 1 may remove the tracking echo component by projecting k-space data onto the eigenvector of the tracking echo component.

Alternatively, the magnetic resonance imaging apparatus 1 according to another embodiment may remove the tracking echo component from the gated k-spatial data by adding two adjacent components in the ky direction among the gated k-spatial data. . Since the second RF pulse for obtaining the motion information is reversed in phase, the tracking echo component may be removed by adding adjacent components in the ky direction among the gated tracking echo components.

Finally, the magnetic resonance imaging apparatus 1 may generate the magnetic resonance image using the k-space data from which the tracking echo component has been removed.

Claims (15)

1. Irradiating a first RF pulse for a first cross section of the object and a second RF pulse for a second cross section of the object every period, and applying the image echo component and the second RF pulse generated in response to the first RF pulse. An RF coil unit for receiving an RF echo signal including a correspondingly generated tracking echo component;

   Construct a k-space based on the received RF echo signal, synchronize the data of the k-space to motion information obtained from the tracking echo component, and remove the tracking echo component from the synchronized k-space data An image processor configured to generate a magnetic resonance image using the k-spatial data from which the tracking echo component is removed; And

   An output unit displaying the generated magnetic resonance image; Magnetic resonance imaging apparatus comprising a.
2. The method of claim 1,

   The RF coil unit,

   And a magnetic resonance imaging device configured to reverse the second RF pulse phases of the adjacent periods.
3. The method of claim 1,

   A gradient magnetic field forming unit configured to apply a gradient magnetic field for phase encoding to the object after the first RF pulse irradiation and before the second RF pulse irradiation; Magnetic resonance imaging device further comprising.
4. The method of claim 1,

   The image processor,

   Magnetic resonance imaging apparatus for acquiring the motion information of the object by using the center of gravity for each frequency component of the tracking echo component.
5. The method of claim 1,

   The image processor,

   And extracting the synchronized k-spatial data within the effective range determined by the motion information, and removing the tracking echo component from the extracted k-spatial data.
6. The method of claim 5, wherein

   The image processor,

   When a plurality of k-spaces are configured by the first RF pulse and the second RF pulse irradiated repeatedly for each period, the k-space data extracted from the plurality of k-spaces are acquired in the same phase. And reconstruct one k-space by accumulating data and removing the tracking echo component from the reconstructed one k-space data.
7. The method of claim 1,

   The image processor,

   Magnetic resonance imaging apparatus for removing the tracking echo component from the synchronized k-spatial data by using the eigenvector (Eigen Vector) of the tracking echo component.
8. The method of claim 7, wherein

   The image processor,

   The eigenvector of the tracking echo component is obtained by using a frequency component equal to or greater than a predetermined reference frequency among the synchronized k-space data, and the synchronized k-space in the eigenvector space excluding the eigenvector of the tracking echo component. Magnetic resonance imaging apparatus for projecting the data, to remove the tracking echo component from the synchronized k-spatial data.
9. The method of claim 1,

   The image processor,

   And summing two adjacent components in the ky direction of the synchronized k-spatial data to remove the tracking echo component from the synchronized k-spatial data.
10. The method of claim 1,

    The image processor,

    And reconstructing the k-spatial data from which the tracking echo component has been removed through a parallel imaging method, and generating the magnetic resonance image using the reconstructed k-spatial data.
11. Irradiating a first RF pulse for a first cross section of the object and a second RF pulse for a second cross section of the object at each period;

    Receiving an RF echo signal comprising an image echo component generated in response to the first RF pulse and a tracking echo component generated in response to the second RF pulse;

    Constructing k-space based on the received RF echo signal;

    Synchronizing the k-space data with motion information obtained from the tracking echo component;

    Removing the tracking echo component from the synchronized k-spatial data;

    Generating a magnetic resonance image using the k-spatial data from which the tracking echo component has been removed; And

    Displaying the generated magnetic resonance image; Control method of a magnetic resonance imaging apparatus comprising a.
12. The method of claim 11,

    Irradiating the first RF pulse and the second RF pulse,

    And controlling the second RF pulse so that the second RF pulse phases of the adjacent periods are opposite to each other.
13. The method of claim 11,

    Applying a gradient magnetic field for phase encoding to the object after the first RF pulse irradiation and before the second RF pulse irradiation for each period; Control method of the magnetic resonance imaging apparatus further comprising.
14. The method of claim 11,

    Synchronizing the k-spatial data with the motion information,

    And obtaining motion information of the object using the center of gravity for each frequency component of the tracking echo component, and synchronizing the k-spatial data with the obtained motion information.
15. The method of claim 11,

    Removing the tracking echo component from the synchronized k-spatial data,

    Extracting the synchronized k-spatial data that falls within an effective range determined by the motion information; And

    Removing the tracking echo component from the extracted k-spatial data; Control method of a magnetic resonance imaging apparatus comprising a.

Images