KR101852098B1 - Device and method for magnet resonance imaging - Google Patents

Abstract

The present invention provides a magnetic resonance imaging apparatus for scanning an object. The magnetic resonance imaging apparatus according to an embodiment of the present invention comprises: a scanner for forming a plurality of radio frequencies (RFs) and gradient magnetic fields inside a bore in which an object is located, and receiving an echo signal from the object; and a controller for controlling the scanner according to a pulse sequence, wherein the controller applies at least one RF pulse and a spatial encoding gradient pulse to the object through the scanner, applies a plurality of readout gradient pulses and a plurality of blip pulses for acquiring the plurality of echo signals emitted from the object to the object through the scanner, sequentially acquires a plurality of echo signals including different spatial information according to the plurality of blip pulses, and maps the plurality of the echo signals to a plurality of k-spaces, respectively, based on the different spatial information. Thus, the scanning time can be reduced.

Description

Technical Field [0001] The present invention relates to a magnetic resonance imaging apparatus and a magnetic resonance imaging method,

The present invention relates to a magnetic resonance imaging apparatus and a magnetic resonance imaging method.

BACKGROUND ART In general, a device for processing magnetic resonance imaging (MRI) is a device for acquiring a tomographic image of a specific region of a patient by using a resonance phenomenon caused by supply of electromagnetic energy. The X- There is no exposure and a single-layer image can be relatively easily obtained. For example, MRI devices are widely used for accurate disease diagnosis because they show the bone, disc, joint, and nerve ligament in three dimensions from a desired angle.

Specifically, in order to generate a magnetic resonance image, a RF signal of a high frequency is applied to a target object to be photographed a plurality of times to excite a nucleus spin in a target object. Through the application of a pulse train to such a magnetic resonance apparatus, various signals such as a free induction attenuation signal (FID) and a spin echo are generated in a magnetic resonance imaging apparatus, and these signals are selectively acquired to generate a magnetic resonance image.

Particularly, in order to obtain a water-fat separation image using a phase difference due to a chemical shift in a human body, a magnetic resonance signal must be acquired in at least two different echo times, and a field map capable of evaluating the degree of homogenization of a magnetic field the image of the same part must be obtained by changing the echo time at least three times in order to obtain the field map. This requires a long scan time of the conventional image acquisition method.

Therefore, there is a need for a method and apparatus for restoring a high-resolution magnetic resonance image while shortening a scan time.

U.S. Patent No. 7176683 (entitled "Iterative decomposition of water and fat with echo asymmetry and least square estimation"

SUMMARY OF THE INVENTION It is an object of the present invention to provide a scanning method and a magnetic resonance imaging apparatus for reducing scan time in some embodiments of the present invention.

It is another object of the present invention to provide an image reconstruction method and a magnetic resonance imaging apparatus for reconstructing a high resolution water-lip magnetic resonance imaging.

It should be understood, however, that the technical scope of the present invention is not limited to the above-described technical problems, and other technical problems may exist.

According to an aspect of the present invention, there is provided a magnetic resonance imaging apparatus that scans a target object according to an embodiment of the present invention includes a plurality of radio frequency (RF) a scanner for forming a gradient and receiving an echo signal from the object; And a control unit for controlling the scanner in accordance with the pulse sequence, wherein the control unit applies at least one RF pulse and a spatial encoding gradient pulse to the object through a scanner, and generates a plurality of echo signals for acquiring a plurality of echo signals emitted from the object, A readout gradient pulse and a plurality of blip pulses are applied to a target object through a scanner and sequentially acquire a plurality of echo signals including different spatial information according to a plurality of blip pulses, And maps each of the plurality of echo signals to each of the plurality of k-space based on other spatial information.

According to another aspect of the present invention, there is provided a method of scanning a target object, the method comprising: (a) applying a plurality of gradient magnetic fields for at least one RF pulse and a spatial encoding gradient pulse to a target object; (b) applying a plurality of readout gradient pulses and a plurality of blip pulses to the object to obtain a plurality of echo signals emitted from the object; (c) sequentially acquiring a plurality of echo signals including different spatial information according to the plurality of blip pulses; And (d) mapping each of the plurality of echo signals to each of the plurality of k-space based on different spatial information.

According to an embodiment of the present invention, a magnetic resonance imaging apparatus according to an embodiment of the present invention maps echo signals including different spatial information to k-space that are separated from each other by a blip pulse, By restoring the water-fat separation image from the spaces, the total scan time required to restore a plurality of magnetic resonance images can be shortened. In addition, the magnetic resonance imaging apparatus according to the disclosed embodiment can recover a water-lipid separation image having a high signal-to-noise ratio (SNR).

1 is a view showing an MRI system.
2 is a diagram showing a configuration of a magnetic resonance imaging apparatus according to an embodiment of the present invention.
3 is a diagram illustrating a pulse sequence according to an embodiment of the present invention.
FIG. 4 is a diagram illustrating an RF pulse sequence applied by the control unit of FIG. 2 as a target object.
5 is another diagram illustrating a pulse sequence according to an embodiment of the present invention.
6A and 6B are diagrams illustrating a method of mapping the echo signals to different k-spaces according to an embodiment of the present invention.
7 is a flowchart illustrating a method of scanning a magnetic resonance imaging apparatus according to an embodiment of the present invention.
FIG. 8 is a flowchart illustrating a method of reconstructing an image of a magnetic resonance imaging apparatus according to an embodiment of the present invention. Referring to FIG.
9 is a diagram illustrating a method by which a control unit interpolates undetected data in k-space according to an embodiment of the present invention.
10 is an example of reconstructing a magnetic resonance image corresponding to each of water and fat components from a plurality of interpolated k-spaces according to an embodiment of the present invention.
11 and 12 are flowcharts illustrating a method of performing a phase correction scan operation for correcting a phase shift according to an exemplary embodiment of the present invention.
13 is a diagram illustrating a pulse sequence for a phase calibration scan operation according to an embodiment of the present invention.
Figure 14 is another diagram illustrating a pulse sequence for a phase calibration scan operation in accordance with an embodiment of the present invention.
15 is another diagram illustrating a pulse sequence for a phase calibration scan operation in accordance with an embodiment of the present invention.
16 is an example of correcting the phase shift of the magnetic resonance image of FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification, when a part is referred to as being "connected" to another part, it includes not only "directly connected" but also "electrically connected" with another part in between . Also, when an element is referred to as "comprising ", it means that it can include other elements as well, without departing from the other elements unless specifically stated otherwise.

In the present specification, "MRI (Magnetic Resonance Imaging)" means an image of a target object obtained using the nuclear magnetic resonance principle.

Further, the term "image" or " image " refers to multi-dimensional data consisting of discrete elements. It means that a plurality of pixels in a two-dimensional image and a plurality of voxels .

Also, the "object" is an object of imaging of a magnetic resonance imaging apparatus, and may include a person, an animal, or a part thereof. The subject may also include various organs such as heart, brain or blood vessels or various types of phantoms.

The term "user" may be, but is not limited to, a medical professional such as a doctor, a nurse, a medical imaging specialist, or a device repair technician.

The term "pulse sequence" means a signal repeatedly applied in a magnetic resonance imaging apparatus. The pulse sequence may include a repetition time (TR) or an echo time (Time to Echo, TE) as a time parameter of the RF pulse.

Hereinafter, embodiments of a magnetic resonance imaging apparatus will be described with reference to the accompanying drawings.

1 is a view showing an MRI system.

The MRI system 1 may include an MRI scanner 10, a signal processing unit 20, a control unit 40, a monitoring unit 50, and an interface unit 30.

The MRI scanner 10 forms a magnetic field and generates a resonance phenomenon with respect to an atomic nucleus. A magnetic resonance image is photographed when the object is positioned inside the MRI scanner 10. The MRI scanner 10 includes a main magnet 12, a gradient coil 14, an RF coil 16 and the like, through which a static magnetic field and a gradient magnetic field are formed, and an RF signal is radiated toward a target object.

The main magnet 12, the gradient coil 14 and the RF coil 16 are arranged in the MRI scanner 10 according to a predetermined direction. The object is positioned on a table that can be inserted into the cylinder along the horizontal axis of the cylinder and the object can be positioned inside the bore of the MRI scanner 10 as the table moves.

The main magnet 12 generates a static magnetic field that aligns the direction of the magnetic dipole moment of the nuclei included in the object in a predetermined direction.

The gradient coil 14 includes an X-coil, a Y-coil, and a Z-coil that generate mutually orthogonal X-axis, Y-axis, and Z-axis gradient magnetic fields. The gradient coil 14 induces different resonance frequencies for the respective parts of the object so that position information of each part of the object can be obtained.

The RF coil 16 can radiate an RF signal to a target object and receive a magnetic resonance image signal emitted from the target object. The RF coil 16 outputs an RF signal having the same frequency as the frequency of the carrot motion toward the nucleus of the car wash motion, and can receive the magnetic resonance image signal emitted from the target body.

For example, the RF coil 16 generates an RF signal having a frequency corresponding to the atomic nucleus, and applies the RF signal to the object, in order to transition the atomic nucleus from a low energy state to a high energy state. Thereafter, when the RF coil 16 stops transmitting the RF signal, the atomic nucleus to which the electromagnetic wave has been applied transits from a high energy state to a low energy state and emits an electromagnetic wave having a Lamor frequency, and the RF coil 16 And receives the corresponding electromagnetic wave signal.

The RF coil 16 includes a transmitting RF coil for transmitting an RF signal having a radio frequency corresponding to the type of the atomic nucleus and a receiving RF coil for receiving electromagnetic waves emitted from the atomic nucleus.

Further, the RF coil 16 may be fixed to the MRI scanner 10, or may be detachable. The removable RF coil 16 may be implemented in the form of 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 may be coupled to a part of a target object .

The MRI scanner 10 can provide various information to a user or a target through a display, and can include a display 18 disposed on the outside and a display (not shown) disposed on the inside.

The signal processing unit 20 controls a gradient magnetic field formed inside the MRI scanner 10 according to a predetermined MR pulse sequence and can control transmission and reception of an RF signal and a magnetic resonance image signal.

The signal processing section 20 may include a gradient magnetic field amplifier 22, a switching section 24, an RF transmission section 26 and an RF reception section 28.

The gradient magnetic field amplifier 22 drives the gradient coil 14 included in the MRI scanner 10 and applies an inclined pulse signal for generating a gradient magnetic field under the control of the gradient magnetic field control unit 44 to the gradient coil 14 . The oblique magnetic field in the X-axis, Y-axis, and Z-axis directions can be synthesized by controlling the inclination pulse signal supplied from the oblique magnetic field amplifier 22 to the gradient coil 14. [

The RF transmitting unit 26 supplies RF pulses to the RF coil 16 to drive the RF coil 16. [ The RF receiver 28 receives the MRI image signal transmitted by the RF coil 16 after receiving the RF signal.

The switching unit 24 can adjust the transmission and reception directions of the RF signal and the magnetic resonance image signal. For example, during a transmit operation, an RF signal is applied to an object through an RF coil 16, and during a receive operation, a magnetic resonance image signal from a subject is received via the RF coil 16. [ The switching unit 24 is controlled in switching operation by a control signal from the RF control unit 46. [

The interface unit 30 may instruct the control unit 40 to transmit the pulse sequence information according to an operation of the user and may transmit a command for controlling the operation of the entire MRI system. The interface unit 30 may include an image processing unit 36, an output unit 34, and an input unit 32 for processing a magnetic resonance image signal received from the RF receiving unit 38.

The image processing unit 36 can process the MR image signal received from the RF receiving unit 28 to generate MR image data for the object.

The image processor 36 applies various signal processing such as amplification, frequency conversion, phase detection, low frequency amplification, filtering, and the like to the MRI image signal received by the RF receiver 28.

The image processing unit 36 can arrange the digital data in the k space, for example, and reconstruct the image data into two-dimensional or three-dimensional Fourier transformed data.

In addition, various signal processes applied to the magnetic resonance image signal by the image processing unit 36 can be performed in parallel. For example, a plurality of magnetic resonance image signals may be reconstructed into image data by applying signal processing in parallel to a plurality of magnetic resonance image signals received by the multi-channel RF coil.

The output unit 34 can output the image data or the reconstructed image data generated by the image processing unit 36 to the user. The output unit 34 may output information necessary for a user to operate 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 means.

The user can input object information, parameter information, scan condition, pulse sequence, information on image synthesis and calculation of difference through the input unit 32. The input unit 32 may include a keyboard, a mouse, a trackball, a voice recognition unit, a gesture recognition unit, a touch screen, and the like, and may include various input devices within a range obvious to those skilled in the art.

The control unit 40 includes a sequence control unit 42 for controlling a sequence of signals formed in the MRI scanner 10 and a scanner control unit 48 for controlling the MRI scanner 10 and the devices mounted on the MRI scanner 10, . ≪ / RTI >

The sequence control unit 42 includes an inclination magnetic field control unit 44 for controlling the gradient magnetic field amplifier 22 and an RF control unit 46 for controlling the RF transmission unit 26, the RF reception unit 28 and the switching unit 24. [ do. The sequence control unit 42 can control the gradient magnetic field amplifier 22, the RF transmission unit 26, the RF reception unit 28 and the switching unit 24 according to the pulse sequence received from the interface unit 30. [ The pulse sequence includes all the information necessary to control the gradient magnetic field amplifier 22, the RF transmitter 26, the RF receiver 28 and the switching unit 24, Information on the intensity of a pulse signal, an application time, an application timing, and the like.

The monitoring unit 50 monitors or controls devices mounted on the MRI scanner 10 or the MRI scanner 10. The monitoring unit 50 may include a system monitoring unit 52, an object monitoring unit 54, a table control unit 56, and a display control unit 58.

The system monitoring unit 52 monitors the state of the static magnetic field, the state of the gradient magnetic field, the state of the RF signal, the state of the RF coil, the state of the table, the state of the device for measuring the body information of the object, You can monitor and control the state of the compressor.

The object monitoring unit 54 monitors the state of the object and may be a camera for photographing the movement or position of the object, a respiration measuring unit for measuring the respiration of the object, an ECG measuring unit for measuring the electrocardiogram of the object, And a temperature measuring device for measuring temperature.

The table control unit 56 controls the movement of the table in which the object is located. The table control unit 56 can control the movement of the table in synchronization with the sequence control signal output by the sequence control unit 42. [ For example, in moving imaging of a subject, the table control unit 56 may move the table in accordance with the sequence control, thereby causing the FOV (field of view) of the MRI scanner to move to the target object Can be photographed.

The display control unit 58 controls on / off of a display located outside and inside of the MRI scanner 10 or a screen to be output to the display. When the speaker is located inside or outside the MRI scanner 10, the display controller 58 may control on / off of the speaker or 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 wirelessly or wired, (Not shown) for synchronizing the clocks of the mobile stations. 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 is performed by a high-speed digital communication unit such as LVDS (Low Voltage Differential Signaling) Interface, an asynchronous serial communication such as a universal asynchronous receiver transmitter (UART), a hypo-synchronous serial communication, or a CAN (Controller Area Network) can be used. A communication method can be used.

2 is a diagram showing a configuration of a magnetic resonance imaging apparatus according to an embodiment of the present invention.

The magnetic resonance imaging apparatus 200 may be any image processing apparatus capable of restoring a magnetic resonance image using a magnetic resonance signal obtained by magnetic resonance imaging. Further, the magnetic resonance imaging apparatus 200 may be a magnetic computing apparatus capable of controlling acquisition of a magnetic resonance signal in magnetic resonance imaging.

Referring to FIG. 2, the magnetic resonance imaging apparatus 200 may include a scanner 210 and a controller 220.

Specifically, the magnetic resonance imaging apparatus 200 may be included in the MRI system 1 described with reference to FIG. In this case, the scanner 210 and the control unit 220 of the MRI apparatus 200 correspond to the MRI scanner 10 and the control unit 40 shown in FIG. 1, respectively. In addition, according to the embodiment, the scanner 210 of FIG. 2 may further perform the function of the signal processing unit 20 shown in FIG.

According to an embodiment, the scanner 210 forms a plurality of RF and oblique magnetic fields within a bore where the object is located under the control of the controller 220, and includes one or more components. For example, the scanner 210 may comprise a multi-channel RF coil. In addition, the controller 220 can receive echo signals (i.e., MR signals) through the multi-channel RF coils in the scanner 210. This has been described with reference to FIG. 1, and a detailed description thereof will be omitted.

According to an embodiment, the controller 220 applies at least one RF pulse and a spatial encoding gradient pulse to the object via the scanner 210. At this time, the spatial encoding gradient pulse is a slice selection gradient that forms a slice selection gradient magnetic field, a phase encoding gradient magnetic field, and a frequency encoding gradient magnetic field through Z, Y, and X- A pulse, a phase encoding gradient pulse, and a frequency encoding gradient pulse. Thus, the slice selection slope pulse includes spatial information about the Z axis, the phase encoding slope pulse includes spatial information about the Y axis, and the frequency encoding slope pulse may include spatial information about the X axis. On the other hand, the frequency encoding gradient pulse may be a read-out gradient pulse for acquiring an echo signal.

For example, the controller 220 may apply at least one RF pulse and a spatial encoding gradient pulse to the object through the scanner 210 based on a gradient and spin echo (GRASE) technique. The GRASE technique is a high-speed imaging technique that uses both spin echo and gradient echo signals, and can be a technique of switching the polarity of the lead-out gradient magnetic field to acquire a plurality of echo signals. To this end, the control unit 220 includes a plurality of echo trays including one excitation RF pulse and a plurality of refocusing RF pulses for one repetition time (TR) It can be applied to objects.

In addition, the control unit 220 applies a plurality of lead-out warp pulses for acquiring a plurality of echo signals through the scanner 210 as a target object. At this time, the controller 220 further applies a plurality of blip pulses to the scanner 210 to distinguish the echo signals. At this time, the plurality of blip pulses forms at least one other oblique magnetic field other than the oblique magnetic field (that is, the lead-out oblique magnetic field) formed by the lead-out oblique pulse. That is, the blip pulse can form at least one of the slice selection gradient magnetic field and the phase encoding gradient magnetic field.

 On the other hand, the controller 220 applies a plurality of lead-out warp pulses as a target according to a plurality of echo times (TE) determined based on a phase difference between tissue components in a target object, Each of the blip pulses is applied as a target at the time between the lead-out gradient pulses (see t1 and t2 shown in Figs. 3 and 5). Generally, the water and fat components in the object have different resonant frequencies, producing a phase difference of about 3.5 ppm and having different echo times (TE). In consideration of this, the control unit 220 can obtain an echo signal reflecting the chemical shift of the components by applying the respective lead-out slant pulses as a target in different TEs. That is, echo signals obtained at different echo times include different phase information.

On the other hand, the magnitude of the blip pulse applied to the object may be constant, but is not limited thereto. The control unit 220 sequentially receives a plurality of echo signals including different spatial information according to the plurality of blip pulses. At this time, the plurality of echo signals have the characteristics of a spin echo or a gradient echo.

The control unit 220 maps each of the plurality of echo signals to each of the plurality of k-space based on the spatial information according to the blip pulse. At this time, the echo signals mapped to the same k-space include the same phase information obtained in the same TE. Thus, there is a phase difference between the different k-spaces.

In addition, the control unit 220 may further perform the function of the image processing unit 36 shown in FIG. The control unit 220 restores the water-fat separation image from the plurality of k-spaces. Specifically, the water and fat components in the object have different resonant frequencies and produce a phase difference of about 3.5 ppm. The controller 220 can recover the water-fat separation image from the plurality of k-space based on the phase-independent image restoration technique based on the phase difference.

In addition, the controller 220 may perform a phase correction operation for correcting the phase shift. In addition, the control unit 220 can obtain a high SNR by extending a convolution kernel vector in the echo direction in order to improve a signal-to-noise ratio (SNR) of an image. This will be described later with reference to Figs. 12 to 16. Fig.

As described above, the magnetic resonance imaging apparatus 200 according to the disclosed embodiment has a plurality of echo signals having different spatial information by a blip pulse and considering the phase difference between water and fat, thereby effectively reducing the scan time , A water-separated image with a high signal-to-noise ratio (SNR) can be reconstructed.

3 is a diagram illustrating a pulse sequence according to an embodiment of the present invention.

Referring to the pulse sequence 300 of FIG. 3, the controller 220 may apply N refocusing RF pulses 310 having one excitation RF pulse 309 and a variable flip angle to the object . The control unit 220 may further apply M lead-out warp pulses and (M-1) blip pulses after each of the re-focusing RF pulses is applied to the object.

Specifically, based on the phase difference between water and fat, the control unit 220 determines the time (t1, t2) between the timing (i.e., TE) and the lead-out gradient pulses to which each lead-out gradient pulse is applied. If the determined times t1 and t2 are the same, the first echo signal 331 and the third echo signal 333 are gradient echoes and the second echo signal 332 is a spin echo. However, if the determined inter-times tl, t2 are different, the first to third echo signals 331, 332, 333 are all gradient echoes.

After the first refocusing RF pulse 311 is applied as a target object, the controller 220 controls the slice selection slope 304 at the time t1, t2 between the lead-out gradient pulses forming the lead-out gradient magnetic field 304 The first blip pulse group 321 and the second blip pulse group 322 forming the magnetic field 302 and the phase encoding gradient magnetic field 303 can be additionally applied. Accordingly, the control unit 220 can acquire the first echo signal 331, the second echo signal 332, and the third echo signal 333 having different spatial information (ky-kz).

The control unit 220 repeatedly performs the above-described operation even after the second re-focusing RF pulse 312 is applied to the object so that the echo signals 334, 335, 336 may have different spatial information.

While the pulse sequence 300 has been shown in the above description to acquire three echo signals 334 through 336 during one echo train, the pulse sequence may include a lead out slope pulse for acquiring four or more echo signals . In this case, the pulse sequence may include three or more group of blip pulses.

3 shows a pulse sequence 300 including re-focusing RF pulses including a non-selective excitation pulse RF pulse and a variable flip angle for restoring a cut-off image, But is not limited thereto.

4, the control unit 220 outputs a pulse sequence 400 including a selective excitation RF pulse and a re-focusing RF pulse including a variable flip angle for restoring the selective slice image, .

At this time, the size of each of the re-focusing RF pulses is set based on the magnitude of the signal generated by the previous re-focusing RF pulse. The control unit 220 applies the re-focusing RF pulses having the variable flip angle to the object so that the re-focusing RF pulses of the same size (for example, one reference size) are repeatedly applied to the object, It is possible to obtain a magnetic resonance signal (i.e., an echo signal) at a high speed while reducing the absorption rate of electromagnetic waves. In addition, it is possible to overcome the T2 attenuation phenomenon, which is a modulation of a magnitude signal caused by a high-speed spin-echo pulse sequence, and obtain a high-resolution image.

Meanwhile, after each of the re-focusing RF pulses of FIG. 4 is applied to the target object, the controller 220 may apply a plurality of read-out gradient pulses and a plurality of blur pulses to the target object by the method described above with reference to FIG.

5 is another diagram illustrating a pulse sequence according to an embodiment of the present invention.

Referring to FIG. 5, the controller 220 may apply a pulse sequence 500 including N excitation RF pulses according to a gradient echo (GE) technique as a target object. In addition, the control unit 220 may apply M lead-out warp pulses and (M-1) number of blip pulses as a target object after each excitation RF pulse is applied. In this case, the pulse sequence 500 of FIG. 5 may further comprise a pre-paging pulse 520 for prephasing the resonance of the excited atoms by each excitation RF pulse.

Based on the phase difference between water and fat, the control unit 220 determines the time (t1, t2) between the timing (i.e., TE) at which each lead-out warp pulse is applied and the lead-out warp pulses. At this time, the first to third echo signals 541, 542 and 543 obtained by the pulse sequence 500 of FIG. 5 are all gradient echoes.

Specifically, the control unit 220 generates a lead-out oblique magnetic field 504 in accordance with the determined timing (i.e., TE) after each excitation RF pulse is applied to the object, in accordance with the pulse sequence 500 of FIG. A first blip pulse group 531 that applies a slope pulse to a target object and forms a slice selection gradient magnetic field 502 and a phase encoding gradient magnetic field 503 at times t1 and t2 between the readout gradient pulses, 2-blip pulse group 532 can be further applied as a target object. Accordingly, the controller 220 can acquire the first echo signal 541, the second echo signal 542, and the third echo signal 543 having different spatial information.

FIGS. 6A and 6B are diagrams illustrating a method for the controller 220 of FIG. 2 to map echo signals to different k-spaces according to an embodiment of the present invention.

Referring to FIG. 6A, the control unit 220 outputs echo signals within each echo train (in the case of FIGS. 3 and 4) or repetition time (in the case of FIG. 5) Spaces 621 to 623, respectively. At this time, the echo signals can be mapped to each k-space in an interleaved manner.

The control unit 220 forms a phase encoding gradient magnetic field, and can apply blip pulses of size (+ i). Accordingly, when the ky spatial information of the obtained first echo signal 611 is (j), the ky spatial information of the second echo signal 612 is (j + i), and the ky spatial information of the third echo signal 611 ky spatial information may be (j + 2 * i). Thus, each of the echo signals obtained in one echo train (or one TR) may be mapped to a different ky space.

Specifically, the control unit 220 can determine the k-space corresponding to each echo signal using ky spatial information (i.e., + i) of each echo signal. Thus, the first echo signal 611 of the first echo train (or first TR) and the first echo signal 614 of the second echo train (or second TR) are mapped to the first k- And the second echo signal 612 of the first echo train (or first TR) and the second echo signal 615 of the second echo train (or second TR) are mapped to the second k-space 621 do. Further, the third echo signal 613 of the first echo train (or first TR) and the third echo signal 616 of the second echo train (or second TR) are mapped to the third k-space 623 . Also, the first to third echo signals 211 to 213, or 214 to 216 may be mapped to different lines in the ky directions of the first to third k-space 621 to 623. Here, the lines to which the first to third echo signals 211 to 213, or 214 to 216, respectively, are mapped to the first to third k-spaces 621 to 623 may be separated from each other by (+ i) . If the size of the blip pulses applied to the object is (+ 2 * i), each of the first to third echo signals 211 to 213, or 214 to 216, (+ 2 * i) in the ky direction of the first and second lines 623 and 623, respectively.

6A, an example in which the control unit 220 performs full sampling of the echo signals to each line of k-space has been described for convenience of explanation, but the present invention is not limited thereto. For example, the controller 220 may under-sample the echo signals (e.g., sampling the echo signal corresponding to the center of the k-space and interpolating the other data) lt; RTI ID = 0.0 > (k-space) < / RTI > At this time, the controller 220 may sample at a Nyquist rate in the low-frequency region (center portion) of the k-space and at a rate lower than the Nyquist rate at the high-frequency region (peripheral portion) of the k- .

Also, as shown in FIG. 6B, the controller 220 may further perform ky-kz sampling for k-space for three-dimensional image reconstruction. At this time, the first to third k spaces 631, 632, and 633 may be classified based on ky-kz spatial information.

FIG. 7 is a flowchart illustrating a method of scanning a magnetic resonance imaging apparatus 200 according to an embodiment of the present invention. Referring to FIG.

The control unit 220 of the magnetic resonance imaging apparatus 200 applies at least one RF pulse and a spatial encoding gradient pulse to the target object (S710).

The control unit 220 includes a plurality of lead-out warp pulses and a plurality of blip pulses for acquiring a plurality of echo signals generated from the object (S720). At this time, the plurality of blip pulses forms at least one other oblique magnetic field (for example, a phase encoding gradient magnetic field and / or a slice selection oblique magnetic field) other than the oblique magnetic field formed by the lead-out oblique pulse.

On the other hand, the controller 220 applies a plurality of lead-out warp pulses as a target according to a plurality of echo times (TE) determined based on a phase difference between tissue components in a target object, Each of the blip pulses is applied as a target in time between lead-out slant pulses.

Thereafter, the control unit 220 sequentially acquires a plurality of echo signals including different spatial information according to the plurality of blip pulses (s730). For example, the control unit 220 may be connected to the scanner 210 by wired or wireless connection, and may receive echo signals received from the scanner 210.

The control unit 220 maps each of the plurality of echo signals to each of the plurality of k-space based on different spatial information (s740). At this time, the echo signals mapped to the same k-space include the same phase information as those obtained in the same echo time (TE). Thus, there is a phase difference between the different k-spaces.

FIG. 8 is a flowchart illustrating a method of restoring an image by the MRI apparatus 200 according to an embodiment of the present invention.

According to one embodiment, the control unit 220 obtains a convolution kernel vector extended in the echo direction (s810). Specifically, the controller 220 can obtain the convolution kernel vector G extended in the echo direction using the following equations (1) and (2).

[Equation 1]

및

는 에코 신호의 인덱스,

및

은 RF 코일의 인덱스, 및

및

는 k-공간의 인덱스를 의미한다. 또한,

는 하이브리드 커널(hybrid kernel)인

내에서의

번째 에코 신호와

번째 RF 코일에 대응하는 복원 신호를 의미하며,

는 결측 신호와 L 반경 이내에 위치하며,

및

에 대응하여 측정된 신호를 의미한다. 또한,

은 컨볼루션 커널

의 인덱스이며,

은

및

의 결측 신호를 복원하기 위한 컨벌루션 커널 벡터(G)의

번째 엘리먼트를 의미한다. In Equation (1)

And

Is an index of an echo signal,

And

Is the index of the RF coil, and

And

Denotes an index of k-space. Also,

Is a hybrid kernel.

Within

Echo signal

Lt; RTI ID = 0.0 > RF < / RTI > coil,

Is located within the radius L of the missing signal,

And

Quot; signal " Also,

Convolution kernel

≪ / RTI >

silver

And

Of the convolution kernel vector G for recovering the missing signal of the

≪ / RTI >

는 타겟 캘리브레이션 신호를 의미하며,

는타겟 캘리브레이션 신호와 L 반경 이내에 위치하는 소스 캘리브레이션 신호를 의미한다. On the other hand, Equation (1) is replaced by Equation (2). here,

Means a target calibration signal,

Means a source calibration signal located within a radius L of the target calibration signal.

&Quot; (2) "

The following equation (3) is an example of a Moore-Penrose pseudo inverse performed using the generalized equation (2).

&Quot; (3) "

, 결측 신호를 나타내는

, 및 컨볼루션 커널 벡터(G)를 획득할 수 있다.Referring to FIG. 9, the controller 220 obtains, from a plurality of k-spaces including different phase information E1, E2, and E3, a matrix representing a measured signal

, Indicating a missing signal

, And a convolution kernel vector (G).

Referring back to FIG. 8, the controller 220 interpolates data corresponding to the missing signal using the convolution kernel vector G (S820).

In the above description, a method of interpolating missing data using a convolution kernel extended in the echo direction based on convolution interpolation has been described. However, the present invention is not limited to this, and various interpolation methods can be used to interpolate missing data Interpolation can be performed. For example, the control unit 220 may apply a compression sensing technique to the image space.

Thereafter, the controller 220 reconstructs the water-lipid separation image using the phase-independent image reconstruction method based on the interpolated data (s830). The control unit 220 can restore the water-fat separation image using the convolution kernel (see the left drawing of FIG. 9) extended in the echo direction with respect to the plurality of interpolated k-spaces.

In addition, according to an embodiment, the controller 220 can restore a water-lipid separation image according to a phase difference between water and fat components using a compression sensing technique for an image space obtained from a plurality of k-spaces .

10 is an example in which the controller 220 reconstructs a magnetic resonance image corresponding to each of water and fat components from a plurality of interpolated k-spaces according to an embodiment of the present invention. The controller 220 can perform a fourier transform on a plurality of k-space interpolated by the above-described method. Thereafter, the controller 220 may restore the first MRI image 1010 corresponding to the water component and the second MRI image 1020 corresponding to the fat component based on the phase-independent image reconstruction technique.

11 and 12 are flowcharts for explaining a method for the controller 220 to perform a phase correction scan operation for correcting a phase shift according to an embodiment of the present invention.

Referring to FIGS. 11 and 12, the control unit 220 may perform a phase correction scan operation 1102 for correcting the phase shift, in addition to the imaging scan operation 1101 described above with reference to FIGS. The phase calibration scan job 1102 is a job for correcting a phase shift of echo signals acquired in the imaging scan job 1101 so that the MRI apparatus 200 can acquire a high resolution image have. For example, the control unit 220 may correct the data in each k-space to correspond to the center of the k-space based on the information obtained in the phase correction scan job 1102. [

On the other hand, the phase calibration scan job 1102 may be performed before the imaging scan job 1101 is performed or after the imaging scan job 1101 is performed. For example, the control unit 220 performs phase correction of data of each k-space in the imaging scan job 1101 using the result of the phase correction scan job 1102, as shown in Fig. 11 can do. In this case, the controller 220 may perform phase correction in a hybrid domain.

Alternatively, the control unit 220 may use the result of the phase correction scan job 1102 to correct the magnetic resonance image data in the image domain in the imaging scan job 1101, as shown in FIG. 12 It is possible.

13 is a diagram illustrating a pulse sequence for a phase calibration scan operation 1102 in accordance with an embodiment of the present invention.

Referring to the pulse sequence 1300 of FIG. 13, the controller 220 applies a first pulse sequence group 1301 and a second pulse sequence group 1302 for performing a phase correction scan operation 1102 to a target object .

Specifically, the first pulse sequence group 1301 and the second pulse sequence group 1302 include excitation RF pulses and re-focusing RF pulses, and correspondingly, a plurality of lead-out warp pulses for acquiring a plurality of echo signals Lt; / RTI > However, the first pulse sequence group 1301 and the second pulse sequence, a group 1302 is read-out gradient magnetic field (G frequency) other gradient magnetic field other than (that is, a slice selection gradient magnetic field (G slice) and the phase encoding gradient magnetic field ( G phase ) is not included.

In addition, the lead-out gradient pulse of the first pulse sequence group 1301 and the lead-out gradient pulse of the second pulse sequence group 1302 have different polarities. The control unit 220 outputs the echo signals generated by the lead-out gradient pulses of different polarities corresponding to the same TE (the first TE, the second TE, and the third TE) of the first and second pulse sequences 1301 and 1302, The phase difference value of the imaging scan job 1101 may be used to perform phase correction of the data obtained in the imaging scan job 1101. [ For example, the control unit 220 uses the phase difference values (i.e., the difference values of 1311 and 1312) of the echo signals generated by the lead-out gradient pulses of different polarities corresponding to the first TE, The first echo signal 331 can be corrected.

14 is another diagram illustrating a pulse sequence for a phase calibration scan operation 1102 in accordance with an embodiment of the present invention.

14, the pulse sequence 1400 includes a first pulse sequence group 1401 and a second pulse sequence group 1402, wherein each pulse sequence group further includes an excitation RF pulse and a pre-paging oblique pulse And may be configured as a lead-out gradient pulse.

In addition, the lead-out gradient pulses of each pulse sequence group may have different polarities, as shown in FIG. 13, the control unit 220 outputs the first and second pulse sequences 1301 and 1302 having the same polarity (i.e., the first TE, the second TE, and the third TE) of the first and second pulse sequences 1301 and 1302, The phase difference value of the echo signals generated by the oblique pulse can be used to perform the phase correction of the data obtained in the imaging scan operation 1101. [

15 is another diagram illustrating a pulse sequence for a phase calibration scan operation 1102 in accordance with one embodiment of the present invention.

Referring to FIG. 15, the pulse sequences 1500 and 1600 for the phase calibration scan job 1102 can be composed of one pulse sequence group. In this case, the control unit 220 can perform phase correction of data obtained in the imaging scan job 1101 using echo signals acquired in different TEs.

Specifically, the pulse sequence 1500 of FIG. 15 includes an excitation RF pulse and a refocusing RF pulse, and may include lead-out warp pulses for acquiring a plurality of echo signals corresponding thereto. In this case, the control unit 220 can perform phase correction of the data obtained in the imaging scan operation 1101 based on the value obtained by averaging sig1 and sig3 and the phase difference value of sig2.

Meanwhile, the pulse sequence for the phase calibration scan operation 1102 may be composed of a lead-out gradient pulse including one RF excitation pulse and a pre-paging pulse, but is not limited thereto, and various pulses Sequence can be applied to the present invention.

16 is an example of correcting the phase shift of the magnetic resonance image of FIG.

16, the control unit 220 corrects the phase difference with respect to the first MRI image 1010 corresponding to the water component and the second MRI image 1020 corresponding to the fat component, The magnetic resonance images 1610 and 1620 can be generated.

One embodiment of the present invention may also be embodied in the form of a recording medium including instructions executable by a computer, such as program modules, being executed by a computer. The recording medium is a computer-readable medium, which may be any available medium that can be accessed by a computer, and includes both volatile and nonvolatile media, removable and non-removable media. The computer-readable medium may also include computer storage media, which may be volatile and / or non-volatile, implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data, Nonvolatile, removable and non-removable media.

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims rather than the detailed description and all changes or modifications derived from the meaning and scope of the claims and their equivalents are to be construed as being included within the scope of the present invention do.

1: MRI system
10: MRI Scanner
20: Signal processor
30:
40:
50: Monitoring section

Claims (22)

A magnetic resonance imaging apparatus for scanning a target object,
A scanner for forming a plurality of radio frequency (RF) and gradient magnetic fields in a bore where the object is located and receiving an echo signal from the object; And
And a controller for controlling the scanner according to a pulse sequence,
The control unit
At least one RF pulse and a spatial encoding gradient pulse are applied to the object through the scanner,
A plurality of readout tilt pulses and a plurality of blip pulses for acquiring a plurality of echo signals emitted from the object are applied to the object through the scanner,
Sequentially acquiring a plurality of echo signals including different spatial information according to the plurality of blip pulses,
And maps each of the plurality of echo signals to each of a plurality of k-space based on the different spatial information. The method according to claim 1,
The plurality of blip pulses
And at least one other oblique magnetic field other than the oblique magnetic field formed by the lead-out oblique pulse is formed. 3. The method of claim 2,
Wherein,
Out gradient pulse to the object according to an echo time (TE) determined based on a phase difference between water-lipid components in the object,
And applying each blip pulse to the object in time between consecutive lead-out warp pulses. The method of claim 3,
The control unit
Wherein the water-fat separation image is reconstructed from the plurality of k-space based on a phase difference between water and fat components. 3. The method of claim 2,
The control unit
Applying one excitation RF pulse and N refocusing RF pulses to the subject during one TR,
And applying M reed out slope pulses and (M-1) blip pulses to the subject after each refocusing RF pulse is applied. 3. The method of claim 2,
The control unit
Applying N excitation RF pulses to the object during one TR,
Wherein after applying each excitation RF pulse, M lead-out gradient pulses and (M-1) blip pulses are applied to the object. 3. The method of claim 2,
The control unit
And a convolution kernel vector extending in the echo direction, and interpolates data corresponding to the missing signal in the plurality of k-space based on the convolution kernel vector. 3. The method of claim 2,
The control unit
Wherein the water-fat separation image is reconstructed according to a phase difference between water and fat components using a compression sensing technique for the image space acquired from the plurality of k-spaces. The method according to claim 1,
The control unit
A first pulse sequence group and a second pulse sequence group each including at least one RF pulse and a lead-out gradient pulse for correcting a phase difference of each k-space,
Wherein the lead-out gradient pulse in the first pulse sequence group and the lead-out gradient pulse in the second pulse sequence group are configured to have different polarities. 10. The method of claim 9,
The control unit
And performing phase correction of the data in the plurality of k-space based on a difference between an echo signal received corresponding to the first pulse sequence group and an echo signal received corresponding to the second pulse sequence group. Magnetic resonance imaging device. 10. The method of claim 9,
The control unit
Performing phase correction of the image data reconstructed from the plurality of k-space based on the difference between the echo signal received corresponding to the first pulse sequence group and the echo signal received corresponding to the second pulse sequence group Magnetic resonance imaging device. The method according to claim 1,
Wherein,
Applying at least one RF pulse, a first lead-out gradient pulse, a second lead-out gradient pulse, and a third lead-out gradient pulse to the target object to correct a phase difference of each k-space,
Sequentially receiving first echo signals, second echo signals, and third echo signals corresponding to the first through third lead-out gradient pulses,
And performs phase correction of data in the plurality of k-space based on a difference between an average value of the first echo signal and the third echo signal and the second echo signal. A method for a magnetic resonance imaging apparatus to scan a target object,
(a) applying at least one RF pulse and a spatial encoding gradient pulse to a target object;
(b) applying a plurality of read-out tilt pulses and a plurality of blip pulses to obtain a plurality of echo signals emitted from the object;
(c) sequentially acquiring a plurality of echo signals including different spatial information according to the plurality of blip pulses; And
(d) mapping each of the plurality of echo signals to each of a plurality of k-space based on the different spatial information. 14. The method of claim 13,
The plurality of blip pulses
And at least one other oblique magnetic field other than the oblique magnetic field formed by the lead-out oblique pulse is formed. 15. The method of claim 14,
The step (b)
Out gradient pulse is applied to the object in accordance with an echo time (TE) determined based on a phase difference between water-lipid components in the object, And applying each blip pulse to the object in time between the blip pulses. 16. The method of claim 15,
The method
(e) reconstructing a water-fat separation image from the plurality of k-space based on a phase difference between water and fat components. 15. The method of claim 14,
Wherein the step (a) applies an excitation RF pulse and N refocusing RF pulses to the object,
Wherein the step (b) applies M lead-out warp pulses and (M-1) blip pulses to the object after each refocusing RF pulse is applied. 15. The method of claim 14,
In the step (a), N excitation RF pulses are applied to the object,
The step (b)
Wherein after each excitation RF pulse is applied, M lead-out warp pulses and (M-1) blip pulses are applied to the object. 15. The method of claim 14,
The method
(f) calculating a convolution kernel vector extending in an echo direction, interpolating data corresponding to the missing signal in the plurality of k-space based on the convolution kernel vector; ≪ / RTI > 15. The method of claim 14,
The method comprises:
(g) a first pulse sequence group including at least one RF pulse and a lead-out gradient pulse for correcting the phase difference of each k-space before (a) or after (d) A second pulse sequence group is applied as the object,
Wherein the lead-out gradient pulse in the first pulse sequence group and the lead-out gradient pulse in the second pulse sequence group are configured with different polarities. 21. The method of claim 20,
The method comprises:
(h) performing phase correction of data in the plurality of k-space based on a difference between an echo signal received corresponding to the first pulse sequence group and an echo signal received corresponding to the second pulse sequence group And performing phase correction of the reconstructed image data from the plurality of k-space. A computer-readable recording medium having recorded thereon a program for implementing the method of any one of claims 13 to 21.

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