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1. (WO2018221831) METHOD OF GENERATING MAGNETIC RESONANCE IMAGE AND MAGNETIC RESONANCE IMAGING APPARATUS THEREFOR
Document

Description

Title of Invention

Technical Field

1  

Background Art

2   3   4  

Disclosure of Invention

Technical Problem

5  

Solution to Problem

6   7   8  

Advantageous Effects of Invention

9  

Brief Description of Drawings

10   11   12   13   14   15   16  

Best Mode for Carrying out the Invention

17   18   19   20   21   22   23   24   25   26   27   28   29   30   31   32   33   34   35   36   37   38   39   40   41   42   43   44   45   46   47   48   49   50   51   52   53   54   55   56   57   58   59   60   61   62   63   64   65   66   67   68   69   70   71   72   73   74   75   76  

Claims

1   2   3   4   5   6   7   8   9   10   11  

Drawings

1   2   3   4   5   6   7  

Description

Title of Invention : METHOD OF GENERATING MAGNETIC RESONANCE IMAGE AND MAGNETIC RESONANCE IMAGING APPARATUS THEREFOR

Technical Field

[1]
The present disclosure relates to a method of generating a magnetic resonance image and a magnetic resonance imaging apparatus therefor, and more particularly to a method of generating a magnetic resonance image based on a simultaneous multi-slice technique.

Background Art

[2]
A spin echo technique has been most widely used in the field of magnetic resonance imaging technology and applies a 90° excitation pulse followed by a 180° refocusing pulse to an object to acquire an echo signal for imaging. The spin echo technique has received a lot of attention since it can generate an image with excellent signal to noise ratio (SNR) and contrast ratio.
[3]
Meanwhile, the spin echo technique has developed to a multi-echo method of acquiring multiple echo signals during a TR (time of reptition) in order to reduce scan time, and based on this, a multi-slice technique of acquiring echo signals for respective slices during each TR section in a cross manner and a simultaneous multi-slice (SMS) technique of simultaneously acquiring echo signals from multiple slices by exciting the multiple slices during each TR section have been developed.
[4]
Particularly, the SMS technique has received a lot of attention since it can remarkably reduce scan time. However, in the conventional SMS technique, the application of RF pulses of multiple frequency bands has caused a specific absorption rate (SAR) problem for an object, and, thus, there has been difficulty in commercializing the conventional SMS technique. Further, in the conventional SMS technique, 180° refocusing pulses of multiple frequency bands are applied, and, thus, it is necessary to maintain a constant echo spacing (ESP). This has limited the number of refocusing pulses (i.e., echo train length (ETL)) which can be applied during each TR section and thus has been an obstacle to reduction in scan time. Therefore, in order to commercialize the SMS technique while maximizing the advantage thereof, a method capable of solving the stability problem and also reducing the ESP needs to be researched.

Disclosure of Invention

Technical Problem

[5]
The present disclosure has been conceived to solve the above-described problems of the conventional technology, and some exemplary embodiments of the present disclosure provide a pulse sequence capable of increasing an ETL based on a SMS technique and also solving a SAR problem for an object. Further, some exemplary embodiments of the present disclosure are provided to generate an image having high SNR and contrast ratio.

Solution to Problem

[6]
As a means for solving the above-described technical problem, a first aspect of the present disclosure provides a method of generating a magnetic resonance image including: applying a selective excitation pulse corresponding to multiple slices during each TR section based on a simultaneous multi-slice (SMS) technique, applying multiple refocusing pulses having a spatial bandwidth including two or more slices; and generating a magnetic resonance image for each slice on the basis of magnetic resonance signals acquired from the multiple slice regions in an overlay manner.
[7]
Further, a second aspect of the present disclosure provides a magnetic resonance imaging apparatus including a memory in which a program configured to give pulse sequence information to a MRI scanner and generate a magnetic resonance image on the basis of a magnetic resonance signal received from the MRI scanner and a processor configured to execute the program. Herein, the processor applies a selective excitation pulse corresponding to multiple slices during each TR section based on a SMS technique and then consecutively applies multiple refocusing pulses having a spatial bandwidth including two or more slices and generates a magnetic resonance image for each slice on the basis of magnetic resonance signals acquired from the multiple slice regions in an overlay manner.
[8]
Furthermore, a third aspect of the present disclosure provides a computer-readable storage medium in which a program configured to implement the method of the first aspect is recorded.

Advantageous Effects of Invention

[9]
According to the above-described means for solving the technical problem, a multi-band excitation pulse and a wideband refocusing pulse or non-selective refocusing pulse with a flip angle of 180° or less are applied to an object, and, thus, it is possible to solve a SAR problem for the object and increase an ETL and thus possible to reduce scan time. Also, a phase-shifted refocusing pulse corresponding to a pulse sequence for a single or more TR sections is further applied, and, thus, it is possible to generate an FID artifact-free image enhancing imaging efficiency.

Brief Description of Drawings

[10]
FIG. 1 is a diagram illustrating a magnetic resonance imaging apparatus according to an exemplary embodiment of the present disclosure.
[11]
FIG. 2 is a flowchart illustrating a magnetic resonance imaging method according to an exemplary embodiment of the present disclosure.
[12]
FIG. 3 is a diagram illustrating a spatial bandwidth for an excitation pulse and a refocusing pulse according to an exemplary embodiment of the present disclosure.
[13]
FIG. 4 is a diagram illustrating a pulse sequence according to an exemplary embodiment of the present disclosure.
[14]
FIG. 5 is a flowchart illustrating a method of removing a FID signal according to an exemplary embodiment of the present disclosure.
[15]
FIG. 6 is a diagram illustrating the result of extraction of a FID signal according to an exemplary embodiment of the present disclosure.
[16]
FIG. 7 is a diagram illustrating the result of generation of a magnetic resonance image according to an exemplary embodiment of the present disclosure.

Best Mode for Carrying out the Invention

[17]
Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings so that the present disclosure may be readily implemented by those skilled in the art. However, it is to be noted that the present disclosure is not limited to the embodiments but can be embodied in various other ways. In drawings, parts irrelevant to the description are omitted for the simplicity of explanation, and like reference numerals denote like parts through the whole document.
[18]
Through the whole document, the term "connected to" or "coupled to" that is used to designate a connection or coupling of one element to another element includes both a case that an element is "directly connected or coupled to" another element and a case that an element is "electronically connected or coupled to" another element via still another element. Further, it is to be understood that the term "comprises or includes" and/or "comprising or including" used in the document means that one or more other components, steps, operation and/or existence or addition of elements are not excluded in addition to the described components, steps, operation and/or elements unless context dictates otherwise.
[19]
In the present specification, the term ""magnetic resonance image (MRI)" refers to an image of an object acquired by using the nuclear magnetic resonance principle.
[20]
Further, the term "image" refers to multi-dimensional data composed of discrete elements and may include multiple pixels for 2-dimensinal image and multiple voxels for 3-dimensional image.
[21]
Furthermore, the term "object" refers to a target to be taken by the MRI apparatus and may include a person or animal or a part thereof. Also, the object may include various organs such as the heart, brain, or blood vessels or a variety of phantoms. The phantom means a material having a volume having approximately the same density and effective atomic number as a living thing, and may include a sphere phantom having properties similar to a human body.
[22]
Moreover, the term "user" refers to a medical expert such as a doctor, a nurse, a medical imaging expert, and the like or an engineer repairing a medical apparatus, but is not limited thereto.
[23]
Further, the term "pulse sequence (or pulse train)" refers to a signal repeatedly applied from the MRI apparatus. The pulse sequence is a time parameter for a RF pulse and may include Time of Repetition (TR) or Time to Echo (TE).
[24]
Hereinafter, exemplary embodiments of a magnetic resonance imaging apparatus will be described with reference to the accompanying drawings.
[25]
FIG. 1 is a diagram illustrating a magnetic resonance imaging apparatus according to an exemplary embodiment of the present disclosure.
[26]
A magnetic resonance imaging apparatus 1 may include a MRI scanner 10, a signal processing unit 20, a control unit 40, a monitoring unit 50, and an interface unit 60.
[27]
The MRI scanner 10 generates a magnetic field and generates a resonance with respect to an atomic nucleus, and a magnetic resonance image is taken while an object is present inside the MRI scanner 10. The MRI scanner 10 includes a main magnet 12, a gradient coil 14, a RF coil, and the like and thus generates a static magnetic field and a gradient magnetic field and irradiates a RF signal toward the object.
[28]
The main magnet 12, the gradient coil 14, and the RF coil 16 are arranged within the MRI scanner 10 along a predetermined direction. The object may be positioned on a table which can be inserted into a cylinder along a horizontal axis of the cylinder, and as the table moves, the object can be positioned within a bore of the MRI scanner 10.
[29]
The main magnet 12 generates a static magnetic field that aligns for aligning magnetic dipole moments of atomic nucleuses included in the object in a certain direction.
[30]
The gradient coil 14 includes X, Y, and Z coils that respectively generate gradient magnetic fields in X-axis, Y-axis, and Z-axis directions orthogonal to each other. The gradient coil 14 may induce different resonance frequencies for respective parts of the object and provide position information of each part of the object.
[31]
The RF coil 16 may irradiate a RF signal to the object and receive a magnetic resonance image signal emitted from the object. The RF coil 16 may output a RF signal having the same frequency as a precessional motion toward an atomic nucleus performing the precessional motion and then receive a magnetic resonance image signal emitted from the object.
[32]
For example, in order to transition an atomic nucleus from a low energy level to a high energy level, the RF coil 16 may generate a RF signal having a frequency corresponding to the atomic nucleus and apply the RF signal to the object. Then, when the RF coil 16 stops the transmission of the RF signal, the atomic nucleus to which the electromagnetic wave was applied may transition from the high energy level to the low energy level and emit an electromagnetic wave having a Larmor frequency, and the RF coil 16 receives a signal of the electromagnetic wave.
[33]
The RF coil 16 includes a RF transmission coil that transmits a RF signal having a radio frequency corresponding to the kind of an atomic nucleus and a RF reception coil that receives an electromagnetic wave emitted from an atomic nucleus.
[34]
Further, the RF coil 16 may be fixed to the MRI scanner 10 or may be detachably attached to the MRI scanner 10. The detachable RF coil 16 may be implemented as a head RF coil, a chest RF coil, a leg RF coil, a neck RF coil, a shoulder RF coil, a wrist RF coil, and an ankle RF coil which can be coupled to a part of the object.
[35]
The MRI scanner 10 may provide various kinds of information to a user or the object through a display and may include a display 18 provided outside the MRI scanner 10 and a display (not illustrated) provided inside the MRI scanner 10.
[36]
The signal processing unit 20 may control a gradient magnetic field which is formed inside the MRI scanner 10 and control transmission and reception of a RF signal and a magnetic resonance image signal according to a predetermined MR pulse sequence (i.e., pulse train).
[37]
The signal processing unit 20 may include a gradient amplifier 22, a switching unit 24, a RF transmitter 26, and a RF receiver 28.
[38]
The gradient amplifier 22 drives the gradient coil 14 included in the MRI scanner 10 and supplies the gradient coil 14 with a pulse signal that generates a gradient magnetic field under the control of a gradient magnetic field controller 44. Gradient magnetic fields in the X-axis, Y-axis, and Z-axis directions may be synthesized by controlling the pulse signal supplied from the gradient amplifier 22 to the gradient coil 92.
[39]
The RF transmitter 26 drives the RF coil 16 by supplying a RF pulse to the RF coil 16. The RF receiver 28 receives a magnetic resonance image signal received and then transferred by the RF coil 16.
[40]
The switching unit 24 may adjust a transmission/reception direction of each of a RF signal and a magnetic resonance image signal. For example, in a transmission mode, the switching unit 24 may irradiate a RF signal to the object through the RF coil 16, and in a reception mode, the switching unit 24 may receive a magnetic resonance image signal from the object through the RF coil 16. The switching unit 24 is controlled by a control signal from a RF controller 46.
[41]
The interface unit 30 may give pulse sequence information to the control unit 40 and transfer a command to control an operation of the entire MRI system at the same time by manipulation of the user. The interface unit 30 may include an image processing unit 36 configured to process a magnetic resonance image signal received by the RF receiver 28, an output unit 34, and an input unit 32.
[42]
The image processing unit 36 may process a magnetic resonance image signal received by the RF receiver 28 and generate MR image data for the object.
[43]
The image processing unit 36 may perform various signal processing operations, such as amplification, frequency conversion, phase detection, low-frequency amplification, and filtering, to the magnetic resonance image signal received by the RF receiver 28.
[44]
For example, the image processing unit 36 may arrange digital data in a k-space and perform a 2-dimensioanl or 3-dimensional Fourier transform to the digital data to reconfigure the digital data into image data.
[45]
Further, the image processing unit 36 may parallelly perform the signal processing operations to the magnetic resonance image signal. For example, the image processing unit 36 may parallelly perform a signal processing operation to multiple magnetic resonance image signals received by a multi-channel RF coil to reconfigure the multiple magnetic resonance image signals into image data.
[46]
The output unit 34 may output the image data generated or reconfigured by the image processing unit 36 to the user. Further, the output unit 34 may output information, which is necessary for the user to manipulate the MRI system, such as a user interface (UI), user information, or object information. The output unit 34 may include a speaker, a printer, or various image display devices.
[47]
The input unit 32 enables the user to input object information, parameter information, a scanning condition, a pulse sequence, information on image synthesis or differential operation, and the like. The input unit 32 may include a keyboard, a mouse, a trackball, a voice recognizer, a gesture recognizer, a touch screen, etc., and include various input devices within a scope obvious to those skilled in the art.
[48]
The control unit 40 may include a sequence controller 42 configured to control a sequence of signals generated within the MRI scanner 10 and a scanner controller 48 configured to control the MRI scanner 10 and devices provided in the MRI scanner 10.
[49]
The sequence controller 42 includes the gradient magnetic field controller 44 configured to control the gradient amplifier 22 and the RF controller 46 configured to control the RF transmitter 26, the RF receiver 28, and the switching unit 24. The sequence controller 42 may control the gradient amplifier 22, the RF transmitter 26, the RF receiver 28, and the switching unit 24 according to a pulse sequence received from the interface unit 30. The pulse sequence may include all information required to control the gradient amplifier 22, the F transmitter 26, the RF receiver 28, and the switching unit 24, and may include, for example, information on an intensity of a pulse signal applied to the gradient coil 14, an application time, an application timing, and the like.
[50]
The monitoring unit 50 may monitor or control the MRI scanner 10 or the devices provided in the MRI scanner 10. The monitoring unit 50 may include a system monitor 52, an object monitor 54, a table controller 56, and a display controller 58.
[51]
The system monitor 52 may monitor and control a state of a static magnetic field, a state of a gradient magnetic field, a state of a RF signal, a state of a RF coil, a state of a table, a state of a device that measures body information of the object, a power supply state, a state of a heat exchanger, a state of a compressor, and the like.
[52]
The object monitor 54 monitors a state of the object, and may include a camera for taking a picture of a movement or position of the object, a breath measurer for measuring a breath of the object, an electrocardiogram (ECG) measurer for measuring an ECG of the object, or a body temperature measurer for measuring a body temperature of the object.
[53]
The table controller 56 controls a movement of the table on which the object is positioned. The table controller 56 may control the movement of the table according to a sequence control signal output by the sequence controller 42. For example, during moving imaging of the object, the table controller 56 may move the table according to the sequence control and thus take a picture of the object in a field of view (FOV) greater than that of the MRI scanner.
[54]
The display controller 58 controls an on/off operation of the displays respectively positioned outside and inside the MRI scanner 10 or screen images output on the displays. Also, in the case where a speaker is positioned inside or outside the MRI scanner 10, the display controller 58 may control the speaker to be turned on or off or may control sound to be output through the speaker.
[55]
The MRI scanner 10, the RF coil 16, the signal processing unit 20, the monitoring unit 50, the control unit 40, and the interface unit 30 may be connected to each other in a wireless or wired manner, and when they are connected in a wireless manner, the magnetic resonance imaging apparatus 1 may further include an apparatus (not illustrated) for synchronizing clocks therebetween. Communication between the MRI scanner 10, the RF coil 16, the signal processing unit 20, the monitoring unit 50, the control unit 40, and the interface unit 30 may be performed by using a high-speed digital interface such as low voltage differential signaling (LVDS), asynchronous serial communication such as a universal asynchronous receiver transmitter (UART), a low-delay network protocol such as error synchronous serial communication or a controller area network (CAN), optical communication, or any of other various communication methods within a scope obvious to those skilled in the art.
[56]
The magnetic resonance imaging apparatus 1 according to an exemplary embodiment of the present disclosure is characterized by a configuration of the interface unit 30. Herein, the interface unit 30 may be implemented in the form of a separate computing system and performs an operation of generating a magnetic resonance image on the basis of a memory and a processor installed in the computing system.
[57]
Herein, the memory stores a program configured to generate a magnetic resonance image. The memory may collectively refer to a non-volatile storage device that retains information stored therein even when power is not supplied and a volatile storage device that requires power to retain information stored therein.
[58]
Upon execution of the program stored in the memory, the processor gives pulse sequence information and then generates a magnetic resonance image using a magnetic resonance signal emitted from the object. In this case, the magnetic resonance signal may be image data including multiple frames displaying spaces with the passage of time in a spatio-temporal encoding area (k,t-space).
[59]
As described above with reference to FIG. 1, the MRI scanner 10 irradiates RF signals of multiple frequency bands to excite multiple slices together. Further, the MRI scanner 10 may generate a magnetic field on the basis of multiple gradient coils 14 to acquire magnetic resonance signals emitted from the multiple slices to a spatio-temporal area in an overlay manner. As such, the processor of the magnetic resonance imaging apparatus 1 may receive the acquired signals from the MRI scanner 10. Further, the magnetic resonance imaging apparatus 1 may generate a magnetic resonance image for each slice by separating and imaging the magnetic resonance signals acquired from the MRI scanner 10.
[60]
FIG. 2 is a flowchart illustrating a magnetic resonance imaging method according to an exemplary embodiment of the present disclosure.
[61]
Referring to FIG. 2, the magnetic resonance imaging apparatus 1 applies a selective excitation pulse corresponding to multiple slices during each TR section based on a SMS technique and then consecutively applies multiple refocusing pulses having a spatial bandwidth including at least two slices (S110). Herein, the SMS technique refers to a technique of simultaneously exciting multiple slices to simultaneously acquire magnetic resonance signals from the multiple slices through multiple coils in order to reduce scan time and separating the magnetic resonance signals for the respective slices using a difference in coil sensitivity information between the slices, and corresponds to a parallel imaging process. Herein, the coil sensitivity information may refer to the sensitivity of receiving a magnetic resonance signal which varies depending on the position of each of the multiple coils.
[62]
The magnetic resonance imaging apparatus 1 applies a refocusing pulse having a wide spatial bandwidth which may include two or more slice regions during a TR section. Desirably, the spatial bandwidth of the refocusing pulse may be a wideband refocusing pulse corresponding to a FOV in a slice direction or a non-selective refocusing pulse including the FOV. FIG. 3 is a diagram illustrating a spatial bandwidth for an excitation pulse and a refocusing pulse according to an exemplary embodiment of the present disclosure. Referring to FIG. 3, the magnetic resonance imaging apparatus 1 may apply a selective excitation pulse (i.e., a 90° RF pulse) corresponding to three slices 301, 302, and 303 to the object and then consecutively apply a refocusing pulse corresponding to a FOV 304 of the MRI scanner 10.
[63]
Meanwhile, the magnetic resonance imaging apparatus 1 uses refocusing pulses having a wide spatial bandwidth, and, thus, it is possible to minimize a specific absorption rate (SAR) and also possible to consecutively apply the refocusing pulses to the object with a short echo spacing (ESP). Thus, in the above-described exemplary embodiment, an echo train length (ETL) can be increased.
[64]
Meanwhile, the refocusing pulses may have a fixed flip angle or a variable flip angle during a TR section as illustrated in FIG. 4A and FIG. 4B. Meanwhile, if the refocusing pulses have a variable flip angle according to an exemplary embodiment, a flip angle α° 1 of a refocusing pulse applied first after the excitation pulse may be 180°. As such, the magnetic resonance imaging apparatus 1 may apply refocusing pulses having a wide spatial bandwidth and a flip angle of 180° or less and thus can reduce scan time and minimize the SAR at the same time.
[65]
Then, the magnetic resonance imaging apparatus 1 generates a magnetic resonance image for each slice on the basis of magnetic resonance signals acquired from the multiple slice regions in an overlay manner (S120). More specifically, the magnetic resonance imaging apparatus 1 may generate a multi-band image on the basis of the magnetic resonance signals and separate the multi-band image into a single-band image on the basis of reference data for a frequency band corresponding to each slice. Herein, the multi-band image may include multiple slice images in an overlay manner, and the single-band image may include a single slice image. Further, the reference data may refer to the above-described coil sensitivity information. For example, the magnetic resonance imaging apparatus 1 may apply a single-band excitation pulse corresponding to each slice to the object to acquire the reference data before performing the step S110. However, the magnetic resonance imaging apparatus 1 is not limited thereto and may apply a pulse sequence to the object in order to acquire the reference data at various timings.
[66]
Meanwhile, the method of separating a multi-band image may employ a method of separating a multi-band image by using the sensitivity of multiple coils in an image domain and a k-domain, but is not limited thereto.
[67]
Meanwhile, in the above-described exemplary embodiment, the refocusing pulses a flip angle of 180° or less are applied to the object, and, thus, a free induction decay (FID) signal emitted from a region except the selectively excited slice regions can also be acquired together with an echo signal. In this case, the FID signal may act as an artifact in an image and thus lower a SNR and a contrast ratio of the image. Therefore, according to an exemplary embodiment, the magnetic resonance imaging apparatus 1 may further apply a calibration pulse sequence for removing the FID signal from the acquired magnetic resonance signal to the object. Hereinafter, a detailed explanation will be provided with reference to FIG. 5.
[68]
Referring to FIG. 5, the magnetic resonance imaging apparatus 1 extracts a FID signal by applying a calibration pulse sequence corresponding to a pulse sequence for one of multiple TR sections for imaging and including multiple phase-shifted refocusing pulses (S510). In this case, the calibration pulse sequence requires a single or more TR and may be applied earlier or later than the imaging pulse sequence illustrated in FIG. 2. Otherwise, the calibration pulse sequence may be applied in the middle of the imaging pulse sequence.
[69]
Specifically, the magnetic resonance imaging apparatus 1 may acquire a first magnetic resonance signal acquired during the single TR section and a second magnetic resonance signal acquired when the calibration pulse sequence is applied and then extract a FID signal by subtracting the second magnetic resonance signal from the first magnetic resonance signal. That is, the first magnetic resonance signal includes an echo signal emitted from multiple slices excited during the single TR section and a FID signal emitted from a FOV region in a slice direction, and the second magnetic resonance signal includes an echo signal generated by re-excitation of the multiple slices and a phase-shifted FID signal emitted from the FOV region. Therefore, the magnetic resonance imaging apparatus 1 can extract the FID signal from which the echo signal is removed by subtracting the second magnetic resonance signal from the first magnetic resonance signal. FIG. 6 is a diagram illustrating the result of extraction of a FID signal 630 by applying a calibration pulse sequence 600 according to an exemplary embodiment of the present disclosure. Herein, FID signals included in a first magnetic resonance signal 610 and a second magnetic resonance signal 620, respectively, have phases inverted to each other.
[70]
Then, the magnetic resonance imaging apparatus 1 subtracts a FID signal from a magnetic resonance signal acquired during each TR (S520). Thus, the magnetic resonance imaging apparatus 1 may extract an echo signal suitable for imaging by removing the FID signal from the magnetic resonance signal. Then, the magnetic resonance imaging apparatus 1 may perform the step S120 illustrated in FIG. 2 using the magnetic resonance signal from which the FID signal is removed and thus generate a magnetic resonance image having high SNR and contrast ratio.
[71]
Meanwhile, FIG. 5 illustrates that the magnetic resonance imaging apparatus 1 extracts the FID signal by subtracting the second magnetic resonance signal from the first magnetic resonance signal, but in some exemplary embodiments, the magnetic resonance imaging apparatus 1 may reconstruct an image in which artifacts caused by the FID signal are suppressed by adding the second magnetic resonance signal from the first magnetic resonance signal. Therefore, in this case, the step S520 may be omitted.
[72]
FIG. 7 is a diagram illustrating the result of generation of a magnetic resonance image according to an exemplary embodiment of the present disclosure. FIG. 7A illustrates the result of imaging of magnetic resonance signals corresponding to respective slices and acquired in a non-overlay manner, and shows a comparison value for measuring the SNR and the contrast ratio of a magnetic resonance image generated according to an exemplary embodiment of the present disclosure. FIG. 7B illustrates the result of imaging of magnetic resonance signals acquired in an overlay manner by applying a non-selective refocusing pulse of 180° or less and a calibration pulse sequence to an object and then separated for each slice according to an exemplary embodiment of the present disclosure. Further, FIG. 7C is an error map generated on the basis of a difference between FIG. 7A and FIG. 7B. As shown in FIG. 7C, the magnetic resonance imaging apparatus 1 according to an exemplary embodiment of the present disclosure can remarkably reduce scan time and solve the SAR problem for the object by using a multi-band excitation pulse and a non-selective refocusing pulse (or wideband refocusing pulse) of 180° or less and can also generate a magnetic resonance image having high SNR and contrast ratio by adding a calibration pulse sequence.
[73]
An exemplary embodiment of the present disclosure can be embodied in a storage medium including instruction codes executable by a computer such as a program module executed by the computer. A computer-readable medium can be any usable medium which can be accessed by the computer and includes all volatile/non-volatile and removable/non-removable media. Further, the computer-readable medium may include all computer storage. The computer storage medium includes all volatile/non-volatile and removable/non-removable media embodied by a certain method or technology for storing information such as computer-readable instruction code, a data structure, a program module or other data.
[74]
The system and method of the present disclosure has been explained in relation to a specific embodiment, but its components or a part or all of its operations can be embodied by using a computer system having general-purpose hardware architecture.
[75]
The above description of the present disclosure is provided for the purpose of illustration, and it would be understood by those skilled in the art that various changes and modifications may be made without changing technical conception and essential features of the present disclosure. Thus, it is clear that the above-described embodiments are illustrative in all aspects and do not limit the present disclosure. For example, each component described to be of a single type can be implemented in a distributed manner. Likewise, components described to be distributed can be implemented in a combined manner.
[76]
The scope of the present disclosure is defined by the following claims rather than by the detailed description of the embodiment. It shall be understood that all modifications and embodiments conceived from the meaning and scope of the claims and their equivalents are included in the scope of the present disclosure.

Claims

[Claim 1]
A method of generating a magnetic resonance image by a magnetic resonance imaging apparatus, comprising: applying a selective excitation pulse corresponding to multiple slices during each TR section based on a simultaneous multi-slice (SMS) technique; applying multiple refocusing pulses having a spatial bandwidth including at least two slices; and generating a magnetic resonance image for each slice on the basis of magnetic resonance signals acquired from the multiple slice regions in an overlay manner.
[Claim 2]
The method of generating a magnetic resonance image of Claim 1, further comprising: extracting a free induction decay (FID) signal by applying a calibration pulse sequence corresponding to a pulse sequence for a single or more TR sections and including the multiple refocusing pulses whose phases are inverted; and correcting the FID signal from a magnetic resonance signal acquired during each TR.
[Claim 3]
The method of generating a magnetic resonance image of Claim 2, wherein the extracting of a FID signal includes: acquiring a first magnetic resonance signal acquired during the single TR section and a second magnetic resonance signal acquired when the calibration pulse sequence is applied; and extracting the FID signal by subtracting the second magnetic resonance signal from the first magnetic resonance signal.
[Claim 4]
The method of generating a magnetic resonance image of Claim 1, wherein a spatial bandwidth of the refocusing pulse is a wideband refocusing pulse or non-selective refocusing pulse corresponding to a FOV region in a slice direction
[Claim 5]
The method of generating a magnetic resonance image of Claim 1, wherein at least one of the multiple refocusing pulses has a flip angle of 180° or less.
[Claim 6]
The method of generating a magnetic resonance image of Claim 1, wherein the generating of a magnetic resonance image for each slice includes: generating a multi-band image on the basis of the magnetic resonance signal; and separating the multi-band image into a single-band image on the basis of reference data for a frequency band corresponding to each slice.
[Claim 7]
A magnetic resonance imaging apparatus comprising: a memory in which a program configured to give pulse sequence information to a MRI scanner and generate a magnetic resonance image on the basis of a magnetic resonance signal received from the MRI scanner; and a processor configured to execute the program, wherein the processor applies a selective excitation pulse corresponding to multiple slices during each TR section based on a simultaneous multi-slice (SMS) technique and then consecutively applies multiple refocusing pulses having a spatial bandwidth including at least two slices and generates a magnetic resonance image for each slice on the basis of magnetic resonance signals acquired from the multiple slice regions in an overlay manner.
[Claim 8]
The magnetic resonance imaging apparatus of Claim 7, wherein the processor extracts a free induction decay (FID) signal by applying a calibration pulse sequence corresponding to a pulse sequence for a single or more TR section and including the multiple refocusing pulses whose phases are inverted and corrects the FID signal from a magnetic resonance signal acquired during each TR.
[Claim 9]
The magnetic resonance imaging apparatus of Claim 8, wherein the processor acquires a first magnetic resonance signal acquired during the single TR section and a second magnetic resonance signal acquired when the calibration pulse sequence is applied and extracts the FID signal by subtracting the second magnetic resonance signal from the first magnetic resonance signal.
[Claim 10]
The magnetic resonance imaging apparatus of Claim 7, wherein the processor generates a multi-band image on the basis of the magnetic resonance signal and separates the multi-band image into a single-band image on the basis of reference data for a frequency band corresponding to each slice.
[Claim 11]
A computer-readable storage medium in which a program configured to implement a method of Claim 1 is recorded.

Drawings

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[ Fig. 2]

[ Fig. 3]

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[ Fig. 5]

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[ Fig. 7]