KR101958093B1 - Magnet resonance imaging device and method for generating blood imaging thereof - Google Patents

Abstract

Disclosed herein is a method for reconstructing a blood flow image based on non-contrast magnetic resonance angiography (MRA) and a magnetic resonance imaging apparatus thereof. In particular, the blood flow image reconstruction method according to an embodiment of the present invention acquires a plurality of first echoes at each TR corresponding to the diastole of the heart, and acquires a plurality of second echoes at each TR corresponding to the systole of the heart Generating a field map from a plurality of first echos or a plurality of second echoes; And reconstructing a fat-supressed blood flow image from the plurality of first echoes and the second echoes based on the chemical shift value and the water-lipid component chemical shift value and the field map.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging apparatus and a blood flow image restoration method using the same,

The present invention relates to a magnetic resonance imaging apparatus and a blood flow image reconstruction method using the same, and more particularly, to a method of reconstructing a blood flow image based on non-contrast magnetic resonance angiography (MRA) And a magnetic resonance imaging apparatus.

In recent years, there have been increasing cases of acquiring images of the human body in the transverse axis direction, longitudinal axis direction, oblique direction and the like using the MRI (Magnetic Resonance Imaging) apparatus and inspecting and diagnosing the condition of the testee through such images. Magnetic resonance imaging is a very important and useful imaging tool because it enables noninvasive imaging of the human body and unlike CT / PET, there is no risk of radiation exposure.

MRA (magnetic resonance angiography) is known as a technique for acquiring blood flow images in the field of the magnetic resonance imaging. MRA is mainly used for ischemic or infarcted areas of the brain or heart. Conventional MRA is a method of administering a contrast agent, which causes side effects or risks due to contrast agents. In order to solve this problem, non-contrast MRA without contrast agent is being actively studied.

Recently, the FBI (Fresh Blood Imaging) method, which captures and visualizes blood flow at a high flow rate according to heartbeat using an electrocardiogram, is widely known. However, since the blood flow image generated by the FBI technique has lower SNR (Signal to Noise Ratio) and resolution as compared with the enhanced blood flow image due to the residual signal from the background tissue (especially, adipose tissue) There is a limit. In addition, the background tissue signal blurred in the image is not distinguishable from the minute blood vessel, and there is a risk that the user can misdiagnose.

Japanese Patent No. 5537623 (titled Magnetic Resonance Imaging Apparatus)

SUMMARY OF THE INVENTION The present invention has been made in order to solve the problems of the prior art described above, and in some embodiments of the present invention, a fat-suppressed blood flow image is restored in a non-contrast enhancement MRA technique, It has its purpose. Furthermore, it is an object of the present invention to restore a high-resolution blood flow image by correcting errors generated according to hardware characteristics of a MRI apparatus.

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.

As a technical solution to achieve the above technical object, a first aspect of the present invention is a method for acquiring a plurality of first echoes at each TR corresponding to a diastole of a heart, Acquiring a plurality of second echoes from the plurality of second echoes; Generating a field map from a plurality of first echos or a plurality of second echoes; Recovering a fat-supressed blood flow image from a plurality of first echoes and a second echo, based on a chemical shift value and a water-lipid component chemical shift value and a field map, Non-contrast magnetic resonance angiography (MRA), in which each of the first echoes and the plurality of second echoes of the first and second echoes are acquired from different TEs according to the resonance frequency difference of the respective water- Based blood flow image reconstruction method.

According to a second aspect of the present invention, there is provided a magnetic resonance imaging apparatus comprising: a memory for storing a program for reconstructing a blood flow image from a magnetic resonance signal; And a processor for executing the program. Wherein the processor is configured to obtain a plurality of first echoes at each TR corresponding to a diastole of the heart and to obtain a plurality of second echoes at each TR corresponding to a systole of the heart, Generating a field map from the plurality of first echos or the plurality of second echoes based on the water-lipid component chemical shift value and the field map, generating a field map from the plurality of first echos and the second echos, (fat-supressed) blood flow images. At this time, each of the plurality of first echoes and the plurality of second echoes obtained in each TR is obtained in different TEs according to the resonance frequency difference of each water-lipid component.

A third aspect of the present invention provides a computer-readable recording medium having recorded thereon a program for implementing the first aspect.

According to the above-mentioned object of the present invention, the magnetic resonance imaging apparatus separates and restores the background tissue surrounding the blood vessels of the water component and the fat component by encoding the chemical movement of the water-lipid component into the imaging pulse train, Blood flow images can be reconstructed. In addition, the magnetic resonance imaging apparatus can restore a high-resolution blood flow image by correcting the phase of each echo by adding a phase correction pulse train.

1 is a block diagram of a magnetic resonance imaging apparatus according to an embodiment of the present invention.
2 is a block diagram illustrating a magnetic resonance imaging apparatus according to an embodiment of the present invention.
3 is a flowchart illustrating a method of restoring a blood flow image of the processor of FIG. 2 according to an embodiment of the present invention.
4 is a diagram showing a part of an imaging pulse train according to an embodiment of the present invention.
FIG. 5 is a diagram showing an example of obtaining a difference value between the plurality of first echoes and the second echoes obtained in FIG.
6 is a diagram illustrating an example of a processor reconstructing a blood flow image according to an embodiment of the present invention.
7 is a flowchart illustrating a fat suppressed blood flow image restoration method of a processor according to another embodiment of the present invention.
8 is a diagram illustrating an example in which a processor reconstructs a blood flow image according to the embodiment of FIG.
9 is a flow chart illustrating a method for a processor to correct for phase error of an echo obtained in an imaging pulse train, in accordance with an embodiment of the present invention.
10 is a diagram illustrating an example of a phase correction pulse train according to an embodiment of the present invention.
11 is a diagram showing an example of a phase correction pulse train according to another embodiment of the present invention.

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.

As used herein, the term " Magnetic Resonance Imaging (MRI) device "refers to a device that acquires a magnetic field and non-ionizing radiation (radio high frequency) as an object in order to acquire an image based on a physical principle called nuclear magnetic resonance Means a device that is authorized.

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 (or 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 block diagram of a magnetic resonance imaging apparatus according to an embodiment of the present invention.

The magnetic resonance imaging apparatus 1 may include an MRI scanner 10, a signal processing unit 20, a control unit 40, a monitoring unit 50, and an interface unit 60.

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 (i.e., a pulse train), and can control the 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 outputs a pulse signal for generating a gradient magnetic field under the control of the gradient magnetic field control unit 44 to the gradient coil 14, . By controlling the pulse signals supplied from the oblique magnetic field amplifier 22 to the gradient coil 14, gradient magnetic fields in the X axis, Y axis, and Z axis directions can be synthesized.

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 information necessary for controlling the gradient magnetic field amplifier 22, the RF transmitter 26, the RF receiver 28 and the switching unit 24, and for example, a pulse applied to the gradient coil 14 the intensity of the pulse signal, the application time, the 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.

The magnetic resonance imaging apparatus 1 according to an embodiment of the present invention is characterized by the configuration of a sequence controller 42 and an image processor 36 for indicating imaging pulse sequences. 2, the magnetic resonance imaging apparatus 1 may be implemented as a magnetic resonance imaging apparatus 100 in the form of a separate computing apparatus, and may include a memory 110 mounted on the computing apparatus and a processor 120 ) Can be used to perform a non-contrast MRA (Magnetic Resonance Angiography) -based blood flow image restoration operation described later.

At this time, a program for restoring the blood flow image is stored in the memory 110. A memory is a nonvolatile storage device that keeps stored information even when no power is supplied, and a volatile storage device that requires power to maintain stored information.

The processor 120 instructs the signal processing unit 20 of FIG. 1 to display an imaging pulse train and receives a magnetic resonance signal from the signal processing unit 20 according to the execution of the program stored in the memory 110. FIG. At this time, the imaging pulse train may be a chemical shift of a water-lipid component encoded and may be applied to the subject in synchronization with the diastole and systole of the heart. Thereafter, the processor 120 applies the received magnetic resonance signals to blood flow-lipid modeling to reconstruct the blood flow image separated from the fat signal, thereby generating a robust blood flow image. Hereinafter, this will be described in detail with reference to Figs. 3 to 11. Fig.

FIG. 3 is a flowchart illustrating a method for restoring a blood flow image by the processor 120 of FIG. 2 according to an embodiment of the present invention.

Referring to FIG. 3, the processor 120 first applies a plurality of first echoes corresponding to the diastolic phase and a systolic phase by applying an imaging pulse train in which the chemical shift of the water-lipid component is encoded to the subject in synchronization with the heart's diastole and systole And acquires a plurality of corresponding second echoes (S310). Here, the chemical shift of the water-lipid component exists as water and fat have resonance frequencies different from each other, and the processor 120 calculates the chemical shift of the water- The imaging pulse train can be encoded such that a frequency encoding gradient magnetic field is formed at a point in time (i.e., different echo time, TE). In this way, the processor 120 may obtain a first echo or a second echo at different TEs.

The imaging pulse train may include various pulse sequences capable of chemical movement encoding and may include, for example, a fast spin echo (FSE), a gradient echo, a gradient and spin echo (GRASE) Or the like.

FIG. 4 is a diagram illustrating a portion of an imaging pulse sequence 400 according to an embodiment of the present invention. Referring to FIG. 4, the imaging pulse train 400 may be configured to acquire echoes in three TEs, taking into account the phase difference between water and fat. For example, each TE of the imaging pulse train 400 may have a positional difference of about 2.0 ms, but this may vary depending on the intensity of the strong field.

In addition, the imaging pulse train 400 can be synchronized to the systolic and diastolic phases of the heart of the subject. For example, each TR of the imaging pulse train 400 may be delayed according to the diastolic or systolic periods of the heart so as to obtain a plurality of first echos corresponding to the diastole of the heart and a plurality of second echoes corresponding to the systole of the heart . At this time, the processor 120 adds a navigator pulse string to the imaging pulse string 400 for monitoring the cardiac activity state, synchronizes each TR of the imaging pulse string 400 with the cardiac activity cycle, (E. G., Electrocardiogram data, etc.). The external device may be, for example, an ECG device, a pulse oximeter, or the like.

Meanwhile, the imaging pulse sequence 400 may further include blip pulses 410 and 420 for allowing echoes obtained in each TR to have different spatial information. 4, the blip pulses 410 and 420 are shown to form the phase encoding gradient magnetic field Gy and the slice selection gradient magnetic field Gz, but the present invention is not limited thereto, and the phase encoding gradient magnetic field Gy or the slice selection gradient But may be formed only in the magnetic field Gz. The processor 120 can distinguish echoes obtained from different TEs by allowing echoes obtained from different TEs to have different spatial information via the blip pulse.

Referring again to FIG. 3, the processor 120 may generate a field map from a plurality of first echos or a plurality of second echoes (S320). Here, the field map is a map indicating the uniformity of the strong field, and includes the phase change information per zone in the image reconstructed by the magnetic resonance imaging apparatus 100.

In order to generate the field map, the processor 120 may divide a plurality of first echos or a plurality of second echoes by TE, and may sample the image data into a plurality of k-spaces, or restore the plurality of image spaces. At this time, the processor 120 can distinguish the first echo or the second echo using the spatial information and the time information of each echo. Then, the processor 120 may extract the low-frequency data of each k-space or each image space to recover a plurality of low-frequency images. Here, the low-frequency data may be data extracted from the center of each k-space or image space. Thereafter, the processor 120 may generate a field map from a plurality of low frequency images. For example, the processor 120 may generate a field map by applying a region growing technique to the low frequency images extended in the echo direction.

Next, the processor 120 calculates a first echo (echo obtained in the diastole) and a second echo (echo obtained in the systole) based on the chemical shift values and the field map of the water- A fat-supressed blood flow image is reconstructed (S330). For this purpose, the processor 120 divides the first echo and the second echo into TEs, and then samples the TE-specific k-space corresponding to the diastolic period of the heart and the TE-specific k-space corresponding to the systolic period of the heart Or undersampling). Thereafter, the processor 120 may calculate a difference value between the first echo and the second echo for each TE. FIG. 5 illustrates a plurality of first echoes and a second echo obtained through the imaging pulse sequence of FIG. 4 as the k-space (three k-space) 510 of the diagonal and the k-space (K-space) 520, and then calculates a difference 530 between the first echo and the second echo for each TE.

)과 혈류 영상(

)을 분리하여 획득할 수 있다. Thereafter, the processor 120 may perform blood flow-lipid modeling based on the difference between the first echo and the second echo and the field map in the same TE. The blood flow-fat modeling can be expressed by the following equation (1). The processor 120 linearizes the following equation (1) so that the background tissue image around the blood vessel having the minimum value of the solution

) And blood flow image

) Can be separated and obtained.

,

,

는 ㅣ(ㅣ=1, 2, 3, n, n은 인코딩된 TE의 개수)번째 TE에 대응하는 제1 에코로부터 제2 에코를 감산한 결과를 나타내며,

는 물-지방 성분의 주파수 차이값을 나타내며,

는 필드맵을 나타낸다. 또한,

,

는 각각 p번째와 q번째 스파시파잉 변환(sparsifying transform) 연산자를 나타내며,

,

는 각각 사용되는 연산자의 총 개수를 나타낸다. In the above equation,

Represents the result of subtracting the second echo from the first echo corresponding to l (TE = l, 2, 3, n, n is the number of encoded TE) th TE,

Represents the frequency difference value of the water-lipid component,

Indicates a field map. Also,

,

Represents a p-th and a q-th sparsifying transform operator, respectively,

,

Represents the total number of operators used.

)을 출력함으로써, 혈관 주변의 배경 영상이 분리된 혈류 영상을 제공할 수 있다. Processor 120 may use the blood flow image ("

), It is possible to provide a blood flow image in which a background image around the blood vessel is separated.

6 is a diagram illustrating an example in which the processor 120 reconstructs a blood flow image according to an embodiment of the present invention.

FIG. 6A shows an image reconstructed using a conventional non-contrast MRA technique, FIG. 6B shows a reconstructed image of a blood flow image (left) obtained in accordance with an embodiment of the present invention and a background tissue image Right side). (b), it can be confirmed that the background tissue around the blood vessel is removed as compared with the blood flow image of (a). It can also be seen that the blood flow image of (b) further includes fine blood flow (blood vessel) information (shown by an arrow) that does not appear in the blood flow image of (a).

According to another embodiment of the present invention, instead of using the above-described blood-lipid model (Equation 1), the processor 120 separately extracts and extracts a blood flow signal from the obtained echoes, Can be obtained. At this time, the processor 120 can improve the resolution of the reconstructed image by using the k-space or the image space extended in the echo direction. Hereinafter, this will be described in detail with reference to FIG.

Referring to FIG. 7, the processor 120 can extract a blood flow signal from a plurality of first echos and second echos using phase difference according to chemical shift of a water-lipid component and phase change information for each field of a field map (S710).

Thereafter, the processor 120 may recover the k-space or image space for each of the diastolic and systolic periods of the heart using the extracted blood flow signal (S720). At this time, the processor 120 may classify the echos by TE and sample them in k-space for each TE using the spatial information and the time information of each echo. Or processor 120 may relocate and / or restore two k-spaces of echoes obtained in each of the heart's diastole and systole to the TE per-image space.

Next, the processor 120 can restore the image by subtracting the k-space of the systole from the diagonal k-space extended in the echo direction or by subtracting the image space of the systole from the image space of the diastole extending in the echo direction (S730).

FIG. 8 is a diagram illustrating an example in which the processor 120 reconstructs a blood flow image according to the embodiment of FIG.

FIG. 8A shows a restored blood flow image according to the conventional MRA technique, and FIG. 8B shows a restored blood flow image according to the embodiment of FIG. (b), it can be confirmed that the background tissue around the blood vessel is removed as compared with the blood flow image of (a). On the other hand, the blood flow image of (a) is blurred with the residual signal from the background tissue and the fine blood flow (blood vessel) signal, so that it is not distinguished whether the signal is due to the blood flow caused by the background tissue. This may make it difficult for the user of the magnetic resonance imaging apparatus 100 to analyze the image. However, the blood flow image of (b) efficiently removes the signal from the background tissue and restores the image containing only the blood flow (blood vessel) information, so that the user can easily perform the image analysis.

Meanwhile, the magnetic resonance imaging apparatus 100 according to an embodiment of the present invention may further perform an operation for correcting a phase error generated according to hardware characteristics. When the frequency-coded gradient magnetic fields included in one TR are formed in a flyback manner according to the embodiment, the phase error correction operation is not required since the same or similar phase errors occur in each echo. However, as shown in FIG. 4, when a frequency encoding gradient magnetic field having different polarities is formed in one TR, phase errors (i.e., (+) phase error, (-) phase Error) occurs, it is necessary to correct it. In particular, since the disclosed embodiments recover the blood flow image using the phase difference of the water-lipid component, the phase error can provide erroneous information in restoring the blood flow image. Therefore, according to the embodiment, the magnetic resonance imaging apparatus 100 can improve the resolution of the image by correcting the phase error. This will be described later in detail with reference to Figs. 9 to 11.

9 is a flow chart illustrating a method by which processor 120 corrects the phase error of an echo obtained in an imaging pulse train, in accordance with an embodiment of the present invention.

Referring to FIG. 9, first, the processor 120 applies a phase correction pulse sequence to a target object (S910). The phase correction pulse sequence is composed of two TRs as chemically motion-encoded pulse sequences in the same manner as the imaging pulse sequence, and each TR can be composed of at least one RF pulse and a plurality of frequency encoding gradient pulses. At this time, a plurality of frequency-coded gradient magnetic fields of each TR can have opposite polarities. Further, the phase correction pulse sequence does not include the remaining oblique pulses (i.e., the phase encoding oblique pulse Gy, the slice encoding oblique pulse Gz).

Thereafter, the processor 120 may acquire a plurality of first phase correction echoes in the first TR and a plurality of second phase correction echoes in the second TR in accordance with the phase correction pulse sequence (S920).

Thereafter, the processor 120 determines echoes (e. G., Echo) obtained through the imaging pulse sequence based on the difference value (i.e., the phase correction value) between the first phase correction echo and the second phase correction echo obtained at the same TE of each TR , The first echo and the second echo) (S930). For example, the processor 120 can use the TE information of each echo to correct the first echo or second echo of the same TE as the phase correction value. Through this, the processor 120 can prevent each echo obtained in the imaging pulse train from being shifted in k-space.

10 is a diagram showing an example of a phase correction pulse train 1000 according to an embodiment of the present invention. Each TR of the phase correction pulse train 1000 includes at least one RF pulse (e. G., An excitation pulse and at least one refocusing pulse) that is the same as the imaging pulse train and includes frequency encoding gradient pulses 1030 and 1040, .

Thereafter, the processor 120 may sequentially acquire a plurality of first phase correction echoes 1010 and a plurality of second phase correction echoes 1020 in each TR. At this time, the TE from which the plurality of first phase correcting echoes 1010 and the second phase correcting echoes 1020 are acquired may be equal to the TE where each echo is obtained in the imaging pulse train.

9 and 10, the phase correction pulse train composed of two TRs has been described. However, the present invention is not limited thereto. For example, the processor 120 may extract phase correction values using echoes obtained in different TEs for one TR. For example, as shown in FIG. 11, the processor 120 applies at least one RF pulse RF and three frequency encoding gradient pulses Gx, which are the same as the imaging pulse train, to a target object, 1110, the second phase correction echo 1120, and the third phase correction echo 1130 in sequence. In this case, the processor 120 converts the difference value between the average value of the first and third phase correction echoes 1110 and 1130 of the same polarity and the second phase correction echo 1120 having the opposite polarity to the phase correction value . In addition, the above-mentioned phase correction value can be used to correct the phase of all echoes irrespective of TE.

Thus, one embodiment of the present invention provides a method and apparatus for applying a chemically mapped encoded imaging pulse train of a water-lipid component to a subject, performing blood-lipid modeling, or recovering a fat-suppressed blood flow image, Blood flow images can be obtained. In addition, in one embodiment, a high-resolution blood flow image can be obtained by further applying a phase correction pulse string.

The above-described method of reconstructing a blood flow image of a magnetic resonance imaging apparatus and a magnetic resonance imaging apparatus according to an embodiment of the present invention may be in the form of a recording medium including instructions executable by a computer such as a program module executed by a computer Can also be implemented. Computer readable media can be any available media 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. Computer storage media includes both volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data.

While the systems and methods of the present invention have been described with reference to particular embodiments, some or all of their components or operations may be implemented using a computer system having a general purpose hardware architecture.

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.

10: MRI scanner 20: Signal processor
40: control unit 50: monitoring unit
60:
110: Memory
120: Processor

Claims (13)

A method for reconstructing a blood flow image based on non-contrast magnetic resonance angiography (MRA) of a MRI apparatus,
Obtaining a plurality of first echoes at each TR corresponding to a diastole of the heart and acquiring a plurality of second echoes at each TR corresponding to the systole of the heart;
Generating a field map from the plurality of first echos or the plurality of second echoes; And
Recovering a fat-supressed blood flow image from the plurality of first echoes and the second echoes based on the water-lipid component chemical shift value and the field map,
Wherein each of the plurality of first echoes obtained in each TR and each of the plurality of second echoes is obtained in different TEs according to resonance frequency differences of respective water-lipid components. The method according to claim 1,
The step of obtaining the plurality of first echoes and the second echo
Wherein one or more blip pulses are formed in at least one oblique magnetic field so that each of the plurality of first echoes or second echoes obtained in each TR has different spatial information. The method according to claim 1,
The step of generating the field map
Dividing the plurality of first echoes or the second echoes into TEs, and restoring a plurality of k-spaces or a plurality of image spaces;
Generating a plurality of low-frequency images using low-frequency data of each k-space or each image space; And
And generating a field map from the plurality of low frequency images. The method according to claim 1,
The step of restoring the fat-suppressed blood flow image
Performing blood flow-lipid modeling based on the difference between the first echo and the second echo for the same TE and the field map to separate and reconstruct the background tissue image and the blood flow image around the blood vessel, How to restore. 5. The method of claim 4,
The step of restoring the fat-suppressed blood flow image
Wherein a background tissue image and a blood flow image around the blood vessel having a minimum value are obtained by linearizing the following equation (1).
[Equation 1]

,

Represents the result of subtracting the echo of the systolic from the echo of the diastole corresponding to the l < th > TE,

Represents the frequency difference value of the water-lipid component,

Represents a field map,

Represents a blood flow image,

Represents a background tissue image around the blood vessel,

,

Represents a p-th and a q-th sparsifying transform operator, respectively,

,

Represents the total number of operators used. The method according to claim 1,
The step of restoring the fat-suppressed blood flow image
Extracting a blood flow signal from the plurality of first echos and the second echoes using the phase difference value according to the chemical movement of the water-lipid component and the field map;
Reconstructing k-space or image space for each of the diastolic and systolic periods of the heart using the extracted blood flow signal; And
And reconstructing the image based on the difference between the k-space of the diastole extending in the echo direction or the k-space of the systole or the image space. The method according to claim 1,
The blood flow image restoration method
Applying at least one RF pulse and a plurality of frequency-coded gradient magnetic fields to the object in each of the two TRs to obtain a plurality of first phase correction echoes and a plurality of second phase correction echoes; And
Further comprising correcting the phase of each of the plurality of first echoes and the second echo based on a phase difference between a first phase correction echo and a second phase correction echo corresponding to each TE,
Wherein the plurality of first phase correction echoes and the second phase correction echo are obtained in different TEs according to the resonance frequency of each of the water-
Wherein the frequency-coded gradient magnetic field of each TR has an opposite polarity to each other. In a magnetic resonance imaging apparatus,
A memory for storing a program for reconstructing a blood flow image from a magnetic resonance signal; And
And a processor for executing the program,
Wherein the processor is configured to obtain a plurality of first echoes at each TR corresponding to a diastole of the heart and to obtain a plurality of second echoes at each TR corresponding to a systole of the heart,
Generating a field map from the plurality of first echos or the plurality of second echoes,
Recovering a fat-supressed blood flow image from the plurality of first echoes and the second echoes based on the water-lipid chemical shift value and the field map,
Wherein each of the plurality of first echoes obtained in each TR and each of the plurality of second echoes is obtained in different TEs according to the resonance frequency difference of each of the water-lipid components. 9. The method of claim 8,
The processor
Wherein at least one blip pulse is formed in at least one oblique magnetic field so that each of the plurality of first echoes obtained in each TR or each of the second echoes has different spatial information. 9. The method of claim 8,
The processor
And performing blood flow-lipid modeling based on the difference between the first echo and the second echo for the same TE and the field map, thereby separating and reconstructing a background tissue image and a blood flow image around the blood vessel, Imaging device. 9. The method of claim 8,
The processor
Extracting a blood flow signal from the plurality of first echoes and the second echo using the phase difference value according to the chemical shift of the water-lipid component and the field map, and using the extracted blood flow signal to calculate the diastolic and systolic Reconstructing the k-space or image space for each TE for each of the images and reconstructing the image based on the difference between the k-space or image space of the diastole extending in the echo direction and the k-space or image space of the systole, Imaging device. 9. The method of claim 8,
The processor
Applying at least one RF pulse and a plurality of frequency-coded gradient magnetic fields in each of the two TRs to a target to obtain a plurality of first phase correction echoes and a plurality of second phase correction echoes, Correcting the phase of each of the first echo and the second echo based on a phase difference between the correction echo and the second phase correction echo,
Wherein the plurality of first phase correction echoes and the second phase correction echo are obtained in different TEs according to the resonance frequency of each of the water-
Wherein the frequency-coded gradient magnetic field of each TR has an opposite polarity to each other. 8. A computer-readable recording medium on which a program for implementing the method of any one of claims 1 to 7 is recorded.

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