KR102016422B1 - Magnet resonance imaging device and method for generating blood imaging thereof - Google Patents

Abstract

Disclosed is a method for restoring 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 includes the steps of obtaining MR signals including blood flow information as a flow sensitive pulse sequence is applied to a subject; Dividing the MR signals according to the cardiac activity state of the subject; Mapping MR signals corresponding to different cardiac activity states into different k-spaces and mapping them; And reconstructing the blood flow image using different k-spatial data.

Description

Magnetic Resonance Imaging Device and Blood Flow Image Restoration Method Using the Same {MAGNET RESONANCE IMAGING DEVICE AND METHOD FOR GENERATING BLOOD IMAGING THEREOF}

The present invention relates to a magnetic resonance imaging apparatus and a blood flow image restoration method using the same, and more particularly, to a method for restoring a blood flow image based on non-contrast magnetic resonance angiography (MRA), and The magnetic resonance imaging device.

Recently, images of a horizontal axis, a vertical axis, and an oblique direction of a human body are acquired by using a magnetic resonance imaging (MRI) device, and a case of examining and diagnosing a subject's condition through these images is increasing. Magnetic resonance imaging is a very important and useful imaging device because it enables noninvasive imaging of the human body and unlike the CT / PET, there is no risk of radiation exposure.

Magnetic resonance angiography (MRA) is known as a technique for obtaining blood flow images in the field of magnetic resonance imaging. MRA is commonly used to test for ischemic or infarct areas of the brain or heart. Conventional MRA is made by administering a contrast agent has been a problem of side effects and risks for the contrast agent. In order to solve this problem, researches on non-contrast MRAs using no contrast medium have been actively conducted.

Recently, the Fresh Blood Imaging (FBI) method, which uses an electrocardiogram to capture blood flow at a high flow rate as the heart beats, is widely known. However, the FBI technique has to image the volume of two cardiac activity states, namely systolic and diastolic of the heart, and has a difficulty in acquiring MR signals by capturing specific cardiac activity states. In addition, there is a problem that it is difficult to apply to patients with arrhythmias appearing irregularly systolic and diastolic.

Japanese Patent No. 4632535 (Invention name: MRI device)

The present invention is to solve the above-mentioned problems of the prior art, and some embodiments of the present invention to provide a method for reconstructing a blood flow image based on non-enhanced MRA that can scan the subject irrespective of the specific heart activity state of the subject. The purpose is. Furthermore, the aim is to restore blood flow images that are robust to cardiac activity and noise.

However, the technical problem to be achieved by the present embodiment is not limited to the technical problem as described above, and other technical problems may exist.

As a technical solution for achieving the above-described technical problem, a first aspect of the present invention comprises the steps of obtaining MR signals including blood flow information as a flow sensitive pulse sequence is applied to an object; Dividing the MR signals according to the cardiac activity state of the subject; Mapping MR signals corresponding to different cardiac activity states into different k-spaces and mapping them; And reconstructing a blood flow image using different k-spatial data.

In addition, a second aspect of the present invention includes a memory for storing a program for processing a magnetic resonance image and a processor for executing the program. The processor acquires MR signals including blood flow information as a flow sensitive pulse sequence is applied to the subject according to the execution of the program, classifies the MR signals according to the cardiac activity state of the subject, MR signals corresponding to different cardiac activity states are separated and mapped into different k-spaces, and blood flow images are reconstructed using different k-space data.

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

According to the above-described problem solving means of the present invention, the magnetic resonance imaging apparatus can scan the subject irrespective of the cardiac activity state of the subject by retrospectively synchronizing the MR signals obtained according to the flow sensitive pulse sequence with the multiple cardiac activity state. have. In addition, the MR signals of different cardiac activity states are retrospectively mapped to different k-spaces, and then reconstructed blood flow images through residual images therebetween, which are robust to artifacts and noise. In addition to acquiring blood flow images, it is possible to naturally remove signals from surrounding tissues other than blood flow.

FIG. 1 is a block diagram of a magnetic resonance imaging apparatus according to an exemplary embodiment.
2 is a block diagram of a magnetic resonance imaging apparatus according to another exemplary embodiment of the present invention.
3 is a flowchart illustrating a method of reconstructing a blood flow image based on a non-enhanced MRA by a magnetic resonance imaging apparatus according to an embodiment of the present invention.
4 illustrates an example in which a magnetic resonance imaging apparatus records a time stamp according to a cardiac activity state to MR signals according to an embodiment of the present invention.
5 illustrates an example of a time stamp according to an embodiment of the present invention.
6 is a diagram illustrating an example in which a magnetic resonance imaging apparatus maps MR signals into a plurality of k-spaces according to an embodiment of the present invention.
FIG. 7 is a diagram illustrating an example in which a magnetic resonance imaging apparatus directly reconstructs a blood flow image from k-spaces in which unacquired data exists, according to an exemplary embodiment.
8A to 8 are views showing blood flow images reconstructed by maximal intensity projection of each k-space difference image acquired according to the method of FIG. 7, and FIG. 8 k shows blood flow images shown by time. FIG. 2 is a diagram illustrating a blood flow image reconstructed by projecting the maximum intensity again in the time direction.
9 is an example in which a restored blood flow image according to an embodiment of the present invention is compared with a restored blood flow image according to a conventional method.
10 is another example in which a restored blood flow image according to an embodiment of the present invention is compared with a restored blood flow image according to a conventional method.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is "connected" to another part, this includes not only "directly connected" but also "electrically connected" with another element in between. . In addition, when a part is said to "include" a certain component, which means that it may further include other components, except to exclude other components unless otherwise stated.

In the present specification, "MRI (Magnetic Resonance Imaging) device" refers to a magnetic field and non-electron radiation (radio frequency) as an object to acquire an image based on a physical principle called Nuclear Magnetic Resonace (NMR). Means a device to be applied.

In addition, “image” or “image” means multi-dimensional data composed of discrete elements, and includes a plurality of pixels in a two-dimensional image and a plurality of voxels in a three-dimensional image. It means consisting of.

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

In addition, the "user" may be a doctor, a nurse, a medical imaging expert, or a device repair technician as a medical expert, but is not limited thereto.

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

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

FIG. 1 is a block diagram of a magnetic resonance imaging apparatus according to an exemplary embodiment.

The magnetic resonance imaging apparatus 1 may include an MRI scanner 10, a signal processor 20, an interface unit 30, a controller 40, and a monitoring unit 50.

The MRI scanner 10 forms a magnetic field and generates a resonance phenomenon for the atomic nucleus, and the magnetic resonance image is photographed while the object is located 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 irradiated toward the object.

The main magnet 12, the gradient coil 14 and the RF coil 16 are disposed in the MRI scanner 10 according to a preset direction. The object may be positioned on a table that can be inserted into the cylinder along the horizontal axis of the cylinder, and the object may 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 in a direction the direction of the magnetic dipole moment of the nuclei contained in the object.

The gradient coil 14 includes X coils, Y coils, and Z coils that generate gradient magnetic fields in the X, Y, and Z axis directions that are perpendicular to each other. The gradient coil 14 induces resonant frequencies differently for each part of the object to obtain location information of each part of the object.

The RF coil 16 may radiate an RF signal to the object and receive a magnetic resonance image signal emitted from the object. The RF coil 16 may output an RF signal having a frequency equal to the frequency of the precession toward the atomic nucleus that performs the precession, and then receive a magnetic resonance image signal emitted from the object.

For example, the RF coil 16 generates and applies an RF signal having a frequency corresponding to the atomic nucleus to the object in order to transition the nucleus from the low energy state to the high energy state. Thereafter, when the RF coil 16 stops transmitting the RF signal, the nuclear nucleus to which the electromagnetic wave is applied radiates an electromagnetic wave having a Lamor frequency while transitioning from a high energy state to a low energy state, and the RF coil 16 Receive the corresponding electromagnetic signal.

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

In addition, the RF coil 16 may be fixed to the MRI scanner 10 or may be in a removable form. The detachable 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 an object. Can be.

The MRI scanner 10 may provide various information to a user or an object through a display, and may include a display 18 disposed outside and a display (not shown) disposed inside.

The signal processor 20 may control the gradient magnetic field formed inside the MRI scanner 10 according to a predetermined MR pulse sequence (that is, a pulse train) and control transmission and reception of an RF signal and a magnetic resonance image signal.

The signal processor 20 may include a gradient magnetic field amplifier 22, a switching unit 24, an RF transmitter 26, and an RF receiver 28.

The gradient amplifier 22 drives the gradient coil 14 included in the MRI scanner 10, and generates a gradient signal that generates a gradient magnetic field under the control of the gradient magnetic field controller 44. To feed. By controlling the pulse signal supplied from the gradient 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 transmitter 26 supplies an RF pulse to the RF coil 16 to drive the RF coil 16. The RF receiver 28 receives a magnetic resonance image signal transmitted after the RF coil 16 receives it.

The switching unit 24 may adjust a transmission / reception direction of the RF signal and the magnetic resonance image signal. For example, the RF signal is irradiated to the object through the RF coil 16 during the transmission operation, and the magnetic resonance image signal from the object is received through the RF coil 16 during the reception operation. The switching unit 24 controls the switching operation by the control signal from the RF control unit 46.

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

The image processor 36 may process the MR image signal received from the RF receiver 28 to generate MR image data of the object.

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

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

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

The output unit 34 may output image data or reconstructed image data generated by the image processor 36 to the user. In addition, the output unit 34 may output information necessary for the 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 may input object information, parameter information, scan conditions, pulse sequences, information on image composition or difference calculation, etc. through the input unit 32. The input unit 32 may include a keyboard, a mouse, a trackball, a voice recognizer, a gesture recognizer, a touch screen, and the like, and may include various input devices within a range apparent to those skilled in the art.

The controller 40 is a sequence controller 42 for controlling a sequence of signals formed in the MRI scanner 10, and a scanner controller 48 for controlling devices mounted on the MRI scanner 10 and the MRI scanner 10. It may include.

The sequence controller 42 includes a gradient magnetic field controller 44 that controls the gradient magnetic field amplifier 22, and an RF controller 46 that controls the RF transmitter 26, the RF receiver 28, and the switching unit 24. do. 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 contains all the information necessary to control the gradient amplifier 22, the RF transmitter 26, the RF receiver 28 and the switch 24, for example a pulse applied to the gradient coil 14 It may include information on the strength of the pulse signal, an application time, an application timing, and the like.

The monitoring unit 50 monitors or controls the MRI scanner 10 or devices mounted on 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 includes a state of a static magnetic field, a state of a gradient magnetic field, a state of an RF signal, a state of an RF coil, a state of a table, a state of a device measuring body information of an object, a state of a power supply, a state of a heat exchanger, It can monitor and control the condition of the compressor.

The object monitoring unit 54 monitors the state of the object, and includes a camera for photographing the movement or position of the object, a respiration meter for measuring the respiration of the object, an ECG meter for measuring the electrocardiogram of the object, or a body temperature of the object. It may include a body temperature meter.

The table controller 56 controls the movement of the table where the object is located. The table controller 56 may control the movement of the table in synchronization with the sequence control signal output from the sequence controller 42. For example, in moving imaging of an object, the table control unit 56 may move the table according to sequence control, whereby the object has a larger FOV than the field of view of the MRI scanner. You can shoot.

The display control unit 58 controls the display positioned on the outside and the inside of the MRI scanner 10 on / off or a screen to be output to the display. In addition, 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 wirelessly or wired to each other, and in the case of wirelessly connecting to each other. The apparatus may further include an apparatus (not shown) 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 is a high-speed digital such as Low Voltage Differential Signaling (LVDS). Interface, asynchronous serial communication such as universal asynchronous receiver transmitter (UART), low delay network protocol such as error synchronization serial communication or controller area network (CAN), optical communication, and the like can be used. Communication methods can be used.

The magnetic resonance imaging apparatus 1 according to the exemplary embodiment of the present invention has a feature in the configuration of the image processor 36. In this case, as illustrated in FIG. 2, the interface processor 30 including the image processor 36 or the image processor 36 may be implemented as the magnetic resonance imaging apparatus 100 in the form of a separate computing device. A non-contrast magnetic resonance angiography (MRA) based blood flow image reconstruction operation is performed using the memory 110 and the processor 120 mounted in the device.

The memory 110 stores a program for restoring the blood flow image. A memory is a general term for a nonvolatile storage device that maintains stored information even when power is not supplied, and a volatile storage device that requires power to maintain stored information.

The processor 120 restores the blood flow image based on the MR signal provided from the signal processor 20 according to the execution of the program stored in the memory 110. In this case, the MR signal includes blood flow information of the subject. For example, the processor 120 may obtain an MR signal having blood flow information by providing a flow sensitive pulse sequence to the controller 40 (or the signal processor 20) of FIG. 1. In addition, the processor 120 monitors the cardiac activity state of the subject affecting blood flow to retrospectively classify MR signals according to the cardiac activity state, and maps the separated MR signals to different k-spaces. That is, processor 120 rearranges MR signals corresponding to the same or similar cardiac activity state into the same k-space.

Subsequently, the processor 120 may reconstruct a blood flow image using different k-spatial data, thereby reconstructing a robust image of heart rate and noise compared to a conventional non-contrast MRA.

Meanwhile, as described with reference to FIG. 1, the MRI scanner 10 connected to the signal processor 20 (or the controller 40) of FIG. 1 uses one electromagnetic field to fix another magnetic field using electromagnetic pulses. By adjusting, the spin system can be excited. The MRI scanner 10 may obtain an MR signal for a space-time region by forming a magnetic field based on the plurality of gradient coils 14. As such, the processor 120 of the magnetic resonance imaging apparatus 1 may generate a blood flow image using MR signals formed by the MRI scanner 10.

Hereinafter, a detailed method of reconstructing a blood flow image by using the acquired MR signals by the processor 120 of the magnetic resonance imaging apparatus 100 of FIG. 2 will be described. However, it will be readily understood by those skilled in the art that the embodiments described below may be performed by the image processor 36 (or the interface unit 30 including the image processor 36) of the magnetic resonance imaging apparatus 1 of FIG. 1. There will be.

3 is a flowchart illustrating a method of reconstructing a blood flow image based on a non-enhanced MRA by the magnetic resonance imaging apparatus 100 according to an embodiment of the present invention.

First, the magnetic resonance imaging apparatus 100 acquires an MR signal as a flow sensitive pulse sequence is applied to an object (S110). Here, the flow-sensitive pulse sequence may be various pulse sequences capable of acquiring an MR signal including blood flow information. For example, the flow-sensitive pulse sequence may be based on a fast spin echo (FSE) sequence. In addition, the flow sensitive pulse sequence may include various pulse sequences within a range apparent to those skilled in the art.

Meanwhile, the magnetic resonance imaging apparatus 100 may apply a flow sensitive pulse sequence to the subject and simultaneously monitor the heart activity of the subject. For example, the MRI apparatus 100 may acquire a projection echo (or a navigator echo) indicating a cardiac activity state by adding a navigator pulse train to the flow sensitive pulse sequence of the object. In this case, the navigator pulse train may be added inside or outside the flow sensitive pulse train.

Alternatively, the magnetic resonance imaging apparatus 100 may monitor the heart activity state of the subject using data received from an external heart rate monitoring apparatus. The heart rate monitoring device may be, for example, a pulse oximeter, an ECG device, or the like, and the data received therefrom may be, for example, pulse oximeter waveform data, electrocardiogram data, or the like.

Thereafter, the MR imaging apparatus 100 classifies MR signals according to the heart activity state of the object (S120). For example, the magnetic resonance imaging apparatus 100 may record a time stamp based on a cardiac activity state corresponding to the point in time at which the MR signal is obtained.

4 illustrates an example in which the magnetic resonance imaging apparatus 100 records a time stamp according to a cardiac activity state in MR signals according to an embodiment of the present invention. In the following, the flow sensitive pulse sequence is illustrated as an FSE having a variable flip angle (VFA), but various flow sensitive pulse sequences may be used as described above.

Referring to FIG. 4, the magnetic resonance imaging apparatus 100 acquires MR signals by applying the flow sensitive pulse sequence 402 to the subject irrespective of the subject's heart activity (ie, heart rate), while the heart activity of the subject is acquired. Monitor the status 401. The magnetic resonance imaging apparatus 100 may record a time stamp at the time point at which the MR signals are acquired (shown by the shade in each TR of FIG. 4) in order to classify the MR signals according to the heart activity state. In this case, the time stamp may be represented as relative time information in each cardiac activity cycle (eg, R-R interval of ECG data). For example, as shown in FIG. 4, the time stamp may be recorded as a delay time from the start of the cardiac activity cycle.

Thus, as shown in FIG. 5, time stamp 500 may include the delay time of each MR signal within an average cardiac activity cycle 501. Through this, the time stamp 500 may function as a reference for backward synchronization of the cardiac activity state and MR signals of the object. In the example of FIG. 5, the magnetic resonance imaging apparatus 100 obtains first to eighth MR signals corresponding to different heart activity states in the first to eighth TRs, and then, based on different delay times, The first to eighth MR signals may be distinguished. As such, the MRI apparatus 100 may retrospectively classify MR signals corresponding to the same or similar heart activity state through the time stamp 500.

Meanwhile, although FIGS. 4 and 5 show that the time stamp is recorded based on the TR, one echo train is formed in one TR. Therefore, when two or more echo trains are formed in one TR and an MR signal is acquired at different time points, two or more time stamps may be recorded in one TR.

Referring to FIG. 3 again, the MRI apparatus 100 may display MR signals corresponding to different cardiac activity states (ie, MR signals recorded with different time stamps) in different k-spaces (hereinafter, ' Bin ('bin') (S130). In this way, the MR imaging apparatus 100 may rearrange MR signals corresponding to the same cardiac activity state to the same bin.

In this case, each bin may be a three-dimensional k space. Accordingly, MR signals may be under-sampled through a Cartesian technique in a ky-kz space such as a radial trajectory or a spiral trajectory in three-dimensional space. As a result, the MRI apparatus 100 may be sampled at a relatively high density in the low frequency region (ie, the central region) of each k-space. However, the present invention is not limited thereto, and MR signals may be non-Cartesian undersampled in three-dimensional space.

FIG. 6 is a diagram illustrating an example in which the magnetic resonance imaging apparatus 100 maps MR signals to a plurality of bins, according to an exemplary embodiment. As illustrated in FIG. 6, the MRI apparatus 100 may set N k-spaces and then undersample MR signals recorded with the same time stamp into the same k-space. Also, as shown in FIG. 6, MR signals are sampled at a relatively high rate in the low frequency region of the k-space. Since the low frequency region of the k-space determines the overall signal strength of the reconstructed image, the above scheme can improve the resolution of the reconstructed image.

Thereafter, referring back to FIG. 3, the MRI apparatus 100 reconstructs a blood flow image using a plurality of k-spaces (that is, a plurality of bins) (S140). The MRI apparatus 100 may reconstruct a blood flow image directly from each k-spatial data (or image) in which unacquired data exists. For example, the magnetic resonance imaging apparatus 100 generates a reference image based on k-space data averaged in a time direction (ie, an empty direction), and then k-space data and reference image in which unacquired data exists. The residual image of the liver is imaged. For example, the MRI apparatus 100 may reconstruct an image by applying a limited optimization image reconstruction method to a difference image. As such, the magnetic resonance imaging apparatus 100 may image using a difference image based on data of the same or similar intensity in each of the plurality of k-spaces so that signals generated from non-flowing tissues other than the flowing blood stream are removed. It is possible to restore clearer blood flow images.

Alternatively, the magnetic resonance imaging apparatus 100 may first interpolate unacquired data of each k-space, and then reconstruct an image using k-space data from which the unacquired data is interpolated. For example, the magnetic resonance imaging apparatus 100 may restore blood flow images using convolution interpolation, compressed sensing, or the like of multiple coils.

Hereinafter, a method of directly reconstructing a blood flow image from a plurality of k-spatial data according to an embodiment of the present invention will be described in detail.

First, an MR signal having blood flow information may be expressed by Equation 1 below.

는 l 번째 코일에서 획득된 MR 신호를 나타내며, r 은 이미지 공간에서의 좌표를 나타내며,

은 ㅣ번째 코일 민감도(coil sensitivity)를 나타내며,

는 혈류 영상을 포함하고 있는 MR 영상을 나타내며,

는 잡음신호(noise)를 나타낸다. In the above formula, l represents the number of coils, and (k, b) represents the coordinates and the index according to time (or bin) in k-space. Also,

Denotes the MR signal obtained from the l-th coil, r denotes the coordinate in image space,

Represents the | th coil sensitivity,

Represents an MR image including blood flow images,

Denotes a noise signal.

In this case, the MR image including the blood flow image to be restored may be represented by a Casorati matrix as shown in Equation 2 below. Applying this to Equation 1, Equation 1 may be represented by Equation 3 below.

는 코일 민감도와 푸리에 변환을 포함하는 민감도 인코딩 연산자(sensitivity encoding operator)이다. 이때, 구현예에 따라 민감도 인코딩 연산자에는 언더샘플링 패턴이 추가로 가해질 수 있다. In the above formula,

Is a sensitivity encoding operator that includes coil sensitivity and Fourier transform. In this case, an undersampling pattern may be additionally applied to the sensitivity encoding operator.

On the other hand, the MR image (X) having blood flow information in the above equation can be represented by the following equation (4).

는 심장 활동 상태 또는 시간의 흐름에 따라 변화하지 않는 레퍼런스 영상으로, 특정한 심장 활동 상태 또는 동맥, 정맥, 주변 조직 영상을 나타내며,

는 차 영상(residual image)을 나타낸다. 즉,

는 심장 활동 상태 및 시간의 흐름에 따라 변화하는 영상으로, 예컨대 동맥 혈류 영상일 수 있다. In the above formula,

Is a reference image that does not change over time or over time, and represents a specific state of cardiac activity or arteries, veins, and surrounding tissue.

Represents a residual image. In other words,

Is an image that changes over time and the state of cardiac activity, for example, may be an arterial blood flow image.

Therefore, based on the result of substituting Equation 4 into Equation 3, the magnetic resonance imaging apparatus 100 may model a blood flow image that changes according to the heart activity state as in Equation 5 below.

FIG. 7 illustrates an example in which the magnetic resonance imaging apparatus 100 directly restores a blood flow image from k-spaces in which unacquired data exists based on the above description.

)으로부터 레퍼런스 영상(

)을 감산하여 차 영상(residual image)을 모델링한다. 차 영상은 STEP 2로 입력된다. STEP 1: The magnetic resonance imaging apparatus 100 displays an image in a time direction (ie, an empty direction)

From the reference image (

) To model the residual image. The difference image is input into STEP 2.

)을 획득한다. STEP 2: The magnetic resonance imaging apparatus 100 optimizes the difference image based on the limited optimization image reconstruction method represented by Equation 6 below.

).

는 희박화 연산(sparsifying operator)을 나타내며,

는 푸리에 변환(Fourier transform)에 대한 핸캘 연산(Hankel operator) 결과를 나타낸다. In the above formula,

Represents a sparifying operator,

Denotes the result of a Hankel operator for a Fourier transform.

The magnetic resonance imaging apparatus 100 has a property of similarity between the sparsity prior of the difference image represented by Equation 7 below and the k-spatial data represented by Equation 8 below. The solution of Equation 6 can be obtained based on the low rank prior.

는 희박화 연산의 수반 연산자(adjoint operator)를 나타내며,

는 수축 연산자를 나타내며,

는 n 번째 반복 연산 결과로서,

의 희박화 연산 결과를 나타낸다. Where n is the number of iterations

Represents the adjoint operator of the thinning operation,

Represents the contraction operator,

Is the result of the n th iteration operation,

Shows the result of the thinning operation of.

는 푸리에 변환에 대한 헨캘 연산의 수반 연산을 나타내며,

는 특이값 분해에 따른 특이값 행렬(

)을 랭크(rank)(

)로 단절(truncation)한 것을 나타내며,

은 n 번째 반복 연산 결과로서

의 푸리에 변환에 대한 헨캘 연산의 결과를 나타낸다. In the above formula,

Denotes the attendant operation of the Henkel operation on the Fourier transform,

Is the singular value matrix according to the singular value decomposition (

Rank)

) And truncation

Is the result of the n th iteration

Represents the result of the Henkel operation on the Fourier transform of.

The MRI apparatus 100 may repeat STEP 2 to optimize the difference image. In this case, the MRI apparatus 100 may adjust the number of repetitive operations of Equations 7 and 8 to optimize the calculation.

STEP 3: The MRI apparatus 100 restores and outputs a blood flow image based on the optimized difference image.

8A to 8 are views showing blood flow images reconstructed by maximal intensity projection of difference images of k-spaces (that is, bins) obtained according to the method of FIG. 7, and FIG. FIG. 2 is a diagram illustrating a blood flow image reconstructed by performing maximum intensity projection on the blood flow image represented by FIG.

Referring to FIG. 8, each k-spatial data a to j includes blood flow information (illustrated by arrows) that is not shown in other k-spatial data according to the heart activity state of the subject. Therefore, the blood flow image k reconstructed by projecting the maximum intensity in the temporal direction (for example, the empty direction) includes all the blood flow information included in the k-spatial data acquired at different time points, thereby representing more accurate blood flow information. have. In this way, the MRI apparatus 100 may minimize artifacts generated as the cardiac activity state of the object is asynchronous. In addition, no effort is required to obtain MR signals corresponding to specific cardiac activity states (eg, systolic, diastolic, etc.).

In addition, since the magnetic resonance imaging apparatus 100 classifies blood flow information according to various cardiac activity states into separate k-spatial data, the magnetic resonance imaging apparatus 100 may selectively restore a blood flow image of a desired heart activity time point.

9 is an example in which a restored blood flow image according to an embodiment of the present invention is compared with a restored blood flow image according to a conventional method. At this time, the cardiac activity of the subject is assumed to be regular.

Figure 9 (a) is an example of restoring the image by using the velocity difference between the systolic and diastolic blood flow of the heart based on the FBI (free blood imaging) technique, a non-contrast MRA technique of Toshiba (TOSHIBA), (b ) Is an example of fat supression (FS) in the above method. (c) is an example of reconstruction using MR signals retrospectively divided according to multiple cardiac activity states according to an embodiment of the present invention.

Comparing (c) of Figure 9 with (a) and (b), the blood flow image reconstruction method according to an embodiment of the present invention takes a total time similar to the prior art image with almost no artifacts and noise It can be confirmed that the restoration. In addition, it can be seen that signals from surrounding tissues except blood flow are removed.

10 is another example in which a restored blood flow image according to an embodiment of the present invention is compared with a restored blood flow image according to a conventional method. At this time, it is assumed that the heart activity of the subject is irregular.

(A) and (b) of FIG. 10 are examples of restoring an image based on the FBI technique of Toshiba as in FIG. 9, and (c) is an example of restoring an image according to an embodiment of the present invention. As the heart of the subject acts irregularly, it can be seen that images (a) and (b) according to the FBI technique for imaging using a specific heart activity state do not properly extract blood flow information. In addition, in the case of (a) and (b), it is difficult to specify the systolic and diastolic stages of the heart as the heart of the subject acts irregularly, thus confirming that the scan time is increased.

However, the blood flow image reconstruction method according to an embodiment of the present invention synchronizes the heart activity state and the MR signals retrospectively, and thus takes the same scan time regardless of the heart activity state. In addition, even if the cardiac activity is irregular, the MR signals of the same or similar cardiac activity state are separated and sampled into different spaces, and then restored, thereby recognizing (a) and (b) as shown in (c). It can be seen that clear images that are clearly distinguished are restored. In addition, it can be seen that signals from surrounding tissues except blood flow are removed. That is, the present invention may have an effect of naturally removing a signal of surrounding tissues other than blood vessels by imaging the difference image of MR signals having the same intensity through a time stamp.

As such, embodiments of the present invention have the advantage of scanning the subject irrespective of cardiac activity by backward synchronizing the MR signals obtained from the subject with multiple cardiac activity states of the subject. In addition, embodiments of the present invention can obtain robust blood flow images against artifacts and noise by sampling MR signals into k-spaces separated according to cardiac activity and then directly reconstructing the blood flow images.

The above-described method for restoring blood flow images of a magnetic resonance imaging apparatus and a magnetic resonance imaging apparatus according to an exemplary 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. May 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. In addition, the computer readable medium may include a computer storage medium. 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.

Although the systems and methods of the present invention have been described in connection with specific embodiments, some or all of their components or operations may be implemented using a computer system having a general hardware architecture.

The foregoing description of the present invention is intended for illustration, and it will be understood by those skilled in the art that the present invention may be easily modified in other specific forms without changing the technical spirit or essential features of the present invention. will be. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form.

The scope of the present invention is shown by the following claims rather than the above description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present invention. do.

10: MRI scanner 20: signal processor
40: control unit 50: monitoring unit
60: interface unit
110: memory
120: processor

Claims (15)

In the magnetic resonance imaging apparatus for restoring the blood flow image based on non-contrast magnetic resonance angiography (MRA),
Acquiring MR signals including blood flow information as a flow sensitive pulse sequence is applied to the subject and monitoring the cardiac activity state of the subject;
Retrospectively classifying the MR signals according to the cardiac activity state of the subject;
Mapping MR signals corresponding to different cardiac activity states into different k-spaces for each cardiac activity state; And
Reconstructing the blood flow image using the different k-spatial data,
Retrospectively dividing the MR signals,
Recording a time stamp based on the state of cardiac activity at the time each MR signal is acquired,
The mapping of the different k-spaces may be performed by:
And mapping MR signals recorded with the same or similar time stamps to the same k-space based on the time stamps. The method of claim 1,
The flow sensitive pulse sequence is a fast spin echo (FSE) having a variable flip angle (VFA). The method of claim 1,
Wherein the MR signals are undersampled into three-dimensional k-space. The method of claim 1,
The time stamp is
Blood flow image restoration method that is represented by a delay time (deleay time) in the cardiac activity cycle of the subject. The method of claim 1,
The cardiac activity state
And a projection echo obtained by adding a navigator pulse train to the flow sensitive pulse sequence or monitored by data received from an external heart rate monitoring device. The method of claim 1,
Restoring the blood flow image is
Generating a reference image based on k-space data averaged in a time direction with respect to a plurality of k-spaces;
Modeling a residual image by subtracting the reference image from k-space data of each k-space; And
And obtaining and imaging the optimized difference image based on the limited optimized image restoration method. The method of claim 6,
Acquiring the optimized difference image
Obtaining an optimized difference image according to the limited optimization image reconstruction method based on a sparsity priority of the difference image and a low rank priority between the k-spatial data Way. The method of claim 6,
The imaging of the optimized difference image comprises applying a maximum intensity projection (MIP) technique in a time direction to the optimized difference image. In the magnetic resonance imaging apparatus,
A memory storing a program for processing a magnetic resonance image; And
A processor for executing the program,
The processor acquires MR signals including blood flow information as a flow sensitive pulse sequence is applied to the subject, and monitors the cardiac activity state of the subject, as the program executes the program.
The MR signals are retrospectively classified according to the cardiac activity state of the subject, and MR signals corresponding to different cardiac activity states are separated and mapped into different k-spaces for each cardiac activity state, and the different k signals are mapped. Restoring blood flow images using spatial data,
The retrospective classification of the MR signals is
Recording a time stamp based on the state of cardiac activity at the time each MR signal is acquired,
Mapping the different k-spaces separately
And an MR signal having the same or similar time stamps mapped to the same k-space based on the time stamp. The method of claim 9,
The flow sensitive pulse sequence is a fast spin echo (FSE) having a variable flip angle (VFA) magnetic resonance imaging apparatus. The method of claim 9,
The MR signals are undersampled into three-dimensional k-space. The method of claim 9,
The cardiac activity state
Magnetic resonance imaging device, which is monitored by projection echo obtained by adding a navigator pulse train to the flow sensitive pulse sequence or data received from an external heart rate monitoring device. The method of claim 9,
The processor is
A reference image is generated based on k-space data averaged in a time direction with respect to a plurality of k-spaces, and the residual image is modeled by subtracting the reference image from k-space data of each k-space. ,
A magnetic resonance imaging apparatus for acquiring and imaging an optimized difference image based on a limited optimization image reconstruction method. The method of claim 13,
The processor is
Magnetic resonance image obtaining an optimized difference image according to the limited optimization image reconstruction method based on sparsity priority of the difference image and low rank priority between the k-spatial data Device. A computer-readable recording medium having recorded thereon a program for implementing the method of any one of claims 1 to 8.

Images