KR101438758B1 - Apparatus and method for magnetic resonance image processing - Google Patents

Abstract

An apparatus for processing a magnetic resonance image includes a data initializing unit which initializes magnetic resonance image signal data by estimating data which is not obtained by performing interpolation according to each channel with regard to a magnetic resonance image signal which is sampled through under sampling, a multi-scale data generating unit which generates multi-scale data by performing the multiple band decomposition of the initialized data, a calibration performing unit which performs a broadband calibration process based on the multi-scale data and the initialized data according to each channel, an image reconstituting unit which recovers the data which is not obtained from the magnetic resonance image signal data based on the calibration data generated through the calibration performing unit, and an image outputting unit which outputs the image generated through the image reconstituting unit.

Description

TECHNICAL FIELD [0001] The present invention relates to a magnetic resonance imaging apparatus,

The present invention relates to an apparatus and a method for processing a magnetic resonance image (MRI).

BACKGROUND ART In general, a device for processing magnetic resonance imaging (MRI) is a device for acquiring a tomographic image of a specific region of a patient by using a resonance phenomenon caused by supply of electromagnetic energy. The X- It is widely used because it has no exposure and can acquire a tomographic image relatively easily.

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

In the conventional parallel magnetic resonance imaging method, data is acquired at a central portion of a k-space (k-space), that is, at a low frequency region, at a Nyquist rate, , That is, the data is acquired at a lower rate in the high frequency region. Then, a step of reconstructing data that has not been acquired sequentially in the low-frequency region and the high-frequency region is performed. That is, interpolation is performed on the data in the low-frequency region using the calibration data obtained in the calibration process for the data in the low-frequency region. Then, a step of recovering unacquired data in the high frequency region is performed using the interpolation method performed on the data in the low frequency region.

On the other hand, unlike the processing method in the frequency space, the sensitivity of the channel is used in the image space. In the conventional parallel magnetic resonance imaging method, sample data of a low frequency region is obtained before acquiring data to calculate the sensitivity of each channel. Then, undersampled data is acquired at regular intervals in this data acquisition time. We utilize the sensitivity of multi-channel to recover the image by processing the remaining aliasing artifacts generated by undersampling.

However, according to the conventional technique, when the data of a video signal is overwhelmed by the noise in the frequency-domain image restoration method, noise may be amplified in a process of restoring a high-frequency signal, resulting in a problem of appearing in an image. In addition, since the calibration process and the restoration process are separated in the image space image restoration method, not only the data acquisition time is long, but also the sensitivity of the channel is estimated using only the low frequency signal, so that residual artifacts may appear in the image .

In this regard, US Patent No. 6841998 (US Pat. No. 6,841,998) discloses a partial parallel data acquisition method, which employs a partial parallel data acquisition method, And the calibration is performed using the calibration data.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems of the conventional art, and it is an object of the present invention to provide a magnetic resonance image processing apparatus and method capable of performing image reconstruction over a low frequency band and a high frequency band.

According to a first aspect of the present invention, there is provided a magnetic resonance imaging apparatus including an interpolation method for each channel of a magnetic resonance image signal sampled through undersampling, A multi-scale data generation unit for generating multi-scale data by performing multi-band decomposition on the initialized data, a multi-scale data generation unit for generating multi-scale data based on the data initialized for each channel, An image reconstructing unit for reconstructing non-acquired data of magnetic resonance image signal data based on the calibration data generated by the calibration performing unit, and an image reconstructing unit for reconstructing an image generated through the image reconstructing unit, Ha Includes an image output unit.

According to a second aspect of the present invention, there is provided a method for processing a magnetic resonance image, comprising: receiving a sampled MRI image signal through undersampling; interpolating the MRI image signal for each channel; Estimating the multirespecific data by performing multiband decomposition on the initialized data to generate multiscale data, and performing broadband calibration based on the multiscale data and data initialized for each channel Reconstructing the non-acquired data of the magnetic resonance image signal data based on the calibration data generated through the wideband calibration, and restoring the non-acquired data to output the reconstructed image.

According to the present invention, it is possible to perform arbitrary sampling without restriction of a sampling form in the process of acquiring data of a parallel image, and effectively suppress noise appearing in an image by using multi-scale band data .

In addition, according to the present invention, it is possible to remove residual artifacts by increasing the accuracy through a broadband calibration process performed over a low frequency band and a high frequency band.

In addition, by performing the calibration process and the image restoration process alternately, it is possible to restore the image stably and stably even at a high acceleration factor.

1 is a diagram illustrating a magnetic resonance imaging apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram illustrating a signal processing unit of a magnetic resonance imaging apparatus according to an embodiment of the present invention. Referring to FIG.
3 is a diagram for explaining a signal processing method in a frequency space according to an embodiment of the present invention.
4 is a diagram for explaining a signal processing method in an image space according to an 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.

1 is a diagram illustrating a magnetic resonance imaging apparatus according to an embodiment of the present invention.

The magnetic resonance imaging apparatus 10 includes a magnetic resonance imaging apparatus 100, a signal transmission and reception unit 200, a signal processing unit 300, an image output unit 400, a control unit 500, and a user interface 600.

The magnetic resonance apparatus 100 includes a shield of a cylindrical structure surrounding a subject to be photographed, a main magnet provided inside the shield, a gradient coil, an RF coil, and the like. The main magnet, the gradient coil, the RF coil, etc., generate a magnetic field for inducing magnetic resonance signals from the nuclei in the human body. The gradient coil has an inclined magnetic field which varies in a plurality of directions, for example, a constant gradient for each of the x direction, the y direction, and the z direction, in proportion to the distance from the reference position in the sperm field generated by the main magnet . Here, the reference position may be the origin of the three-dimensional coordinate system when the space in which the static magnetic field generated by the main magnet exists is represented by a three-dimensional coordinate system. By the gradient magnetic field generated by the gradient coil, each of the magnetic resonance signals received through the RF coil has position information in the three-dimensional space. On the other hand, the gradient coil may be composed of an X gradient coil that generates a gradient magnetic field that varies in the x direction, a Y gradient coil that generates a gradient magnetic field that varies in the y direction, and a Z gradient coil that generates a gradient magnetic field that varies in the z direction.

The RF coil outputs an electromagnetic wave signal having a radio frequency corresponding to the kind of the atomic nucleus in order to transition the atomic nucleus from a low energy state to a high energy state. Also, the RF coil receives an electromagnetic wave signal radiated from the nuclei inside the object, and the electromagnetic wave signal thus received is called a free induction decay (FID) signal or an echo signal. The length of the section from the application time point of the electromagnetic wave signal to the object, that is, the generation time point of the electromagnetic wave signal to the reception time point of the electromagnetic wave signal from the object is called an echo time (TE) The length of the repeated section is called the repetition time (TR).

The signal transmitting and receiving unit 200 generates an AC signal whose frequency varies at a constant slope with respect to the x direction, the y direction, and the z direction according to the control signal input from the controller 500, and outputs the generated AC signal to the gradient coil. Further, the control unit 500 generates an AC signal having a pulse train according to the control signal, and outputs the AC signal to the RF coil. Also, the signal transmitting and receiving unit 200 receives the magnetic resonance signal received through the RF coil.

The received magnetic resonance signal is transmitted to the signal processing unit 300, and the signal processing unit 300 generates a magnetic resonance image using the signal. The specific operation and configuration of the signal processing unit 300 will be described later.

The image output unit 400 outputs a magnetic resonance image generated through the signal processing unit 300 through a display or the like.

The control unit 500 controls operations of the MRI apparatus 100, the signal transmission / reception unit 200, the signal processing unit 300, and the video output unit 400 according to a command input from the user through the user interface 600 do. For example, the signal transmitting and receiving unit 200 controls the RF coil to output an AC signal to the RF coil, or the magnetic resonance signal received through the RF coil passes through the signal transmitting and receiving unit 200, .

The user interface 600 receives a command from a user and transmits the command to the control unit 500. The user interface 600 may be implemented by a graphic user interface (GUI) flow chart and an input device such as a keyboard, a mouse, and the like, but is not limited thereto.

FIG. 2 is a block diagram of a signal processing unit of a magnetic resonance imaging apparatus according to an embodiment of the present invention. FIG. 3 is a view for explaining a signal processing method in a frequency space according to an embodiment of the present invention, 4 is a diagram for explaining a signal processing method in an image space according to an embodiment of the present invention.

The signal processing unit 300 includes a data initialization unit 310, a multiscale data generation unit 320, a calibration execution unit 330, an image reconstruction unit 340, and an image output unit 350.

2 refers to a hardware component such as software or an FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuit), and performs predetermined roles .

However, 'components' are not meant to be limited to software or hardware, and each component may be configured to reside on an addressable storage medium and configured to play one or more processors.

Thus, by way of example, an element may comprise components such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, Routines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables.

The components and functions provided within those components may be combined into a smaller number of components or further separated into additional components.

The data initialization unit 310 estimates unacquired data by performing interpolation on the MRI image signal received through the signal transmission / reception unit 220, and initializes data of each channel. The magnetic resonance image signal is acquired according to various sampling schemes. That is, data can be acquired at regular intervals, data can be acquired in a random manner, or data can be acquired according to any sampling trajectory.

For example, in a compressive sensing scheme, if the original signal has sparsity, reconstruct the original signal through undersampling that samples at a frequency lower than the Nyquist sampling frequency. In order to reconstruct the original signal by the compression sensing technique, it is necessary to convert the original signal into the region where the sparseness of the original signal is maximized. In the conversion region, a method of repeatedly estimating the original signal so as to maximize the sparseness of the original signal Reconstruct the original signal.

In the compression sensing method, unacquired data in the K space of the individual coils can be estimated by solving the following equation.

[Equation 1]

W: wavelet coefficient, F: Fourier transform,?: Sparsifying transform, Ds: sampling operator, y: measured data

Meanwhile, the data initialization unit 310 may generate global K-space data in a frequency space and generate an individual channel image in an image space.

Next, the multiscale data generation unit 320 generates multiscale band-specific data using the images of each channel that has been initialized. In the present invention, in order to perform calibration for not only low frequency but also high frequency range data, K-space data is decomposed to generate multiscale data for each frequency band.

Referring to FIG. 3, K-space data including a plurality of sub-bands can be generated through the multi-band decomposition on the global K-space data generated by the data initialization unit 310. For example, individual subbands at each scale in the wavelet domain are multiplied by the binary mask. At this time, the binary mask may be set to 1 for the subband of interest and to 0 for the remaining subbands.

Similarly, referring to FIG. 4, it is possible to generate image data including a plurality of subbands, through multi-band decomposition, for an individual channel image.

Next, the calibration performing unit 330 performs a wideband calibration including a high frequency band as well as a low frequency band. The spatial correlation or the channel sensitivity is calculated using the multiscale band data and the data initialized for each channel through the data initialization unit 310 through the wideband calibration process.

That is, in the frequency space, as shown in FIG. 3, spatial correlation is calculated between data for each band. Also, in the image space, channel sensitivity of each band is calculated as shown in FIG.

In this way, broadband calibration is performed using initialized data from the low-frequency band to the high-frequency band using the multiscale band-specific data and the data initialized for each channel.

Next, the image reconstructing unit 340 reconstructs the unacquired data using the spatial correlation or the channel sensitivity acquired through the calibration performing unit 330. [ For example, in the frequency space, as shown in FIG. 3, the spatial correlation is used to recover unacquired data in the frequency domain. Also, in the image space, as shown in FIG. 4, the image is restored using the channel sensitivity. At this time, the restored image is multiplied by the channel sensitivity of the multi-scale band, and the acquired data is refilled for each channel.

In this manner, the image is reconstructed through the process of restoring the unacquired data using the spatial correlation or the channel sensitivity acquired in the calibration process.

Meanwhile, the image reconstructing unit 340 repeats the above-described process until the difference between the broadband calibration information and the reconstructed image information converges within a threshold value. For example, if the difference between the information of the broadband calibration information and the reconstructed image exceeds the threshold value, the calibration performing unit 330 is made to perform the wideband calibration again, and based on the spatial correlation or channel sensitivity generated based thereon And restores the unacquired data.

The image output unit 350 outputs the image generated by the image reconstruction unit 340 to the outside. That is, the difference between the broadband calibration information and the reconstructed image information converges within a threshold value, and the image reconstructed image is output.

One embodiment of the present invention may also be embodied in the form of a recording medium including instructions executable by a computer, such as program modules, being executed by a computer. 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 both computer storage media and communication 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. Communication media typically includes any information delivery media, including computer readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave, or other transport mechanism.

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.

100: magnetic resonance instrument
200: Signal transmission /
300: Signal processor
400: Video output unit
500:
600: User Interface
310: Data initialization unit
320: Multiscale data generation unit
330: Calibration execution unit
340: Image reconstruction unit
350: image output section

Claims (11)

A magnetic resonance imaging apparatus comprising:
A data initialization unit for initializing magnetic resonance image signal data by estimating unacquired data by performing an interpolation method for each channel on a magnetic resonance image signal sampled through undersampling,
A multi-scale band-specific data generation unit for performing multi-band decomposition on the initialized data to generate multi-scale band-specific data,
A calibration performing unit for performing a wideband calibration process of generating calibration data based on multi-scale band-specific data and data initialized for each channel,
An image reconstructing unit for reconstructing non-acquired data of the magnetic resonance image signal data based on the calibration data generated through the calibration performing unit;
And an image output unit outputting an image generated through the image reconstruction unit,
Wherein the wideband calibration process estimates a correlation between data for each frequency band. The method according to claim 1,
Wherein the magnetic resonance image signal sampled through the undersampling is one of a signal sampled at regular intervals, a signal sampled at random intervals, or a signal sampled according to an arbitrary sampling trajectory. The method according to claim 1,
The data initialization unit generates global K-space data in a frequency space,
The multi-scale band-specific data generation unit generates K-space data including a plurality of subbands through multi-band decomposition,
The calibration performing unit calculates the spatial correlation between the bands using the multiscale band data and the data initialized for each channel,
And the image reconstructing unit reconstructs the unacquired data using the spatial correlation. The method according to claim 1,
The data initialization unit generates an individual channel image in the image space,
The multi-scale band-specific data generation unit generates image data including a plurality of sub-bands through multi-band decomposition,
The calibration unit may calculate the channel sensitivity using the multi-scale band data and the data initialized for each channel,
And the image reconstruction unit restores the unacquired data using the channel sensitivity. The method according to claim 1,
The image reconstruction unit
Wherein the calibrating unit performs the wideband calibration process again when the difference between the calibration data and information of the image reconstructed through the image reconstructing unit exceeds a threshold value, A desired magnetic resonance image processing apparatus. The method according to claim 1,
The image reconstruction unit
The calibration execution unit may again perform the wideband calibration procedure until the difference between the calibration data and the image information reconstructed through the image reconstruction unit converges to a threshold value, The magnetic resonance image processing apparatus repeats the process of rewriting an image. A magnetic resonance imaging method using a magnetic resonance imaging apparatus,
Receiving the sampled magnetic resonance imaging signal through undersampling,
Initializing magnetic resonance image signal data by estimating unacquired data by interpolation on a channel-by-channel basis for the magnetic resonance image signal,
Performing multi-band decomposition on the initialized data to generate multi-scale band-specific data,
Performing a wideband calibration process of generating calibration data based on the multi-scale band-specific data and the data initialized for each channel,
Reconstructing non-acquired data of magnetic resonance image signal data based on the calibration data generated through the broadband calibration process; and
And reconstructing the non-acquired data to output a reconstructed image. 8. The method of claim 7,
Wherein the magnetic resonance image signals sampled through the undersampling are any one of a signal sampled at regular intervals, a signal sampled at random intervals, or a signal sampled according to an arbitrary sampling trajectory. 8. The method of claim 7,
Wherein the initializing the data comprises generating global K-space data in a frequency space,
Wherein the generating of the multi-scale band-specific data generates K-space data including a plurality of subbands through multi-band decomposition,
The step of performing the wideband calibration process may include calculating spatial correlation using multi-scale band-specific data and data initialized for each channel,
And reconstructing the non-acquired data comprises reconstructing the non-acquired data using the spatial correlation. 8. The method of claim 7,
Wherein the initializing the data comprises generating an individual channel image in an image space,
Wherein the generating of the multi-scale band-specific data generates image data including a plurality of subbands through multi-band decomposition,
The step of performing the wideband calibration step may include calculating channel sensitivity using multi-scale band-specific data and data initialized for each channel,
Wherein the step of reconstructing the non-acquired data comprises reconstructing the non-acquired data using the channel sensitivity. 8. The method of claim 7,
Performing the wideband calibration process again when the difference between the calibration data and the information of the reconstructed image exceeds a threshold value and performing a process of rewriting the image according to the calibration data generated according to the re- Further comprising a magnetic resonance imaging method.

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