KR102038627B1 - Magnetic resonance imaging system and magnetic resonance imaging method - Google Patents

Abstract

The magnetic resonance imaging method applies RF pulses and a selection gradient including a plurality of frequency components to the subject, performs three-dimensional encoding on each of the sub-volumes, and generates magnetic resonance signals from the plurality of sub-volumes. Acquire and reconstruct the acquired magnetic resonance signals into image data corresponding to each of the plurality of sub-volumes.

Description

Magnetic resonance imaging system and magnetic resonance imaging method

A magnetic resonance imaging system and a magnetic resonance imaging method are disclosed.

The magnetic resonance imaging system may acquire images of biological tissues of a human body using a magnetic field generated by magnetic force. In addition, the magnetic resonance imaging system applies a high frequency signal to the biological tissue to induce resonance from the biological tissue, and applies gradient signals to the biological tissue to obtain spatial information about the biological tissue.

Japanese Patent Laid-Open: JP 2001-198100 A (published: July 24, 2001)
Japanese Patent Application Publication: JP 2006-175223 A (Published: 2006.07.06)

Disclosed are a magnetic resonance imaging system and a magnetic resonance imaging method for reconstructing high resolution image data while shortening an imaging time. Also provided is a computer readable recording medium having recorded thereon a program for executing the method on a computer. The technical problem to be solved is not limited to the above technical problems, and other technical problems may exist.

Magnetic Resonance Imaging (MRI) method for solving the technical problem is grouping so that adjacent sub-volumes of the plurality of sub-volumes constituting the volume of the subject belong to different groups. Applying radio frequency (RF) pulses including a plurality of frequency components and a selection gradient to the subject such that a plurality of sub-volumes included in each of the at least two or more groups are simultaneously excited. step; Performing three-dimensional encoding on each of the excited sub-volumes, and obtaining magnetic resonance signals from the plurality of sub-volumes; And reconstructing the obtained magnetic resonance signals into image data corresponding to each of the plurality of sub-volumes.

Magnetic resonance imaging method for solving the other technical problem is to apply a predetermined pulse sequence to the subject, grouping the adjacent sub-volumes of the plurality of sub-volumes constituting the volume of the subject belong to different groups Restoring image data corresponding to each of the plurality of sub-volumes included in any one of the at least two groups; Determining whether restoring the image data has been performed for all groups constituting the subject; And restoring the image data for all groups constituting the subject, combining image data corresponding to each of the plurality of sub-volumes included in each of the groups constituting the subject ( fusion) to generate a 3D volume image.

In order to solve the another technical problem, a computer-readable recording medium having a program for executing the above-described magnetic resonance imaging methods on a computer is provided.

The magnetic resonance imaging system for solving the another technical problem is included in each of at least two groups grouped so that adjacent sub-volumes of the plurality of sub-volumes constituting the volume of the subject belong to different groups RF pulses including a plurality of frequency components and a selection gradient are applied to the subject so as to simultaneously excite the plurality of sub-volumes, perform three-dimensional encoding on each of the excited sub-volumes, and A magnetic resonance imaging apparatus for acquiring magnetic resonance signals from the sub-volumes of the apparatus; And a data processing device for restoring the obtained magnetic resonance signals to image data corresponding to each of the plurality of sub-volumes.

As described above, high resolution image data or high resolution volume images may be acquired at high speed.

1 is a diagram illustrating an example of a magnetic resonance imaging (MRI) system according to an embodiment.
2A to 2B illustrate a method of grouping a plurality of sub-volumes.
3 illustrates a multi-volume imaging technique for each of a plurality of groups.
4 is a view showing another embodiment of a magnetic resonance imaging system.
5 is a diagram illustrating an example of a pulse sequence applied to a subject.
6 is a diagram illustrating an example in which a plurality of sub-volumes are excited at the same time according to the present embodiment.
7 is a diagram showing an example of a restoration operation of the image data according to the present embodiment.
8 is a flowchart illustrating an example of a magnetic resonance imaging method according to the present embodiment.

Hereinafter, exemplary embodiments will be described in detail with reference to the accompanying drawings.

1 is a diagram illustrating an embodiment of a magnetic resonance image (MRI) system. Referring to FIG. 1, the magnetic resonance imaging system 100 includes a magnetic resonance imaging apparatus 110 and a data processing apparatus 120.

In the magnetic resonance imaging system 100 of FIG. 1, only components related to the present exemplary embodiment are illustrated. Therefore, it will be understood by those skilled in the art that other general purpose components may be further included in addition to the components shown in FIG. 1.

The magnetic resonance imaging system 100 is a device for non-invasively obtaining an image including information on the biological tissue of the subject. For example, the magnetic resonance imaging system 100 may be an apparatus for obtaining a diagnostic image of a subject using a magnetic field generated by magnetic force, but is not limited thereto. In addition, the subject may include a human body, a brain, a spine, a heart, a liver, a fetus, and the like, but is not limited thereto. In addition, the magnetic resonance imaging system 100 may include a hybrid magnetic resonance imaging system which is combined with other medical imaging apparatus such as PET (Positron Emission Tomography).

The magnetic resonance imaging apparatus 110 acquires magnetic resonance signals from a plurality of sub-volumes constituting a volume of a subject. In this case, each of the plurality of sub-volumes may include a predetermined number of slices. The predetermined number may be automatically determined according to the characteristics of the subject and the environment of use, or may be determined by the user. In addition, the thickness of the slices may be automatically determined according to the characteristics of the subject and the environment of use, or may be determined by the user.

For example, the magnetic resonance imaging apparatus 110 may include a plurality of sub-volumes included in each of at least two groups grouped so that adjacent sub-volumes among the plurality of sub-volumes belong to different groups. To be simultaneously excited, RF (Radio Frequency) pulses including a plurality of frequency components and a selective gradient are applied to the subject, and three-dimensional encoding is performed on each of the excited sub-volumes. Magnetic resonance signals are obtained from the plurality of sub-volumes.

The magnetic resonance imaging apparatus 110 applies RF pulses and a selection gradient including a plurality of frequency components to a subject located in a static magnetic field. Accordingly, the plurality of sub-volumes included in each of the at least two or more groups grouped such that adjacent sub-volumes among the plurality of sub-volumes constituting the volume of the subject belong to different groups are simultaneously excited. When at least two or more groups include the first to Nth groups, each of the plurality of sub-volumes constituting the volume of the subject is sequentially included in the first to Nth groups. When the plurality of sub-volumes includes the first sub-volume to the S-th sub-volume, each of the plurality of sub-volumes is sequentially included in the first group to the N-th group, so that the first sub-volume The second sub-volume is included in the first group, and the N-th sub-volume is included in the N-th group in this manner. In addition, the (N + 1) sub-volume is cyclically included in the first group, the (N + 2) sub-volume is included in the second group, and the (2N) sub-volume is included in the Nth group. In this manner, the S sub-volume is included in the (SN) group. Accordingly, each of the first to S-th sub-volumes may be grouped such that adjacent sub-volumes belong to different groups.

In this case, the first sub-volume to the S-th sub-volume constituting the subject may be sequentially set based on any one direction. For example, the first sub-volume may be the first sub-volume, and the last sub-volume may be the S sub-volume, based on the direction in which the selection gradient is applied to the subject. In this case, when the volume of the subject is defined with respect to the x-axis, the y-axis, and the z-axis, the direction in which the selection gradient is applied may be the z-axis, but is not limited thereto. For example, the x-axis may represent the sagittal plane direction, the y-axis may represent the coronal plane direction, the z-axis may represent the axial plane direction, the transverse plane direction, or the slice direction. have.

An example of at least two or more groups grouped such that adjacent sub-volumes among the plurality of sub-volumes constituting the volume of the subject belong to different groups will be described below with reference to FIGS. 2A to 2B. do.

The magnetic resonance imaging apparatus 110 applies RF pulses including a plurality of frequency components and a selection gradient to the subject so that the plurality of sub-volumes included in the first group of the at least two groups are simultaneously excited. . Each of the RF pulses may have a different phase.

For example, when the M sub-volumes are simultaneously excited, the RF pulses applied to the subject may be multi-band RF pulses in which M single-volume selective RF pulses are modulated. have.

As another example, RF pulses applied to a subject may be spatially encoded, such as a Hadamard Encoding method or a phase offset multiplanar volume imaging method for exciting M specified sub-volumes. encoding) may be RF pulses.

Accordingly, each of the RF pulses may have a frequency offset or may have a frequency offset and a phase offset. For example, RF pulses according to the present embodiment may be defined by Equation 1.

는 자기 회전비(Gyromagnetic Ratio), G는 그레디언트, D는 서브-볼륨의 두께, d(m)은 m번째 서브-볼륨의 위치, φ(m)은 m번째 서브-볼륨의 위상, t는 시간을 나타낸다. 예를 들어, 수학식 1의 그레디언트 G는 약 1KHz/cm가 될 수 있으나, 이에 한정되지 않는다. 이러한 RF 펄스들에 주파수 모듈레이션 및 위상 모듈레이션이 수행됨에 의하여, RF 펄스들에 주파수 오프셋 및 위상 오프셋이 구현될 수 있다. 또한, RF 펄스들 각각이 서로 다른 위상을 가짐으로 인하여 RF 위상 인코딩을 수행할 수도 있다.In Equation 1, Ψ (t) represents RF pulses, A is a constant, and m is a m th sub-volume among M sub-volumes simultaneously excited.

Is the magnetic magnetic ratio, G is the gradient, D is the thickness of the sub-volume, d (m) is the position of the m-th sub-volume, φ (m) is the phase of the m-th sub-volume, t is the time Indicates. For example, the gradient G of Equation 1 may be about 1 KHz / cm, but is not limited thereto. By frequency modulation and phase modulation being performed on these RF pulses, frequency offset and phase offset can be implemented on the RF pulses. In addition, RF phase encoding may be performed because each of the RF pulses has a different phase.

For example, the magnetic resonance imaging apparatus 110 may provide a plurality of sub-volumes included in the first group while applying a selection gradient based on a predetermined axial direction to a subject located in a static field. RF pulses including a frequency component corresponding to each Lamor frequency may be applied to the subject.

The L'ormo frequency is the precession frequency of the atomic magnetic moment. The nucleus has a magnetic moment or magnetic dipole moment due to spin motion. If there is no external magnetic field in the atom, the magnetic moment of the nucleus is random, with no regular rule in the direction, but when the atom is located in the static field, the nuclei are aligned in the direction of the static field to reach a low energy state. At this time, as the atomic nucleus spins, the magnetic moment of the atomic nucleus undergoes precessional motion. The precession frequency of the magnetic moment of the atomic nucleus is called the Ramo frequency. For example, the Lamo frequency may be determined by the product of the magnetic rotation ratio and the intensity of the externally applied magnetic field.

The magnetic resonance imaging apparatus 110 applies a selection gradient to distribute a magnetic field that changes linearly in a predetermined direction to a subject located in the static field, and simultaneously applies a plurality of sub-volumes included in the first group. In order to excite, RF pulses including a frequency component corresponding to a Ramo frequency of each of the plurality of sub-volumes included in the first group are applied to the subject.

1 and 5, the magnetic resonance imaging apparatus 110 performs three-dimensional encoding on each of a plurality of sub-volumes excited as RF pulses 511 and a selection gradient 512 are applied to a subject. To perform the operation, gradient signals 513, 514, and 516 are applied to a subject. For example, the magnetic resonance imaging apparatus 110 may include a first encoding gradient 513 for a first direction, a second encoding gradient 514 for a second direction, and a frequency encoding gradient 516 for a third direction. May be applied to a subject to perform 3D encoding, but is not limited thereto. In this case, any one of the first and second directions may be the same as the direction in which the selection gradient 512 is applied.

For example, the first encoding gradient 513 provides position information in the y-axis direction, the second encoding gradient 514 provides position information in the z-axis direction, and the frequency encoding gradient 516 provides position information in the x-axis direction. May be applied to the subject. Accordingly, the first encoding gradient 513 may perform y-axis direction phase encoding, and the second encoding gradient 514 may perform slice encoding or slice direction encoding in the z-axis direction. Slice encoding in the z-axis direction will be described below with reference to FIG. 3.

Referring back to FIG. 1, the magnetic resonance imaging apparatus 110 may read out the magnetic resonance signals from the plurality of sub-volumes by applying a frequency encoding gradient to the subject. In this case, the frequency encoding gradient may be a readout gradient. For example, the magnetic resonance imaging apparatus 110 may apply a lead-out gradient to the subject to sample the magnetic resonance signals, and the gradient of the direction in which the selection gradient is applied while the lead-out gradient is applied to the subject. May not be authorized, but is not limited thereto. When the selection gradient is applied in the z-axis direction, the readout gradient may be applied in the x-axis direction.

For example, as a gradient echo method, a polarity of a readout gradient applied to a subject may change from negative to positive. As such, the spin of the nucleus is dephased as the lead-out gradient having a negative polarity is applied to the subject, and the spin of the nucleus is dephased as the lead-out gradient with the positive polarity is applied to the subject. It is rephased. Magnetic resonant signals having the same frequency may be obtained by refocusing as the lead-out gradient of which the polarity changes from negative to positive is applied to the subject. As described above, since no magnetic resonance signals having the same frequency are acquired in the magnetic resonance imaging apparatus 110, the magnetic resonance imaging system 100 may generate a high resolution image.

For example, as a spin echo method, a readout gradient applied to a subject may have a positive polarity. In this case, the MRI apparatus 110 may apply a 180 ° pulse to the subject for refocusing.

The magnetic resonance imaging apparatus 110 performs 3D encoding on each of the excited sub-volumes, and acquires magnetic resonance signals from the plurality of sub-volumes. In this case, the plurality of sub-volumes may represent sub-volumes included in the first group excited by the RF pulses and the selection gradient. For example, the magnetic resonance imaging apparatus 110 may acquire magnetic resonance signals using multi-channel receiving coils, and the obtained magnetic resonance signals are acquired by a readout gradient. Can be signals.

The data processing apparatus 120 restores the magnetic resonance signals acquired by the magnetic resonance imaging apparatus 110 to image data corresponding to each of the plurality of sub-volumes. For example, the data processing apparatus 120 may reconstruct magnetic resonance signals into image data by using a parallel image algorithm considering channel information of multi-channel receiving coils. In this case, the channel information of the multi-channel receiving coils may indicate coil sensitivity of each of the multi-channel receiving coils. However, the present invention is not limited thereto, and the data processing apparatus 120 may reconstruct the magnetic resonance signals into image data by using a parallel image algorithm in consideration of information on current elements of the RF coil.

In other words, the magnetic resonance signals obtained in each of the multi-channel receiving coils have overlapping information on the plurality of sub-volumes. As such, the data processing apparatus 120 separates overlapping information for the plurality of sub-volumes by using a parallel image algorithm considering channel information of the multi-channel receiving coils, and thus, the plurality of sub-volumes. It is possible to restore the image data corresponding to each. The parallel imaging algorithm may use Sensitivity encoding (SENSE), Generalized Autocalibrating Partially Parallel Acquisitions (GRAPPA), Simultaneous Acquisition of Spatial Harmonics (SMASH), and Partially Parallel Imaging with Localized Sensitivities (PILS).

Accordingly, the data processing apparatus 120 considers the de-aliasing technique according to the parallel image algorithm and the channel information of the multi-channel receiving coils, and the magnetic resonance of the information on the plurality of sub-volumes is superimposed. The signals may be separated and reconstructed into image data corresponding to each of the plurality of sub-volumes.

According to the magnetic resonance imaging system 100 according to the present exemplary embodiment, among at least two groups grouped such that adjacent sub-volumes among a plurality of sub-volumes constituting a volume of a subject belong to different groups, Since a plurality of sub-volumes included in one group are excited at the same time, it is possible to generate a high-resolution three-dimensional volume image having a high signal to noise ratio (SNR) while increasing the magnetic resonance imaging speed.

2A to 2B illustrate a method of grouping a plurality of sub-volumes. 2A and 2B illustrate two groups grouped so that adjacent sub-volumes belong to different groups among a plurality of sub-volumes constituting a volume of a subject for convenience of description. Rather, it may include three or more groups.

Referring to FIG. 2A, a first group 211 and a second group 212 are shown, each of the first group 211 and the second group 212 including three sub-volumes. Each of the sub-volumes included in each of the first group 211 and the second group 212 shows a form in which four slices are accumulated. However, the present invention is not limited thereto, and the sub-volumes may include at least two slices. It can include all accumulated forms.

As described above, a method of exciting sub-volumes in which a plurality of slices are accumulated is missing in image information due to occurrence of an inter-slice gap between adjacent images, as compared with a 2D magnetic resonance imaging technique in which slices are excited. This can be prevented from occurring.

2A, the first sub-volume 201, the third sub-volume 203, and the fifth sub-volume 205 are included in the first group 211 based on the z-axis direction. The second sub-volume 202, the fourth sub-volume 204, and the sixth sub-volume 206 may be included in the second group 212 based on the z-axis direction. Accordingly, the magnetic resonance imaging apparatus 110 applies RF pulses and a selection gradient to the subject such that the plurality of sub-volumes 201, 203, and 205 included in the first group 211 are simultaneously excited. . In addition, after the restoration of the image data for the first group 211 is completed, the magnetic resonance imaging apparatus 110 includes a plurality of sub-volumes 202, 204, and 206 included in the second group 212. RF pulses and a selection gradient are applied to the subject so that they are excited at the same time.

In other words, the magnetic resonance imaging apparatus 110 applies the first RF pulses and the first selection gradient to the subject, thereby providing a plurality of sub-volumes 201, 203, and 205 included in the first group 211. This can be excited at the same time. The first RF pulses may include a plurality of frequency components. The plurality of frequency components excite a first frequency component for exciting the first sub-volume 201, a second frequency component for exciting the third sub-volume 203, and a fifth sub-volume 205. It may include a third frequency component for. In addition, each of the first RF pulses including the plurality of frequency components may have a different phase. As such, the first RF pulses may have a frequency offset and a phase offset. In this case, the first sub-volume 201 is excited by an RF pulse having a first frequency component and a first phase of the first RF pulses, and the third sub-volume 203 is of the first RF pulses. It is excited by an RF pulse having a second frequency component and a second phase, and the fifth sub-volume 205 may be excited by an RF pulse having a third frequency component and a third phase of the first RF pulses. .

After exciting the plurality of sub-volumes 201, 203, and 205 included in the first group 211, the magnetic resonance imaging apparatus 110 may apply the second RF pulses and the second selection gradient to the subject. May be applied to cause the plurality of sub-volumes 202, 204, 206 included in the second group 212 to be excited at the same time.

Referring to FIG. 2B, a first group 221 and a second group 222 are shown. Referring to FIG. 2B, the first sub-volume, the third sub-volume, the fifth sub-volume, and the seventh sub-volume, based on the z-axis direction, are included in the first group 221 and the z-axis direction is determined. By reference, the second sub-volume, the fourth sub-volume, the sixth sub-volume and the eighth sub-volume may be included in the second group 222. In this case, in order to perform 3D encoding in the magnetic resonance imaging apparatus 110 of FIG. 1, a first encoding gradient (for example, a phase encoding gradient) for the first direction and a second encoding for the second direction When a gradient (for example, a slice encoding gradient) is applied to a subject, a first direction may be a y-axis direction and a second direction may be a z-axis direction.

The manner of simultaneously exciting the plurality of sub-volumes can reduce the time to perform slice encoding for the second direction. The number of slice encodings performed in the second direction may be reduced in proportion to the number of sub-volumes included in each of the groups. As illustrated in FIG. 2B, a case in which four sub-volumes are included in each of the first group 221 and the second group 222 will be described as an example. It can be reduced to 1/4 as compared with the case of not performing. As the scan time is shortened, the MRI system 100 may generate a high resolution 3D full volume image at a high speed.

3 illustrates a multi-volume imaging technique for each of a plurality of groups. Referring to the drawing 31 in which a plurality of sub-volumes are simultaneously excited, a plurality of sub-volumes included in the first group 311 are simultaneously excited and also a plurality of sub-volumes included in the second group 312. The volumes are excited at the same time. When the number of groups is n and the number of sub-volumes included in each of the groups and simultaneously excited is M, the 3D magnetic resonance image may be performed with the total volume of the subject divided into M × n. Referring to FIG. 3, three sub-volumes are included in each of the first group 311 and the second group 312, so that the subject is imaged in three dimensions by being divided into six states.

Also, referring to a diagram 32 illustrating z-axis direction encoding, performing z-axis direction encoding 321 for the first group 311 and z-axis direction encoding 322 for the second group 312 Performance is shown.

Assume that frequency encoding is performed for the x-axis direction, phase encoding is performed for the y-axis direction, and slice encoding is performed for the z-axis direction. When the plurality of sub-volumes constituting the subject are not grouped into a plurality of groups, assuming that the number of z-axis slice encodings for the entire volume of the subject is Nz, the magnetic resonance imaging system 100 according to the present exemplary embodiment may perform the subject. The number of slice encodings in the z-axis direction is Nz / (M) in order to perform a 3D MR image by dividing the total volume of M × n.

Therefore, when the plurality of sub-volumes constituting the subject are not grouped into a plurality of groups, the number of y-axis phase encodings for the total volume of the subject is Ny, and the number of z-axis slice encodings for the entire volume of the subject. Is Nz, and the total scan time for the entire volume of the subject is TA = (Ny) × (Nz), the magnetic resonance imaging system 100 according to the present embodiment has a TA ′ for the entire volume of the subject. = (Ny) x ((Nz) / (M)) = TA / M.

However, the number of encoding and the total scan time in the magnetic resonance imaging system 100 described above may be the minimum number of encoding and the minimum total scan time according to the present embodiment. For example, when there are regions overlapping each other among the plurality of sub-volumes, the number of slice encodings in the z-axis direction may increase more than Nz / (M), and thus, the overall scan time may increase.

As described above, the magnetic resonance imaging method according to the present embodiment performs three-dimensional encoding while simultaneously exciting sub-volumes in which a plurality of slices are accumulated, thereby reducing the number of z-axis slice encoding. The scan time required to acquire the full volume image of the can be reduced. In addition, when three-dimensional encoding is performed in units of sub-volumes in which a plurality of slices are accumulated, gaps between slabs are performed when two-dimensional encoding is performed in slab units in which slices are accumulated. It is possible to prevent the performing of the magnetic resonance imaging in a plurality of orientations to eliminate the.

4 is a view showing another embodiment of a magnetic resonance imaging system. Referring to FIG. 4, the magnetic resonance imaging system 100 includes a magnetic resonance imaging apparatus 110, a data processing apparatus 120, and a user interface 130, and the magnetic resonance imaging apparatus 110 is a control unit. (111), the RF driver 112, the gradient driver 113, the magnet device 114, the signal acquisition unit 115, the magnet device 114 is a magnetic force generator 1141, RF coils 1142 ), Gradient coils 1143, and the data processing device 120 includes a recovery unit 122 and a synthesis unit 124, and the user interface unit 130 includes an input device 132 and an output device ( 134). The magnetic resonance imaging system 100 illustrated in FIG. 4 corresponds to an example of the magnetic resonance imaging system 100 illustrated in FIG. 1. Therefore, since the description described with reference to the magnetic resonance imaging system 100 in FIG. 1 is also applicable to the magnetic resonance imaging system 100 of FIG. 4, redundant descriptions thereof will be omitted.

The magnetic resonance imaging system 100 is a device for non-invasively obtaining an image including information on the biological tissue of the subject. In this case, the image may be a 3D volume image, but is not limited thereto. The MRI apparatus 110 obtains magnetic resonance signals emitted from a subject by applying a predetermined pulse sequence to the subject.

The controller 111 controls the overall operation of the magnetic resonance imaging apparatus 110. For example, the controller 111 may control the RF driver 112, the gradient driver 113, the magnet device 114, and the signal acquirer 115. The RF driver 112 controls the RF coils 1142, and the gradient driver 113 controls the gradient coils 1143.

The magnet device 114 applies a magnetic field, RF pulses and a gradient to a subject, and acquires magnetic resonance signals from the subject. In order to measure the magnetic property of the subject, the magnet device 114 may be present in an outer space and a shielded space, but the present invention is not limited thereto and may be implemented as an open type.

The magnetic force generating unit 114 generates magnetic force to position the subject in the static magnetic field.

The RF coils 1142 apply RF pulses including a plurality of frequency components to a subject and obtain magnetic resonance signals from the subject. In this case, the RF coils 1142 may include both transmitting RF coils and receiving RF coils, or may include transmitting and receiving RF coils. Hereinafter, for convenience of description, the RF coils 1142 are classified into an RF transmitting coil and an RF receiving coil, but are not limited thereto.

The RF pulses applied to the subject in the RF transmitting coil of the RF coils 1142 may include both multi-band RF pulses or spatially encoded RF pulses. The RF receiving coil among the RF coils 1142 acquires signals from a subject and outputs the obtained signals to the data processing apparatus 120. In this case, the RF receiving coils may be multi-channel receiving coils. For example, the RF receiving coil may be multi-channel receiving coils including 32 channels, but is not limited thereto.

The gradient coils 1143 apply a selection gradient, a first encoding gradient, a second encoding gradient, and a frequency encoding gradient to the subject. For example, the gradient coils 1143 include a selection gradient, a z coil applying a second encoding gradient, an x coil applying a frequency encoding gradient, and a y coil applying a first encoding gradient.

A pulse sequence for signals applied to the subject from the RF coils 1142 and the gradient coils 1143 will be described in detail with reference to FIG. 5.

The signal acquirer 115 acquires magnetic resonance signals output from the RF coils 1142 and performs predetermined tasks. For example, the signal acquirer 115 may include an amplifier for amplifying the acquired magnetic resonance signals, a demodulator for demodulating the amplified magnetic resonance signals, an analog to digital converter (ADC) for converting the demodulated magnetic resonance signals into a digital form, and the like. It may be implemented as, and may have a storage for storing the magnetic resonance signal converted into a digital form.

The data processing apparatus 120 performs predetermined processing operations on the magnetic resonance signals output from the magnetic resonance imaging apparatus 110.

The reconstructor 122 restores the magnetic resonance signals output from the magnetic resonance imaging apparatus 110 to image data corresponding to each of the plurality of sub-volumes.

In addition, the restoration unit 122 configures k-space using magnetic resonance signals output from the magnetic resonance imaging apparatus 110 and performs k-space data on the k-space in order to perform a restoration operation. Fourier transform can also be performed. In this case, the k-space data is present in a form in which image data for the plurality of sub-volumes are all overlapped.

In more detail with respect to the reconstruction operation, the multi-channel receiving coils receive magnetic resonance signals for the superimposed image for all of the plurality of excited sub-volumes. Therefore, the reconstructor 122 separates the magnetic resonance signals for the superimposed images into image data for each of the plurality of sub-volumes in consideration of the channel information of the multi-channel receiving coils. In addition, when each of the RF pulses applied to the subject in the RF coils 1142 has a different phase, the reconstructor 122 may further consider the channel information of the multi-channel receiving coils and the phase of each of the RF pulses. have.

The parallel image algorithm is a technique for dealiasing aliasing that occurs as the number of sampling lines for signal acquisition decreases to increase the photographing speed. For example, the parallel imaging algorithm is a SENSE technique using coil field sensitivity corresponding to channel information of each of the multi-channel receiving coils or the value of the peripheral unacquired signal line of the acquired magnetic resonance signals. GRAPPA technique for estimating using an autocalibration signal (ACS) kernel. The reconstructor 122 reconstructs the superimposed magnetic resonance signals into image data corresponding to each of the plurality of sub-volumes using channel information of the multi-channel receiving coils and a dealiasing technique of a parallel image algorithm. This will be described in more detail below with reference to FIG. 7.

The combining unit 124 synthesizes the image data reconstructed by the reconstructing unit 122. Synthesis may be a fusion operation. For example, the magnetic resonance imaging apparatus 110 includes a plurality of frequency components to simultaneously excite a plurality of sub-volumes included in the first group. Applying RF pulses and a selection gradient to the subject, performing three-dimensional encoding on each of the excited sub-volumes, obtaining magnetic resonance signals from the plurality of sub-volumes, and the reconstructor 122 performs a first The image data corresponding to each of the plurality of sub-volumes included in the group is restored. In the same manner, the magnetic resonance imaging apparatus 110 obtains magnetic resonance signals from the plurality of sub-volumes included in the second group, and the reconstructor 122 includes the plurality of sub-volumes included in the second group. The image data corresponding to each of them is restored. The synthesizing unit 124 synthesizes the image data corresponding to each of the plurality of sub-volumes included in the first group and the image data corresponding to each of the plurality of sub-volumes included in the second group. Volume images can be created.

The user interface 130 obtains input information from the user and displays output information. In FIG. 4, the input device 132 and the display device 134 are shown separately for convenience of description, but the present disclosure is not limited thereto. The input device 132 and the display device 134 may be integrated into one device. May be

The input device 132 obtains input information for selecting the resolution of the magnetic resonance image, the thickness of the slices, and the like from the user, and the display device 134 displays the full volume image of the subject or the subject generated by the synthesis unit 124. An image of the ROI is displayed among the entire volume images. Although FIG. 4 illustrates that the MRI system 100 includes the display device 134, the present invention is not limited thereto, and the display device 134 may be provided outside the MRI system 100.

5 is a diagram illustrating an example of a pulse sequence 51 applied to a subject. 4 to 5, the RF pulses 511 and the selection gradient 512 are applied to the subject such that the plurality of sub-volumes included in the first group of the plurality of groups constituting the subject are simultaneously excited. do.

In this case, the RF pulses 511 may be applied to the subject by the RF coils 1142, and the selection gradient 512 may be applied by the z coil among the gradient coils 1143.

In order to perform three-dimensional encoding on the excited plurality of sub-volumes, the first encoding gradient 513 and the second encoding gradient 514 are applied to the subject. In this case, each of the first encoding gradient 513 and the second encoding gradient 514 may be applied by the y coil and the z coil of the gradient coils 1143. In this case, the first encoding gradient 513 performs phase encoding in the y-axis direction, and the second encoding gradient 514 performs slice encoding in the z-axis direction.

In addition, the frequency encoding gradient 515 may be additionally applied together with the first encoding gradient 513 and the second encoding gradient 514, but is not limited thereto. In this case, the frequency encoding gradient 515 may be applied by the x coil of the gradient coils 1143.

In order to read out the magnetic resonance signals from the plurality of sub-volumes, a frequency encoding gradient 516 is applied to the subject. In this case, the frequency encoding gradient 516 is applied by the x coil of the gradient coils 1143. As such, after the first encoding gradient 513 and the second encoding gradient 514 are applied, as the frequency encoding gradient 515 is applied, the MRI apparatus 110 may perform 3D encoding. . In this case, the first encoding gradient 513, the second encoding gradient 514, and the frequency encoding gradient 515 may perform spatial encoding on the subject in cooperation with each other.

Also, if the pulse sequence 51 shown in FIG. 5 is a gradient echo scheme, the polarity of the frequency encoding gradient 516 may vary from negative to positive.

6 is a diagram illustrating an example in which a plurality of sub-volumes are excited at the same time according to the present embodiment. Referring to the pulse sequence 51 of FIG. 5 and the multi-volume imaging technique 61 of FIG. 6, as the selection gradient 512 is applied to the subject existing in the static field, the gradient field changes linearly to the subject. magnetic field gradient 611 is generated. Accordingly, each of the sub-volumes 612 to 616 constituting the subject may have a different LMO frequency.

When the first sub-volume 612, the third sub-volume 613, and the fifth sub-volume 614 are included in the first group, the first sub-volume 612, the third sub-volume ( 613 and the plurality of sub-volumes 612 to 614 included in the first group as RF pulses 511 having a plurality of frequency components that excite the fifth sub-volume 614 are applied to the subject. This can be excited at the same time. Additionally, when the RF pulses 511 having the plurality of frequency components have different phases, the first sub-volume 612 is excited by the RF pulse having the first LMO frequency and the first phase, and the third The sub-volume 613 may be excited by an RF pulse having a third LMO frequency and a third phase, and the fifth sub-volume 614 may be excited by an RF pulse having a fifth LMO frequency and a fifth phase. . As such, when the RF pulses 511 have different phases, image data of the first sub-volume 612, the third sub-volume 613, and the fifth sub-volume 614 simultaneously excited. In performing the reconstruction operation, as the first phase, the third phase, and the fifth phase are further considered, image data with less distortion may be reconstructed.

7 is a diagram showing an example of a restoration operation of the image data according to the present embodiment. Referring to FIG. 7, there are shown multi-channel RF receiving coils 71 including L channels and a coil field map 72 for each of the coils. In this case, the coil field map 72 may be a sensitivity profile for each coil included in the multi-channel RF receiving coils 71. As the plurality of sub-volumes included in the first group 73 among the plurality of sub-volumes constituting the subject are simultaneously excited, the multi-channel RF receiving coils 71 are included in the first group 73. Magnetic resonance signals are obtained from the plurality of sub-volumes.

The signal received at the multi-channel RF receiving coils 71 including 32 channels is S, the coil field map 72 for each of the multi-channel RF receiving coils 71 is B, and the first group ( When the signal representing the reconstructed image data for the plurality of sub-volumes included in 73 is F, S, B, and F may be defined as Equations 2 to 3 below.

In Equation 2, b represents a sensitivity profile for each coil included in the multi-channel RF receiving coils 71. Further, when RF pulses having a plurality of frequency components and a plurality of phases are applied for each of the plurality of sub-volumes included in the first group 73, R is the phase for each of the plurality of sub-volumes. Information can be displayed. In addition, R can be a matrix representing an RF encoding configuration that gives a change in phase. For example, the first sub-volume included in the first group 73 is excited by an RF pulse having a first L'Omo frequency and the first phase, and the second sub-volume included in the first group 73. Is excited by an RF pulse having a second LMO frequency and a second phase, and in this manner each of the other sub-volumes included in the first group 73 is excited by a different Lamo frequency and a different phase. Can be. As defined in Equation 2, B representing the coil field map 72 is R representing the phase information of the RF pulses and a sensitivity profile for each coil included in the multi-channel RF receiving coils 71. Can be defined.

However, when RF pulses having a plurality of frequency components have the same phase, the coil field map 72 may be defined without considering phase information of the RF pulses. In this case, R corresponding to the phase information of Equation 2 may be used as an identity matrix.

In Equation 3, S _p represents a signal received at the coil of the p-th channel of the multi-channel RF receiving coils 71. B ^m _p represents a coil field map for the m th sub-volume of the plurality of sub-volumes included in the first group 73 and the coil of the p th channel of the multi-channel RF receiving coils 71. In addition, f ^m is a multiple sub included in the first group (73) represents the image data for the volume-of the m-th sub-volume. Therefore, the reconstructor 122 shown in FIG. 4 performs an operation as shown in Equation 4, thereby performing a plurality of magnetic resonance signals received from the multi-channel RF receiver coils 71 included in the first group 73. The image data corresponding to each of the sub-volumes may be restored.

In Equation 4, the superscript T of the matrix represents a transpose matrix for the matrix.

As described above, the reconstructor 122 of FIG. 4 uses the channel information of the multi-channel receiving coils 71 and the dealiasing technique of the parallel image algorithm, so that the superimposed magnetic resonance signals are applied to each of the plurality of sub-volumes. It can be restored to the corresponding image data.

As the magnetic resonance signals are received by being superimposed in the multi-channel RF receiving coils 71, the magnetic resonance signals overlapping in the k-space are obtained by using an RF decoding operation considering coil sensitivity and phase information of RF pulses. Can be separated. However, when the phase information of the RF pulses is not used, the RF decoding operation may be performed without considering the phase information of the RF pulses.

8 is a flowchart illustrating a magnetic resonance imaging method according to the present embodiment. Referring to FIG. 8, the magnetic resonance imaging method includes steps processed in time series in the magnetic resonance imaging system illustrated in FIGS. 1 and 4. Therefore, even if omitted below, the contents described above with respect to the MRI system illustrated in FIGS. 1 and 4 may be applied to the MRI method of FIG. 8. Hereinafter, for convenience of description, a case where the subject is composed of N groups will be described as an example.

In step 801, the control unit 111 of the magnetic resonance imaging apparatus 110 sets n to 1.

In operation 802, the magnetic resonance imaging apparatus 110 may include an n-th group among at least two groups grouped such that adjacent sub-volumes among the plurality of sub-volumes constituting the volume of the subject belong to different groups. RF pulses comprising a plurality of frequency components and a selection gradient are applied to the subject such that the included sub-volumes are simultaneously excited. In this case, the RF pulses may be applied from the RF coils 1142 under the control of the RF driver 112 of the magnetic resonance imaging apparatus 110, and the selection gradient is a gradient driver of the magnetic resonance imaging apparatus 110. By the control of 113 may be applied in the gradient coils 1143.

In operation 803, the MRI apparatus 110 performs 3D encoding on each of the excited sub-volumes, and acquires magnetic resonance signals from the plurality of sub-volumes. For example, the MRI apparatus 110 may apply a first encoding gradient with respect to a first direction and a second encoding gradient with respect to a second direction to a subject to perform 3D encoding. In this case, any one of the first direction and the second direction may be the same as the direction in which the selection gradient is applied in step 801. In addition, the first to second encoding gradients may be applied to the gradient coils 1143 under the control of the gradient driver 113 of the magnetic resonance imaging apparatus 110.

In operation 804, the restoration unit 122 of the data processing apparatus 120 restores the magnetic resonance signals obtained in operation 803 to image data corresponding to each of the plurality of sub-volumes included in the n-th group.

In step 805, the control unit 111 of the magnetic resonance imaging apparatus 110 determines whether steps 802 to 804 have been performed on all groups constituting the subject. According to the determination result, when steps 802 to 804 are not performed for all the groups constituting the subject, the operation proceeds to step 806, and when steps 802 to 804 are performed on all the groups constituting the subject 807 Proceed to step.

In step 806, the control unit 111 of the magnetic resonance imaging apparatus 110 sets n to a value increased by 1 and proceeds to step 802.

In operation 807, the combiner 124 combines image data corresponding to each of the plurality of sub-volumes included in each of the groups constituting the subject to generate a 3D volume image. In this case, all groups constituting the subject may be first to Nth groups.

Accordingly, the magnetic resonance imaging method according to the present embodiment can generate a high resolution 3D volume image at high speed.

According to the magnetic resonance imaging method and the magnetic resonance imaging system 100 according to the present embodiment, a multi-volume excitation technique for simultaneously exciting a plurality of sub-volumes, and using the x-axis, y-axis, and z Three-dimensional gradient encoding may be performed on the axis, RF encoding may be performed due to RF phases having different phases, and the image may be reconstructed using coil sensitivity and RF decoding.

On the other hand, the above-described method can be written as a program that can be executed in a computer, it can be implemented in a general-purpose digital computer to operate the program using a computer-readable recording medium. In addition, the structure of the data used in the above-described method can be recorded on the computer-readable recording medium through various means. The computer-readable recording medium may be a magnetic storage medium (eg, ROM, RAM, USB, floppy disk, hard disk, etc.), an optical reading medium (eg, CD-ROM, DVD, etc.), PC interface (PC Interface). (Eg, PCI, PCI-express, Wifi, etc.).

Those skilled in the art will appreciate that the present invention may be embodied in a modified form without departing from the essential characteristics of the above-described substrate. Therefore, the disclosed methods should be considered in descriptive sense only and not for purposes of limitation.

100 ... Magnetic Resonance Imaging System
110 ... Magnetic Resonance Imaging Device
120 ... Data Processing Unit

Claims (20)

In magnetic resonance imaging (MRI) method,
A plurality of sub-volumes included in each of at least two or more groups grouped such that adjacent sub-volumes of the plurality of sub-volumes constituting the volume of the subject belong to different groups are simultaneously excited. applying radio frequency (RF) pulses including a plurality of frequency components and a selection gradient to the subject to be excised;
Performing three-dimensional encoding on each of the excited sub-volumes, and obtaining magnetic resonance signals from the plurality of sub-volumes; And
Reconstructing the obtained magnetic resonance signals into image data corresponding to each of the plurality of sub-volumes. The method of claim 1,
When the at least two groups include the first group to the Nth group, each of the plurality of sub-volumes is sequentially included in the first group to the Nth group, wherein N is a natural number of two or more. Characterized in that the method. The method of claim 1,
The performing of the three-dimensional encoding includes applying a first encoding gradient in a first direction and a second encoding gradient in a second direction to the subject to three-dimensionally encode each of the excited sub-volumes,
Wherein the direction of either the first direction or the second direction is the same as the direction in which the selection gradient is applied. The method of claim 1,
Reading out magnetic resonance signals from the plurality of sub-volumes by applying a readout gradient;
The acquiring step includes acquiring the readout signals using multi-channel receiving coils. The method of claim 1,
The reconstructing may include reconstructing the obtained magnetic resonance signals into image data corresponding to each of the plurality of sub-volumes using a parallel imaging algorithm considering channel information of multi-channel receiving coils. . The method of claim 1,
Wherein each of the RF pulses may have a different phase. The method of claim 6,
The reconstructing may include image data corresponding to each of the plurality of sub-volumes using the acquired magnetic resonance signals using a parallel image algorithm considering channel information of multi-channel receiving coils and a phase of each of the RF pulses. How to restore. The method of claim 1,
Fusing the image data obtained by performing the applying, acquiring, and reconstructing with respect to each of the at least two groups. In the magnetic resonance imaging method,
By applying a predetermined pulse sequence to the subject, any one of at least two groups grouped so that adjacent sub-volumes among the plurality of sub-volumes constituting the volume of the subject belong to different groups Restoring image data corresponding to each of the plurality of sub-volumes included;
Determining whether restoring the image data has been performed for all groups constituting the subject; And
When the restoring of the image data is performed on all groups constituting the subject, image data corresponding to each of the plurality of sub-volumes included in each of the groups constituting the subject is fused. Generating a 3D volume image. The method of claim 9,
When the at least two groups include the first group to the N-th group, each of the plurality of sub-volumes is sequentially included in the first group to the N-th group, and N is a natural number of two or more. Characterized in that the method. The method of claim 9,
The reconstructing may be performed by using a parallel imaging algorithm considering channel information of multi-channel receiving coils obtaining magnetic resonance signals from the plurality of sub-volumes. Restoring image data corresponding to each of the sub-volumes. A computer-readable recording medium storing a computer program for executing the method of any one of claims 1 to 11. In the magnetic resonance imaging system,
A plurality of frequencies such that a plurality of sub-volumes included in each of at least two or more groups grouped such that adjacent sub-volumes of the plurality of sub-volumes constituting the volume of the subject belong to different groups are simultaneously excited Magnetic resonance imaging for applying RF pulses and selection gradients including components to the subject, performing three-dimensional encoding on each of the excited sub-volumes, and obtaining magnetic resonance signals from the plurality of sub-volumes. Photographing apparatus; And
And a data processing device for restoring the obtained magnetic resonance signals into image data corresponding to each of the plurality of sub-volumes. The method of claim 13,
When the at least two groups include the first group to the N-th group, each of the plurality of sub-volumes is sequentially included in the first group to the N-th group, and N is a natural number of two or more. Magnetic resonance imaging system, characterized in that. The method of claim 13,
The magnetic resonance imaging apparatus may apply gradient coils to the subject to apply a first encoding gradient in a first direction and a second encoding gradient in a second direction to three-dimensionally encode each of the excited sub-volumes. Including;
Magnetic resonance imaging system, characterized in that any one of the first direction or the second direction is the same as the direction in which the selection gradient is applied. The method of claim 13,
The magnetic resonance imaging apparatus
Gradient coils applying a readout gradient to the subject to read out magnetic resonance signals from the plurality of sub-volumes; And
RF coils for acquiring the magnetic resonance signals;
The data processing apparatus further includes a reconstruction unit for reconstructing the magnetic resonance signals obtained from the RF coils into image data corresponding to each of the plurality of sub-volumes. The method of claim 13,
The data processing apparatus reconstructs the obtained magnetic resonance signals into image data corresponding to each of the plurality of sub-volumes using a parallel image algorithm in consideration of channel information of multi-channel receiving coils. The method of claim 13,
The magnetic resonance imaging apparatus includes RF coils for applying RF pulses, which may have different phases, to the subject. The method of claim 18,
The data processing apparatus uses the parallel image algorithm in consideration of the channel information of the multi-channel receiving coils and the phase of each of the RF pulses, so that the acquired magnetic resonance signals are image data corresponding to each of the plurality of sub-volumes. Magnetic resonance imaging system comprising a; restoring unit to restore. The method of claim 13,
The data processing apparatus may include: a synthesizer configured to reconstruct the obtained magnetic resonance signals into image data corresponding to each of the plurality of sub-volumes included in each of the groups, and to synthesize the reconstructed image data. system.

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