Magnetic resonance imaging system and method, computer readable storage medium

Abstract

A magnetic resonance imaging system and method, a computer readable storage medium. The present invention provides a magnetic resonance imaging method, a magnetic resonance imaging system and a computer readable storage medium. The magnetic resonance imaging method comprises: acquiring a plurality of parts of k-space using a plurality of imaging sequences to obtain a plurality of k-space data sets, each imaging sequence comprising a pre-spread phase gradient pulse and a plurality of phase encoding gradient pulses applied after the pre-spread phase gradient pulse, wherein the pre-spread phase gradient pulses in the plurality of imaging sequences have a standard area difference in turn when sorted by area value, the standard area difference being 2 / N of the area of any phase encoding gradient, wherein N is the number of groups of the plurality of imaging sequences; reconstructing a magnetic resonance image from each of the plurality of k-space data sets, respectively; and processing the plurality of k-space data sets to obtain a magnetic resonance image.

Description

Technical Field

[0001] This invention relates to the field of medical imaging, and in particular to a magnetic resonance imaging (MRI) system and method, and a computer-readable storage medium. Background Technology

[0002] Traditional magnetic resonance echo-planar imaging (EPI) is a fast imaging technique where the entire image can be formed from multiple echo signals generated by a single radio frequency (RF) excitation, thus enabling rapid imaging. However, this imaging technique is prone to Nyquist artifacts, which can be caused by factors such as eddy currents, gradient coil heating, and gradient delay. Furthermore, because EPI typically employs parallel imaging acceleration techniques, acceleration artifacts appear in the image edge regions.

[0003] Existing technologies have proposed some methods to suppress or accelerate Nyquist artifacts, but it is difficult to suppress these two different types of artifacts simultaneously, and the suppression effect of artifacts also needs to be further improved.

[0004] For example, in order to solve the problems of phase change and parallel acceleration artifacts between multiple acquisitions, the MUSE (multiplexed sensitivity-encoding) method was proposed. However, the MUSE method still has difficulty eliminating Nyquist artifacts in images. Summary of the Invention

[0005] One aspect of the present invention provides a magnetic resonance imaging method capable of eliminating Nyquist artifacts in magnetic resonance imaging, the method comprising:

[0006] Multiple k-space datasets are obtained by acquiring multiple portions of k-space using multi-group imaging sequences. Each group imaging sequence includes a pre-phasing gradient pulse and multiple phase-encoded gradients applied after the pre-phasing gradient pulse. The pre-phasing gradient pulses in the multi-group imaging sequences have a standard area difference when ordered by their area values. The standard area difference is 2 / N of the area of ​​any phase-encoded gradient, where N is the number of groups in the multi-group imaging sequence.

[0007] The multiple k-space datasets are processed to obtain magnetic resonance images.

[0008] On the other hand, the number of imaging sequences is greater than 2.

[0009] On the other hand, the steps for processing multiple k-space datasets include: processing the multiple k-space datasets based on a multi-sensitivity coding algorithm.

[0010] On the other hand, the steps for processing multiple k-space datasets include:

[0011] The multiple k-space datasets are respectively processed to accelerate the solution and obtain multiple phase maps;

[0012] The corrected coil sensitivity map is obtained based on the multiple phase maps;

[0013] The magnetic resonance image is obtained based on the corrected coil sensitivity map and the multiple k-space datasets.

[0014] On the other hand, each imaging sequence also includes a radio frequency excitation pulse, a radio frequency refocusing pulse, and a diffusion gradient pulse. The diffusion gradient pulse includes a phase-shifting gradient pulse and a re-phase-fixing gradient pulse. The phase-shifting gradient pulse and the re-phase-fixing gradient pulse are applied symmetrically before and after the radio frequency refocusing pulse, respectively. The pre-dephase gradient pulse is applied after the re-phase-fixing gradient pulse.

[0015] In another aspect, the present invention provides a magnetic resonance imaging method, comprising:

[0016] Multiple k-space datasets are obtained by acquiring multiple portions of k-space using multiple imaging sequences. Each imaging sequence includes an echo-plane imaging sequence and a preparation sequence applied before the echo-plane imaging sequence portion. The echoes of the multiple k-space datasets have a standard phase offset when ordered by phase value, and the standard phase offset is 2π / N, where N is the number of k-space datasets; and,

[0017] The multiple k-space datasets are processed to obtain magnetic resonance images.

[0018] On the other hand, the number of k-space datasets is greater than 2.

[0019] On the other hand, the prepared sequences include spin echo sequences, gradient echo sequences, diffusion-weighted sequences, or spin echo-diffusion-weighted sequences.

[0020] In another aspect, the present invention provides a computer-readable storage medium comprising a stored computer program, wherein the magnetic resonance imaging method of any of the above aspects is executed when the computer program is run.

[0021] In another aspect, the present invention provides a magnetic resonance imaging (MRI) system, comprising:

[0022] Gradient coils, configured to generate encoded gradients;

[0023] A radio frequency (RF) coil configured to generate RF pulses; and

[0024] A processor, connected to the gradient coil and the RF coil, is configured to:

[0025] The gradient coil and the RF coil are instructed to generate multiple imaging sequences to acquire multiple portions of k-space and obtain multiple k-space datasets. Each imaging sequence includes a pre-dephasing gradient pulse and multiple phase-encoded gradients applied after the pre-dephasing gradient pulse. The pre-dephasing gradient pulses in the multiple imaging sequences are ordered by area value and have a standard area difference, where the standard area difference is 2 / N of the area of ​​any phase-encoded gradient, and N is the number of groups in the multiple imaging sequences.

[0026] Magnetic resonance images were obtained based on these multiple k-space datasets.

[0027] It should be understood that the brief description provided above is intended to introduce some concepts further described in the detailed embodiments in a simplified form. This is not intended to identify key or essential features of the claimed subject matter, the scope of which is uniquely defined by the claims following the detailed description. Furthermore, the claimed subject matter is not limited to the implementation of any shortcomings mentioned above or in any paragraph of this disclosure. Attached Figure Description

[0028] The invention will be better understood by referring to the accompanying drawings and by reading the following description of non-limiting embodiments, in which:

[0029] Figure 1 This is a schematic diagram of a magnetic resonance imaging (MRI) system according to an exemplary embodiment;

[0030] Figure 2 This is a flowchart of a magnetic resonance imaging method according to an exemplary embodiment of the present invention;

[0031] Figure 3 yes Figure 2 A schematic diagram of an exemplary imaging sequence used in the method shown;

[0032] Figure 4 This is a schematic diagram of a k-space data acquisition trajectory obtained according to an exemplary embodiment of the present invention;

[0033] Figure 5 This is a flowchart of a magnetic resonance imaging method according to another exemplary embodiment of the present invention;

[0034] Figure 6 This is a flowchart of a magnetic resonance imaging method according to another exemplary embodiment of the present invention;

[0035] Figure 7 This is a flowchart of a magnetic resonance imaging method according to another exemplary embodiment of the present invention;

[0036] Figure 8 This is a comparison between an image obtained by the method according to an exemplary embodiment of the present invention and an image obtained by a conventional method.

[0037] The accompanying drawings illustrate the components, systems, and methods described in the magnetic resonance imaging methods and systems. Together with the following description, the drawings illustrate and explain the structural principles, methods, and concepts described herein. In the drawings, the thickness and dimensions of components may be enlarged or otherwise modified for clarity. Well-known structures, materials, or operations are not shown or described in detail to avoid obscuring the described components, systems, and methods. Detailed Implementation

[0038] The following describes specific embodiments of the present invention. It should be noted that, in order to provide a concise description, this specification cannot exhaustively describe all features of the actual embodiments. It should be understood that, in the actual implementation of any embodiment, just as in any engineering or design project, various specific decisions are often made to achieve the developer's specific goals and to meet system-related or business-related constraints, and this can change from one embodiment to another. Furthermore, it is understood that although the efforts made in this development process may be complex and lengthy, for those skilled in the art related to the content disclosed in this invention, some design, manufacturing, or production modifications based on the technical content disclosed herein are merely conventional technical means and should not be construed as insufficient content of this disclosure.

[0039] Unless otherwise defined, the technical or scientific terms used in the claims and description shall have the ordinary meaning understood by one of ordinary skill in the art. The terms “first,” “second,” and similar terms used in this specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. The terms “an” or “a” and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms “comprising” or “including” and similar terms mean that the elements or objects preceding “comprising” or “including” encompass the elements or objects listed following “comprising” or “including” and their equivalents, and do not exclude other elements or objects. The terms “connected” or “linked” and similar terms are not limited to physical or mechanical connections, nor are they limited to direct or indirect connections. Furthermore, it should be understood that references to “an embodiment” or “an embodiment” in this disclosure are not intended to exclude the existence of additional embodiments that also include the referenced features.

[0040] Referring to the accompanying drawings, this disclosure describes a magnetic resonance imaging system and a magnetic resonance imaging method capable of suppressing Nyquist and acceleration artifacts. Multiple k-space datasets are obtained by acquiring multiple portions of k-space using multiple imaging sequences, and image reconstruction is performed on these multiple k-space datasets to generate magnetic resonance images. Each of the aforementioned imaging sequences includes a pre-dephasing gradient pulse and multiple phase-encoded gradients applied after the pre-dephasing gradient pulse, wherein the pre-dephasing gradient pulses in the multiple imaging sequences have a standard area difference when ordered by area value, the standard area difference being 2 / N of the area of ​​any phase-encoded gradient, where N is the number of the multiple imaging sequences. In this way, artifacts in the echoes of the multiple imaging pulse sequences are attenuated, thereby simultaneously suppressing Nyquist and acceleration artifacts in the final obtained MR image.

[0041] refer to Figure 1 This diagram illustrates an exemplary MRI (Magnetic Resonance Imaging) system 100 according to some embodiments. Operation of the MRI system 100 is controlled by an operator workstation 110, which includes an input device 114, a control panel 116, and a display 118. The input device 114 may be a joystick, keyboard, mouse, trackball, touch-activated screen, voice control, or any similar or equivalent input device. The control panel 116 may include a keyboard, touch-activated screen, voice control, buttons, sliders, or any similar or equivalent control device. The operator workstation 110 is coupled to and communicates with a computer system 120, which enables the operator to control the generation and viewing of images on the display 118. The computer system 120 includes multiple components that communicate with each other via an electrical and / or data connection module 122. The connection module 122 may be a direct wired connection, a fiber optic connection, a wireless communication link, etc. The computer system 120 may include a central processing unit (CPU) 124, a memory 126, and an image processor 128. In some implementations, the image processor 128 may be replaced by image processing functions implemented in the CPU 124. The computer system 120 may be connected to an archive media device, permanent or backup storage, or a network. The computer system 120 may be coupled to and communicate with a separate MRI system controller 130.

[0042] The MRI system controller 130 includes a set of components that communicate with each other via an electrical and / or data connection module 132. The connection module 132 can be a direct wired connection, a fiber optic connection, a wireless communication link, etc. The MRI system controller 130 may include a CPU 131, a sequence pulse generator 133 that communicates with the operator workstation 110, and a transceiver (or RF transceiver).

[0043] 135, memory 137, and array processor 139. In some embodiments, a sequence pulse generator 133 may be integrated into the resonant assembly 140 of the MRI system 100. The MRI system controller 130 may receive commands from the operator workstation 110 to indicate the MRI scan sequence to be performed during an MRI scan. The MRI system controller 130 is also coupled to and communicates with a gradient driver system 150, which is coupled to a gradient coil assembly 142 to generate a magnetic field gradient during an MRI scan.

[0044] The sequence pulse generator 133 may also receive data from a physiological acquisition controller 155, which receives signals from multiple different sensors, such as electrocardiogram (ECG) signals from electrodes attached to the patient, connected to the subject or patient 170 undergoing an MRI scan. The sequence pulse generator 133 is coupled to and communicates with a scan room interface system 145, which receives signals from various sensors associated with the state of the resonant assembly 140. The scan room interface system 145 is also coupled to and communicates with a patient positioning system 147, which sends and receives signals to control the movement of the patient table to the desired position for the MRI scan.

[0045] MRI system controller 130 provides gradient waveforms to gradient driver system 150, the gradient driver system including G x G y and G z Amplifiers, etc. Each G x G y and G z Gradient amplifiers excite corresponding gradient coils in gradient coil assembly 142 to generate magnetic field gradients for spatial encoding of MR signals during MRI scans. Gradient coil assembly 142 is disposed within resonant assembly 140, which also includes a superconducting magnet with a superconducting coil 144 that provides a static, uniform longitudinal magnetic field B0 throughout the cylindrical imaging volume 146 during operation. Resonant assembly 140 also includes an RF body coil 148 that provides a transverse magnetic field B1 during operation, which is substantially perpendicular to B0 throughout the cylindrical imaging volume 146. Resonant assembly 140 may also include an RF surface coil 149 for imaging different anatomical structures of a patient undergoing an MRI scan. RF body coil 148 and RF surface coil 149 may be configured to operate in transmit and receive modes, transmit mode, or receive mode.

[0046] The MRI scan subject or patient 170 can be positioned within the cylindrical imaging volume 146 of the resonance assembly 140. The transceiver 135 in the MRI system controller 130 generates RF excitation pulses amplified by the RF amplifier 162 and provides them to the RF body coil 148 via the transmit / receive switch (T / R switch) 164.

[0047] As described above, the RF body coil 148 and RF surface coil 149 can be used to transmit RF excitation pulses and / or receive resulting MR signals from a patient undergoing an MRI scan. MR signals emitted by nuclei excited within the patient during an MRI scan can be sensed and received by the RF body coil 148 or RF surface coil 149 and transmitted back to the preamplifier 166 via a T / R switch 164. The T / R switch 164 can be controlled by a signal from the sequence pulse generator 133 to electrically connect the RF amplifier 162 to the RF body coil 148 during transmit mode and to connect the preamplifier 166 to the RF body coil 148 during receive mode. The T / R switch 164 can also enable the RF surface coil 149 to be used in either transmit or receive mode.

[0048] In some implementations, the MR signal sensed and received by the RF body coil 148 or the RF surface coil 149 and amplified by the preamplifier 166 is stored in the memory 137 as a raw k-space data array for post-processing.

[0049] The reconstructed magnetic resonance image can be obtained by transforming / processing the stored raw k-space data.

[0050] In some implementations, the MR signal sensed and received by the RF body coil 148 or RF surface coil 149 and amplified by the preamplifier 166 is demodulated, filtered, and digitized in the receiving section of the transceiver 135 and transmitted to the memory 137 in the MRI system controller 130. For each image to be reconstructed, the data is rearranged into separate k-space data arrays, and each of these separate k-space data arrays is input to the array processor 139, which is operated to perform a Fourier transform on the data into an array of image data.

[0051] The array processor 139 uses a transformation method, most commonly Fourier transform, to create an image from the received MR signal. These images are transmitted to the computer system 120 and stored in the memory 126. In response to a command received from the operator workstation 110, the image data may be stored in long-term memory, or it may be further processed by the image processor 128 and transmitted to the operator workstation 110 for display on the monitor 118.

[0052] In various implementations, components of the computer system 120 and the MRI system controller 130 may be implemented on the same computer system or multiple computer systems. It should be understood that... Figure 1 The MRI system 100 shown is for illustrative purposes. Suitable MRI systems may include more, fewer, and / or different components.

[0053] The MRI system controller 130 and image processor 128 may each include a computer processor and a storage medium, either individually or jointly. The storage medium records a program for predetermined data processing to be executed by the computer processor. For example, the storage medium may store programs for performing scan processing (e.g., scan procedures, imaging sequences), image reconstruction, image processing, etc. For instance, it may store programs for implementing the magnetic resonance imaging method of the embodiments of the present invention. The storage medium may include, for example, a ROM, floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, or a non-volatile memory card.

[0054] The aforementioned "imaging sequence" refers to a combination of pulses with specific amplitude, width, direction, and timing applied during magnetic resonance imaging (MRI) scanning. These pulses typically include, for example, radio frequency (RF) pulses and gradient pulses. The RF pulses can include, for example, RF excitation pulses, RF refocusing pulses, inversion recovery pulses, etc. The gradient pulses can include, for example, the gradient pulses used for slice selection, gradient pulses used for phase encoding, gradient pulses used for frequency encoding, gradient pulses used for phase shifting (phase shifting), gradient pulses used for discrete phase (associated phase), etc.

[0055] Typically, multiple scanning sequences can be pre-set in a magnetic resonance imaging system to allow selection of sequences that meet clinical testing needs, such as imaging sites, imaging functions, and imaging effects.

[0056] For example, a magnetic resonance imaging sequence capable of simultaneously suppressing Nyquist artifacts and acceleration artifacts, as described in this embodiment of the invention, can be pre-configured. This imaging sequence may include a preparation sequence and an echo-plane imaging (EPI) sequence, wherein the preparation sequence is applied before the EPI sequence. Conventional EPI is an accelerated imaging technique in which the entire image can be formed from multiple echo signals generated after a single radio frequency (RF) excitation. In k-space, one echo is generated along each phase line of k-space. During k-space acquisition, two adjacent echoes are acquired in opposite directions, such as a forward echo and a reverse echo. Eddy currents caused by rapid gradient changes, gradient coil heating, gradient system delays, etc., can prevent the forward and reverse echoes from perfectly mirroring each other, thus introducing artifacts into the image during reconstruction. For example, a delay in the start of the first echo will propagate to all subsequent echoes, resulting in timing differences between the peaks of odd and even echoes. When a Fourier transform is performed, this phase error will cause the signal intensity to shift in half of the phase-encoded direction of the image, a phenomenon known as Nyquist ghosting. In addition, because EPI usually implements parallel imaging acceleration techniques simultaneously, parallel acceleration artifacts caused by wrapping appear in the image edge areas.

[0057] In MUSE, multi-shot EPI is used instead of traditional single-shot EPI, thus achieving higher image resolution. In multi-shot EPI, the trajectory lines acquired in k-space can be shifted sequentially. Where N is the number of times EPI is executed.

[0058] refer to Figure 2 The diagram shows a flowchart of a magnetic resonance imaging method 200 according to an exemplary embodiment.

[0059] In step 210, multiple parts of the k-space are acquired using a multi-group imaging pulse sequence to obtain multiple k-space datasets. The multi-group imaging pulse sequence may include multiple EPIs. When the multiple parts of the k-space are merged, the entire k-space is formed. For example, when a 3-group imaging pulse sequence is used, such as 3 EPIs, 1 / 3 of the entire k-space data is acquired each time.

[0060] In step 220, the multiple k-space datasets are processed to obtain magnetic resonance images.

[0061] refer to Figure 3This diagram illustrates an exemplary imaging sequence 300 to which the method 200 is applied. Each imaging sequence includes an EPI sequence 204 and a preparation sequence 202 applied prior to the EPI sequence. As an example, the preparation sequence 202 may include a SE-DWI (spin echo-diffusion weighted) sequence, for example, which may include sequentially applied radio frequency (RF) excitation pulse 212 and RF refocusing pulse 214, and a slice selection gradient (G) applied accompanying the RF excitation pulse 212 and RF refocusing pulse 214, respectively. SS Pulses 222 and 224.

[0062] Furthermore, the preparation sequence 202 may also include a diffusion gradient (G) for proton diffusion weighting. DG Diffusion-weighted imaging (DWI) can be applied to the diagnosis of tissue function in various organs (e.g., brain, cartilage, and liver) and to various applications (e.g., pathology, oncology). Diffusion refers to the random movement of molecules within a system. In biological tissues, the diffusion of water molecules follows a pattern based on tissue structure and properties. In some disease states, diffusion patterns may be disrupted, and the amount of diffusion may vary in areas affected by the disease. Therefore, abnormalities in tissues can be detected by studying changes in diffusion. DWI utilizes the diffusion of water molecules to reveal internal physiology. The contrast of diffusion-weighted images reflects differences in diffusion rates between tissues. DWI is particularly useful when conventional MRI sequences (e.g., T2-weighted imaging) do not show significant changes in the images. For example, in pathological conditions similar to stroke caused by local ischemia, signal intensity on T2 remains unchanged for at least 8 hours after stroke onset. On the other hand, DWI can show changes in the brain as early as 30 minutes after stroke onset and show significant signal differences within one hour of onset.

[0063] The diffusion gradient pulse includes a phase-shifting gradient pulse 232 and a repositioning gradient pulse 234, which are applied symmetrically on both sides (before and after) the radio frequency refocusing pulse 214.

[0064] The aforementioned radio frequency excitation pulse 212 can be, for example, a 90-degree radio frequency pulse, and the radio frequency refocusing pulse 214 can be a 180-degree radio frequency pulse, both of which can be transmitted through a transmitting coil (e.g., Figure 1 The RF excitation pulse 212 is generated by the RF body coil 148 in the embodiment. In some embodiments, the RF excitation pulse 212 itself can be selectively tuned to excite only water protons. Slice selection gradient pulses 222 and 224 and diffusion gradient pulses 232 and 234 can be generated by the gradient coil assembly (e.g., Figure 1 The gradient coil component 142 in the middle is generated.

[0065] The phase-shifting gradient pulse 232 introduces a phase shift into the proton based on its position, while the re-phase-gradient pulse 234 reverses the change made by the phase-shifting gradient pulse 232. For a fixed spin, its phase is unaffected by the diffusion gradient pulse, as any phase accumulation from the phase-shifting gradient pulse 232 is reversed by the re-phase-gradient pulse 234. However, the diffused spin moves to a different position between the phase-shifting gradient pulse 232 and the re-phase-gradient pulse 234, losing phase and signal. That is, if the proton moves, the re-phase-gradient pulse 234 cannot completely undo the phase shift caused by the phase-shifting gradient pulse 232. Therefore, signal attenuation occurs. This signal attenuation from the net motion of the proton is given by the Stejskal-Tanner equation:

[0066] S(b)=S0e -bD (1),

[0067] Where S(b) is the signal received when a specific diffusion gradient pulse pair is applied, S0 is the signal strength without any diffusion gradient, e is a constant, D is the diffusion or apparent diffusion coefficient (ADC), and b is the diffusion weighting applied to the specific diffusion gradient pulse pair. The value of b can be controlled by manipulating the intensity, duration, and spacing of the diffusion gradient pulse pairs 232 and 234.

[0068] Specifically, the value of b is given as follows:

[0069]

[0070] Where γ is the gyromagnetic ratio of hydrogen protons, a constant, G is the amplitude of the diffusion gradient pulse, δ is the duration of the diffusion gradient pulse, and Δ is the time between the application of two diffusion gradient pulses. In clinical applications, sequences are typically configured to provide multiple images with varying diffusion directions and b-values, and sometimes ADC mapping can be computed. For example, several DW (diffusion-weighted) images with different b-values ​​can be obtained by changing the configuration of the diffusion gradient pulse pairs. At higher b-values, the effect of diffusion is more pronounced in the images and in tissues with high diffusion, as shown in low-signal regions in the images, while tissues with limited diffusion are shown in high-signal regions.

[0071] Using an SE-DWI sequence as the preparation sequence is just one example of its application. In other examples, the preparation sequence 202 can be other types of sequences, such as GRE (gradient echo) sequences, SE sequences, DWI sequences, etc.

[0072] After sequence 202 is prepared, EPI sequence 204 can be executed immediately for rapid acquisition of k-space data. Rapid image acquisition minimizes the impact of overall motion on the image. EPI sequence 204 includes a pre-dephasing gradient pulse 240 and multiple phase-coded gradients (G) applied after the pre-dephasing gradient pulse 240. PE ) pulses (241, 242, 243…) and multiple frequency-coded gradients (G FE ) pulses (251, 252, 253…). Pre-dephased gradient pulse 240, multiple phase-coded gradient pulses, and multiple frequency-coded gradient pulses can be generated by gradient coils (e.g., Figure 1 The gradient coil component 142 in the middle is generated.

[0073] like Figure 3 As shown, after the pre-dephasing gradient pulse 240 ends, multiple small "spikes," i.e., the aforementioned multiple phase-coded gradient pulses, exist at each position where the frequency-coded gradient pulses reverse. These multiple phase-coded gradient pulses oscillate rapidly to generate multiple gradient echoes. The directions of these multiple frequency-coded gradient pulses reverse alternately, and the multiple phase-coded gradient pulses are applied as the directions of the multiple frequency-coded gradient pulses reverse. For example, spike 241 is applied at the beginning of the negative frequency-coded (or readout) gradient pulse 251; spike 242 is placed at the reversal point between the negative readout gradient 251 and the positive readout gradient 252; spike 243 is placed at the reversal point between the positive readout gradient 252 and the negative readout gradient 253, and so on. The spikes have a constant size, and each adds further phase coding to the previous spike.

[0074] In each imaging sequence, the phase of the corresponding multiple gradient echoes can be controlled by setting the area of ​​the pre-phase gradient 240. In the magnetic resonance imaging method of this embodiment, the areas of the pre-phase gradient pulses 240 in the multiple imaging sequences are different. Specifically, the pre-phase gradient pulses 240 in the multiple imaging sequences are ordered according to their area values ​​and have a standard area difference. This standard area difference is 2 / N of the area of ​​any phase-encoded gradient (241, 242, 243…), where N is the number of groups in the multiple imaging sequence. For example, if the area of ​​the phase-encoded gradient pulse is A3, taking a 5-group imaging sequence as an example, the standard area difference… If the area of ​​the pre-dephasing gradient pulse in the first image sequence is A1, then the areas of the pre-dephasing gradient pulses in the second to fifth image sequences are respectively...

[0075] Furthermore, in embodiments of the present invention, the execution order of the aforementioned multi-group imaging sequences can be the same as or different from the sorting according to area value. That is, the multi-group imaging sequences can be executed sequentially, with the area of ​​the pre-dephasing gradient pulse 240 gradually increasing or decreasing by a fixed value according to the execution order of the sequence; alternatively, the multi-group imaging sequences can be executed sequentially, with the area value of the pre-dephasing gradient pulse 240 not increasing or decreasing sequentially according to the execution order of the sequence. In this way, by changing the area value of the pre-dephasing gradient pulse 240 in this manner, when a large number of k-space datasets are acquired, the Nyquist artifacts and acceleration artifacts in the final image obtained from the magnetic resonance images based on these multiple k-space datasets can be better suppressed.

[0076] For example, if 5 image sequences are used, and the first image sequence is as follows: Figure 3 As shown ( Figure 3 In the image sequence 240, the pre-astigmatic gradient pulse 240 has an initial area A1 (with a standard area difference A2 indicated by a dashed line). Therefore, in the second to fifth image sequences, the areas of the pre-astigmatic gradient pulses can be A1+A2, A1+2A2, A1+3A2, A1+4A2, or A1-A2, A1-2A2, A1-3A2, A1-4A2, respectively. In the above examples, for the first image sequence, there exists a second image sequence with an area difference of A2 or -A2 between it and its pre-astigmatic gradient pulse; for the second image sequence, there exists a third image sequence with an area difference of A2 or -A2 between it and its pre-astigmatic gradient pulse, and so on. The first to fifth image sequences are not necessarily executed sequentially. For example, the execution order of the imaging sequence can be the second, fifth, first, fourth, and third image sequences, or any other combination of these sequences.

[0077] Since the area of ​​the pre-phase gradient pulse 240 affects the phase of multiple gradient echoes in the corresponding sequence, the k-space phase encoding line also shifts overall.

[0078] refer to Figure 4 ,according to Figure 2The pulse sequence illustrates an exemplary schematic of the k-space data acquisition trajectory. First, k-space dataset 411 is acquired along the lowest line in the presence of a frequency-coded gradient pulse 251. When a spike 242 is applied, k-space dataset 412 is acquired along the second lowest line in the presence of a frequency-coded gradient pulse gradient 252, and so on, acquiring more k-space datasets each time a spike 242 is applied in the presence of a frequency-coded gradient pulse gradient 252. Each spike adds a constant phase code to the previous spike, forming a regular path through k-space. The amplitude of the frequency-coded gradient pulse is typically large, allowing for rapid sampling of appropriate values ​​and enabling the entire dataset to be collected within a single free-inducible decay (FID).

[0079] Re-reference Figure 2 Multiple portions of the k-space are acquired by using multiple sets (e.g., 3 sets) of imaging sequences. In the first set of imaging sequences, the pre-dephasing gradient pulse 240 has an initial area A1. The first portion of the k-space is acquired through the first set of imaging sequences to obtain a first k-space dataset. An exemplary schematic diagram of the k-space data acquisition trajectory is shown below. Figure 4 As shown in Figure 411, the solid line represents the data acquisition trajectory of this EPI, i.e., the first part of k-space. The first dashed line 412 and the second dashed line 413 represent the k-space data not acquired in this EPI, i.e., the second and third parts of k-space. In the second imaging sequence, the standard area difference A2 (e.g., ...) is subtracted (or added) from the initial area A1 of the pre-phasing gradient pulse 240. A3 is the area of ​​peak 241), therefore, the k-space data acquisition trajectory line corresponding to this second imaging sequence is as follows: Figure 4 As shown by the first dashed line 412, the solid line 411 and the second dashed line 413 represent the k-space data not collected in this EPI. Trajectory line 412, compared to 411, is shifted downwards as a whole (in this collection). The spacing between adjacent trajectory lines is... The k-space data acquisition trajectory line corresponding to this third imaging sequence becomes Figure 4 The third dashed line 413 in the middle, where, compared to Figure 4 In section 412, the trajectory line, as a whole, moves downwards again (in this data collection). The spacing between adjacent trajectory lines...

[0080] In the existing MUSE acquisition method (e.g., the spacing between adjacent trajectory lines during each movement) When making improvements, the starting positions of trajectory lines 411 and 413 in space can be kept unchanged, while the starting position of trajectory line 412 can be shifted three small units backward relative to the starting position of trajectory line 411. This means that the spacing between adjacent trajectory lines (in this data collection) can be adjusted.

[0081] Image reconstruction and processing based on these k-space data can effectively suppress Nyquist and acceleration artifacts. An appropriate number of sequence executions and corresponding imaging sequence groups can be selected based on the artifact suppression effect.

[0082] Figure 5 A flowchart of a magnetic resonance imaging method according to another embodiment of the present invention is shown, which includes steps 210 and 520. In step 520, the multiple k-space datasets are processed based on the multiple sensitivity-encoding (MUSE) algorithm. For a detailed description of the processing of multiple scan data based on the MUSE algorithm, please refer to the reference (A robust multi-shot scan strategy for high-resolution diffusion weighted MRI enabled by multiplexedsensitivity-encoding (MUSE), authors: Nan-kuei Chen, Arnaud Guidon, Hing-Chiu Chang, Allen W. Song et al.).

[0083] Figure 6 A flowchart of a magnetic resonance imaging method according to another embodiment of the present invention is shown, which includes steps 210 and 621-613.

[0084] In step 621, the multiple k-space datasets are de-accelerated (or de-wound) to obtain multiple phase maps. In one embodiment, each k-space dataset can first be preprocessed (e.g., k-space data padding), and then de-accelerated based on a pre-defined coil sensitivity map to obtain a de-accelerated or de-wound (aliased) image. The phase map of each de-accelerated or de-wound (aliased) image is then obtained. The pre-defined coil sensitivity map may have fewer channels, such as 8 channels.

[0085] In step 622, a corrected (or new) coil sensitivity map is obtained based on the multiple phase maps. When N acquisitions are performed using the method of this embodiment of the invention to obtain N k-space datasets, the corrected coil sensitivity map can have more channels, such as N*8 channels.

[0086] In step 623, magnetic resonance images are acquired based on the corrected coil sensitivity map and multiple k-space datasets. The corrected coil sensitivity map can be used to de-accelerate or de-wind the k-space dataset of each channel acquired each time to obtain MR.

[0087] refer to Figure 7 The diagram illustrates a flowchart 700 of a magnetic resonance imaging method according to another exemplary embodiment of the present invention. This method can be implemented using an MRI system (e.g., Figure 1 The process is performed using an MRI system 100. In step 710, multiple sets of magnetic resonance imaging sequences are used to acquire multiple portions of k-space to obtain multiple k-space datasets. Each imaging sequence includes an echo-plane imaging (EPI) sequence and a preparation sequence applied before the EPI sequence. The echoes of these multiple k-space datasets have a standard phase shift when ordered by phase value. For example, these multiple k-space datasets can be compared with... Figure 3 The dataset shown is similar.

[0088] Among them, the preparation sequence can be with Figure 2 The preparation sequence shown is similar and, for example, may include a pair of diffusion gradient pulses symmetrical to the RF refocusing pulse, comprising a phase-shifting gradient pulse and a re-phase-fixing gradient pulse. The phase-shifting gradient pulse introduces a phase shift into the proton according to its position, and the re-phase-fixing gradient pulse reverses the change made by the phase-shifting gradient pulse. The phase of the fixed spin is unaffected by the diffusion gradient pulse because any phase accumulation from the phase-shifting gradient pulse is reversed by the re-phase-fixing gradient pulse. If the proton moves, the re-phase-fixing gradient pulse will not completely reverse the phase shift caused by the phase-shifting gradient pulse, and there will be signal attenuation. The diffusion weighting can be controlled by adjusting the configuration of the diffusion gradients (e.g., intensity, duration, and spacing). The preparation sequence can also have other variations; for example, sequences such as individual GRE, SE, DWI, or any combination thereof can be used as the preparation sequence.

[0089] The readout sequence following the preparation sequence can include an EPI sequence. In the EPI sequence, after the pre-dephasing gradient, there are small phase-coded gradient pulses, such as the aforementioned "spikes," at each location where the frequency-coded gradient pulses invert. These spikes have a constant size, and each adds further phase coding to the previous spike, forming regular paths in k-space. Based on k-space data acquisition, even-numbered echoes are in opposite directions to odd-numbered echoes. For example, if an odd-numbered echo (or line) is positive, then an even-numbered echo (or line) is negative, and vice versa.

[0090] Between multiple acquisitions, the odd and even echoes in one group have a standard phase offset relative to another group. In one embodiment, this standard phase offset is 2π / N, where N is the number of k-space datasets, and N can be greater than 2. Taking the above five sets of k-space data acquisitions as an example, in the first k-space dataset, the k-space data acquisition trajectory has an initial phase, while in the second k-space dataset, the trajectory as a whole shifts the spacing between the odd and even trajectory lines. That is, the phase has shifted. In the third k-space dataset, the trajectory lines are moved again as a whole, altering the spacing between the odd and even trajectory lines. The phase has shifted compared to the initial phase. Similarly, in the fourth k-space dataset, the phase shifts compared to the initial phase. In the fifth k-space dataset, the phase has shifted compared to the initial phase.

[0091] In step 720, after acquiring multiple sets of k-space data based on multiple imaging sequences, an MR image is obtained based on these multiple k-space datasets. For example, the multiple k-space datasets can be reconstructed and processed to obtain a magnetic resonance image that simultaneously suppresses parallel acceleration artifacts and Nyquist artifacts. In some embodiments, the reconstruction includes a Fourier transform from k-space to image space, as is known in the art.

[0092] Step 720 can be similar to steps 520 and 620 above, and will not be repeated here.

[0093] refer to Figure 8 According to an exemplary embodiment, an image obtained by the method disclosed herein is compared with an image obtained by a conventional multiple EPI method. Image 810 is acquired using a conventional method, in which Nyquist ghosting 812 is clearly visible. In comparison, image 820 is acquired using the method of the embodiments of the present invention, in which both Nyquist ghosting and acceleration artifacts are effectively suppressed.

[0094] An exemplary embodiment of the present invention may also provide a computer-readable storage medium comprising a stored computer program, wherein the magnetic resonance imaging method of any of the above embodiments is executed when the computer program is run.

[0095] Based on the above description, an exemplary embodiment of the present invention may also provide a magnetic resonance imaging (MRI) system, comprising:

[0096] Gradient coils are configured to generate encoded gradients;

[0097] Radio frequency (RF) coils are configured to generate RF pulses; and

[0098] A processor, connected to the gradient coil and the RF coil, is used to execute the magnetic resonance imaging method of any of the above embodiments. For example, the processor is used to instruct the gradient coil and the RF coil to generate multiple imaging sequences to acquire multiple portions of k-space to obtain multiple k-space datasets, and to process the multiple k-space datasets to obtain magnetic resonance images. Each of the multiple imaging sequences includes a pre-dephasing gradient pulse and multiple phase-encoded gradients applied after the pre-dephasing gradient pulse, wherein the pre-dephasing gradient pulses in the multiple imaging sequences have a standard area difference when ordered by area value, the standard area difference being 2 / N of the area of ​​any phase-encoded gradient, where N is the number of the multiple imaging sequences.

[0099] In addition to any modifications previously indicated, those skilled in the art can devise many other variations and alternative arrangements without departing from the spirit and scope of this description, and the appended claims are intended to cover such modifications and arrangements. Therefore, although the information has been described above in a specific and detailed manner in conjunction with what is currently considered to be the most practical and preferred aspects, it will be apparent to those skilled in the art that many modifications can be made without departing from the principles and concepts set forth herein, including but not limited to changes in form, function, mode of operation, and use. Likewise, as used herein, in all respects, examples and embodiments are intended to be illustrative only and should not be construed as restrictive in any way.

[0100] The purpose of providing the above specific embodiments is to enable a more thorough and comprehensive understanding of the disclosure of this invention, but this invention is not limited to these specific embodiments. Those skilled in the art should understand that various modifications, equivalent substitutions, and changes can be made to this invention, and all such modifications and changes should be within the scope of protection of this invention, provided they do not depart from the spirit of this invention.

Claims

1. A magnetic resonance imaging method, the magnetic resonance imaging method comprising: Multiple k-space datasets are obtained by acquiring multiple portions of k-space using multi-group imaging sequences. Each group imaging sequence includes a pre-aberration gradient pulse and multiple phase-encoded gradients applied after the pre-aberration gradient pulse. The pre-aberration gradient pulses in the multi-group imaging sequences, when ordered by their area values, have the same standard area difference, which is 2 / N of the area of ​​any phase-encoded gradient, where N is the number of groups in the multi-group imaging sequence. The multiple k-space datasets are processed to obtain magnetic resonance images.

2. The magnetic resonance imaging method of claim 1, wherein, The number of groups in the multi-group imaging sequence is greater than 2.

3. The magnetic resonance imaging method of claim 1, wherein, The steps for processing the multiple k-space datasets include: processing the multiple k-space datasets based on a multi-sensitivity coding algorithm.

4. The magnetic resonance imaging method of claim 1, wherein, The steps for processing the multiple k-space datasets include: The multiple k-space datasets are respectively processed to accelerate the solution and obtain multiple phase maps; The corrected coil sensitivity map is obtained based on the multiple phase maps; The magnetic resonance image is obtained based on the corrected coil sensitivity map and the multiple k-space datasets.

5. The magnetic resonance imaging method of claim 1, wherein, Each imaging sequence also includes a radio frequency excitation pulse, a radio frequency refocusing pulse, and a diffusion gradient pulse. The diffusion gradient pulse includes a phase-shifting gradient pulse and a re-phase-fixing gradient pulse. The phase-shifting gradient pulse and the re-phase-fixing gradient pulse are applied symmetrically before and after the radio frequency refocusing pulse, respectively. The pre-dephase gradient pulse is applied after the re-phase-fixing gradient pulse.

6. A magnetic resonance imaging method, the magnetic resonance imaging method comprising: Multiple k-space datasets are obtained by acquiring multiple portions of k-space using multiple imaging sequences. Each imaging sequence includes a pre-dephasing gradient pulse and multiple phase-encoded gradients applied after the pre-dephasing gradient pulse. The pre-dephasing gradient pulses in the multiple imaging sequences, when ordered by their area values, have the same standard area difference, which is 2 / N of the area of ​​any phase-encoded gradient, where N is the number of the multiple imaging sequences. Each imaging sequence includes an echo-plane imaging sequence and a preparation sequence applied before the echo-plane imaging sequence. The echoes from the multiple k-space datasets, when ordered by their phase values, have a standard phase shift, which is... Where N is the number of the plurality of k-space datasets; and, The multiple k-space datasets are processed to obtain magnetic resonance images.

7. The magnetic resonance imaging method according to claim 6, wherein, The number of the multiple k-space datasets is greater than 2.

8. The magnetic resonance imaging method according to claim 6, wherein, The prepared sequences include spin echo sequences, gradient echo sequences, diffusion-weighted sequences, or spin echo-diffusion-weighted sequences.

9. A computer-readable storage medium comprising a stored computer program, wherein, When the computer program is run, it performs the magnetic resonance imaging method according to any one of claims 1 to 8.

10. A magnetic resonance imaging system, comprising: Gradient coils, configured to generate encoded gradients; A radio frequency coil configured to generate radio frequency pulses; as well as A processor, connected to the gradient coil and the radio frequency coil, is configured to: The gradient coil and the radio frequency coil are instructed to generate multiple imaging sequences to acquire multiple parts of k-space and obtain multiple k-space datasets. Each imaging sequence includes a pre-dephasing gradient pulse and multiple phase-coded gradients applied after the pre-dephasing gradient pulse. The pre-dephasing gradient pulses in the multiple imaging sequences have the same standard area difference when ordered according to their area values. The standard area difference is 2 / N of the area of ​​any phase-coded gradient, where N is the number of groups in the multiple imaging sequences. as well as Magnetic resonance images are obtained based on the multiple k-space datasets.

11. The magnetic resonance imaging system according to claim 10, wherein, The echoes of the multiple k-space datasets are sorted by phase value and have a standard phase offset, which is 2π / N, where N is the number of the k-space datasets.

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