Echo time shift method, system, magnetic resonance imaging method, and storage medium

Abstract

Embodiments of the present specification provide an echo time shift method, a system, a magnetic resonance imaging method and a storage medium. The echo time shift method comprises: acquiring an original EPI sequence, the original EPI sequence comprising at least two sub-sequences, each sub-sequence being used to perform one excitation on a region of interest to generate an echo train comprising at least two echoes; each sub-sequence comprising at least two readout gradients with alternating positive and negative polarities; wherein there is a target echo time shift between echo trains generated by two adjacent excitations; acquiring a time length of the readout gradient, a number of excitations of the original EPI sequence on the region of interest, and a minimum time interval of issuing the readout gradient; determining a null time according to the time length of the readout gradient, the number of excitations of the original EPI sequence on the region of interest, the minimum time interval of issuing the readout gradient, and the target echo time shift; and adding the null time between adjacent readout gradients in each sub-sequence to generate a target EPI sequence.

Description

Technical Field

[0001] This specification relates to the field of imaging, and in particular to echo time-shift methods, systems, magnetic resonance imaging methods, and storage media. Background Technology

[0002] Echo planar imaging (EPI) is a magnetic resonance imaging technique that acquires echo signals by alternating the positive and negative polarities of the readout gradient field. The partial resonance effect of some hydrogen protons can cause phase discontinuities in the data lines spanning different polarities of the readout gradient in k-space after the echo signal acquired by EPI is filled into k-space, resulting in artifacts in the image generated based on k-space. Echo time shifting (ETS) is typically used to eliminate the partial resonance effect, where the echo time shift equals the duration of the readout gradient divided by the number of readout gradient sequences.

[0003] However, the imaging system has a minimum time interval when sending out the readout gradient, and the echo time displacement may not be an integer multiple of the minimum time interval. Simply rounding the echo time displacement to an integer multiple of the minimum time interval can lead to inconsistent echo time displacements for different sequences, and adjacent data lines in k-space may have phase steps that are not exactly equal, thus failing to completely eliminate artifacts in the image.

[0004] Therefore, it is necessary to provide an echo time-shift and / or magnetic resonance imaging scheme to eliminate artifacts caused by the off-resonance effect in planar echo imaging techniques. Summary of the Invention

[0005] This specification provides one or more embodiments of an echo time-shifting method, the method comprising: acquiring an original EPI sequence, the original EPI sequence comprising at least two subsequences, each subsequence being used to excite a region of interest once to generate an echo chain comprising at least two echoes; each subsequence comprising at least two readout gradients with alternating positive and negative polarities; wherein a target echo time shift exists between echo chains generated by adjacent excitations; acquiring the duration of the readout gradients, the number of times the original EPI sequence excites the region of interest, and the minimum time interval for sending the readout gradients; determining a null time based on the duration of the readout gradients, the number of times the original EPI sequence excites the region of interest, the minimum time interval for sending the readout gradients, and the target echo time shift; and adding a null time between adjacent readout gradients in each subsequence to generate a target EPI sequence.

[0006] This specification provides one or more embodiments of an echo time displacement method, the method comprising: in a target EPI sequence, based on space time, the echo time difference between a first echo and a second echo is equal to the target echo time displacement; wherein, the first echo is the echo generated in the last excitation of the target EPI sequence, the second echo is the echo generated in the first excitation of the target EPI sequence, and the first echo and the second echo correspond to adjacent positions in the echo chain.

[0007] This specification provides one or more embodiments of an echo time-shifting method, the method comprising: determining an original echo time-shift based on the duration of the readout gradient and the number of times the original EPI sequence excites the region of interest; determining whether the original echo time-shift is an integer multiple of the minimum time interval for sending the readout gradient; and, in response to the original echo time-shift not being an integer multiple of the minimum time interval for sending the readout gradient, determining a spacetime based on the number of times the original EPI sequence excites the region of interest and a target echo time-shift. The target echo time-shift is an integer multiple of the minimum time interval for sending the readout gradient and is greater than the original echo time-shift.

[0008] This specification provides one or more embodiments of a magnetic resonance imaging method, the method comprising: acquiring imaging data of a region of interest based on an EPI sequence; wherein the EPI sequence includes at least two subsequences, each subsequence exciting the region of interest once to generate an echo train including at least two echoes; each subsequence includes at least two readout gradients with alternating positive and negative polarities; there is a target echo time shift between echo trains generated by adjacent excitations; there is a spacetime between adjacent readout gradients in each subsequence; and an image of the region of interest is generated based on the imaging data.

[0009] This specification provides one or more embodiments of a magnetic resonance imaging method, the method comprising: determining the space time based on the duration of the readout gradient, the number of times the EPI sequence excites the region of interest, the minimum time interval for sending the readout gradient, and the target echo time displacement.

[0010] This specification provides one or more embodiments of a magnetic resonance imaging method, the method comprising: the target echo time displacement being an integer multiple of the minimum time interval for sending the readout gradient, and greater than the original echo time displacement; the original echo time displacement being determined based on the duration of the readout gradient and the number of times the original EPI sequence excites the region of interest, and the original echo time displacement being not an integer multiple of the minimum time interval for sending the readout gradient.

[0011] This specification provides one or more embodiments of a magnetic resonance imaging method, the method comprising: based on space time, the echo time difference between a first echo and a second echo is equal to the target echo time displacement; wherein, the first echo is the echo generated in the last excitation of the EPI sequence, the second echo is the echo generated in the first excitation of the EPI sequence, and the first echo and the second echo correspond to adjacent positions in the echo chain.

[0012] This specification provides one or more embodiments of an echo time-shifting system, the system comprising: a raw EPI sequence acquisition module for acquiring a raw EPI sequence, the raw EPI sequence comprising at least two subsequences, each subsequence being used to excite a region of interest once to generate an echo chain comprising at least two echoes; each subsequence comprising at least two readout gradients with alternating positive and negative polarities; wherein a target echo time shift exists between echo chains generated by adjacent excitations; a data acquisition module for acquiring the duration of the readout gradients, the number of times the raw EPI sequence excites the region of interest, and the minimum time interval for sending the readout gradients; a spacetime determination module for determining spacetime based on the duration of the readout gradients, the number of times the raw EPI sequence excites the region of interest, the minimum time interval for sending the readout gradients, and the target echo time shift; and a target EPI sequence acquisition module for adding spacetime between adjacent readout gradients in each subsequence to generate a target EPI sequence.

[0013] This specification provides one or more embodiments of a computer-readable storage medium that stores computer instructions. When a computer reads the computer instructions from the storage medium, the computer executes an echo time shift method. Attached Figure Description

[0014] This specification will be further described by way of exemplary embodiments, which will be described in detail with reference to the accompanying drawings. These embodiments are not limiting; in these embodiments, the same reference numerals denote the same structures, wherein:

[0015] Figure 1 These are schematic diagrams illustrating application scenarios of magnetic resonance imaging systems according to some embodiments of this specification;

[0016] Figure 2 This is an exemplary block diagram of magnetic resonance imaging according to some embodiments of this specification;

[0017] Figure 3 This is an exemplary flowchart of magnetic resonance imaging according to some embodiments of this specification;

[0018] Figure 4 This is an exemplary flowchart illustrating the generation of a target EPI sequence according to some embodiments of this specification;

[0019] Figure 5 This is a schematic diagram of a segmented, staggered acquisition k-space filling method according to some embodiments of this specification;

[0020] Figure 6A This is a schematic diagram of an EPI sequence without ETS according to some embodiments of this specification;

[0021] Figure 6B As shown in some embodiments of this specification, and Figure 6A A schematic diagram of the phase change along the ky direction in the k-space corresponding to the EPI sequence at kx=0;

[0022] Figure 6C This is a schematic diagram of the original EPI sequence according to some embodiments of this specification;

[0023] Figure 6D This is a schematic diagram of the phase change along the ky direction in the k-space corresponding to the original EPI sequence at kx = 0, according to some embodiments of this specification;

[0024] Figure 7A This is a schematic diagram of a target EPI sequence according to some embodiments of this specification;

[0025] Figure 7B This is a schematic diagram illustrating the phase change along the ky direction in the k-space corresponding to the target EPI sequence at kx = 0, according to some embodiments of this specification.

[0026] Figure 8A and Figure 8B These are schematic diagrams of magnetic resonance images generated based on the original EPI sequence and magnetic resonance images generated based on the target EPI sequence, according to some embodiments of this specification. Detailed Implementation

[0027] To more clearly illustrate the technical solutions of the embodiments in this specification, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some examples or embodiments of this specification. For those skilled in the art, these drawings can be applied to other similar scenarios without creative effort. Unless obvious from the context or otherwise specified, the same reference numerals in the drawings represent the same structures or operations.

[0028] It should be understood that the terms “system,” “device,” “unit,” and / or “module” used herein are one way to distinguish different components, elements, parts, sections, or assemblies at different levels. However, if other terms can achieve the same purpose, they may be replaced by other expressions.

[0029] As indicated in this specification and claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" do not specifically refer to the singular and may also include the plural. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of expressly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0030] Flowcharts are used in this specification to illustrate the operations performed by the system according to embodiments of this specification. It should be understood that the preceding or following operations are not necessarily performed in exact order. Instead, the steps can be processed in reverse order or simultaneously. Furthermore, other operations can be added to these processes, or one or more steps can be removed from them.

[0031] Figure 1 This is a schematic diagram illustrating application scenarios of a magnetic resonance imaging system according to some embodiments of this specification.

[0032] In some embodiments, such as Figure 1 As shown, the magnetic resonance imaging system 100 may include an imaging device 110, a processing device 120, a terminal device 130, a network 140, and a storage device 150. The components of the magnetic resonance imaging system 100 may be connected in one or more ways. This is merely an example. Figure 1 As shown, imaging device 110 can be connected to processing device 120 via network 140. Alternatively, imaging device 110 can be directly connected to processing device 120 (as indicated by the dashed double-headed arrow connecting imaging device 110 and processing device 120). As a further example, storage device 150 can be connected to processing device 120 directly or via network 140. As a further example, terminal device 130 can be directly (as indicated by the dashed double-headed arrow connecting terminal device 130 and processing device 120) and / or via network 140 to processing device 120.

[0033] Imaging device 110 can use an imaging sequence to excite the scanned object and / or acquire the echo signal of the scanned object. In some embodiments, the scanned object may include, but is not limited to, the human body, organs, organisms, damaged sites, tumors, objects, phantoms, etc. In some embodiments, the imaging sequence may include a combination of radio frequency pulses and gradient pulses applied in a certain time sequence. In some embodiments, imaging device 110 may include a magnetic resonance imaging device.

[0034] Processing device 120 can process data and / or information acquired from imaging device 110, terminal device 130, and / or storage device 150. For example, processing device 120 can acquire echo signals from imaging device. As another example, processing device 120 can acquire imaging data based on echo signals. Yet another example, processing device 120 can generate an image based on imaging data of a region of interest. In some embodiments, processing device 120 may include a central processing unit (CPU), digital signal processor (DSP), system-on-a-chip (SoC), microcontroller unit (MCU), and / or any combination thereof. In some embodiments, processing device 120 may include a computer, user console, a single server, or a group of servers. The server group may be centralized or distributed. In some embodiments, processing device 120 may be local or remote. For example, processing device 120 may access information and / or data stored in imaging device 110, terminal device 130, and / or storage device 150 via network 140. For example, processing device 120 can directly connect to imaging device 110, terminal device 130, and / or storage device 150 to access stored information and / or data. In some embodiments, processing device 120 can be implemented on a cloud platform. By way of example only, cloud platforms can include private clouds, public clouds, hybrid clouds, community clouds, distributed clouds, inter-cloud, multi-cloud, etc., or any combination thereof. In some embodiments, processing device 120 or a portion thereof can be integrated into imaging device 110.

[0035] Terminal device 130 can display images to a user. Terminal device 130 may include mobile device 131, tablet computer 132, laptop computer 133, etc., or any combination thereof. In some embodiments, terminal device 130 may be part of processing device 120.

[0036] Network 140 may include any suitable network that facilitates the exchange of information and / or data between the magnetic resonance imaging system 100 and the system. In some embodiments, one or more components of the magnetic resonance imaging system 100 (e.g., imaging device 110, processing device 120, terminal device 130, storage device 150) may communicate information and / or data with one or more other components of the magnetic resonance imaging system 100 via network 140. In some embodiments, network 140 may be and / or include public networks, private networks, wide area networks (WANs), wired networks, wireless networks, cellular networks, frame relay networks, virtual private networks, satellite networks, telephone networks, routers, hubs, switches, and any combination thereof. In some embodiments, network 140 may include one or more network access points. For example, network 140 may include wired and / or wireless network access points such as base stations and / or internet switching points, through which one or more components of the magnetic resonance imaging system 100 may connect to network 140 to exchange data and / or information.

[0037] Storage device 150 can store data, instructions, and / or any other information. In some embodiments, storage device 150 can store data acquired from imaging device 110, terminal device 130, and / or processing device 120. In some embodiments, storage device 150 may include mass storage, removable storage, volatile read-write memory, read-only memory (ROM), and any combination thereof. In some embodiments, storage device 150 may be executed on a cloud platform. In some embodiments, storage device 150 may be connected to network 140 to communicate with one or more other components of magnetic resonance imaging system 100 (e.g., imaging device 110, processing device 120, terminal device 130). One or more components of magnetic resonance imaging system 100 may access data or instructions stored in storage device 150 via network 140. In some embodiments, storage device 150 may be directly connected to or communicate with one or more other components of magnetic resonance imaging system 100 (e.g., imaging device 110, processing device 120, storage device 150, terminal device 130). In some embodiments, storage device 150 may be part of processing device 120.

[0038] It should be noted that the above description is provided for illustrative purposes only and is not intended to limit the scope of this specification. Various changes and modifications can be made by those skilled in the art based on the content of this specification. Features, structures, methods, and other features of the exemplary embodiments described herein can be combined in various ways to obtain other and / or alternative exemplary embodiments. However, these changes and modifications will not depart from the scope of this specification.

[0039] Figure 2These are exemplary block diagrams of a magnetic resonance imaging system according to some embodiments of this specification. Figure 2 As shown, the magnetic resonance imaging system 200 may include an imaging data acquisition module 210 and an image generation module 220.

[0040] The imaging data acquisition module 210 can be used to acquire imaging data of a region of interest based on an EPI sequence. In some embodiments, the EPI sequence may include at least two sub-sequences. In some embodiments, each sub-sequence may excite the region of interest once, generating an echo chain including at least two echoes. In some embodiments, each sub-sequence may include at least two readout gradients with alternating positive and negative polarities. In some embodiments, a target echo time shift may exist between echo chains generated by adjacent excitations. In some embodiments, a space time may exist between adjacent readout gradients in each sub-sequence. In some embodiments, the space time may be determined based on the duration of the readout gradient, the number of times the EPI sequence excites the region of interest, the minimum time interval for sending the readout gradient, and the target echo time shift. In some embodiments, the target echo time shift may be an integer multiple of the minimum time interval for sending the readout gradient and greater than the original echo time shift. In some embodiments, the original echo time shift may be determined based on the duration of the readout gradient and the number of times the original EPI sequence excites the region of interest. The original echo time shift may not be an integer multiple of the minimum time interval for sending the readout gradient. In some embodiments, based on space time, the echo time difference between the first echo and the second echo can be equal to the target echo time displacement. The first echo can be the echo generated in the last excitation of the EPI sequence, and the second echo can be the echo generated in the first excitation of the EPI sequence. The first and second echoes can correspond to adjacent positions in the echo chain, respectively. A detailed description of the imaging data acquisition module 210 can be found in the relevant description of step 310, and will not be repeated here.

[0041] The image generation module 220 can be used to generate an image of the region of interest based on the imaging data. A detailed description of the image generation module 220 can be found in the relevant description of step 320, and will not be repeated here.

[0042] In some embodiments, the magnetic resonance imaging system 200 may further include a raw EPI sequence acquisition module 230, a data acquisition module 240, a spacetime determination module 250, and a target EPI sequence acquisition module 260. In some embodiments, the raw EPI sequence acquisition module 230, the data acquisition module 240, the spacetime determination module 250, and the target EPI sequence acquisition module 260 may be sub-modules of the imaging data acquisition module 210.

[0043] The original EPI sequence acquisition module 230 can be used to acquire the original EPI sequence. In some embodiments, the original EPI sequence may include at least two subsequences. In some embodiments, each subsequence can be used to excite the region of interest once to generate an echo chain including at least two echoes. In some embodiments, each subsequence may include at least two readout gradients with alternating positive and negative polarities. A target echo time shift may exist between the echo chains generated by two adjacent excitations. A detailed description of the original EPI sequence acquisition module 230 can be found in the relevant description of step 410, and will not be repeated here.

[0044] The data acquisition module 240 can be used to acquire the duration of the readout gradient, the number of times the original EPI sequence excites the region of interest, and the minimum time interval for sending the readout gradient. A detailed description of the data acquisition module 240 can be found in the relevant description of step 420, and will not be repeated here.

[0045] The empty time determination module 250 can be used to determine the empty time based on the duration of the readout gradient, the number of times the original EPI sequence excites the region of interest, the minimum time interval for sending the readout gradient, and the target echo time displacement. In some embodiments, the empty time determination module 250 can perform one or more of the following operations: determine the original echo time displacement based on the duration of the readout gradient and the number of times the original EPI sequence excites the region of interest; determine whether the original echo time displacement is an integer multiple of the minimum time interval for sending the readout gradient; in response to the original echo time displacement not being an integer multiple of the minimum time interval for sending the readout gradient, determine the empty time based on the number of times the original EPI sequence excites the region of interest and the target echo time displacement. In some embodiments, the target echo time displacement can be an integer multiple of the minimum time interval for sending the readout gradient and is greater than the original echo time displacement. For a detailed description of the empty time determination module 250, please refer to the relevant description of step 430, which will not be repeated here.

[0046] The target EPI sequence acquisition module 260 can be used to add a time interval between adjacent readout gradients in each subsequence to generate a target EPI sequence. In some embodiments, based on the time interval, the echo time difference between the first echo and the second echo in the target EPI sequence can be equal to the target echo time displacement. The first echo can be the echo generated in the last excitation of the target EPI sequence, and the second echo can be the echo generated in the first excitation of the target EPI sequence. The first echo and the second echo can correspond to adjacent positions in the echo chain, respectively. A detailed description of the target EPI sequence acquisition module 260 can be found in the relevant description of step 440, and will not be repeated here.

[0047] Figure 3This is an exemplary flowchart of a magnetic resonance imaging method according to some embodiments of this specification. In some embodiments, process 300 may be executed by processing device 120 or magnetic resonance imaging system 200. For example, process 300 may be stored in a storage device (e.g., storage device 150, system storage unit) in the form of a program or instructions, and process 300 may be implemented when processing device 120 or magnetic resonance imaging system 200 executes the instructions. The operational schematic diagram of process 300 presented below is illustrative. In some embodiments, the process may be accomplished using one or more additional operations not described and / or one or more operations not discussed. Additionally, Figure 3 The order of operations shown in the diagram and described below in process 300 is not restrictive.

[0048] Step 310: Based on the EPI sequence, acquire imaging data of the region of interest. Specifically, step 310 can be performed by the imaging data acquisition module 210.

[0049] The region of interest can be a specific part of the scanned object. For example, the scanned object can be patient A, and the region of interest can be patient A's heart.

[0050] EPI (Echo Planar Imaging) sequences are sequences of echoes acquired by alternating the positive and negative polarities of the readout gradient field.

[0051] In some embodiments, the EPI sequence may include at least two subsequences. Each subsequence is used to excite the region of interest once, generating an echo train comprising at least two echoes. In some embodiments, each subsequence may include at least two readout gradients with alternating positive and negative polarities. A detailed description of the readout gradients can be found in the relevant description of step 410, and will not be repeated here.

[0052] In some embodiments, the EPI sequence incorporates the echo time shifting (ETS) method. In some embodiments, there may be a time difference between the readout gradients of adjacent subsequences, equal to the target echo time shift; there may also be a target echo time shift between echo chains generated by two adjacent excitations. For example, there may be a time difference between readout gradients at the same position in adjacent subsequences, equal to the target echo time shift; and there may be a target echo time shift between echoes at the same position in echo chains generated by adjacent excitations.

[0053] In some embodiments, there may be a time gap between adjacent readout gradients in each subsequence.

[0054] Empty time can be the blank interval time between two adjacent readout gradients.

[0055] In some embodiments, the empty time can be determined based on the duration of the readout gradient, the number of times the EPI sequence excites the region of interest, the minimum time interval for sending the readout gradient, and the target echo time displacement.

[0056] The readout gradient duration can be the duration of a readout gradient. The number of times the EPI sequence excites the region of interest can be equal to the number of subsequences in the EPI sequence. The minimum time interval for sending readout gradients can be the time interval between two adjacent readout gradients when the imaging system sends readout gradients at its fastest speed. For a detailed description of the readout gradient duration, the number of times the EPI sequence excites the region of interest, and the minimum time interval for sending readout gradients, please refer to the relevant description in step 420, which will not be repeated here.

[0057] In some embodiments, the original echo time offset can be determined based on the duration of the readout gradient and the number of times the region of interest is excited by the original EPI sequence. The original echo time offset can be an integer multiple of the minimum time interval for sending the readout gradient. For a detailed description of determining the original echo time offset, please refer to the relevant description in step 430, which will not be repeated here.

[0058] In some embodiments, the target echo time displacement can be an integer multiple of the minimum time interval for sending the readout gradient, and greater than the original echo time displacement. A detailed description of the target echo time displacement can be found in the relevant description of step 410, and will not be repeated here.

[0059] In some embodiments, the imaging data acquisition module 210 can determine the empty time based on the number of excitations and the target echo time displacement. For example, the empty time can be obtained by subtracting the original echo time displacement from the target echo time displacement and then multiplying the difference by the number of excitations. Alternatively, the empty time can be obtained by multiplying the target echo time displacement by the number of excitations and then subtracting the readout gradient duration from the product. A detailed description of determining the empty time can be found in the relevant description of step 430, and will not be repeated here.

[0060] The EPI sequence in step 310 can be based on Figure 4 The method for generating the target EPI sequence is determined and will not be elaborated here.

[0061] Imaging data of the region of interest can be k-space data of the region of interest.

[0062] In some embodiments, the imaging data acquisition module 210 may use an imaging device to acquire imaging data of the region of interest.

[0063] Specifically, in some embodiments, the imaging device can use an EPI sequence to excite the region of interest to generate an echo signal, and then fill the k-space with the echo signal to generate imaging data (k-space data). In some embodiments, the echo signal can be filled into the k-space in a segmented interleaved acquisition manner. A detailed description of the segmented interleaved acquisition method can be found in [link to relevant documentation]. Figure 5 The relevant descriptions will not be repeated here.

[0064] In some embodiments, the first readout gradient can be the readout gradient in the subsequence corresponding to the last excitation in the EPI sequence, and the second readout gradient can be the readout gradient in the subsequence corresponding to the first excitation in the EPI sequence. The first and second readout gradients can correspond to adjacent positions in the subsequences, respectively. Due to the existence of space time, the time difference between the first and second readout gradients can be equal to the target echo time displacement; the first echo can be the echo generated in the last excitation in the EPI sequence, and the second echo can be the echo generated in the first excitation in the EPI sequence. In some embodiments, the first and second echoes can correspond to adjacent positions in the echo chain, respectively. In some embodiments, based on space time, the echo time difference between the first and second echoes can be equal to the target echo time displacement. For a detailed description of the first and second echoes, please refer to the relevant description in step 440, which will not be repeated here.

[0065] Step 320: Generate an image of the region of interest based on the imaging data. Specifically, step 320 can be performed by the image generation module 220.

[0066] The image of the region of interest (ROI) can be a magnetic resonance imaging (MRI) image of the ROI. In some embodiments, the image format of the ROI may include, but is not limited to, Joint Photographic Experts Group (JPEG) format, Tagged Image File Format (TIFF) format, Graphics Interchange Format (GIF) format, KodakFlash PiX (FPX) format, Digital Imaging and Communications in Medicine (DICOM) format, etc. In some embodiments, the image of the ROI may include 2D images, 3D images, 4D images, etc.

[0067] In some embodiments, the image determination module 220 can reconstruct and generate an image of the region of interest based on the imaging data of the region of interest acquired by the imaging device.

[0068] In some embodiments of this specification, an echo signal can be generated by exciting the region of interest based on the EPI sequence after adding space time, and the echo signal can be filled into the k space, so that the phase of the data line corresponding to the echo signal in the k space changes continuously and smoothly, thereby eliminating the artifacts caused by the off-resonance effect in the image generated based on the k space.

[0069] In some embodiments, phase correction can be performed on the imaging data acquired by the EPI sequence to eliminate the influence of eddy currents on the signal in positive and negative gradient acquisition, and image reconstruction can be performed based on the corrected imaging data to obtain the final image.

[0070] It should be noted that the above description of process 300 is provided for illustrative purposes only and is not intended to limit the scope of this specification. Various changes and modifications can be made by those skilled in the art based on the description herein. However, these changes and modifications do not depart from the scope of this specification. In some embodiments, process 300 may include one or more additional operations, or one or more of the aforementioned operations may be omitted.

[0071] Figure 4 This is an exemplary flowchart illustrating the generation of a target EPI sequence according to some embodiments of this specification. In some embodiments, process 400 may be executed by processing device 120 or magnetic resonance imaging system 200. For example, process 400 may be stored in a storage device (e.g., storage device 150, system storage unit) in the form of a program or instructions, and process 400 may be implemented when processing device 120 or magnetic resonance imaging system 200 executes the instructions. The operational schematic diagram of process 400 presented below is illustrative. In some embodiments, the process may be accomplished using one or more additional operations not described and / or one or more operations not discussed. Additionally, Figure 4 The order of operations of process 400 shown and described below is not limiting. In some embodiments, process 400 may be executed by target projection value determination module 230. Process 400 may generate a target EPI sequence using an echo time-shifting method.

[0072] Step 410: Obtain the raw EPI sequence. Specifically, step 410 can be performed by the imaging data acquisition module 210 and / or the raw EPI sequence acquisition module 230.

[0073] In some embodiments, the original EPI sequence may include at least two subsequences.

[0074] As an example, Figure 6C This is a schematic diagram of the original EPI sequence according to some embodiments of this specification. For example... Figure 6CAs shown, the original EPI sequence may include four subsequences, such as subsequence 1, subsequence 2, subsequence 3 and subsequence 4.

[0075] In some embodiments, there is no empty time between adjacent readout gradients in each subsequence of the original EPI sequence. In some embodiments, the original EPI sequence may incorporate the echo time shifting (ETS) method. For example, readout gradients at the same position in adjacent subsequences have a time difference equal to the original echo time shift or the target echo time shift; echoes at the same position in echo chains generated by adjacent excitations have an original echo time shift or a target echo time shift.

[0076] In some embodiments, each subsequence may include at least two readout gradients with alternating positive and negative polarities. The readout gradient, or frequency-encoded gradient, may be a magnetic field gradient that marks the corresponding spatial location by causing different voxel magnetization vectors to precess at different frequencies.

[0077] by Figure 6C For example, the readout gradients included in subsequence 1 are as follows: positive readout gradient 631 (represented by a black trapezoid), negative readout gradient 635 (represented by a dark gray trapezoid), positive readout gradient 636 (represented by a light gray trapezoid)...

[0078] In some embodiments, each subsequence can be used to excite the region of interest once, generating an echo chain comprising at least two echoes. The echo chain can consist of at least two echoes generated after the region of interest is excited.

[0079] Figure 6D This is a schematic diagram illustrating the phase change along the ky direction in the k-space corresponding to the original EPI sequence 600-3 at kx = 0, according to some embodiments of this specification. Figure 6C and Figure 6D For example, subsequences 1-4 can excite the region of interest respectively to generate echo chain 1 (including echoes 1a, 1b, 1c), echo chain 2 (including echoes 2a, 2b, 2c), echo chain 3 (including echoes 3a, 3b, 3c) and echo chain 4 (including echoes 4a, 4b, 4c).

[0080] In some embodiments, each echo in each echo chain may correspond to a readout gradient in a subsequence corresponding to that echo chain.

[0081] For example, with Figure 6C and Figure 6DFor example, echoes 1a, 1b, 1c... in echo chain 1 can correspond to the positive readout gradient 631 (represented by a black trapezoid), the negative readout gradient 635 (represented by a dark gray trapezoid), the positive readout gradient 636 (represented by a light gray trapezoid)... in subsequence 1, respectively.

[0082] In some embodiments, echo signals can be filled into the k-space in a segmented, interleaved acquisition manner to acquire imaging data. For example, the k-space can be divided into multiple partitions, with echoes from the same echo chain filling different partitions of the k-space, and echoes from the same position in different echo chains filling the same partition of the k-space. The number of partitions can be equal to the number of echoes in the echo chain.

[0083] Figure 5 This is a schematic diagram illustrating the segmented, staggered acquisition k-space filling method according to some embodiments of this specification. For example... Figure 5 As shown, the horizontal axis Kx and the vertical axis Ky in k-space can represent the phase encoding direction and the frequency encoding direction, respectively. As an example, echoes 1a-1c, 2a-2c, 3a-3c, and 4a-4c generated using the EPI sequence 600-3 can be filled into k-space using a segmented, interleaved acquisition method. For example... Figure 5 As shown, the k-space can be divided into three partitions 501-503. Echoes from the same echo chain fill different partitions of the k-space, while echoes from the same position in different echo chains (echoes generated in the same order within the echo chain) fill the same partition of the k-space. For example, the three echoes 1a-1c in echo chain 1 are filled into segments 501-503 respectively. As another example, echoes 1a, 2a, 3a, and 4a from echo chains 1-3 are filled into segment 501; echoes 1b, 2b, 3b, and 4b from echo chains 1-3 are filled into segment 502; and echoes 1c, 2c, 3c, and 4c from echo chains 1-3 are filled into segment 503.

[0084] In some embodiments, the echo time difference between two echoes can be equal to the time difference of the corresponding readout gradients. For example, as... Figure 6C As shown, the time difference between readout gradient 631 and readout gradient 635 is the duration T of the readout gradient. Therefore, the time difference between the echoes 1a and 1b corresponding to readout gradient 631 and readout gradient 635, respectively, is equal to T. For example, as... Figure 6C As shown, the time differences between reading out gradient 631 and reading out gradients 632, 633, and 634 are t, respectively. m 2t m 3t m Then the echo time differences between echo 1a corresponding to readout gradient 631 and echoes 2a, 3a, and 4a corresponding to readout gradients 632, 633, and 634, respectively, are equal to t. m 2tm 3t m For example, such as Figure 6C As shown, the time difference between reading out gradient 634 and reading out gradient 635 is t. c Then the echo time difference between the echoes 4a and 1b corresponding to the readout gradient 634 and readout gradient 635, respectively, is equal to t. c .

[0085] In the EPI sequence, a series of readout gradients with alternating positive and negative polarities are used to generate echo signals. Due to the fact that the precession frequency of some hydrogen protons deviates from the resonance frequency in actual acquisition (off resonance effect), there will be phase discontinuity, or phase step, when crossing the data line of the echo signal acquired with gradients of different polarities along kx=0 in k space, which will produce artifacts in the image.

[0086] In some embodiments, the phase θ1 of the echo generated by an EPI sequence excited without ETS can be represented by formula (1). θ1=2πΔfT[j-(N-1) / 2]+2πΔfTs s (±k ro (1) Where Δf is the frequency shift of the protons in the partial resonance; N is the number of echoes excited by the EPI sequence; j is the echo ordinal number, taking an integer value between 0 and N-1; T s k is the sampling duration of a single echo signal. ro It is the normalized spatial frequency of the readout direction, with a value range of [-1, 1], where k is the frequency from the beginning to the end of the readout sampling phase. ro The transition from 1 to -1 occurs at the readout center, which is also the echo center position, k ro =0.

[0087] As an example, Figure 6A This is a schematic diagram of an EPI sequence 600-1 without ETS, as shown in some embodiments of this specification. Figure 6B As shown in some embodiments of this specification, and Figure 6A A schematic diagram of the phase change along the ky direction in k-space at kx = 0 for the EPI sequence 600-1. Figure 6A and Figure 6BAs shown, the readout gradients at the same position in each subsequence of EPI sequence 600-1 (readout gradients of the same color in sequence 600-1) have no time shift. The echo times of echoes 1a”-4a” (acquired through the readout gradients of the positive electrode represented by black trapezoids in each subsequence of sequence 600-1) generated by EPI sequence 600-1 are equal, the echo times of echoes 1b”-4b” (acquired through the readout gradients of the negative electrode represented by dark gray trapezoids in each subsequence of sequence 600-1) are equal, and the echo times of echoes 1c”-4c” (acquired through the readout gradients of the positive electrode represented by light gray trapezoids in each subsequence of sequence 600-1) are equal. There is a time difference between the echo times of echoes 1a”-4a”, 1b”-4b”, and 1c”-4c”, which is equal to the duration of the readout gradient. Therefore, if echoes 1a”-4a”, 1b”-4b”, and 1c”-4c” are acquired in a segmented, interleaved manner (for example, such as...) Figure 5 As shown, fill the k space, such as Figure 6B As shown, in k-space, the data lines in the same partition have the same phase, but the data lines in adjacent partitions may have phase discontinuities or phase steps.

[0088] Therefore, the Echo Time Shifting (ETS) method can be incorporated into EPI sequences. This involves adding a time shift between the readout gradients of adjacent subsequences (a time difference exists between readout gradients at the same position in adjacent subsequences), resulting in an echo time shift between echo chains generated by two adjacent excitations (an echo time difference exists between echoes at the same position in echo chains generated by two adjacent excitations). This ensures that each data line in k-space receives a smooth, linear, and equally spaced phase step along the kx=0 direction, suppressing image artifacts caused by off-resonance effects due to factors such as inhomogeneous main magnetic fields, fat chemical shifts, and differences in magnetic susceptibility of tissues or interfaces. For example, the time shift added to the readout gradient can be equal to the duration of the readout gradient divided by the total number of excitations in the segmented interleaved acquisition (the original echo time shift). However, this value is often not an integer multiple of the minimum gradient downswing time interval allowed by the hardware. If this value is rounded to an integer multiple of the minimum time interval (target echo time shift), it will result in an overall inconsistent echo time shift, that is, there are not precisely equal phase steps in adjacent data lines in k-space, so artifacts will still be produced in the image.

[0089] In some embodiments, the phase θ2 of the echo generated by the original EPI sequence can be represented by formula (2). θ2=2πΔfT(Nk PE / 2)+2πΔfT s (±k ro (2) Where Δf is the frequency shift of the protons in the partial resonance; N is the number of echoes excited by the EPI sequence; j is the echo ordinal number, taking an integer value between 0 and N-1; T s k is the sampling duration of a single echo signal. ro It is the normalized spatial frequency of the readout direction, with a value range of [-1, 1], where k is the frequency from the beginning to the end of the readout sampling phase. ro The transition from 1 to -1 occurs at the readout center, which is also the echo center position, k ro =0;k PE The spatial frequency of the normalized phase coding direction, with a value range of [-1, 1].

[0090] Figure 6C This is a schematic diagram of the original EPI sequence 600-3 as shown in some embodiments of this specification. Figure 6D This is a schematic diagram illustrating the phase change along the ky direction in the k-space corresponding to the original EPI sequence 600-3 at kx = 0, according to some embodiments of this specification. Figure 6C As shown, the readout gradients at the same position in each subsequence of EPI sequence 600-3 exhibit target echo time displacement t. m For example, in readout gradients 631-634, there is a target echo time displacement t between two adjacent readout gradients. m As an example, dividing the gradient readout duration T = 210 μs by the number of excitations N = 4 yields the original echo time displacement t. y =T / N = 210 / 4 = 52.5 μs. If the minimum time interval Δt for the system hardware to read the gradient is 10 μs, the target echo time displacement can be set to t. m = 60μs. In this case, the time shift between two adjacent readout gradients 631-634 is 60μs, but the time shift between readout gradients 634 and 635 is t. c =30μs. That is to say, there is an equal target echo time displacement between the echo chains generated by two adjacent excitations (there is an equal echo time difference between the echoes at the same position in the echo chains generated by two adjacent excitations), so that the phase of the corresponding data line in the k space filled by the segmented staggered acquisition method gradually changes along the kx=0 direction, but there is still a phase step at the position of switching between different partitions in the k space.

[0091] For example, such as Figure 6D As shown, echoes 1a-4a, 1b-4b, and 1c-4c correspond to the same positions in the echo chain and are filled into the same partition of the k-space. The time displacement of two adjacent echoes at the same position is t. mHowever, the time displacement between echoes 4a and 1b, and between echoes 4b and 1c, is t. c ≠t m Therefore, although there are smooth, linear, and equally spaced phase changes between data lines within the same partition of k-space, phase steps still exist at the transition points between different partitions in k-space. For example, ... Figure 6D As shown, the phase difference between the data lines corresponding to echoes 4a and 1b, and the phase difference between the data lines corresponding to echoes 4b and 1c, are not equal to the phase difference between the data lines corresponding to echoes 1a and 2a.

[0092] In some embodiments, the original EPI sequence may include an EPI sequence incorporating an ETS method, for example, an EPI sequence in which the readout gradients at the same position in the subsequence have time displacements (e.g., original echo time displacement or target echo time displacement), for example... Figure 6C The EPI sequence shown is 600-3. In some embodiments, the time interval between two adjacent readout gradients in the same subsequence of the original EPI sequence is not included.

[0093] In some embodiments, raw EPI sequences can be obtained from the storage device (e.g., storage device 150) of the magnetic resonance imaging system 200. In some embodiments, users (e.g., doctors, engineers, technicians, etc.) can design sequences through an operating interface (e.g., the operating interface of processing device 120 or terminal device 130) to obtain raw EPI sequences. For example, users can determine the number of subsequences and the number of readout gradients in each subsequence, and calculate the shape and duration of the readout gradients based on basic sequence parameters such as bandwidth and field of view (FOV), thereby obtaining an EPI sequence in which the readout gradients at the same position in the subsequences have no time shift (EPI sequence without ETS), for example, Figure 6A The EPI sequence shown is 600-1. Users can further divide the readout gradient duration by the total number of excitations (the number of subsequences) to obtain the original echo time shift, and determine if the original echo time shift is an integer multiple of the minimum allowable transmission time interval. If it is an integer multiple, the original echo time shift is added to the readout gradients of adjacent subsequences to directly obtain the target EPI sequence. If it is not an integer multiple, the original echo time shift is rounded to an integer multiple of the minimum time interval to obtain the target echo time shift, and then the target echo time shift is added to the readout gradients of adjacent subsequences. For example, for... Figure 6A For the EPI sequence 600-1, using subsequence 1 as a reference, the readout gradients of subsequences 2-4 are shifted by t as a whole. m 2t m 3t m ,get Figure 6CThe original EPI sequence 600-3. Alternatively, it can be obtained directly from a storage device. Figure 6A The EPI sequence 600-1 is obtained, and then an echo time shift is added to the readout gradient of the EPI sequence 600-1 on the operation interface to obtain... Figure 6C The original EPI sequence 600-3.

[0094] Step 420 involves acquiring the readout gradient duration, the number of times the original EPI sequence excites the region of interest, and the minimum time interval for sending the readout gradient. Specifically, step 420 can be performed by the imaging data acquisition module 210 and / or the data acquisition module 240.

[0095] The duration of a readout gradient can be the duration of a readout gradient. In some embodiments, the duration of each readout gradient for each subsequence in the original EPI sequence can be equal. For example, the duration of each readout gradient is 210 μs.

[0096] like Figure 6C As shown, the duration of the readout gradient in subsequence 1 can be the duration T of the readout gradient 631 of the first positive electrode (represented by a black trapezoid), for example, 210 μs. Further, the durations of the readout gradients 635 (represented by a dark gray trapezoid) of the second negative electrode, 636 (represented by a light gray trapezoid) of the third positive electrode, ... in subsequence 1 are all T. Similarly, the durations of the readout gradients of the first positive electrode, the second negative electrode, the third positive electrode, ... in subsequence 2 are all T = 210 μs; the durations of the readout gradients of the first positive electrode, the second negative electrode, the third positive electrode, ... in subsequence 3 are all T = 210 μs.

[0097] In some embodiments, the data acquisition module 240 can calculate the duration of the readout gradient based on parameters such as receiver bandwidth and field of view (FOV).

[0098] In some embodiments, the difference between adjacent echo times in the same echo chain can be equal to the duration of the readout gradient.

[0099] For example, such as Figure 6DAs shown, in echo chain 1, the difference between the time of the first echo 1a and the time of the second echo 1b is equal to the gradient readout duration T = 210 μs. Furthermore, the difference between the time of the second echo 1b and the time of the third echo 1c in echo chain 1 is also equal to the gradient readout duration T = 210 μs. Similarly, in echo chain 2, the differences between the times of the first echo 2a, the second echo 2b, and the third echo 2c are all equal to the gradient readout duration T = 210 μs; and in echo chain 3, the differences between the times of the first echo 3a, the second echo 3b, and the third echo 3c are all equal to the gradient readout duration T = 210 μs.

[0100] The minimum time interval for sending readout gradients can be the time interval between two adjacent readout gradients when the imaging system sends readout gradients at its fastest speed. For example, if the imaging system sends a readout gradient every 10 μs at its fastest speed, then the time interval between two adjacent readout gradients is 10 μs, that is, the minimum time interval for sending readout gradients is Δt = 10 μs.

[0101] In some embodiments, the data acquisition module 240 can obtain the minimum time interval for sending readout gradients from the set of hardware performance parameters of the imaging system.

[0102] As mentioned above, each subsequence can be used to excite the region of interest once. Therefore, in some embodiments, the number of excitations can be equal to the number of subsequences in the original EPI sequence. For example... Figure 6C As shown, the original sequence includes 4 subsequences, and the number of excitations N is 4.

[0103] Step 430: Based on the readout gradient duration, the number of times the original EPI sequence excites the region of interest, the minimum time interval for issuing the readout gradient, and the target echo time displacement, the empty time is determined. Specifically, step 430 can be executed by the imaging data acquisition module 210 and / or the empty time determination module 250.

[0104] In some embodiments, the empty time determination module 250 can determine the original echo time displacement based on the duration of the readout gradient and the number of times the original EPI sequence excites the region of interest. Specifically, the original echo time displacement can be obtained by dividing the duration of the readout gradient by the number of excitations.

[0105] For example, dividing the gradient readout time T = 210 μs by the number of excitations N = 4 yields the original echo time displacement t. y =T / N=210 / 4=52.5μs.

[0106] In some embodiments, the empty time determination module 250 can determine whether the original echo time displacement is an integer multiple of the minimum time interval for sending the readout gradient.

[0107] Continuing with the example above, using the original echo time displacement t y =52.5μs divided by the minimum time interval Δt = 10μs for sending the gradient, we get a non-integer 5.25. Therefore, we can determine that the original echo time displacement T is not an integer multiple of the minimum time interval Δt for sending the gradient.

[0108] In some embodiments, the empty time determination module 250 may determine the empty time based on the target echo time displacement and the original echo time displacement in response to the original echo time displacement not being an integer multiple of the minimum time interval for sending the readout gradient.

[0109] In some embodiments, the target echo time displacement can be an integer multiple of the minimum time interval for sending the readout gradient, and greater than the original echo time displacement.

[0110] Continuing with the example above, the target echo time displacement t m The minimum time interval for sending the readout gradient can be an integer multiple of Δt = 10 μs, and greater than the original echo time displacement ty = 52.5 μs. For example, the target echo time displacement t m It can be 60μs, 70μs, 80μs...

[0111] Empty time can be the blank interval time between two adjacent readout gradients.

[0112] In some embodiments, the empty time determination module 250 can determine the empty time based on the number of excitations and the target echo time displacement. For example, the empty time can be obtained by subtracting the original echo time displacement from the target echo time displacement and then multiplying the difference by the number of excitations. Alternatively, the empty time can be obtained by multiplying the target echo time displacement by the number of excitations and then subtracting the readout gradient duration from the product.

[0113] Continuing with the example above, the target echo time displacement t can be used. m =60μs minus the original echo time shift ty = 52.5μs, and then multiply the difference by the number of excitations to obtain the space time t. k = (60-52.5)×4 = 30μs. Alternatively, the empty time t can be obtained by multiplying the target echo time displacement by the number of excitations, and then subtracting the readout gradient duration from the product (e.g., the modification time T' of the readout gradient) from the readout gradient duration. k =60×4-210=30μs.

[0114] In some embodiments of this specification, the target echo time displacement is determined based on the minimum time interval of the downlink readout gradient and the original echo time displacement. On the one hand, this ensures that the target echo time displacement is an integer multiple of the minimum time interval of the downlink readout gradient, thereby ensuring the consistency of the target echo time displacement among the entire echo signal. On the other hand, it ensures that the target EPI sequence corresponding to the target echo time displacement can be determined based on the original EPI sequence.

[0115] Step 440 involves adding idle time between adjacent readout gradients in each subsequence to generate the target EPI sequence. Specifically, step 440 can be performed by the imaging data acquisition module 210 and / or the target EPI sequence acquisition module 260.

[0116] The target EPI sequence can be an EPI sequence that makes the echo phase change smoothly.

[0117] Figure 7A This is a schematic diagram of an exemplary target EPI sequence according to some embodiments of this specification. For example... Figure 7A As shown, an empty time t can be added between the first readout gradient (black readout gradient) and the second readout gradient (dark gray readout gradient) of subsequence 1 in the original EPI sequence (e.g., EPI sequence 600-3). k An empty time t is added between the second readout gradient (dark gray readout gradient) and the third readout gradient (light gray readout gradient) of subsequence 1. k Similarly, empty time t can be added between the first and second readout gradients of subsequences 2, 3, and 4, and between the second and third readout gradients, etc., in the original EPI sequence. k Thus, the target EPI sequence 700 is obtained.

[0118] In some embodiments of this specification, the empty time is determined based on the target echo time displacement, and then the empty time is added to the original EPI sequence to obtain the target EPI sequence, which can ensure the phase continuity of the echo signal generated by the excitation of the target EPI sequence.

[0119] The target EPI sequence 700 can excite the region of interest to generate echo chain 1 (including echoes 1a', 1b', 1c'), echo chain 2 (including echoes 2a', 2b', 2c'), echo chain 3 (including echoes 3a', 3b', 3c'), and echo chain 4 (including echoes 4a', 4b', 4c').

[0120] The first readout gradient can be the readout gradient in the subsequence corresponding to the last excitation in the target EPI sequence, and the second readout gradient can be the readout gradient in the subsequence corresponding to the first excitation in the target EPI sequence. The first and second readout gradients can correspond to adjacent positions in the subsequence. For example, the first and second readout gradients can be readout gradients 701 and 702, or readout gradients 703 and 704, respectively.

[0121] The first echo can be the echo generated during the last excitation of the target EPI sequence. Figure 7B This is a schematic diagram illustrating the phase change along the ky direction in the k-space corresponding to the target EPI sequence 700 at kx = 0, according to some embodiments of this specification. Figure 7B As shown, the first echo may include echoes 4a' and 4b' generated during the last excitation. The second echo may be an echo generated during the first excitation of the target EPI sequence. In some embodiments, the first and second echoes may correspond to adjacent positions in the echo chain. Continuing with the above example, as... Figure 7B As shown, the first and second echoes can be echoes 4a' and 1b', or echoes 4b' and 1c'.

[0122] It is understandable that after adding empty time, in the target EPI sequence, the time difference between the first readout gradient and the second readout gradient is equal to the time difference between the readout gradients at the same position in adjacent subsequences. This makes the echo time difference between the first echo and the second echo equal to the echo time difference at the same position in adjacent echo chains. If the echoes are filled into the k-space in a segmented alternating acquisition manner, the phase difference between adjacent data lines located in different partitions in the k-space is equal to the phase difference between adjacent data lines in the same partition. This achieves a precise equal phase difference between adjacent data lines in the k-space, eliminates or weakens the phase step of data lines in the k-space, and achieves a smooth and linear change in the phase of the data lines in the k-space as a whole.

[0123] like Figure 7A and 7B As shown, the readout gradients at the same position in each subsequence of the target EPI sequence 700 exhibit target echo time displacement t. m For example, the readout gradients 705 and 706 show a target echo time displacement t. m The first and second readout gradients of the target EPI sequence 700 also exhibit target echo time displacement t. m For example, the readout gradients 701 and 702 show a target echo time displacement t. m As an example, dividing the gradient readout duration T = 210 μs by the number of excitations N = 4 yields the original echo time displacement t. y=T / N = 210 / 4 = 52.5 μs. If the minimum time interval Δt for the system hardware to read the gradient is 10 μs, the target echo time displacement can be set to t. m = 60μs, empty time t k = 30μs. In this case, the time shift for reading gradients 705 and 706 is 60μs, and the time shift between reading gradients 701 and 702 is also t. m =60μs. That is to say, if the echoes are filled into the k-space in a segmented, alternating acquisition manner, such as... Figure 7B As shown, echoes 1a'-4a', 1b'-4b', and 1c'-4'c correspond to the same positions in the echo chain, filling the same partition in k-space. The time displacement of two adjacent echoes at the same position is t. m The time displacement between echoes 4a and 1b, and between echoes 4b and 1c, is also t. m Therefore, the phase difference between adjacent data lines located in different partitions in k-space is equal to the phase difference between adjacent data lines in the same partition, thus achieving a precise equal phase difference between adjacent data lines in k-space. This eliminates or reduces the phase step of data lines in k-space and achieves a smooth and linear phase change for the data lines in k-space as a whole.

[0124] Figure 8A and Figure 8B These are schematic diagrams illustrating magnetic resonance images generated based on the original EPI sequence and magnetic resonance images generated based on the target EPI sequence, according to some embodiments of this specification. Figure 8A As shown, magnetic resonance images generated from the original EPI sequence without added space time exhibit stripe artifacts caused by phase steps; as... Figure 8B As shown, in the magnetic resonance images generated based on the target EPI sequence with added space time, the stripe artifacts have been reduced or essentially eliminated.

[0125] In some embodiments of this specification, the target EPI sequence can ensure that the echo time difference between the first echo and the second echo is equal to the time difference between any two adjacent echoes excited by the same subsequence, thereby ensuring that the target echo time displacement between any two adjacent echoes is not affected by the minimum time interval of the readout gradient and remains consistent overall.

[0126] In some embodiments of this specification, a space-time target EPI sequence is added to the original EPI sequence, so that the target echo time displacement between echoes excited based on the target EPI sequence can be kept consistent, thereby ensuring that the target echo time displacement can eliminate the artifacts caused by the off-resonance effect.

[0127] In some embodiments, the empty time determination module 250 may directly use the original EPI sequence as the target EPI sequence in response to the original echo time displacement being an integer multiple of the minimum time interval for sending the readout gradient. In some embodiments, the step of determining whether the original echo time displacement is an integer multiple of the minimum time interval for sending the readout gradient may also be omitted.

[0128] It is understood that the echo time-shifting method based on adding space time in this application is not limited to EPI sequences, but can also be applied to other imaging sequences with EPI acquisition modes. For example, the Gradient Spin Echo (GRASE) sequence is a combination of Echo Plane Imaging (EPI) and Fast Spin Echo (FSE). Due to its EPI acquisition mode, the ETS method can also be applied to GRASE. Therefore, space time can be added to the GRASE sequence according to the echo time-shifting method of this application to eliminate artifacts caused by the off-resonance phase step due to the discreteness of the timing. Furthermore, imaging data of the region of interest can be acquired based on the GRASE sequence with added space time, and magnetic resonance images of the region of interest can be generated based on the imaging data.

[0129] The beneficial effects that the embodiments of this specification may bring include, but are not limited to: (1) determining the empty time based on the target echo time displacement and the original echo time displacement, and then adding the empty time to the original EPI sequence to obtain the target EPI sequence, so that the target EPI sequence can ensure that the echo time difference between the first echo and the second echo is equal to the time difference between any two adjacent echoes excited by the same subsequence, thereby ensuring that the target echo time displacement between any two adjacent echoes is not affected by the minimum time interval of the downlink readout gradient, and remains consistent overall, so as to ensure that the target echo time displacement can eliminate the artifacts generated by the off-resonance effect; (2) based on the downlink readout The minimum time interval of the gradient and the original echo time displacement determine the target echo time displacement. On the one hand, it can ensure that the target echo time displacement is an integer multiple of the minimum time interval of the gradient readout, thereby ensuring the consistency of the target echo time displacement among the entire echo signal. On the other hand, it can ensure that the target EPI sequence corresponding to the target echo time displacement can be determined based on the original EPI sequence. (3) Based on the EPI sequence after adding the empty time, the region of interest is excited to generate an echo signal, and the echo signal is filled into the k space, so that the phase of the data line corresponding to the echo signal in the k space is continuous, thereby eliminating the artifacts caused by the partial resonance effect in the image generated based on the k space.

[0130] The basic concepts have been described above. Obviously, for those skilled in the art, the detailed disclosure above is merely illustrative and does not constitute a limitation of this specification. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements, and corrections to this specification. Such modifications, improvements, and corrections are suggested in this specification and therefore remain within the spirit and scope of the exemplary embodiments described herein.

[0131] Furthermore, this specification uses specific terms to describe embodiments thereof. For example, "an embodiment," "one embodiment," and / or "some embodiments" refer to a particular feature, structure, or characteristic associated with at least one embodiment of this specification. Therefore, it should be emphasized and noted that references to "an embodiment," "one embodiment," or "an alternative embodiment" in different locations throughout this specification do not necessarily refer to the same embodiment. Moreover, certain features, structures, or characteristics in one or more embodiments of this specification can be appropriately combined.

[0132] Furthermore, unless expressly stated in the claims, the order of processing elements and sequences, the use of numbers and letters, or other names described in this specification are not intended to limit the order of the processes and methods described herein. Although various examples have been discussed in the foregoing disclosure of some embodiments of the invention that are currently considered useful, it should be understood that such details are for illustrative purposes only, and the appended claims are not limited to the disclosed embodiments; rather, the claims are intended to cover all modifications and equivalent combinations that conform to the spirit and scope of the embodiments described herein. For example, while the system components described above can be implemented using hardware devices, they can also be implemented solely using software solutions, such as installing the described system on existing servers or mobile devices.

[0133] Similarly, it should be noted that, in order to simplify the description disclosed herein and thus aid in the understanding of one or more embodiments of the invention, the foregoing description of embodiments in this specification may sometimes combine multiple features into a single embodiment, drawing, or description thereof. However, this method of disclosure does not imply that the subject matter of this specification requires more features than those mentioned in the claims. In fact, the embodiments contain fewer features than all the features of a single embodiment disclosed above.

[0134] In some embodiments, numbers describing the quantity of components and attributes are used. It should be understood that such numbers used in the description of embodiments are modified in some examples with the terms "approximately," "approximately," or "generally." Unless otherwise stated, "approximately," "approximately," or "generally" indicates that the numbers are allowed to vary by ±20%. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximate values, which may be changed depending on the characteristics required by individual embodiments. In some embodiments, numerical parameters should take into account specified significant digits and employ a general method of digit reservation. Although the numerical ranges and parameters used to confirm their breadth of range in some embodiments of this specification are approximate values, in specific embodiments, such values ​​are set as precisely as feasible.

[0135] For each patent, patent application, patent application publication, and other material, such as articles, books, specifications, publications, and documents, referenced in this specification, the entire contents of which are incorporated herein by reference. This excludes historical application documents that are inconsistent with or conflict with the content of this specification, as well as documents that limit the broadest scope of the claims in this specification (currently or subsequently appended to this specification). It should be noted that in the event of any inconsistency or conflict between the descriptions, definitions, and / or terminology used in the supplementary materials to this specification and the content of this specification, the descriptions, definitions, and / or terminology used in this specification shall prevail.

[0136] Finally, it should be understood that the embodiments described in this specification are merely illustrative of the principles of the embodiments described herein. Other variations may also fall within the scope of this specification. Therefore, alternative configurations of the embodiments described herein are intended to be illustrative rather than limiting, and should be considered consistent with the teachings of this specification. Accordingly, the embodiments described herein are not limited to those explicitly introduced and described herein.

Claims

1. An echo time-shifting method, characterized in that, include: Obtain the original EPI sequence, which includes at least two subsequences. Each subsequence is used to excite the region of interest once to generate an echo chain including at least two echoes. Each subsequence includes at least two readout gradients with alternating positive and negative polarities. There is a target echo time shift between the echo chains generated by two adjacent excitations. The duration of the readout gradient, the number of times the original EPI sequence excites the region of interest, and the minimum time interval for sending the readout gradient are obtained. The empty time is determined based on the duration of the readout gradient, the number of times the original EPI sequence excites the region of interest, the minimum time interval for sending the readout gradient, and the target echo time displacement; The empty time is added between adjacent readout gradients in each of the subsequences to generate the target EPI sequence; The step of determining the empty time based on the duration of the readout gradient, the number of times the original EPI sequence excites the region of interest, the minimum time interval for sending the readout gradient, and the target echo time displacement includes: The original echo time shift is determined based on the duration of the readout gradient and the number of times the original EPI sequence excites the region of interest. Determine whether the original echo time displacement is an integer multiple of the minimum time interval for sending the readout gradient; In response to the fact that the original echo time displacement is not an integer multiple of the minimum time interval for sending the readout gradient, the empty time is determined based on the number of times the original EPI sequence excites the region of interest and the target echo time displacement.

2. The method as described in claim 1, characterized in that, The target echo time displacement is an integer multiple of the minimum time interval for sending the readout gradient, and is greater than the original echo time displacement.

3. The method as described in claim 1, characterized in that, In the target EPI sequence, based on the empty time, the echo time difference between the first echo and the second echo is equal to the target echo time displacement; wherein, the first echo is the echo generated in the last excitation of the target EPI sequence, the second echo is the echo generated in the first excitation of the target EPI sequence, and the first echo and the second echo correspond to adjacent positions in the echo chain.

4. A magnetic resonance imaging method, characterized in that, include: Imaging data of the region of interest is obtained based on the EPI sequence; among which... The EPI sequence includes at least two subsequences, each of which excites the region of interest once to generate an echo train including at least two echoes; Each subsequence includes at least two readout gradients with alternating positive and negative polarities; There is a target echo time shift between the echo chains generated by adjacent excitations; There is a space time between adjacent readout gradients in each of the subsequences; wherein the space time is determined in the following manner: The original echo time shift is determined based on the duration of the readout gradient and the number of times the original EPI sequence excites the region of interest. Determine whether the original echo time displacement is an integer multiple of the minimum time interval for sending the readout gradient; In response to the fact that the original echo time displacement is not an integer multiple of the minimum time interval for sending the readout gradient, the empty time is determined based on the number of times the original EPI sequence excites the region of interest and the target echo time displacement; An image of the region of interest is generated based on the imaging data.

5. The method as described in claim 4, characterized in that, The target echo time displacement is an integer multiple of the minimum time interval of the downlink readout gradient, and is greater than the original echo time displacement.

6. The method as described in claim 4, characterized in that, Based on the empty time, the echo time difference between the first echo and the second echo is equal to the target echo time displacement; wherein, the first echo is the echo generated in the last excitation of the EPI sequence, the second echo is the echo generated in the first excitation of the EPI sequence, and the first echo and the second echo correspond to adjacent positions in the echo chain.

7. An echo time-displacement system, characterized in that, include: The original EPI sequence acquisition module is used to acquire the original EPI sequence, which includes at least two sub-sequences. Each sub-sequence is used to excite the region of interest once to generate an echo chain including at least two echoes. Each sub-sequence includes at least two readout gradients with alternating positive and negative polarities. There is a target echo time shift between the echo chains generated by two adjacent excitations. The data acquisition module is used to acquire the duration of the readout gradient, the number of times the original EPI sequence excites the region of interest, and the minimum time interval for sending the readout gradient. The empty time determination module is used to determine the empty time based on the duration of the readout gradient, the number of times the original EPI sequence excites the region of interest, the minimum time interval for sending the readout gradient, and the target echo time displacement, including: The original echo time shift is determined based on the duration of the readout gradient and the number of times the original EPI sequence excites the region of interest. Determine whether the original echo time displacement is an integer multiple of the minimum time interval for sending the readout gradient; In response to the fact that the original echo time displacement is not an integer multiple of the minimum time interval for sending the readout gradient, the empty time is determined based on the number of times the original EPI sequence excites the region of interest and the target echo time displacement; The target EPI sequence acquisition module is used to add the empty time between adjacent readout gradients in each of the sub-sequences to generate the target EPI sequence.

8. A computer-readable storage medium storing computer instructions that, when read by a computer, execute the magnetic resonance imaging method as described in any one of claims 4 to 6.

Images