CN114895228A

CN114895228A - Magnetic resonance imaging method, device, equipment and medium based on multi-segment simultaneous excitation

Info

Publication number: CN114895228A
Application number: CN202210749504.8A
Authority: CN
Inventors: 郭华; 刘思敏; 张洁莹
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2022-06-28
Filing date: 2022-06-28
Publication date: 2022-08-12

Abstract

The application relates to the technical field of image processing, in particular to a magnetic resonance imaging method, a device, equipment and a medium based on multi-segment simultaneous excitation, which comprises the following steps: using a plurality of sections which are added with parallel imaging gradient control aliasing to simultaneously excite an imaging sequence, and acquiring multi-channel k-space data; establishing a four-dimensional k-space signal model, dividing gradient codes in the layer direction corresponding to the sequence diagram into intra-segment codes and inter-segment codes, and forming the data into four-dimensional k-space signals; and correcting interference phases generated by the intra-segment codes and the inter-segment codes on the four-dimensional k-space signals by sharing the same physical z-axis, and performing image reconstruction based on the interference phases to generate a magnetic resonance imaging result of the target object. Therefore, the method and the device can apply the blipided-CAIPI technology, eliminate phase interference of the same physical z axis shared by intra-segment and inter-segment codes, are suitable for simultaneous excitation of a plurality of three-dimensional thick segments, acquisition of EPI imaging signals and image reconstruction of any form and contrast, and improve acquisition efficiency and image signal to noise ratio.

Description

Magnetic resonance imaging method, device, equipment and medium based on multi-section simultaneous excitation

Technical Field

The present application relates to the field of image processing technologies, and in particular, to a magnetic resonance imaging method, apparatus, device, and medium based on multi-segment simultaneous excitation.

Background

MRI (magnetic resonance imaging) is a non-ionizing radiation-free, non-invasive medical imaging technique, has excellent soft tissue contrast, and is an important means in clinical examination and neuroscience research. For EPI (echo-planar imaging), the acquisition mode of magnetic resonance imaging includes two-dimensional acquisition and three-dimensional acquisition: the traditional two-dimensional acquisition mode has high efficiency, but the SNR (signal-to-noise ratio) is limited; the three-dimensional acquisition mode can achieve higher spatial resolution or SNR, but the acquisition time is too long. Therefore, a series of two-dimensional/three-dimensional hybrid acquisition modes are proposed in succession. The SMS (multiple simultaneous excitation) technique performs acquisition by simultaneously exciting multiple layers, and the number of simultaneously excited layers is measured using MB (multi-band) factor. 3D multi-slab imaging divides a slice-direction imaging field of view into a plurality of three-dimensional thick segments to be excited one by one (MB ═ 1), and uses phase encoding in the slice direction for each thick segment to reconstruct a different slice in the segment. SMSlab (simultaneous multi-slice, multi-slice simultaneous excitation) imaging is an acquisition technique that combines three-dimensional multi-slice imaging and multi-slice simultaneous excitation, i.e. MB > 1. The phase encoding for reconstructing the different slices in each segment is referred to as intra-segment encoding, and the phase encoding for simultaneously excited inter-segment images is referred to as inter-segment encoding.

In two-dimensional multilayer simultaneous excitation imaging, parallel blanking-CAIPI (parallel imaging gradient control in parallel imaging) technology is used, imaging field offset of different degrees in the phase coding direction can be introduced into each layer of image excited simultaneously, so that coil sensitivity information is fully utilized, and signal-to-noise ratio loss related to coil sensitivity geometric arrangement is reduced. However, in the SMSlab imaging, the challenge of applying the bliped-CAIPI technique to the SMSlab imaging is that both intra-segment encoding and inter-segment encoding require the use of gradient axes in the layer direction, while in actual imaging there is only one physical z-axis, which needs to be shared by both. However, sharing a physical z-axis causes the intra-segment coding and the inter-segment coding to interfere with each other and not to be coded independently from each other, requiring special measures to deal with the signal acquisition in this case.

Disclosure of Invention

The application provides a magnetic resonance imaging method, a magnetic resonance imaging device, electronic equipment and a storage medium based on multi-segment simultaneous excitation, which can eliminate phase interference that intra-segment coding and inter-segment coding dimensions share the same physical z axis, so that a blippod-CAIPI acceleration technology can be applied to multi-segment simultaneous excitation imaging, the acquisition efficiency and the image signal to noise ratio are improved, and the scanning quality is improved; the method is suitable for simultaneous excitation of a plurality of three-dimensional thick sections, EPI imaging signal acquisition and image reconstruction with any contrast and any form, and has a wide application range.

The embodiment of the first aspect of the present application provides a magnetic resonance imaging method based on multiple simultaneous excitation segments, which includes the following steps: step S101: using a plurality of sections added with a parallel imaging gradient control aliasing function to simultaneously excite an imaging sequence, and carrying out data acquisition to obtain multi-channel k-space data; step S102: establishing a four-dimensional k-space signal model, dividing gradient codes in the layer direction corresponding to the sequence diagram into intra-segment codes and inter-segment codes, and forming four-dimensional k-space signals by the acquired k-space data; step S103: and correcting the interference phase generated by the intra-segment codes and the inter-segment codes sharing the same physical z axis on the four-dimensional k space signals, and performing image reconstruction based on the corrected four-dimensional k space signals to generate a magnetic resonance imaging result of the target to be imaged.

Optionally, the method is suitable for planar echo imaging with any contrast and simultaneously excited by a plurality of three-dimensional thick segments in any form, and the step S101 specifically includes: applying a kz encoding gradient along a slice direction for intra-segment encoding, the kz gradient having an area size of:

A _z ＝n _kz ·2π/(γ·FOV _z )，

wherein n is _kz Is k _z The coding number, gamma is the gyromagnetic ratio constant, FOV _z Is the thickness of each segment; and applying alternating polarity k in the layer direction during EPI readout _m Gradients are used for inter-segment coding, said k _m The gradient area size is:

A _blip ＝2π/(γ·Δz _m ·R _m )，

wherein gamma is a gyromagnetic ratio constant, and delta z _m For the centre distance of adjacent segments excited simultaneously, R _m The number of segments excited simultaneously; and/or for diffusion weighted imaging at said each k _z In the process of coding, navigation echo is collected to obtain k each time _z Phase information of the excitation.

Optionally, the four-dimensional k-space signal model pre-established in step S102 is:

wherein n is _m ∈[0,R _m -1]Number n of the image field in the inter-segment encoding direction _km ∈[0,R _m -1]For the sequence number, n, of the four-dimensional k-space in the inter-segment coding direction _z ∈[0,N _z -1]Number of encoding directions within a segment for an image field, n _kz ∈[-N _z /2,N _z /2-1]For the four-dimensional k-space, s (n) is the number of the encoding directions within a segment _km ,n _kz ) For the nth coding dimension along the segment in said four-dimensional k-space _km Coding along the n-th coding dimension _kz An encoded signal, mu (n) _m ,n _z ) For n th of simultaneous excitation _m N in the section _z Signal of layer, k _x 、k _y 、k _m And k _z Representing four dimensions of the four-dimensional k-space, wherein k _m And k _z Representing inter-segment and intra-segment encoding dimensions, respectively, x, y, m and z representing four dimensions of the image domain;

is k _z The phase of the intersegment interference caused by the gradient,

is k _m Gradient induced intra-segment interference phase.

Optionally, correcting the interference phase generated by the intra-segment encoding and the inter-segment encoding sharing the same physical z-axis on the four-dimensional k-space signal in step S103 includes: for k _z Phase of gradient-induced inter-segment interference

Applying phase compensation to RF pulses in a multi-segment simultaneous excitation sequence to cancel

Or the four-dimensional k-space signal edge k is subjected to a preset reconstruction algorithm _m Performing one-dimensional inverse Fourier transform on the dimension, and correcting a linear phase after Fourier transform, or performing cyclic shift in an image domain; for k _m Phase of gradient-induced linear disturbance within a segment

For four-dimensional k-space signal edges k when belonging to the non-diffusion weighted data type _z Performing one-dimensional inverse Fourier transform on the dimensions, and performing Fourier transform on each k _m Correction of coded signals from different layer positions, respectively

Or when the data belongs to the diffusion weighted data type, the data are corrected sequentially or simultaneously through a preset reconstruction algorithm

And different k _z Phase differences between excitations due to motion; when applied to diffusion weighted imaging, for different k _z Removing phase difference caused by inconsistent motion between excitations according to the navigation echo; when the actual position of the excitation section corresponding to the reference layer is not at the physical z-axis gradient center position during multi-section simultaneous excitation imaging, calculating the relative position of the reference layer and the physical z-axis gradient center according to the actual position, and correcting the relative position at k _z And k _m Off-center phase error induced by the gradient.

The second aspect of the present application provides a magnetic resonance imaging apparatus based on multiple simultaneous excitation segments, including: the acquisition module is used for simultaneously exciting an imaging sequence through a plurality of sections with the function of parallel imaging gradient control aliasing, and acquiring data to obtain multi-channel k-space data; the modeling module is used for establishing a four-dimensional k-space signal model, dividing gradient codes in the layer direction corresponding to the sequence diagram into intra-segment codes and inter-segment codes, and forming the acquired k-space data into four-dimensional k-space signals; and the reconstruction module is used for correcting the interference phase generated by the intra-segment codes and the inter-segment codes sharing the same physical z axis on the four-dimensional k space signals, carrying out image reconstruction based on the corrected four-dimensional k space signals and generating a magnetic resonance imaging result of the target to be imaged.

Optionally, the method is suitable for any-contrast, any-form planar echo imaging with multiple three-dimensional thick segments simultaneously excited, and the acquisition module is further used for: applying a kz encoding gradient along a slice direction for intra-segment encoding, the kz gradient having an area size of:

A _z ＝n _kz ·2π/(γ·FOV _z )，

wherein n is _kz Coding serial number for kz, gamma is gyromagnetic ratio constant, FOV _z Is the thickness of each segment; and during EPI readout, applying a km gradient of alternating polarity along the layer direction for inter-segment encoding, the km gradient having an area size of:

A _blip ＝2π/(γ·Δz _m ·R _m )，

wherein gamma is a gyromagnetic ratio constant, and delta z _m For the centre distance of adjacent segments excited simultaneously, R _m The number of segments excited simultaneously; and/or acquiring navigation echoes during each kz encoding to obtain phase information of each kz excitation when the method is used for diffusion weighted imaging.

Optionally, the four-dimensional k-space signal model pre-established by the modeling module is:

wherein n is _m ∈[0,R _m -1]Number n of the image field in the inter-segment encoding direction _km ∈[0,R _m -1]For the sequence number, n, of the four-dimensional k-space in the inter-segment coding direction _z ∈[0,N _z -1]For encoding direction within segments for image domainNumber, n _kz ∈[-N _z /2,N _z /2-1]For the four-dimensional k-space, s (n) is the number of the encoding directions within a segment _km ,n _kz ) For the nth coding dimension along the inter-segment in four-dimensional k-space _km Coding along the n-th coding dimension _kz An encoded signal, mu (n) _m ,n _z ) For n th of simultaneous excitation _m N in the section _z Signal of layer, k _x 、k _y 、k _m And k _z Representing four dimensions of the four-dimensional k-space, wherein k _m And k _z Respectively representing intra-segment encoding dimensions and inter-segment encoding dimensions, x, y, m and z representing four dimensions of the image domain;

is k _z The phase of the intersegment interference caused by the gradient,

is k _m Gradient induced intra-segment interference phase.

Optionally, the reconstruction module is further configured to: for k _z Phase of gradient-induced inter-segment interference

An embodiment of a third aspect of the present application provides an electronic device, including: a memory, a processor and a computer program stored on the memory and executable on the processor, the processor executing the program to realize the magnetic resonance imaging method based on multiple simultaneous excitation segments as described in the above embodiments.

A fourth aspect of the present application provides a computer-readable storage medium, on which a computer program is stored, where the program is executed by a processor to implement the magnetic resonance imaging method based on multiple simultaneous excitation segments as described in the foregoing embodiments.

Therefore, the application has at least the following beneficial effects:

the aliasing function can be controlled by using parallel imaging gradients in multi-segment simultaneous excitation imaging, the problem of phase interference caused by sharing the same physical z axis by intra-segment coding and inter-segment coding is solved, the two coding dimensions are decoupled into two independent dimensions, the signal-to-noise ratio of an image is improved, and the scanning quality is improved; the method can be suitable for simultaneous excitation of a plurality of three-dimensional thick sections, EPI (including gradient echo EPI, spin echo EPI and other possible EPI forms) imaging signal acquisition and image reconstruction with any contrast and any form by using a blipped-CAIPI technology, and has wide application range; and the embodiment of the application also carries out special treatment aiming at the special property of diffusion imaging: acquiring navigation echo information by acquiring additional navigation echoes or adopting other forms, and performing phase correction among different excitations caused by physiological motion in reconstruction; it may also involve the use of motion compensated (1 st order or both 2 nd order) diffusion coding gradients to eliminate motion effects between different excitations.

Additional aspects and advantages of the present application will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the present application.

Drawings

The foregoing and/or additional aspects and advantages of the present application will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

fig. 1 is a flowchart of a magnetic resonance imaging method based on multiple simultaneous excitation segments according to an embodiment of the present application;

FIG. 2 is a schematic diagram of a bliped-SMSlab sequence with two segments excited simultaneously and sampling thereof according to an embodiment of the present application;

fig. 3 is a schematic diagram of an SMSlab excitation and its four-dimensional k-space provided according to an embodiment of the present application;

fig. 4 is a schematic diagram of an SMSlab excitation provided according to an embodiment of the present application and k _z And k _m A coded phase distribution;

FIG. 5 is a schematic diagram of a computer system according to an embodiment of the present application

A blipied-SMSlab non-diffusion weighted (b is 0) image result graph before and after correction;

FIG. 6 is a schematic diagram of a computer system according to an embodiment of the present application

Before and after correction, bliped-SMSlab non-diffusion weighting (b is 0) and diffusion weighting (b is 1000 s/mm) ² ) An image result graph;

FIG. 7 is a comparison graph of SMSlab image reconstruction performance of bliped-CAIPI sampling and non-CAIPI sampling provided by the embodiment of the application;

FIG. 8 is a comparison graph of diffusion imaging using blipped-SMSlab and conventional 2Dblipped-SMS provided in accordance with an embodiment of the present application;

figure 9 is an exemplary diagram of a magnetic resonance imaging apparatus providing multiple simultaneous excitation based phases according to an embodiment of the present application;

fig. 10 is a schematic structural diagram of an electronic device according to an embodiment of the present application.

Description of reference numerals:

fig. 2 shows a diagram a in sequence of blippid-SMSlab provided according to an embodiment of the present application, a diagram b in sequence of a four-dimensional k-space sampling provided according to an embodiment of the present application, and a diagram c in sequence of a four-dimensional k-space frame of existing non-CAIPI sampling provided according to an embodiment of the present application; the a and b plots in FIG. 3 show the image domain and k-space, respectively, with 4D FT representing the four-dimensional Fourier transform, and k not shown in FIG. 3 _x Dimension, each dot can represent an entire row k _x Coding; the first three columns in FIG. 8 show the anisotropy plot FA and the fourth column shows the plot ODF of the fiber orientation distribution function.

Detailed Description

Reference will now be made in detail to embodiments of the present application, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are exemplary and intended to be used for explaining the present application and should not be construed as limiting the present application.

A magnetic resonance imaging method, an apparatus, an electronic device, and a storage medium based on multi-segment simultaneous excitation according to embodiments of the present application are described below with reference to the drawings. In view of the problems mentioned in the background art, the present application provides a magnetic resonance imaging method based on multi-segment simultaneous excitation, which can eliminate the phase interference that the intra-segment encoding dimension and the inter-segment encoding dimension share the same physical z-axis, so that the parallel imaging gradient control aliasing (blipided-CAIPI) acceleration technique can be applied to multi-segment simultaneous excitation imaging, thereby improving the acquisition efficiency and the image signal-to-noise ratio, and improving the scanning quality; the method is suitable for simultaneous excitation of a plurality of three-dimensional thick sections, EPI imaging signal acquisition and image reconstruction with any contrast and any form, and has a wide application range.

Specifically, fig. 1 is a schematic flowchart of a magnetic resonance imaging method based on multiple simultaneous excitation segments according to an embodiment of the present application.

As shown in fig. 1, the magnetic resonance imaging method based on multi-segment simultaneous excitation comprises the following steps:

in step S101, a multi-segment simultaneous excitation imaging sequence added with a parallel imaging gradient control aliasing (bliped-CAIPI, SMSlab based on bliped-CAIPI) function is used to acquire data, so as to obtain multi-channel k-space data.

The sequence is suitable for planar echo imaging with any contrast and any form, wherein a plurality of three-dimensional thick sections are simultaneously excited.

It is understood that the embodiments of the present application may use the four-dimensional k-space concept in SMSlab imaging and may use a blipeped-CAIPI sampling mode under a four-dimensional k-space framework, where k is along the four-dimensional k-space _y -k _m Dimension using a blipped-CAIPI sampling pattern is shown in the b diagram of FIG. 3, and a conventional non-CAIPI sampling pattern in the four-dimensional k-space framework is shown in the c diagram of FIG. 3. The four-dimensional k-space will be described in the following embodiments, and will not be described herein again to avoid redundancy.

In this embodiment, step S101 specifically includes:

applying a kz encoding gradient along the slice direction for intra-segment encoding, the kz gradient having an area size of:

A _z ＝n _kz ·2π/(γ·FOV _z )，

wherein n is _kz Is k _z The coding number, gamma is the gyromagnetic ratio constant, FOV _z Is the thickness of each segment; and

during EPI readout, applying alternate polarity k in the layer direction _m Gradients (i.e. blipped-CAIPI gradients) for inter-segment coding, k _m The gradient area size is:

A _blip ＝2π/(γ·Δz _m ·R _m )，

wherein gamma is a gyromagnetic ratio constant, and delta z _m For the centre distance of adjacent segments excited simultaneously, R _m The number of segments excited simultaneously; and/or

For diffusion weighted imaging, at each k _z In the process of coding, navigation echo is collected to obtain k each time _z Phase information of the excitation.

It is understood that the bliped-SMSlab (bliped-CAIPI-based SMSlab) sequence can be used in the embodiment of the present application, and as shown in a diagram in fig. 2, k is added on the basis of the two-dimensional EPI imaging sequence _z Code, k _z Gradient area of A _z ＝n _kz ·2π/(γ·FOV _z ) Wherein n is _kz Is k _z The coding number, gamma is the gyromagnetic ratio constant, FOV _z Is the thickness of each segment; acquiring imaging echoes after the refocusing pulse; imaging echo at k _x -k _y EPI acquisition is used in dimensions, both single and multiple excitations being applicable. If a blipped-SMSlab sequence is used for acquiring diffusion weighted images, a diffusion weighted gradient needs to be applied before and after a first refocusing pulse, and a second refocusing pulse needs to be applied after an imaging echo; applying a reverse k before the second refocusing pulse _z Encoding gradient, k before EPI readout _z The codes are cancelled out; two-dimensional navigator echoes are acquired after the second refocusing pulse for recording k each time _z Phase changes caused by physiological motion in the excitation. Navigation echo at k _x -k _y Dimension is acquired by using single-shot EPI, and the number of the shot sections is consistent with that of imaging echoes. The blipided-CAIPI is realized by applying k in the layer selection direction _m Encoding gradient, application time and k applied during EPI readout _y The encoding gradients are uniform, the width of the applied gradient is uniform, and adjacent k _m Coding the corresponding effective gradient area increment as A _blip ＝2π/(γ·Δz _m ·R _m ) Wherein gamma is a gyromagnetic ratio constant.

Note that the navigator echo is at k _x -k _y Dimensionality can be reduced or full, and k is _x -k _y When dimensionality reduction is adopted, both bliped-CAIPI sampling and non-CAIPI sampling can be carried outThe method is applicable. Wherein for setting any form of k before EPI read-out _m Cases of pre-rewinding gradients (pre-rewind), such as R _m When n is 2, n is _km ∈[0,1]Is changed into n _km ∈[-1/2,1/2]However, the embodiments of the present application are still applicable. Wherein the bliped-CAIPI sampling pattern under the four-dimensional k-space frame is shown as b diagram in FIG. 2, along k _m -k _y Dimension uses blipeped-CAIPI sampling mode; a conventional non-CAIPI sampling pattern in a four-dimensional k-space framework is shown in the c-diagram in fig. 2.

In step S102, a four-dimensional k-space signal model is established, gradient encoding in the layer direction corresponding to the sequence diagram is divided into intra-segment encoding and inter-segment encoding, and the acquired k-space data is formed into a four-dimensional k-space signal.

It can be understood that, as shown in a diagram of fig. 3, when the four-dimensional k-space concept is used in SMSlab imaging, the embodiment of the present application may split the coding in the layer direction into two dimensions, i.e., intra-segment coding and inter-segment coding, which are respectively k _z And k _m Shown as diagram b in figure 3.

Specifically, for the complete SMSlab four-dimensional k-space, the lamellar image inside the simultaneously excited segments can be reconstructed by iFT (four-dimensional inverse fourier transform). In the four-dimensional Fourier transform relationship, the dimensions of the image domain and k-space are x-y-m-z and k respectively _x -k _y -k _m -k _z And (4) showing.

As shown in FIG. 3, the resolution Δ z corresponding to the intra-segment encoding is defined as the layer thickness of the thin-layer image to be reconstructed, with a field of view having the size of the FOV _z ＝N _z Δ z, wherein FOV _z Is the thickness of each segment, N _z The number of lamellae (including oversampling layers) contained in each segment; resolution Δ z corresponding to inter-segment coding _m Defined as the centre-to-centre spacing of simultaneously excited segments with a field of view of size FOV _m ＝R _m ·Δz _m Wherein R is _m The number of segments excited simultaneously; the two k-space encoding steps are respectively delta k _z ＝1/FOV _z ，Δk _m ＝1/FOV _m 。

In the embodiment of the present application, the pre-established four-dimensional k-space signal model is:

wherein n is _m ∈[0,R _m -1]Number n of the image field in the inter-segment encoding direction _km ∈[0,R _m -1]Number n for the direction of inter-segment coding of four-dimensional k-space _z ∈[0,N _z -1]Number of encoding directions within a segment for an image field, n _kz ∈[-N _z /2,N _z /2-1]Coding the sequence number of the direction within a segment, s (n), for four-dimensional k-space _km ,n _kz ) For the nth coding dimension along the inter-segment in four-dimensional k-space _km Coding along the n-th coding dimension _kz An encoded signal, mu (n) _m ,n _z ) For n th of simultaneous excitation _m N in the section _z Signal of layer, k _x 、k _y 、k _m And k _z Representing four dimensions of a four-dimensional k-space, where k _m And k _z Respectively representing an inter-segment encoding dimension and an intra-segment encoding dimension, x, y, m and z representing four dimensions of an image domain;

is k _z The phase of the intersegment interference caused by the gradient,

is k _m Gradient induced intra-segment interference phase.

It will be appreciated that according to the formula of the pre-established four-dimensional k-space signal model, when k is _z And k _m When the codes share the same physical z-axis, the segment spacing Δ z is due to _m At k _z The encoding gradient will generate phase shift

And k is _m The encoding gradient will introduce an additional set of linearly varying phases at different slice positions in each segment

Therefore, the intra-segment encoding dimension and the inter-segment encoding dimension are not independent from each other, that is, the four-dimensional k-space signal model cannot directly satisfy the four-dimensional fourier encoding condition, and therefore, the embodiment of the present application may correct the two interference phases in step S103.

In step S103, correcting the interference phase generated to the four-dimensional k-space signal by the intra-segment encoding and the inter-segment encoding sharing the same physical z-axis includes:

for k _z Phase of gradient-induced inter-segment interference

Or the four-dimensional k-space signal edge k is subjected to a preset reconstruction algorithm _m Performing one-dimensional inverse Fourier transform on the dimension, and correcting a linear phase after Fourier transform, or performing cyclic shift in an image domain;

for k _m Phase of gradient-induced linear disturbance within a segment

And different k _z Phase differences between excitations due to motion;

when applied to diffusion addingWhen weights are imaged, for different k _z Removing phase difference caused by inconsistent motion between excitations according to the navigation echo;

when the actual position of the excitation section corresponding to the reference layer is not at the physical z-axis gradient center position during multi-section simultaneous excitation imaging, calculating the relative position of the reference layer and the physical z-axis gradient center according to the actual position, and correcting the relative position at k _z And k _m Off-center phase error caused by the gradient.

It is assumed that the sequence number of the lowermost segment among all the segments excited simultaneously is n _m 0, the sequence number of the lowest layer in the segment is n _z 0 (hereinafter, n) _z Layer 0 is the reference layer); when the reference layer 1 is located at the gradient center (z ═ 0), the phase is disturbed as shown in graph a in fig. 4

And

are shown in fig. 4 as b and c, respectively. Wherein the a-c reference layer center positions in FIG. 4 are at the gradient center; the d-e reference layer position is offset from the gradient center.

When applying k _z When encoding a gradient, along the z-axis, the gradient will be at segment intervals Δ z _m Under the action of (2) introducing an interference phase for the segment 1

When applying k _m When encoding the gradient, along the z-axis, the gradient will be in the FOV of each segment _z Generating an additional set of linear interference phases within range

Specifically, the interference phase correction of the embodiment of the present application may include off-center phase correction,

Correction sum

And correcting, namely sequentially performing the three steps as follows:

(1) off-center phase correction:

in the embodiment of the application, when the actual position of the excitation section corresponding to the reference layer is not at the physical z-axis gradient center position during multi-section simultaneous excitation imaging, the relative position of the reference layer and the physical z-axis gradient center is calculated according to the actual position, and the relative position is corrected at k _z And k _m Off-center phase error induced by the gradient.

It is understood that the embodiments of the present application may employ an off-center phase correction. In particular, as shown in the d-plot in FIG. 4, when the reference layer position of the excitation segment is not at the center of the z-axis encoding gradient, k _z And k _m The encoding gradients all produce an additional phase error due to the off-center distance, as shown in the e and f plots of fig. 4, which is called off-center phase:

wherein d is _{off_iso} The relative position of the reference layer off the center of the z-axis encoding gradient. The corresponding k can be directly processed according to the formula in the k-space data preprocessing process _z And k _m Encoded k-space data removal

(2)

And (3) correction:

in the examples of the present application, for k _z Phase of gradient-induced inter-segment interference

Or the four-dimensional k-space signal edge k is subjected to a preset reconstruction algorithm _m The dimensions are one-dimensional inverse fourier transformed and the linear phase is corrected after the fourier transform, or a cyclic shift is performed in the image domain.

It will be appreciated that in accordance with the above

Can calculate k each time _z Encoding corresponding inter-segment interference phases

The phase is band-specific. Therefore, the embodiment of the application can be corrected in various ways

For example, embodiments of the present application may compensate by adding rf pulse modulation during excitation of the signal

Can also be removed in the image reconstruction process

The method comprises the following specific steps:

as a possible implementation manner, the embodiment of the application can adopt a method for applying phase compensation to the radio frequency pulse in the multi-segment simultaneous excitation sequence, and the removal is based on the radio frequency pulse phase modulation

Specifically, by k at each time _z During excitation, the waveform of a particular frequency band of a multi-band radio frequency pulse is subtracted

Such that the acquired signal is free of

And (4) interference.

For a gradient echo EPI sequence, applying phase modulated SMSlab radio frequency pulses is:

wherein the RF (t) -based single band pulses,

is n th _m The center frequency of each band.

For spin echo EPI sequences, the acquisition of the imaging echo is performed by exciting and refocusing two radio frequency pulses:

wherein, RF _ex (t) based single band excitation pulse, RF _{echo_1} (t) is the first refocusing pulse.

For diffusion imaging based on spin echo EPI sequences, a second refocusing pulse is also applied to acquire two-dimensional navigator echoes for phase correction between different kz excitations:

wherein, RF _{echo_2} (t) is the second fundamental single band refocusing pulse.

As another possible implementation manner, the embodiment of the present application may adopt a removal in the image reconstruction process

I.e. by means of a predetermined reconstruction algorithm, for the four-dimensional k-space signal edge k _m The dimensions are one-dimensional inverse fourier transformed and the linear phase is corrected after the fourier transform, or a cyclic shift is performed in the image domain.

It will be appreciated that for both non-diffusion weighted and diffusion weighted data, each k may be preceded by a separate weighting for each k _z Encoding reconstructs the image in the x-y-m domain, and then for each k _z Coding in frequency band n _m Removing phase from

The process is substantially equivalent to reconstructing a thin layer image of all the segments and then subjecting the thin layer image to a process

And carrying out cyclic shift processing on the thin-layer image in the affected frequency band section in the layer direction.

Specifically, as shown in FIG. 5, FIG. 5 illustrates

Image results before and after correction: in the examples of the present application, when Δ z _m /(N _z Δ z) is an integer, k _z The interference phase generated by the encoding gradient is exactly integral multiple of 2 pi, and the method is not required to be carried out

And (6) correcting. When Δ z is equal to _m /(N _z Δ z) is not an integer, if not

Correction of the interference phase causing the segment 1' to produce an image shift in the layer direction, through

After correction, correct reconstruction is possible.

(3)

And (3) correction:

in the examples of the present application, for k _m Phase of gradient-induced linear disturbance within a segment

And different k _z Phase differences between excitations due to motion.

Among them, in the embodiments of the present application

The correction is performed during data preprocessing and the pre-set reconstruction algorithms may include k-space based, image domain based and mixed k-space and image domain based reconstruction algorithms.

In particular, for non-diffusion weighted data, it is possible to pass directly along k _z Removing the direction after one-dimensional inverse Fourier transform

For diffusion weighted data, since k is each time _z The phase inconsistency caused by the motion inconsistency among excitations cannot be directly along k in the embodiment of the application _z The direction is subjected to one-dimensional inverse Fourier transform, and the phase between each time of excitation is required to be additionally carried out, namely

The two corrections can be selected to be performed sequentially or simultaneously according to different reconstruction algorithms.

As a possible implementation, the corrections are made sequentially or simultaneously by a pre-set reconstruction algorithm

And

the method comprises the following steps: sequential correction using k-space based image reconstruction algorithms

And

specifically, first correction

Recalibration

The correction steps are as follows: first, a preliminary reconstruction of the acquired diffusion weighted data is performed, at x-y-m-k _z Domain-oriented navigation echo information removal of different k _z Motion induced phase difference between excitations

At this time, k may be followed _z Performing one-dimensional Fourier transform on the direction; conversion to k _x -k _y -k _m -after the z-domain, removing the interference phase at each z-position

The process is then reversed, i.e. at x-y-m-k _z Domain handle

Add back and then change to k _x -k _y -k _m -k _z Domain, to be received

K of influence _m Extracting data of actual sampling position in code to replace original position

And correcting the sampling points, and then performing subsequent reconstruction.

As another possible implementation, the correction is performed sequentially or simultaneously by a pre-set reconstruction algorithm

And

the method comprises the following steps: diffusion weighted image reconstruction algorithm based on mixed space of k-space and image domain to correct simultaneously

And

in particular, when reconstructing a diffusion weighted image using a reconstruction algorithm based on a mixed space of k-space and an image domain, the embodiment of the present application can correct the two phases simultaneously, and build a signal model, which is only used when k is in the signal model _y -k _m Examples of the case of mining with dimensionality reduction:

wherein I denotes the image to be reconstructed, C denotes coil sensitivity information, F _{y_m} Representing a Fourier transform in a dimension other than the intra-segment encoding dimension and with downscaling, M representing a downscaling trajectory, s representing a signal of the mixture space, in the example case x-k _y -k _m -a signal in the z-domain. The reconstruction process is to solve the inverse problem of the model, and can be solved by using an optimization algorithm such as a least square method.

In step (2), the

In correction, if removal during image reconstruction is chosen

In the step (3)

The correction needs to be considered simultaneously

Can be influenced by

To be regarded as another kind

And (6) processing.

It will be appreciated that, as shown in FIG. 6, FIG. 6 illustrates

Image results before and after correction: in the examples of this application, if not

Correcting, wherein the interference phase causes a certain degree of image aliasing, such as a region indicated by an arrow; through

After correction, correct reconstruction is possible.

In the embodiment of the present application, the embodiment of the present application may perform image reconstruction on a four-dimensional k-space signal based on correction. K-space based (e.g., GRAPPA and its extended algorithm), image domain based (e.g., SENSE and its extended algorithm), and a reconstruction algorithm based on a mixed space of k-space and image domain are all applicable to the proposed four-dimensional k-space blipped-SMSlab sampling mode. Correcting k above _z And k _m After the interference phase generated in the encoding process, k can be respectively generated for each time _z The excited data reconstruct an image. At this time, for non-diffusion weighted data, k may be directly followed _z Carrying out one-dimensional inverse Fourier transform on the dimension to obtain a final image; for diffusion weighted data, it is necessary to use motion-induced phase information of the navigator echo recordings for different k _z The excited image is motion phase corrected, which is also needed when the intra-layer coding uses multiple excitations, and then along k _z And carrying out one-dimensional inverse Fourier transform on the dimension to obtain a final image.

In the embodiment of the application, the SMSlab image g factor calculation reconstructed by using the bliped-CAIPI and non-CAIPI sampling modes is used for comparing SMSlab bliped-CAIPI sampling results with the existing non-CAIPI sampling results, and two different levels are shown as a diagram in FIG. 7. The results show that the g-factor for CAIPI samples is generally lower than for non-CAIPI samples. This means that in the CAIPI sampling mode, the g-factor dependent signal-to-noise ratio loss is lower, which may explain that the SNR of the CAIPI samples is higher than that of the non-CAIPI samples (the region shown by the box of the b-diagram in fig. 7); the reconstructed B-0 image is enlarged and displayed in red frame and blue frame regions respectively selected in the layer a and the layer B, as shown in a c diagram in fig. 7, and it can also be directly seen that the signal-to-noise ratio of the CAIPI sampling imaging is obviously higher than that of the non-CAIPI sampling.

In the embodiment of the application, the bliped-SMSlab and the traditional two-dimensional multi-layer simultaneous excitation imaging are compared, wherein the results of the bliped-SMSlab imaging and the traditional two-dimensional bliped-CAIPI accelerated multi-layer simultaneous excitation technology (2 Dbliped-SMS) are shown in FIG. 8. Both were sampled using blipeped-CAIPI, with the same scan time. Therefore, the blipeped-SMSlab technology of the embodiment of the application shows obvious signal to noise ratio advantage and smoother depicting capability of the trend of the nerve fiber bundle.

In summary, the embodiment of the application can use a parallel imaging gradient control aliasing function in multi-segment simultaneous excitation imaging, solve the problem of phase interference caused by sharing the same physical z axis by intra-segment coding and inter-segment coding, decouple the two coding dimensions into two independent dimensions, enable the blipped-CAIPI acceleration technology to be applied to multi-segment simultaneous excitation imaging, improve the scanning efficiency and the image signal to noise ratio, and improve the image quality; the method can be suitable for acquiring imaging signals and reconstructing images of a plurality of three-dimensional thick-section simultaneously excited EPIs (including gradient echo EPI, spin echo EPI and other possible EPI forms) with any contrast and any form, and has wide application range; and the embodiment of the application also carries out special treatment aiming at the special property of diffusion imaging: acquiring navigation echo information by acquiring additional navigation echoes or adopting other forms, and performing phase correction among different excitations caused by physiological motion in reconstruction; it may also involve the use of motion compensated (1 st order or both 2 nd order) diffusion coding gradients to eliminate motion effects between different excitations.

Next, a magnetic resonance imaging apparatus based on multiple simultaneous excitation segments according to an embodiment of the present application will be described with reference to the drawings.

Fig. 9 is a block diagram of a magnetic resonance imaging apparatus based on multiple simultaneous excitation segments according to an embodiment of the present application.

As shown in fig. 9, the magnetic resonance imaging apparatus 10 based on multiple simultaneous excitation segments includes: an acquisition module 100, a modeling module 200, and a reconstruction module 300.

The acquisition module 100 is configured to acquire a sequence diagram of an object to be imaged when multiple sections of the object are simultaneously excited for imaging; the modeling module 200 is configured to establish a four-dimensional k-space signal model, divide the gradient codes in the layer direction corresponding to the sequence diagram into intra-segment codes and inter-segment codes, and form the acquired k-space data into four-dimensional k-space signals; the reconstruction module 300 is configured to correct an interference phase of intra-segment encoding and/or inter-segment encoding, and perform image reconstruction based on the corrected encoding, so as to generate a magnetic resonance imaging result of the target to be imaged.

In this embodiment of the present application, the method is suitable for planar echo imaging excited by multiple three-dimensional thick segments with any contrast and any form, and the acquisition module 100 is further configured to: applying a kz encoding gradient in the slice direction for intra-segment encoding, the kz gradient having an area size of:

A _z ＝n _kz ·2π/(γ·FOV _z )，

wherein n is _kz Coding serial number for kz, gamma is gyromagnetic ratio constant, FOV _z Is the thickness of each segment; and during the EPI readout, applying a km gradient of alternating polarity in the layer direction for inter-segment encoding, the km gradient having an area size of:

A _blip ＝2π/(γ·Δz _m ·R _m )，

wherein gamma is a gyromagnetic ratio constant, and delta z _m For the centre distance of adjacent segments excited simultaneously, R _m The number of segments excited simultaneously; and/or for diffusion weighted imaging, acquiring navigator echoes during each kz encoding to obtain phase information for each kz excitation.

In the embodiment of the present application, the four-dimensional k-space signal model pre-established by the modeling module 200 is:

wherein n is _m ∈[0,R _m -1]Number n of the image field in the inter-segment encoding direction _km ∈[0,R _m -1]Number n for the direction of inter-segment coding of four-dimensional k-space _z ∈[0,N _z -1]Number of encoding directions within a segment for an image field, n _kz ∈[-N _z /2,N _z /2-1]Coding the sequence number of the direction within a segment, s (n), for four-dimensional k-space _km ,n _kz ) For the nth coding dimension along the inter-segment in four-dimensional k-space _km Coding along the n-th coding dimension _kz An encoded signal, mu (n) _m ,n _z ) For n th of simultaneous excitation _m N in the section _z Signal of layer, k _x 、k _y 、k _m And k _z Representing four dimensions of a four-dimensional k-space, where k _m And k _z Respectively representing an intra-segment coding dimension and an inter-segment coding dimension, and x, y, m and z represent four dimensions of an image domain;

is k _z The phase of the intersegment interference caused by the gradient,

is k _m Gradient induced intra-segment interference phase.

In an embodiment of the present application, the reconstruction module 300 is further configured to: for k _z Phase of gradient-induced inter-segment interference

Or the four-dimensional k-space signal edge k is subjected to a preset reconstruction algorithm _m Performing one-dimensional inverse Fourier transform on the dimension, and correcting a linear phase after Fourier transform, or performing cyclic shift in an image domain; for phase of linear disturbance in section caused by km gradient

For four-dimensional k-space signal edges k when belonging to the non-diffusion weighted data type _z Performing one-dimensional inverse Fourier transform on the dimensions, and performing Fourier transform on each k _m The encoded signals being corrected in the z-direction, respectively

And different k _z The reason of the excitation chamberMotion-induced phase differences; when applied to diffusion weighted imaging, for different k _z Removing phase difference caused by inconsistent motion between excitations according to the navigation echo; when the actual position of the excitation section corresponding to the reference layer is not at the central position of the physical z-axis corresponding to the encoding gradient during multi-section simultaneous excitation imaging, the relative position of the reference layer and the physical z-axis is calculated according to the actual position, and the off-center phase error caused by the relative position under the action of the encoding gradient is corrected.

It should be noted that the foregoing explanation of the embodiment of the magnetic resonance imaging method based on multi-segment simultaneous excitation is also applicable to the magnetic resonance imaging apparatus based on multi-segment simultaneous excitation of this embodiment, and is not repeated here.

According to the magnetic resonance imaging device based on multi-segment simultaneous excitation, the parallel imaging gradient control aliasing function can be used in multi-segment simultaneous excitation imaging, the problem of phase interference caused by sharing of the same physical z axis by intra-segment encoding and inter-segment encoding is solved, the two encoding dimensions are decoupled into two independent dimensions, so that the blipided-CAIPI acceleration technology can be applied to multi-segment simultaneous excitation imaging, the scanning efficiency and the image signal to noise ratio are improved, and the image quality is improved; the method is suitable for acquiring imaging signals and reconstructing images of a plurality of three-dimensional thick-section simultaneously excited EPIs (including gradient echo EPI, spin echo EPI and other possible EPI forms) with any contrast and any form, and has wide application range.

Fig. 10 is a schematic structural diagram of an electronic device according to an embodiment of the present application. The electronic device may include:

memory 1001, processor 1002, and computer programs stored on memory 1001 and executable on processor 1002.

The processor 1002, when executing the program, implements the magnetic resonance imaging method based on multiple simultaneous excitation provided in the above-described embodiments.

Further, the electronic device further includes:

a communication interface 1003 for communicating between the memory 1001 and the processor 1002.

A memory 1001 for storing computer programs that may be run on the processor 1002.

The Memory 1001 may include a high-speed RAM (Random Access Memory) Memory, and may also include a nonvolatile Memory such as at least one disk Memory.

If the memory 1001, the processor 1002, and the communication interface 1003 are implemented independently, the communication interface 1003, the memory 1001, and the processor 1002 may be connected to each other through a bus and perform communication with each other. The bus may be an ISA (Industry Standard Architecture) bus, a PCI (Peripheral Component interconnect) bus, an EISA (Extended Industry Standard Architecture) bus, or the like. The bus may be divided into an address bus, a data bus, a control bus, etc. For ease of illustration, only one thick line is shown in FIG. 10, but this is not intended to represent only one bus or type of bus.

Optionally, in a specific implementation, if the memory 1001, the processor 1002 and the communication interface 1003 are integrated on one chip, the memory 1001, the processor 1002 and the communication interface 1003 may complete communication therebetween through an internal interface.

The processor 1002 may be a Central Processing Unit (CPU), an Application Specific Integrated Circuit (ASIC), or one or more Integrated circuits configured to implement embodiments of the present Application.

Embodiments of the present application also provide a computer-readable storage medium, on which a computer program is stored, which when executed by a processor, implements the above magnetic resonance imaging method based on multiple simultaneous excitation segments.

In the description herein, reference to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the application. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or N embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present application, "N" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

Any process or method descriptions in flow charts or otherwise described herein may be understood as representing modules, segments, or portions of code which include one or more N executable instructions for implementing steps of a custom logic function or process, and alternate implementations are included within the scope of the preferred embodiment of the present application in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of implementing the embodiments of the present application.

It should be understood that portions of the present application may be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, the N steps or methods may be implemented in software or firmware stored in a memory and executed by a suitable instruction execution system. If implemented in hardware, as in another embodiment, any one or combination of the following techniques, which are known in the art, may be used: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application specific integrated circuit having an appropriate combinational logic gate circuit, a programmable gate array, a field programmable gate array, or the like.

It will be understood by those skilled in the art that all or part of the steps carried by the method for implementing the above embodiments may be implemented by hardware related to instructions of a program, which may be stored in a computer readable storage medium, and when the program is executed, the program includes one or a combination of the steps of the method embodiments.

Claims

1. A magnetic resonance imaging method based on multi-segment simultaneous excitation is characterized by comprising the following steps:

step S101: using a plurality of sections added with a parallel imaging gradient control aliasing function to simultaneously excite an imaging sequence, and carrying out data acquisition to obtain multi-channel k-space data;

step S102: establishing a four-dimensional k-space signal model, dividing gradient codes in the layer direction corresponding to the sequence diagram into intra-segment codes and inter-segment codes, and forming four-dimensional k-space signals by the acquired k-space data;

step S103: and correcting the interference phase generated by the intra-segment codes and the inter-segment codes sharing the same physical z axis on the four-dimensional k space signals, and performing image reconstruction based on the corrected four-dimensional k space signals to generate a magnetic resonance imaging result of the target to be imaged.

2. The method according to claim 1, wherein the method is suitable for any-contrast, any-form planar echo imaging with simultaneous excitation of multiple three-dimensional thick segments, and the step S101 specifically includes:

applying a kz encoding gradient along a slice direction for intra-segment encoding, the kz gradient having an area size of:

A _z ＝n _kz ·2π/(γ·FOV _z )，

during EPI readout, applying alternate polarity k in the layer direction _m Gradients are used for inter-segment coding, said k _m The gradient area size is:

A _blip ＝2π/(γ·Δz _m ·R _m )，

For diffusion weighted imaging, at said each time k _z In the process of coding, navigation echo is collected to obtain k each time _z Phase information of the excitation.

3. The method according to claim 1, wherein the four-dimensional k-space signal model pre-established in step S102 is:

wherein n is _m ∈[0，R _m -1]Number n of the image field in the inter-segment encoding direction _km ∈[0，R _m -1]For the sequence number, n, of the four-dimensional k-space in the inter-segment coding direction _z ∈[0，N _z -1]Number of encoding directions within a segment for an image field, n _kz ∈[-N _z /2，N _z /2-1]For the four-dimensional k-space, s (n) is the number of the encoding directions within a segment _km ，n _kz ) For the nth coding dimension along the segment in said four-dimensional k-space _km Coding along the n-th coding dimension _kz An encoded signal, mu (n) _m ，n _z ) For n th of simultaneous excitation _m N in the section _z Signal of layer, k _x 、k _y 、k _m And k _z Representing four dimensions of the four-dimensional k-space, wherein k _m And k _z Representing inter-segment and intra-segment encoding dimensions, respectively, x, y, m and z representing four dimensions of the image domain;

is k _z The phase of the intersegment interference caused by the gradient,

is k _m Gradient induced intra-segment interference phase.

4. The method according to claim 1, wherein the step S103 of correcting the phase of the interference generated to the four-dimensional k-space signal by the intra-segment encoding and the inter-segment encoding sharing the same physical z-axis comprises:

for said k _z Phase of gradient-induced inter-segment interference

Applying phase compensation to RF pulses in the multi-segment simultaneous excitation sequence to cancel

for said k _m Phase of gradient-induced linear disturbance within a segment

And different k _z Phase differences between excitations due to motion;

when applied to diffusion weighted imaging, for different k _z Caused by motion inconsistency between excitationsRemoving the phase difference according to the navigation echo;

when the actual position of the excitation section corresponding to the reference layer is not at the physical z-axis gradient center position during the multi-section simultaneous excitation imaging, calculating the relative position of the reference layer and the physical z-axis gradient center according to the actual position, and correcting the relative position at k _z And k _m Off-center phase error induced by the gradient.

5. A magnetic resonance imaging apparatus based on multiple simultaneous excitation segments, comprising:

the acquisition module is used for simultaneously exciting an imaging sequence through a plurality of sections with the function of parallel imaging gradient control aliasing, and acquiring data to obtain multi-channel k-space data;

the modeling module is used for establishing a four-dimensional k-space signal model, dividing gradient codes in the layer direction corresponding to the sequence diagram into intra-segment codes and inter-segment codes, and forming the acquired k-space data into four-dimensional k-space signals;

and the reconstruction module is used for correcting the interference phase generated by the intra-segment codes and the inter-segment codes sharing the same physical z axis on the four-dimensional k space signals, carrying out image reconstruction based on the corrected four-dimensional k space signals and generating a magnetic resonance imaging result of the target to be imaged.

6. The apparatus of claim 5, wherein the method is suitable for arbitrary contrast, arbitrary form, and multiple three-dimensional thick segment simultaneously excited planar echo imaging, and the acquisition module is further configured to:

A _z ＝n _kz ·2π/(γ·FOV _z )，

wherein n is _kz Coding serial number for kz, gamma is gyromagnetic ratio constant, FOV _z Is the thickness of each segment; and

during EPI readout, a km gradient of alternating polarity is applied in the layer direction for inter-segment encoding, the km gradient area size being:

A _blip ＝2π/(γ·Δz _m ·R _m )，

When the method is used for diffusion weighted imaging, in the process of each kz encoding, the navigation echo is acquired so as to obtain the phase information of each kz excitation.

7. The apparatus of claim 5, wherein the four-dimensional k-space signal model pre-established by the modeling module is:

wherein n is _m ∈[0，R _m -1]Number n of the image field in the inter-segment encoding direction _km ∈[0，R _m -1]For the sequence number, n, of the four-dimensional k-space in the inter-segment coding direction _z ∈[0，N _z -1]Number of encoding directions within a segment for an image field, n _kz ∈[-N _z /2，N _z /2-1]For the four-dimensional k-space, s (n) is the number of the encoding directions within a segment _km ，n _kz ) For the nth coding dimension along the inter-segment in four-dimensional k-space _km Coding along the n-th coding dimension _kz An encoded signal, mu (n) _m ，n _z ) For n th of simultaneous excitation _m N in the section _z Signal of layer, k _x 、k _y 、k _m And k _z Representing four dimensions of the four-dimensional k-space, wherein k _m And k _z Respectively representing intra-segment encoding dimensions and inter-segment encoding dimensions, x, y, m and z representing four dimensions of the image domain;

is k _z The phase of the intersegment interference caused by the gradient,

is k _m Gradient induced intra-segment interference phase.

8. The apparatus of claim 5, wherein the reconstruction module is further configured to:

for said k _z Phase of gradient-induced inter-segment interference

for linear disturbance phase within the km gradient induced segment

And different from k _z Phase differences between excitations due to motion;

when applied to diffusion weighted imaging, for different k _z Phase differences between excitations due to motion inconsistencies,removing according to the navigation echo;

when the actual position of the excitation section corresponding to the reference layer is not at the central position of the physical z-axis corresponding to the encoding gradient during the multi-section simultaneous excitation imaging, calculating the relative position of the reference layer and the physical z-axis according to the actual position, and correcting the relative position at k _z And k _m Off-center phase error induced by the gradient.

9. An electronic device, comprising: a memory, a processor and a computer program stored on the memory and executable on the processor, the processor executing the program to implement the magnetic resonance imaging method based on multiple simultaneous excitation according to any one of claims 1 to 4.

10. A computer-readable storage medium, on which a computer program is stored which is executable by a processor for implementing a magnetic resonance imaging method based on multiple simultaneous excitation segments as claimed in any one of claims 1 to 4.