CN115436855B

CN115436855B - Eddy current correction method, magnetic resonance image correction method, device, equipment and medium

Info

Publication number: CN115436855B
Application number: CN202110615012.5A
Authority: CN
Inventors: 陈伟梁; 李博
Original assignee: Shanghai United Imaging Healthcare Co Ltd
Current assignee: Shanghai United Imaging Healthcare Co Ltd
Priority date: 2021-06-02
Filing date: 2021-06-02
Publication date: 2025-05-30
Anticipated expiration: 2041-06-02
Also published as: CN115436855A

Abstract

The present application relates to an eddy current correction method, a magnetic resonance image correction method, an apparatus, a computer device and a storage medium. The method comprises: acquiring a first magnetic resonance signal of a plurality of echo times acquired after a first gradient is applied and a second magnetic resonance signal of a plurality of echo times acquired after a second gradient is applied; determining two magnetic resonance images of each echo time according to the first magnetic resonance signal and the second magnetic resonance signal of each echo time, and determining a phase difference between the two magnetic resonance images of each echo time; determining an eddy current field distribution at at least one imaging echo time according to each phase difference; and performing eddy current correction on the magnetic resonance signal corresponding to the imaging echo time using the eddy current field distribution at the imaging echo time. The use of the present method can improve the accuracy of eddy current correction of magnetic resonance.

Description

Eddy current correction method, magnetic resonance image correction method, apparatus, device and medium

Technical Field

The present application relates to the field of data processing technologies, and in particular, to an eddy current correction method, a magnetic resonance image correction method, a device, a computer apparatus, and a storage medium.

Background

During operation of a magnetic resonance pulse imaging sequence, a series of time-varying gradient fields are used which cause a time-varying magnetic flux in the space around the gradient coils, while at the same time a time-varying current is generated in the metallic conductive material in the components around the gradient, which induced current is called eddy current. The influence of the eddy current on the later magnetic resonance imaging is serious, so that the influence of the eddy current on the later image must be eliminated as much as possible, and the correction of the eddy current is a means for eliminating the influence on the image.

In the related art, when the eddy current is corrected, it is generally implemented by a pre-emphasis method. That is, a reverse gradient is applied to the hardware of the magnetic resonance system (e.g., gradient coils, etc.) in the early stage, and then correction of eddy currents is achieved by the reverse gradient.

However, after the eddy current is corrected, the eddy current residue still exists in the above technology, that is, the accuracy of the eddy current correction is low.

Disclosure of Invention

In view of the foregoing, it is desirable to provide an eddy current correction method, a magnetic resonance image correction method, an apparatus, a computer device, and a storage medium that can improve the accuracy of eddy current correction for magnetic resonance.

A method of eddy current correction, the method comprising:

Acquiring a first magnetic resonance signal of a plurality of echo times acquired after the application of a first gradient and a second magnetic resonance signal of a plurality of echo times acquired after the application of a second gradient, wherein the acquisition time of the first magnetic resonance signal of the plurality of echo times corresponds to the acquisition time of the second magnetic resonance signal of the plurality of echo times;

Determining two magnetic resonance images of each echo time according to the first magnetic resonance signal and the second magnetic resonance signal of each echo time, and determining a phase difference between the two magnetic resonance images of each echo time;

determining a vortex field distribution at least one imaging echo time according to each phase difference;

and carrying out eddy current correction on the magnetic resonance signals corresponding to the imaging echo time by utilizing the eddy current field distribution under the imaging echo time.

In one embodiment, determining the vortex field distribution at least one imaging echo time according to each phase difference includes:

Processing each phase difference to determine vortex field distribution at each echo time;

and solving the vortex field distribution under each echo time, and determining the vortex field distribution under at least one imaging echo time.

In one embodiment, the above-mentioned solving the vortex field distribution at each echo time, determining the vortex field distribution at least one imaging echo time includes:

Coefficient expansion is carried out on vortex field distribution under each echo time according to a preset spherical harmonic function, and vortex spherical harmonic coefficients under each imaging echo time are determined;

and obtaining vortex field distribution under at least one imaging echo time according to the vortex spherical harmonic coefficient under each imaging echo time.

In one embodiment, the acquiring the first magnetic resonance signal of the plurality of echo times acquired after the first gradient is applied and the second magnetic resonance signal of the plurality of echo times acquired after the second gradient is applied includes:

after the first gradient is applied, carrying out multi-layer data cross acquisition by adopting a pre-scanning sequence to obtain first magnetic resonance signals of a plurality of echo times after the first gradient is applied;

And after the second gradient is applied, carrying out multi-layer data cross acquisition by adopting a pre-scanning sequence, and obtaining a second magnetic resonance signal of a plurality of echo times after the second gradient is applied.

In one embodiment, the first gradient and the second gradient are two gradients with equal gradient intensity and opposite gradient directions, and the determining the vortex field distribution at each imaging echo time according to each phase difference includes:

and determining the vortex field distribution at each imaging echo time after the first gradient is applied or after the second gradient is applied according to each phase difference.

In one embodiment, the method further comprises:

Acquiring a first intensity ratio between the preset intensity of the third gradient and the intensity of the first gradient, or a second intensity ratio between the intensity of the third gradient and the intensity of the second gradient;

And according to the first intensity proportion or the second intensity proportion, carrying out linear superposition processing on the vortex field distribution under each imaging echo time after the first gradient is applied and the second gradient is applied, and determining the vortex field distribution under each imaging echo time under the third gradient.

In one embodiment, determining the two magnetic resonance images of each echo time according to the first magnetic resonance signal and the second magnetic resonance signal of each echo time, and determining a phase difference between the two magnetic resonance images of each echo time includes:

Performing image reconstruction on the first magnetic resonance signal and the second magnetic resonance signal of each echo time to obtain a first magnetic resonance image and a second magnetic resonance image of each echo time;

obtaining a first phase of each echo time according to the first magnetic resonance image of each echo time, and obtaining a second phase of each echo time according to the second magnetic resonance image of each echo time;

and performing difference operation on the first phase and the second phase of each echo time to obtain a phase difference between the first magnetic resonance image and the second magnetic resonance image of each echo time.

A method of magnetic resonance image correction, the method comprising:

Acquiring a plurality of groups of magnetic resonance images of a scanned object, wherein each group of magnetic resonance images comprises a first magnetic resonance image and a second magnetic resonance image which correspond to the same echo time, the first magnetic resonance image is obtained by reconstructing a first magnetic resonance signal acquired after a first gradient is applied, and the second magnetic resonance image is obtained by reconstructing a second magnetic resonance signal acquired after a second gradient is applied;

Determining a phase difference between the first magnetic resonance image and the second magnetic resonance image in each set of magnetic resonance images;

Determining a vortex field distribution of at least one imaging echo time based on the phase difference;

And correcting the magnetic resonance image to be processed corresponding to the imaging echo time according to the vortex field distribution, and obtaining a corrected magnetic resonance image.

An eddy current correction device, the device comprising:

The system comprises a signal acquisition module, a signal processing module and a signal processing module, wherein the signal acquisition module is used for acquiring a first magnetic resonance signal of a plurality of echo times acquired after a first gradient is applied and a second magnetic resonance signal of a plurality of echo times acquired after a second gradient is applied;

A first phase difference determining module, configured to determine two magnetic resonance images of each echo time according to the first magnetic resonance signal and the second magnetic resonance signal of each echo time, and determine a phase difference between the two magnetic resonance images of each echo time;

the first vortex field determining module is used for determining vortex field distribution under at least one imaging echo time according to each phase difference;

the eddy current correction module is used for carrying out eddy current correction by utilizing the eddy current field distribution under the imaging echo time.

A magnetic resonance image correction apparatus, the apparatus comprising:

The image acquisition module is used for acquiring a plurality of groups of magnetic resonance images of a scanned object, each group of magnetic resonance images comprises a first magnetic resonance image and a second magnetic resonance image which correspond to the same echo time, the first magnetic resonance image is obtained by reconstructing a first magnetic resonance signal acquired after a first gradient is applied, and the second magnetic resonance image is obtained by reconstructing a second magnetic resonance signal acquired after a second gradient is applied;

A second phase difference determination module for determining a phase difference between the first magnetic resonance image and the second magnetic resonance image in each set of magnetic resonance images;

a second vortex field determining module for determining a vortex field distribution of at least one imaging echo time according to the phase difference;

And the image correction module is used for correcting the magnetic resonance image to be processed corresponding to the imaging echo time according to the vortex field distribution, and obtaining a corrected magnetic resonance image.

A computer device comprising a memory storing a computer program and a processor which when executing the computer program performs the steps of:

And performing eddy current correction on the magnetic resonance signals corresponding to the imaging echo time by using the eddy current field distribution under the at least one imaging echo time.

A computer readable storage medium having stored thereon a computer program which when executed by a processor performs the steps of:

According to the eddy current correction method, the magnetic resonance image correction method, the device, the computer equipment and the storage medium, the first magnetic resonance signals of a plurality of echo times after the first gradient corresponding to the acquisition time is applied and the second magnetic resonance signals of a plurality of echo times after the second gradient is applied are used, the two magnetic resonance images of each echo time and the phase difference between the two magnetic resonance images are determined through the two magnetic resonance signals of each echo time, the eddy current field distribution under the imaging echo time is determined according to each phase difference, and the eddy current correction is carried out on the magnetic resonance signals corresponding to the imaging echo time by utilizing the eddy current field distribution under the imaging echo time. In the method, the eddy current field distribution under any imaging echo time can be determined through the phase difference between the magnetic resonance images after the application of different gradients of each echo time, so that the eddy current at any imaging echo time can be accurately corrected when the eddy current is corrected, and no great eddy current residue exists, thereby realizing the accurate correction of the eddy current, and improving the accuracy of correcting the eddy current.

Drawings

FIG. 1 is an internal block diagram of a computer device in one embodiment;

FIG. 2 is a flow chart of a method of eddy current correction in one embodiment;

FIG. 3 is a flow chart of an eddy current correction step according to another embodiment;

FIG. 3a is a diagram illustrating a phase difference between two magnetic resonance images at corresponding echo times in another embodiment;

FIG. 3b is an exemplary graph of the amplitude of the spherical harmonic coefficients over time in another embodiment;

FIG. 4 is a flow chart of a method of eddy current correction in another embodiment;

FIG. 4a is a diagram illustrating an example of acquisition timing of magnetic resonance signals in another embodiment;

FIG. 5 is a flow chart of a method of eddy current correction in another embodiment;

FIG. 6 is a flow chart of a method of magnetic resonance image correction in another embodiment;

FIG. 6a is a diffusion image and a composite image of a plurality of diffusion directions to be corrected obtained in another embodiment;

FIG. 6b is a corrected multiple diffusion direction diffusion image and corrected composite image obtained in another embodiment;

FIG. 7 is a block diagram of an eddy current correction device in one embodiment.

Detailed Description

The present application will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present application more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the application.

The eddy current correction method provided by the embodiment of the application can be applied to a magnetic resonance system or computer equipment, wherein the magnetic resonance system can comprise a magnetic resonance scanning device and the computer equipment which are connected with each other, when a detection object is scanned, the detection object can be scanned through the magnetic resonance scanning device, and scanned data are transmitted to the computer equipment for processing, so that eddy current correction is realized. The eddy current correction method is applied to a computer device, which may be a terminal or a server, and the computer device is a terminal, and the internal structure thereof may be as shown in fig. 1. The computer device includes a processor, a memory, a communication interface, a display screen, and an input device connected by a system bus. Wherein the processor of the computer device is configured to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage media. The communication interface of the computer device is used for carrying out wired or wireless communication with an external terminal, and the wireless mode can be realized through WIFI, an operator network, NFC (near field communication) or other technologies. The computer program is executed by a processor to implement a method of eddy current correction. The display screen of the computer equipment can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer equipment can be a touch layer covered on the display screen, can also be keys, a track ball or a touch pad arranged on the shell of the computer equipment, and can also be an external keyboard, a touch pad or a mouse and the like.

It will be appreciated by those skilled in the art that the architecture shown in fig. 1 is merely a block diagram of some of the architecture relevant to the present inventive arrangements and is not limiting as to the computer device to which the present inventive arrangements may be implemented, as a particular computer device may include more or less components than those shown, or may be combined with some components, or may have a different arrangement of components.

The execution body of the embodiment of the present application may be a magnetic resonance system, a computer device in the magnetic resonance system, or an eddy current correction device in the computer device, or any other device, and the technical solution of the present application will be described below using the computer device as the execution body.

In one embodiment, as shown in FIG. 2, a method of eddy current correction is provided, which may include the steps of:

s202, acquiring a first magnetic resonance signal of a plurality of echo times acquired after the first gradient is applied and a second magnetic resonance signal of a plurality of echo times acquired after the second gradient is applied.

The corresponding times of the first magnetic resonance signals of the plurality of echo times and the corresponding times of the second magnetic resonance signals of the plurality of echo times may be equal to each other in the number of times of the acquisition of the plurality of echo times after the application of the first gradient and the number of times of the acquisition of the plurality of echo times after the application of the second gradient, for example, the times of the acquisition of the plurality of echo times after the application of the first gradient may be T1 to Tn, and the times of the acquisition of the plurality of echo times after the application of the second gradient may be T1 to Tn. The number of acquisition instants of the echo times may be preset, for example, 50 points, i.e. 50 acquisition instants, may be acquired, and the 50 instants may be equally or unequally spaced, for example, equally spaced acquisition instants of 5ms, 10ms, etc.

Here, the intensity of the first gradient and the intensity of the second gradient may be equal or unequal. The direction of the first gradient and the direction of the second gradient may be the same direction, may be opposite directions, may of course be other types of directions, etc.

Specifically, when magnetic resonance scanning is actually performed on a detection object, different gradients can be generated through a gradient system in the magnetic resonance equipment, the generated gradients are applied to the scanning object, a first gradient can be applied first, and a pre-scanning sequence is adopted to acquire magnetic resonance signals after the first gradient is applied at the acquisition time of each echo time, so that first magnetic resonance signals of each echo time are obtained. Then, a second gradient can be applied to the magnetic resonance coil, and the magnetic resonance signals after the second gradient is applied are acquired by adopting the same pre-scanning sequence at the acquisition time of each echo time, the number of which is the same as that of the acquisition time after the first gradient is applied, so that the second magnetic resonance signals of each echo time are obtained. The second magnetic resonance signals obtained here correspond to the acquisition instants of the echo times of the first magnetic resonance signals, i.e. a first magnetic resonance signal and a second magnetic resonance signal are obtained at the corresponding acquisition instants. In addition, the pre-scan sequence may be a GRE sequence, but may be other sequences, such as SE sequences, etc.

S204, determining two magnetic resonance images of each echo time according to the first magnetic resonance signal and the second magnetic resonance signal of each echo time, and determining the phase difference between the two magnetic resonance images of each echo time.

In this step, after the first magnetic resonance signal and the second magnetic resonance signal under each echo time are obtained, magnetic resonance images corresponding to the two magnetic resonance signals under each echo time can be obtained by means of image reconstruction or the like, and phases of each magnetic resonance image can be obtained by parameters on the magnetic resonance images. The phase difference between each two magnetic resonance images can then be obtained by differencing the two magnetic resonance images at the respective echo times, etc.

S206, determining vortex field distribution under at least one imaging echo time according to each phase difference.

The echo time may be, for example, 1ms, 2ms, 3ms, etc., and the imaging echo time may be any echo time, for example, 1.2ms, 1.5ms, 2.3ms, etc., when the imaging scanning sequence is performed.

In this step, after obtaining the phase difference between every two magnetic resonance images at each echo time, where each two magnetic resonance images is a magnetic resonance image after two different gradients corresponding to the echo time are applied, mathematical arithmetic processing can be performed on the phase difference between every two magnetic resonance images by using a mathematical algorithm related to the time characteristic and the spatial characteristic of the eddy current, so as to obtain a vortex field at any spatial position at each echo time, where the echo time is any echo time, i.e., each imaging echo time, and then, the vortex field at any spatial position at each imaging echo time can be obtained.

S208, performing eddy current correction on the magnetic resonance signals corresponding to the imaging echo time by using the eddy current field distribution under the imaging echo time.

In this step, after the eddy current field at any spatial position under each echo time is obtained, that is, the eddy current field at any spatial position under any imaging echo time can be obtained, when the eddy current field correction is actually performed, the eddy current at any imaging echo time and at any spatial position can be corrected by using the obtained eddy current field after the magnetic resonance signal acquired by the imaging scanning sequence is performed. In this embodiment, the magnetic resonance signal may refer to the acquisition of raw data by the receiving coil of the magnetic resonance system, or may be filled only into the cartesian data lines and non-cartesian data lines in K space. The magnetic resonance signals are subjected to Fourier transformation to obtain a magnetic resonance image to be processed. Optionally, the eddy current correction of the magnetic resonance signal corresponding to the imaging echo time by using the eddy current field distribution under the imaging echo time may be performed by directly correcting the magnetic resonance signal by using the eddy current field distribution, or may be performed by correcting the magnetic resonance image to be processed by using the eddy current field distribution.

As can be seen from the above description, the obtained eddy current field distribution may be used to perform eddy current correction on the image at any imaging echo time and any spatial position, so that there is no case where eddy current correction is not performed on the image at any one or more echo times or at any one or more spatial positions, so that eddy current correction can be accurately performed on the image at each echo time and each spatial position, and thus accurate eddy current correction can be finally achieved, and a more accurate geomagnetic resonance image can be obtained.

In the eddy current correction method, the first magnetic resonance signals of a plurality of echo times after the application of the first gradient and the second magnetic resonance signals of a plurality of echo times after the application of the second gradient corresponding to the acquisition time are used for determining the two magnetic resonance images of each echo time and the phase difference between the two magnetic resonance images through the two magnetic resonance signals of each echo time, determining the eddy current field distribution under one or a plurality of imaging echo times according to each phase difference, and performing eddy current correction by utilizing the eddy current field distribution under the imaging echo time. In the method, the eddy current field distribution under any imaging echo time can be determined through the phase difference between the magnetic resonance images after the application of different gradients of each echo time, so that the eddy current at any imaging echo time can be accurately corrected when the eddy current is corrected, and no great eddy current residue exists, thereby realizing the accurate correction of the eddy current, and improving the accuracy of correcting the eddy current.

In another embodiment, another method for correcting eddy currents is provided, and based on the above embodiment, as shown in fig. 3, the step S206 may include the following steps:

S302, processing each phase difference, and determining the vortex field distribution at each echo time.

Wherein the vortex field distribution is related to the phase (or phase difference), the following formula (1) or a modified expression of formula (1) can be adopted, and formula (1) is as follows:

Bz=φ/(2·pi·γ·TE·2) (1)

wherein pi refers to the circumferential rate pi, gamma refers to the gyromagnetic ratio, which can be known after the magnetic resonance coil is set, is a known quantity, TE refers to the echo time, which refers to the time interval between the radio frequency pulse and the corresponding echo, is also a known quantity, phi refers to the phase difference between two magnetic resonance images at the corresponding moment, and Bz refers to the eddy field distribution.

The phase difference between the two magnetic resonance images at the corresponding echo times is a phase difference that characterizes the space, i.e., the phase difference is not simply a value, but may be a phase space distribution. For example, referring to fig. 3a, in the echo time 0-200ms, magnetic resonance signals are acquired every 10ms (i.e. two magnetic resonance images are acquired every 10 ms), 20 times, i.e. 20 times, the phase difference between the two magnetic resonance images at 20 acquisition times can be acquired, and the 20 acquired phase difference distribution diagrams are shown in fig. 3 a. In addition, FIG. 3a is merely an example and does not affect the essence of embodiments of the present application.

After the phase difference between the two magnetic resonance images and the related calculation parameters under each corresponding echo time are obtained, the phase difference is provided with spatial distribution, namely the spatial position can be represented, and then the eddy field distribution Bz at any spatial position under each imaging echo time can be obtained by calculating through the deformation of the formula (1) or the formula (1).

S304, solving the vortex field distribution under each echo time, and determining one or more vortex fields under imaging echo time.

In this step, optionally, the following steps A1 and A2 may be used to solve for the eddy current field at any spatial position at multiple echo times:

And A1, carrying out coefficient expansion on vortex field distribution under each echo time according to a preset spherical harmonic function, and determining vortex spherical harmonic coefficients under each imaging echo time.

Wherein the spherical harmonics are related to the spatial positions of the points, the following formula (2) or a deformed representation of formula (2) can be adopted, and the formula (2) is as follows:

Here Bz (x, y, z) is the same as Bz described above, except that the spatial position x, y, z of each point is shown in Bz (x, y, z) here. The first term in equation (2) is generally referred to as the eddy current B ₀ term, the second through fourth terms are generally referred to as the eddy current linear term or first order term, and by simplification these three terms correspond exactly to the gradient coils (magnetic resonance coils) to produce gradients in the x, y, z directions. Higher orders than the above four items are generally referred to as eddy current higher order items.

Specifically, after obtaining the eddy field distribution Bz (x, y, z) at any spatial position under each corresponding echo time, the spatial position of each point can be known, and then Bz (x, y, z) of each point can be expressed by adopting the formula (2) or the deformation of the formula (2), and only the formula (2) is adopted in the expressed formulasThese coefficients are unknown and then can be solved by combining the multiple formulas to obtain the values of these coefficients, which can be noted as the eddy current spherical harmonic coefficients at each imaging echo time, since the coefficients are at each imaging echo time.

It should be noted that the number of the substrates, each spherical harmonic coefficient obtained hereThe coefficients are time-dependent, i.e. each spherical harmonic coefficient will have a value at the acquisition instant of each imaging echo time. Referring to fig. 3b, in different echo times of 0-200ms, the variation trend of the Amplitude of each spherical harmonic coefficient with Time (ms) can be obtained through the above solving process. In addition, FIG. 3b is merely an example and does not affect the essence of embodiments of the present application.

And step A2, obtaining vortex field distribution under each imaging echo time according to the vortex spherical harmonic coefficient under each imaging echo time.

In this step, after obtaining the spherical harmonic coefficients of the eddy currents at each imaging echo time, the eddy currents are typically represented in terms of time by a multi-exponential decay function model, typically represented by the following equation (3) or a deformation of equation (3):

Wherein G _eddy (t) is the vortex size related to time, e (t) is impulse response, N is multi-index vortex component, and alpha and tau are the amplitude and time constant of each vortex component, and can be known quantity.

Then the vortex under any imaging echo time can be obtained by using the above formula (3) or the deformation of the formula (3), and the vortex spherical harmonic coefficient under each imaging echo time is combined and substituted into the formula (2), so that the vortex field at any spatial position under each imaging echo time can be obtained. When the vortex field at any space position under any imaging echo time needs to be obtained, the vortex field at the corresponding space position of the corresponding adjacent imaging echo time can also be selected from the vortex spherical harmonic coefficients, and then fitting operation is carried out on the vortex field at the known space position of the known imaging echo time by adopting fitting algorithms such as interpolation algorithm, so as to obtain the vortex field at the space position required by the required imaging echo time, namely the vortex field at any space position under each imaging echo time.

In this embodiment, the phase difference between the two magnetic resonance images at each echo time is mathematically processed by using a spherical harmonic related to the phase, so as to obtain a spherical harmonic coefficient of the vortex field at any spatial position at each echo time, and the vortex field at any spatial position at each corresponding moment is solved by using a multi-exponential decay model or an interpolation algorithm, so as to obtain the vortex field at any spatial position at each imaging echo time. The phase difference is subjected to mathematical operation by adopting spherical harmonic function to determine the vortex field at any spatial position of any imaging echo time, and the calculation process is visual and accurate, so that the accuracy of the obtained vortex field at any spatial position of any imaging echo time can be further improved. Further, the coefficient of the vortex field at any spatial position under each imaging echo time is solved by adopting spherical harmonics related to the spatial position, and each spherical harmonic coefficient can be accurately obtained, so that the vortex field at any spatial position under each imaging echo time can be conveniently and quickly obtained later.

In another embodiment, another eddy current correction method is provided, and based on the above embodiment, as shown in fig. 4, the step S202 may include the following steps:

S402, after the first gradient is applied, performing multi-layer data cross acquisition by adopting a pre-scanning sequence, and obtaining first magnetic resonance signals of a plurality of echo times after the first gradient is applied.

In the step, when data acquisition is carried out, the pre-scanning sequence is a GRE sequence, and the GRE sequence is adopted for data acquisition, so that the interactive excitation among each layer of data can be realized, and magnetic resonance signals at a plurality of moments can be acquired simultaneously in a time period, and the data acquisition efficiency can be improved.

In addition, the multi-layer data cross acquisition refers to cross acquisition of data of each layer at the acquisition time of each echo time, namely, the data of each layer are fused together for acquisition, and the other layer of data is acquired after the acquisition of one layer of data is not completed, namely, the excitation acquisition of the data of a single layer is not realized.

For example, taking three-layer data acquisition as an example, echo time of three layers of data, namely, SLICE1, SLICE2 and SLICE3, is from T1-TN, and data of each layer of data in the phase encoding direction is respectively filled in PE1-PEend (PE 1-PEend respectively represents a filling region along the phase encoding direction in K space), then when multi-layer data cross-acquisition in this embodiment is adopted, acquisition time sequence of the whole sequence corresponding to fig. 4a is as follows:

Specifically, as shown above, the whole pre-scan comprises three different excitations, each excitation detecting multiple layers of the object, and echo times of two or more layers are different, magnetic resonance signals of different echo times of three layers of SLICE1-SLICE3 are acquired simultaneously in the first excitation process, in this embodiment, magnetic resonance signals of SLICE1-T1, SLICE2-T12, SLICE3-T3 and SLICE1-T4 are acquired respectively, different echoes belonging to the same SLICE of the same excitation are filled in different positions (PE 1, PE2 and the like in the above table) in K space, magnetic resonance signals belonging to different SLICEs and/or different echo times are filled in different K space respectively, magnetic resonance signals of SLICE2-T1, SLICE3-T12, SLICE1-T3 and SLICE2-T4 are acquired respectively in the second excitation, and magnetic resonance signals of SLICE3-T1, SLICE1-T12, SLICE2-T3 and SLICE3-T4 are acquired respectively in the third excitation. The GRE sequence is adopted to carry out multi-layer data cross acquisition on the magnetic resonance signals of each echo time under the first gradient in the mode, so that the magnetic resonance signals of each echo time after the first gradient is applied can be obtained and all the magnetic resonance signals are recorded as first magnetic resonance signals.

As can be seen from the above description, the magnetic resonance signals of multiple echo times can be acquired simultaneously after the first gradient is applied, that is, magnetic resonance images of multiple echo times can be acquired simultaneously, for example, N K spaces filled with magnetic resonance signals are acquired from the acquisition time of multiple echo times of T1-TN, and compared with the prior art, one K space filled with magnetic resonance signals is acquired at one echo time, where the magnetic resonance signals can be improved by N times, that is, the acquisition efficiency of the magnetic resonance signals or images can be improved.

In addition, by adopting the existing data acquisition mode, the time interval for acquiring each layer of data is assumed to be TR, so that the acquisition time sequence of the whole sequence can know that the time interval when each layer of data is acquired is n×tr, where n is the number of layers of the acquired data (for example, n is 3 in the above example), therefore, the time interval when the magnetic resonance signals of the same layer are acquired by adopting the scheme of the embodiment is enlarged, the longitudinal magnetization vector of each layer has enough time to recover, the mutual influence between different excitations can be avoided, each acquired magnetic resonance signal can obtain an image with high signal-to-noise ratio, and signal distortion generated by multiple excitations is reduced.

S404, after the second gradient is applied, performing multi-layer data cross acquisition by adopting a pre-scanning sequence, and obtaining second magnetic resonance signals of a plurality of echo times after the second gradient is applied.

In this step, in the same manner as in S402, the multiple-layer data cross acquisition is performed on the magnetic resonance signals of the echo times after the second gradient is applied by using the GRE sequence in the same acquisition time of the echo times, so that the magnetic resonance signals of the echo times after the second gradient is applied can be obtained and all the magnetic resonance signals are recorded as the second magnetic resonance signals.

For example, referring to fig. 4a, the number of data acquisition layers is n, and magnetic resonance signals obtained by performing excitation acquisition on each layer in different echo Times (TE) respectively obtain data of a plurality of K spaces, wherein TR (repetition time) represents a time interval between two adjacent executions. The magnetic resonance signals are subjected to multi-layer data cross acquisition after the first gradient is applied (for example, under Gtest gradients), so that the first magnetic resonance signals at acquisition moments of different echo times can be obtained, and then the magnetic resonance signals are subjected to multi-layer data cross acquisition after the second gradient is applied (for example, the gradient of which the Gtest gradient is reversed), so that the second magnetic resonance signals at the acquisition moments of different echo times can be obtained. In addition, it should be noted that fig. 4a is only an example, and does not affect the essence of the embodiment of the present application.

In this embodiment, the first magnetic resonance signals of the plurality of echo times after the application of the first gradient and the second magnetic resonance signals of the plurality of echo times after the application of the second gradient may be obtained by performing multi-layer data cross acquisition on the magnetic resonance signals of the plurality of echo times after the application of the first gradient by using the pre-scan sequence. In this embodiment, on the one hand, the magnetic resonance signals of multiple echo times may be acquired simultaneously after the first gradient and the second gradient are applied, that is, the magnetic resonance images of multiple echo times may be acquired simultaneously, so that the acquisition efficiency of the signals or the images may be improved. On the other hand, the pre-scanning sequence adopts the GRE sequence to carry out multi-layer data cross acquisition after the first gradient and the second gradient are applied, and the effective recovery time of the magnetization vector is changed from TR to n-TR, so that the signal-to-noise ratio of the image quality can be effectively improved.

In another embodiment, another method for correcting eddy currents is provided, wherein the first gradient and the second gradient are two gradients with equal magnitudes and opposite directions based on the above embodiment, and the step S206 may specifically include the following step B:

and B, determining the vortex field distribution at each imaging echo time after the first gradient is applied or after the second gradient is applied according to each phase difference.

In this step, the intensity of the first gradient is equal to the intensity of the second gradient and opposite in direction. Then in this step, the vortex field distribution at any spatial position in the respective imaging echo times under the first gradient may be obtained in the steps of S302 to S304, and since the intensities of the first gradient and the second gradient are equal, the vortex field distribution at any spatial position in the respective imaging echo times after the application of the second gradient may be also obtained. That is, a vortex field distribution at any spatial location at each imaging echo time at a certain gradient can be obtained here.

In general, the gradient system is a linear system, and after the vortex field distribution at any spatial position under each imaging echo time after a certain gradient is applied is obtained, the vortex field distribution at any spatial position under each imaging echo time under any gradient can be obtained by performing linear calculation on the vortex field distribution at any spatial position under each imaging echo time after the gradient is applied. The specific calculation method may include the following calculation steps C1 and C2:

And C1, acquiring a first intensity ratio between the preset intensity of the third gradient and the intensity of the first gradient, or a second intensity ratio between the intensity of the third gradient and the intensity of the second gradient.

In this step, when it is necessary to obtain the eddy current field distribution after application of an arbitrary gradient, the arbitrary gradient and its intensity, which is referred to herein as a third gradient, may be obtained in advance. Then, the intensity of the third gradient may be divided by the intensity of the first gradient to obtain a proportion of the intensity of the third gradient to the intensity of the first gradient, which is denoted as a first intensity proportion. Similarly, the ratio of the intensity of the third gradient to the intensity of the second gradient may be obtained and may be referred to as a second intensity ratio. Here, since the intensity of the first gradient and the intensity of the second gradient are equal in magnitude, the first intensity ratio and the second intensity ratio are also generally equal.

And C2, carrying out linear superposition processing on the vortex field distribution under each imaging echo time after the first gradient is applied and after the second gradient is applied according to the first intensity proportion or the second intensity proportion, and determining the vortex field distribution under each imaging echo time under the third gradient.

In this step, after the first intensity ratio or the second intensity ratio is obtained, the vortex field at any spatial position under each imaging echo time after the application of the first gradient or the second gradient can be obtained at the same time, so that the product can be obtained by multiplying the first intensity ratio or the second intensity ratio by the vortex field at any spatial position under each imaging echo time after the application of the first gradient or the second gradient, and the obtained product is the vortex field at any spatial position under each imaging echo time after the application of the third gradient.

In this embodiment, the intensity of the first gradient and the intensity of the second gradient are equal and opposite, so that the vortex field distribution at any spatial position of each imaging echo time after the application of the first gradient or the second gradient can be obtained through the phase difference of the two magnetic resonance images at each imaging echo time. Further, the vortex field at any spatial position under each imaging echo time under any gradient can be obtained through the intensity ratio between any gradient and the known first gradient or the known second gradient, so that the method is not limited by the intensity of the gradient of the vortex, and the application range of vortex correction is improved.

In another embodiment, another method for correcting eddy currents is provided, and based on the above embodiment, as shown in fig. 5, the step S204 may include the following steps:

S502, performing image reconstruction on the first magnetic resonance signal and the second magnetic resonance signal of each echo time to obtain a first magnetic resonance image and a second magnetic resonance image of each echo time.

In the step, after each first magnetic resonance signal is obtained, respectively carrying out image reconstruction on the first magnetic resonance signal obtained at present to obtain a first magnetic resonance image under the current echo time, so that the first magnetic resonance image of each echo time corresponding to each slice can be finally obtained; of course, after the first magnetic resonance signals of all echo times are obtained, the first magnetic resonance signals of each echo time may be reconstructed for each slice, and a first magnetic resonance image of each echo time may be obtained for each slice.

Likewise, the image reconstruction may be performed on the second magnetic resonance signal of each echo time of each slice in the above manner, so as to obtain a second magnetic resonance image of each echo time of each slice.

The first magnetic resonance image of each echo time obtained here corresponds to the second magnetic resonance image of each echo time one by one, both corresponding to the same slice. For example, the first magnetic resonance image obtained at the first echo time and the second magnetic resonance image obtained at the first echo time are two magnetic resonance images obtained at the corresponding echo time, the first magnetic resonance image obtained at the mth echo time and the second magnetic resonance image obtained at the mth echo time are two magnetic resonance images obtained at the corresponding time, and m is any positive integer.

In addition, when the image reconstruction is carried out on the magnetic resonance signals, any image reconstruction algorithm can be selected for image reconstruction so as to obtain a first magnetic resonance image and a second magnetic resonance image.

S504, a first phase of each echo time is obtained from the first magnetic resonance image of each echo time, and a second phase of each echo time is obtained from the second magnetic resonance image of each echo time.

In this step, after the image reconstruction is performed on the magnetic resonance signals at each echo time to obtain a magnetic resonance image, the phases corresponding to the magnetic resonance images may also be obtained, where the phases of each two magnetic resonance images are generally phase distributions that may represent spatial positions, and generally the phases obtained at each echo time may be different.

The phases of the first magnetic resonance image of each echo time can be marked as a first phase, and the phases of the second magnetic resonance image of each echo time can be marked as a second phase, so that the first phase and the second phase of each corresponding echo time can be obtained.

S506, performing a difference operation on the first phase and the second phase of each echo time to obtain a phase difference between the first magnetic resonance image and the second magnetic resonance image of each echo time.

In this step, after the first phase and the second phase of each corresponding echo time are obtained, a difference operation may be performed on the first phase and the second phase of each corresponding echo time, where the difference operation may be subtracting the second phase from the first phase or subtracting the first phase from the second phase, and in any case, a difference between the two phases at each corresponding echo time may be obtained, that is, a phase difference between the first magnetic resonance image and the second magnetic resonance image of each corresponding echo time may be obtained.

In this embodiment, by performing image reconstruction on the first magnetic resonance signal and the second magnetic resonance signal with different corresponding echo times, two magnetic resonance images and respective phases under each corresponding echo time are obtained, and performing a difference operation on the two phases of the two magnetic resonance images corresponding to the echo time, a phase difference between the two magnetic resonance images corresponding to the echo time is obtained.

The correction of eddy currents is described in the above embodiments, on the basis of which the magnetic resonance image can also be corrected, as will be explained below.

In another embodiment, a magnetic resonance image correction method is provided, and based on the above embodiment, referring to fig. 6, the method may include the following steps:

S602, acquiring a plurality of groups of magnetic resonance images of a scanned object, wherein each group of magnetic resonance images comprises a first magnetic resonance image and a second magnetic resonance image corresponding to the same echo time, the first magnetic resonance image is obtained by reconstructing a first magnetic resonance signal acquired after a first gradient is applied, and the second magnetic resonance image is obtained by reconstructing a second magnetic resonance signal acquired after a second gradient is applied. The scan object comprises a plurality of slices and the plurality of sets of magnetic resonance images comprises a series of first and second magnetic resonance images at different echo times for each slice.

Wherein the scan object may be any one or more parts of the body of a human or animal body. The first magnetic resonance images can be obtained by applying a first gradient to the scan subject and acquiring the first magnetic resonance signals of each layer under the first gradient, i.e. acquiring the first magnetic resonance signals at each echo time and performing image reconstruction on the first magnetic resonance signals of each layer.

The acquisition mode of each second magnetic resonance image may be the same as that of the first magnetic resonance image, and the difference is only that a second gradient different from the first gradient is applied, which will not be described here again.

S604, determining a phase difference between the first magnetic resonance image and the second magnetic resonance image in each set of magnetic resonance images.

The explanation of this step may be referred to the explanation of S204, and will not be repeated here.

S606, determining vortex field distribution of at least one imaging echo time according to the phase difference.

The explanation of this step may be referred to the explanation of S206, and will not be repeated here.

S608, correcting the magnetic resonance image to be processed corresponding to the imaging echo time according to the vortex field distribution, and obtaining a corrected magnetic resonance image.

In this step, taking the magnetic resonance image to be processed as a diffusion image as an example, after the vortex field distribution of at least one imaging echo time is obtained, the vortex field distribution can be used to perform image correction on the diffusion image to be processed, so as to obtain a corrected diffusion image.

In one embodiment, the imaging scan sequence adopts a planar echo diffusion weighted imaging (EPI-DWI) sequence, which excites magnetic resonance signals in different diffusion directions acquired after the object is detected, the magnetic resonance signals in the different diffusion directions are reconstructed to obtain a plurality of initial diffusion images (the plurality of initial diffusion images are magnetic resonance images to be processed), the plurality of initial diffusion images can be corrected by adopting the eddy field distribution to obtain a plurality of corrected diffusion images respectively, and the plurality of corrected diffusion images are combined to obtain a synthesized diffusion image.

In one embodiment, a Diffusion Weighted (DWI) image obtained by reconstructing and combining magnetic resonance signals in different diffusion directions is used as a magnetic resonance image to be processed, where the DWI image is obtained by multiplying pixels of a diffusion image in multiple directions (for example, three directions) point by point and then opening up the cube, as follows:

Wherein, VOX represents the value of any pixel point in the DWI image, and D1, D2 and D3 respectively represent the values of the corresponding pixel points of three different diffusion directions. Due to the fact that the dispersion gradients are different in size in different directions, different vortex flows can be generated at the moment of image acquisition, and bandwidth is low along the direction of Phase Encoding (PE) in the process of DWI sequence acquisition. Thus, the PE direction of the image is shifted. And the composite DWI image is blurred because of the different diffusion gradient vortices in different directions. By way of example, the shift of the magnetic resonance image to be processed can be expressed as:

Where Δy represents the displacement along the phase encoding direction, t _esp is the adjacent echo time interval of EPI_DWI, and G _yτ_y represents the zero-order moment of the PE-direction spike. And obtaining displacement along the phase encoding direction in the DWI image according to the vortex field distribution Bz, and correcting the DWI image according to the displacement along the phase encoding direction.

As shown in fig. 6a, from left to right, the initial diffusion image of direction 1, the initial diffusion image of direction 2, the initial diffusion image of direction 3, and the composite DWI image are obtained according to the first embodiment of the present application. The initial diffusion image is affected by vortex of different sizes, so that different deformation is generated, and the composite DWI image has serious blurring. The flow of FIG. 6, an embodiment of the present application, is used to correct the composite DWI image for eddy current effects. As shown in fig. 6b, the initial diffusion image of the direction 1, the initial diffusion image of the direction 2, the initial diffusion image of the direction 3, and the corrected DWI image are corresponding to the corrected DWI image, respectively, from left to right. The image positions of the corrected diffusion images in the single direction tend to be consistent, and the corrected DWI image boundaries become clear.

In this embodiment, by acquiring a plurality of sets of magnetic resonance images of a plurality of slices of a scan object, each set of magnetic resonance images includes a first magnetic resonance image and a second magnetic resonance image corresponding to the same echo time, determining a phase difference between the first magnetic resonance image and the second magnetic resonance image in each set of magnetic resonance images, determining a vortex field distribution of each imaging echo time according to the phase difference, and correcting a diffusion image to be processed according to the vortex field distribution, a corrected diffusion image is obtained. In this way, it is possible to accurately perform eddy current correction for each echo time and for each image at each spatial position, and correct the diffusion image on the basis of this, to obtain a more accurate corrected image.

It should be understood that, although the steps in the flowcharts of fig. 2,3, 4,5, and 6 are shown in order as indicated by the arrows, these steps are not necessarily performed in order as indicated by the arrows. The steps are not strictly limited to the order of execution unless explicitly recited herein, and the steps may be executed in other orders. Moreover, at least some of the steps of fig. 2,3, 4,5, 6 may comprise a plurality of steps or stages, which are not necessarily performed at the same time, but may be performed at different times, nor does the order in which the steps or stages are performed necessarily occur in sequence, but may be performed alternately or alternately with other steps or at least a portion of the steps or stages in other steps.

In one embodiment, as shown in FIG. 7, there is provided an eddy current correction apparatus comprising a signal acquisition module 10, a first phase difference determination module 11, a first eddy current field determination module 12, and an eddy current correction module 13, wherein:

The signal acquisition module 10 is configured to acquire a first magnetic resonance signal of a plurality of echo times acquired after a first gradient is applied and a second magnetic resonance signal of a plurality of echo times acquired after a second gradient is applied;

A first phase difference determining module 11, configured to determine two magnetic resonance images of each echo time according to the first magnetic resonance signal and the second magnetic resonance signal of each echo time, and determine a phase difference between the two magnetic resonance images of each echo time;

A first vortex field determination module 12 for determining a vortex field distribution at one or more imaging echo times from the respective phase differences;

the eddy current correction module 13 is used for performing eddy current correction by using the eddy current field distribution at the imaging echo time.

For specific limitations of the eddy current correction device, reference may be made to the above limitations of the eddy current correction method, which are not repeated here.

In another embodiment, another eddy current correction device is provided, and the first eddy current field determining module 12 may include a mathematical operation processing unit and an eddy current field determining unit based on the above embodiment, wherein:

The mathematical operation processing unit is used for performing mathematical operation processing on each phase difference and determining the vortex field distribution at each echo time;

the vortex field determining unit is used for solving the vortex field distribution under each echo time and determining the vortex field distribution under each imaging echo time.

Optionally, the vortex field determining unit may include a coefficient expansion subunit and a vortex field determining subunit, wherein:

The coefficient expansion subunit is used for carrying out coefficient expansion on the vortex field distribution under each echo time according to a preset spherical harmonic function and determining the vortex spherical harmonic coefficient under each imaging echo time;

And the vortex field determining subunit is used for obtaining the vortex field distribution under each imaging echo time according to the vortex spherical harmonic coefficient under each imaging echo time.

In another embodiment, another eddy current correction device is provided, and the acquisition module 10 may include a first signal acquisition unit and a second signal acquisition unit based on the above embodiment, where:

The first signal acquisition unit is used for carrying out multi-layer data cross acquisition by adopting a pre-scanning sequence after the first gradient is applied to obtain first magnetic resonance signals of a plurality of echo times after the first gradient is applied;

and the second signal acquisition unit is used for carrying out multi-layer data cross acquisition by adopting a pre-scanning sequence after the second gradient is applied, so as to obtain second magnetic resonance signals of a plurality of echo times after the second gradient is applied.

In another embodiment, another eddy current correction device is provided, wherein the first gradient and the second gradient are two gradients with equal gradient intensity and opposite gradient intensity, and the eddy current field determining module 12 is specifically configured to determine the eddy current field distribution at each imaging echo time after the first gradient is applied or after the second gradient is applied according to each phase difference.

In another embodiment, another eddy current correction device is provided, and the phase difference determining module 11 may include an image reconstructing unit, a phase acquiring unit, and a phase difference determining unit, wherein:

The image reconstruction unit is used for carrying out image reconstruction on the first magnetic resonance signal and the second magnetic resonance signal of each echo time to obtain a first magnetic resonance image and a second magnetic resonance image of each echo time;

a phase acquisition unit for acquiring a first phase of each echo time from a first magnetic resonance image of each echo time and a second phase of each echo time from a second magnetic resonance image of each echo time;

And the phase difference determining unit is used for carrying out difference operation on the first phase and the second phase of each echo time to obtain the phase difference between the first magnetic resonance image and the second magnetic resonance image of each echo time.

In another embodiment, there is provided a magnetic resonance image correction apparatus, including, on the basis of the above embodiment:

The image acquisition module is used for acquiring a plurality of groups of magnetic resonance images of a plurality of slices of a scanned object, each group of magnetic resonance images comprises a first magnetic resonance image and a second magnetic resonance image corresponding to the same echo time, the first magnetic resonance image is obtained by reconstructing a first magnetic resonance signal acquired after a first gradient is applied, and the second magnetic resonance image is obtained by reconstructing a second magnetic resonance signal acquired after a second gradient is applied;

and the image correction module is used for correcting the magnetic resonance image to be processed corresponding to the imaging echo time according to the vortex field distribution, and acquiring a corrected magnetic resonance image.

The above-described eddy current correction device and the respective modules in the magnetic resonance image correction device may be implemented in whole or in part by software, hardware, and combinations thereof. The above modules may be embedded in hardware or may be independent of a processor in the computer device, or may be stored in software in a memory in the computer device, so that the processor may call and execute operations corresponding to the above modules.

In one embodiment, a computer device is provided comprising a memory and a processor, the memory having stored therein a computer program, the processor when executing the computer program performing the steps of:

The method comprises the steps of acquiring a first magnetic resonance signal of a plurality of echo times acquired after a first gradient is applied and a second magnetic resonance signal of a plurality of echo times acquired after a second gradient is applied, acquiring the first magnetic resonance signal of the plurality of echo times and the second magnetic resonance signal of the plurality of echo times, determining two magnetic resonance images of each echo time according to the first magnetic resonance signal and the second magnetic resonance signal of each echo time, determining a phase difference between the two magnetic resonance images of each echo time, determining vortex field distribution under one or more imaging echo times according to each phase difference, and performing vortex correction on the magnetic resonance signals corresponding to the imaging echo times by utilizing the vortex field distribution under the imaging echo times.

In one embodiment, the processor when executing the computer program further performs the steps of:

The method comprises the steps of carrying out mathematical operation on each phase difference to determine the vortex field distribution under each echo time, solving the vortex field distribution under each echo time, and determining the vortex field distribution under each imaging echo time.

according to the preset spherical harmonic function, coefficient expansion is carried out on the vortex field distribution under each echo time, the vortex spherical harmonic coefficient under each imaging echo time is determined, and according to the vortex spherical harmonic coefficient under each imaging echo time, the vortex field distribution under each imaging echo time is obtained.

and after the second gradient is applied, the multilayer data cross acquisition is performed by adopting the pre-scanning sequence, so as to obtain a second magnetic resonance signal of the echo times after the second gradient is applied.

The method comprises the steps of carrying out image reconstruction on a first magnetic resonance signal and a second magnetic resonance signal of each echo time to obtain a first magnetic resonance image and a second magnetic resonance image of each echo time, obtaining a first phase of each echo time according to the first magnetic resonance image of each echo time and a second phase of each echo time according to the second magnetic resonance image of each echo time, and carrying out difference operation on the first phase and the second phase of each echo time to obtain a phase difference between the first magnetic resonance image and the second magnetic resonance image of each echo time.

The method comprises the steps of acquiring a plurality of groups of magnetic resonance images of a plurality of slices of a scanned object, wherein each group of magnetic resonance images comprises a first magnetic resonance image and a second magnetic resonance image corresponding to the same echo time, the first magnetic resonance image is obtained by reconstructing a first magnetic resonance signal acquired after a first gradient is applied, the second magnetic resonance image is obtained by reconstructing a second magnetic resonance signal acquired after a second gradient is applied, determining a phase difference between the first magnetic resonance image and the second magnetic resonance image in each group of magnetic resonance images, determining vortex field distribution of at least one imaging echo time according to the phase difference, correcting the magnetic resonance image to be processed corresponding to the imaging echo time according to the vortex field distribution, and obtaining a corrected magnetic resonance image.

In one embodiment, a computer readable storage medium is provided having a computer program stored thereon, which when executed by a processor, performs the steps of:

the method comprises the steps of acquiring a first magnetic resonance signal of a plurality of echo times acquired after a first gradient is applied and a second magnetic resonance signal of a plurality of echo times acquired after a second gradient is applied, acquiring time points of the first magnetic resonance signals of the plurality of echo times and the second magnetic resonance signals of the plurality of echo times, determining two magnetic resonance images of each echo time according to the first magnetic resonance signal and the second magnetic resonance signals of each echo time, determining phase differences between the two magnetic resonance images of each echo time, determining vortex field distribution under one or more imaging echo times according to each phase difference, correcting to-be-processed magnetic resonance images corresponding to the imaging echo time by utilizing the vortex field distribution under the imaging echo time, and acquiring corrected magnetic resonance images to perform vortex correction.

In one embodiment, the computer program when executed by the processor further performs the steps of:

Those skilled in the art will appreciate that implementing all or part of the above described methods may be accomplished by way of a computer program stored on a non-transitory computer readable storage medium, which when executed, may comprise the steps of the embodiments of the methods described above. Any reference to memory, storage, database, or other medium used in embodiments provided herein may include at least one of non-volatile and volatile memory. The nonvolatile Memory may include Read-Only Memory (ROM), magnetic tape, floppy disk, flash Memory, optical Memory, or the like. Volatile memory can include random access memory (Random Access Memory, RAM) or external cache memory. By way of illustration, and not limitation, RAM can be in various forms such as static random access memory (Static Random Access Memory, SRAM) or dynamic random access memory (Dynamic Random Access Memory, DRAM), etc.

The technical features of the above embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.

The above examples illustrate only a few embodiments of the application, which are described in detail and are not to be construed as limiting the scope of the application. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the application, which are all within the scope of the application. Accordingly, the scope of protection of the present application is to be determined by the appended claims.

Claims

1. An eddy current correction method, characterized in that the method comprises:

After the first gradient is applied, a pre-scan sequence is used to perform multi-layer data cross-collection to obtain a first magnetic resonance signal of a plurality of echo times after the first gradient is applied; after the second gradient is applied, a pre-scan sequence is used to perform multi-layer data cross-collection to obtain a second magnetic resonance signal of a plurality of echo times after the second gradient is applied;

Determine two magnetic resonance images at each echo time according to the first magnetic resonance signal and the second magnetic resonance signal at each echo time, and determine a phase difference between the two magnetic resonance images at each echo time;

Determining the eddy current field distribution at at least one imaging echo time according to each of the phase differences;

The eddy current field distribution at the imaging echo time is used to perform eddy current correction on the magnetic resonance signal corresponding to the imaging echo time.

2. The method according to claim 1, characterized in that the step of determining the eddy current field distribution at at least one imaging echo time according to each of the phase differences comprises:

Processing each of the phase differences to determine the eddy current field distribution at each of the echo times;

Perform coefficient expansion on the eddy current field distribution at each of the echo times according to a preset spherical harmonic function to determine the eddy current spherical harmonic coefficients at each imaging echo time;

According to the eddy current spherical harmonic coefficients at each imaging echo time, the eddy current field distribution at at least one imaging echo time is obtained.

3. The method according to claim 1, characterized in that the first gradient and the second gradient are two gradients with equal gradient strength and opposite directions; and determining the eddy current field distribution at each imaging echo time according to each phase difference comprises:

The eddy current field distribution at each imaging echo time after the first gradient is applied or after the second gradient is applied is determined according to each phase difference.

4. The method according to claim 1 or 2, characterized in that the determining of two magnetic resonance images at each echo time based on the first magnetic resonance signal and the second magnetic resonance signal at each echo time, and determining a phase difference between the two magnetic resonance images at each echo time, comprises:

Performing image reconstruction on the first magnetic resonance signal and the second magnetic resonance signal at each echo time to obtain a first magnetic resonance image and a second magnetic resonance image at each echo time;

obtaining a first phase at each echo time according to the first magnetic resonance image at each echo time, and obtaining a second phase at each echo time according to the second magnetic resonance image at each echo time;

A difference operation is performed on the first phase and the second phase at each echo time to obtain a phase difference between the first magnetic resonance image and the second magnetic resonance image at each echo time.

5. A magnetic resonance image correction method, characterized in that the method comprises:

Acquire multiple groups of magnetic resonance images of the scanned object, each group of magnetic resonance images includes a first magnetic resonance image and a second magnetic resonance image corresponding to the same echo time, the first magnetic resonance image is obtained by reconstructing first magnetic resonance signals of multiple echo times after the first gradient is applied by performing multi-layer data cross-acquisition using a pre-scan sequence, and the second magnetic resonance image is obtained by reconstructing second magnetic resonance signals of multiple echo times after the second gradient is applied by performing multi-layer data cross-acquisition using a pre-scan sequence;

determining an eddy current field distribution of at least one imaging echo time according to the phase difference;

The magnetic resonance image to be processed corresponding to the imaging echo time is corrected according to the eddy current field distribution to obtain a corrected magnetic resonance image.

6. An eddy current correction device, characterized in that the device comprises:

A signal acquisition module is used to perform multi-layer data cross acquisition using a pre-scan sequence after a first gradient is applied, to obtain a first magnetic resonance signal of a plurality of echo times after the first gradient is applied; and to perform multi-layer data cross acquisition using a pre-scan sequence after a second gradient is applied, to obtain a second magnetic resonance signal of a plurality of echo times after the second gradient is applied;

a first phase difference determining module, configured to determine two magnetic resonance images at each echo time according to the first magnetic resonance signal and the second magnetic resonance signal at each echo time, and to determine a phase difference between the two magnetic resonance images at each echo time;

A first eddy current field determination module, used to determine the eddy current field distribution at at least one imaging echo time according to each of the phase differences;

The eddy current correction module is used to perform eddy current correction on the magnetic resonance signal corresponding to the imaging echo time by utilizing the eddy current field distribution under the imaging echo time.

7. A computer device, comprising a memory and a processor, wherein the memory stores a computer program, wherein the processor implements the steps of the method according to any one of claims 1 to 5 when executing the computer program.

8. A computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 5 are implemented.