CN115436855A

CN115436855A - Eddy current correction method, magnetic resonance image correction apparatus, magnetic resonance image correction device, and medium

Info

Publication number: CN115436855A
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: 2022-12-06

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 the following steps: 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 eddy current field distribution under 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 by using the eddy current field distribution under the imaging echo time. By adopting the method, the accuracy of correcting the magnetic resonance eddy current can be improved.

Description

Eddy current correction method, magnetic resonance image correction apparatus, magnetic resonance image correction 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, an apparatus, a computer device, and a storage medium.

Background

During the operation of a magnetic resonance pulse imaging sequence, a series of time-varying gradient fields are used, which cause time-varying magnetic flux in the space surrounding the gradient coil, and at the same time, time-varying currents are generated in the metallic conductive material of the components surrounding the gradient, which are called eddy currents. The eddy current has a serious influence on the later magnetic resonance imaging, 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 correcting the eddy current, it is usually realized by means of pre-emphasis. That is, an inverse gradient is applied to the hardware of the magnetic resonance system (e.g., gradient coils, etc.) in the previous period, and then the correction of the eddy current is performed by the inverse gradient.

However, after the eddy current is corrected, the eddy current still remains, that is, the accuracy of the eddy current correction is low.

Disclosure of Invention

In view of the above, it is necessary to provide an eddy current correction method, a magnetic resonance image correction method, an apparatus, a computer device, and a storage medium capable of improving accuracy of magnetic resonance eddy current correction in view of the above technical problems.

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; 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 eddy current field distribution under 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 by using eddy current field distribution under the imaging echo time.

In one embodiment, the determining the eddy current field distribution at the at least one imaging echo time according to the phase differences includes:

processing each phase difference, and determining eddy current field distribution at each echo time;

and solving the eddy current field distribution at each echo time, and determining the eddy current field distribution at least one imaging echo time.

In one embodiment, the solving the eddy current field distribution at each echo time to determine the eddy current field distribution at least one imaging echo time includes:

performing coefficient expansion on the eddy current field distribution at each echo time according to a preset spherical harmonic function, and determining the eddy current spherical harmonic coefficient at each imaging echo time;

and obtaining the eddy current field distribution in at least one imaging echo time according to the eddy current spherical harmonic coefficient in each imaging echo time.

In one embodiment, the acquiring the first magnetic resonance signals of a plurality of echo times acquired after the application of the first gradient and the second magnetic resonance signals of a plurality of echo times acquired after the application of the second gradient includes:

after the first gradient is applied, a pre-scanning sequence is adopted to carry out multi-layer data cross acquisition, and first magnetic resonance signals of a plurality of echo times after the first gradient is applied are obtained;

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

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

and determining the eddy current field distribution at each imaging echo time after the first gradient application or the second gradient application according to each phase difference.

In one embodiment, the method further includes:

acquiring a first intensity ratio between the intensity of a preset 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, performing linear superposition processing on eddy current field distribution at each imaging echo time after the first gradient is applied and after the second gradient is applied, and determining eddy current field distribution at each imaging echo time at the third gradient.

In one embodiment, the determining two magnetic resonance images at each echo time and the phase difference between the 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 includes:

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 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 magnetic resonance image correction method, the method comprising:

acquiring multiple 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;

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

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

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

An eddy current correction device, comprising:

the signal acquisition module is used for 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; 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;

the first phase difference determining module is used for determining 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 determining the phase difference between the two magnetic resonance images at each echo time;

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

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

A magnetic resonance image correction apparatus, the apparatus comprising:

the system comprises an image acquisition module, a data acquisition module and a data processing module, wherein 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 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;

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;

the second eddy current field determining module is used for determining eddy current 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 eddy current field distribution to obtain a corrected magnetic resonance image.

A computer device comprising a memory and a processor, the memory storing a computer program, the processor implementing the following steps when executing the computer program:

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; 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 the eddy current field distribution under 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 by using the eddy current field distribution under at least one imaging echo time.

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;

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

A computer-readable storage medium, on which a computer program is stored which, when executed by a processor, carries out 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 application of the first gradient corresponding to the moment and the second magnetic resonance signals of a plurality of echo times after the application of the second gradient are acquired, 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 of the imaging echo time is determined according to each phase difference, and the eddy current correction is performed on the magnetic resonance signals corresponding to the imaging echo time by using the eddy current field distribution of the imaging echo time. In the method, the eddy current field distribution at any imaging echo time can be determined through the phase difference between the magnetic resonance images applied with 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 large eddy current residue exists, so that the eddy current can be accurately corrected, and the accuracy of correcting the eddy current can be improved.

Drawings

FIG. 1 is a diagram of the internal structure of a computer device in one embodiment;

FIG. 2 is a schematic flow chart diagram illustrating an exemplary method for eddy current calibration;

FIG. 3 is a schematic flow chart showing an eddy current correction step in another embodiment;

figure 3a is an exemplary graph of the phase difference of two magnetic resonance images at echo time in another embodiment;

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

FIG. 4 is a schematic flow chart illustrating an eddy current correction method according to another embodiment;

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

FIG. 5 is a schematic flow chart illustrating an eddy current correction method according to another embodiment;

FIG. 6 is a flow chart of a magnetic resonance image correction method 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 diffusion image and a corrected composite image of a plurality of diffusion directions obtained in another embodiment;

FIG. 7 is a block diagram showing the structure of an eddy current correction apparatus according to an embodiment.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of and not restrictive on the broad application.

The eddy current correction method provided by the embodiment of the application can be applied to a magnetic resonance system or a computer device, the magnetic resonance system can comprise a magnetic resonance scanning device and a computer device which are connected with each other, when a detected object is scanned, the detected object can be scanned through the magnetic resonance scanning device, and scanned data is transmitted to the computer device to be processed, so that eddy current correction is realized. Here, the eddy current correction method is applied to a computer device, which may be a terminal or a server, and the internal structure diagram of the computer device is 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 comprises a nonvolatile 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 an operating system and computer programs in the non-volatile storage medium. The communication interface of the computer device is used for carrying out wired or wireless communication with an external terminal, and the wireless communication 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 an eddy current correction method. 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, a key, a track ball or a touch pad arranged on the shell of the computer equipment, an external keyboard, a touch pad or a mouse and the like.

Those skilled in the art will appreciate that the architecture shown in fig. 1 is merely a block diagram of some of the structures associated with the disclosed aspects and is not intended to limit the computing devices to which the disclosed aspects apply, as particular computing devices may include more or less components than those shown, or may combine certain components, or have a different arrangement of components.

It should be noted that the executing subject of the embodiment of the present application may be a magnetic resonance system, a computer device in the magnetic resonance system, an eddy current correction device in the computer device, or other devices, and the technical solution of the present application will be described below with the computer device as the executing subject.

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

s202, 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 are acquired.

The acquisition time of the first magnetic resonance signal of the multiple echo times corresponds to the acquisition time of the second magnetic resonance signal of the multiple echo times, and the correspondence may mean that the number of the acquisition times of the multiple echo times after the first gradient application is equal to the number of the acquisition times of the multiple echo times after the second gradient application, for example, the acquisition times of the multiple echo times after the first gradient application may be T1 to Tn, and the acquisition times of the multiple echo times after the second gradient application may be T1 to Tn. The number of the acquisition moments of the multiple echo times may be preset, for example, 50 points need to be acquired, that is, 50 acquisition moments, and the 50 acquisition moments may be equal-interval or unequal-interval moments, for example, equal-interval acquisition moments of 5ms, 10ms, and so on.

The magnitude of the intensity of the first gradient and the magnitude of the intensity of the second gradient may or may not be equal. The direction of the first gradient and the direction of the second gradient may be the same direction, or may be opposite directions, or of course, may be other types of directions, and so on.

Specifically, when the magnetic resonance scan is actually performed on the detection object, different gradients may be generated by a gradient system in the magnetic resonance device, and the generated gradients are applied to the scan object, where a first gradient may be applied first, and at the acquisition time of each echo time, the magnetic resonance signal after the application of the first gradient is acquired by using a pre-scan sequence, so as to obtain the first magnetic resonance signal of each echo time. Then, a second gradient may be applied to the magnetic resonance coil, and at the acquisition time of each echo time of which the number is the same as that of the acquisition time after the first gradient is applied, the magnetic resonance signal after the second gradient is applied may be acquired by using the same pre-scan sequence, so as to obtain a second magnetic resonance signal of each echo time. 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 can be a GRE sequence, but can also be other sequences, such as an SE sequence, etc.

And 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 at each echo time are obtained, magnetic resonance images corresponding to the two magnetic resonance signals at each echo time may be obtained by image reconstruction or the like, and the phase of each magnetic resonance image is 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.

And S206, determining the eddy current field distribution under at least one imaging echo time according to the phase differences.

The echo time refers to the echo time set for executing the pre-scan sequence, and may be, for example, 1ms, 2ms, 3ms, or the like; the imaging echo time here refers to the echo time when the imaging scan sequence is executed, and may be any echo time, for example, 1.2ms, 1.5ms, 2.3ms, and so on.

In this step, after obtaining the phase difference between every two magnetic resonance images at each echo time, where every two magnetic resonance images are magnetic resonance images to which two different gradients corresponding to the echo time are applied, a mathematical algorithm related to the time characteristic and the spatial characteristic of the eddy current may be used to perform mathematical operation processing on the phase difference between every two magnetic resonance images, so as to obtain the eddy current field at any spatial position at each echo time, where the echo time is any echo time, i.e., each imaging echo time, i.e., the eddy current field at any spatial position at each imaging echo time may be obtained.

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

In this step, after obtaining the eddy current field at any spatial position at each echo time, that is, the eddy current field at any spatial position at any imaging echo time, when actually performing eddy current field correction, the eddy current field obtained here may be used to correct the eddy current at any imaging echo time and any spatial position after executing the magnetic resonance signal acquired by the imaging scanning sequence. In this embodiment, the magnetic resonance signal may refer to the raw data acquired by the receiving coil of the magnetic resonance system, or may be only filled into the cartesian data line and the non-cartesian data line in the K space. The magnetic resonance image to be processed can be obtained by performing Fourier transform on the magnetic resonance signal. Optionally, performing eddy current correction on the magnetic resonance signal corresponding to the imaging echo time by using the eddy current field distribution under the imaging echo time may be: the magnetic resonance signals are directly corrected by using the eddy current field distribution, or the magnetic resonance image to be processed is corrected by using the eddy current field distribution.

As can be seen from the above description, the obtained eddy current field distribution can be used to perform eddy current correction on an image at any imaging echo time and any spatial position, so that there is no case where no eddy current correction is performed on an image at any one or more echo times or at any one or more spatial positions, and thus, accurate eddy current correction can be performed on the image at each echo time and each spatial position, 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 which correspond to the time are acquired, 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 in one or a plurality of imaging echo times is determined according to each phase difference, and the eddy current field distribution in the imaging echo time is utilized for performing eddy current correction. In the method, the eddy current field distribution at any imaging echo time can be determined through the phase difference between the magnetic resonance images applied with different echo time gradients, so that eddy current correction can be accurately performed on the eddy current at any imaging echo time when the eddy current is corrected, and large eddy current residues can not exist, so that the eddy current can be accurately corrected, and the accuracy of eddy current correction can be improved.

In another embodiment, another eddy current correction method is provided, and on the basis of the above embodiment, as shown in fig. 3, the step S206 may include the steps of:

s302, processing the phase differences, and determining the eddy current field distribution at each echo time.

Wherein the eddy current field distribution is related to phase (or phase difference), and can be expressed by the following formula (1) or the deformation of formula (1), and formula (1) is as follows:

Bz＝φ/(2·pi·γ·TE·2) (1)

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

It should be noted that the phase difference between the two magnetic resonance images at the corresponding echo time is a phase difference that can be characterized in space, that is, the phase difference is not simply a numerical value, and may be a phase space distribution. Illustratively, referring to fig. 3a, within the echo time 0-200ms, magnetic resonance signals are acquired once every 10ms (i.e. two magnetic resonance images are acquired at an interval of 10 ms), 20 times, i.e. 20 time instants, then the phase difference between the two magnetic resonance images at 20 acquisition time instants can be acquired, and the obtained 20 phase difference profiles are as shown in fig. 3 a. In addition, fig. 3a is only an example here, and does not affect the essence of the embodiments of the present application.

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

S304, solving the eddy current field distribution at each echo time, and determining the eddy current field at one or more imaging echo times.

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

and A1, performing coefficient expansion on eddy current field distribution at each echo time according to a preset spherical harmonic function, and determining eddy current spherical harmonic coefficients at each imaging echo time.

The spherical harmonic function is related to the spatial position of each point, and may be represented by the following formula (2) or a variant of formula (2), where formula (2) is as follows:

here, bz (x, y, z) is the same as the above-described Bz, except that the spatial positions x, y, z of each point are shown in Bz (x, y, z). The first term in equation (2) is generally referred to as vortex B ₀ The terms, second to fourth terms, are generally called eddy current linear terms or first order terms, and these three terms after simplification correspond exactly to gradients in the x, y, z directions generated by a gradient coil (magnetic resonance coil). Higher order terms than the above four terms are generally referred to as eddy current higher order terms.

Specifically, after obtaining the eddy current field distribution Bz (x, y, z) at any spatial position at each corresponding echo time, the spatial position of each point can be obtained, and then the Bz (x, y, z) of each point can be expressed by the formula (2) or the deformation of the formula (2), and only the formula in the formula (2) is expressed in the formula

And when the coefficients are unknown quantities, solving the coefficients by using the multiple expression formulas simultaneously to obtain the values of the coefficients, wherein the coefficients are the coefficients at each imaging echo time and can be recorded as the eddy current spherical harmonic coefficients at each imaging echo time.

It should be noted that each spherical harmonic coefficient obtained here

The equal is time dependent, i.e. each spherical harmonic coefficient has a value at the acquisition instant at each imaging echo time. Referring to fig. 3b, in echo Time of 0-200ms, through the above solving process, the variation trend of Amplitude of each spherical harmonic coefficient with Time (ms) can be obtained. In addition, fig. 3b is only an example here, and does not affect the essence of the embodiments of the present application.

And A2, obtaining eddy current field distribution at each imaging echo time according to the eddy current spherical harmonic coefficient at each imaging echo time.

In this step, after obtaining the eddy current spherical harmonic coefficient at each imaging echo time, the eddy current is generally represented by a multi-exponential decay function model in time, and is generally represented by the following formula (3) or a deformation of the formula (3):

wherein, G _eddy (t) is the time-dependent eddy current magnitude; e (t) is impulse shock response; n is a multi-index vortex component, a known quantity; α, τ are the amplitude and time constant of each eddy current component, and may also be known quantities.

Then, eddy current at any imaging echo time can be obtained by using the above formula (3) or the modification of the formula (3), and meanwhile, by substituting the above eddy current spherical harmonic coefficient at each imaging echo time into the formula (2), eddy current fields at any spatial position at each imaging echo time can be obtained. When the eddy current field at any spatial position at any imaging echo time needs to be obtained, the eddy current field at the corresponding spatial position of the corresponding adjacent imaging echo time can be selected from the eddy current spherical harmonic coefficients, and then fitting operation is performed on the eddy current field at the known spatial position at the known imaging echo time by adopting fitting algorithms such as an interpolation algorithm and the like to obtain the eddy current field at the spatial position required by the required imaging echo time, namely the eddy current field at any spatial position at each imaging echo time is obtained.

In this embodiment, a phase difference between two magnetic resonance images at each echo time is mathematically processed by using a spherical harmonic function for phase correlation, so as to obtain a spherical harmonic coefficient of an eddy current field at any spatial position at each echo time, and the eddy current field at any spatial position at each corresponding time is solved by using a multi-exponential decay model or an interpolation algorithm, so as to obtain an eddy current field at any spatial position at each imaging echo time. The phase difference is subjected to mathematical operation by adopting the spherical harmonic function to determine the eddy current field at any imaging echo time and any space position, and the calculation process is intuitive and accurate, so that the accuracy of the acquired eddy current field at any imaging echo time and any space position can be further improved. Furthermore, the spherical harmonic function related to the space position is adopted to carry out coefficient solving on the eddy current field at any space position under each imaging echo time, each spherical harmonic coefficient can be accurately obtained, and therefore the eddy current field at any space position under each imaging echo time can be conveniently and quickly obtained in the follow-up process.

In another embodiment, another eddy current calibration 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, multilayer data cross acquisition is carried out by adopting a pre-scanning sequence, and first magnetic resonance signals of a plurality of echo times after the first gradient is applied are obtained.

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

In addition, the multi-layer data cross acquisition refers to that data of each layer is cross acquired at the acquisition time of each echo time, that is, the data of each layer is fused together for acquisition, and the data of another layer is acquired before one layer of data is acquired, that is, the data of a single layer is not triggered for acquisition.

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

specifically, as shown above, the entire pre-scan includes three different excitations, each exciting multiple slices of the test object, and the echo times of two or more slices are different: in the first excitation process, magnetic resonance signals of three layers of SLICE1-SLICE3 at different echo times are simultaneously acquired, in this embodiment, magnetic resonance signals of SLICE1-T1, SLICE2-T12, SLICE3-T3 and SLICE1-T4 are respectively acquired, different echoes of the same SLICE which is excited at the same time are filled at different positions (such as PE1, PE2 and the like in the above table) in a K space, and magnetic resonance signals of different SLICEs and/or different echo times are respectively filled in different K spaces; respectively acquiring magnetic resonance signals of SLICE2-T1, SLICE3-T12, SLICE1-T3 and SLICE2-T4 by the second excitation; the third excitation acquires magnetic resonance signals of SLICE3-T1, SLICE1-T12, SLICE2-T3 and SLICE3-T4 respectively. By adopting the GRE sequence to perform multi-layer data cross acquisition on the magnetic resonance signals at each echo time under the first gradient in the above manner, the magnetic resonance signals at each echo time after the first gradient is applied can be obtained and are all recorded as the 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, i.e. the magnetic resonance images in multiple echo times can be acquired simultaneously, for example, N K spaces filled with the magnetic resonance signals are acquired from the acquisition time of T1-TN multiple echo times, and compared with the prior art in which one K space filled with the magnetic resonance signals is acquired at one echo time, the magnetic resonance signals can be increased by N times, i.e. the acquisition efficiency of the magnetic resonance signals or images can be increased.

In addition, with the existing data acquisition method, the time interval for acquiring each layer of data is assumed to be TR, and then it can be known from the acquisition timing sequence of the whole sequence that the time interval for acquiring each layer of data is n × TR in this embodiment, where n is the number of layers of acquired data (for example, in the above example, n is 3).

And S404, after the second gradient is applied, performing multi-layer data cross acquisition by adopting a pre-scanning sequence to obtain 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, in the same acquisition time of a plurality of echo times, the magnetic resonance signals at each echo time after the application of the second gradient can be acquired by performing multi-layer data cross acquisition on the magnetic resonance signals at each echo time by using the GRE sequence in the manner described above, and the magnetic resonance signals at each echo time after the application of the second gradient can be obtained and all recorded as the second magnetic resonance signals.

For example, referring to fig. 4a, the number of data acquisition layers is n, each layer respectively performs one excitation acquisition in different echo Times (TE) to obtain a plurality of K-space data, and TR (repetition time) in the figure represents the time interval between two adjacent executions. After the first gradient is applied (for example, in the Gtest gradient), the magnetic resonance signals are subjected to multi-layer data cross acquisition, so that first magnetic resonance signals at acquisition times of different echo times can be obtained, and then, after the second gradient is applied (for example, in the gradient of which the Gtest gradient is reversed), the magnetic resonance signals are subjected to multi-layer data cross acquisition, so that second magnetic resonance signals at acquisition times 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 embodiments of the present application.

In this embodiment, by performing multi-layer data cross acquisition on the magnetic resonance signals of the multiple echo times after the application of the first gradient and the second gradient by using the pre-scan sequence, the first magnetic resonance signals of the multiple echo times after the application of the first gradient and the second magnetic resonance signals of the multiple echo times after the application of the second gradient can be obtained. In this embodiment, on the one hand, after the first gradient and the second gradient are applied, the magnetic resonance signals of a plurality of echo times can be acquired at the same time, that is, the magnetic resonance images of a plurality of echo times can be acquired at the same time, so that the acquisition efficiency of the signals or the images can be improved. On the other hand, the pre-scanning sequence adopts a GRE sequence to perform 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 eddy current calibration method is provided, in which, on the basis of the above embodiment, the first gradient and the second gradient are two gradients with equal magnitude and opposite directions; the step S206 may specifically include the following step B:

and step B, determining the eddy current field distribution at each imaging echo time after the first gradient application or the second gradient application according to each phase difference.

In this step, the intensity of the first gradient is equal to the intensity of the second gradient, and the directions are opposite. Then in this step, under the steps of S302-S304, the eddy current field distribution at any spatial position at each imaging echo time under the first gradient can be obtained, and since the strength of the first gradient and the second gradient is equal, it can also be said as obtaining the eddy current field distribution at any spatial position at each imaging echo time after the second gradient is applied. That is to say, the eddy current field distribution at any spatial position at each imaging echo time under a certain gradient can be obtained.

Generally, the gradient system is a linear system, and then after obtaining the eddy current field distribution at any spatial position at each imaging echo time after a certain gradient is applied, the eddy current field distribution at any spatial position at each imaging echo time after the gradient is applied can be obtained by performing linear calculation on the eddy current field distribution at any spatial position at 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 acquiring a second intensity ratio between the intensity of the third gradient and the intensity of the second gradient.

In this step, when the eddy current field distribution after application of any gradient needs to be obtained, the any gradient and the intensity thereof, which are referred to as a third gradient, can be obtained in advance. Then, the intensity of the third gradient may be divided by the intensity of the first gradient to obtain a ratio of the intensity of the third gradient to the intensity of the first gradient, which is recorded as the first intensity ratio. Similarly, the ratio of the intensity of the third gradient to the intensity of the second gradient can be obtained and expressed as the second intensity ratio. Here, since the strength of the first gradient and the strength of the second gradient are equal in magnitude, the first intensity ratio and the second intensity ratio are also generally equal.

And step C2, performing linear superposition processing on eddy current field distribution at 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 eddy current field distribution at each imaging echo time at the third gradient.

In this step, after the first intensity ratio or the second intensity ratio is obtained, the eddy current field at any spatial position at each imaging echo time after the first gradient or the second gradient is applied may also be obtained at the same time, so that the product may be obtained by multiplying the first intensity ratio or the second intensity ratio by the eddy current field at any spatial position at each imaging echo time after the first gradient or the second gradient is applied, and the obtained product is the eddy current field at any spatial position at each imaging echo time after the third gradient is applied.

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

In another embodiment, another eddy current correction method is provided, and on the basis of the above embodiment, as shown in fig. 5, the above S204 may include the following steps:

s502, image reconstruction is carried out on the first magnetic resonance signal and the second magnetic resonance signal of each echo time, and a first magnetic resonance image and a second magnetic resonance image of each echo time are obtained.

In this step, image reconstruction may be performed on the currently obtained first magnetic resonance signal after each first magnetic resonance signal is obtained, so as to obtain a first magnetic resonance image at the current echo time, and thus a first magnetic resonance image at each echo time corresponding to each slice layer may be finally obtained; of course, after obtaining all the first magnetic resonance signals at each echo time, the first magnetic resonance signals at each echo time of each slice may be respectively subjected to image reconstruction to obtain the first magnetic resonance image at each echo time of each slice.

Similarly, the second magnetic resonance signals at the respective echo times of each slice may be subjected to image reconstruction in the above manner, so as to obtain a second magnetic resonance image at the respective echo time of each slice.

The first magnetic resonance images of the respective echo times obtained here correspond one-to-one to the second magnetic resonance images of the respective echo times, both corresponding to the same slice. For example, a first magnetic resonance image obtained at a first echo time and a second magnetic resonance image obtained at a first echo time are two magnetic resonance images obtained at the corresponding echo time, a first magnetic resonance image obtained at an mth echo time and a second magnetic resonance image obtained at an mth echo time are two magnetic resonance images obtained at the corresponding time, and m is any positive integer.

In addition, when the magnetic resonance signals are subjected to image reconstruction, any image reconstruction algorithm can be selected for image reconstruction, so that the first magnetic resonance image and the second magnetic resonance image can be obtained.

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

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

The phase of the first magnetic resonance image at each echo time may be referred to as a first phase, and the phase of the second magnetic resonance image at each echo time may be referred to as a second phase, so that the first phase and the second phase at each corresponding echo time may be obtained.

S506, performing a difference operation 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.

In this step, after obtaining the first phase and the second phase for each corresponding echo time, a difference operation may be performed on the first phase and the second phase for 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 short, 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 at each corresponding echo time is obtained.

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

The correction of eddy currents is described in the above embodiments, and the correction of magnetic resonance images is also possible on the basis of this, which is explained below.

In another embodiment, a magnetic resonance image correction method is provided, which may include the following steps, based on the above-mentioned embodiment, as shown in fig. 6:

s602, multiple sets of magnetic resonance images of the scanned object are obtained, where each set of magnetic resonance image 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 a first magnetic resonance signal acquired after applying a first gradient, and the second magnetic resonance image is obtained by reconstructing a second magnetic resonance signal acquired after applying a second gradient. The scan subject includes a plurality of slices, and the plurality of sets of magnetic resonance images includes a series of first and second magnetic resonance images at different echo times for each slice.

Wherein, the scanning object can be any one or more parts of the human body or animal body. Each first magnetic resonance image may be obtained by applying a first gradient to the scan subject and acquiring the first magnetic resonance signals of each slice at the first gradient, that is, acquiring the first magnetic resonance signals at each echo time, and performing image reconstruction on the first magnetic resonance signals of each slice.

The acquisition mode for each second magnetic resonance image may be the same as the acquisition mode for the first magnetic resonance image, except that a second gradient different from the first gradient is applied, and will not be described herein again.

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

For the explanation of this step, reference may be made to the explanation of S204 above, which is not described herein again.

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

For the explanation of this step, reference may be made to the explanation of S206 described above, which is not described herein again.

And S608, correcting the to-be-processed magnetic resonance image corresponding to the imaging echo time according to the eddy current field distribution, and acquiring a corrected magnetic resonance image.

In this step, taking the magnetic resonance image to be processed as a diffusion image as an example, after obtaining the eddy current field distribution of at least one imaging echo time, the eddy current field distribution may 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 scanning sequence adopts an echo planar diffusion weighted imaging (EPI-DWI) sequence, which excites magnetic resonance signals in different diffusion directions acquired after a detection object is detected, reconstructs the magnetic resonance signals in the different diffusion directions to obtain a plurality of initial diffusion images (the plurality of initial diffusion images are magnetic resonance images to be processed), and can respectively correct the plurality of initial diffusion images by adopting eddy current field distribution to obtain a plurality of corrected diffusion images; and merging the corrected diffusion images 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 a magnetic resonance image to be processed, and the DWI image is obtained by multiplying pixels of a diffusion image in multiple directions (for example, three directions) point by point and then cubing, as follows:

the VOX represents the value of any pixel point in the DWI image; d1, D2 and D3 respectively represent the values of the pixel points corresponding to three different diffusion directions. Because the diffusion gradient is different in size in different directions, different eddy currents can be generated at the moment of image acquisition, and the bandwidth along the Phase Encoding (PE) direction is very low during DWI sequence acquisition. Thus, the PE direction of the image is shifted. And because diffusion gradient eddy currents in different directions are different, a synthesized DWI image is blurred. For example, the shift of the magnetic resonance image to be processed can be expressed as:

where Δ y represents a displacement along the phase encoding direction; t is t _esp Adjacent echo time intervals for EPI _ DWI; g _y τ _y Representing the zero order moment of the PE direction spike. The displacement in the DWI image along the phase encoding direction can be obtained from the eddy current field distribution Bz, and the DWI image can be corrected based on the displacement in the phase encoding direction.

As shown in fig. 6a, the initial diffusion image in the direction 1, the initial diffusion image in the direction 2, the initial diffusion image in the direction 3, and the composite DWI image obtained in the embodiment of the present application are shown from left to right. The initial diffusion image is affected by eddy currents of different sizes, so that different deformations are generated, and the synthesized DWI image is seriously blurred. The eddy current effect is corrected for the composite DWI image using the flowchart of fig. 6 of the embodiment of the present application. As shown in fig. 6b, the initial diffusion image in the direction 1, the initial diffusion image in the direction 2, the initial diffusion image in the direction 3, and the corrected DWI image correspond to the corrected DWI image, respectively, from left to right. The image positions of the diffusion images in the single direction after correction treatment tend to be consistent, and the boundary of the DWI images after correction becomes clear.

In this embodiment, a plurality of sets of magnetic resonance images of a plurality of slices of a scanned object are acquired, each set of magnetic resonance images includes a first magnetic resonance image and a second magnetic resonance image corresponding to the same echo time, a phase difference between the first magnetic resonance image and the second magnetic resonance image in each set of magnetic resonance images is determined, eddy current field distribution of each imaging echo time is determined through the phase difference, and a diffusion image to be processed is corrected through the eddy current field distribution, so that a corrected diffusion image is obtained. By the method, eddy current correction can be accurately carried out on the image at each echo time and each space position, and the diffusion image is corrected on the basis of the eddy current correction, so that a more accurate corrected image is obtained.

It should be understood that although the steps in the flowcharts of fig. 2, 3, 4, 5, 6 are shown in order as indicated by the arrows, the steps are not necessarily performed in order as indicated by the arrows. The steps are not limited to being performed in the exact order illustrated and, unless explicitly stated herein, may be performed in other orders. Moreover, at least some of the steps in fig. 2, 3, 4, 5, and 6 may include multiple steps or multiple stages, which are not necessarily performed at the same time, but may be performed at different times, and the order of performing the steps or stages is not necessarily sequential, but may be performed alternately or alternatingly with other steps or at least some of the other steps or stages.

In one embodiment, as shown in fig. 7, there is provided an eddy current correction apparatus including: 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:

a signal acquiring module 10, configured to acquire a first magnetic resonance signal of multiple echo times acquired after a first gradient is applied and a second magnetic resonance signal of multiple echo times acquired after a second gradient is applied; 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;

a first phase difference determining module 11, 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 determine a phase difference between the two magnetic resonance images at each echo time;

the first eddy current field determining module 12 is configured to determine eddy current field distribution at one or more imaging echo times according to each phase difference;

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

For specific definition of the eddy current correction device, reference may be made to the above definition of the eddy current correction method, which is not described in detail here.

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

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

and the eddy current field determining unit is used for solving the eddy current field distribution at each echo time and determining the eddy current field distribution at each imaging echo time.

Optionally, the eddy current field determining unit may include a coefficient expansion subunit and an eddy current field determining subunit, wherein:

the coefficient expansion subunit is used for performing coefficient expansion on the eddy current field distribution at each echo time according to a preset spherical harmonic function and determining an eddy current spherical harmonic coefficient at each imaging echo time;

and the eddy current field determining subunit is used for obtaining eddy current field distribution at each imaging echo time according to the eddy current spherical harmonic coefficient at each imaging echo time.

In another embodiment, another eddy current calibration apparatus is provided, and on the basis of the above embodiment, the above acquisition module 10 may include a first signal acquisition unit and a second signal acquisition unit, wherein:

the device comprises a first signal acquisition unit, a second signal acquisition unit and a third signal acquisition unit, wherein the first signal acquisition unit is used for carrying out multi-layer data cross acquisition by adopting a pre-scanning sequence after a 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 performing multi-layer data cross acquisition by adopting a pre-scanning sequence after the second gradient is applied to obtain a plurality of echo time second magnetic resonance signals after the second gradient is applied.

In another embodiment, another eddy current calibration apparatus is provided, in addition to the above embodiment, the first gradient and the second gradient are two gradients with equal gradient strength and opposite gradient directions; the eddy current field determining module 12 is specifically configured to determine, according to each phase difference, eddy current field distribution at each imaging echo time after the first gradient application or after the second gradient application.

In another embodiment, another eddy current correction apparatus is provided, and on the basis of the above embodiment, the phase difference determination module 11 may include an image reconstruction unit, a phase acquisition unit, and a phase difference determination unit, wherein:

the image reconstruction unit is used for 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;

the phase acquisition unit is used for acquiring a first phase of each echo time according to the first magnetic resonance image of each echo time and acquiring a second phase of each echo time according to the second magnetic resonance image of each echo time;

and the phase difference determining unit is used for performing 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, on the basis of the above-described embodiments, the apparatus comprising:

an image acquisition module, configured to acquire multiple sets of magnetic resonance images of multiple slices of a scanned object, where each set of magnetic resonance image 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 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 modules in the eddy current correction device and the magnetic resonance image correction device can be wholly or partially realized by software, hardware and a combination thereof. The modules can be embedded in a hardware form or independent of a processor in the computer device, and can also be stored in a memory in the computer device in a software form, so that the processor can call and execute operations corresponding to the modules.

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

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; 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 eddy current field distribution under one or more imaging echo time according to the phase differences; and performing eddy current correction on the magnetic resonance signal corresponding to the imaging echo time by using eddy current field distribution under the imaging echo time.

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

performing mathematical operation processing on each phase difference, and determining the eddy current field distribution at each echo time; and solving the eddy current field distribution at each echo time, and determining the eddy current field distribution at each imaging echo time.

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

performing coefficient expansion on the eddy current field distribution at each echo time according to a preset spherical harmonic function, and determining the eddy current spherical harmonic coefficient at each imaging echo time; and obtaining the eddy current field distribution at each imaging echo time according to the eddy current spherical harmonic coefficient at each imaging echo time.

after a first gradient is applied, a pre-scanning sequence is adopted to carry out multi-layer data cross acquisition, and first magnetic resonance signals of a plurality of echo times after the first gradient is applied are obtained; and after the second gradient is applied, performing multi-layer data cross acquisition by adopting a pre-scanning sequence to obtain a plurality of echo time second magnetic resonance signals after the second gradient is applied.

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 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.

acquiring multiple groups of magnetic resonance images of multiple 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, 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 and second magnetic resonance images in each set of magnetic resonance images; determining an eddy current field distribution of at least one imaging echo time according to the phase difference; and correcting the magnetic resonance image to be processed corresponding to the imaging echo time according to the eddy current field distribution to obtain 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:

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; 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 eddy current field distribution under one or more imaging echo time according to the phase differences; and correcting the magnetic resonance image to be processed corresponding to the imaging echo time by using the eddy current field distribution in the imaging echo time, and acquiring the corrected magnetic resonance image for eddy current correction.

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

performing mathematical operation processing on each phase difference, and determining eddy current field distribution at each echo time; and solving the eddy current field distribution at each echo time, and determining the eddy current field distribution at each imaging echo time.

and determining 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.

It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by hardware instructions of a computer program, which can be stored in a non-volatile computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. Any reference to memory, storage, database or other medium used in the embodiments provided herein can include at least one of non-volatile and volatile memory. Non-volatile Memory may include Read-Only Memory (ROM), magnetic tape, floppy disk, flash Memory, optical storage, or the like. Volatile Memory can include Random Access Memory (RAM) or external cache Memory. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM), among others.

The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is specific and detailed, but not to be understood as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. An eddy current correction method, characterized in that 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;

and performing eddy current correction on the magnetic resonance signal corresponding to the imaging echo time by using the eddy current field distribution under the imaging echo time.

2. The method of claim 1, wherein determining an eddy current field distribution at least one imaging echo time from each of the phase differences comprises:

processing the phase differences to determine eddy current field distribution at each echo time;

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

3. The method of claim 2, wherein solving the eddy current field distribution at each of the echo times to determine the eddy current field distribution at least one imaging echo time comprises:

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

4. The method of any one of claims 1-3, wherein acquiring the first magnetic resonance signals of the plurality of echo times acquired after the first gradient is applied and the second magnetic resonance signals of the plurality of echo times acquired after the second gradient is applied comprises:

after the first gradient is applied, multilayer data cross acquisition is carried out by adopting a pre-scanning sequence, and first magnetic resonance signals of a plurality of echo times after the first gradient is applied are obtained;

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

5. The method of claim 1, wherein the first gradient and the second gradient are two gradients with equal gradient strength and opposite gradient directions; determining eddy current field distribution at each imaging echo time according to each phase difference, comprising:

6. The method of any one of claims 1-3, wherein determining the two magnetic resonance images at each echo time and determining the phase difference between the two magnetic resonance images at each echo time from the first and second magnetic resonance signals at each echo time comprises:

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

8. An eddy current correction apparatus, characterized in that the apparatus comprises:

the signal acquisition module is used for acquiring first magnetic resonance signals of a plurality of echo times acquired after a first gradient is applied and second magnetic resonance signals 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 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;

the first eddy current field determining module is used for determining eddy current field distribution under at least one imaging echo time according to the phase differences;

and the eddy current correction module is used for performing eddy current correction on the magnetic resonance signal corresponding to the imaging echo time by using the eddy current field distribution under the imaging echo time.

9. A computer device comprising a memory and a processor, the memory storing a computer program, characterized in that the processor, when executing the computer program, implements the steps of the method of any of claims 1 to 7.

10. A computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, carries out the steps of the method of any one of claims 1 to 7.