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

Abstract

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

Description

Technical Field

[0001] The present application relates to the technical field of data processing, 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 Art

[0002] During the operation of a magnetic resonance pulse imaging sequence, a series of time-varying gradient fields are used. Such time-varying gradient fields cause the magnetic flux in the space around the gradient coil to vary with time. At the same time, time-varying currents are generated in the metal conductive materials of the components around the gradient. Such induced currents are called eddy currents. Eddy currents have a relatively serious impact on subsequent magnetic resonance imaging. Therefore, it is necessary to eliminate the influence of eddy currents on the subsequent image as much as possible, and correcting the eddy currents is a means to eliminate the influence on the image.

[0003] In the related art, when correcting eddy currents, it is usually achieved by pre-emphasis. That is, a reverse gradient is applied to the hardware of the magnetic resonance system (such as a gradient coil, etc.) in the early stage, and then the eddy current is corrected by the reverse gradient.

[0004] However, after the above-mentioned technology corrects the eddy currents, there will still be eddy current residues, that is, the accuracy of this method for eddy current correction is relatively low. Summary of the Invention

[0005] Based on this, in view of the above technical problems, 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 that can improve the accuracy of magnetic resonance eddy current correction.

[0006] An eddy current correction method, the method includes:

[0007] Obtain a first magnetic resonance signal of a plurality of echo times collected after a first gradient is applied and a second magnetic resonance signal of a plurality of echo times collected after a second gradient is applied; the acquisition moments of the first magnetic resonance signal of the plurality of echo times correspond to the acquisition moments of the second magnetic resonance signal of the plurality of echo times;

[0008] Determine two magnetic resonance images for each echo time according to the first magnetic resonance signal and the second magnetic resonance signal of each echo time, and determine the phase difference between the two magnetic resonance images for each echo time;

[0009] Determine the eddy current field distribution at at least one imaging echo time according to each phase difference;

[0010] Use the eddy current field distribution at the imaging echo time to correct the eddy current of the magnetic resonance signal corresponding to the imaging echo time.

[0011] In one embodiment, determining the eddy current field distribution at at least one imaging echo time according to each phase difference includes:

[0012] Processing each phase difference to determine the eddy current field distribution at each echo time;

[0013] Solving the eddy current field distribution at each echo time to determine the eddy current field distribution at at least one imaging echo time.

[0014] In one embodiment, solving the eddy current field distribution at each echo time to determine the eddy current field distribution at at least one imaging echo time includes:

[0015] Performing coefficient expansion on the eddy current field distribution at each echo time according to a preset spherical harmonic function to determine the eddy current spherical harmonic coefficients at each imaging echo time;

[0016] Obtaining the eddy current field distribution at at least one imaging echo time according to the eddy current spherical harmonic coefficients at each imaging echo time.

[0017] In one embodiment, obtaining the first magnetic resonance signals at multiple echo times collected after applying the first gradient and the second magnetic resonance signals at multiple echo times collected after applying the second gradient includes:

[0018] After applying the first gradient, performing multi-layer data cross-acquisition using a pre-scan sequence to obtain the first magnetic resonance signals at multiple echo times after applying the first gradient;

[0019] After applying the second gradient, performing multi-layer data cross-acquisition using a pre-scan sequence to obtain the second magnetic resonance signals at multiple echo times after applying the second gradient.

[0020] In one embodiment, the first gradient and the second gradient are two gradients with equal gradient intensity magnitudes and opposite directions; determining the eddy current field distribution at each imaging echo time according to each phase difference includes:

[0021] Determining the eddy current field distribution at each imaging echo time after applying the first gradient or the second gradient according to each phase difference.

[0022] In one embodiment, the method further includes:

[0023] Obtaining 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;

[0024] According to the above first intensity ratio or second intensity ratio, perform linear superposition processing on the eddy current field distributions at each imaging echo time after the application of the above first gradient and after the application of the second gradient, and determine the eddy current field distributions at each imaging echo time under the above third gradient.

[0025] In one embodiment, determining 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 the phase difference between the two magnetic resonance images at each echo time includes:

[0026] Perform image reconstruction on the first magnetic resonance signal and the second magnetic resonance signal at each echo time to obtain the first magnetic resonance image and the second magnetic resonance image at each echo time;

[0027] Obtain the first phase at each echo time based on the first magnetic resonance image at each echo time, and obtain the second phase at each echo time based on the second magnetic resonance image at each echo time;

[0028] Perform a subtraction operation on the first phase and the second phase at each echo time to obtain the phase difference between the first magnetic resonance image and the second magnetic resonance image at each echo time.

[0029] A magnetic resonance image correction method, the method includes:

[0030] Obtain multiple sets of magnetic resonance images of a scanning object, each set of magnetic resonance images including a first magnetic resonance image and a second magnetic resonance image corresponding to the same echo time, where the above first magnetic resonance image is reconstructed from the first magnetic resonance signal collected after the application of the first gradient, and the above second magnetic resonance image is reconstructed from the second magnetic resonance signal collected after the application of the second gradient;

[0031] Determine the phase difference between the first magnetic resonance image and the second magnetic resonance image in each set of magnetic resonance images;

[0032] Determine the eddy current field distribution at at least one imaging echo time according to the above phase difference;

[0033] Correct the magnetic resonance image to be processed corresponding to the imaging echo time according to the above eddy current field distribution to obtain a corrected magnetic resonance image.

[0034] An eddy current correction device, the device includes:

[0035] A signal acquisition module, configured to acquire the first magnetic resonance signals at multiple echo times collected after the application of the first gradient and the second magnetic resonance signals at multiple echo times collected after the application of the second gradient; the acquisition moments of the first magnetic resonance signals at the above multiple echo times correspond to the acquisition moments of the second magnetic resonance signals at the above multiple echo times;

[0036] A first phase difference determination 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 the phase difference between the two magnetic resonance images at each echo time;

[0037] A first eddy current field determination module, configured to determine the eddy current field distribution at at least one imaging echo time according to each phase difference;

[0038] An eddy current correction module, configured to perform eddy current correction by using the eddy current field distribution at the imaging echo time.

[0039] A magnetic resonance image correction device, the device includes:

[0040] An image acquisition module, configured to acquire multiple groups of magnetic resonance images of a 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 reconstructed from the first magnetic resonance signal acquired after the first gradient is applied, and the second magnetic resonance image is reconstructed from the second magnetic resonance signal acquired after the second gradient is applied;

[0041] A second phase difference determination module, configured to determine the phase difference between the first magnetic resonance image and the second magnetic resonance image in each group of magnetic resonance images;

[0042] A second eddy current field determination module, configured to determine the eddy current field distribution at at least one imaging echo time according to the phase difference;

[0043] An image correction module, configured to correct the magnetic resonance image to be processed corresponding to the imaging echo time according to the eddy current field distribution, and acquire the corrected magnetic resonance image.

[0044] A computer device, including a memory and a processor, the memory stores a computer program, and when the processor executes the computer program, the following steps are implemented:

[0045] Acquire the first magnetic resonance signal at multiple echo times acquired after the first gradient is applied and the second magnetic resonance signal at multiple echo times acquired after the second gradient is applied; the acquisition moments of the first magnetic resonance signals at the multiple echo times correspond to the acquisition moments of the second magnetic resonance signals at the multiple echo times;

[0046] According to the first magnetic resonance signal and the second magnetic resonance signal at each echo time, determine two magnetic resonance images at each echo time, and determine the phase difference between the two magnetic resonance images at each echo time;

[0047] According to each phase difference, determine the eddy current field distribution at at least one imaging echo time;

[0048] Perform eddy current correction on the magnetic resonance signal corresponding to the imaging echo time using the eddy current field distribution at at least one imaging echo time.

[0049] A computer device, comprising a memory and a processor, the memory storing a computer program, and the processor implementing the following steps when executing the computer program:

[0050] Obtain multiple sets of magnetic resonance images of a scanning object, each set of magnetic resonance images including a first magnetic resonance image and a second magnetic resonance image corresponding to the same echo time, the first magnetic resonance image being reconstructed from a first magnetic resonance signal acquired after a first gradient is applied, and the second magnetic resonance image being reconstructed from a second magnetic resonance signal acquired after a second gradient is applied;

[0051] Determine the phase difference between the first magnetic resonance image and the second magnetic resonance image in each set of magnetic resonance images;

[0052] Determine the eddy current field distribution at at least one imaging echo time according to the phase difference;

[0053] Perform correction on the magnetic resonance image to be processed corresponding to the imaging echo time according to the eddy current field distribution, and obtain the corrected magnetic resonance image.

[0054] A computer-readable storage medium, on which a computer program is stored, and the computer program implements the following steps when executed by a processor:

[0055] Obtain the first magnetic resonance signals at multiple echo times acquired after a first gradient is applied and the second magnetic resonance signals at multiple echo times acquired after a second gradient is applied; the acquisition times of the first magnetic resonance signals at the multiple echo times correspond to the acquisition times of the second magnetic resonance signals at the multiple echo times;

[0056] 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 the phase difference between the two magnetic resonance images at each echo time;

[0057] Determine the eddy current field distribution at at least one imaging echo time according to each phase difference;

[0058] Perform eddy current correction on the magnetic resonance signal corresponding to the imaging echo time using the eddy current field distribution at at least one imaging echo time.

[0059] A computer-readable storage medium, on which a computer program is stored, and the computer program implements the following steps when executed by a processor:

[0060] Obtain multiple sets of magnetic resonance images of a scanning 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. The above-mentioned first magnetic resonance image is reconstructed from the first magnetic resonance signal collected after the application of the first gradient, and the above-mentioned second magnetic resonance image is reconstructed from the second magnetic resonance signal collected after the application of the second gradient;

[0061] Determine the phase difference between the first magnetic resonance image and the second magnetic resonance image in each set of magnetic resonance images;

[0062] According to the above phase difference, determine the eddy current field distribution at at least one imaging echo time;

[0063] Correct the magnetic resonance image to be processed corresponding to the imaging echo time according to the above eddy current field distribution to obtain a corrected magnetic resonance image.

[0064] The above eddy current correction method, magnetic resonance image correction method, device, computer device and storage medium collect the first magnetic resonance signal at multiple echo times after the application of the first gradient and the second magnetic resonance signal at multiple echo times after the application of the second gradient corresponding to the acquisition time. Determine the two magnetic resonance images at each echo time and the phase difference between the two magnetic resonance images through the two magnetic resonance signals at each echo time. Determine the eddy current field distribution at the imaging echo time according to each phase difference, and use the eddy current field distribution at the imaging echo time to correct the eddy current of the magnetic resonance signal corresponding to the imaging echo time. In this method, since the eddy current field distribution at any imaging echo time can be determined through the phase difference between the magnetic resonance images after different gradient applications at each echo time, when correcting the eddy current, the eddy current at any imaging echo time can be accurately corrected, so that there will be no large eddy current residue, thereby realizing accurate correction of the eddy current, that is, improving the accuracy of eddy current correction. Description of the Drawings

[0065] Figure 1 It is the internal structure diagram of a computer device in an embodiment;

[0066] Figure 2 It is the schematic flow chart of the eddy current correction method in an embodiment;

[0067] Figure 3 It is the schematic flow chart of the eddy current correction steps in another embodiment;

[0068] Figure 3a It is an example diagram of the phase difference between two magnetic resonance images at the corresponding echo time in another embodiment;

[0069] Figure 3b It is an example diagram of the amplitude of the spherical harmonic coefficient changing with time in another embodiment;

[0070] Figure 4 It is a schematic flowchart of the eddy current correction method in another embodiment;

[0071] Figure 4a It is an example diagram of the acquisition timing of magnetic resonance signals in another embodiment;

[0072] Figure 5 It is a schematic flowchart of the eddy current correction method in another embodiment;

[0073] Figure 6 It is a schematic flowchart of the magnetic resonance image correction method in another embodiment;

[0074] Figure 6a They are diffusion images and synthetic images of multiple diffusion directions to be corrected obtained in another embodiment;

[0075] Figure 6b They are corrected diffusion images of multiple diffusion directions and corrected synthetic images obtained in another embodiment;

[0076] Figure 7 It is a structural block diagram of an eddy current correction device in one embodiment. Detailed implementation manners

[0077] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0078] The eddy current correction method provided by the embodiments of the present application can be applied to a magnetic resonance system or a computer device. The magnetic resonance system may include a magnetic resonance scanning device and a computer device connected to each other. When scanning a detection object, the magnetic resonance scanning device can scan the detection object and transmit the scanned data to the computer device for processing to achieve eddy current correction. Here, taking the eddy current correction method applied to a computer device as an example, the computer device may be a terminal or a server. Taking the computer device as a terminal as an example, its internal structure diagram may be as Figure 1As shown in the figure. The computer device includes a processor, a memory, a communication interface, a display screen, and an input device connected via a system bus. Among them, the processor of the computer device is used 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 the computer program in the non-volatile storage medium. The communication interface of the computer device is used to communicate with an external terminal in a wired or wireless manner, and the wireless manner can be achieved through WIFI, a carrier network, NFC (Near Field Communication), or other technologies. When the computer program is executed by the processor, it implements a method for eddy current correction. The display screen of the computer device can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer device can be a touch layer covering the display screen, or a button, a trackball, or a touchpad provided on the housing of the computer device, or an external keyboard, a touchpad, or a mouse, etc.

[0079] Those skilled in the art can understand that Figure 1 the structure shown in the figure is only a block diagram of some structures related to the solution of this application, and does not constitute a limitation on the computer device to which the solution of this application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine some components, or have different component arrangements.

[0080] It should be noted that the execution subject of the embodiments of this application can be a magnetic resonance system, or a computer device in the magnetic resonance system, or an eddy current correction device in the computer device. Of course, it can also be other devices. Hereinafter, the technical solution of this application will be described with the computer device as the execution subject.

[0081] In one embodiment, as Figure 2 shown, a method for eddy current correction is provided, and the method may include the following steps:

[0082] S202, obtain a first magnetic resonance signal of multiple echo times collected after the first gradient is applied and a second magnetic resonance signal of multiple echo times collected after the second gradient is applied.

[0083] Among them, the acquisition times of the first magnetic resonance signals at the above-mentioned multiple echo times correspond to the acquisition times of the second magnetic resonance signals at the above-mentioned multiple echo times. Here, the correspondence can mean that the number of acquisition times of the multiple echo times after the application of the first gradient is equal to the number of acquisition times of the multiple echo times after the application of the second gradient. For example, the acquisition times of the multiple echo times after the application of the first gradient can be T1 - Tn, and the acquisition times of the multiple echo times after the application of the second gradient can also be T1 - Tn. The number of acquisition times of the multiple echo times here can be preset. For example, it is necessary to collect 50 points, that is, 50 acquisition times. These 50 times can be equally spaced or unequally spaced times. For example, the acquisition times can be equally spaced at 5 ms, 10 ms, etc.

[0084] Here, the intensity of the first gradient and the intensity of the second gradient can be equal or not equal. The direction of the first gradient and the direction of the second gradient can be the same direction, the opposite direction, or of course other types of directions, etc.

[0085] Specifically, when actually performing magnetic resonance scanning on the detection object, different gradients can be generated through the gradient system in the magnetic resonance device and the generated gradients can be applied to the scanning object. Here, the first gradient can be applied first, and at the acquisition times of each echo time, a pre-scanning sequence is used to collect the magnetic resonance signals after the application of the first gradient to obtain the first magnetic resonance signals at each echo time. After that, the second gradient can be applied to the magnetic resonance coil, and at the acquisition times of each echo time with the same number as the acquisition times after the application of the first gradient, the same pre-scanning sequence is used to collect the magnetic resonance signals after the application of the second gradient to obtain the second magnetic resonance signals at each echo time. The acquisition times of the echo times of each of the obtained second magnetic resonance signals correspond to those of the first magnetic resonance signals, that is, a first magnetic resonance signal and a second magnetic resonance signal will be obtained at the corresponding acquisition times. In addition, the pre-scanning sequence here can be a GRE sequence, or of course other sequences, such as an SE sequence, etc.

[0086] S204, determine two magnetic resonance images at each echo time according to the first magnetic resonance signals and the second magnetic resonance signals at each echo time, and determine the phase difference between the two magnetic resonance images at each echo time.

[0087] In this step, after obtaining the first magnetic resonance signals and the second magnetic resonance signals at each echo time, two magnetic resonance images corresponding to the two magnetic resonance signals at each echo time can be obtained through image reconstruction and other means, and the phases of each magnetic resonance image can be obtained through the parameters on the magnetic resonance images. After that, the phase difference between every two magnetic resonance images can be obtained by subtracting the two magnetic resonance images at each echo time, etc.

[0088] S206. Determine the eddy current field distribution at at least one imaging echo time according to each phase difference.

[0089] Wherein, the above echo time refers to the echo time set by performing a pre-scan sequence, for example, it can be 1 ms, 2 ms, 3 ms, etc.; the imaging echo time here refers to the echo time when performing an imaging scan sequence, which can be any echo time, for example, it can be 1.2 ms, 1.5 ms, 2.3 ms, etc.

[0090] 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 the magnetic resonance images after applying two different gradients corresponding to the echo time, then a mathematical algorithm related to the time characteristics and spatial characteristics of the eddy current can be used to perform mathematical operation processing on the phase difference between every two magnetic resonance images to obtain the eddy current field at any spatial position at each echo time. The echo time here is any echo time, that is, each imaging echo time, so that the eddy current field at any spatial position at each imaging echo time can be obtained.

[0091] S208. Perform eddy current correction on the magnetic resonance signal corresponding to the imaging echo time by using the eddy current field distribution at the imaging echo time.

[0092] 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 can be obtained. Then, when actually performing eddy current field correction, after the magnetic resonance signal collected by performing the imaging scan sequence, the obtained eddy current field can be used to correct the eddy current at any imaging echo time and any spatial position. In this embodiment, the magnetic resonance signal can refer to the raw data collected by the receiving coil of the magnetic resonance system, or can also be only the Cartesian data line and non-Cartesian data line filled into the k-space. The magnetic resonance signal can be Fourier-transformed to obtain the magnetic resonance image to be processed. Optionally, performing eddy current correction on the magnetic resonance signal corresponding to the imaging echo time by using the eddy current field distribution at the imaging echo time can be: directly correcting the magnetic resonance signal by using the eddy current field distribution, or correcting the magnetic resonance image to be processed by using the eddy current field distribution.

[0093] It can be seen from the above description that the obtained eddy current field distribution can be used to perform eddy current correction on the images at any imaging echo time and any spatial position, so that there will be no situation where the images at one or more echo times or one or more spatial positions are not eddy current corrected. Thus, it is possible to accurately perform eddy current correction on the images at each echo time and each spatial position, and finally accurate eddy current correction can be achieved to obtain more accurate magnetic resonance images.

[0094] In the above eddy current correction method, by collecting the first magnetic resonance signals at multiple echo times after the application of the first gradient corresponding to the acquisition time and the second magnetic resonance signals at multiple echo times after the application of the second gradient, two magnetic resonance images at each echo time and the phase difference between the two magnetic resonance images are determined through the two magnetic resonance signals at each echo time. An eddy current field distribution at one or more imaging echo times is determined based on each phase difference, and eddy current correction is performed using the eddy current field distribution at the imaging echo times. In this method, since the eddy current field distribution at any imaging echo time can be determined through the phase difference between the magnetic resonance images after different gradient applications at each echo time, when correcting the eddy current, the eddy current at any imaging echo time can be accurately corrected, so that there will be no large eddy current residue, and thus accurate correction of the eddy current can be achieved, that is, the accuracy of eddy current correction can be improved.

[0095] In another embodiment, another eddy current correction method is provided. On the basis of the above embodiment, as Figure 3 shown, the above S206 may include the following steps:

[0096] S302. Process each phase difference to determine the eddy current field distribution at each echo time.

[0097] Among them, the eddy current field distribution is related to the phase (or phase difference), and can be represented by the following formula (1) or a variant of formula (1). Formula (1) is as follows:

[0098] Bz = φ / (2·pi·γ·TE·2) (1)

[0099] Among them, pi refers to the pi; γ refers to the gyromagnetic ratio, which can be obtained after the magnetic resonance coil is set and is a known quantity; TE refers to the echo time, which is the time interval between the radio frequency pulse and the corresponding echo and is also a known quantity; φ is the phase difference between the two magnetic resonance images at the corresponding moment; Bz is the eddy current field distribution.

[0100] 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 characterize the space, that is, this phase difference is not simply a numerical value and can be a phase space distribution. Exemplarily, as Figure 3a shown, within the echo time of 0 - 200 ms, magnetic resonance signals are collected once every 10 ms (that is, two magnetic resonance images are obtained every 10 ms), and 20 times are collected, that is, 20 moments. Then, the phase differences between the two magnetic resonance images at 20 acquisition moments can be obtained, and the 20 phase difference distribution maps are as Figure 3a shown. In addition, here Figure 3aIt is just an example and does not affect the essential content of the embodiments of the present application.

[0101] After obtaining the phase difference and related calculation parameters between the two magnetic resonance images at each corresponding echo time, since the phase difference has a spatial distribution, that is, it can represent the spatial position, then by calculating through formula (1) or a variation of formula (1), the eddy current field distribution Bz at any spatial position at each imaging echo time can be obtained.

[0102] S304, solving the eddy current field distribution at each echo time to determine the eddy current field at one or more imaging echo times.

[0103] In this step, optionally, the following steps A1 and A2 may be used to solve the eddy current field at any spatial position under multiple echo times:

[0104] Step A1, 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 coefficients at each imaging echo time.

[0105] The spherical harmonic function is related to the spatial position of each point and can be expressed by the following formula (2) or a modified version of formula (2). Formula (2) is as follows:

[0106]

[0107] Here, Bz(x, y, z) is the same as Bz above, except that Bz(x, y, z) here represents the spatial position x, y, z of each point. The first term in formula (2) is generally called eddy current B 0 The second to fourth terms are generally called eddy current linear terms or first-order terms. After simplification, these three terms correspond to the gradients generated by the gradient coil (magnetic resonance coil) in the x, y, and z directions. Terms with an order higher than the above four terms are generally called eddy current high-order terms.

[0108] 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 known. Then, Bz(x, y, z) of each point can be expressed by formula (2) or a variation of formula (2). Among these expressions, only the formula (2) contains When these coefficients are unknown quantities, we can then combine these multiple formulas to solve these coefficients and obtain the values ​​of these coefficients. Since the coefficients here are the coefficients at each imaging echo time, they can be recorded as eddy current spherical harmonic coefficients at each imaging echo time.

[0109] It should be noted that each spherical harmonic coefficient obtained here All of the above are related to time, that is, each spherical harmonic coefficient has a value at the acquisition moment of each imaging echo time. See Figure 3b As shown in Figure 3b , within different echo times from 0 to 200 ms, through the above solution process, the variation trend of the amplitude of each spherical harmonic coefficient with time (ms) can be obtained. In addition, here

[0110] Step A2: Obtain the eddy current field distribution at each imaging echo time according to the eddy current spherical harmonic coefficients at the above-mentioned respective imaging echo times.

[0111] In this step, after obtaining the eddy current spherical harmonic coefficients at each imaging echo time, generally, the eddy current in time generally adopts a multi-exponential decay function model, and is generally expressed by the following formula (3) or a variation of formula (3):

[0112]

[0113] where G eddy (t) is the eddy current magnitude related to time; e(t) is the impulse response; N is the multi-exponential eddy current component, which is a known quantity; α and τ are the amplitude and time constant of each eddy current component, respectively, and can also be known quantities.

[0114] Then, the eddy current at any imaging echo time can be obtained by using the above formula (3) or a variation of formula (3). At the same time, by substituting the eddy current spherical harmonic coefficients at the above-mentioned respective imaging echo times into formula (2), the eddy current field at any spatial position at each imaging echo time can be obtained. When it is necessary to obtain the eddy current field at any spatial position at any imaging echo time, the eddy current field at the corresponding spatial position of the corresponding adjacent imaging echo times can also be selected from the above eddy current spherical harmonic coefficients, and then a fitting algorithm such as an interpolation algorithm is used to perform a fitting operation on the eddy current field at the known imaging echo time and known spatial position, so as to obtain the eddy current field at the required imaging echo time and required spatial position, that is, the eddy current field at any spatial position at each imaging echo time.

[0115] In this embodiment, by performing mathematical operation processing on the phase difference between two magnetic resonance images at each echo time using spherical harmonic functions related to the phase, the spherical harmonic coefficients of the eddy current field at any spatial position at each echo time are obtained, and the eddy current field at any spatial position at each corresponding moment is solved by a multi-exponential decay model or an interpolation algorithm to obtain the eddy current field at any spatial position at each imaging echo time. Here, spherical harmonic functions are used to perform mathematical operation processing on the phase difference to determine the eddy current field at any spatial position at any imaging echo time, and the calculation process is intuitive and accurate, thereby further improving the accuracy of the eddy current field at any spatial position at any imaging echo time. Further, by using spherical harmonic functions related to the spatial position to solve the coefficients of the eddy current field at any spatial position at each imaging echo time, each spherical harmonic coefficient can be accurately obtained, which is convenient for quickly obtaining the eddy current field at any spatial position at each imaging echo time subsequently.

[0116] In another embodiment, another eddy current correction method is provided. On the basis of the above embodiment, as Figure 4 shown, the above S202 may include the following steps:

[0117] S402, after the first gradient is applied, a pre-scan sequence is used to perform multi-layer data cross-acquisition to obtain the first magnetic resonance signals at multiple echo times after the application of the first gradient.

[0118] In this step, when performing data acquisition, the pre-scan sequence used is the GRE sequence. Here, using the GRE sequence for data acquisition can achieve interactive excitation between each layer of data, and magnetic resonance signals at multiple moments can be simultaneously acquired within a period of time, which can improve the data acquisition efficiency.

[0119] In addition, the multi-layer data cross-acquisition here refers to cross-acquiring the data of each layer at the acquisition moments of each echo time, that is, the data of each layer is acquired in a fused manner, rather than acquiring the data of another layer after the data of one layer is acquired, that is, it is not single-layer data excitation acquisition.

[0120] Exemplarily, taking the three-layer data acquisition as an example, the three-layer data are SLICE1, SLICE2, and SLICE3 respectively, and the echo times range from T1 to TN. The data in the phase encoding direction of each layer are filled in PE1 - PEend (PE1 - PEend respectively represent the filling regions along the phase encoding direction in the K space). Then, when using the multi-layer data cross-acquisition of this embodiment, Figure 4a the acquisition timing of the entire corresponding sequence is as follows:

[0121]

[0122] Specifically, as shown above, the entire pre-scan includes three different excitations. Each excitation detects multiple slices of the object, and the echo times of two or more slices are different: During the first excitation, magnetic resonance signals with different echo times of SLICE1 - SLICE3 are simultaneously acquired. In this embodiment, the magnetic resonance signals of SLICE1 - T1, SLICE2 - T12, SLICE3 - T3, and SLICE1 - T4 are acquired respectively. And the different echoes of the same slice belonging to the same excitation are filled in different positions in the K-space (such as PE1, PE2, etc. in the above table), and the magnetic resonance signals belonging to different slices and / or different echo times are filled in different K-spaces respectively; During the second excitation, the magnetic resonance signals of SLICE2 - T1, SLICE3 - T12, SLICE1 - T3, and SLICE2 - T4 are acquired respectively; During the third excitation, the magnetic resonance signals of SLICE3 - T1, SLICE1 - T12, SLICE2 - T3, and SLICE3 - T4 are acquired respectively. By using the GRE sequence to perform multi-layer data cross-acquisition on the magnetic resonance signals of each echo time under the above method, the magnetic resonance signals of each echo time after the application of the first gradient can be obtained, all of which are recorded as the first magnetic resonance signals.

[0123] As can be seen from the above description, after the application of the first gradient, magnetic resonance signals of multiple echo times can be simultaneously acquired, that is, magnetic resonance images at multiple echo times can be obtained simultaneously. For example, within the acquisition time of N echo times from T1 - TN, N K-spaces filled with magnetic resonance signals are acquired. Compared with the prior art where one K-space filled with a magnetic resonance signal is acquired for one echo time, the magnetic resonance signals here can be increased by N times, that is, the acquisition efficiency of the magnetic resonance signals or images can be improved.

[0124] In addition, assuming that the time interval for acquiring each layer of data using the existing data acquisition method is TR, then from the acquisition timing sequence of the entire sequence above, the time interval for acquiring each layer of data in this embodiment is n * TR, where n is the number of layers of data acquired (for example, in the above example, n is 3). Thus, it can be seen that the time interval for acquiring the magnetic resonance signals of the same layer using the solution of this embodiment is enlarged, and the longitudinal magnetization vector of each layer has sufficient time to recover, which can avoid the mutual influence between different excitations, and each acquired magnetic resonance signal can obtain an image with a high signal-to-noise ratio, reducing the signal distortion generated by multiple excitations.

[0125] S404, after the application of the second gradient, use the pre-scan sequence to perform multi-layer data cross-acquisition to obtain the second magnetic resonance signals of multiple echo times after the application of the second gradient.

[0126] In this step, in the same way as in S402 above, within the acquisition moments of the same multiple echo times, the GRE sequence can be used to perform multi-layer data cross-acquisition on the magnetic resonance signals at each echo time after the application of the second gradient in the above manner, and the magnetic resonance signals at each echo time after the application of the second gradient can be obtained, all of which are denoted as the second magnetic resonance signals.

[0127] Exemplarily, referring to Figure 4a As shown, the number of data acquisition layers is n, and for each layer, magnetic resonance signals obtained by performing excitation acquisition once at different echo times (TE) respectively acquire multiple K-space data. In the figure, TR (repetition time) represents the time interval between two adjacent executions. After the application of the first gradient (for example, under the Gtest gradient), multi-layer data cross-acquisition is performed on the magnetic resonance signals to obtain the first magnetic resonance signals at the acquisition moments of different echo times. Then, after the application of the second gradient (for example, the gradient obtained by reversing the Gtest gradient), multi-layer data cross-acquisition is performed on the magnetic resonance signals to obtain the second magnetic resonance signals at the acquisition moments of different echo times. In addition, it should be noted that this Figure 4a is only an example and does not affect the substantial content of the embodiments of the present application.

[0128] In this embodiment, by using a pre-scan sequence to perform multi-layer data cross-acquisition on the magnetic resonance signals at multiple echo times after the application of the first gradient and the second gradient, the first magnetic resonance signals at multiple echo times after the application of the first gradient and the second magnetic resonance signals at multiple echo times after the application of the second gradient can be obtained. In this embodiment, on the one hand, here, after the application of the first gradient and the second gradient, magnetic resonance signals at multiple echo times can be acquired simultaneously, that is, magnetic resonance images at multiple echo times can be acquired simultaneously, thereby improving the acquisition efficiency of signals or images. On the other hand, the pre-scan sequence uses the GRE sequence to perform multi-layer data cross-acquisition after the application of the first gradient and the second gradient, and the effective recovery time of the magnetization vector changes from TR to n*TR, thereby effectively improving the signal-to-noise ratio of the image quality.

[0129] In another embodiment, another eddy current correction method is provided. On the basis of the above embodiment, the above first gradient and the above second gradient are two gradients with equal magnitudes and opposite directions; the above S206 may specifically include the following step B:

[0130] Step B: Determine the eddy current field distribution at each imaging echo time after the application of the first gradient or the second gradient according to each phase difference.

[0131] In this step, the intensity of the first gradient is equal in magnitude and opposite in direction to the intensity of the second gradient. Then, in this step, under the steps of S302 - S304 above, the eddy current field distribution at any spatial position at each imaging echo time under the first gradient can be obtained. Since the intensities of the first gradient and the second gradient are equal, it can also be recorded as obtaining the eddy current field distribution at any spatial position at each imaging echo time after the application of the second gradient. 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 here.

[0132] Generally, the gradient system is a linear system. Then, after obtaining the eddy current field distribution at any spatial position at each imaging echo time after the application of a certain gradient, by performing linear calculations on the eddy current field distribution at any spatial position at each imaging echo time after the application of this gradient, the eddy current field distribution at any spatial position at each imaging echo time under any gradient can be obtained. The specific calculation method can include the following calculation steps C1 and C2:

[0133] Step C1, obtain the first intensity ratio between the intensity of a preset third gradient and the intensity of the first gradient, or the second intensity ratio between the intensity of the third gradient and the intensity of the above - mentioned second gradient.

[0134] In this step, when it is necessary to obtain the eddy current field distribution after the application of any gradient, the arbitrary gradient and its intensity can be obtained in advance, which is recorded as the third gradient here. Then, the intensity of the third gradient can be divided by the intensity of the first gradient to obtain the 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 also be obtained, which is recorded as the second intensity ratio. Here, since the intensities of the first gradient and the second gradient are equal in magnitude, the first intensity ratio and the second intensity ratio are usually also equal.

[0135] Step C2, according to the above - mentioned first intensity ratio or second intensity ratio, perform linear superposition processing on the eddy current field distributions at each imaging echo time after the application of the first gradient and the second gradient, and determine the eddy current field distribution at each imaging echo time under the above - mentioned third gradient.

[0136] In this step, after obtaining the first intensity ratio or the second intensity ratio, at the same time, the eddy current field at any spatial position at each imaging echo time after the application of the first gradient or the second gradient can also be obtained. In this way, 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 application of the first gradient or the second gradient, the product obtained is the eddy current field at any spatial position at each imaging echo time after the application of the third gradient.

[0137] In this embodiment, the intensities of the first gradient and the second gradient are equal in magnitude and opposite in direction. Then, the eddy current field distribution at any spatial position at each imaging echo time after the application of the first gradient or the second gradient can be obtained through the phase difference between the two magnetic resonance images at each of the above-mentioned imaging echo times. In this way, the eddy current field distribution at any spatial position at each imaging echo time under a certain specific gradient can be obtained, which is convenient for accurately correcting the eddy current under this gradient. 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 applicable range of eddy current correction can be improved without being limited by the intensity of the eddy current gradient.

[0138] In another embodiment, another eddy current correction method is provided. On the basis of the above embodiment, as Figure 5 shown, the above S204 may include the following steps:

[0139] S502, perform image reconstruction on the first magnetic resonance signal and the second magnetic resonance signal at each echo time to obtain the first magnetic resonance image and the second magnetic resonance image at each echo time.

[0140] In this step, image reconstruction can be performed on the currently obtained first magnetic resonance signal respectively after each first magnetic resonance signal is obtained to obtain the first magnetic resonance image at the current echo time, so that finally the first magnetic resonance images at each echo time corresponding to each slice can be obtained; of course, it can also be that after all the first magnetic resonance signals at each echo time are obtained, image reconstruction is performed on the first magnetic resonance signals at each echo time of each slice respectively to obtain the first magnetic resonance images at each echo time of each slice.

[0141] Similarly, the second magnetic resonance signals at each echo time of each slice can be reconstructed in the above manner to obtain the second magnetic resonance images at each echo time of each slice.

[0142] The first magnetic resonance images at each echo time obtained here correspond one-to-one to the second magnetic resonance images at each echo time, and both correspond 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, and the first magnetic resonance image obtained at the m-th echo time and the second magnetic resonance image obtained at the m-th echo time are two magnetic resonance images obtained at the corresponding time, where m is any positive integer.

[0143] In addition, when performing image reconstruction on the magnetic resonance signal, any image reconstruction algorithm can be selected for image reconstruction to obtain the first magnetic resonance image and the second magnetic resonance image.

[0144] S504. Obtain the first phase at each echo time from the first magnetic resonance image at each echo time, and obtain the second phase at each echo time from the second magnetic resonance image at each echo time.

[0145] In this step, after reconstructing the magnetic resonance signals at each echo time to obtain the magnetic resonance images as described above, the phase corresponding to the magnetic resonance images can also be obtained. Generally, the phases of every two magnetic resonance images can represent the phase distribution of the spatial positions, and the phases obtained at each echo time may be different.

[0146] Among them, the phases of the first magnetic resonance images at each echo time can all be denoted as the first phase, and the phases of the second magnetic resonance images at each echo time can all be denoted as the second phase, so that the first phase and the second phase at each corresponding echo time can be obtained.

[0147] S506. Perform a subtraction operation on the first phase and the second phase at each echo time to obtain the phase difference between the first magnetic resonance image and the second magnetic resonance image at each echo time.

[0148] In this step, after obtaining the first phase and the second phase at each corresponding echo time, a subtraction operation can be performed on the first phase and the second phase at each corresponding echo time. The subtraction operation can be subtracting the second phase from the first phase, or subtracting the first phase from the second phase. In short, the difference between the two phases at each corresponding echo time can be obtained, that is, the phase difference between the first magnetic resonance image and the second magnetic resonance image at each corresponding echo time can be obtained.

[0149] In this embodiment, by reconstructing the first magnetic resonance signals and the second magnetic resonance signals at different corresponding echo times, two magnetic resonance images and their respective phases at each corresponding echo time are obtained, and a subtraction operation is performed on the two phases of the two magnetic resonance images corresponding to the echo time to obtain the phase difference between the two magnetic resonance images corresponding to the echo time. This calculation process is simple and intuitive, so the efficiency of obtaining the phase difference between two magnetic resonance images can be improved, and further the efficiency of eddy current correction can be improved.

[0150] In the above embodiments, the correction of eddy currents is introduced. On this basis, the magnetic resonance images can also be corrected. The following will describe this process.

[0151] In another embodiment, a method for correcting magnetic resonance images is provided. On the basis of the above embodiments, as shown in Figure 6 This method may include the following steps:

[0152] S602. Obtain multiple sets of magnetic resonance images of the scanned 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. The above-mentioned first magnetic resonance image is reconstructed from the first magnetic resonance signal acquired after the application of the first gradient, and the above-mentioned second magnetic resonance image is reconstructed from the second magnetic resonance signal acquired after the application of the second gradient. The scanned object includes multiple slices, and the multiple sets of magnetic resonance images include a series of first magnetic resonance images and second magnetic resonance images at different echo times for each slice.

[0153] Among them, the scanned object can be any one or more parts of the body of a human or an animal. The first gradient can be applied to the scanned object, and the first magnetic resonance signals of each layer can be obtained under this first gradient, that is, the first magnetic resonance signals at each echo time are obtained, and the first magnetic resonance images of each layer are obtained by reconstructing the first magnetic resonance signals of each layer.

[0154] The acquisition method of each second magnetic resonance image can be the same as that of the first magnetic resonance image, and the only difference is that a second gradient different from the first gradient is applied, which will not be elaborated here.

[0155] S604. Determine the phase difference between the first magnetic resonance image and the second magnetic resonance image in each set of magnetic resonance images.

[0156] For the explanatory notes of this step, please refer to the explanatory notes of S204 above, which will not be elaborated here.

[0157] S606. Determine the eddy current field distribution at at least one imaging echo time according to the above-mentioned phase difference.

[0158] For the explanatory notes of this step, please refer to the explanatory notes of S206 above, which will not be elaborated here.

[0159] S608. Correct the magnetic resonance image to be processed corresponding to the imaging echo time according to the above-mentioned eddy current field distribution, and obtain the corrected magnetic resonance image.

[0160] 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 at at least one imaging echo time, the eddy current field distribution can be used to correct the magnetic resonance image to be processed, and the corrected diffusion image can be obtained.

[0161] In one embodiment, the imaging scan sequence adopts an echo planar imaging diffusion weighted imaging (EPI-DWI) sequence. After exciting the detection object, magnetic resonance signals in different diffusion directions are collected. The magnetic resonance signals in 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 eddy current field distribution can be used to correct the plurality of initial diffusion images respectively to obtain a plurality of corrected diffusion images; and the plurality of corrected diffusion images are merged to obtain a synthesized diffusion image.

[0162] In one embodiment, the diffusion weighted (DWI) image obtained by reconstructing and merging the magnetic resonance signals in different diffusion directions can be used as the magnetic resonance image to be processed. The DWI image is obtained by multiplying the pixels of the diffusion images in multiple directions (taking three directions as an example) point by point and then taking the cube root, as follows:

[0163]

[0164] Wherein, 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. Since the magnitudes of the diffusion gradients are different in different directions, different eddy currents will be generated at the moment of image acquisition. When the DWI sequence is acquired, the bandwidth along the phase encoding (PE) direction is very low. Therefore, there will be a position shift in the PE direction of the image. Also, due to different eddy currents of the diffusion gradients in different directions, the synthesized DWI image will be blurred. Exemplarily, the shift of the magnetic resonance image to be processed can be expressed as:

[0165]

[0166] Wherein, Δy represents the displacement along the phase encoding direction; t esp is the adjacent echo time interval of EPI_DWI; G y τ y represents the zero-order moment of the spike pulse in the PE direction. According to the aforementioned eddy current field distribution Bz, the displacement along the phase encoding direction in the DWI image can be obtained, and the DWI image can be corrected according to the displacement in the phase encoding direction.

[0167] As Figure 6a shown, from left to right are the initial diffusion image in direction 1, the initial diffusion image in direction 2, the initial diffusion image in direction 3, and the synthesized DWI image obtained in an embodiment of the present application. Among them, due to the influence of eddy currents of different magnitudes, the initial diffusion images have different deformations, and the synthesized DWI image is seriously blurred. The flow attached to the embodiment of the present application Figure 6 is used to correct the influence of eddy currents on the synthesized DWI image. As Figure 6bAs shown, from left to right are the initial diffusion images in direction 1, the initial diffusion images in direction 2, the initial diffusion images in direction 3, and the corrected DWI image corresponding to the corrected DWI image. The image positions of the individual directions of the corrected diffusion images tend to be consistent, and the boundary of the corrected DWI image becomes clear.

[0168] In this embodiment, by acquiring multiple sets of magnetic resonance images of multiple slices of a scanning object, each set of magnetic resonance images including a first magnetic resonance image and a second magnetic resonance image corresponding to the same echo time, determining the phase difference between the first magnetic resonance image and the second magnetic resonance image in each set of magnetic resonance images, and determining the eddy current field distribution of each imaging echo time through the phase difference, and correcting the diffusion image to be processed through the eddy current field distribution to obtain a corrected diffusion image. In this way, accurate eddy current correction can be achieved for the images at each echo time and each spatial position, and on this basis, the diffusion image is corrected to obtain a more accurate corrected image.

[0169] It should be understood that although Figure 2 , 3 , 4, 5, 6 in the flowchart of each step is displayed in sequence according to the arrow indication, but these steps are not necessarily executed in the order indicated by the arrow. Unless there is a clear indication in this article, the execution of these steps has no strict order limit, and these steps can be executed in other orders. Moreover, Figure 2 , 3 , 4, 5, 6 at least a part of the steps may include multiple steps or multiple stages, these steps or stages are not necessarily executed at the same moment, but can be executed at different moments, and the execution order of these steps or stages is not necessarily in sequence, but can be executed alternately or alternately with at least a part of the steps or stages in other steps or other steps.

[0170] In one embodiment, as Figure 7 shown, an eddy current correction device is provided, 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:

[0171] The signal acquisition module 10 is configured to acquire a first magnetic resonance signal of multiple echo times acquired after the first gradient application and a second magnetic resonance signal of multiple echo times acquired after the second gradient application; the acquisition moments of the first magnetic resonance signals of the multiple echo times correspond to the acquisition moments of the second magnetic resonance signals of the multiple echo times;

[0172] The first phase difference determination module 11 is 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 the phase difference between the two magnetic resonance images at each echo time;

[0173] The first eddy current field determination module 12 is configured to determine the eddy current field distribution at one or more imaging echo times according to each phase difference;

[0174] The eddy current correction module 13 is configured to perform eddy current correction by using the eddy current field distribution at the imaging echo time.

[0175] For the specific limitations of the eddy current correction device, reference may be made to the limitations on the eddy current correction method in the above text, which will not be elaborated here.

[0176] In another embodiment, another eddy current correction device is provided. 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, where:

[0177] The mathematical operation processing unit is configured to perform mathematical operation processing on each phase difference to determine the eddy current field distribution at each echo time;

[0178] The eddy current field determination unit is configured to solve the eddy current field distribution at each echo time to determine the eddy current field distribution at each imaging echo time.

[0179] Optionally, the eddy current field determination unit may include a coefficient expansion subunit and an eddy current field determination subunit, where:

[0180] The coefficient expansion subunit is configured to perform coefficient expansion on the eddy current field distribution at each echo time according to a preset spherical harmonic function to determine the eddy current spherical harmonic coefficients at each imaging echo time;

[0181] The eddy current field determination subunit is configured to obtain the eddy current field distribution at each imaging echo time according to the eddy current spherical harmonic coefficients at each imaging echo time.

[0182] In another embodiment, another eddy current correction device is provided. On the basis of the above embodiment, the acquisition module 10 may include a first signal acquisition unit and a second signal acquisition unit, where:

[0183] The first signal acquisition unit is configured to perform multi-layer data cross-acquisition using a pre-scan sequence after the first gradient is applied, and obtain the first magnetic resonance signal at multiple echo times after the first gradient is applied;

[0184] A second signal acquisition unit, configured to perform multi-layer data cross-acquisition using a pre-scan sequence after the second gradient is applied, so as to obtain second magnetic resonance signals at multiple echo times after the second gradient is applied.

[0185] In another embodiment, another eddy current correction device is provided. On the basis of the above embodiment, the first gradient and the second gradient are two gradients with equal gradient intensity magnitudes and opposite directions; the eddy current field determination 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.

[0186] In another embodiment, another eddy current correction device is provided. 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, where:

[0187] The image reconstruction unit is configured to perform image reconstruction on the first magnetic resonance signals and the second magnetic resonance signals at each echo time, so as to obtain a first magnetic resonance image and a second magnetic resonance image at each echo time;

[0188] The phase acquisition unit is configured to obtain a first phase at each echo time according to the first magnetic resonance image at each echo time, and obtain a second phase at each echo time according to the second magnetic resonance image at each echo time;

[0189] The phase difference determination unit is configured to perform a subtraction operation on the first phase and the second phase at each echo time, so as to obtain the phase difference between the first magnetic resonance image and the second magnetic resonance image at each echo time.

[0190] For the specific limitations on the eddy current correction device, reference may be made to the limitations on the eddy current correction method in the above text, which will not be elaborated here.

[0191] In another embodiment, a magnetic resonance image correction device is provided. On the basis of the above embodiment, the device includes:

[0192] An image acquisition module, configured to acquire multiple groups of magnetic resonance images of multiple slices of a scanned object, each group of magnetic resonance images including a first magnetic resonance image and a second magnetic resonance image corresponding to the same echo time, where the first magnetic resonance image is reconstructed from the first magnetic resonance signals acquired after the first gradient is applied, and the second magnetic resonance image is reconstructed from the second magnetic resonance signals acquired after the second gradient is applied;

[0193] A second phase difference determination module, configured to determine the phase difference between the first magnetic resonance image and the second magnetic resonance image in each group of magnetic resonance images;

[0194] A second eddy current field determination module, configured to determine the eddy current field distribution at at least one imaging echo time according to the above phase difference;

[0195] An image correction module, configured to correct a to-be-processed magnetic resonance image corresponding to an imaging echo time according to the above eddy current field distribution, and obtain a corrected magnetic resonance image.

[0196] Each module in the above eddy current correction device and magnetic resonance image correction device can be implemented in whole or in part by software, hardware, and their combination. Each of the above modules can be embedded in the processor in the computer device in hardware form or be independent of the processor, or can be stored in the memory in the computer device in software form, so as to facilitate the processor to call and execute the operations corresponding to each of the above modules.

[0197] In one embodiment, a computer device is provided, including a memory and a processor. A computer program is stored in the memory. When the processor executes the computer program, the following steps are implemented:

[0198] Obtain a first magnetic resonance signal at multiple echo times collected after applying a first gradient and a second magnetic resonance signal at multiple echo times collected after applying a second gradient; the acquisition moments of the first magnetic resonance signals at the multiple echo times correspond to the acquisition moments of the second magnetic resonance signals at the multiple echo times; according to the first magnetic resonance signal and the second magnetic resonance signal at each echo time, determine two magnetic resonance images at each echo time, and determine the phase difference between the two magnetic resonance images at each echo time; according to each phase difference, determine the eddy current field distribution at one or more imaging echo times; use the eddy current field distribution at the imaging echo time to perform eddy current correction on the magnetic resonance signal corresponding to the imaging echo time.

[0199] In one embodiment, when the processor executes the computer program, the following steps are further implemented:

[0200] Perform mathematical operation processing on each phase difference to determine the eddy current field distribution at each echo time; solve the eddy current field distribution at each echo time to determine the eddy current field distribution at each imaging echo time.

[0201] In one embodiment, when the processor executes the computer program, the following steps are further implemented:

[0202] Perform coefficient expansion on the eddy current field distribution at each echo time 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, obtain the eddy current field distribution at each imaging echo time.

[0203] In one embodiment, when the processor executes the computer program, the following steps are further implemented:

[0204] After the first gradient is applied, multi-slice data cross-acquisition is performed using a pre-scan sequence to obtain first magnetic resonance signals at multiple echo times after the application of the first gradient; after the second gradient is applied, multi-slice data cross-acquisition is performed using a pre-scan sequence to obtain second magnetic resonance signals at multiple echo times after the application of the second gradient.

[0205] In one embodiment, when the processor executes the computer program, the following steps are further implemented:

[0206] According to each phase difference, determine the eddy current field distribution at each imaging echo time after the application of the first gradient or the second gradient.

[0207] In one embodiment, when the processor executes the computer program, the following steps are further implemented:

[0208] Perform image reconstruction on the first magnetic resonance signals and the second magnetic resonance signals at each echo time to obtain a first magnetic resonance image and a second magnetic resonance image at each echo time; obtain a first phase at each echo time according to the first magnetic resonance image at each echo time, and obtain a second phase at each echo time according to the second magnetic resonance image at each echo time; perform a subtraction operation on the first phase and the second phase at each echo time to obtain the phase difference between the first magnetic resonance image and the second magnetic resonance image at each echo time.

[0209] In one embodiment, when the processor executes the computer program, the following steps are further implemented:

[0210] Obtain multiple groups of magnetic resonance images of multiple slices of a scanned object, each group of magnetic resonance images including a first magnetic resonance image and a second magnetic resonance image corresponding to the same echo time, the first magnetic resonance image being reconstructed from the first magnetic resonance signals acquired after the application of the first gradient, and the second magnetic resonance image being reconstructed from the second magnetic resonance signals acquired after the application of the second gradient; determine the phase difference between the first magnetic resonance image and the second magnetic resonance image in each group of magnetic resonance images; according to the phase difference, determine the eddy current field distribution at at least one imaging echo time; correct 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.

[0211] In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored, and when the computer program is executed by a processor, the following steps are implemented:

[0212] Obtain a first magnetic resonance signal of multiple echo times acquired after the application of a first gradient and a second magnetic resonance signal of multiple echo times acquired after the application of a second gradient; the acquisition times of the first magnetic resonance signal of the multiple echo times correspond to the acquisition times of the second magnetic resonance signal of the multiple echo times; determine two magnetic resonance images for each echo time according to the first magnetic resonance signal and the second magnetic resonance signal of each echo time, and determine the phase difference between the two magnetic resonance images for each echo time; determine the eddy current field distribution at one or more imaging echo times according to each phase difference; use the eddy current field distribution at the imaging echo times to correct the magnetic resonance image to be processed corresponding to the imaging echo times, and obtain a corrected magnetic resonance image for eddy current correction.

[0213] In one embodiment, when the computer program is executed by a processor, the following steps are further implemented:

[0214] Perform mathematical operation processing on each phase difference to determine the eddy current field distribution at each echo time; solve the eddy current field distribution at each echo time to determine the eddy current field distribution at each imaging echo time.

[0215] In one embodiment, when the computer program is executed by a processor, the following steps are further implemented:

[0216] Perform coefficient expansion on the eddy current field distribution at each echo time according to a preset spherical harmonic function to determine the eddy current spherical harmonic coefficients at each imaging echo time; obtain the eddy current field distribution at each imaging echo time according to the eddy current spherical harmonic coefficients at each imaging echo time.

[0217] In one embodiment, when the computer program is executed by a processor, the following steps are further implemented:

[0218] After the application of the first gradient, perform multi-layer data cross-acquisition using a pre-scan sequence to obtain the first magnetic resonance signal of multiple echo times after the application of the first gradient; after the application of the second gradient, perform multi-layer data cross-acquisition using a pre-scan sequence to obtain the second magnetic resonance signal of multiple echo times after the application of the second gradient.

[0219] In one embodiment, when the computer program is executed by a processor, the following steps are further implemented:

[0220] Determine the eddy current field distribution at each imaging echo time after the application of the first gradient or the second gradient according to each phase difference.

[0221] In one embodiment, when the computer program is executed by a processor, the following steps are further implemented:

[0222] Perform image reconstruction on the first magnetic resonance signal and the second magnetic resonance signal at each echo time to obtain the first magnetic resonance image and the second magnetic resonance image at each echo time; obtain the first phase at each echo time based on the first magnetic resonance image at each echo time, and obtain the second phase at each echo time based on the second magnetic resonance image at each echo time; perform a subtraction operation on the first phase and the second phase at each echo time to obtain the phase difference between the first magnetic resonance image and the second magnetic resonance image at each echo time.

[0223] In one embodiment, when the computer program is executed by a processor, the following steps are further implemented:

[0224] Obtain multiple sets of magnetic resonance images of multiple slices of a scanned object, each set of magnetic resonance images including a first magnetic resonance image and a second magnetic resonance image corresponding to the same echo time, where the first magnetic resonance image is obtained by reconstructing the first magnetic resonance signal collected after the application of a first gradient, and the second magnetic resonance image is obtained by reconstructing the second magnetic resonance signal collected after the application of a second gradient; determine the phase difference between the first magnetic resonance image and the second magnetic resonance image in each set of magnetic resonance images; determine the eddy current field distribution at at least one imaging echo time according to the phase difference; correct 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.

[0225] Those of ordinary skill in the art can understand that all or part of the processes of implementing the methods in the above embodiments can be completed by instructing relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above methods. Among them, any reference to a memory, storage, database, or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memories. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, or optical memory, etc. Volatile memory can include 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 (SRAM) or dynamic random access memory (DRAM), etc.

[0226] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0227] The above-described embodiments merely represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A method for eddy current correction, characterized in that, the method includes: After the first gradient is applied, multi-slice data cross-acquisition is performed using a pre-scan sequence to obtain a first magnetic resonance signal at multiple echo times after the first gradient is applied; after the second gradient is applied, multi-slice data cross-acquisition is performed using a pre-scan sequence to obtain a second magnetic resonance signal at multiple echo times after the second gradient is applied; According to the first magnetic resonance signal and the second magnetic resonance signal at each echo time, two magnetic resonance images at each echo time are determined, and the phase difference between the two magnetic resonance images at each echo time is determined; According to each of the phase differences, the eddy current field distribution at at least one imaging echo time is determined; The magnetic resonance signal corresponding to the imaging echo time is corrected for eddy current using the eddy current field distribution at 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 includes: Processing each of the phase differences to determine the eddy current field distribution at each of the echo times; Performing 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 intensity magnitudes and opposite directions; the step of determining the eddy current field distribution at each imaging echo time according to each of the phase differences includes: According to each of the phase differences, 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.

4. The method according to claim 1 or 2, characterized in that, the step of 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 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 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; Performing a difference operation on the first phase and the second phase at each echo time to obtain the phase difference between the first magnetic resonance image and the second magnetic resonance image at each echo time.

5. A method for magnetic resonance image correction, characterized in that, the method includes: Obtain multiple sets of magnetic resonance images of a scanning 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. The first magnetic resonance image is obtained by performing multi-layer data cross-acquisition using a pre-scan sequence after the application of a first gradient, and reconstructing the first magnetic resonance signals at multiple echo times after the application of the first gradient. The second magnetic resonance image is obtained by performing multi-layer data cross-acquisition using a pre-scan sequence after the application of a second gradient, and reconstructing the second magnetic resonance signals at multiple echo times after the application of the second gradient; Determine the phase difference between the first magnetic resonance image and the second magnetic resonance image in each set of magnetic resonance images; Determine the eddy current field distribution at at least one imaging echo time according to the phase difference; Correct the magnetic resonance image to be processed corresponding to the imaging echo time according to the eddy current field distribution, and obtain the corrected magnetic resonance image.

6. An eddy current correction device, Characterized in that, The device includes: A signal acquisition module, configured to perform multi-layer data cross-acquisition using a pre-scan sequence after the application of a first gradient to obtain the first magnetic resonance signals at multiple echo times after the application of the first gradient; and perform multi-layer data cross-acquisition using a pre-scan sequence after the application of a second gradient to obtain the second magnetic resonance signals at multiple echo times after the application of the second gradient; A first phase difference determination module, configured to determine two magnetic resonance images at each echo time according to the first magnetic resonance signals and the second magnetic resonance signals at each echo time, and determine the phase difference between the two magnetic resonance images at each echo time; A first eddy current field determination module, configured to determine the eddy current field distribution at at least one imaging echo time according to each of the phase differences; An eddy current correction module, configured to perform eddy current correction on the magnetic resonance signals corresponding to the imaging echo time by using the eddy current field distribution at the imaging echo time.

7. A computer device, including a memory and a processor, the memory stores a computer program, Characterized in that, When the processor executes the computer program, the steps of the method according to any one of claims 1 to 5 are implemented.

8. A computer-readable storage medium, on which a computer program is stored, Characterized in that, 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.

Images