A method, device, equipment and medium for correcting magnetic resonance image distortion

Abstract

The present application discloses a magnetic resonance image distortion correction method, device, equipment and medium, which relates to the field of magnetic resonance image processing technology, including: collecting a static field map to be corrected and a magnetic resonance image to be corrected in a preset sampling pixel bandwidth and a preset frequency encoding direction; using the magnetic field map information of a superconducting magnet, the preset sampling pixel bandwidth and the preset frequency encoding direction to construct the constraint problem of each point in the static field map to be corrected; using the measurement points selected in the magnetic field map to locate the measurement points of the static field map to be corrected, so as to obtain the measurement points of the static field map to be corrected, and performing regional search and regional solution in the static field map to be corrected according to the constraint problem and the measurement points of the static field map to be corrected, so as to obtain the corrected static field map; based on the coordinate transformation relationship constructed by the corrected static field map, coordinate transformation is performed on the image coordinates in the magnetic resonance image to be corrected, so as to obtain the corrected magnetic resonance image. Use a more accurate static field to correct image distortion.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic resonance image processing, and in particular to a magnetic resonance image distortion correction method, device, equipment and medium. Background Art

[0002] In magnetic resonance imaging (MRI), an inhomogeneous B0 field can have many adverse effects on MRI images, the most significant and common of which is image distortion. Theoretically, according to the Larmor equation, the precession frequency of hydrogen nuclei in the human body is proportional to the B0 field. The larger the B0 field, the higher the precession frequency. The encoding principle of magnetic resonance signals is to artificially change the uniformity of the B0 field in space by applying a linear gradient field related to the spatial position, thereby causing changes in the precession frequency and phase of hydrogen nuclei. This change corresponds to the spatial coordinates. Therefore, the source of the signal in space can be determined by distinguishing the frequency and phase of the signal, thereby forming an image. The above are all based on the assumption that the B0 field is absolutely uniform. If the B0 field itself is not uniform, its inhomogeneous part will be superimposed on the gradient magnetic field, causing the gradient field to change linearly, which in turn affects the spatial encoding and causes image distortion.

[0003] Frequency encoding is a way of spatial encoding of magnetic resonance imaging. During sampling, a gradient magnetic field is applied to generate a magnetic field that changes linearly with the spatial position in a specific direction, so that the precession frequency of the hydrogen nucleus changes linearly with the spatial position. Different frequency components of the sampled signal can correspond to different spatial positions, thereby completing the encoding of the spatial position in this direction. The frequency range corresponding to each pixel is called the pixel bandwidth, which is equal to the inverse of the sampling time. If the B0 field at a certain point is deviated, this point will be encoded to a position that is multiple pixels different from the actual position. The existing technology increases the sampling bandwidth, thereby increasing the pixel bandwidth and reducing the spatial encoding error in the frequency encoding direction. Use a structured model to scan and save the spatial distortion correction information, and apply this information to perform distortion correction after the image is scanned. Use the B0 map scan before each scan to obtain the spatial distortion correction information and perform distortion correction. However, the above processing method often results in too long scanning time, errors between the distortion correction information and the actual scan, or inability to solve and correct normally.

[0004] In summary, how to correct the distortion of distorted images of magnetic resonance imaging while reducing the image dependence on the distorted images is a technical problem to be solved in the field. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a method, device, equipment and medium for magnetic resonance image distortion correction, which can correct the distortion of magnetic resonance imaging distorted images while reducing the image dependence on the distorted images. The specific scheme is as follows:

[0006] In a first aspect, the present application discloses a method for correcting magnetic resonance image distortion, comprising:

[0007] Acquiring a static field image to be corrected and a magnetic resonance image to be corrected in a preset sampling pixel bandwidth and a preset frequency encoding direction;

[0008] Using the magnetic field diagram information of the superconducting magnet, the preset sampling pixel bandwidth and the preset frequency encoding direction, the constraint problem of each point in the static field diagram to be corrected is constructed;

[0009] Using the measurement points selected in the magnetic field map, the measurement points of the static field map to be corrected are positioned to obtain the measurement points of the static field map to be corrected, and according to the constraint problem and the measurement points of the static field map to be corrected, regional search and regional solution are performed in the static field map to be corrected to obtain the corrected static field map;

[0010] The image coordinates in the magnetic resonance image to be corrected are transformed based on the coordinate transformation relationship constructed by the corrected static field map to obtain the corrected magnetic resonance image.

[0011] Optionally, the collecting of the static field image to be corrected in a preset sampling pixel bandwidth and a preset frequency encoding direction includes:

[0012] At two different preset echo times, a small-angle spoiler gradient echo sequence is scanned twice in a preset frequency encoding direction to obtain first image data and second image data after Fourier transformation, respectively; wherein the preset echo time is the reciprocal of the preset sampling pixel bandwidth;

[0013] The phase difference of the same image position in the first image data and the second image data is calculated, and the static field image to be corrected is obtained according to the phase difference, the gyromagnetic ratio, and the time difference between two different preset echo times.

[0014] Optionally, before constructing the constraint problem of each point in the static field map to be corrected by using the magnetic field map information of the superconducting magnet, the preset sampling pixel bandwidth and the preset frequency encoding direction, the method further includes:

[0015] A meniscus-type magnetic field camera is placed in the center of a superconducting magnet, and is rotated by a preset angle along the Z-axis direction of the camera to collect magnetic field values ​​of points on a spherical surface with a diameter of the shim range at each rotation, so as to obtain a corresponding magnetic field map and shim range information of the spherical surface.

[0016] Optionally, performing regional search and regional solution in the static field map to be corrected according to the constraint problem and the measurement points of the static field map to be corrected to obtain the corrected static field map includes:

[0017] Starting from the current measurement point of the static field image to be corrected, a regional search is performed toward the center of the static field image to be corrected, and a phase change cycle number correction parameter of the current measurement point of the static field image to be corrected is determined according to the number of phase change cycles experienced by the path in the regional search;

[0018] Substituting the phase change cycle number correction parameter into the constraint problem to obtain a solution result of the current measurement point of the static field diagram to be corrected;

[0019] Each of the remaining measurement points of the static field map to be corrected is taken as a new current measurement point, and the step of performing an area search from the current measurement point of the static field map to be corrected to the center of the static field map to be corrected is jumped to execute, and determining a correction parameter for the number of phase change cycles of the current measurement point of the static field map to be corrected according to the number of phase change cycles experienced by the path in the area search, so as to determine the corrected static field map based on the solution results of all the current measurement points.

[0020] Optionally, the magnetic resonance image distortion correction method further includes:

[0021] If the static field map to be corrected has a target area that passes through all the current measurement points but is not searched, an interpolation processing method is used to obtain a solution result for the target area.

[0022] Optionally, the coordinate transformation of the image coordinates in the magnetic resonance image to be corrected based on the coordinate transformation relationship constructed based on the corrected static field image to obtain the corrected magnetic resonance image includes:

[0023] A coordinate conversion relationship is established based on the corrected static field image, the preset sampling pixel bandwidth, the target vector of the preset frequency encoding direction, the gyromagnetic ratio, and the image coordinates and the real coordinates;

[0024] The image coordinates in the magnetic resonance image to be corrected are transformed according to the coordinate transformation relationship to obtain a corrected magnetic resonance image.

[0025] Optionally, the coordinate conversion relationship is constructed based on the corrected static field image, the preset sampling pixel bandwidth, the target vector of the preset frequency encoding direction, the gyromagnetic ratio, and the image coordinates and the real coordinates, including:

[0026] according to Construct a coordinate transformation relationship; where, represents the real coordinates, represents the gyromagnetic ratio, represents the static field map after correction, represents the target vector of the preset frequency encoding direction, Indicates the preset sampling pixel bandwidth, Represents image coordinates.

[0027] In a second aspect, the present application discloses a magnetic resonance image distortion correction device, comprising:

[0028] An image acquisition module, used for acquiring a static field image to be corrected and a magnetic resonance image to be corrected in a preset sampling pixel bandwidth and a preset frequency encoding direction;

[0029] A constraint construction module, used to construct the constraint problem of each point in the static field map to be corrected by using the magnetic field map information of the superconducting magnet, the preset sampling pixel bandwidth and the preset frequency encoding direction;

[0030] A first correction module is used to locate the measurement points of the static field map to be corrected by using the measurement points selected in the magnetic field map to obtain the measurement points of the static field map to be corrected, and perform regional search and regional solution in the static field map to be corrected according to the constraint problem and the measurement points of the static field map to be corrected to obtain the corrected static field map;

[0031] The second correction module is used to perform coordinate transformation on the image coordinates in the magnetic resonance image to be corrected based on the coordinate transformation relationship constructed by the corrected static field map to obtain a corrected magnetic resonance image.

[0032] In a third aspect, the present application discloses an electronic device, comprising:

[0033] Memory, used to store computer programs;

[0034] The processor is used to execute the computer program to implement the steps of the magnetic resonance image distortion correction method disclosed above.

[0035] In a fourth aspect, the present application discloses a computer-readable storage medium for storing a computer program; wherein, when the computer program is executed by a processor, the steps of the magnetic resonance image distortion correction method disclosed above are implemented.

[0036] It can be seen that the present application discloses a method for correcting magnetic resonance image distortion, including: collecting a static field map to be corrected and a magnetic resonance image to be corrected in a preset sampling pixel bandwidth and a preset frequency encoding direction; using the magnetic field map information of the superconducting magnet, the preset sampling pixel bandwidth and the preset frequency encoding direction to construct the constraint problem of each point in the static field map to be corrected; using the measurement points selected in the magnetic field map to locate the measurement points of the static field map to be corrected, so as to obtain the measurement points of the static field map to be corrected, and performing regional search and regional solution in the static field map to be corrected according to the constraint problem and the measurement points of the static field map to be corrected, so as to obtain the corrected static field map; based on the coordinate transformation relationship constructed by the corrected static field map, the image coordinates in the magnetic resonance image to be corrected are transformed to obtain the corrected magnetic resonance image. It can be seen that the present application can measure the real B0 field more accurately through the original B0 field measurement information. A larger scanning field of view can be achieved by using the magnetic field outside the uniform field of view. The magnetic field map and the scanning sequence in the preset sampling pixel bandwidth and preset frequency encoding direction are used to measure and obtain the true B0 field map. The magnetic field map provides constraints for more accurately releasing the phase wrapping of the scanning sequence, and the scanning sequence can reflect the influence of the specific scanning part on the magnetic field. Then, a more accurate B0 field is used to correct the image distortion. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0038] Figure 1 A flow chart of a magnetic resonance image distortion correction method disclosed in the present application;

[0039] Figure 2 A magnetic field diagram disclosed in this application;

[0040] Figure 3 A flowchart of a specific magnetic resonance image distortion correction method disclosed in this application;

[0041] Figure 4 This is a schematic structural diagram of a magnetic resonance image distortion correction device disclosed in the present application;

[0042] Figure 5 This is a structural diagram of an electronic device disclosed in this application. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0044] Magnetic resonance imaging has become one of the most important examination methods for modern medical imaging due to its excellent soft tissue contrast, multi-weighted imaging and arbitrary section imaging. The hardware system of modern MRI equipment is mainly divided into: a superconducting magnet system that provides the main magnetic field B0, a gradient system that provides gradient magnetic fields Gx, Gy, and Gz, a radio frequency system that provides the radio frequency field B1, and a spectrometer system responsible for control and acquisition. For superconducting magnets, in addition to the main magnetic field strength, another core indicator is the main magnetic field uniformity, which is often required to be less than 10ppm (one millionth). However, affected by factors such as design and processing errors, magnetic components, and the surrounding environment of the magnetic field, the uniformity of the B0 field generated by the superconducting magnet after excitation is generally less than 1000ppm, and needs to be further optimized through additional passive shimming technology, but the quality of the optimization depends on the shimming algorithm and whether the shimming space is sufficient.

[0045] The uneven B0 field will have many adverse effects on MRI images, the most significant and common of which is image distortion. Theoretically, according to the Larmor equation, the precession frequency of hydrogen nuclei in the human body is proportional to the B0 field. The larger the B0 field, the higher the precession frequency. , It is called the gyromagnetic ratio. The encoding principle of the magnetic resonance signal is to artificially change the uniformity of the B0 field in space by applying a linear gradient field related to the spatial position, thereby causing changes in the frequency and phase of the precession of hydrogen nuclei. This change corresponds to the spatial coordinates. Therefore, we can determine the source of the signal in space by distinguishing the frequency and phase of the signal, thereby forming an image. The above are all based on the assumption that the B0 field is absolutely uniform. If the B0 field itself is not uniform, its uneven part will be superimposed on the gradient magnetic field, causing the gradient field to change linearly, which in turn affects the spatial encoding and causes image distortion.

[0046] Frequency encoding is a way of spatial encoding of magnetic resonance imaging. During sampling, a gradient magnetic field is applied to produce a magnetic field in a specific direction that changes linearly with the spatial position, so that the precession frequency of the hydrogen nuclei changes linearly with the spatial position. The different frequency components of the sampled signal can correspond to different spatial positions, thereby completing the encoding of the spatial position in that direction. The frequency range corresponding to each pixel is called the pixel bandwidth ( ), which is equal to the inverse of the sampling time. If the B0 field at a certain point has This will be encoded as a deviation from the actual position The position of pixels.

[0047] The existing technology increases the sampling bandwidth, thereby increasing the pixel bandwidth and reducing the spatial encoding error in the frequency encoding direction. Use a structurally determined phantom to scan and save the spatial distortion correction information, and apply this information to perform distortion correction after the image is scanned. Use the B0 map scan before each scan to obtain the spatial distortion correction information and perform distortion correction. However, increasing the sampling bandwidth will reduce the sampling time, which will lead to a decrease in the signal-to-noise ratio, which needs to be offset by increasing the number of averaging times, resulting in an increase in scanning time. Use a structurally determined phantom to scan and save the spatial distortion correction information: different scanned objects have different effects on the magnetic field, and the initially determined distortion correction information deviates from the actual scan. Use the B0map scan before each scan to obtain the spatial distortion correction information and perform distortion correction: the phase wrapping of the B0 map may not be correctly solved, resulting in a failure to correct.

[0048] To this end, the present invention provides a magnetic resonance image distortion correction solution, which can correct the distortion of the distorted image of magnetic resonance imaging while reducing the image dependence on the distorted image.

[0049] Reference Figure 1 As shown, an embodiment of the present invention discloses a method for correcting magnetic resonance image distortion, comprising:

[0050] Step S11: Acquire a static field image to be corrected and a magnetic resonance image to be corrected in a preset sampling pixel bandwidth and a preset frequency encoding direction.

[0051] In this embodiment, at two different preset echo times, the small-angle spoiled gradient echo sequence is scanned twice in a preset frequency encoding direction to obtain the first image data and the second image data after Fourier transformation, respectively; wherein the preset echo time is the inverse of the preset sampling pixel bandwidth; the phase difference of the same image position in the first image data and the second image data is calculated, and the static field map to be corrected is obtained based on the phase difference, the gyromagnetic ratio, and the time difference between the two different preset echo times. It can be understood that when scanning the small-angle spoiled gradient echo sequence twice, it should be noted that the echo times of the two small-angle spoiled gradient echo sequences are different, namely the first preset echo time and the second preset echo time. and the second preset echo time Then, the obtained K-space data is Fourier transformed to obtain the first image data corresponding to the first preset echo time. , second image data corresponding to the second preset echo time ,according to Calculate the phase difference of the two images at the same spatial position, then the difference between the B0 field at that position and the magnetic induction intensity corresponding to the observation frequency is ,in, is an integer, is the gyromagnetic ratio, Indicates the second image data The conjugate of The result is the static field map to be corrected , static field map to be corrected This includes B0 value warping caused by phase warping and image distortion in the frequency encoding direction. In addition, a magnetic resonance image of a certain part is obtained using the same MRI device at a preset echo time as the magnetic resonance image to be corrected. It should be noted that the sampling pixel bandwidth and frequency encoding direction of the magnetic resonance image to be corrected are consistent with the sampling pixel bandwidth and frequency encoding direction of the static field image to be corrected. If the frequency encoding direction is inconsistent, the corresponding coordinate rotation transformation needs to be added later to adjust the frequency encoding direction to be consistent, and the sampling pixel bandwidth and frequency encoding direction are pre-set.

[0052] Step S12: constructing the constraint problem of each point in the static field map to be corrected by using the magnetic field map information of the superconducting magnet, the preset sampling pixel bandwidth and the preset frequency encoding direction.

[0053] In this embodiment, before the constraint problem of each point in the static field map to be corrected is constructed using the magnetic field map information of the superconducting magnet, the preset sampling pixel bandwidth and the preset frequency encoding direction, it also includes: placing a meniscus-type magnetic field camera in the center of the superconducting magnet, and rotating the meniscus-type magnetic field camera in a manner of rotating by a preset angle along the Z-axis direction of the camera, so as to collect the magnetic field value of the point on the spherical surface with a diameter of the shim range at each rotation, so as to obtain the corresponding magnetic field map and the shim range information of the spherical surface. It can be understood that, because the magnetic field stability of the static field B0 generated by the superconducting magnet is very high, often at 0.001ppm / h, the change of the magnetic field can be ignored, so after the MRI equipment is installed, it is only necessary to collect the magnetic field map once. The acquisition method uses a meniscus-type magnetic field camera for direct measurement. The camera has 14 probes in the Z direction, and its diameter is the nominal shim range of the MRI equipment. Specifically, the magnetic field test method is to place the meniscus-type magnetic field camera in the center of the superconducting magnet, collect a set of data (1*14), and then rotate the field camera 15° along the Z axis to collect the second set of data. By analogy, a total of 24 sets of data (24*14) are obtained, corresponding to the magnetic field values ​​of 24*14 points on the spherical surface with a diameter of the shim range, that is, the magnetic field map, as shown in Figure 2As shown, the horizontal axis is the 14 spatial geometric coordinates in the Z direction, the vertical axis is the 24 angular coordinates in the circumferential direction, and the numerical unit shown in the figure is the deviation from the average value (ppm). This set of data is saved in the computer after the MRI system is installed and the shimming is completed, and is recorded as .

[0054] In this way, only one magnetic field map needs to be collected to meet the post-processing requirements of the distorted images taken by the MRI equipment currently installed with the superconducting magnet, saving time and resources and improving work efficiency. By collecting multiple sets of data through measurements at multiple angles, the magnetic field distribution of the central sphere of the superconducting magnet can be more comprehensively and accurately reflected. Since the static field B0 magnetic field generated by the superconducting magnet has high stability and negligible changes, one acquisition can meet subsequent needs, ensuring the reliability and validity of the data; a meniscus-type magnetic field camera with 14 probes and a diameter adapted to the uniform field range is used, which can well meet the measurement requirements of the MRI equipment. The 24 sets of data collected correspond to a large number of measurement points, providing a rich and detailed data basis for subsequent magnetic field analysis and processing. Clear and standardized acquisition methods, including rotation angles and the number of data acquisition groups, make the results have good repeatability. The data after acquisition is saved in the computer, which is convenient for subsequent call and analysis and processing at any time.

[0055] In this embodiment, the magnetic field map is required to calculate the real B0 field map (corrected static field map). Corrected B0 field map (static field map to be corrected) is wound to obtain the real B0 field map. Specifically, the constraint conditions of the static field map to be corrected are constructed according to the magnetic field map information (the measurement range involved when collecting the magnetic field map). Specifically, N points are taken as constraint conditions in the area where the magnetic field measurement sphere intersects with the static field map to be corrected. In addition, in addition to the constraint conditions, there are constraint targets to be solved. The two jointly construct the constraint problem of each point in the static field map to be corrected. It is assumed that X is the frequency encoding direction when scanning the electrostatic field map to be corrected. Otherwise, the frequency encoding direction can be transformed to the X direction through coordinate rotation transformation. The specific constraint problem is as follows: ;

[0056] in, represents the difference between the measured B0 field and the initial measured value, represents the x-coordinate of spatial encoding reconstruction, Represents the real x, y, z position coordinates, Indicates the preset sampling pixel bandwidth, represents the gyromagnetic ratio, and N represents the number of test points selected in the intersection area, which is a positive integer. It should be noted that due to the influence of the magnetic susceptibility of the scanning part on the B0 field and measurement errors, In the process of solving the constraint problem, the sum of squares should be minimized.

[0057] Step S13: Using the measurement points selected in the magnetic field map, the measurement points of the static field map to be corrected are located to obtain the measurement points of the static field map to be corrected, and according to the constraint problem and the measurement points of the static field map to be corrected, regional search and regional solution are performed in the static field map to be corrected to obtain the corrected static field map.

[0058] In this embodiment, a regional search is performed from the current measurement point of the static field map to be corrected to the center of the static field map to be corrected, and a correction parameter for the number of phase change cycles of the current measurement point of the static field map to be corrected is determined according to the number of phase change cycles experienced by the path in the regional search; the correction parameter for the number of phase change cycles is substituted into the constraint problem to obtain a solution result of the current measurement point of the static field map to be corrected; each of the remaining measurement points of the static field map to be corrected is used as a new current measurement point, and the steps of performing a regional search from the current measurement point of the static field map to be corrected to the center of the static field map to be corrected and determining the correction parameter for the number of phase change cycles of the current measurement point of the static field map to be corrected according to the number of phase change cycles experienced by the path in the regional search are jumped to determine the corrected static field map based on the solution results of all the current measurement points. It can be understood that the correction parameter for the number of phase change cycles of the current measurement point of the static field map to be corrected is substituted into the constraint problem to obtain a solution result of the current measurement point of the static field map to be corrected; each of the remaining measurement points of the static field map to be corrected is used as a new current measurement point, and the steps of performing a regional search from the current measurement point of the static field map to be corrected to the center of the static field map to be corrected are jumped to execute. Select a measurement point in the intersection area with the static field map to be corrected and locate it on the static field map to be corrected. Search from the measurement point to the center of the static field map to be corrected, and determine the phase change cycle number of the path. For the area that has not been searched, select other measurement points to repeat the search from the measurement point to the center of the static field map to be corrected, and determine the phase change cycle number of the point according to the path. The process of solving the problem is to use the continuity of the static field to solve the problem. The corrected static field map is determined based on the solution results of all current measurement points. .

[0059] It should be noted that if the static field map to be corrected has a target area that passes through all the current measurement points but is not searched, an interpolation processing method is used to obtain a solution result for the target area.

[0060] Step S14: performing coordinate transformation on the image coordinates in the magnetic resonance image to be corrected based on the coordinate transformation relationship constructed by the corrected static field map to obtain a corrected magnetic resonance image.

[0061] In this embodiment, a coordinate transformation relationship is established based on the corrected static field image, the preset sampling pixel bandwidth, the target vector of the preset frequency encoding direction, the gyromagnetic ratio, and the image coordinates and the real coordinates; the image coordinates in the magnetic resonance image to be corrected are transformed according to the coordinate transformation relationship to obtain the corrected magnetic resonance image. Specifically, according to Construct a coordinate transformation relationship; where, represents the real coordinates, represents the gyromagnetic ratio, represents the static field map after correction, represents the target vector of the preset frequency encoding direction, Indicates the preset sampling pixel bandwidth, Represents image coordinates.

[0062] It can be understood that when the sampling pixel bandwidth is When The magnetic field will generate The image is shifted by pixels. According to the corrected static field map obtained above , the transformation from the real space coordinates of any frequency encoding direction to the distorted image coordinates can be obtained, and the image can be inversely transformed according to the above coordinate transformation relationship to obtain the distortion-corrected magnetic resonance image.

[0063] like Figure 3As shown, the invention discloses a specific magnetic resonance image distortion correction process. Specifically, first, the magnetic field map is measured by a field camera to obtain the magnetic field map of the superconducting magnet. Then, after the superconducting magnet is installed in the MRI device, the B0 map sequence is scanned twice to obtain a B0 field map with winding (static field map to be corrected). At the same time, the obtained static field map to be corrected also carries corresponding scanning condition labels such as pixel bandwidth and frequency encoding direction. Then, the static field map to be corrected is corrected and calculated for the real B0 field map through the magnetic field map. The specific correction calculation process is as described in the above-mentioned embodiment, which will not be repeated here. Then, according to the image sequence scanning under the same scanning condition label, the magnetic resonance image to be corrected is obtained. At this time, the magnetic resonance image to be corrected is a distorted image. Then, the pixel bandwidth and frequency encoding direction represented in the scanning condition label are used as the condition information of the spatial distortion coordinate transformation, and the coordinate transformation of the magnetic resonance image to be corrected is performed in combination with the obtained corrected static field map and according to the coordinate transformation relationship, the distortion correction of the magnetic resonance image is completed, and the corrected magnetic resonance image is output. It can be seen that the present invention simultaneously utilizes magnetic field map and B0 map sequence scanning to measure and correct the real B0 field map. The magnetic field map provides constraints for more accurately removing the phase wrapping of the B0 map, and the B0 map can reflect the influence of a specific scanning part on the magnetic field. The corrected static field map can generate a more accurate image distortion correction. Specifically, using the original B0 field measurement information (magnetic field map), the real B0 field (static field to be corrected) can be measured more accurately. The magnetic field outside the uniform field of view can be used to achieve a larger scanning field of view. There is no need to increase the pixel bandwidth to reduce image distortion at the expense of reducing the signal-to-noise ratio or extending the scanning time. The calculation of the spatial distortion coordinate transformation does not depend on the image to be corrected, but only on some scanning parameters, so it can be calculated simultaneously with the scan, thereby saving time for image reconstruction.

[0064] It can be seen that the present application discloses a method for correcting magnetic resonance image distortion, including: collecting a static field map to be corrected and a magnetic resonance image to be corrected in a preset sampling pixel bandwidth and a preset frequency encoding direction; using the magnetic field map information of the superconducting magnet, the preset sampling pixel bandwidth and the preset frequency encoding direction to construct the constraint problem of each point in the static field map to be corrected; using the measurement points selected in the magnetic field map to locate the measurement points of the static field map to be corrected, so as to obtain the measurement points of the static field map to be corrected, and performing regional search and regional solution in the static field map to be corrected according to the constraint problem and the measurement points of the static field map to be corrected, so as to obtain the corrected static field map; based on the coordinate transformation relationship constructed by the corrected static field map, the image coordinates in the magnetic resonance image to be corrected are transformed to obtain the corrected magnetic resonance image. It can be seen that the present application can measure the real B0 field more accurately through the original B0 field measurement information. A larger scanning field of view can be achieved by using the magnetic field outside the uniform field of view. The magnetic field map and the scanning sequence in the preset sampling pixel bandwidth and preset frequency encoding direction are used to measure and obtain the true B0 field map. The magnetic field map provides constraints for more accurately releasing the phase wrapping of the scanning sequence, and the scanning sequence can reflect the influence of the specific scanning part on the magnetic field. Then, a more accurate B0 field is used to correct the image distortion.

[0065] Reference Figure 4 As shown, the present invention also discloses a magnetic resonance image distortion correction device, comprising:

[0066] An image acquisition module 11, for acquiring a static field image to be corrected and a magnetic resonance image to be corrected in a preset sampling pixel bandwidth and a preset frequency encoding direction;

[0067] A constraint construction module 12, for constructing the constraint problem of each point in the static field map to be corrected by using the magnetic field map information of the superconducting magnet, the preset sampling pixel bandwidth and the preset frequency encoding direction;

[0068] A first correction module 13 is used to locate the measurement points of the static field map to be corrected by using the measurement points selected in the magnetic field map to obtain the measurement points of the static field map to be corrected, and perform regional search and regional solution in the static field map to be corrected according to the constraint problem and the measurement points of the static field map to be corrected to obtain the corrected static field map;

[0069] The second correction module 14 is used to perform coordinate transformation on the image coordinates in the magnetic resonance image to be corrected based on the coordinate transformation relationship constructed by the corrected static field map to obtain a corrected magnetic resonance image.

[0070] It can be seen that the present application discloses the acquisition of a static field map to be corrected and a magnetic resonance image to be corrected in a preset sampling pixel bandwidth and a preset frequency encoding direction; the constraint problem of each point in the static field map to be corrected is constructed using the magnetic field map information of the superconducting magnet, the preset sampling pixel bandwidth and the preset frequency encoding direction; the measurement point positioning of the static field map to be corrected is performed using the measurement points selected in the magnetic field map to obtain the measurement points of the static field map to be corrected, and the regional search and regional solution are performed in the static field map to be corrected according to the constraint problem and the measurement points of the static field map to be corrected to obtain the corrected static field map; the image coordinates in the magnetic resonance image to be corrected are converted based on the coordinate conversion relationship constructed by the corrected static field map to obtain the corrected magnetic resonance image. It can be seen that the present application can measure the real B0 field more accurately through the original B0 field measurement information. A larger scanning field of view can be achieved by using the magnetic field outside the uniform field of view. The magnetic field map and the scanning sequence in the preset sampling pixel bandwidth and preset frequency encoding direction are used to measure and obtain the true B0 field map. The magnetic field map provides constraints for more accurately releasing the phase wrapping of the scanning sequence, and the scanning sequence can reflect the influence of the specific scanning part on the magnetic field. Then, a more accurate B0 field is used to correct the image distortion.

[0071] Furthermore, the present application also discloses an electronic device. Figure 5 This is a structural diagram of an electronic device 20 according to an exemplary embodiment. The content in the diagram cannot be regarded as any limitation on the scope of use of the present application.

[0072] Figure 5 The present invention provides a schematic diagram of the structure of an electronic device 20 provided in an embodiment of the present application. The electronic device 20 may specifically include: at least one processor 21, at least one memory 22, a power supply 23, a communication interface 24, an input / output interface 25, and a communication bus 26. The memory 22 is used to store a computer program, and the computer program is loaded and executed by the processor 21 to implement the relevant steps in the magnetic resonance image distortion correction method disclosed in any of the aforementioned embodiments. In addition, the electronic device 20 in this embodiment may specifically be an electronic computer.

[0073] In this embodiment, the power supply 23 is used to provide working voltage for each hardware device on the electronic device 20; the communication interface 24 can create a data transmission channel between the electronic device 20 and the external device, and the communication protocol it follows is any communication protocol that can be applied to the technical solution of the present application, and is not specifically limited here; the input and output interface 25 is used to obtain external input data or output data to the outside world, and its specific interface type can be selected according to specific application needs and is not specifically limited here.

[0074] Among them, the processor 21 may include one or more processing cores, such as a 4-core processor, an 8-core processor, etc. The processor 21 can be implemented in at least one hardware form of DSP (Digital Signal Processing), FPGA (Field-Programmable Gate Array), and PLA (Programmable Logic Array). The processor 21 may also include a main processor and a coprocessor. The main processor is a processor for processing data in the awake state, also known as a CPU (Central Processing Unit); the coprocessor is a low-power processor for processing data in the standby state. In some embodiments, the processor 21 may be integrated with a GPU (Graphics Processing Unit), which is responsible for rendering and drawing the content to be displayed on the display screen. In some embodiments, the processor 21 may also include an AI (Artificial Intelligence) processor, which is used to process computing operations related to machine learning.

[0075] In addition, the memory 22, as a carrier for storing resources, can be a read-only memory, a random access memory, a disk or an optical disk, etc. The resources stored thereon can include an operating system 221, a computer program 222, etc., and the storage method can be temporary storage or permanent storage.

[0076] The operating system 221 is used to manage and control the hardware devices and computer programs 222 on the electronic device 20, so as to realize the operation and processing of the massive data 223 in the memory 22 by the processor 21, which can be Windows Server, Netware, Unix, Linux, etc. In addition to including a computer program that can be used to complete the magnetic resonance image distortion correction method performed by the electronic device 20 disclosed in any of the aforementioned embodiments, the computer program 222 can further include a computer program that can be used to complete other specific tasks. In addition to data transmitted from an external device received by the electronic device, the data 223 can also include data collected by its own input and output interface 25.

[0077] Furthermore, the present application also discloses a computer-readable storage medium for storing a computer program; wherein, when the computer program is executed by a processor, the magnetic resonance image distortion correction method disclosed above is implemented. For the specific steps of the method, reference may be made to the corresponding contents disclosed in the above embodiments, and no further description will be given here.

[0078] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0079] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented with electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in terms of function in the above description. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel may use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application. The steps of the method or algorithm described in conjunction with the embodiments disclosed herein can be implemented directly with hardware, a software module executed by a processor, or a combination of the two. The software module can be placed in a random access memory RAM (Random Access Memory), memory, read-only memory ROM (Read Only Memory), electrically programmable EPROM (Electrically Programmable Read Only Memory), electrically erasable programmable EEPROM (ElectricErasable Programmable Read Only Memory), register, hard disk, removable disk, CD-ROM (CompactDisc-Read Only Memory), or any other form of storage medium known in the technical field.

[0080] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0081] The scheme provided by the present invention is introduced in detail above. Specific examples are used in this article to illustrate the principle and implementation mode of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation mode and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for correcting magnetic resonance image distortion, characterized in that: include: Acquiring a static field image to be corrected and a magnetic resonance image to be corrected in a preset sampling pixel bandwidth and a preset frequency encoding direction; Using the magnetic field diagram information of the superconducting magnet, the preset sampling pixel bandwidth and the preset frequency encoding direction, the constraint problem of each point in the static field diagram to be corrected is constructed; Using the measurement points selected in the magnetic field map, the measurement points of the static field map to be corrected are positioned to obtain the measurement points of the static field map to be corrected, and according to the constraint problem and the measurement points of the static field map to be corrected, regional search and regional solution are performed in the static field map to be corrected to obtain the corrected static field map; Performing coordinate transformation on the image coordinates in the magnetic resonance image to be corrected based on the coordinate transformation relationship constructed by the corrected static field map to obtain a corrected magnetic resonance image; The method of using the magnetic field map information of the superconducting magnet, the preset sampling pixel bandwidth and the preset frequency encoding direction to construct the constraint problem of each point in the static field map to be corrected includes: Construct the constraint problem, which is: ； in, Indicates the magnetic field diagram information of the measured superconducting magnet The difference from the initial measurement, represents the x-coordinate of spatial encoding reconstruction, Indicates the preset sampling pixel bandwidth, represents the gyromagnetic ratio, N represents the number of test points selected in the intersection area, which is a positive integer. Indicates the first preset echo time, Indicates the second preset echo time; The coordinate transformation relationship constructed based on the corrected static field map is used to transform the image coordinates in the magnetic resonance image to be corrected to obtain the corrected magnetic resonance image, including: A coordinate conversion relationship is established based on the corrected static field image, the preset sampling pixel bandwidth, the target vector of the preset frequency encoding direction, the gyromagnetic ratio, and the image coordinates and the real coordinates; Performing coordinate transformation on the image coordinates in the magnetic resonance image to be corrected according to the coordinate transformation relationship to obtain a corrected magnetic resonance image; The coordinate conversion relationship is constructed based on the corrected static field image, the preset sampling pixel bandwidth, the target vector of the preset frequency encoding direction, the gyromagnetic ratio, and the image coordinates and the real coordinates, including: according to Construct a coordinate transformation relationship; where, represents the real coordinates, represents the gyromagnetic ratio, represents the static field map after correction, The target vector representing the preset frequency encoding direction, Indicates the preset sampling pixel bandwidth, Represents image coordinates.

2. The magnetic resonance image distortion correction method according to claim 1, characterized in that: The collecting of the static field image to be corrected in the preset sampling pixel bandwidth and the preset frequency encoding direction includes: At two different preset echo times, a small-angle spoiler gradient echo sequence is scanned twice in a preset frequency encoding direction to obtain first image data and second image data after Fourier transformation, respectively; wherein the preset echo time is the reciprocal of the preset sampling pixel bandwidth; The phase difference of the same image position in the first image data and the second image data is calculated, and the static field image to be corrected is obtained according to the phase difference, the gyromagnetic ratio, and the time difference between two different preset echo times.

3. The magnetic resonance image distortion correction method according to claim 1, characterized in that: Before constructing the constraint problem of each point in the static field map to be corrected by using the magnetic field map information of the superconducting magnet, the preset sampling pixel bandwidth and the preset frequency encoding direction, the method further includes: A meniscus-type magnetic field camera is placed in the center of a superconducting magnet, and is rotated by a preset angle along the Z-axis direction of the camera to collect magnetic field values ​​of points on a spherical surface with a diameter of the shim range at each rotation, so as to obtain a corresponding magnetic field map and shim range information of the spherical surface.

4. The magnetic resonance image distortion correction method according to claim 1, characterized in that: The method of performing a regional search and a regional solution in the static field map to be corrected according to the constraint problem and the measurement points of the static field map to be corrected to obtain the corrected static field map includes: Starting from the current measurement point of the static field image to be corrected, a regional search is performed toward the center of the static field image to be corrected, and a phase change cycle number correction parameter of the current measurement point of the static field image to be corrected is determined according to the number of phase change cycles experienced by the path in the regional search; Substituting the phase change cycle number correction parameter into the constraint problem to obtain a solution result of the current measurement point of the static field diagram to be corrected; Each of the remaining measurement points of the static field map to be corrected is taken as a new current measurement point, and the step of performing an area search from the current measurement point of the static field map to be corrected to the center of the static field map to be corrected is jumped to execute, and determining a correction parameter for the number of phase change cycles of the current measurement point of the static field map to be corrected according to the number of phase change cycles experienced by the path in the area search, so as to determine the corrected static field map based on the solution results of all the current measurement points.

5. The magnetic resonance image distortion correction method according to claim 4, characterized in that: Also includes: If the static field map to be corrected has a target area that passes through all the current measurement points but is not searched, an interpolation processing method is used to obtain a solution result for the target area.

6. A magnetic resonance image distortion correction device, characterized in that: include: An image acquisition module, used for acquiring a static field image to be corrected and a magnetic resonance image to be corrected in a preset sampling pixel bandwidth and a preset frequency encoding direction; A constraint construction module, used to construct the constraint problem of each point in the static field map to be corrected by using the magnetic field map information of the superconducting magnet, the preset sampling pixel bandwidth and the preset frequency encoding direction; A first correction module is used to locate the measurement points of the static field map to be corrected by using the measurement points selected in the magnetic field map to obtain the measurement points of the static field map to be corrected, and perform regional search and regional solution in the static field map to be corrected according to the constraint problem and the measurement points of the static field map to be corrected to obtain the corrected static field map; A second correction module, configured to perform coordinate transformation on the image coordinates in the magnetic resonance image to be corrected based on the coordinate transformation relationship constructed by the corrected static field image, so as to obtain a corrected magnetic resonance image; The constraint building module is specifically used to build the constraint problem, which is: ； in, Indicates the magnetic field diagram information of the measured superconducting magnet The difference from the initial measurement, represents the x-coordinate of spatial encoding reconstruction, Indicates the preset sampling pixel bandwidth, represents the gyromagnetic ratio, N represents the number of test points selected in the intersection area, which is a positive integer. Indicates the first preset echo time, Indicates the second preset echo time; The second correction module is specifically used to establish a coordinate transformation relationship based on the corrected static field image, the preset sampling pixel bandwidth, the target vector of the preset frequency encoding direction, the gyromagnetic ratio, and the image coordinates and the real coordinates; and perform coordinate transformation on the image coordinates in the magnetic resonance image to be corrected according to the coordinate transformation relationship to obtain the corrected magnetic resonance image; The magnetic resonance image distortion correction device is also used according to Construct a coordinate transformation relationship; where, represents the real coordinates, represents the gyromagnetic ratio, represents the static field map after correction, The target vector representing the preset frequency encoding direction, Indicates the preset sampling pixel bandwidth, Represents image coordinates.

7. An electronic device, characterized in that: include: Memory, used to store computer programs; A processor, configured to execute the computer program to implement the steps of the magnetic resonance image distortion correction method as described in any one of claims 1 to 5.

8. A computer-readable storage medium, characterized in that: Used to store a computer program; wherein, when the computer program is executed by a processor, the steps of the magnetic resonance image distortion correction method as described in any one of claims 1 to 5 are implemented.

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