High-order shimming control method and device integrated with B0 field coupling compensation

Abstract

The invention relates to a high-order shimming control method and device integrated with B0 field coupling compensation. The method comprises the following steps: acquiring a shimming reference field and a coupling reference field after each channel in a high-order shimming coil is purified and separated; acquiring a three-dimensional field graph of a region of interest of a patient, and acquiring the current center frequency of a magnetic resonance imaging system; determining an initial current value of each channel based on the shimming reference field and the three-dimensional field pattern, the initial current values being not interfered by the coupling reference field; determining a B0 offset according to the initial current value and the coupling reference field, and eliminating uniformity interference of the B0 offset on a B0 field according to the B0 offset and the current center frequency; and after the uniformity interference is eliminated, the initial current value of each channel is set in the corresponding channel, and high-order shimming setting is completed. According to the invention, the high-order shimming quality is improved.

Description

Technical Field

[0001] This application relates to the field of magnetic resonance imaging, and in particular to a high-order shimming control method and apparatus integrating B0 field coupling compensation. Background Technology

[0002] In the field of magnetic resonance imaging (MRI), the homogeneity of the static magnetic field (B0 field) is a core prerequisite for ensuring image quality. Non-uniformity in the B0 field directly leads to image distortion, signal loss, and spectral broadening, severely reducing the accuracy of diagnostic results. For example, in echo-plane imaging mode, non-uniformity of the main magnetic field easily causes pixel shifts and geometric distortions in the reconstructed image. Furthermore, related research indicates that the improvement in imaging quality from high-field superconducting magnet technology largely depends on optimizing and upgrading the magnetic field homogeneity.

[0003] To compensate for higher-order inhomogeneities in the B0 field, such as distortions caused by higher-order terms of the spherical harmonic function, higher-order shimming coils are commonly used in the industry. These coils can generate complex magnetic field distributions to counteract higher-order distortions in the main magnetic field. Currently, high-end MRI systems typically come standard with second-order shimming coils, which correct for second-order magnetic field inhomogeneities in the imaging region by applying a specific current to the coil. However, MRI systems are complex electromagnetic systems, and electromagnetic interference can easily occur between components. A typical problem is the potential for inductive coupling between the magnet and the even-order shimming coil. When the shimming coil is powered, this inductive coupling can cause fluctuations in the magnet current, further disrupting the stability of the main magnetic field and negatively impacting the shimming effect.

[0004] Several high-order shimming algorithms exist for calculating the applied current of shimming coils to improve magnetic field uniformity. These algorithms mainly fall into two categories: one maps the six projections of the magnetic field and fits a mathematical model to each shimming coil to output the current value; the other calculates the shimming current in the region of interest by measuring the three-dimensional field map and using regularization methods. However, all of these algorithms rely on the premise that the magnetic field sensitivity provided by the shimming coil is stable. If there is a coupling effect between the shimming coil and the B0 field, it will cause a shift in the magnetic field resonance frequency, thereby weakening the shimming effect. Summary of the Invention

[0005] This application provides a high-order shimming control method and apparatus with integrated B0 field coupling compensation to solve the problem of decreased shimming quality caused by magnetic field deviation when the high-order shimming coil is coupled with the main magnetic field.

[0006] In a first aspect, this application provides a high-order uniform field control method integrating B0 field coupling compensation, the method comprising: Obtain the pure separated shimming reference field and coupled reference field for each channel in the high-order shimming coil; Acquire a three-dimensional field map of the patient's region of interest and acquire the current center frequency of the magnetic resonance imaging system; The initial current value of each channel is determined based on the homogenized reference field and the three-dimensional field map, wherein the initial current value is not affected by the coupled reference field; The B0 offset is determined based on the preliminary current value and the coupled reference field, and the B0 offset is used to eliminate the uniformity interference of the B0 field on the B0 field based on the B0 offset and the current center frequency. After eliminating uniformity interference, the initial current value of each channel is set to the corresponding channel to complete the high-order shimming setting.

[0007] Optionally, obtaining the purified, separated shimming reference field and coupled reference field for each channel in the higher-order shimming coil includes: Iterate through each channel in the higher-order shimming coil and perform the following operation on each channel; A B0 field measurement is performed on the input current of the channel to obtain the comprehensive reference field corresponding to the channel, wherein the comprehensive reference field includes the higher-order field and the coupling field generated by the channel; The center frequency and B0 field are measured on the input current of the channel to obtain the homogenization reference field corresponding to the channel, wherein the homogenization reference field is a higher-order field generated by the channel; The coupling reference field of the channel is determined based on the difference between the integrated reference field and the uniform reference field.

[0008] Optionally, performing a B0 field measurement on the input current of the channel to obtain the comprehensive reference field corresponding to the channel includes: A standard positive current is input into the channel of the high-order shimming coil, and the first magnetic field distribution superimposed with the high-order field and the coupled field is obtained by using the B0 field measurement method. A standard negative current is input into the channel of the high-order shimming coil, and the second magnetic field distribution superimposed with the high-order field and the coupled field is obtained by using the B0 field measurement method. The comprehensive reference field corresponding to the channel is determined based on the difference between the first magnetic field distribution and the second magnetic field distribution, and the difference between the standard positive current and the standard negative current.

[0009] Optionally, center frequency measurement and B0 field measurement are performed on the input current of the channel to obtain the uniform reference field corresponding to the channel, including: A standard positive current is input into the channel of the higher-order shimming coil, and the first center frequency of the magnetic resonance imaging system is obtained by center frequency measurement. The measurement frequency of the magnetic resonance imaging system is calibrated to the first center frequency, and the third magnetic field distribution is obtained by using the B0 field measurement method. The third magnetic field distribution includes the higher-order field generated when the standard positive current is input into the channel. A standard negative current is input into the channel of the higher-order shimming coil, and the second center frequency of the magnetic resonance imaging system is obtained by center frequency measurement. The measurement frequency of the magnetic resonance imaging system is calibrated to the second center frequency, and a fourth magnetic field distribution is obtained using the B0 field measurement method. The fourth magnetic field distribution includes a higher-order field generated when the standard negative current is input into the channel. The homogenization reference field corresponding to the channel is determined based on the difference between the third magnetic field distribution and the fourth magnetic field distribution, as well as the difference between the standard positive current and the standard negative current.

[0010] Optionally, determining the preliminary current value for each channel based on the homogenizing reference field and the three-dimensional field map includes: The magnetic field data in the three-dimensional field diagram is compressed to obtain a one-dimensional matrix. A shim reference field matrix is ​​constructed based on the shim reference field of all channels, and the shim reference field matrix is ​​subjected to singular value decomposition to obtain three initial matrices, wherein the three initial matrices include a left singular vector matrix, a singular value matrix and a right singular vector matrix. The three initial matrices are truncated according to the k dimensions that contribute the most to the shimming, and the truncated matrices are subjected to a preset operation to obtain three target matrices. The product of the three target matrices and the one-dimensional matrix is ​​calculated in a set order to determine the initial current value of each channel.

[0011] Optionally, the three initial matrices are truncated according to the k dimensions that contribute the most to the shimming, and a preset operation is performed on the truncated matrices to obtain three target matrices, including: Based on the number of channels of the higher-order shimming coil, an integer threshold k is determined according to a preset channel ratio; By taking the first k columns of the left singular vector matrix, the first k rows and first k columns of the singular value matrix, and the first k columns of the right singular vector matrix, three optimized matrices are obtained. Perform a transpose operation on the optimized left singular vector matrix and a pseudo-inverse operation on the optimized singular value matrix; The optimized right singular vector matrix, the transposed left singular vector matrix, and the pseudo-inverse singular value matrix are used as the three target matrices.

[0012] Optionally, eliminating the B0 offset's interference with the uniformity of the B0 field based on the B0 offset and the current center frequency includes one of the following two methods: The frequency offset corresponding to the B0 offset is determined by a preset magnetogyroscope ratio. This frequency offset is then applied to the current center frequency to obtain the offset B0 field frequency. The acquisition frequency of the magnetic resonance imaging system is then adjusted to match the offset B0 field frequency; or... The B0 offset is used as the correction target for B0 compensation to trigger the B0 compensation channel to generate a compensation magnetic field with the same magnitude but opposite direction as the B0 offset, thereby counteracting the B0 offset's interference with the uniformity of the B0 field.

[0013] Secondly, this application provides a high-order uniform field control device with integrated B0 field coupling compensation, the device comprising: The acquisition module is used to acquire the pure separated shimming reference field and coupling reference field of each channel in the high-order shimming coil; The acquisition module is used to acquire three-dimensional field images of the patient's region of interest and to acquire the current center frequency of the magnetic resonance imaging system; A determination module is used to determine the preliminary current value of each channel based on the homogenizing reference field and the three-dimensional field map, wherein the preliminary current value is not affected by the coupling reference field; The elimination module is used to determine the B0 offset based on the preliminary current value and the coupled reference field, and to eliminate the uniformity interference of the B0 offset on the B0 field based on the B0 offset and the current center frequency. The setting module is used to set the initial current value of each channel to the corresponding channel after eliminating uniformity interference, thus completing the high-order shimming setting.

[0014] Thirdly, this application provides an electronic device, comprising: at least one communication interface; at least one bus connected to the at least one communication interface; at least one processor connected to the at least one bus; and at least one memory connected to the at least one bus.

[0015] Fourthly, this application also provides a computer storage medium storing computer-executable instructions for executing the high-order uniform field control method with integrated BO field coupling compensation as described in any of the preceding claims of this application.

[0016] Compared with the prior art, the technical solution provided in this application has the following advantages: In the high-order shimming coil, firstly, by separating the pure shimming reference field and the coupling reference field of each channel, the interference of the coupling field on the reference field measurement is eliminated, and accurate reference data is obtained; then, the three-dimensional field map of the patient's region of interest and the current center frequency are acquired; next, the preliminary current value is calculated based on the shimming reference field and the three-dimensional field map to ensure that the current does not contain redundant components to cancel coupling interference; then, the B0 offset is determined by combining the preliminary current and the coupling reference field, and the B0 field uniformity interference caused by coupling is eliminated by correcting the B0 offset and the center frequency; finally, after the interference is eliminated, the current is applied to complete the high-order shimming setting. This application establishes a complete coupling field correction system, and the high-order field and the coupling field are measured in tandem, realizing the accurate measurement of the high-order field changes generated by the high-order shimming coil and the B0 field coupling offset caused by it, thereby improving the accuracy and stability of the high-order shimming, and ultimately improving the quality of the high-order shimming. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] One or more embodiments are illustrated by way of example with reference numerals in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0020] Figure 1 A flowchart of a high-order uniform field control method integrating B0 field coupling compensation provided in an embodiment of this application; Figure 2 This is a comparison diagram of the effects of this application and existing technologies in water-based simulated body testing; Figure 3 This is a comparison diagram of the effects of this application and existing technologies in magnetic resonance spectroscopy scanning of cerebrospinal fluid; Figure 4 A schematic diagram of a high-order uniform field control device integrating B0 field coupling compensation provided in an embodiment of this application; Figure 5 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] The following disclosure provides numerous different embodiments or examples for implementing various structures of this application. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the scope of this application. Furthermore, reference numerals and / or letters may be repeated in different examples. Such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed.

[0023] The following will describe in detail, with reference to specific implementation methods, a high-order shimming control method integrating B0 field coupling compensation provided in the embodiments of this application, taking the control module applied to a magnetic resonance imaging system as an example, such as... Figure 1 As shown, the specific steps are as follows: Step 101: Obtain the pure separated shimming reference field and coupling reference field for each channel in the high-order shimming coil; Step 102: Acquire a three-dimensional field image of the patient's region of interest and acquire the current center frequency of the magnetic resonance imaging system; Step 103: Determine the preliminary current value of each channel based on the homogenized reference field and the three-dimensional field map, wherein the preliminary current value is not affected by the coupled reference field; Step 104: Determine the B0 offset based on the preliminary current value and the coupled reference field, and eliminate the B0 offset's interference with the uniformity of the B0 field based on the B0 offset and the current center frequency; Step 105: After eliminating uniformity interference, set the initial current value of each channel to the corresponding channel to complete the high-order shimming setting.

[0024] First, some terms in the embodiments of this application will be explained, including the following.

[0025] Higher-order shimming coils: These are specialized coils used to compensate for higher-order inhomogeneities in the main magnetic field (B0 field) of a magnetic resonance imaging system. Their core function is to generate a complex magnetic field distribution by passing in a specific current, thereby offsetting higher-order distortions in the B0 field that cannot be corrected by conventional first-order coils.

[0026] Channel: refers to a unit in a high-order shimming coil that independently inputs current and generates a specific magnetic field component. Each channel can control the current magnitude individually and corresponds to a specific magnetic field distribution.

[0027] Shimming reference field: refers to the magnetic field distribution generated by a single channel of a high-order shimming coil under unit current, which is used only to counteract the high-order inhomogeneities of the B0 field.

[0028] Coupled reference field: refers to the magnetic field distribution that is generated when current is applied to the high-order shimming coil channel due to the inductive coupling effect with the main magnetic field (B0), which causes the overall B0 field to shift. It is an interfering magnetic field brought about by electromagnetic coupling, which will affect the uniformity of the B0 field and cause shimming error.

[0029] Pure separation: refers to the process of accurately separating the shimming reference field and the coupled reference field from the combined magnetic field distribution of the two, ensuring the independent characterization of the two fields and avoiding the decrease in shimming accuracy caused by mutual interference.

[0030] Patient region of interest: refers to a specific area within the patient's body selected by doctors or technicians for diagnostic purposes, requiring magnetic resonance imaging (such as the brain, neck, trunk, etc.), and where B0 field homogeneity must be ensured.

[0031] Three-dimensional field map: refers to the three-dimensional spatial magnetic field distribution map formed by collecting B0 field strength data of all spatial points in the region of interest of the patient through the B0 field measurement function of the MRI system. It directly reflects the uniformity of the B0 field in the region, such as whether there is distortion and the degree of distortion.

[0032] Magnetic resonance imaging (MRI) system: refers to medical equipment that uses the principle of magnetic resonance to generate images of the internal structure of the human body. Its core components include: a magnet that generates the B0 field, a shimming coil to compensate for non-uniformity of the B0 field, a signal acquisition and processing unit, and a center frequency control unit. Its imaging quality is highly dependent on the uniformity of the B0 field.

[0033] Current center frequency: refers to the reference value of the nuclear resonance frequency in the MRI system corresponding to the current B0 field state. B0 field shift will directly cause changes in the center frequency.

[0034] Preliminary current value: refers to the current value of each channel of the high-order shimming coil obtained by singular value decomposition optimization calculation based on the separated shimming reference field (Bref) and the three-dimensional field map of the patient's region of interest (b).

[0035] B0 offset: refers to the change in field strength of the B0 field that deviates from the ideal uniform state due to the effect of the coupled reference field (Bcoup) after the initial current is applied to the high-order shimming coil. It is the core interference source that causes the uniformity of the B0 field to decrease.

[0036] Uniformity interference of the B0 field: refers to the phenomenon that the B0 field deviates from the ideal uniform magnetic field distribution due to factors such as coupling reference field and external electromagnetic interference. This directly leads to problems such as geometric distortion, signal loss, and spectral line broadening in MRI images, which seriously affects the accuracy of diagnosis.

[0037] Higher-order shimming setup: This refers to the process of applying a corrected initial current value (i1) to each corresponding channel of the higher-order shimming coil after eliminating B0 offset interference caused by the coupling field. After application, the coil generates a precise compensating magnetic field to counteract the higher-order inhomogeneities of the B0 field, ultimately optimizing the uniformity of the B0 field in the patient's region of interest.

[0038] In step 101, during the system preprocessing stage before routine equipment maintenance and calibration or the actual patient scan, the MRI system completes its power-on self-test and enters the high-order shimming calibration stage. The MRI system's control module, for each independent channel of the high-order shimming coil (including the first-order term coil), inputs two typical currents (positive and negative) to each channel, combined with B0 field measurement and center frequency recording, ultimately separating the pure shimming reference field and the coupled reference field. The separated coupled reference field provides a pure high-order field reference, eliminating interference from the coupled field on the reference field measurement. The control module follows this process to traverse all shimming coil channels, acquiring the shimming reference field and coupled reference field for all channels.

[0039] In step 102, for example, after the patient lies down and the head coil is fixed during the brain scan, the control module drives the B0 field measurement component to scan the region of interest (such as the area around the lesion) specified by the doctor, and obtains a three-dimensional field map reflecting the actual magnetic field distribution in that area. The three-dimensional field map is a data carrier that can accurately capture the local magnetic field inhomogeneity caused by the density difference of the patient's brain tissue, such as the high-frequency magnetic field fluctuations that may occur in the cerebrospinal fluid area due to the abnormal density of the lesion area. At the same time, the control module records the current center frequency of the magnetic resonance imaging system. The current center frequency is the actual operating frequency of the system after being affected by the magnetic susceptibility difference of the patient's brain tissue and the coupling effect of the shimming coil, reflecting the overall resonance state of the current B0 field.

[0040] In step 103, the control module constructs a matrix using the separated shimming reference field. After singular value decomposition and optimization, it calculates the preliminary current value for each channel by combining the obtained three-dimensional field diagram. If coupling field components are mixed into the shimming reference field, the calculated current will simultaneously contain correction components for higher-order magnetic field inhomogeneities and redundant components to cancel coupling interference, thus causing the shimming direction to deviate from the expected direction and failing to accurately improve higher-order magnetic field distortion. However, the shimming reference field has already removed the interference from the coupling reference field. Using a pure shimming reference field for calculation ensures that the preliminary current focuses only on correcting the higher-order inhomogeneities of the B0 field and does not contain redundant components to cancel coupling interference. This avoids current calculation errors caused by coupling effects from the source and ensures that the current of each channel can accurately match its assigned higher-order magnetic field correction task.

[0041] In step 104, the control module combines the initial current value of each channel with the corresponding coupled reference field to calculate the B0 offset. This B0 offset is the change in field strength of the B0 field due to coupling effect after the initial current is applied to the shimming coil, causing it to deviate from the ideal uniform state. Then, combining this with the acquired current center frequency, the interference is eliminated using one of two methods: first, by generating a reverse magnetic field with the same magnitude but opposite direction as the B0 offset through the B0 compensation channel, thus counteracting the overall offset interference of the B0 field; second, by superimposing the frequency change value corresponding to the total B0 offset onto the current center frequency to obtain the corrected center frequency, and setting the corrected center frequency as the new operating frequency of the system, indirectly eliminating the impact of the B0 offset on imaging through frequency correction. Both methods ensure that after the initial current value is applied, it only generates an effective magnetic field to correct higher-order inhomogeneities, without introducing further B0 field uniformity interference caused by coupling.

[0042] In step 105, after confirming the elimination of interference, the control module sends instructions to each channel of the higher-order shimming coil to precisely load the calculated preliminary current value i1 into the corresponding channel. For example, channel 1 loads i1, channel 2 loads i2, and so on. After loading is complete, the higher-order shimming coil will generate a compensating magnetic field that completely cancels out the higher-order inhomogeneity of the B0 field. At this point, the uniformity of the B0 field in the patient's region of interest meets the imaging requirements, the higher-order shimming setup is officially completed, and the MRI system can proceed to the subsequent image acquisition stage.

[0043] In this application, in the high-order shimming coil, the pure shimming reference field and the coupling reference field of each channel are first separated to eliminate the interference of the coupling field on the reference field measurement and obtain accurate reference data. Then, the three-dimensional field map of the patient's region of interest and the current center frequency are acquired. Next, the preliminary current value is calculated based on the shimming reference field and the three-dimensional field map to ensure that the current does not contain redundant components to cancel coupling interference. Then, the B0 offset is determined by combining the preliminary current and the coupling reference field, and the B0 field uniformity interference caused by coupling is eliminated by correcting the B0 offset and the center frequency. Finally, after the interference is eliminated, the current is applied to complete the high-order shimming setting. This application establishes a complete coupling field correction system, and the high-order field and the coupling field are measured in tandem. This enables accurate measurement of the high-order field changes generated by the high-order shimming coil and the resulting B0 field coupling offset, thereby improving the accuracy and stability of the high-order shimming and ultimately improving the quality of the high-order shimming.

[0044] As an optional implementation, in step 101, obtaining the purified shimming reference field and coupling reference field of each channel in the higher-order shimming coil includes: Iterate through each channel in the higher-order shimming coil and perform the following operation on each channel; Step S11: Perform B0 field measurement on the input current of the channel to obtain the comprehensive reference field corresponding to the channel, wherein the comprehensive reference field includes the higher-order field and coupling field generated by the channel; Step S12: Perform center frequency measurement and B0 field measurement on the input current of the channel to obtain the homogenization reference field corresponding to the channel, wherein the homogenization reference field is a higher-order field generated by the channel; Step S13: Determine the coupling reference field of the channel based on the difference between the integrated reference field and the uniform reference field.

[0045] The high-order shimming coil is a dedicated component in a magnetic resonance imaging (MRI) system used to compensate for higher-order inhomogeneities in the B0 field. Each channel is an independent current control unit, capable of receiving individual current inputs and generating a specific magnetic field component to specifically counteract higher-order inhomogeneities in a particular dimension of the B0 field. The control module needs to traverse all channels to ensure that the reference field measurement covers all magnetic field control dimensions of the coil, avoiding residual coupling interference due to unprocessed individual channels. This ensures that subsequent shimming correction can act on the B0 field in all dimensions, guaranteeing the integrity and accuracy of the overall shimming effect.

[0046] In step S11, when a current is input to any target channel of the higher-order shimming coil, the channel simultaneously generates two magnetic fields: one is a higher-order field used to correct the higher-order inhomogeneities of the B0 field, and the other is a coupling field, i.e., an interference magnetic field, generated due to the inductive coupling between the channel and the B0 field. B0 field measurement is a measurement method used in MRI systems to acquire the actual distribution of the B0 field within a specific region. This method generates a field map reflecting the changes in field strength within the region, directly presenting the magnetic field homogeneity. Because the characteristic of B0 field measurement is to capture the overall magnetic field distribution under the current, it cannot distinguish or separate the higher-order field and the coupling field. Therefore, the reference field obtained through this measurement is a comprehensive reference field that simultaneously contains both the higher-order field and the coupling field.

[0047] In step S12, when the control module inputs current into the target channel of the higher-order shimming coil again, the channel will still generate two magnetic fields simultaneously: a higher-order field and a coupling field. The coupling field causes a shift in the overall B0 field. According to the principle of magnetic resonance, the strength of the B0 field is proportional to the resonance frequency of the atomic nucleus; therefore, the shift in the B0 field directly causes a change in the system's center frequency. To eliminate this coupling field interference, the control module must first perform a center frequency measurement. Center frequency measurement is a technique used in MRI systems to detect the reference value of the atomic nucleus' resonance frequency under the current B0 field state. This measurement can accurately capture the center frequency shift caused by the coupling field after the target channel receives the input current.

[0048] After acquiring the offset, the control module uses the offset center frequency as a reference to re-perform the B0 field measurement on the target channel. This time, the B0 field measurement uses the offset center frequency as a reference standard, automatically filtering out the interference of frequency offset caused by coupling field on the magnetic field measurement results, and focusing only on capturing the spatial distribution of the higher-order field generated by the channel current. The final reference field becomes a pure uniform reference field stripped of coupling field interference, retaining only the core correction component of the higher-order field used to correct the higher-order inhomogeneities of the B0 field.

[0049] In step S13, the composite reference field consists of higher-order fields and coupled fields, while the shimming reference field consists only of higher-order fields. Based on the clear difference in their components, the higher-order field components in the composite reference field are precisely removed through the difference calculation between the composite reference field and the shimming reference field. The remaining magnetic field distribution is the coupled reference field generated after the target channel is coupled with the B0 field. This coupled reference field can accurately characterize the specific distribution of the interference magnetic field generated by the coupling effect when current is passed through the channel.

[0050] In this application, firstly, a B0 field measurement is performed on the channel input current to obtain a comprehensive reference field containing the higher-order field generated by the channel (the core magnetic field that corrects the higher-order inhomogeneity of the B0 field) and the coupling field (the interference magnetic field generated by the inductive coupling between the channel and the B0 field). This measurement accurately captures the overall magnetic field distribution under the action of the channel current. Then, the center frequency shift caused by the coupling field is captured by the center frequency measurement, and the B0 field measurement is re-performed based on the shift frequency. The interference of the coupling field on the magnetic field measurement is automatically eliminated by the offset frequency reference, and finally a pure uniform reference field containing only the higher-order field is obtained. Finally, the uniform reference field is separated from the comprehensive reference field to obtain the separated uniform reference field and the coupling reference field, eliminating the interference of the coupling field on the reference field measurement, thereby obtaining a purer and more accurate uniform reference field.

[0051] In addition, the shimming reference field and the coupled reference field can also be separated as follows: A B0 field measurement is performed on the input current of the channel to obtain the comprehensive reference field B1 corresponding to the channel; a central voxel (usually the region where the main magnetic field B0 is most stable) is selected as a reference point, and its field strength value is zeroed; the field strength difference between each point of the comprehensive reference field B1 and the central voxel is calculated, and this difference is the coupled field component; the coupled field component is subtracted from the comprehensive reference field B1 to obtain an approximate value of the shimming reference field. This method is based only on the reference correction of a single voxel, and the separation accuracy is affected by the selected position of the central voxel. It is suitable for scenarios where the shimming accuracy requirement is not high, while steps S11-S13 are also suitable for high-precision scenarios.

[0052] As an optional implementation, in step S11, performing a B0 field measurement on the input current of the channel to obtain the comprehensive reference field corresponding to the channel includes: Step S111: Input a standard positive current into the channel of the high-order shimming coil, and use the B0 field measurement method to obtain the first magnetic field distribution superimposed with the high-order field and the coupled field under the action of the standard positive current; Step S112: Input a standard negative current into the channel of the high-order shimming coil, and use the B0 field measurement method to obtain the second magnetic field distribution superimposed with the high-order field and the coupled field under the action of the standard negative current; Step S113: Determine the comprehensive reference field corresponding to the channel based on the difference between the first magnetic field distribution and the second magnetic field distribution, and the difference between the standard positive current and the standard negative current.

[0053] In step S111, the control module inputs a preset standard positive current N1 into any channel of the high-order shimming coil. The value of N1 is set by the control module according to hardware parameters such as the rated current range and magnetic field excitation efficiency of the high-order shimming coil, ensuring that the channel can generate a sufficiently strong and stable magnetic field signal while avoiding exceeding the coil's safe operating threshold. Subsequently, the control module drives the B0 field measurement component of the magnetic resonance imaging system to perform a full-space scan of the magnetic field action area of ​​the target channel. Since the input of the standard positive current N1 into the channel will simultaneously generate two magnetic fields: one is a high-order field used to correct the high-order inhomogeneity of the B0 field, and the other is a coupling field generated due to the inductive coupling between the channel and the main magnetic field B0. Furthermore, the B0 field measurement can only capture the overall magnetic field distribution under the current action and cannot distinguish the specific components of the high-order field and the coupling field. Therefore, the first magnetic field distribution A1 obtained after scanning is essentially a mixed magnetic field distribution formed by the superposition of the high-order field and the coupling field.

[0054] In step S112, the control module keeps the target channel unchanged and switches the input current to a standard negative current N2. N2 and N1 have the same absolute value but opposite directions. The core purpose of setting this reverse current is to generate a reverse magnetic field, providing data support for subsequent cancellation of fixed interference in the system. Next, the control module restarts the B0 field measurement component to scan the magnetic field area of ​​the target channel using the same scanning parameters as in step S111. At this time, the higher-order field and coupling field generated by the channel according to the standard negative current N2 are both in the opposite direction to the current direction, but the generation mechanism of the two fields remains unchanged. The B0 field measurement can still only capture the overall mixed magnetic field distribution. Therefore, the final second magnetic field distribution A2 is a mixed magnetic field distribution formed by the superposition of the reverse higher-order field and the reverse coupling field.

[0055] In step S113, the control module first performs a difference calculation on the acquired first magnetic field distribution A1 and second magnetic field distribution A2 to obtain the result A1-A2. During this process, fixed interference components such as the basic uniform distribution of the B0 field and the inherent noise of the B0 field measurement component have completely consistent values ​​and characteristics in both measurements. The difference calculation can completely cancel out these irrelevant interferences, retaining only the effective changes in the higher-order field and coupling field generated by the target channel current. Since N1 and N2 are in opposite directions, this effective change is equivalent to twice the magnetic field strength under a single current (N1 or N2). Subsequently, the control module calculates the difference between the standard positive current N1 and the standard negative current N2 to obtain the result N1-N2. Since the absolute values ​​of N1 and N2 are equal, this difference is equivalent to twice the value of N1. Finally, the control module performs a calculation using the formula (A1-A2) / (N1-N2), which not only cancels out the influence of the magnetic field strength multiple caused by the current difference but also further eliminates irrelevant interferences. The final result is the comprehensive reference field corresponding to the target channel. This integrated reference field accurately characterizes the mixed magnetic field distribution of the higher-order field and the coupled field generated by the target channel under unit current.

[0056] As an optional implementation, in step S12, performing center frequency measurement and B0 field measurement on the input current of the channel to obtain the uniform reference field corresponding to the channel includes: Step S121: Input a standard positive current into the channel of the higher-order shimming coil, and obtain the first center frequency of the magnetic resonance imaging system by center frequency measurement. Step S122: The measurement frequency of the magnetic resonance imaging system is calibrated to the first center frequency, and the third magnetic field distribution is obtained by using the B0 field measurement method, wherein the third magnetic field distribution includes the higher-order field generated when the standard positive current is input into the channel; Step S123: Input a standard negative current into the channel of the higher-order shimming coil, and obtain the second center frequency of the magnetic resonance imaging system by center frequency measurement. Step S124: The measurement frequency of the magnetic resonance imaging system is calibrated to the second center frequency, and the fourth magnetic field distribution is obtained by using the B0 field measurement method, wherein the fourth magnetic field distribution includes the higher-order field generated when the standard negative current is input into the channel; Step S125: Determine the uniform reference field corresponding to the channel based on the difference between the third magnetic field distribution and the fourth magnetic field distribution, and the difference between the standard positive current and the standard negative current.

[0057] In step S121, the control module inputs a preset standard positive current N1 into any target channel. Subsequently, the control module drives the center frequency measurement component of the magnetic resonance imaging system to detect the current resonance frequency of the system and obtain the first center frequency O1. After N1 is introduced into the channel, in addition to generating a higher-order field used to correct the higher-order inhomogeneity of the B0 field, a coupling field is also generated due to the inductive coupling with the main magnetic field B0. The coupling field causes the overall B0 field to shift. Since the strength of the B0 field is proportional to the resonance frequency of the atomic nucleus, O1 is the actual resonance frequency of the system after being affected by the coupling field, containing information about the effect of the coupling field on the B0 field.

[0058] In step S122, after acquiring the first center frequency O1, the control module immediately performs frequency calibration on the B0 field measurement component of the magnetic resonance imaging system, precisely adjusting the measurement frequency of the B0 field measurement component to O1. The core purpose of this calibration is to counteract the interference of the B0 field frequency shift caused by the coupling field on subsequent B0 field measurements by matching the resonant frequency currently affected by the coupling field. After calibration, the control module drives the B0 field measurement component to perform a full-space scan of the magnetic field area of ​​the target channel, obtaining the third magnetic field distribution A3. Since the measurement frequency is completely matched with O1, which includes the influence of the coupling field, the B0 field measurement process will only capture the higher-order field generated when the channel is connected to N1 (used to correct the core magnetic field of higher-order inhomogeneity in the B0 field). The frequency shift interference caused by the coupling field has been completely canceled by the calibration action. Therefore, A3 only contains the higher-order field distribution generated by the target channel under the action of N1, without any interference from the coupling field component.

[0059] In step S123, the control module keeps the target channel unchanged and switches the input current from a standard positive current N1 to a standard negative current N. N2 has the same absolute value as N1 but opposite direction. The purpose of setting the reverse current is to excite a reverse magnetic field. Subsequently, the control module drives the center frequency measurement component again to detect the current system resonance frequency and obtain the second center frequency O2. At this time, N2 is introduced into the channel, and the direction of the resulting coupling field is opposite to that when N1 is applied, causing the overall offset direction of the B0 field to be reversed. The corresponding atomic nucleus resonance frequency also changes in the opposite direction. Therefore, O2 is the actual resonance frequency of the system after being affected by the reverse coupling field, and it also contains information about the effect of the reverse coupling field on the B0 field.

[0060] In step S124, the control module, based on the acquired second center frequency O2, repeats the frequency calibration logic of step S122 to precisely adjust the measurement frequency of the B0 field measurement component to O2, thereby counteracting the frequency shift interference of the B0 field caused by the reverse coupling field under the action of N2. After calibration, the control module drives the B0 field measurement component to perform a scan of the target channel's operating area with the same parameters as in step S122, obtaining the fourth magnetic field distribution A4. Since the measurement frequency has been matched with O2, which includes the influence of the reverse coupling field, the B0 field measurement only captures the reverse higher-order field generated when the channel is energized by N2. The interference of the reverse coupling field is calibrated and canceled out. Therefore, A4 only contains the reverse higher-order field distribution generated by the target channel under the action of N2, without any interference from the coupling field component.

[0061] In step S125, the control module first performs a difference calculation on the acquired third magnetic field distribution A3 and fourth magnetic field distribution A4 to obtain the result A3-A4. During this process, fixed interference components such as the basic uniform distribution of the system's B0 field and the inherent noise of the B0 field measurement components have completely consistent values ​​and characteristics in both measurements. The difference calculation can completely cancel out these irrelevant interferences, retaining only the effective change in the higher-order field generated by the target channel current. Subsequently, the control module calculates the difference between the standard positive current N1 and the standard negative current N2 to obtain the result N1-N2. Since the absolute values ​​of N1 and N2 are equal, this difference is equivalent to twice the value of N1. Finally, the control module performs a calculation using the formula (A3-A4) / (N1-N2), which not only cancels out the influence of the higher-order field intensity multiple caused by the current difference but also further eliminates residual interference. The final result is the uniform reference field corresponding to the target channel. This uniform reference field accurately characterizes the pure higher-order field distribution generated by the target channel under unit current, completely eliminating coupling field interference.

[0062] As an optional implementation, in step 103, determining the preliminary current value for each channel based on the shimming reference field and the three-dimensional field map includes: Step S21: Compress the magnetic field data in the three-dimensional field diagram to obtain a one-dimensional matrix; Step S22: Construct a shimming reference field matrix based on the shimming reference field of all channels, and perform singular value decomposition on the shimming reference field matrix to obtain three initial matrices, wherein the three initial matrices include a left singular vector matrix, a singular value matrix and a right singular vector matrix. Step S23: Extract the three initial matrices according to the k dimensions that contribute the most to the shimming, and perform a preset operation on the extracted matrices to obtain three target matrices; Step S24: Calculate the product of the three target matrices and the one-dimensional matrix in the set order to determine the preliminary current value of each channel.

[0063] In step S21, the three-dimensional field map is obtained by scanning with the B0 field measurement component. It is a data carrier reflecting the actual distribution of the B0 field in the region of interest (such as around a brain lesion). It contains field strength information at multiple points in space and is in the form of a three-dimensional tensor. Since subsequent steps require matrix operations to calculate the shimming current, and the three-dimensional tensor data has high dimensionality and computational complexity, the control module will activate a preset data compression algorithm. Following the principle of preserving key information on magnetic field inhomogeneity, the magnetic field strength data of each spatial point in the three-dimensional field map is expanded and integrated in a specific order, ultimately converting the three-dimensional field map into a one-dimensional matrix b. This compression process reduces the computational load of subsequent matrix operations while completely preserving the core data of the high-order inhomogeneity of the B0 field in the patient's region of interest, providing simplified and effective input data for accurate calculation of the shimming current.

[0064] In step S22, the control module first integrates the shimming reference fields of all channels obtained in the previous step. Each channel's shimming reference field is a pure high-order field distribution stripped of coupling field interference, which can characterize the channel's ability to correct high-order inhomogeneities of the B0 field under unit current. The control module arranges the shimming reference fields of each channel as a column according to the channel order to form a shimming reference field matrix. The number of rows in the matrix corresponds to the number of data points after the 3D field diagram is compressed, and the number of columns corresponds to the total number of channels of the high-order shimming coil. Subsequently, the control module calls the singular value decomposition algorithm to decompose the shimming reference field matrix. This algorithm can decompose the complex magnetic field and current mapping relationship into three independent initial matrices: the left singular vector matrix U (characteristic vectors representing the magnetic field distribution, reflecting the magnetic field correlation characteristics of different spatial points), the singular value matrix S (a diagonal matrix, where the values ​​on the diagonal are singular values, and the magnitude of the singular values ​​directly corresponds to the degree of contribution of each dimension to the shimming effect), and the right singular vector matrix V (characteristic vectors representing the current distribution, reflecting the current correlation characteristics of different channels).

[0065] In step S23, the control module first determines the optimization integer threshold k according to the preset channel ratio. For example, k is set to 80% of the total number of channels in the high-order shimming coil. Setting k is to retain the main dimensions that contribute the most to shimming and eliminate redundant dimensions with small contributions. This avoids amplification of computational noise or overfitting due to too many dimensions, while ensuring coverage of the vast majority of effective shimming dimensions. Subsequently, the control module truncates the three initial matrices: it truncates the first k columns of the left singular vector matrix U to obtain the optimized left singular vector matrix Uk; it truncates the first k rows and k columns of the singular value matrix S to obtain the optimized singular value matrix Sk; and it truncates the first k columns of the right singular vector matrix V to obtain the optimized right singular vector matrix Vk. Next, the control module performs preset operations on the optimized matrices: it performs a pseudo-inverse operation on Sk. Since Sk is a diagonal matrix, the pseudo-inverse operation can be achieved by taking the reciprocal of the singular values ​​on the diagonal to obtain the pseudo-inverse optimized singular value matrix S_k1; and it performs a transpose operation on Uk to obtain the transposed optimized left singular vector matrix U_k1. The three target matrices obtained are Vk, S_k1, and U_k1.

[0066] In step S24, the control module initiates the calculation process according to the matrix operation sequence. First, it performs matrix multiplication on matrix Vk and matrix S_k1 to obtain intermediate matrix M1. Then, it performs multiplication on matrix M1 and matrix U_k1 to obtain intermediate matrix M2. M2 is essentially an optimized pseudo-inverse matrix of the shimming reference field matrix, which can realize the mapping transformation from magnetic field inhomogeneity data to current data. Finally, it performs multiplication on M2 and a one-dimensional matrix b, and the result is the initial current value i1 for each channel, i.e., i1 = V_k * S_k1 * U_k1 * b. The number of current values ​​is consistent with the number of channels of the high-order shimming coil, and each value corresponds to the current setting value of one channel. Since the entire calculation process is based on the pure shimming reference field matrix and the optimized matrix operation, the initial current value i1 only focuses on correcting the high-order inhomogeneity of the B0 field and does not contain any coupling field interference components, ensuring that the current of each channel can accurately match its responsible high-order magnetic field correction task.

[0067] As an optional implementation, in step 104, eliminating the uniformity interference of the B0 offset on the B0 field based on the B0 offset and the current center frequency includes one of the following two methods: The frequency offset corresponding to the B0 offset is determined by a preset magnetogyroscope ratio. This frequency offset is then applied to the current center frequency to obtain the offset B0 field frequency. The acquisition frequency of the magnetic resonance imaging system is then adjusted to match the offset B0 field frequency; or... The B0 offset is used as the correction target for B0 compensation to trigger the B0 compensation channel to generate a compensation magnetic field with the same magnitude but opposite direction as the B0 offset, thereby counteracting the B0 offset's interference with the uniformity of the B0 field.

[0068] In this application, the control module combines the B0 offset and the current center frequency to eliminate the interference of the B0 offset on the uniformity of the B0 field through one of the following two methods.

[0069] Method 1: Counteract B0 offset interference through frequency adaptation.

[0070] The control module calls the system's preset gyrometry ratio γ and calculates the frequency offset Δf corresponding to the B0 offset using the formula Δf=γ*ΔB0 / (2π). Here, ΔB0 is the B0 offset determined in the early stage, and Δf reflects the degree of deviation of the system's resonant frequency caused only by the B0 offset. This eliminates interference from other factors such as the magnetic sensitivity of the patient's tissue and ensures that subsequent corrections are only for the B0 offset problem caused by the coupling field.

[0071] Subsequently, the control module directly applies the calculated Δf to the previously acquired current center frequency, obtaining the offset B0 field frequency f_offset. The core purpose of applying Δf here is to ensure that f_offset perfectly matches the actual magnetic field state after the B0 offset. Since the B0 offset has changed the actual field strength of the B0 field, its corresponding nuclear resonance frequency will inevitably change synchronously. f_offset is precisely the true resonance frequency reference after this change, containing only the influence of the B0 offset.

[0072] Finally, the control module adjusts the acquisition frequency of the magnetic resonance imaging system to f_offset, achieving complete synchronization between the acquisition frequency and the offset B0 field frequency. This process, by actively adapting to the magnetic field frequency change caused by the B0 offset, avoids problems such as image geometric distortion, signal loss, or spectral broadening caused by the misalignment between the acquisition frequency and the actual B0 field resonance frequency. It indirectly counteracts the interference of the B0 offset on the uniformity of the B0 field from the signal acquisition perspective, ensuring that subsequent imaging signals accurately reflect the true characteristics of the patient's tissues, unaffected by the B0 offset caused by the coupling field.

[0073] Method 2: Counteract B0 offset interference through hardware magnetic field compensation.

[0074] The control module directly uses the previously determined B0 offset ΔB0 as the sole correction target for B0 compensation, ensuring that subsequent compensation actions only target the B0 field offset caused by the coupling field and do not involve other magnetic field interference factors such as the magnetic sensitivity of patient tissues, thus guaranteeing the targetedness and accuracy of the correction.

[0075] Subsequently, the control module sends a control signal to the system's dedicated B0 compensation channel, triggering it to generate a targeted compensation magnetic field B_comp. The control module strictly controls the key parameters of B_comp: based on the principle of magnetic field vector superposition and cancellation, the magnitude of the field strength of B_comp is exactly equal to ΔB0, and the direction of the magnetic field is opposite to ΔB0. For example, if ΔB0 increases the field strength of B0, then the magnetic field generated by B_comp will decrease the field strength of B0; if ΔB0 decreases the field strength of B0, then the magnetic field generated by B_comp will increase the field strength of B0, ensuring that the two can form a precise vector cancellation effect.

[0076] When the compensating magnetic field B_comp acts on the main magnetic field B0, it vectorally superimposes with the interfering magnetic field generated by the B0 offset ΔB0, ultimately achieving the effect of ΔB0 + B_comp = 0. This completely cancels out the damage to the uniformity of the B0 field caused by the B0 offset from the perspective of the magnetic field itself, restoring the B0 field to a near-ideal uniform state. After compensation, the control module can quickly scan and verify the patient's region of interest through the B0 field measurement component, confirming that the uniformity error of the B0 field has been reduced to within the system's preset threshold. This clears the way for the accurate loading of subsequent higher-order shimming currents, ensuring that higher-order shimming only needs to focus on correcting the higher-order non-uniformity of the B0 field, without having to deal with the basic B0 offset problem caused by the coupling field.

[0077] This application also provides an overall process for high-order uniform field control with integrated B0 field coupling compensation, including the following steps.

[0078] I. Measurement method of reference field for each channel of a high-order shimming coil.

[0079] 1. Input a standard positive current N1 into the first channel of the high-order shimming coil and scan it using the B0 field measurement method to obtain the magnetic field distribution field diagram A1 under the action of the current; then input a standard negative current N2 into the same channel and scan it using the same B0 field measurement method to obtain the magnetic field distribution field diagram A2 under the action of the current.

[0080] 2. Calculate the combined reference field B1 of the higher-order field and coupling field of the first channel according to the formula (A1-A2) / (N1-N2). (This reference field includes the higher-order correction magnetic field generated by the channel and the interference magnetic field generated by the coupling of the coil and the main magnetic field.)

[0081] 3. Keep the standard positive current N1 input to the first channel, and use the center frequency measurement method to detect the system resonance frequency to obtain the first center frequency O1 after inputting N1; use the first center frequency O1 as a reference, and use the B0 field measurement method to scan again to obtain the magnetic field distribution field diagram A3 at this frequency.

[0082] 4. Switch the first channel to input a standard negative current N2, and use the center frequency measurement method to detect the system resonance frequency to obtain the second center frequency O2 after inputting N2; using the second center frequency O2 as a reference, scan again using the B0 field measurement method to obtain the magnetic field distribution field diagram A4 at this frequency.

[0083] 5. Calculate the higher-order reference field Bref1 of the first channel by performing the calculation according to the formula (A3-A4) / (N1-N2) (this reference field has been stripped of coupling interference).

[0084] 6. By performing the difference calculation between the comprehensive reference field B1 and the higher-order reference field Bref1, the coupling reference field Bcoup1 of the first channel is obtained (this reference field only contains the interference magnetic field generated by the coupling between the coil and the B0 field).

[0085] 7. Repeat the above steps 1-6 to iterate through all channels of the higher-order shimming coil (including the channels of the conventional first-order shimming coil) and finally obtain the higher-order reference field Bref and the coupled reference field Bcoup corresponding to all channels.

[0086] II. Method for calculating and setting the uniform current during patient scanning.

[0087] 1. The patient's region of interest is scanned using the B0 field measurement method to obtain a three-dimensional magnetic field distribution map B0 of the region; the three-dimensional field map B0 is compressed into one-dimensional data according to preset rules to generate a one-dimensional matrix b; at the same time, the current center frequency O3 of the magnetic resonance imaging system is detected using the center frequency measurement method.

[0088] 2. Integrate the higher-order reference fields Bref of all channels to construct a shim reference field matrix; perform singular value decomposition on this matrix to obtain three basic matrices: left singular vector matrix U, singular value matrix S, and right singular vector matrix V.

[0089] 3. Based on the total number of channels of the higher-order shimming coil, take 80% of the number of channels as the optimization integer threshold k.

[0090] 4. Based on the optimized integer threshold k, the three basic matrices are truncated: the first k columns of the left singular vector matrix U are taken to obtain Uk; the first k rows and first k columns of the singular value matrix S are taken to obtain Sk; and the first k columns of the right singular vector matrix V are taken to obtain Vk.

[0091] 5. Perform a pseudo-inverse operation on the optimized singular value matrix Sk to obtain S_k1.

[0092] 6. Perform a transpose operation on the optimized left singular vector matrix Uk to obtain U_k1.

[0093] 7. Calculate the initial current value i1 of the high-order shim coil channel by performing the matrix multiplication formula i1=Vk×S_k1×U_k1×b.

[0094] 8. Multiply the initial current value i1 of each channel with the corresponding coupling reference field Bcoup to obtain the B0 offset B01 (B01 quantifies the magnetic field offset generated by the coupling between the coil and the B0 field after the initial current value i1 is applied).

[0095] 9. Compensate for B01: Either superimpose the frequency corresponding to B01 onto the current center frequency O3 of the system, or use B01 as the correction target of the B0 compensation channel and offset the coupling offset through hardware fine-tuning.

[0096] 10. Apply the initial current value i1 to the corresponding channels of the high-order shimming coil to complete the parameter setting of the entire high-order shimming.

[0097] Figure 2 This is a comparison of the performance of the high-order shimming algorithm without coupling correction in the present application and the prior art in water simulation volume testing. Figure 2 The left side shows a setup consisting of a spherical cerebrospinal fluid water model and a cylindrical water-oil mixture water model, simulating the structure of the brain and neck. This setup will increase the magnetic field inhomogeneity in the spherical cerebrospinal fluid water model area. Figure 2 The right side shows the field distribution after shimming using the decoupled higher-order shimming method and the undecoupled higher-order shimming method. It can be seen that the decoupled higher-order shimming method improves the magnetic field uniformity.

[0098] Figure 3 The figure shows a comparison of the effects of this application and existing technologies in magnetic resonance spectroscopy scanning of cerebrospinal fluid. It can be seen that after using the decoupled higher-order shimming method, the magnetic field homogeneity is improved, and the magnetic resonance spectral quality is significantly better than that of the undecoupled higher-order shimming method.

[0099] This application also provides a high-order uniform field control device with integrated B0 field coupling compensation, such as... Figure 4 As shown, the device includes: The acquisition module 401 is used to acquire the pure separated shimming reference field and coupling reference field of each channel in the high-order shimming coil; The acquisition module 402 is used to acquire a three-dimensional field map of the patient's region of interest and to acquire the current center frequency of the magnetic resonance imaging system. The determination module 403 is used to determine the preliminary current value of each channel based on the homogenizing reference field and the three-dimensional field map, wherein the preliminary current value is not affected by the coupling reference field; Elimination module 404 is used to determine the B0 offset based on the preliminary current value and the coupled reference field, and to eliminate the B0 offset's interference with the uniformity of the B0 field based on the B0 offset and the current center frequency. The setting module 405 is used to set the initial current value of each channel to the corresponding channel after eliminating uniformity interference, thereby completing the high-order shimming setting.

[0100] Optionally, the acquisition module 401 is used for: Iterate through each channel in the higher-order shimming coil and perform the following operation on each channel; A B0 field measurement is performed on the input current of the channel to obtain the comprehensive reference field corresponding to the channel, wherein the comprehensive reference field includes the higher-order field and the coupling field generated by the channel; The center frequency and B0 field are measured on the input current of the channel to obtain the homogenization reference field corresponding to the channel, wherein the homogenization reference field is a higher-order field generated by the channel; The coupling reference field of the channel is determined based on the difference between the integrated reference field and the uniform reference field.

[0101] Optionally, the acquisition module 401 is specifically used for: A standard positive current is input into the channel of the high-order shimming coil, and the first magnetic field distribution superimposed with the high-order field and the coupled field is obtained by using the B0 field measurement method. A standard negative current is input into the channel of the high-order shimming coil, and the second magnetic field distribution superimposed with the high-order field and the coupled field is obtained by using the B0 field measurement method. The comprehensive reference field corresponding to the channel is determined based on the difference between the first magnetic field distribution and the second magnetic field distribution, and the difference between the standard positive current and the standard negative current.

[0102] Optionally, the acquisition module 401 is specifically used for: A standard positive current is input into the channel of the higher-order shimming coil, and the first center frequency of the magnetic resonance imaging system is obtained by center frequency measurement. The measurement frequency of the magnetic resonance imaging system is calibrated to the first center frequency, and the third magnetic field distribution is obtained by using the B0 field measurement method. The third magnetic field distribution includes the higher-order field generated when the standard positive current is input into the channel. A standard negative current is input into the channel of the higher-order shimming coil, and the second center frequency of the magnetic resonance imaging system is obtained by center frequency measurement. The measurement frequency of the magnetic resonance imaging system is calibrated to the second center frequency, and a fourth magnetic field distribution is obtained using the B0 field measurement method. The fourth magnetic field distribution includes a higher-order field generated when the standard negative current is input into the channel. The homogenization reference field corresponding to the channel is determined based on the difference between the third magnetic field distribution and the fourth magnetic field distribution, as well as the difference between the standard positive current and the standard negative current.

[0103] Optionally, the determining module 403 is used for: The magnetic field data in the three-dimensional field diagram is compressed to obtain a one-dimensional matrix. A shim reference field matrix is ​​constructed based on the shim reference field of all channels, and the shim reference field matrix is ​​subjected to singular value decomposition to obtain three initial matrices, wherein the three initial matrices include a left singular vector matrix, a singular value matrix and a right singular vector matrix. The three initial matrices are truncated according to the k dimensions that contribute the most to the shimming, and the truncated matrices are subjected to a preset operation to obtain three target matrices. The product of the three target matrices and the one-dimensional matrix is ​​calculated in a set order to determine the initial current value of each channel.

[0104] Optionally, module 403 is specifically used for: Based on the number of channels of the higher-order shimming coil, an integer threshold k is determined according to a preset channel ratio; By taking the first k columns of the left singular vector matrix, the first k rows and first k columns of the singular value matrix, and the first k columns of the right singular vector matrix, three optimized matrices are obtained. Perform a transpose operation on the optimized left singular vector matrix and a pseudo-inverse operation on the optimized singular value matrix; The optimized right singular vector matrix, the transposed left singular vector matrix, and the pseudo-inverse singular value matrix are used as the three target matrices.

[0105] Optionally, the elimination module 404 is used for: The frequency offset corresponding to the B0 offset is determined by a preset magnetogyroscope ratio. This frequency offset is then applied to the current center frequency to obtain the offset B0 field frequency. The acquisition frequency of the magnetic resonance imaging system is then adjusted to match the offset B0 field frequency; or... The B0 offset is used as the correction target for B0 compensation to trigger the B0 compensation channel to generate a compensation magnetic field with the same magnitude but opposite direction as the B0 offset, thereby counteracting the B0 offset's interference with the uniformity of the B0 field.

[0106] like Figure 5As shown, this application provides an electronic device including a processor 501, a communication interface 502, a memory 503, and a communication bus 504, wherein the processor 501, the communication interface 502, and the memory 503 communicate with each other through the communication bus 504.

[0107] Memory 503 is used to store computer programs.

[0108] In one embodiment of this application, when the processor 501 executes the program stored in the memory 503, it implements the high-order uniform field control method with integrated BO field coupling compensation provided in any of the aforementioned method embodiments.

[0109] This application also provides a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the steps of the high-order uniform field control method with integrated BO field coupling compensation as provided in any of the foregoing method embodiments.

[0110] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0111] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented using software plus a general-purpose hardware platform, or of course, using hardware. Based on this understanding, the above technical solutions, in essence or the parts that contribute to the related technology, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0112] It should be understood that the terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “described” as used herein may also include the plural forms. The terms “comprising,” “including,” “containing,” and “having” are inclusive and therefore indicate the presence of the stated features, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein are not construed as requiring them to be performed in a particular order described or illustrated unless the order of performance is explicitly indicated. It should also be understood that additional or alternative steps may be used.

[0113] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A high-order uniform field control method integrating B0 field coupling compensation, characterized in that, The method includes: Obtain the pure separated shimming reference field and coupled reference field for each channel in the high-order shimming coil; Acquire a three-dimensional field map of the patient's region of interest and acquire the current center frequency of the magnetic resonance imaging system; The initial current value of each channel is determined based on the homogenized reference field and the three-dimensional field map, wherein the initial current value is not affected by the coupled reference field; The B0 offset is determined based on the preliminary current value and the coupled reference field, and the B0 offset is used to eliminate the uniformity interference of the B0 field on the B0 field based on the B0 offset and the current center frequency. After eliminating uniformity interference, the initial current value of each channel is set to the corresponding channel to complete the high-order shimming setting.

2. The method according to claim 1, characterized in that, Obtaining the pure, separated shimming reference field and coupled reference field for each channel in a high-order shimming coil includes: Iterate through each channel in the higher-order shimming coil and perform the following operation on each channel; A B0 field measurement is performed on the input current of the channel to obtain the comprehensive reference field corresponding to the channel, wherein the comprehensive reference field includes the higher-order field and the coupling field generated by the channel; The center frequency and B0 field are measured on the input current of the channel to obtain the homogenization reference field corresponding to the channel, wherein the homogenization reference field is a higher-order field generated by the channel; The coupling reference field of the channel is determined based on the difference between the integrated reference field and the uniform reference field.

3. The method according to claim 2, characterized in that, Performing a B0 field measurement on the input current of the channel yields the comprehensive reference field corresponding to the channel, including: A standard positive current is input into the channel of the high-order shimming coil, and the first magnetic field distribution superimposed with the high-order field and the coupled field is obtained by using the B0 field measurement method. A standard negative current is input into the channel of the high-order shimming coil, and the second magnetic field distribution superimposed with the high-order field and the coupled field is obtained by using the B0 field measurement method. The comprehensive reference field corresponding to the channel is determined based on the difference between the first magnetic field distribution and the second magnetic field distribution, and the difference between the standard positive current and the standard negative current.

4. The method according to claim 2, characterized in that, Perform center frequency measurement and B0 field measurement on the input current of the channel to obtain the uniform reference field corresponding to the channel, including: A standard positive current is input into the channel of the higher-order shimming coil, and the first center frequency of the magnetic resonance imaging system is obtained by center frequency measurement. The measurement frequency of the magnetic resonance imaging system is calibrated to the first center frequency, and the third magnetic field distribution is obtained by using the B0 field measurement method. The third magnetic field distribution includes the higher-order field generated when the standard positive current is input into the channel. A standard negative current is input into the channel of the higher-order shimming coil, and the second center frequency of the magnetic resonance imaging system is obtained by center frequency measurement. The measurement frequency of the magnetic resonance imaging system is calibrated to the second center frequency, and a fourth magnetic field distribution is obtained using the B0 field measurement method. The fourth magnetic field distribution includes a higher-order field generated when the standard negative current is input into the channel. The homogenization reference field corresponding to the channel is determined based on the difference between the third magnetic field distribution and the fourth magnetic field distribution, as well as the difference between the standard positive current and the standard negative current.

5. The method according to claim 1, characterized in that, Determining the preliminary current value for each channel based on the homogenized reference field and the three-dimensional field map includes: The magnetic field data in the three-dimensional field diagram is compressed to obtain a one-dimensional matrix. A shim reference field matrix is ​​constructed based on the shim reference field of all channels, and the shim reference field matrix is ​​subjected to singular value decomposition to obtain three initial matrices, wherein the three initial matrices include a left singular vector matrix, a singular value matrix and a right singular vector matrix. The three initial matrices are truncated according to the k dimensions that contribute the most to the shimming, and the truncated matrices are subjected to a preset operation to obtain three target matrices. The product of the three target matrices and the one-dimensional matrix is ​​calculated in a set order to determine the initial current value of each channel.

6. The method according to claim 5, characterized in that, The three initial matrices are truncated according to the k dimensions that contribute the most to the shimming, and a preset operation is performed on the truncated matrices to obtain three target matrices, including: Based on the number of channels of the higher-order shimming coil, an integer threshold k is determined according to a preset channel ratio; By taking the first k columns of the left singular vector matrix, the first k rows and first k columns of the singular value matrix, and the first k columns of the right singular vector matrix, three optimized matrices are obtained. Perform a transpose operation on the optimized left singular vector matrix and a pseudo-inverse operation on the optimized singular value matrix; The optimized right singular vector matrix, the transposed left singular vector matrix, and the pseudo-inverse singular value matrix are used as the three target matrices.

7. The method according to claim 1, characterized in that, Eliminating the uniformity interference of the B0 offset on the B0 field based on the B0 offset and the current center frequency includes one of the following two methods: The frequency offset corresponding to the B0 offset is determined by a preset magnetogyroscope ratio. This frequency offset is then applied to the current center frequency to obtain the offset B0 field frequency. The acquisition frequency of the magnetic resonance imaging system is then adjusted to match the offset B0 field frequency; or... The B0 offset is used as the correction target for B0 compensation to trigger the B0 compensation channel to generate a compensation magnetic field with the same magnitude but opposite direction as the B0 offset, thereby counteracting the B0 offset's interference with the uniformity of the B0 field.

8. A high-order uniform field control device integrating B0 field coupling compensation, characterized in that, The device includes: The acquisition module is used to acquire the pure separated shimming reference field and coupling reference field of each channel in the high-order shimming coil; The acquisition module is used to acquire three-dimensional field images of the patient's region of interest and to acquire the current center frequency of the magnetic resonance imaging system; A determination module is used to determine the preliminary current value of each channel based on the homogenizing reference field and the three-dimensional field map, wherein the preliminary current value is not affected by the coupling reference field; The elimination module is used to determine the B0 offset based on the preliminary current value and the coupled reference field, and to eliminate the uniformity interference of the B0 offset on the B0 field based on the B0 offset and the current center frequency. The setting module is used to set the initial current value of each channel to the corresponding channel after eliminating uniformity interference, thus completing the high-order shimming setting.

9. An electronic device, characterized in that, It includes a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other through the communication bus; Memory, used to store computer programs; A processor, when executing a program stored in memory, implements the method described in any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the method described in any one of claims 1-7.

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