Shimming device design method, system, computer device and readable storage medium

Abstract

The application relates to a shimming device design method, a system, computer equipment and a readable storage medium. According to the relationship between the energy of an anti-coupling coil and the current parameter of the anti-coupling coil, a first current parameter is determined when the energy of the anti-coupling coil is maximum. According to the relationship between the energy of a shim coil and the current parameter of the shim coil, a second current parameter is determined when the energy of the shim coil is minimum. The wire distribution of the anti-coupling coil is determined according to the first current parameter, and the wire distribution of the shim coil is determined according to the second current parameter. The shimming device designed by using the shimming device design method provided by the application will not cause damage to a shimming power supply, so that the normal work of the shimming device can be ensured.

Description

Technical Field

[0001] This application relates to the field of magnetic resonance imaging technology, and in particular to a shimming device design method, system, computer equipment, and readable storage medium. Background Technology

[0002] Magnetic resonance imaging (MRI) systems work by applying radio frequency pulses of a specific frequency to a scanned object in a static magnetic field. This excites hydrogen protons in the object, causing them to resonate magnetically. After the radio frequency pulses stop, the hydrogen protons relax, generating magnetic resonance signals. Through processes such as receiving, spatial encoding, and image reconstruction of these signals, an MRI image of the scanned object is produced. The magnet system in an MRI system includes a main magnet, shimming coils, gradient coils, and radio frequency coils. During operation, significant coupling can occur between the shimming coils and gradient coils, leading to instability in the background magnetic field generated by the main magnet and potential damage to the shimming power supply of the shimming coils.

[0003] Traditional techniques involve designing shimming coils using a method that minimizes energy consumption. However, shimming coils designed using traditional techniques often malfunction. Summary of the Invention

[0004] Therefore, it is necessary to provide a design method, system, computer equipment, and readable storage medium for a field shimming device to address the aforementioned technical problems.

[0005] In a first aspect, one embodiment of this application provides a method for designing a field shimming device. The field shimming device includes a field shimming coil and anti-coupling coils disposed at both ends of the field shimming coil. The method for designing the field shimming device includes:

[0006] Based on the relationship between the energy of the anti-coupling coil and the current parameters of the anti-coupling coil, the first current parameter when the energy of the anti-coupling coil is at its maximum is determined; the first current parameter is used to characterize the current passing through each grid of the anti-coupling coil when the energy of the anti-coupling coil is at its maximum.

[0007] Based on the relationship between the energy of the shimming coil and the current parameters of the shimming coil, the second current parameter when the energy of the shimming coil is at its minimum is determined. The second current parameter is used to characterize the current passing through each grid of the shimming coil when the energy of the shimming coil is at its minimum.

[0008] The conductor distribution of the anti-coupling coil is determined based on the first current parameter, and the conductor distribution of the shimming coil is determined based on the second current parameter.

[0009] In one embodiment, the first current parameter when the energy of the anti-coupling coil is at its maximum is determined based on the relationship between the energy of the anti-coupling coil and the current parameter of the anti-coupling coil, including:

[0010] Based on the current flowing through each grid of the anti-coupling coil, the self-inductance of each grid of the anti-coupling coil, and the mutual inductance between the grids of the anti-coupling coil, the relationship between the energy of the anti-coupling coil and the current parameters of the anti-coupling coil is established, and the maximum energy function of the anti-coupling coil is obtained.

[0011] Obtain the first constraint condition of the maximum energy function, and solve the maximum energy function according to the first constraint condition to determine the first current parameter.

[0012] In one embodiment, the first constraint includes an inductance constraint and a current constraint for the anti-coupling coil, wherein the inductance constraint is used to constrain the maximum and minimum inductance of the anti-coupling coil.

[0013] In one embodiment, a first constraint condition for the maximum energy function is obtained, and the maximum energy function is solved based on the first constraint condition to determine the first current parameter, including:

[0014] The energy of the anti-coupling coil is determined based on the current flowing through each grid of the anti-coupling coil.

[0015] The inductance of the anti-coupling coil is determined based on its energy and input current.

[0016] Determine whether the inductance of the anti-coupling coil meets the inductance constraint condition, and whether the current through each grid of the anti-coupling coil meets the current constraint condition, to determine the first current parameter.

[0017] In one embodiment, a second current parameter is determined based on the relationship between the energy of the shimming coil and the current parameter of the shimming coil, wherein the energy of the shimming coil is at its minimum, including:

[0018] Based on the current flowing through each grid of the shimming coil, the self-inductance of each grid of the shimming coil, and the mutual inductance between the grids of the shimming coil, the relationship between the energy of the shimming coil and the current parameters of the shimming coil is established, and the minimum energy function of the shimming coil is obtained.

[0019] Obtain the second constraint condition for the minimum energy function, and solve the minimum energy function based on the second constraint condition to determine the second current parameter.

[0020] In one embodiment, the second constraint includes a magnetic field deviation constraint of the shimming coil.

[0021] In one embodiment, a second constraint condition for the minimum energy function is obtained, and the minimum energy function is solved based on the second constraint condition to determine the second current parameter, including:

[0022] Calculate the magnetic field strength of the anti-coupling coil based on the conductor distribution of the anti-coupling coil;

[0023] The target magnetic field strength of the shimming device is obtained, and the magnetic field deviation of the shimming device is determined based on the current passing through each grid of the shimming coil, the target magnetic field strength, and the magnetic field strength of the anti-coupling coil.

[0024] Determine whether the magnetic field deviation meets the magnetic field deviation constraint condition, and then determine the second current parameter.

[0025] Secondly, one embodiment of this application provides a field shimming device design system, comprising:

[0026] The first determining module is used to determine the first current parameter when the energy of the anti-coupling coil is at its maximum, based on the relationship between the energy of the anti-coupling coil and the current parameter of the anti-coupling coil; the first current parameter is used to characterize the current passing through each grid of the anti-coupling coil when the energy of the anti-coupling coil is at its maximum.

[0027] The second determining module is used to determine the second current parameter when the energy of the shimming coil is at its minimum based on the relationship between the energy of the shimming coil and the current parameter of the shimming coil. The second current parameter is used to characterize the current passing through each grid of the shimming coil when the energy of the shimming coil is at its minimum.

[0028] The third determining module is used to determine the wire distribution of the anti-coupling coil based on the first current parameter and to determine the wire distribution of the shimming coil based on the second current parameter.

[0029] Thirdly, one embodiment of this application provides a computer device including a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the steps of the method provided in the above embodiments.

[0030] Fourthly, one embodiment of this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method provided in the above embodiments.

[0031] This application provides a design method, system, computer device, and readable storage medium for a field shimming device. The method determines a first current parameter based on the relationship between the energy of the anti-coupling coil and its current parameter, when the energy of the anti-coupling coil is at its maximum; it also determines a second current parameter based on the same relationship, when the energy of the shimming coil is at its minimum. The method further determines the conductor distribution of the anti-coupling coil based on the first current parameter and the second current parameter. The field shimming device provided in this application reduces the coupling between the gradient coil and the field shimming device by designing an anti-coupling coil, while ensuring the field shimming device provides a shimming magnetic field. Furthermore, the anti-coupling coil designed based on the principle of maximizing energy, and the shimming coil designed based on the principle of minimizing energy, result in increased inductance of the final field shimming device, resulting in a smaller coupling current that does not damage the field shimming power supply, thus ensuring the normal operation of the field shimming device. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the structure of a magnet system provided in one embodiment of this application;

[0034] Figure 2 This is a schematic diagram of the structure of a field shimming device provided in one embodiment of this application;

[0035] Figure 3 A schematic flowchart illustrating the design steps of a field shimming device provided in one embodiment of this application;

[0036] Figure 4 This is a schematic diagram of the mesh division of an anti-coupling coil provided in one embodiment of this application;

[0037] Figure 5 This is a schematic diagram of the structure of a field shimming device provided in one embodiment of this application;

[0038] Figure 6 A schematic diagram of the current distribution of an anti-coupling coil provided in one embodiment of this application;

[0039] Figure 7 A schematic diagram of the magnetic field distribution of an anti-coupling coil provided in one embodiment of this application;

[0040] Figure 8A schematic diagram of the grid current distribution of a shimming coil provided in one embodiment of this application;

[0041] Figure 9 A schematic diagram of the discretized current distribution of a shimming coil provided in one embodiment of this application;

[0042] Figure 10 A schematic diagram of the magnetic field distribution of a shimming coil provided in one embodiment of this application;

[0043] Figure 11 This is a schematic diagram of the magnetic field distribution of a field shimming device provided in one embodiment of this application;

[0044] Figure 12 A schematic flowchart illustrating the design steps of a field shimming device provided in one embodiment of this application;

[0045] Figure 13 A schematic flowchart illustrating the design steps of a field shimming device provided in one embodiment of this application;

[0046] Figure 14 A schematic flowchart illustrating the design steps of a field shimming device provided in one embodiment of this application;

[0047] Figure 15 A schematic flowchart illustrating the design steps of a field shimming device provided in one embodiment of this application;

[0048] Figure 16 A schematic diagram of the design system of the field shimming device provided in one embodiment of this application;

[0049] Figure 17 This is a schematic diagram of the structure of a computer device provided in one embodiment of this application. Detailed Implementation

[0050] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0051] The serial numbers assigned to components in this article, such as "first" and "second", are used only to distinguish the objects being described and have no sequential or technical meaning.

[0052] The magnet system in a magnetic resonance imaging (MRI) system includes a main magnet, shimming coils, gradient coils, and radio frequency coils. The distribution of the shimming coil 11, gradient coil 12, and shielded gradient coil 13 is as follows: Figure 1As shown. From Figure 1 As can be seen, the shimming coil 11 is nested between the gradient coil 12 and the shielding gradient coil 13. During the operation of the magnetic resonance imaging system, significant coupling occurs between the shimming coil 11 and the gradient coil 12. When running gradient sequences, the gradient current in the Z direction of the gradient coil 12 synchronously flows into the shimming coil 11, inducing a coupling current in the shimming coil 11. This coupling current in the shimming coil 11 generates an additional coupling magnetic field, which is superimposed on the background magnetic field generated by the main magnet, thus affecting the stability of the background magnetic field. Furthermore, the coupling current in the shimming coil 11 is input to the external shimming power supply 14. If the coupling current exceeds the allowable input current of the shimming power supply 14, it will damage the shimming power supply 14, causing the shimming coil 11 to malfunction. The shielding gradient coil 13 is used to shield the magnetic field generated by the gradient coil 12 from being transmitted outwards and damaging the external magnet. The coupling between the shimming coil 11 and the gradient coil 12 can be expressed by the formula... Calculate, where K is the mutual inductance between the shimming coil 11 and the gradient coil 12, L is the self-inductance of the shimming coil 11, and I... K I is the coupling current on the shim coil 11. C This is the coupling current on gradient coil 12. The smaller K is, the greater I is. K The larger L is, the smaller I is. K The smaller the inductance, the better. Therefore, to reduce the coupling current, the mutual inductance between the shimming coil 11 and the gradient coil 12 can be reduced, or the self-inductance of the shimming coil 11 can be increased. In this regard, this application proposes a shimming device design method. The shimming device designed using this method has a larger inductance (self-inductance), which can reduce the coupling current.

[0053] The field shimming device design method provided in this application can be implemented using computer equipment. Computer equipment includes, but is not limited to, control chips, personal computers, laptops, smartphones, tablets, and portable wearable devices. The method provided in this application can be implemented using JAVA software, or applied to other software.

[0054] The technical solution of this application and how it solves the technical problems will be described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of this application will be described below with reference to the accompanying drawings.

[0055] Please see Figure 2 The field shimming device 20 proposed in this application includes a field shimming coil 11 and an anti-coupling coil 21. The anti-coupling coil 21 is disposed at both ends of the field shimming coil 11. The method for distributing and arranging the field shimming coil 11 and the anti-coupling coil 21 in the specific field shimming device 20 will be described in detail below.

[0056] Please see Figure 3 This application provides a method for designing a field shimming device in one embodiment. This application describes the method for designing a field shimming device in detail, using a computer device as the execution subject. The steps of the method include:

[0057] Step 300: Based on the relationship between the energy of the anti-coupling coil and the current parameters of the anti-coupling coil, determine the first current parameter when the energy of the anti-coupling coil is at its maximum; the first current parameter is used to characterize the current passing through each grid of the anti-coupling coil when the energy of the anti-coupling coil is at its maximum.

[0058] Designers divided the placement of the anti-coupling coils into multiple grids based on their location in actual application scenarios. For example... Figure 4 As shown, the anti-coupling coil is positioned in K grids, each grid used to set the coil (wire) of the anti-coupling coil. The size of each grid can be the same or different. The shape of each grid can be a cuboid, a cylinder, or other irregular three-dimensional structure. This embodiment does not limit the number of grids, or the size and shape of each grid. When current flows through the anti-coupling coil, the anti-coupling coil generates energy. The computer device determines the first current parameter when the energy of the anti-coupling coil is at its maximum, based on the relationship between the energy generated by the anti-coupling coil and the current parameters of the anti-coupling coil (the current flowing through each grid). That is, it determines the current flowing through each grid in the anti-coupling coil when the energy is at its maximum. In other words, the computer device calculates the energy of the anti-coupling coil at that current by assuming the current flowing through each grid, based on the relationship between the energy of the anti-coupling coil and the current parameters. The current flowing through each grid when the energy of the anti-coupling coil is at its maximum is used as the first current parameter. The current flowing through each grid assumed by the computer device can be a current value randomly selected by the computer device or a current value input by the operator; this embodiment does not limit this.

[0059] Step 310: Based on the relationship between the energy of the shimming coil and the current parameters of the shimming coil, determine the second current parameter when the energy of the shimming coil is at its minimum. The second current parameter is used to characterize the current passing through each grid of the shimming coil when the energy of the shimming coil is at its minimum.

[0060] Designers divide the distribution of the shimming coils into multiple grids based on their placement in practical applications. The description of each grid for the shimming coils can be found in the detailed description of each grid for the anti-coupling coils described above, and will not be repeated here. When current flows through the shimming coils, they generate energy. The computer device determines the second current parameter at which the shimming coil energy is minimized based on the relationship between the energy generated by the anti-coupling coils and the current parameters of the shimming coils (the current flowing through each grid). In other words, the computer device calculates the energy of the shimming coil at the assumed current flowing through each grid based on the relationship between the shimming coil's energy and current parameters, and uses the current flowing through each grid at the minimum energy of the shimming coil as the second current parameter. The description of the current flowing through each grid assumed by the computer device can be found in the description above, and will not be repeated here.

[0061] Step 320: Determine the wire distribution of the anti-coupling coil based on the first current parameter, and determine the wire distribution of the shimming coil based on the second current parameter.

[0062] After obtaining the first current parameter, namely the current flowing through each grid in the anti-coupling coil, the computer device can determine the distribution of the wires (part of the coils in the anti-coupling coil) in each grid. Connecting the wires in each grid of the anti-coupling coil in series yields the coil distribution throughout the entire anti-coupling coil. Similarly, after obtaining the second current parameter, namely the current flowing through each grid in the shimming coil, the computer device can determine the distribution of the wires (part of the coils in the shimming coil) in each grid. Connecting the wires in each grid of the shimming coil in series yields the coil distribution throughout the entire shimming coil. Thus, the wire distribution of the entire shimming device can be obtained.

[0063] In one optional embodiment, the computer device determines the current density distribution of the anti-coupling coil based on a first current parameter, and determines the wire distribution of the anti-coupling coil based on the current density distribution of the anti-coupling coil. Similarly, the computer device determines the current density distribution of the shimming coil based on a second current parameter, and determines the wire distribution of the shimming coil based on the current density distribution of the shimming coil.

[0064] In an optional embodiment, the shimming device is an A30 shimming device, and the structure of the shimming device is as follows: Figure 5 As shown. Figure 5 (a) shows the grid structure of the anti-coupling coil to the left of the shimming coil. Figure 5 In the diagram, (b) shows the mesh structure of the anti-coupling coil to the right of the shimming coil, and the mesh structure between (a) and (b) is that of the shimming coil. Figure 5The arrows in the diagram indicate the current direction in each grid. The current distribution of the anti-coupling coil is shown below. Figure 6 As shown, the horizontal axis represents the coordinates along the length of the shimming device, and the magnetic field distribution of the anti-coupling coil is as follows. Figure 7 As shown. The grid current distribution of the shimming coil is as follows. Figure 8 As shown, the horizontal axis represents the coordinates along the length of the shimming device. The current distribution (discretized) of the shimming coil is as follows: Figure 9 As shown, Figure 9 The sections with current flow are fitted with conductors using shimming coils, while the sections without current flow are not fitted with such conductors. The magnetic field distribution of the shimming coils is as follows: Figure 10 As shown. The magnetic field distribution of the A30 shimming device is as follows. Figure 11 As shown.

[0065] The field shimming device design method provided in this application determines a first current parameter when the energy of the anti-coupling coil is at its maximum based on the relationship between the energy and current parameters of the anti-coupling coil; and a second current parameter when the energy of the field shimming coil is at its minimum based on the same relationship. The wire distribution of the anti-coupling coil is determined based on the first current parameter, and the wire distribution of the field shimming coil is determined based on the second current parameter. The field shimming device provided in this application reduces the coupling between the gradient coil and the field shimming device by designing an anti-coupling coil, while the placement of the field shimming coil ensures that the field shimming device provides a shimming magnetic field. Furthermore, the anti-coupling coil designed based on the principle of maximizing energy, and the field shimming coil designed based on the principle of minimizing energy, increase the inductance of the field shimming device, resulting in a smaller coupling current that will not damage the field shimming power supply, thus ensuring the normal operation of the field shimming device.

[0066] Please see Figure 12 In one embodiment, a possible method is proposed to determine the first current parameter when the energy of the anti-coupling coil is at its maximum based on the relationship between the energy of the anti-coupling coil and the current parameter of the anti-coupling coil. The method includes the following steps:

[0067] Step 400: Based on the current flowing through each grid of the anti-coupling coil, the self-inductance of each grid of the anti-coupling coil, and the mutual inductance between the grids of the anti-coupling coil, establish the relationship between the energy of the anti-coupling coil and the current parameters of the anti-coupling coil, and obtain the maximum energy function of the anti-coupling coil.

[0068] Calculating the energy of the anti-coupling coil requires obtaining the current flowing through it and its inductance. In this embodiment, the anti-coupling coil is divided into multiple grids. The wires in each grid have self-inductance and mutual inductance with wires in other grids. Based on the current flowing through each grid, the self-inductance of each grid, and the mutual inductance between grids, the computer can establish the relationship between the energy of the anti-coupling coil and its current parameters, thus obtaining the maximum energy function of the anti-coupling coil. This embodiment does not limit the method used to calculate the self-inductance of each grid and the mutual inductance between grids, as long as the function is achieved.

[0069] In an optional embodiment, the self-inductance of each grid in the anti-coupling coil and the mutual inductance between grids can be calculated based on the geometric parameters of each grid in the anti-coupling coil. The geometric parameters of each grid in the anti-coupling coil are related to the shape of the grid. These geometric parameters can be pre-stored in the memory of a computer device and directly obtained by the computer device when calculating the self-inductance of each grid in each anti-coupling coil and the mutual inductance between grids; alternatively, these geometric parameters can be input by the designer. If each grid of the anti-coupling coil is annular, the geometric parameters include the radius, thickness, axial position, and width of the annulus.

[0070] Step 410: Obtain the first constraint condition of the maximum energy function, and solve the maximum energy function according to the first constraint condition to determine the first current parameter.

[0071] After obtaining the energy function of the anti-coupling coil, the computer device acquires the first constraint condition set for the maximum energy function. By solving the maximum energy function based on the first constraint condition, the first current parameter can be obtained. The first constraint condition can be pre-stored in the computer device's memory, which the computer device can directly retrieve when solving for the maximum energy function.

[0072] In one embodiment, the first constraint includes an inductance constraint and a current constraint for the anti-coupling coil. The inductance constraint limits the maximum and minimum inductance of the anti-coupling coil, preventing the inductance from exceeding the maximum and minimum permissible inductance ranges given the calculated first current parameters. In a specific embodiment, the maximum permissible inductance is 1000 mH, and the minimum permissible inductance is 1 mH. The current constraint refers to the maximum current allowed to pass through each grid of the anti-coupling coil.

[0073] In this embodiment, the proposed method for calculating the first current parameter is simple, easy to understand, and easy to implement.

[0074] In one embodiment, the maximum energy function can be expressed as:

[0075]

[0076] Where N is the number of grids in the anti-coupling coil, I i I is the current flowing through the i-th grid of the anti-coupling coil. j Let L be the current flowing through the j-th grid of the anti-coupling coil when i = j. ij For the self-inductance of the i-th grid of the anti-coupling coil, when i ≠ j, L ij The mutual inductance between the i-th and j-th grids of the anti-coupling coil.

[0077] Please see Figure 13 In one embodiment, a possible implementation method for obtaining a first constraint condition for the maximum energy function and solving the maximum energy function based on the first constraint condition to determine a first current parameter includes the following steps:

[0078] Step 500: Determine the energy of the anti-coupling coil based on the current flowing through each grid of the anti-coupling coil.

[0079] The computer equipment calculates the energy of the anti-coupling coil based on the current flowing through each grid of the assumed anti-coupling coil. The specific calculation formula can be expressed as: Where W represents the energy of the anticoupling coil under the current flowing through each grid of the assumed anticoupling coil.

[0080] Step 510: Determine the inductance of the anti-coupling coil based on its energy and input current.

[0081] If the first constraint includes an inductance preset condition, then the computer device can calculate the inductance of the anti-coupling coil based on the obtained energy of the anti-coupling coil and the input current of the anti-coupling coil (i.e., the current supplied to the anti-coupling coil). The specific calculation formula can be expressed as follows: Where L is the inductance of the anti-coupling coil, and I0 is the input current of the anti-coupling coil.

[0082] Step 520: Determine whether the inductance of the anti-coupling coil meets the inductance constraint condition, and determine whether the current through each grid of the anti-coupling coil meets the current constraint condition, and determine the first current parameter.

[0083] After calculating the inductance of the anti-coupling coil, the computer equipment compares it with the inductance constraint conditions to determine whether the inductance of the anti-coupling coil is within the range of the maximum and minimum inductance values ​​constrained by the constraint. Simultaneously, after determining the current flowing through each grid of the anti-coupling coil when its energy is at its maximum, the computer equipment compares it with the current constraint conditions to determine whether the current flowing through each grid of the anti-coupling coil satisfies the current constraint conditions. When the computer equipment determines that both the inductance and the current flowing through each grid of the anti-coupling coil satisfy the constraint conditions, it can define the current flowing through each grid of the anti-coupling coil at this point as the first current parameter.

[0084] The first constraint condition can be expressed by the formula... It means that, among them, L min L is the minimum inductance of the anti-coupling coil. max I is the maximum value of the inductance of the anti-coupling coil, and I0 is the input current of the anti-coupling coil.

[0085] Please see Figure 14 In one embodiment, a possible method is proposed to determine the second current parameter when the energy of the shimming coil is at its minimum based on the relationship between the energy of the shimming coil and the current parameter of the shimming coil. The method includes the following steps:

[0086] Step 600: Based on the current flowing through each grid of the shimming coil, the self-inductance of each grid of the shimming coil, and the mutual inductance between the grids of the shimming coil, establish the relationship between the energy of the shimming coil and the current parameters of the shimming coil, and obtain the minimum energy function of the shimming coil.

[0087] When calculating the energy of a shimming coil, it is necessary to obtain the current flowing through the coil and its inductance. In this embodiment, the shimming coil is divided into multiple grids. The wires in each grid have self-inductance and mutual inductance with the wires in other grids. Based on the current flowing through each grid, the self-inductance of each grid, and the mutual inductance between grids, the computer can establish the relationship between the energy of the shimming coil and its current parameters, thus obtaining the minimum energy function of the shimming coil. This embodiment does not limit the method used to calculate the self-inductance of each grid and the mutual inductance between grids, as long as the function is achieved.

[0088] For a detailed description of the self-inductance of each grid and the mutual inductance between grids in the specific calculation of the shimming coil, please refer to the detailed description of the self-inductance of each grid and the mutual inductance between grids in the calculation of the anti-coupling coil, which will not be repeated here.

[0089] Step 610: Obtain the second constraint condition of the minimum energy function, and solve the minimum energy function according to the second constraint condition to determine the second current parameter.

[0090] After obtaining the minimum energy function of the shimming coil, the computer device acquires the second constraint condition set for the minimum energy function. Solving the minimum energy function based on the second constraint condition yields the second current parameter. The second constraint condition can be pre-stored in the computer device's memory, which the computer device can directly retrieve when solving for the minimum energy function.

[0091] In one embodiment, the second constraint includes a constraint on the magnetic field deviation of the shimming coil, which imposes certain constraints on the magnetic field distribution of the shimming device. By setting the second constraint, it can be ensured that the shimming device provided by the embodiments of this application can provide an accurate shimming magnetic field in actual use, thereby improving the reliability of the design method of the shimming device provided by this application.

[0092] In one embodiment, the minimum energy function can be expressed as:

[0093]

[0094] Where M is the number of grids in the shimming coil, I h I is the current in the h-th grid of the shimming coil. k Let L be the current in the k-th grid of the shimming coil, when h = k. hk Let L be the self-inductance of the h-th grid to which the shim coil is connected. When h ≠ k, L hk The mutual inductance between the h-th grid and the k-th grid of the shimming coil.

[0095] Please see Figure 15 In one embodiment, a possible implementation method for obtaining a second constraint condition for the minimum energy function and determining a second current parameter by solving the minimum energy function based on the second constraint condition is proposed. The method includes the following steps:

[0096] Step 710: Calculate the magnetic field strength of the anti-coupling coil based on the wire distribution of the anti-coupling coil.

[0097] After determining the conductor distribution of the anti-coupling coil according to the method provided in the above embodiments, the computer device calculates the magnetic field strength of the anti-coupling coil based on the Biot-Savart law. Specifically, it calculates the magnetic field strength generated by the anti-coupling coil in the magnetic field region of the shimming device.

[0098] In an optional embodiment, the magnetic field strength of the anti-coupling coil can be calculated using the formula... It means that, among them, Let μa represent the magnetic field strength generated by the anti-coupling coil at region a in the shimming device, μ0 be the free permeability, I be the input current, and L be the total winding path of the anti-coupling coil. Let be the conductor integral element of the anti-coupling coil, and r be the distance between the conductor integral element of the anti-coupling coil and the magnetic field region a of the shimming device. Let be the unit vector of the distance between the conductor integral element of the anti-coupling coil and the magnetic field region a of the shimming device.

[0099] Step 720: Obtain the target magnetic field strength of the shimming device, and determine the magnetic field deviation of the shimming device based on the current passing through each grid of the shimming coil, the target magnetic field strength, and the magnetic field strength of the anti-coupling coil.

[0100] The target magnetic field strength of the shimming device refers to the magnetic field strength that the shimming device needs to provide in actual application scenarios. The target magnetic field strength can be pre-stored in the memory of the computer device, which can directly retrieve it when needed. After obtaining the target magnetic field strength, the computer device can calculate the magnetic field deviation of the shimming device based on the target magnetic field strength, the calculated magnetic field strength of the anti-coupling coil, and the current passing through each grid in the shimming coil.

[0101] In an optional embodiment, the formula for calculating the magnetic field deviation of the shimming device is: Where S represents the magnetic field deviation of the shimming device, and B ah I represents the magnetic field strength of the h-th grid of the shimming coil at location a in the magnetic field region of the shimming device. h Let h be the current flowing through the h-th grid of the shim coil. BTarget represents the magnetic field strength of the anti-coupling coil at magnetic field region a. a This represents the magnetic field strength at point a in the magnetic field region of the shimming device.

[0102] In an optional embodiment, the magnetic field strength of the shimming device at magnetic field region a can be calculated based on the target magnetic field strength of the shimming device. Specifically,

[0103] Where (x,y,z) represents the coordinates of the magnetic field region a. Let represent the magnetic field strength of various shimming devices. For example, for the A30 shimming device, Let represent the magnetic field strength of the A30 shimming device, while the magnetic field strength of all other shimming devices is zero. Then the magnetic field strength of the A30 shimming device can be expressed as:

[0104] Step 730: Determine whether the magnetic field deviation meets the magnetic field deviation constraint condition and determine the second current parameter.

[0105] After calculating the magnetic field deviation, the computer equipment determines whether the magnetic field deviation meets the magnetic field deviation constraint conditions. If the computer equipment determines that the magnetic field deviation meets the magnetic field deviation constraint conditions, it determines the current passing through each grid of the shimming coil used to calculate the magnetic field deviation as the second current parameter.

[0106] In an optional embodiment, the magnetic field deviation constraint refers to whether the difference between the magnetic field deviation and the maximum magnetic field deviation allowed by the shimming device is less than or equal to zero.

[0107] In an optional embodiment, the method for determining the conductor distribution of the shimming coil by the computer device may further include: calculating the magnetic field strength of the anti-coupling coil based on a first current parameter of the anti-coupling coil; determining the magnetic field strength of the shimming coil based on the difference between the target magnetic field strength of the shimming device and the magnetic field strength of the anti-coupling coil; determining the current distribution of the shimming coil based on the magnetic field strength of the shimming coil; and determining the conductor distribution of the shimming coil based on the current distribution of the shimming coil. Specifically, the current of the shimming coil is discretized to determine the conductor distribution of the shimming coil.

[0108] In a specific embodiment, for the A30 shimming device, the maximum allowable coupling current of the shimming power supply is 10A, the required strength of the shimming device is 2000uT / m³, the maximum operating current of the Z-gradient coil is 500A, the maximum gradient strength is 30mT / m, and the maximum ramp rate is 130T / m / s. According to the existing design scheme, the shimming coil is designed based on the principle of minimum energy, meaning that after the shimming coil design is completed, the self-inductance L of the A30 shimming device is minimized. The mutual inductance between the A30 shimming coil and the Z-gradient coil is 100uH, the self-inductance of the shimming coil is 1mH, the self-inductance L of the A30 shimming device is 1000uH, and the maximum operating current of the Z-gradient coil is 500A. The calculated coupling current on the shimming device is 50A. Because the coupling current on the shimming device is 50A, which is greater than the maximum allowable coupling current of the shimming power supply (10A), the shimming power supply will fail to operate normally due to the excessive input coupling current. Using the field shimming device design method provided in this application, an anti-coupling coil is designed. The total inductance of the field shimming coil and the anti-coupling coil is 10mH, and the coupling inductance between the field shimming coil, the anti-coupling coil and the Z gradient coil is 100uH. The calculated coupling current on the field shimming device is 5A, which is less than the maximum allowable coupling current of 10A for the field shimming power supply. Therefore, the field shimming power supply can work normally.

[0109] It should be understood that although the steps in the flowchart are shown sequentially as indicated by the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order constraint on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the diagram may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the sub-steps or stages of other steps.

[0110] Please see Figure 16 One embodiment of this application provides a field shimming device design system 10, which includes a first determining module 11, a second determining module 12, and a third determining module 13. Wherein,

[0111] The first determining module 11 is used to determine the first current parameter when the energy of the anti-coupling coil is at its maximum based on the relationship between the energy of the anti-coupling coil and the current parameter of the anti-coupling coil; the first current parameter is used to characterize the current passing through each grid of the anti-coupling coil when the energy of the anti-coupling coil is at its maximum.

[0112] The second determining module 12 is used to determine the second current parameter when the energy of the shimming coil is at its minimum based on the relationship between the energy of the shimming coil and the current parameter of the shimming coil. The second current parameter is used to characterize the current passing through each grid of the shimming coil when the energy of the shimming coil is at its minimum.

[0113] The third determining module 13 is used to determine the wire distribution of the anti-coupling coil based on the first current parameter and to determine the wire distribution of the shimming coil based on the second current parameter.

[0114] In one embodiment, the first determining module 11 includes a first establishing unit and a first determining unit. The first establishing unit is used to establish the relationship between the energy of the anti-coupling coil and its current parameters based on the current flowing through each grid of the anti-coupling coil, the self-inductance of each grid of the anti-coupling coil, and the mutual inductance between the grids of the anti-coupling coil, thereby obtaining the maximum energy function of the anti-coupling coil. The first determining unit is used to obtain a first constraint condition for the maximum energy function and solve the maximum energy function according to the first constraint condition to determine the first current parameter.

[0115] In one embodiment, the first constraint includes an inductance constraint and a current constraint for the anti-coupling coil, wherein the inductance constraint is used to constrain the maximum and minimum inductance of the anti-coupling coil.

[0116] In one embodiment, the first determining unit is specifically configured to determine the energy of the anti-coupling coil based on the current flowing through each grid of the anti-coupling coil; determine the inductance of the anti-coupling coil based on the energy of the anti-coupling coil and the input current of the anti-coupling coil; determine whether the inductance of the anti-coupling coil satisfies the inductance constraint condition; and determine whether the current flowing through each grid of the anti-coupling coil satisfies the current constraint condition, thereby determining a first current parameter.

[0117] In one embodiment, the second determining module 12 includes a second establishing unit and a second determining unit. The second establishing unit is used to establish the relationship between the energy of the shimming coil and the current parameters of the shimming coil based on the current flowing through each grid of the shimming coil, the self-inductance of each grid of the shimming coil, and the mutual inductance between the grids of the shimming coil, thereby obtaining the minimum energy function of the shimming coil. The second determining unit is used to obtain the second constraint condition of the minimum energy function and solve the minimum energy function according to the second constraint condition to determine the second current parameter.

[0118] In one embodiment, the second constraint includes a constraint on the magnetic field deviation of the shimming coil.

[0119] In one embodiment, the second determining unit is specifically used to calculate the magnetic field strength of the anti-coupling coil based on the wire distribution of the anti-coupling coil; obtain the target magnetic field strength of the shimming device; and determine the magnetic field deviation of the shimming device based on the current passing through each grid of the shimming coil, the target magnetic field strength, and the magnetic field strength of the anti-coupling coil; determine whether the magnetic field deviation meets the magnetic field deviation constraint condition; and determine the second current parameter.

[0120] Specific limitations regarding the above-mentioned field shimming device design system 10 can be found in the limitations of the field shimming device design method described above, and will not be repeated here. Each module in the field shimming device design system 10 can be implemented entirely or partially through software, hardware, or a combination thereof. The aforementioned devices, modules, or units can be embedded in or independent of the processor in a computer device in hardware form, or stored in the memory of a computer device in software form, so that the processor can call and execute the operations corresponding to the aforementioned devices or modules.

[0121] Please see Figure 17 In one embodiment, a computer device is provided, which may be a server, and its internal structure diagram may be as follows: Figure 17As shown, the computer device includes a processor, memory, network interface, and database connected via a system bus. The processor provides computational and control capabilities. The memory includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores the operating system, computer programs, and the database. The internal memory provides the environment for the operation of the operating system and computer programs stored in the non-volatile storage medium. The database stores information such as the grid settings of the anti-coupling coils and the grid settings of the shimming coils. The network interface of the computer device is used for communication with external terminals via a network connection. When executed by the processor, the computer device implements a shimming device design method.

[0122] Those skilled in the art will understand that Figure 17 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0123] In one embodiment, a computer device is provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to perform the following steps:

[0124] Based on the relationship between the energy of the anti-coupling coil and the current parameters of the anti-coupling coil, the first current parameter when the energy of the anti-coupling coil is at its maximum is determined; the first current parameter is used to characterize the current passing through each grid of the anti-coupling coil when the energy of the anti-coupling coil is at its maximum.

[0125] Based on the relationship between the energy of the shimming coil and the current parameters of the shimming coil, the second current parameter when the energy of the shimming coil is at its minimum is determined. The second current parameter is used to characterize the current passing through each grid of the shimming coil when the energy of the shimming coil is at its minimum.

[0126] The conductor distribution of the anti-coupling coil is determined based on the first current parameter, and the conductor distribution of the shimming coil is determined based on the second current parameter.

[0127] In one embodiment, when the processor executes the computer program, it further performs the following steps: establishing the relationship between the energy of the anti-coupling coil and the current parameters of the anti-coupling coil based on the current flowing through each grid of the anti-coupling coil, the self-inductance of each grid of the anti-coupling coil, and the mutual inductance between the grids of the anti-coupling coil, to obtain the maximum energy function of the anti-coupling coil; obtaining the first constraint condition of the maximum energy function, and solving the maximum energy function based on the first constraint condition to determine the first current parameter.

[0128] In one embodiment, when the processor executes the computer program, it further implements the following steps: the first constraint includes an inductance constraint and a current constraint of the anti-coupling coil, wherein the inductance constraint is used to constrain the maximum value and the minimum value of the inductance of the anti-coupling coil.

[0129] In one embodiment, when the processor executes the computer program, it further performs the following steps: determining the energy of the anti-coupling coil based on the current flowing through each grid of the anti-coupling coil; determining the inductance of the anti-coupling coil based on the energy of the anti-coupling coil and the input current of the anti-coupling coil; determining whether the inductance of the anti-coupling coil satisfies the inductance constraint condition and whether the current flowing through each grid of the anti-coupling coil satisfies the current constraint condition, and determining a first current parameter.

[0130] In one embodiment, when the processor executes the computer program, it further performs the following steps: establishing the relationship between the energy of the shimming coil and the current parameters of the shimming coil based on the current flowing through each grid of the shimming coil, the self-inductance of each grid of the shimming coil, and the mutual inductance between the grids of the shimming coil, to obtain the minimum energy function of the shimming coil; obtaining the second constraint condition of the minimum energy function, and solving the minimum energy function according to the second constraint condition to determine the second current parameter.

[0131] In one embodiment, when the processor executes the computer program, it further implements the following steps: the second constraint includes a magnetic field deviation constraint of the shimming coil.

[0132] In one embodiment, when the processor executes the computer program, it further performs the following steps: calculating the magnetic field strength of the anti-coupling coil based on the wire distribution of the anti-coupling coil; obtaining the target magnetic field strength of the shimming device, and determining the magnetic field deviation of the shimming device based on the current passing through each grid of the shimming coil, the target magnetic field strength, and the magnetic field strength of the anti-coupling coil; determining whether the magnetic field deviation meets the magnetic field deviation constraint condition, and determining the second current parameter.

[0133] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon, the computer program performing the following steps when executed by a processor:

[0134] Based on the relationship between the energy of the anti-coupling coil and the current parameters of the anti-coupling coil, the first current parameter when the energy of the anti-coupling coil is at its maximum is determined; the first current parameter is used to characterize the current passing through each grid of the anti-coupling coil when the energy of the anti-coupling coil is at its maximum.

[0135] Based on the relationship between the energy of the shimming coil and the current parameters of the shimming coil, the second current parameter when the energy of the shimming coil is at its minimum is determined. The second current parameter is used to characterize the current passing through each grid of the shimming coil when the energy of the shimming coil is at its minimum.

[0136] The conductor distribution of the anti-coupling coil is determined based on the first current parameter, and the conductor distribution of the shimming coil is determined based on the second current parameter.

[0137] In one embodiment, when the computer program is executed by the processor, it further performs the following steps: establishing the relationship between the energy of the anti-coupling coil and the current parameters of the anti-coupling coil based on the current flowing through each grid of the anti-coupling coil, the self-inductance of each grid of the anti-coupling coil, and the mutual inductance between the grids of the anti-coupling coil, to obtain the maximum energy function of the anti-coupling coil; obtaining the first constraint condition of the maximum energy function, and solving the maximum energy function according to the first constraint condition to determine the first current parameter.

[0138] In one embodiment, when the computer program is executed by the processor, it further implements the following steps: the first constraint includes an inductance constraint and a current constraint of the anti-coupling coil, the inductance constraint being used to constrain the maximum and minimum values ​​of the inductance of the anti-coupling coil.

[0139] In one embodiment, when the computer program is executed by the processor, it further performs the following steps: determining the energy of the anti-coupling coil based on the current flowing through each grid of the anti-coupling coil; determining the inductance of the anti-coupling coil based on the energy of the anti-coupling coil and the input current of the anti-coupling coil; determining whether the inductance of the anti-coupling coil satisfies the inductance constraint condition and whether the current flowing through each grid of the anti-coupling coil satisfies the current constraint condition, and determining a first current parameter.

[0140] In one embodiment, when the computer program is executed by the processor, it further performs the following steps: establishing the relationship between the energy of the shimming coil and the current parameters of the shimming coil based on the current flowing through each grid of the shimming coil, the self-inductance of each grid of the shimming coil, and the mutual inductance between the grids of the shimming coil, to obtain the minimum energy function of the shimming coil; obtaining the second constraint condition of the minimum energy function, and solving the minimum energy function according to the second constraint condition to determine the second current parameter.

[0141] In one embodiment, when the computer program is executed by the processor, it further implements the following steps: the second constraint includes a magnetic field deviation constraint of the shimming coil.

[0142] In one embodiment, when the computer program is executed by the processor, it further performs the following steps: calculating the magnetic field strength of the anti-coupling coil based on the wire distribution of the anti-coupling coil; obtaining the target magnetic field strength of the shimming device, and determining the magnetic field deviation of the shimming device based on the current passing through each grid of the shimming coil, the target magnetic field strength, and the magnetic field strength of the anti-coupling coil; determining whether the magnetic field deviation meets the magnetic field deviation constraint condition, and determining the second current parameter.

[0143] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), Rambus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0144] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0145] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for designing a field homogenizing device, characterized in that, The shimming device includes a shimming coil and anti-coupling coils disposed at both ends of the shimming coil, and the method includes: Based on the relationship between the energy of the anti-coupling coil and the current parameters of the anti-coupling coil, a first current parameter is determined when the energy of the anti-coupling coil is at its maximum; the first current parameter is used to characterize the current passing through each grid of the anti-coupling coil when the energy of the anti-coupling coil is at its maximum. Based on the relationship between the energy of the shimming coil and the current parameter of the shimming coil, a second current parameter is determined when the energy of the shimming coil is at its minimum. The second current parameter is used to characterize the current passing through each grid of the shimming coil when the energy of the shimming coil is at its minimum. The conductor distribution of the anti-coupling coil is determined based on the first current parameter, and the conductor distribution of the shimming coil is determined based on the second current parameter.

2. The design method of the field homogenizing device according to claim 1, characterized in that, The step of determining the first current parameter when the energy of the anti-coupling coil is at its maximum, based on the relationship between the energy of the anti-coupling coil and the current parameter of the anti-coupling coil, includes: Based on the current flowing through each grid of the anti-coupling coil, the self-inductance of each grid of the anti-coupling coil, and the mutual inductance between the grids of the anti-coupling coil, the relationship between the energy of the anti-coupling coil and the current parameters of the anti-coupling coil is established, and the maximum energy function of the anti-coupling coil is obtained. Obtain the first constraint condition of the maximum energy function, and solve the maximum energy function according to the first constraint condition to determine the first current parameter.

3. The design method of the field homogenizing device according to claim 2, characterized in that, The first constraint condition includes the inductance constraint condition and the current constraint condition of the anti-coupling coil. The inductance constraint condition is used to constrain the maximum value and the minimum value of the inductance of the anti-coupling coil.

4. The design method of the field homogenizing device according to claim 3, characterized in that, The step of obtaining the first constraint condition for the maximum energy function and solving the maximum energy function based on the first constraint condition to determine the first current parameter includes: The energy of the anti-coupling coil is determined based on the current flowing through each grid of the anti-coupling coil. The inductance of the anti-coupling coil is determined based on the energy of the anti-coupling coil and the input current of the anti-coupling coil. Determine whether the inductance of the anti-coupling coil satisfies the inductance constraint condition, and determine whether the current flowing through each grid of the anti-coupling coil satisfies the current constraint condition, and determine the first current parameter.

5. The design method of the field homogenizing device according to claim 1, characterized in that, The step of determining the second current parameter when the energy of the shimming coil is at its minimum, based on the relationship between the energy of the shimming coil and the current parameter of the shimming coil, includes: Based on the current flowing through each grid of the shimming coil, the self-inductance of each grid of the shimming coil, and the mutual inductance between the grids of the shimming coil, the relationship between the energy of the shimming coil and the current parameters of the shimming coil is established, and the minimum energy function of the shimming coil is obtained. Obtain the second constraint condition of the minimum energy function, and solve the minimum energy function according to the second constraint condition to determine the second current parameter.

6. The design method of the field homogenizing device according to claim 5, characterized in that, The second constraint condition includes the magnetic field deviation constraint condition of the shimming coil.

7. The design method of the field homogenizing device according to claim 6, characterized in that, The process of obtaining the second constraint condition for the minimum energy function and solving the minimum energy function based on the second constraint condition to determine the second current parameter includes: Calculate the magnetic field strength of the anti-coupling coil based on the wire distribution of the anti-coupling coil; The target magnetic field strength of the shimming device is obtained, and the magnetic field deviation of the shimming device is determined based on the current passing through each grid of the shimming coil, the target magnetic field strength, and the magnetic field strength of the anti-coupling coil. Determine whether the magnetic field deviation meets the magnetic field deviation constraint condition, and then determine the second current parameter.

8. A field homogenizing device design system, characterized in that, The shimming device includes a shimming coil and anti-coupling coils disposed at both ends of the shimming coil; the system includes: The first determining module is used to determine a first current parameter when the energy of the anti-coupling coil is at its maximum, based on the relationship between the energy of the anti-coupling coil and the current parameter of the anti-coupling coil; the first current parameter is used to characterize the current passing through each grid of the anti-coupling coil when the energy of the anti-coupling coil is at its maximum. The second determining module is used to determine a second current parameter when the energy of the shimming coil is at its minimum, based on the relationship between the energy of the shimming coil and the current parameter of the shimming coil. The second current parameter is used to characterize the current passing through each grid of the shimming coil when the energy of the shimming coil is at its minimum. The third determining module is used to determine the wire distribution of the anti-coupling coil based on the first current parameter and to determine the wire distribution of the shimming coil based on the second current parameter.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 7.

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