A method for designing an electromagnetic interference resistant magnetic resonance imaging coil

Abstract

The present application relates to a kind of magnetic resonance imaging anti electromagnetic interference coil design method, the method includes six execution steps: step 1, input superconducting magnet coil structure;Step 2, determine the position of anti electromagnetic interference coil;Step 3, calculate the number of turns of anti electromagnetic interference coil;Step 4, integrate superconducting magnet coil and anti electromagnetic interference coil structure information and calculate magnetic field transfer vector, inductance matrix, coil area vector;Step 5, construct mathematical optimization model with shielding factor as objective function and solve the axial position of anti electromagnetic interference coil;Step 6, anti electromagnetic interference coil number of turns integer optimization and calculate shielding factor.The method can be applied to the anti electromagnetic interference coil design of any magnetic resonance imaging superconducting magnet, has good design flexibility and engineering applicability.

Description

Technical Field

[0001] The invention belongs to the field of superconducting electrical engineering, and in particular relates to a design method for a magnetic resonance imaging anti-electromagnetic interference coil. Background Art

[0002] Magnetic resonance imaging (MRI) requires extremely high magnetic field stability, but in practice, MRI is often subject to interference from external magnetic fields, such as magnetic field fluctuations from surrounding electromagnetic equipment. These magnetic field fluctuations often induce electromagnetic induction in the MRI superconducting magnet coils, causing magnetic field drift and artifacts in the MRI images. These induced magnetic field fluctuations are often low-frequency and can be considered quasi-static. MRI radio frequency shielding cannot effectively block low-frequency magnetic field interference. The addition of anti-EMI coils to MRI superconducting magnets aims to mitigate this low-frequency interference. The main principle is to add an additional set of superconducting coils to form a closed loop with the superconducting magnet coils. After the superconducting magnet is successfully excited, current flows through the superconducting magnet coils, clearing the induced current in the anti-EMI coils and closing the loop. When external magnetic field fluctuations are introduced into the superconducting magnet bore, electromagnetic induction occurs simultaneously between the superconducting magnet coils and the anti-EMI coils. However, the induced magnetic field generated by the anti-EMI coils cancels out the induced magnetic field generated by the superconducting magnet coils, maintaining the stability of the superconducting magnet's magnetic field.

[0003] In summary, the design of the anti-electromagnetic interference coil directly affects the quality of magnetic resonance imaging, so how to design the anti-electromagnetic interference coil is particularly important. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a design method for an MRI anti-electromagnetic interference coil and describes the calculation method of relevant parameters. The method can be applied to the design of an anti-electromagnetic interference coil (EIS) for any MRI superconducting magnet and has strong engineering application value.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for designing an anti-electromagnetic interference coil for magnetic resonance imaging, the method comprising the following steps:

[0007] Step 1: Input the superconducting magnet coil structure, including the coil axial left end position, axial right end position, inner radius, outer radius, axial number of turns, radial number of layers, and current direction.

[0008] Step 2: Determine one or more superconducting magnet coils to support the anti-electromagnetic interference coil, that is, the outer radius of the superconducting magnet coil is consistent with the inner radius of the anti-electromagnetic interference coil, and set the axial position of each anti-electromagnetic interference coil on the superconducting magnet coil. The position of the anti-electromagnetic interference coil on the superconducting magnet coil includes the following two situations: (1) the left ends of the anti-electromagnetic interference coil and the superconducting magnet coil are flush, and the right ends are free; (2) the right ends of the anti-electromagnetic interference coil and the superconducting magnet coil are flush, and the left ends are free.

[0009] Step 3: Select the specifications of the superconducting wire for winding the anti-electromagnetic interference coil and set the number of winding layers. Take the axial position of the anti-electromagnetic interference coil as the variable to be solved, calculate the axial number of turns, set the position variable of the anti-electromagnetic interference coil to be solved as x, and select the width of the wire as w. As in the two cases in step 2, the axial numbers of turns of the anti-electromagnetic interference coil are (x-z1) / w and (z2-x) / w respectively.

[0010] Step 4: Integrate the structural information of the superconducting magnet coil and the anti-electromagnetic interference coil to calculate the magnetic field transfer vector, inductance matrix, and coil area vector.

[0011] Integrate the superconducting magnet coil and the anti-electromagnetic interference coil into the overall coil, and calculate the magnetic field transfer vector B of the overall coil. The magnetic field transfer vector B includes the i-th vector element B i for:

[0012] ,

[0013] Among them, B i is the magnetic induction intensity generated at the center of the superconducting magnet when the i-th coil passes a unit current, μ0 is the vacuum permeability, N i is the total number of turns of the i-th coil, that is, the product of the axial number of turns and the radial number of layers, z1, z2, r1, and r2 are the axial left end position, axial right end position, inner radius, and outer radius of the coil, respectively.

[0014] The inductance matrix L includes the i-th sub-matrix L ii ' is calculated as follows:

[0015] ,

[0016] Among them, L ii ' is the mutual inductance between the ith coil and the i'th coil. If i and i' are the same, it is the self-inductance. V and V' are the volumes of the ith coil and the i'th coil, respectively. j and j' are the direction vectors of the current density of the ith coil and the i'th coil at spatial positions r and r', respectively.

[0017] The coil area vector A includes the i-th element A i The calculation of is as follows:

[0018] ,

[0019] Among them, A i is the total area of ​​the i-th coil, N r is the radial layer number of the i-th coil, N z is the number of axial turns of the i-th coil, r k is the radius of the kth layer in the radial direction of the coil.

[0020] Step 5: Set the initial value of the axial position of the anti-electromagnetic interference coil on the superconducting magnet coil, calculate the shielding factor of the anti-electromagnetic interference coil, use the shielding factor as the objective function, and the constraint condition is that the range of the axial position of the anti-electromagnetic interference coil does not exceed the range of the axial position of the superconducting magnet coil where it is located, and perform the axial position optimization solution of the anti-electromagnetic interference coil.

[0021] The calculation method of the shielding factor of the anti-electromagnetic interference coil is:

[0022] ,

[0023] Among them, S is the shielding factor, B is the magnetic field transfer vector, L is the inductance matrix, and A is the coil area vector.

[0024] The mathematical model for optimization solution is:

[0025] Minimize: ,

[0026] Constraints: ,

[0027] Where f is the objective function, B is the magnetic field transfer vector, L is the inductance matrix, A is the coil area vector, x1 is the axial position of the first anti-electromagnetic interference coil to be solved, z 11 、z 21 are the axial left end position and axial right end position of the superconducting magnet coil supporting the first anti-electromagnetic interference coil, respectively. i is the axial position of the i-th anti-electromagnetic interference coil to be solved, z 1i 、z 2i are the axial left end position and axial right end position of the superconducting magnet coil supporting the i-th anti-electromagnetic interference coil respectively.

[0028] Step 6: Based on step 3, the optimal axial number of turns of the anti-electromagnetic interference coil is calculated according to the numerical solution of the axial position of the anti-electromagnetic interference coil that has been optimized. The integer solution of the axial number of turns is obtained by rounding off, and then the actual shielding factor of the anti-electromagnetic interference coil is calculated according to step 5.

[0029] The beneficial effects of the present invention are:

[0030] The optimal anti-electromagnetic interference coil structure can be quickly found to obtain a high shielding factor. Moreover, the relevant steps fully consider the engineering applicability. The anti-electromagnetic interference coil obtained by the corresponding solution is directly wound on the superconducting magnet coil without the need for additional support. The anti-electromagnetic interference coil is wound from one end of the superconducting magnet coil, which can effectively ensure the coil position accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a flow chart of a method for designing an anti-electromagnetic interference coil for magnetic resonance imaging according to the present invention;

[0032] Figure 2 Schematic diagram of the arrangement of the magnet coils and anti-electromagnetic interference coils of the superconducting magnet in an embodiment of the present invention. DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0034] Such as Figure 1 As shown, the present invention provides a method for designing an anti-electromagnetic interference coil for magnetic resonance imaging, characterized in that the method comprises the following steps:

[0035] Step 1: Input the superconducting magnet coil structure, including the coil axial left end position, axial right end position, inner radius, outer radius, axial number of turns, radial number of layers, and current direction.

[0036] Step 2: Determine one or more superconducting magnet coils to support the anti-electromagnetic interference coil, that is, the outer radius of the superconducting magnet coil is consistent with the inner radius of the anti-electromagnetic interference coil, and set the axial position of each anti-electromagnetic interference coil on the superconducting magnet coil. The position of the anti-electromagnetic interference coil on the superconducting magnet coil includes the following two situations: (1) the left ends of the anti-electromagnetic interference coil and the superconducting magnet coil are flush, and the right ends are free; (2) the right ends of the anti-electromagnetic interference coil and the superconducting magnet coil are flush, and the left ends are free.

[0037] Step 3: Select the specifications of the superconducting wire for winding the anti-electromagnetic interference coil and set the number of winding layers. Take the axial position of the anti-electromagnetic interference coil as the variable to be solved, calculate the axial number of turns, set the position variable of the anti-electromagnetic interference coil to be solved as x, and select the width of the wire as w. As in the two cases in step 2, the axial numbers of turns of the anti-electromagnetic interference coil are (x-z1) / w and (z2-x) / w respectively.

[0038] Step 4: Integrate the structural information of the superconducting magnet coil and the anti-electromagnetic interference coil to calculate the magnetic field transfer vector, inductance matrix, and coil area vector.

[0039] Integrate the superconducting magnet coil and the anti-electromagnetic interference coil into the overall coil, and calculate the magnetic field transfer vector B of the overall coil. The magnetic field transfer vector B includes the i-th vector element B i for:

[0040] ,

[0041] Among them, B i is the magnetic induction intensity generated at the center of the superconducting magnet when the i-th coil passes a unit current, μ0 is the vacuum permeability, N i is the total number of turns of the i-th coil, that is, the product of the axial number of turns and the radial number of layers, z1, z2, r1, and r2 are the axial left end position, axial right end position, inner radius, and outer radius of the coil, respectively.

[0042] The inductance matrix L includes the i-th sub-matrix L ii ' is calculated as follows:

[0043] ,

[0044] Among them, L ii ' is the mutual inductance between the ith coil and the i'th coil. If i and i' are the same, it is the self-inductance. V and V' are the volumes of the ith coil and the i'th coil, respectively. j and j' are the direction vectors of the current density of the ith coil and the i'th coil at spatial positions r and r', respectively.

[0045] The coil area vector A includes the i-th element A i The calculation of is as follows:

[0046] ,

[0047] Among them, A i is the total area of ​​the i-th coil, N r is the radial layer number of the i-th coil, N z is the number of axial turns of the i-th coil, r k is the radius of the kth layer in the radial direction of the coil.

[0048] Step 5: Set the initial value of the axial position of the anti-electromagnetic interference coil on the superconducting magnet coil, calculate the shielding factor of the anti-electromagnetic interference coil, use the shielding factor as the objective function, and the constraint condition is that the range of the axial position of the anti-electromagnetic interference coil does not exceed the range of the axial position of the superconducting magnet coil where it is located, and perform the axial position optimization solution of the anti-electromagnetic interference coil.

[0049] The calculation method of the shielding factor of the anti-electromagnetic interference coil is:

[0050] ,

[0051] Among them, S is the shielding factor, B is the magnetic field transfer vector, L is the inductance matrix, and A is the coil area vector.

[0052] The mathematical model for optimization solution is:

[0053] Minimize: ,

[0054] Constraints: ,

[0055] Where f is the objective function, B is the magnetic field transfer vector, L is the inductance matrix, A is the coil area vector, x1 is the axial position of the first anti-electromagnetic interference coil to be solved, z 11 、z 21 are the axial left end position and axial right end position of the superconducting magnet coil supporting the first anti-electromagnetic interference coil, respectively. i is the axial position of the i-th anti-electromagnetic interference coil to be solved, z 1i 、z 2i are the axial left end position and axial right end position of the superconducting magnet coil supporting the i-th anti-electromagnetic interference coil respectively.

[0056] Step 6: Based on step 3, the axial number of turns of the anti-electromagnetic interference coil is calculated according to the numerical solution of the axial position of the anti-electromagnetic interference coil. The integer solution of the axial number of turns is obtained by rounding off. Based on step 5, the shielding factor of the anti-electromagnetic interference coil is calculated.

[0057] Figure 2 The figure shows an embodiment of the present invention, in which the anti-electromagnetic interference coil design method is applied to the design of a superconducting magnet for animal magnetic resonance imaging. The superconducting magnet has eight coils, numbered 7-14 in the figure. The superconducting magnet support coils for the selected anti-electromagnetic interference coils are numbered 7, 8, 9, 10, 13, and 14, respectively. The corresponding anti-electromagnetic interference coils are numbered 1, 2, 3, 4, 5, and 6 in the figure.

[0058] Among them, the second anti-electromagnetic interference coil 2 and the third anti-electromagnetic interference coil 3, the first anti-electromagnetic interference coil 1 and the fourth anti-electromagnetic interference coil 4, and the fifth anti-electromagnetic interference coil 5 and the sixth anti-electromagnetic interference coil 6 are symmetric about the symmetry axis z=0. In this way, during the optimization process, only the axial positions of the third, fourth, and sixth anti-electromagnetic interference coils 3, 4, and 6 need to be calculated, and the corresponding second, first, and fifth anti-electromagnetic interference coils 2, 1, and 5 are symmetrically processed.

[0059] The third anti-electromagnetic interference coil 3 applies the situation (1) in step 2, the fourth anti-electromagnetic interference coil 4 applies the situation (2) in step 2, and the sixth anti-electromagnetic interference coil 6 applies the situation (1) in step 2. The anti-electromagnetic interference coil structure can be obtained by following the optimization of step 5 and the integer processing of step 6.

[0060] It will be easily understood by those skilled in the art that the above is only an embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for designing an anti-electromagnetic interference coil for magnetic resonance imaging, characterized in that: The method comprises the following steps: Step 1: Input the superconducting magnet coil structure, including the axial left end position, axial right end position, inner radius, outer radius, axial number of turns, radial number of layers, and current direction of all coils; Step 2: Determine one or more superconducting magnet coils for supporting the anti-electromagnetic interference coils, and set the axial position of each anti-electromagnetic interference coil on the superconducting magnet coil, wherein each superconducting magnet coil is used to support one anti-electromagnetic interference coil; Step 3: Select the specifications of the superconducting wire for winding the anti-electromagnetic interference coil and set the number of winding layers. Take the axial position of the anti-electromagnetic interference coil as the variable to be solved and calculate the number of axial turns. Step 4: Integrate the structural information of the superconducting magnet coil and the anti-electromagnetic interference coil to calculate the magnetic field transfer vector, inductance matrix, and coil area vector; Step 5: Set the initial value of the axial position of the anti-electromagnetic interference coil on the superconducting magnet coil, calculate the shielding factor of the anti-electromagnetic interference coil, use the shielding factor as the objective function, and the constraint condition is that the range of the axial position of the anti-electromagnetic interference coil does not exceed the range of the axial position of the superconducting magnet coil where it is located, and perform the axial position optimization solution of the anti-electromagnetic interference coil; Step 6: Based on step 3, the optimal axial number of turns of the anti-electromagnetic interference coil is calculated according to the numerical solution of the axial position of the anti-electromagnetic interference coil that has been optimized. The integer solution of the axial number of turns is obtained by rounding off, and then the actual shielding factor of the anti-electromagnetic interference coil is calculated according to step 5.

2. The method for designing an anti-electromagnetic interference coil for magnetic resonance imaging according to claim 1, characterized in that: The axial position of the anti-electromagnetic interference coil on the superconducting magnet coil in step 2 includes the following two situations: (1) the left ends of the anti-electromagnetic interference coil and the superconducting magnet coil are aligned, and the right ends are free; (2) the right ends of the anti-electromagnetic interference coil and the superconducting magnet coil are aligned, and the left ends are free.

3. The method for designing an MRI anti-electromagnetic interference coil according to claim 2, wherein: In step 3, the axial position of the anti-electromagnetic interference coil to be solved is set as the variable x, and the width of the superconducting wire is selected as w. The axial numbers of turns of the anti-electromagnetic interference coil corresponding to the two cases are (x-z1) / w and (z2-x) / w, respectively, where z1 and z2 are the axial left end position and axial right end position of the superconducting magnet coil, respectively.

4. The method for designing an anti-electromagnetic interference coil for magnetic resonance imaging according to claim 1, wherein: In step 4, the superconducting magnet coil and the anti-electromagnetic interference coil are integrated into the overall coil, and the magnetic field transfer vector B of the overall coil is calculated. The magnetic field transfer vector B includes the i-th vector element B i for: ， Among them, B i is the magnetic induction intensity generated at the center of the superconducting magnet when the i-th coil passes a unit current, μ0 is the vacuum permeability, N i is the total number of turns of the i-th coil, that is, the product of the axial number of turns and the radial number of layers, z1, z2, r1, and r2 are the axial left end position, axial right end position, inner radius, and outer radius of the coil respectively; The inductance matrix L includes the i-th sub-matrix The calculation of is as follows: ， in, is the mutual inductance between the ith coil and the ith' coil, V and V' are the volumes of the ith coil and the ith' coil respectively, j and j' are the current density direction vectors of the ith coil and the ith' coil at the spatial positions r and r' respectively; The coil area vector A includes the i-th element A i The calculation of is as follows: ， Among them, A i is the total area of ​​the i-th coil, N r is the radial layer number of the i-th coil, N z is the number of axial turns of the i-th coil, r k is the radius of the kth layer in the radial direction of the coil.

5. The method for designing an MRI anti-electromagnetic interference coil according to claim 1, wherein: The calculation method of the shielding factor of the anti-electromagnetic interference coil in step 5 is: ， Where S is the shielding factor, B is the magnetic field transfer vector, L is the inductance matrix, and A is the coil area vector; The mathematical model for optimizing the axial position of the anti-electromagnetic interference coil is: Minimize: , Constraints: , Where f is the objective function, B is the magnetic field transfer vector, L is the inductance matrix, A is the coil area vector, x1 is the axial position of the first anti-electromagnetic interference coil to be optimized, z 11 、z 21 are the axial left end position and axial right end position of the superconducting magnet coil supporting the first anti-electromagnetic interference coil, respectively. i is the optimized axial position of the i-th anti-electromagnetic interference coil, z 1i 、z 2i are the axial left end position and axial right end position of the superconducting magnet coil supporting the i-th anti-electromagnetic interference coil respectively.

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