Magnetic resonance imaging anti-electromagnetic interference coil design method

Abstract

The invention relates to a magnetic resonance imaging anti-electromagnetic interference coil design method. The method comprises the following six execution steps: step 1, inputting a superconducting magnet coil structure; 2, determining the position of an anti-electromagnetic interference coil; 3, calculating the number of turns of the anti-electromagnetic interference coil; 4, integrating the structural information of the superconducting magnet coil and the anti-electromagnetic interference coil, and calculating a magnetic field transfer vector, an inductance matrix and a coil area vector; 5, constructing a mathematical optimization model taking the shielding factor as a target function, and solving the axial position of the anti-electromagnetic interference coil; and step 6, performing integer optimization on the number of turns of the anti-electromagnetic interference coil and calculating a shielding factor. The method can be applied to the anti-electromagnetic interference coil design of any magnetic resonance imaging superconducting magnet, and has good design flexibility and engineering applicability.

Description

Technical Field

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

[0002] Magnetic resonance imaging requires extremely high magnetic field stability, but in practice, MRI is often interfered by external magnetic fields, such as magnetic field fluctuations of surrounding electromagnetic equipment. Such magnetic field fluctuations often cause electromagnetic induction of the MRI superconducting magnet coil, thereby causing magnetic field drift and artifacts in the MRI image. This inductive magnetic field fluctuation is often of low frequency and can be considered as a quasi-static magnetic field. The radio frequency shielding of MRI cannot effectively shield low-frequency magnetic field interference. The role of adding anti-electromagnetic interference coils to MRI superconducting magnets is to resist the interference of such low-frequency magnetic fields. Its main principle is: add a set of additional superconducting coils, and form a closed loop with the superconducting magnet coils independently. After the superconducting magnet is successfully excited, the current flows in the superconducting magnet coils, and the induced current in the anti-electromagnetic interference coils is cleared and closed. When the external magnetic field fluctuations are transmitted into the superconducting magnet cavity, the superconducting magnet coils and the anti-electromagnetic interference coils simultaneously generate electromagnetic induction, but the induced magnetic field generated by the anti-electromagnetic interference coils just offsets the induced magnetic field generated by the superconducting magnet coils, achieving the purpose of maintaining the stability of the superconducting magnet 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] In order to solve the above technical problems, the present invention provides a design method for an anti-electromagnetic interference coil for magnetic resonance imaging, 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 magnetic resonance imaging superconducting magnet, and has strong engineering application value.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A method for designing an anti-electromagnetic interference coil for magnetic resonance imaging, the method comprising the following steps: 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.

[0006] 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.

[0007] 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. For 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.

[0008] Step 4: Integrate the structural information of the superconducting magnet coil and the anti-electromagnetic interference coil, and calculate the magnetic field transfer vector, inductance matrix, and coil area vector.

[0009] 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.

[0010] The inductance matrix L includes the i-th submatrix L ii ' is calculated as follows: , 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 current density direction vectors of the ith coil and the i'th coil at the spatial positions r and r' respectively.

[0011] The coil area vector A includes the i-th element A i The calculation of is as follows: , Among them, A iis the total area of ​​the i-th coil, N r is the radial number of layers of the ith coil, N z is the number of axial turns of the i-th coil, r k is the radius of the kth layer of the coil in radial direction.

[0012] 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, take 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, and perform the axial position optimization solution of the anti-electromagnetic interference coil.

[0013] The calculation method of the shielding factor of the anti-electromagnetic interference coil is: , 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.

[0014] The mathematical model for optimization solution 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 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 respectively the axial left end position and the axial right end position of the superconducting magnet coil supporting the i-th anti-electromagnetic interference coil.

[0015] Step 6: Based on step 3, according to the numerical solution of the axial position of the anti-electromagnetic interference coil that has been optimized, the optimal axial number of turns of the anti-electromagnetic interference coil is calculated, and the integer solution of the axial number of turns is obtained by rounding off. Then, according to step 5, the actual shielding factor of the anti-electromagnetic interference coil is calculated.

[0016] The beneficial effects of the present invention are: The optimal anti-electromagnetic interference coil structure can be found quickly to obtain a high shielding factor, and 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

[0017] 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; Figure 2 It is a structural diagram of the arrangement of the magnet coil and the anti-electromagnetic interference coil of the superconducting magnet in an embodiment of the present invention. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0019] like 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: 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.

[0020] 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.

[0021] 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. For 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.

[0022] Step 4: Integrate the structural information of the superconducting magnet coil and the anti-electromagnetic interference coil, and calculate the magnetic field transfer vector, inductance matrix, and coil area vector.

[0023] 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 iis 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.

[0024] The inductance matrix L includes the i-th submatrix L ii ' is calculated as follows: , 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 current density direction vectors of the ith coil and the i'th coil at the spatial positions r and r' respectively.

[0025] 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 number of layers of the ith coil, N z is the number of axial turns of the i-th coil, r k is the radius of the kth layer of the coil in radial direction.

[0026] 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, take 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, and perform the axial position optimization solution of the anti-electromagnetic interference coil.

[0027] The calculation method of the shielding factor of the anti-electromagnetic interference coil is: , 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.

[0028] The mathematical model for optimization solution 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 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 respectively the axial left end position and the axial right end position of the superconducting magnet coil supporting the i-th anti-electromagnetic interference coil.

[0029] Step 6: According to step 3, based on the numerical solution of the axial position of the anti-electromagnetic interference coil, the axial number of turns of the anti-electromagnetic interference coil is calculated, and the integer solution of the axial number of turns is obtained by rounding off. According to step 5, the shielding factor of the anti-electromagnetic interference coil is calculated.

[0030] Figure 2 An implementation example of the present invention is shown, in which the anti-electromagnetic interference coil design method is applied in the design of a superconducting magnet for animal magnetic resonance imaging. The superconducting magnet has a total of 8 coils, namely, the serial numbers 7-14 in the figure, and the superconducting magnet support coils of the selected anti-electromagnetic interference coils are the 7th, 8th, 9th, 10th, 13th, and 14th superconducting magnet coils numbered 7, 8, 9, 10, 13, and 14, and the corresponding anti-electromagnetic interference coils are the 1st to 6th anti-electromagnetic interference coils numbered 1, 2, 3, 4, 5, and 6 in the figure.

[0031] 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, 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.

[0032] 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 optimizing in step 5 and performing integer processing in step 6.

[0033] 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 protection scope 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 coil, 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, set the number of winding layers, take the axial position of the anti-electromagnetic interference coil as the quantity 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, and 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, take 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, and perform the axial position optimization solution of the anti-electromagnetic interference coil; Step 6: Based on step 3, according to the numerical solution of the axial position of the anti-electromagnetic interference coil that has been optimized, the optimal axial number of turns of the anti-electromagnetic interference coil is calculated, and the integer solution of the axial number of turns is obtained by rounding off. Then, according to step 5, the actual shielding factor of the anti-electromagnetic interference coil is calculated.

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 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.

3. The method for designing an anti-electromagnetic interference coil for magnetic resonance imaging according to claim 2, characterized in that: 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 situations are (x-z1) / w and (z2-x) / w, respectively, and 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 MRI anti-electromagnetic interference coil according to claim 1, characterized in that: 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 submatrix L ii ' is calculated as follows: ， Among them, L ii ' is the mutual inductance between the ith coil and the i'th coil, V and V' are the volumes of the ith coil and the i'th coil, respectively, j and j' are the current density direction vectors of the ith coil and the i'th 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 number of layers of the ith coil, N z is the number of axial turns of the i-th coil, r k is the radius of the kth layer of the coil.

5. The method for designing an MRI anti-electromagnetic interference coil according to claim 1, characterized in that: The calculation method of the shielding factor of the anti-electromagnetic interference coil in step 5 is: ， 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; 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 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 optimized axial position of the i-th anti-electromagnetic interference coil to be solved, z 1i 、z 2i are respectively the axial left end position and the axial right end position of the superconducting magnet coil supporting the i-th anti-electromagnetic interference coil.

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