Transcranial magnetic stimulation coil design method and system based on finite element calculation

Abstract

The invention provides a transcranial magnetic stimulation coil design method and system based on finite element calculation. The method is applied to the technical field of transcranial magnetic stimulation and comprises the following steps: acquiring a stimulation part for an actual disease of a patient, and presetting design parameters of a transcranial magnetic stimulation coil based on the stimulation part of the disease; importing a head model, solving based on an eddy current field finite element method, and calculating to obtain a transcranial magnetic stimulation coil magnetic field and an induced electric field; checking the design parameters of the transcranial magnetic stimulation coil according to the magnetic field and the induced electric field, and finishing the design of the transcranial magnetic stimulation coil after checking. In this way, by presetting the shape of the coil, arranging the stimulation focus at the expected position and calibrating the electric induction value, the peak magnetic field and the induced electric field, the design result well meets the requirements of actual engineering manufacturing, the design method is high in universality, and all transcranial magnetic stimulation coils of known structures can be designed.

Description

Technical Field

[0001] The present disclosure relates to the technical field of transcranial magnetic stimulation, and particularly to a transcranial magnetic stimulation coil design method and system based on finite element calculation. Background Art

[0002] Transcranial magnetic stimulation technology uses the induced electric field generated by time-varying pulsed electromagnetic fields to act on the central nervous system of the brain, change the membrane potential of cortical nerve cells in the brain, affect the metabolism and nerve electrical activities in the brain, and thus cause a series of physiological and biochemical reactions, which is a treatment method in the field of central and peripheral nerves. Currently, transcranial magnetic stimulation devices are widely used in neuroscience research and the treatment of diseases in clinical departments such as neurology, psychiatry, and rehabilitation.

[0003] Traditional transcranial magnetic stimulation coils, such as circular and figure-eight coils, have been widely used. Based on these two types of coils, new designs have changed the shape to obtain a deeper or more focused field pattern, which can achieve a deeper magnetic stimulation depth. The shapes of traditional coils are simple, and the magnetic field or induced electric field is easy to calculate using the analytical method, which is convenient for checking and verifying the design parameters of the electric and magnetic fields. Traditional circular and figure-eight coils have good versatility, but the clinical demand for coils dedicated to specific disease sites is increasing, and the analytical method for calculating electromagnetic parameters encounters bottlenecks in design. Especially in the design of coils made of ferromagnetic materials with non-linear B-H characteristics, the analytical method is even more unable to complete.

[0004] Therefore, there is an urgent need for a practical and versatile transcranial magnetic stimulation coil design scheme at present. Summary of the Invention

[0005] The present disclosure provides a transcranial magnetic stimulation coil design method and system based on finite element calculation. By directly solving the magnetic field and induced electric field using the finite element calculation method, it is possible to check the design parameters of coils with any complex shape, and at least solve the technical problems of poor versatility and low practicality of the existing design methods.

[0006] According to the first aspect of the present disclosure, a transcranial magnetic stimulation coil design method based on finite element calculation is provided, including the following steps:

[0007] Obtain the stimulation site for the actual disease of the patient, and preset the transcranial magnetic stimulation coil design parameters based on the disease stimulation site;

[0008] Import the head model, and solve based on the finite element method of the eddy current field to calculate the magnetic field and induced electric field of the transcranial magnetic stimulation coil;

[0009] According to the magnetic field and the induced electric field, check the transcranial magnetic stimulation coil design parameters. After the check is completed, the design of the transcranial magnetic stimulation coil is completed.

[0010] For the aspects and any possible implementation manners described above, a further implementation manner is provided. The design parameters of the transcranial magnetic stimulation coil specifically include: coil focus and wiring shape, preset value of coil inductance, preset value of magnetic field value at a given depth, and preset value of induced electric field value.

[0011] For the aspects and any possible implementation manners described above, a further implementation manner is provided. The process of designing the coil focus and wiring shape is as follows: arranging a high current density or increasing the ampere-turns at the stimulation focus site and reducing the current density or the ampere-turns in other irrelevant areas;

[0012] The range of the preset value of the coil inductance is 15 - 25 μH;

[0013] The preset value of the magnetic field value at a given depth is not less than 0.2 T, and the preset value of the induced electric field value is not less than 70 V / m.

[0014] For the aspects and any possible implementation manners described above, a further implementation manner is provided. The process of importing a head model and solving based on the finite element method of the eddy current field to calculate the magnetic field and induced electric field of the transcranial magnetic stimulation coil is as follows:

[0015] Establish a finite element method engineering project, and set the solution type to the eddy current field;

[0016] Import the coil model, head sphere model and set the boundary region, and set the electric excitation condition and the eddy current effect;

[0017] Set the inductance and calculate the current matrix, and select adaptive meshing to complete the mesh division;

[0018] Set the solution conditions for solution calculation, and solve to obtain the coil magnetic field and induced electric field.

[0019] For the aspects and any possible implementation manners described above, a further implementation manner is provided. The head sphere model is a single-layer sphere model or a three-layer sphere model. Among them, the conductivity of the single-layer sphere model is 0.33 S / m, and the three-layer sphere model includes a scalp layer, a skull layer and a cerebral cortex layer. The conductivities of the scalp layer, the skull layer and the cerebral cortex layer are 0.33 S / m, 0.0042 S / m and 0.75 S / m respectively;

[0020] The electric excitation condition is set to a single-pulse sinusoidal alternating current with a decaying period, and the frequency range is 2.5 - 4 kHz. The eddy current effect selects the head model.

[0021] For the aspects and any possible implementation manners described above, a further implementation manner is provided. The solution conditions include the frequency of the excitation source, the percentage error, and the ratio of the encrypted meshing unit for each iteration;

[0022] Among them, the frequency range of the excitation source is 2.5 - 4 kHz.

[0023] For the aspects and any possible implementation manners as described above, a further implementation manner is provided. The process of checking the design parameters of the transcranial magnetic stimulation coil according to the magnetic field and the induced electric field is as follows:

[0024] Check whether the coil inductance is within the preset value range of the coil inductance. If not, adjust it by adjusting the number of coil turns and the size of the wire loop.

[0025] Generate a distribution map of the induced electric field on the spherical shell of the cerebral cortex head model. Obtain the shape and position of the coil focus through the distribution map. Judge whether the focus is the required focus by judging the shape and position of the coil focus. If not, adjust the coil wiring.

[0026] Check whether the magnetic field value and the induced electric field value at the given depth are respectively within the preset value range of the magnetic field value at the given depth, that is, the preset value range of the induced electric field value.

[0027] Connect the vertex of the stimulation focus of the spherical head model to the center of the sphere, calculate the attenuation curve of the induced electric field on the line segment, evaluate the stimulation depth, and judge whether the depth is within the preset stimulation depth evaluation range.

[0028] For the aspects and any possible implementation manners as described above, a further implementation manner is provided. The preset stimulation depth evaluation range is: the distance d[E / 2] reached by half of the maximum induced electric field value intensity E on the cortical surface at the focus.

[0029] According to the second aspect of the present disclosure, a transcranial magnetic stimulation coil design system based on finite element calculation is provided, including: a transcranial magnetic stimulation coil design parameter preset module, a finite element calculation module, and a design parameter checking module;

[0030] The transcranial magnetic stimulation coil design parameter preset module is used to preset the transcranial magnetic stimulation coil design parameters based on the disease stimulation site;

[0031] The finite element calculation module is used to import the head model, solve based on the finite element method of the eddy current field, and calculate the magnetic field and the induced electric field of the transcranial magnetic stimulation coil;

[0032] The design parameter checking module is used to check the design parameters of the transcranial magnetic stimulation coil according to the magnetic field and the induced electric field, and complete the design of the transcranial magnetic stimulation coil.

[0033] Compared with the prior art, the present invention has the following technical effects:

[0034] The present invention pre-sets the coil shape and arranges the stimulation focus at the expected position; by checking the inductance, peak magnetic field and induced electric field, the design results better meet the requirements of actual engineering production. The design method has strong versatility and can design transcranial magnetic stimulation coils of all known structures, is suitable for the coil design of deep magnetic stimulation with a focus, and has more advantages in the design of stimulation coils made of ferromagnetic materials with non-linear B-H characteristics.

[0035] It should be understood that the content described in the summary of the invention is not intended to limit the key or important features of the embodiments of the present disclosure, nor is it used to limit the scope of the present disclosure. Other features of the present disclosure will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] With reference to the accompanying drawings and the following detailed description, the above and other features, advantages and aspects of the embodiments of the present disclosure will become more obvious. The drawings are used to better understand the solution and do not constitute a limitation to the present disclosure. In the drawings, the same or similar reference numerals represent the same or similar elements, where:

[0037] Figure 1 shows a schematic flow chart of a transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure;

[0038] Figure 2 shows a schematic structural diagram of a finite element simulation three-layer head model of a transcranial magnetic stimulation coil design method according to an embodiment of the present disclosure;

[0039] Figure 3 shows a schematic diagram of a finite element simulation current excitation single-pulse sinusoidal alternating current diagram of a transcranial magnetic stimulation coil design method according to an embodiment of the present disclosure;

[0040] Figure 4 shows a schematic structural diagram of a transcranial magnetic stimulation coil design system based on finite element calculation according to an embodiment of the present disclosure;

[0041] Figure 5 shows the wiring diagram of the H coil designed and verified in Embodiment 1 of a transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure;

[0042] Figure 6 shows the distribution diagram of the induced electric field of the H coil wired in Embodiment 1 of a transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure;

[0043] Figure 7 shows the improved wiring schematic diagram of the H coil obtained after adjusting the wiring in Embodiment 1 of a transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure;

[0044] Figure 8 Shows the schematic diagram of the induced electric field distribution obtained by improving the wiring of the H coil after adjusting the wiring in Embodiment 1 of a transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure;

[0045] Figure 9 Shows the schematic diagram of the magnetic field distribution in the XOZ plane section under a single-layer spherical model obtained by improving the wiring of the H coil after adjusting the wiring in Embodiment 1 of a transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure;

[0046] Figure 10 Shows the schematic diagram of the induced electric field distribution in the XOZ plane section under a single-layer spherical model obtained by improving the wiring of the H coil after adjusting the wiring in Embodiment 1 of a transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure;

[0047] Figure 11 Shows the current wiring diagram of the transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure, where the focus is located in the prefrontal lobe in Embodiment 2. Among them, the focus position uses double-layer wiring, and the other areas use single-layer wiring, and the current traces are dispersed;

[0048] Figure 12 Shows the schematic diagram of the induced electric field distribution obtained by the current wiring of the transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure, where the focus is located in the prefrontal lobe in Embodiment 2;

[0049] Figure 13 Shows the schematic diagram of the magnetic field distribution in the XOZ plane section under the three-layer spherical model of the focus obtained by the current wiring of the transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure, where the focus is located in the prefrontal lobe in Embodiment 2;

[0050] Figure 14 Shows the schematic diagram of the induced electric field distribution in the XOZ plane section under the three-layer spherical model of the focus obtained by the current wiring of the transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure, where the focus is located in the prefrontal lobe in Embodiment 2;

[0051] Figure 15 Shows the schematic diagram of the attenuation curve of the induced electric field on the line segment from the vertex of the stimulation focus to the center of the sphere in Embodiment 2 of a transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure;

[0052] Figure 16 Shows the wiring schematic diagram of the simulation model under a single-layer spherical model of an animal coil with a ferromagnetic material core in Embodiment 3 of a transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure;

[0053] Figure 17 Fig. shows the B-H curve schematic diagram of the silicon steel sheet selected for the coil iron core in Embodiment 3 of a transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure;

[0054] Figure 18 Fig. shows the schematic diagram of the magnetic field distribution obtained by wiring the simulation model under the single-layer spherical model of the animal coil with a ferromagnetic material core in Embodiment 3 of a transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure;

[0055] Figure 19 Fig. shows the schematic diagram of the induced electric field distribution obtained by wiring the simulation model under the single-layer spherical model of the animal coil with a ferromagnetic material core in Embodiment 3 of a transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure;

[0056] Figure 20 Fig. shows the induced electric field distribution in the YOZ plane section obtained by wiring the simulation model under the single-layer spherical model of the animal coil with a ferromagnetic material core in Embodiment 3 of a transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure;

[0057] Figure 21 Fig. shows the schematic diagram of the induced electric field attenuation curve on the line segment 12 from the stimulation focus vertex to the center of the sphere in Embodiment 3 of a transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure. Detailed implementation manners

[0058] To make the objectives, technical solutions and advantages of the embodiments of the present disclosure clearer, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present disclosure. Obviously, the described embodiments are some, but not all, of the embodiments of the present disclosure. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present disclosure without creative efforts shall fall within the protection scope of the present disclosure.

[0059] In the technical field of transcranial magnetic stimulation coil design, C C et.al (Phys. Med. Biol. 62, 2017, pp73–90) is based on including the stream function of the quasi-static current in the boundary element method and solving the field source of the wiring according to the field target, which can be used for the design of transcranial magnetic stimulation coils of any shape. This method does not conduct research on peak current limitation, inductance, and stimulation depth.

[0060] Non-traditional coils, such as H coils (US 2014 / 0235927 A1, US 9254394 B2), pay more attention to matching the head shape to obtain a deeper stimulation depth. Due to their complex shapes, it is difficult to calculate these coils using the analytical method, and the field pattern distribution is not given in the patent. Yiftach Roth, (Journal of Clinical Neurophysiology 19(4):361–370, 2002) wrote a field pattern calculation program for H coils using Mathematica v4.0, and the distributions of the magnetic field and induced electric field are not given in the literature. For the key parameters of transcranial magnetic stimulation coil design, such as inductance, magnetic field, and induced electric field, the focusing property has not been studied in depth. CN104096316A proposes an optimization method for H-type coils for deep brain transcranial magnetic stimulation, using the finite element method to simulate the electric field distribution of H-type coils on a real head conductivity model and setting criteria for evaluating deep characteristics. The H coil wiring method used in this patent determines the optimal wire spacing at different positions in the frontal, top, and lateral parts of the H coil. The wiring method for important parameters such as the focus position of the coil, the inductance of the coil, and the magnetic field value at a given depth is not described.

[0061] According to the stimulation target, the present invention pre-sets the coil focus and gives the current wiring principle; given the desired design parameters: the coil inductance L, the magnetic field and induced electric field E at a given position; using the finite element calculation method to calculate and verify the above three parameters to obtain the design output of the transcranial magnetic stimulation coil of any shape. The design method has strong versatility and can design transcranial magnetic stimulation coils of any known shape and any focus, which is suitable for the coil design of deep magnetic stimulation with a focus and has more advantages in the design of ferromagnetic material stimulation coils with non-linear B-H characteristics.

[0062] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0063] Refer to Figure 1 As shown, this embodiment provides a transcranial magnetic stimulation coil design method based on finite element calculation, including:

[0064] S101. Preset the transcranial magnetic stimulation coil design parameters based on the diseased stimulation site.

[0065] In this embodiment, the design parameters are specifically: the coil focus and wiring shape, the preset value of the coil inductance, the preset value of the magnetic field value at a given depth, and the preset value of the induced electric field value.

[0066] Specifically, the design of the coil focus position is related to the position of the magnetic stimulation treatment site for the disease. For example, the magnetic stimulation treatment sites in the clinical application of mental disorders are mainly the right dorsolateral prefrontal cortex and the left dorsolateral prefrontal cortex; the stimulation sites for patients with movement disorders are the motor area M1 or the supplementary motor area, and the stimulation sites for patients with tinnitus are the temporal lobe or the temporoparietal cortex. According to Faraday's law of electromagnetic induction, in the area with a high source current density, the induced current density generated by the eddy current effect is also high. The distribution of the induced current has a mirror image relationship with the distribution of the coil current. Based on the above theoretical basis, the present embodiment adopts the induction electric field focus wiring principle of the magnetic stimulation coil, specifically: increasing the ampere-turns at the stimulation focus site and decreasing the ampere-turns in other irrelevant areas.

[0067] (2) Selection of Coil Inductance

[0068] The selection of coil inductance is a very important parameter for transcranial magnetic stimulation equipment. The inductance of the coil affects indicators such as the peak current of the discharge circuit, the magnitude of the peak pulse magnetic field, the width of the pulse magnetic field, and the magnetic field change rate. According to the product indicators in the industry, the range of the effective coil inductance value set in the present invention is 15 - 25 μH. When the coil inductance value is higher or lower than this range, the wiring of the design scheme needs to be adjusted, and then the calculation and verification are carried out again.

[0069] (3) Magnetic Field Value and Induced Electric Field Value at a Given Depth

[0070] The designed given depth refers to the distance from the surface of the coil to the stimulation target site. At the stimulation target site, to reach the depolarization threshold, this limit value needs to be exceeded.

[0071] (4) Magnetic Field Constraint and Electric Field Constraint

[0072] The magnetic field constraint designed in the present embodiment: the maximum peak magnetic field value at the stimulation target is not less than 0.2 T.

[0073] The electric field constraint designed in the present embodiment: the maximum induced electric field at the stimulation target is not less than 70 V / m.

[0074] S102. Construct a head model and solve it using the finite element method of the eddy current field to obtain the finite element calculation result.

[0075] In the present embodiment, specifically, the current mainstream finite element software for electromagnetic field analysis includes Ansys Maxwell and Comsol, etc. The solution method of the present invention is not limited to specific finite element tool software. Establish a finite element method engineering project, and set the solution type to the eddy current field.

[0076] First, import the coil model, the head sphere model, and set the boundary region;

[0077] When modeling the coil model, a detailed model with wiring is established. The detailed model with wiring facilitates the adjustment of the wiring position and the number of turns. The coil material is selected as copper. According to the fact that the distribution of the induced current has a mirror image relationship with the distribution of the coil current, when wiring the coil with a focus, the number of current turns is increased at the focus position to increase the current density, and the current density is decreased at non-focus positions.

[0078] As Figure 2 shown, the head sphere model can adopt a single-layer sphere model or a three-layer sphere model. The single-layer sphere model only simulates the simplified scalp layer structure, with the conductivity set to 0.33 S / m, fewer meshes, and a fast solution speed. The three-layer sphere model simulates the human head structure. From the outside to the inside, the first spherical shell 1 is the scalp layer, with the conductivity set to 0.33 S / m; the second spherical shell 2 is the skull layer, with the conductivity set to 0.0042 S / m; the third sphere 3 is the cerebral cortex (including cerebrospinal fluid), with the comprehensive conductivity set to 0.75 S / m.

[0079] Set the boundary region, and the material is vacuum.

[0080] Secondly, set the excitation, and select the head model for the eddy current effect;

[0081] As Figure 3 shown, the current excitation condition is set as a decaying single-pulse sinusoidal alternating current with a period. The actual system magnetic stimulation pulse frequency is 2.5 - 4 kHz, and usually a frequency of 3 kHz is selected. The peak current can be obtained through measurement of the actual system. Select the head model for the eddy current effect as the target region for calculating the induced electric field value.

[0082] Thirdly, set the inductance to calculate the current matrix;

[0083] Set the calculated current matrix as the excitation current source in the coil, and all excitation sources need to be selected. The inductance value of the coil can be obtained according to the current source matrix.

[0084] Then, perform mesh generation;

[0085] Adaptive meshes can be selected for mesh generation to improve the calculation speed. The mesh density can also be increased according to the calculation accuracy at the target point.

[0086] Finally, set the solution conditions and perform the solution calculation;

[0087] In the solution settings, set the percentage error and the proportion of refined dissection units for each iteration. Set the frequency of the excitation source in the solver to 2.5 - 4 kHz, usually set to 3 kHz.

[0088] S103. According to the finite element calculation results, check the design parameters of the transcranial magnetic stimulation coil to complete the electromagnetic design of the coil.

[0089] (1) Check whether the coil inductance is within the range of 15 - 25 μH

[0090] If it is less than 15 μH, increase the number of coil turns or increase the size of the wire loop; if it is greater than 25 μH, reduce the number of coil turns or decrease the size of the wire loop.

[0091] (2) Check the induced electric field and the coil focus

[0092] On the spherical shell of the cerebral cortex head model, generate a distribution map of the induced electric field. The position and area size of the coil focus can be obtained from the distribution map. Observe the shape and position of the focus to see if it is the electric field focus of the target site required. If the position is incorrect, adjust the coil wiring so that the stimulated target is consistent with the position of the induced electric field focus.

[0093] Determine that the peak value of the induced electric field at the target site of the cerebral cortex of the head model is not less than 70 V / m. If it is lower than 70 V / m, the preset coil shape cannot meet the design requirements.

[0094] (3) Check the magnetic field value at the cerebral cortex model

[0095] Determine that the peak value of the magnetic field at the target site of the cerebral cortex of the head model is not less than 0.2 T. If it is lower than 0.2 T, the preset coil shape cannot meet the design requirements.

[0096] (4) Evaluation of the stimulation depth

[0097] The general stimulation depth evaluation criterion is: the distance d[E / 2] reached by half of the maximum induced electric field intensity E on the cortical surface at the focus. Connect the vertex of the stimulation focus of the head model to the center of the sphere, and calculate the induced electric field attenuation curve on the line segment to evaluate the stimulation depth. The stimulation depth can be intuitively obtained from the induced electric field attenuation curve.

[0098] When the inductance, focus shape, stimulation depth, induced electric field, and magnetic field peak all meet the established indicators, the electromagnetic design of the coil is completed and can be exported for engineering design and production.

[0099] As Figure 4 shown, this embodiment also provides a transcranial magnetic stimulation coil design system based on finite element calculation, including: a transcranial magnetic stimulation coil design parameter preset module 111, a finite element calculation module 112, and a design parameter verification module 113;

[0100] The transcranial magnetic stimulation coil design parameter preset module 111 is used to preset the transcranial magnetic stimulation coil design parameters based on the disease stimulation site;

[0101] The finite element calculation module 112 is used to construct a head model and solve it using the finite element method of the eddy current field to obtain the finite element calculation result;

[0102] The design parameter verification module 113 is used to verify the transcranial magnetic stimulation coil design parameters according to the finite element calculation results and complete the electromagnetic design of the coil.

[0103] Example 1

[0104] In this embodiment, among them, the transcranial magnetic stimulation treatment head coil has its focus located in the prefrontal lobe, and the wiring method refers to US 2014 / 0235927 A1. The current direction is as Figure 5 shown by the arrow, and a single-layer spherical model is adopted.

[0105] According to Figure 2 the shown current curve, an excitation is applied, and the excitation current is included in the parameter matrix to calculate the inductance. For the eddy current field calculation, a head spherical model is selected. After solving by the finite element method, the induced electric field distribution is as Figure 6 shown. It can be seen that the focus position of the peak electric field meets the design requirements, and the maximum peak value is 169.7176 V / m. However, the obtained inductance is 12.4 μH < 15 μH, which does not meet the design determination condition and the design needs to be improved.

[0106] Figure 7 To improve the wiring of the H coil obtained after adjusting the wiring, on the basis of Figure 5 , one more turn of winding is added, as shown in Figure 7 Figure 4. The finite element calculation is carried out again. Design result evaluation and analysis:

[0107] The inductance increases to 19 μH, meeting the design requirements.

[0108] The induced electric field distribution is as Figure 8 shown. The focus position is located at the desired part of the prefrontal lobe, meeting the design requirements.

[0109] The magnetic field distribution in the XOZ plane section under the single-layer spherical model is as Figure 9 shown. The upper hemisphere region all meets the requirement of above 0.2 T, meeting the magnetic field condition.

[0110] The induced electric field distribution in the XOZ plane section under the single-layer spherical model is as Figure 10 shown. The induced electric field at the focus position of the transcranial magnetic stimulation coil is as concentrated as possible, while the induced electric field at non-focus positions is as dispersed as possible. Through Figure 10 the induced electric field distribution, it can be seen that in the region shown by the ellipse frame at position 5, the induced electric field value of the irrelevant stimulation is relatively large, approaching the induced electric field value at the focus, which is an undesirable coil design result. The design needs to be improved.

[0111] Example 2

[0112] In this embodiment, according to the principle that the distribution of the induced current has a mirror image relationship with the distribution of the coil current, the coil wiring is improved, asFigure 11 As shown in Figure 11 At the position of 6 in , the focus position adopts double-layer wiring to increase the ampere-turns, so as to obtain a stronger and more concentrated induction electric field focus. The current direction is as shown by the arrow direction in the figure. The other irrelevant areas adopt dispersed wiring to reduce the irrelevant electric field. Compared with the existing winding method, the wiring method proposed by the present invention is mainly wound along the spherical ring, and the winding is simpler and easier to manufacture.

[0113] The intermediate processes such as the adjustment of the number of turns of the coil are not elaborated here. The adjustment is based on the inductance being in the range of 15 - 25 μH. The finally obtained coil inductance value is 19.4 μH, meeting the inductance requirements. The distribution is as Figure 12 shown. The focus is located below the double-layer current concentrated wiring, meeting the design expectations.

[0114] In Embodiment 2, a three-layer sphere model is adopted for finite element calculation, and the obtained magnetic field distribution is as Figure 13 shown. The upper half of the sphere model all meets the design requirements of being greater than 0.2 T. Figure 14 The induced electric field distribution in the XOZ plane section under the three-layer sphere model. It can be seen that Figure 14 the electric field in the irrelevant stimulation area at the position of Region 9 is significantly weakened. Figure 14 In , 7 is the focus area. Figure 14 In , 8 is the line segment connecting the focus vertex to the center of the sphere, Figure 15 and is the curve for calculating the attenuation of the induced electric field on line segment 8. The maximum value of the induced electric field intensity E at the cortex surface at the focus can be obtained as 205 V / m, the half intensity is 102.5, and the stimulation depth d[E / 2] at the focus is 27.5 mm.

[0115] Embodiment 3

[0116] This embodiment demonstrates the design ability of the method of the present invention with a ferromagnetic material coil. Embodiment 3 is the coil design for mouse animal experiments.

[0117] As Figure 16 shown, the iron core 10 of the coil in this embodiment is a 10-sided cylinder with a diameter of 20 mm and a length of 130 mm. The coil 11 is a double-layer coil. 12 is a single-layer sphere model with a sphere diameter of 20 mm. The iron core 10 is laminated with silicon steel sheets, and the B-H curve of the silicon steel sheets selected for the coil iron core is as Figure 17 shown.

[0118] Apply the excitation according to the Figure 2 shown current curve, and include the excitation current in the parameter matrix for calculating the inductance. The eddy current field calculation selects the head sphere model.

[0119] When performing finite element calculations, the coil 11 can use the number of turns as the optimization parameter, and the constraint condition is not less than 15 uH. The final inductance is 15.8 uH. The coil is divided into two layers, with 13 turns in each layer.

[0120] According to the finite element calculation results, parameter verification is added during post-processing.

[0121] Figure 18 For the magnetic field distribution verification of the spherical model, it can be seen that the magnetic field distribution in the entire spherical model is greater than 0.2 T, meeting the design requirements.

[0122] Figure 19 For the electric field distribution verification on the spherical surface of the spherical model, there is no induced electric field focus. The peak electric field is distributed in a ring shape in the upper half of the spherical surface, and the highest peak field 85.3248 V / m > 70 V / m, meeting the constraint conditions.

[0123] Figure 20 For the induced electric field distribution in the YOZ plane section, 13 is the line segment from the focus to the center of the sphere. The electric field attenuation curve along line segment 13 is as Figure 21 shown. It can be directly measured that the half-depth d[E / 2] of the maximum induced electric field value intensity E on the cortical surface at the focus is 4.2 mm.

[0124] It should be noted that for the foregoing method embodiments, for the sake of simple description, they are all expressed as a series of action combinations. However, those skilled in the art should know that the present disclosure is not limited by the described action sequence, because according to the present disclosure, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all optional embodiments, and the actions and modules involved are not necessarily essential to the present disclosure.

[0125] It should be understood that various forms of the processes shown above can be used, reordering, adding, or deleting steps. For example, the steps recorded in the present disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired results of the technical solutions disclosed in the present disclosure can be achieved. This is not limited herein.

[0126] The above specific implementation manners do not constitute a limitation on the protection scope of the present disclosure. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present disclosure shall be included within the protection scope of the present disclosure.

Claims

1. A transcranial magnetic stimulation coil design method based on finite element calculation, characterized in that: The following steps are involved: Obtain the stimulation site according to the patient's actual symptoms, and preset the transcranial magnetic stimulation coil design parameters based on the stimulation site of the symptoms; The head model is imported, and the magnetic field and induced electric field of the transcranial magnetic stimulation coil are calculated based on the eddy current field finite element method. The design parameters of the transcranial magnetic stimulation coil are checked according to the magnetic field and the induced electric field. After the checking is completed, the design of the transcranial magnetic stimulation coil is completed.

2. The transcranial magnetic stimulation coil design method based on finite element calculation according to claim 1, characterized in that: The transcranial magnetic stimulation coil design parameters specifically include: coil focus and wiring shape, coil inductance preset value, magnetic field value preset value at a given depth, and induced electric field value preset value.

3. The transcranial magnetic stimulation coil design method based on finite element calculation according to claim 2, characterized in that: The coil focus and wiring shape design process is: arrange high current density or increase ampere-turns at the stimulation focus and reduce current density or reduce ampere-turns in other irrelevant areas; The preset value of the coil inductance is in the range of 15-25 μH; The preset value of the magnetic field value at the given depth is not less than 0.2T, and the preset value of the induced electric field value is not less than 70V / m.

4. The transcranial magnetic stimulation coil design method based on finite element calculation according to claim 1, characterized in that: Import the head model, solve it based on the eddy current field finite element method, and calculate the process of obtaining the magnetic field and induced electric field of the transcranial magnetic stimulation coil as follows: Establish a finite element method engineering project and set the solution type to eddy current field; Import the coil model and head ball model and set the boundary area, and set the electrical excitation conditions and eddy current effect; Set the inductance and calculate the current matrix, and select adaptive mesh to complete meshing; Set the solution conditions to perform the solution calculation and obtain the coil magnetic field and induced electric field.

5. The transcranial magnetic stimulation coil design method based on finite element calculation according to claim 4, characterized in that: The head ball model is a single-layer ball model or a three-layer ball model, wherein the single-layer ball model has an electrical conductivity of 0.33 S / m, and the three-layer ball model includes a scalp layer, a skull layer, and a cerebral cortex, and the electrical conductivities of the scalp layer, the skull layer, and the cerebral cortex are 0.33 S / m, 0.0042 S / m, and 0.75 S / m, respectively; The electrical excitation condition is set as a single-pulse sinusoidal alternating current with a decaying period and a frequency range of 2.5 to 4 kHz, and the eddy current effect selects a head model.

6. The transcranial magnetic stimulation coil design method based on finite element calculation according to claim 4, characterized in that: The solution conditions include the frequency of the excitation source, the percentage error and the proportion of the encrypted mesh unit in each iteration; Wherein, the frequency range of the excitation source is 2.5-4 kHz.

7. The transcranial magnetic stimulation coil design method based on finite element calculation according to claim 4, characterized in that: The process of verifying the design parameters of the transcranial magnetic stimulation coil according to the magnetic field and the induced electric field is as follows: Check whether the coil inductance is within the range of the preset value of the coil inductance, and if not, adjust it by adjusting the number of coil turns and the size of the wire loop; By generating an induced electric field distribution map on the spherical shell of the cerebral cortex head model, the coil focus shape and position are obtained through the distribution map, and by judging the coil focus shape and position, it is judged whether the focus is the desired focus, and if not, the coil wiring is adjusted; Check whether the magnetic field value and the induced electric field value at the given depth are respectively within the range of the magnetic field value preset value at the given depth, that is, the induced electric field value preset value; A line segment is connected from the vertex of the stimulation focus of the ball model to the center of the ball, and the induced electric field attenuation curve on the line segment is calculated to evaluate the stimulation depth, and it is determined whether the depth is within a preset stimulation depth evaluation range.

8. The transcranial magnetic stimulation coil design method based on finite element calculation according to claim 7, characterized in that: The preset stimulation depth assessment range is: the distance d[E / 2] reached by half of the maximum induced electric field intensity E on the cortical surface at the focal point.

9. A transcranial magnetic stimulation coil design system based on finite element calculation, used to implement the transcranial magnetic stimulation coil design method based on finite element calculation as claimed in any one of claims 1 to 8, characterized in that: include: A cranial magnetic stimulation coil design parameter preset module (111), a finite element calculation module (112) and a design parameter verification module (113); The transcranial magnetic stimulation coil design parameter preset module (111) is used to preset the transcranial magnetic stimulation coil design parameters based on the stimulation site of the disease; The finite element calculation module (112) is used to import the head model, solve based on the eddy current field finite element method, and calculate the magnetic field and induced electric field of the transcranial magnetic stimulation coil; The design parameter verification module (113) is used to verify the design parameters of the transcranial magnetic stimulation coil according to the magnetic field and the induced electric field, so as to complete the design of the transcranial magnetic stimulation coil.

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