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

Abstract

This invention provides a method and system for designing transcranial magnetic stimulation (TMS) coils based on finite element method (FEB) calculations. Applied to the field of TMS technology, the method includes: obtaining stimulation sites based on the patient's actual symptoms, and pre-setting TMS coil design parameters based on these stimulation sites; importing a head model and calculating the magnetic field and induced electric field of the TMS coil using the eddy current finite element method; verifying the TMS coil design parameters based on the magnetic field and induced electric field; and completing the TMS coil design after verification. In this way, by pre-setting the coil shape and arranging the stimulation focus at the expected location, and by verifying the inductance, peak magnetic field, and induced electric field, the design results well meet the needs of actual engineering manufacturing. The design method is highly versatile and can design TMS coils with all known structures.

Description

Technical Field

[0001] This disclosure relates to the field of transcranial magnetic stimulation technology, and in particular to a design method and system for transcranial magnetic stimulation coils based on finite element analysis. Background Technology

[0002] Transcranial magnetic stimulation (TMS) is a treatment method used in the central and peripheral nervous systems. It utilizes time-varying pulsed electromagnetic fields to generate induced electric fields that act on the central nervous system, altering the membrane potential of cortical nerve cells and influencing brain metabolism and neural electrical activity, thereby triggering a series of physiological and biochemical reactions. TMS devices are currently widely used in neuroscience research and in the treatment of diseases in clinical departments such as neurology, psychiatry, and rehabilitation.

[0003] Traditional transcranial magnetic stimulation (TMS) coils, using circular and figure-eight shapes, have been widely used. Based on these two types of coils, new designs have been developed that modify the shape to achieve deeper or more focused field patterns, enabling deeper magnetic stimulation. Traditional coil shapes are simple, and the magnetic or induced electric fields are easily calculated analytically, facilitating the verification and validation of electric and magnetic field design parameters. While traditional circular and figure-eight coils offer good versatility, the increasing clinical demand for coils specifically designed for particular disease sites has created a bottleneck in the analytical calculation of electromagnetic parameters. This is especially true for the design of coils made of ferromagnetic materials with nonlinear BH characteristics, where analytical methods are even less effective.

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

[0005] This disclosure provides a transcranial magnetic stimulation coil design method and system based on finite element method. By directly solving the magnetic field and induced electric field using the finite element method, the design parameters of coils with any complex shape can be designed and verified, which at least solves the technical problems of poor universality and low practicality of existing design methods.

[0006] According to a first aspect of this disclosure, a method for designing transcranial magnetic stimulation coils based on finite element analysis is provided, comprising the following steps:

[0007] The stimulation sites are determined based on the patient's actual symptoms, and the design parameters of the transcranial magnetic stimulation coil are preset based on the stimulation sites of the symptoms;

[0008] Import the head model and solve it using the eddy current field finite element method to obtain the magnetic field and induced electric field of the transcranial magnetic stimulation coil;

[0009] Based on the magnetic field and induced electric field, the design parameters of the transcranial magnetic stimulation coil are checked. After the check is completed, the design of the transcranial magnetic stimulation coil is finished.

[0010] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the transcranial magnetic stimulation coil design parameters specifically include: coil focal point and wiring shape, preset coil inductance value, preset magnetic field value at a given depth, and preset induced electric field value.

[0011] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the coil focus and wiring shape design process is as follows: a high current density or an increase in ampere-turns is arranged at the stimulation focus location, and the current density or ampere-turns is reduced in other unrelated areas;

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

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

[0014] In addition to the aspects and any possible implementations described above, a further implementation is provided, in which a head model is imported, and the process of calculating the magnetic field and induced electric field of the transcranial magnetic stimulation coil based on the eddy current field finite element method is as follows:

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

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

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

[0018] Set the solution conditions and perform the calculation to obtain the coil's magnetic field and induced electric field.

[0019] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the head sphere model is a single-layer sphere model or a three-layer sphere model, wherein the single-layer sphere model has an electrical conductivity of 0.33 S / m, and the three-layer sphere model includes a scalp layer, a skull layer, and a cerebral cortex, wherein 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;

[0020] 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. The eddy current effect is selected by the head model.

[0021] In addition to the aspects and any possible implementations described above, an implementation is further provided in which the solution conditions include the frequency of the excitation source, the percentage error, and the proportion of encrypted subdivision units in each iteration;

[0022] The frequency range of the excitation source is 2.5 to 4 kHz.

[0023] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the process of verifying the design parameters of the transcranial magnetic stimulation coil based on the magnetic field and the induced electric field is as follows:

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

[0025] An induced electric field distribution map is generated on the spherical shell of the head model of the cerebral cortex. The shape and position of the coil focus are obtained from the distribution map. The shape and position of the coil focus are judged to determine whether the focus is the desired focus. If not, the coil wiring is adjusted.

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

[0027] A line segment connecting the apex of the stimulation focus of the head ball model to the center of the ball is used to calculate the induced electric field attenuation curve on the line segment to evaluate the stimulation depth, and to determine whether the depth is within the preset stimulation depth evaluation range.

[0028] In addition to the aspects described above and any possible implementation, a further implementation is provided in which 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.

[0029] According to a second aspect of this disclosure, a transcranial magnetic stimulation coil design system based on finite element calculation is provided, comprising: a transcranial magnetic stimulation coil design parameter preset module, a finite element calculation module, and a design parameter verification 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 stimulation site of the symptom.

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

[0032] The design parameter verification module is used to verify the design parameters of the transcranial magnetic stimulation coil based on the magnetic field and the induced electric field, thereby completing the design of the transcranial magnetic stimulation coil.

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

[0034] This invention pre-sets the coil shape and arranges the stimulation focus at the expected location. By verifying the inductance, peak magnetic field, and induced electric field, the design results well meet the needs of actual engineering manufacturing. The design method is highly versatile and can design transcranial magnetic stimulation coils with all known structures. It is suitable for designing coils for deep magnetic stimulation with a focus and has greater advantages in the design of nonlinear BH characteristic ferromagnetic material stimulation coils.

[0035] It should be understood that the description in the Summary of the Invention is not intended to limit the key or essential features of the embodiments of this disclosure, nor is it intended to restrict the scope of this disclosure. Other features of this disclosure will become readily apparent from the following description. Attached Figure Description

[0036] The above and other features, advantages, and aspects of the embodiments of this disclosure will become more apparent from the accompanying drawings and the following detailed description. The drawings are provided for a better understanding of the invention and are not intended to limit the scope of this disclosure. In the drawings, the same or similar reference numerals denote the same or similar elements, wherein:

[0037] Figure 1 A schematic flowchart of a transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure is shown.

[0038] Figure 2 A schematic diagram of a three-layer head model structure based on finite element simulation is shown for a transcranial magnetic stimulation coil design method according to an embodiment of the present disclosure.

[0039] Figure 3 This diagram illustrates a finite element simulation of a single-pulse sinusoidal alternating current excitation circuit of a transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure.

[0040] Figure 4 A schematic diagram of a transcranial magnetic stimulation coil design system based on finite element calculation according to an embodiment of the present disclosure is shown.

[0041] Figure 5 The following is an example of the design and verification of the H-coil wiring diagram according to Embodiment 1 of a transcranial magnetic stimulation coil design method based on finite element calculation, based on the present disclosure.

[0042] Figure 6 The diagram shows the induced electric field distribution of the H coil 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 This illustration shows an improved wiring 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 The diagram shows the induced electric field distribution obtained by adjusting the wiring of the H coil after embodiment 1 of the transcranial magnetic stimulation coil design method based on finite element calculation according to the present disclosure.

[0045] Figure 9 This paper shows a schematic diagram of the magnetic field distribution in the XOZ plane section of a single-layer sphere model obtained by adjusting 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 This paper shows a schematic diagram of the induced electric field distribution in the XOZ plane section of a single-layer sphere model obtained by adjusting the wiring of the H coil after adjusting the wiring according to Embodiment 1 of the present disclosure of a transcranial magnetic stimulation coil design method based on finite element calculation.

[0047] Figure 11 The illustration shows a current routing diagram of a transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure, with the focal point located in the prefrontal cortex. The focal point is equipped with double-layer routing, while other areas are equipped with single-layer routing, and the current routing is distributed.

[0048] Figure 12 This illustration shows a schematic diagram of the induced electric field distribution obtained by current wiring with the focus located in the prefrontal cortex, according to Embodiment 2 of a transcranial magnetic stimulation coil design method based on finite element calculation according to an embodiment of the present disclosure.

[0049] Figure 13 This illustration shows a schematic diagram of the magnetic field distribution in the XOZ plane cross-section under a three-layer sphere model of a 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 cortex current wiring.

[0050] Figure 14 This paper presents a schematic diagram of the induced electric field distribution in the XOZ plane profile under a three-layer sphere model of a 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 cortex current wiring.

[0051] Figure 15 The diagram shows a schematic of the attenuation curve of the induced electric field on a line segment from the apex of the stimulation focus to the center of the sphere, according to 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 The diagram shows a simulation model wiring diagram of a single-layer spherical animal coil with a ferromagnetic core, according to 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 The diagram shows a schematic of the BH curve of the silicon steel sheet used for the coil 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 The diagram shows a schematic of the magnetic field distribution obtained by wiring a simulation model of a single-layer spherical animal coil with a ferromagnetic core, according to 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 The diagram shows the induced electric field distribution obtained by wiring a simulation model of a single-layer spherical animal coil with a ferromagnetic core, according to 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 The diagram illustrates the induced electric field distribution in the YOZ plane profile obtained by wiring a simulation model of a single-layer spherical animal coil with a ferromagnetic core, according to 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 The diagram shows a schematic of the attenuation curve of the induced electric field on line segment 12 from the apex of the stimulation focal point to the center of the sphere, according to 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

[0058] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0059] In the field of transcranial magnetic stimulation coil design technology, CC et al. (Phys.Med.Biol.62,2017, pp73–90) proposed a method that incorporates the quasi-static current's flow function into the boundary element method to solve for the field source of the wiring based on the field target. This method can be used for the design of transcranial magnetic stimulation coils of arbitrary shapes. However, this method does not address peak current limitations, inductance, or stimulation depth.

[0060] Non-traditional coils, such as H-coils (US 2014 / 0235927 A1, US 9254394 B2), place greater emphasis on matching the head shape to achieve deeper stimulation. Due to their complex shapes, these coils are difficult to calculate analytically, and the field distribution is not given in the patents. Yiftach Roth (Journal of Clinical Neurophysiology 19(4):361–370, 2002) wrote a field calculation program for H-coils using Mathematicav 4.0, but the distribution of the magnetic field and induced electric field is not given in the literature. For key parameters of transcranial magnetic stimulation coil design, such as inductance, magnetic field and induced electric field, focusing has not been studied. 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 standards for evaluating deep characteristics. The H-coil wiring method used in this patent determines the optimal wire spacing of the H-coil at different positions in the anterior, top and side of the frontal lobe. Important parameters for coil design, such as the wiring method at the focal point, coil inductance, and magnetic field value at a given depth, are not described.

[0061] This invention pre-sets the coil focus based on the stimulation target point and provides current routing principles; it gives the desired design parameters: coil inductance L, given position magnetic field and induced electric field E; it uses the finite element method to calculate and verify the above three parameters, and obtains the design output of a transcranial magnetic stimulation coil of arbitrary shape. The design method is highly versatile and can design transcranial magnetic stimulation coils of any known shape and with any focus. It is suitable for the design of deep magnetic stimulation coils with a focus and has greater advantages in the design of nonlinear BH characteristic ferromagnetic material stimulation coils.

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

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

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

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

[0066] Specifically, the design of the coil focus position is related to the location of the magnetic stimulation treatment area for the ailment. For example, in clinical applications of mental disorders, the magnetic stimulation treatment areas are mainly the right dorsolateral prefrontal cortex and the left dorsolateral prefrontal cortex; for patients with movement disorders, the stimulation area is the motor area M1 or the supplementary motor area; and for patients with tinnitus, the stimulation area is the temporal lobe or temporoparietal cortex. According to Faraday's law of electromagnetic induction, regions with high source current density also have high induced current density due to eddy current effects. The induced current distribution is a mirror image of the coil current distribution. Based on the above theoretical foundation, this embodiment adopts the following principle for the wiring of the induced electric field focus of the magnetic stimulation coil: increasing the ampere-turns at the stimulation focus and decreasing the ampere-turns in other unrelated areas.

[0067] (2) Selection of coil inductance

[0068] The selection of coil inductance is a crucial parameter for transcranial magnetic stimulation (TMS) devices. The coil inductance affects parameters such as the peak current of the discharge circuit, the magnitude of the pulse magnetic field peak, the pulse magnetic field width, and the rate of magnetic field change. Based on industry product specifications, the effective coil inductance value set in this invention is within the range of 15-25 μH. When the coil inductance value is higher or lower than this range, the design wiring needs to be adjusted, and then recalculated and verified.

[0069] (3) Magnetic field value and induced electric field value at a given depth

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

[0071] (4) Magnetic field confinement and electric field confinement

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

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

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

[0075] In this embodiment, the mainstream finite element method (FEM) software for electromagnetic field analysis includes Ansys Maxwell and Comsol, but the solution method of this invention is not limited to specific FEM tools. A finite element method engineering project is established, and the solution type is set to eddy current field.

[0076] First, import the coil model and the head ball model, and set the boundary area;

[0077] When modeling the coil, a detailed model with wiring is created. A detailed model with wiring facilitates adjustments to wiring positions and the number of turns. Copper is chosen as the coil material. Based on the mirror relationship between the induced current distribution and the coil current distribution, when wiring the coil with a focal point, the number of current turns is increased at the focal point to increase the current density, while the current density is decreased at non-focal points.

[0078] like Figure 2 As shown, the head spherical model can be a single-layer spherical model or a three-layer spherical model. The single-layer spherical model only simulates a simplified scalp structure, with a conductivity set to 0.33 S / m. It has a small mesh and a fast solution speed. The three-layer spherical model simulates the human head structure. From the outside in, the first spherical shell 1 is the scalp layer, with a conductivity set to 0.33 S / m; the second spherical shell 2 is the skull layer, with a conductivity set to 0.0042 S / m; and the third spherical shell 3 is the cerebral cortex (containing cerebrospinal fluid), with a combined conductivity set to 0.75 S / m.

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

[0080] Secondly, a head model for excitation and eddy current effects is set up;

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

[0082] Next, set up the inductance calculation current matrix;

[0083] To set the current calculation matrix to the excitation current sources in the coil, all excitation sources need to be selected. The inductance value of the coil can be obtained from the current source matrix.

[0084] Then, the grid is divided;

[0085] Mesh generation can be adaptive, thereby improving computation speed. Alternatively, the mesh density can be increased based on the computational accuracy at the target point.

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

[0087] In the solver settings, set the percentage error and the proportion of meshed cells to be refined in each iteration. Set the excitation source frequency in the solver to 2.5–4 kHz, typically 3 kHz.

[0088] S103. Based on the finite element calculation results, the design parameters of the transcranial magnetic stimulation coil are checked, and the electromagnetic design of the coil is completed.

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

[0090] For coils less than 15μH, increase the number of coil turns or increase the wire loop size; for coils greater than 25μH, decrease the number of coil turns or decrease the wire loop size.

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

[0092] An induced electric field distribution map is generated on the spherical shell of a head model of the cerebral cortex. The distribution map shows the location and size of the coil focal point. Observe the shape and position of the focal point to see if it is the electric field focal point of the desired target area. If the position is incorrect, the coil wiring should be adjusted so that the stimulated target point is consistent with the location of the induced electric field focal point.

[0093] The peak value of the induced electric field at the target site in the cerebral cortex of the head model must be no less than 70V / m. If it is lower than 70V / m, the pre-set coil shape cannot meet the design requirements.

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

[0095] The peak value of the magnetic field at the target site in the cerebral cortex of the head model must be no less than 0.2T. If it is lower than 0.2T, the pre-set coil shape cannot meet the design requirements.

[0096] (4) Assessment of stimulus depth

[0097] A common criterion for assessing stimulation depth is the distance d[E / 2] reached by half the maximum induced electric field intensity E at the focal point on the cortical surface. The stimulation depth is assessed by calculating the attenuation curve of the induced electric field along the line segment from the vertex of the stimulation focal point to the center of the sphere in the connector model. The stimulation depth can be visually obtained from the attenuation curve of the induced electric field.

[0098] When the inductance, focal shape, stimulation depth, and peak values ​​of the induced electric and magnetic fields all meet the predetermined specifications, the electromagnetic design of the coil is complete and can be derived for engineering design and manufacturing.

[0099] like Figure 4 As 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 stimulation site of the symptom.

[0101] The finite element calculation module 112 is used to construct the head model and solve it using the vortex field finite element method to obtain the finite element calculation results;

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

[0103] Example 1

[0104] In this embodiment, the transcranial magnetic stimulation (TMS) head coil is positioned with its focal point located in the frontal lobe, and the wiring method follows US 2014 / 0235927 A1. The current direction is as follows. Figure 5 As indicated by the arrow, a single-layer sphere model is used.

[0105] according to Figure 2 The current curve shown is used to apply excitation, and the excitation current is included in the parameter matrix to calculate the inductance. The eddy current field calculation uses a head-sphere model. After solving using the finite element method, the induced electric field distribution is obtained as shown below. Figure 6 As shown, the peak electric field focal position meets the design requirements, with a maximum peak value of 169.7176 V / m. However, the obtained inductance is 12.4 μH < 15 μH, which does not meet the design criteria and requires design improvement.

[0106] Figure 7 To improve the wiring of the H coil obtained after adjusting the wiring, its wiring is as follows: Figure 5 Based on this, an additional turn of winding was added, such as Figure 7 As shown in Figure 4. Finite element calculations were performed again. Evaluation and analysis of design results:

[0107] The inductance was increased to 19μH, which meets the design requirements.

[0108] induced electric field distribution as follows Figure 8 As shown, the focal point is located in the desired area of ​​the prefrontal cortex, meeting the design requirements.

[0109] The magnetic field distribution in the XOZ plane profile under a single-layer sphere model is as follows: Figure 9 As shown, the upper hemisphere region all satisfy the condition of 0.2T or higher, thus meeting the magnetic field requirements.

[0110] The induced electric field distribution in the XOZ plane profile under a single-layer sphere model is as follows: Figure 10 As shown. The induced electric field at the focal position of the transcranial magnetic stimulation coil is as diverse as possible, while the induced electric field at non-focal positions is dispersed as much as possible. Through... Figure 10 The induced electric field distribution shows that in the area indicated by the ellipse at position 5, the induced electric field value for irrelevant stimuli is relatively large, approaching the value at the focal point. This is undesirable for the coil design and requires improvement.

[0111] Example 2

[0112] In this embodiment, based on the principle that the distribution of induced current and the distribution of coil current are mirror images, the coil wiring has been improved, such as... Figure 11 As shown. In Figure 11 At position 6, the focal point employs double-layer wiring to increase the ampere-turns, thereby obtaining a stronger and more concentrated induced electric field focus. The current direction is shown by the arrow in the figure. Other irrelevant areas use distributed wiring to reduce irrelevant electric fields. Compared to existing winding methods, the wiring method proposed in this invention mainly uses spherical ring wiring, which is simpler to wind and easier to manufacture.

[0113] The intermediate processes, such as adjusting the number of coil turns, are not detailed here. The adjustment is based on the inductance being within the range of 15-25 μH. The final coil inductance value is 19.4 μH, which meets the inductance requirements. The distribution is as follows... Figure 12 As shown, the focal point is located below the double-layer current-concentrated wiring, which is in line with the design expectation.

[0114] Example 2 used a three-layer sphere model for finite element calculation, and the obtained magnetic field distribution is as follows: Figure 13 As shown, the upper half of the sphere model meets the design requirement of greater than 0.2T. Figure 14 The induced electric field distribution in the XOZ plane profile under the three-layer sphere model can be seen. Figure 14 The electric field in the irrelevant stimulation area at location 9 was significantly weakened. Figure 14 The central area is 7. Figure 14 In the middle, 8 is the line segment connecting the focal vertex to the center of the sphere. Figure 15 To calculate the attenuation curve of the induced electric field on line segment 8, we can obtain that the maximum induced electric field intensity E at the focal point of the cortical surface is 205 V / m, half intensity is 102.5, and the stimulation depth d[E / 2] at the focal point is 27.5 mm.

[0115] Example 3

[0116] This embodiment demonstrates the ability of the present invention to design coils made of ferromagnetic materials. Example 3 shows a coil design for use in mouse animal experiments.

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

[0118] according to Figure 2 The current curve shown is used to apply excitation, and the excitation current is included in the parameter matrix to calculate the inductance. The head sphere model is selected for eddy current field calculation.

[0119] Coil 11 can be optimized using the number of turns as the parameter during finite element analysis, with a constraint of not less than 15uH. The final inductance is 15.8uH, and the coil is divided into two layers, with 13 turns in each layer.

[0120] Based on the finite element calculation results, parameter verification is added in the post-processing.

[0121] Figure 18 The magnetic field distribution of the sphere model was checked, and it can be seen that the magnetic field distribution in the entire sphere model is greater than 0.2T, which meets the design requirements.

[0122] Figure 19 The electric field distribution on the surface of the sphere model was checked, and no induced electric field focus was found. The peak electric field is distributed in a ring-like pattern on the upper half of the sphere, with the highest peak field of 85.3248 V / m > 70 V / m, which satisfies the constraint conditions.

[0123] Figure 20 To represent the induced electric field distribution in the YOZ plane profile, segment 13 is a line segment passing through the focus to the center of the sphere. The electric field decay curve along line segment 13 is shown below. Figure 21 As shown, the depth d[E / 2] = 4.2 mm is half the maximum induced electric field intensity E on the skin surface at the focal point, which can be directly measured.

[0124] It should be noted that, for the sake of simplicity, the foregoing method embodiments are all described as a series of actions. However, those skilled in the art should understand that this disclosure is not limited to the described order of actions, because according to this disclosure, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are all optional embodiments, and the actions and modules involved are not necessarily essential to this disclosure.

[0125] It should be understood that the various forms of processes shown above can be used to rearrange, add, or delete steps. For example, the steps described in this disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this disclosure can be achieved, and this is not limited herein.

[0126] The specific embodiments described above do not constitute a limitation on the scope of protection of this 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 this disclosure should be included within the scope of protection of this disclosure.

Claims

1. A method for designing transcranial magnetic stimulation coils based on finite element analysis, characterized in that, Includes the following steps: The stimulation sites are determined based on the patient's actual symptoms, and the design parameters of the transcranial magnetic stimulation coil are preset based on the stimulation sites of the symptoms; Import the head model and solve it using the eddy current field finite element method to obtain the magnetic field and induced electric field of the transcranial magnetic stimulation coil; Based on the magnetic field and induced electric field, the design parameters of the transcranial magnetic stimulation coil are checked. After the check is completed, the design of the transcranial magnetic stimulation coil is finished. The specific design parameters of the transcranial magnetic stimulation coil include: coil focal point and wiring shape, preset coil inductance value, preset magnetic field value at a given depth, and preset induced electric field value. The correspondence between the stimulation sites and the symptoms is as follows: mental disorders correspond to the right dorsolateral prefrontal cortex or the left dorsolateral prefrontal cortex; motor disorders correspond to the motor area M1 or the auxiliary motor area; and tinnitus corresponds to the temporal lobe or the temporoparietal cortex. The coil focus and wiring shape are designed based on the principle that the induced current distribution and the coil current distribution have a mirror relationship. The design process for the coil focus and wiring shape is as follows: a high current density or an increase in ampere-turns is arranged at the stimulation focus, while the current density or ampere-turns is reduced in other unrelated areas. The preset value of the coil inductance is in the range of 15-25μH; The preset value of the magnetic field at the given depth is not less than 0.2T, and the preset value of the induced electric field is not less than 70V / m; Importing the head model and solving it using the eddy current finite element method, the process of calculating the magnetic field and induced electric field of the transcranial magnetic stimulation coil is as follows: Establish a finite element method engineering project and set the solution type to eddy current field; Import the coil model and the head ball model, set the boundary region, and set the electrical excitation conditions and eddy current effect; Set the inductance and calculate the current matrix, then select adaptive meshing to complete the mesh generation; The actual inductance value of the coil is calculated based on the current matrix. Set the solution conditions and perform the calculation to obtain the coil's magnetic field and induced electric field. The process of verifying the design parameters of the transcranial magnetic stimulation coil based on the magnetic field and the induced electric field is as follows: Check if the coil inductance is within the preset value. If not, adjust it by adjusting the number of coil turns and the wire loop size. An induced electric field distribution map is generated on the spherical shell of the head model of the cerebral cortex. The shape and position of the coil focus are obtained from the distribution map. The shape and position of the coil focus are judged to determine whether the focus is the desired focus. If not, the coil wiring is adjusted. Check whether the magnetic field value at the given depth and the induced electric field value are respectively within the preset value of the magnetic field value at the given depth, i.e., the preset value of the induced electric field value. Connect the apex of the stimulation focus of the head ball model to the center of the ball, calculate the induced electric field attenuation curve on the line segment to evaluate the stimulation depth, and determine whether the depth is within the preset stimulation depth evaluation range. 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; The head sphere model is either a single-layer sphere model or a three-layer sphere model. The single-layer sphere model has a conductivity of 0.33 S / m, and the three-layer sphere model includes a scalp layer, a skull layer, and a cerebral cortex layer. The conductivity of the scalp layer, skull layer, and cerebral cortex layer 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 2.5~4kHz. The eddy current effect is selected by the head model.

2. The transcranial magnetic stimulation coil design method based on finite element calculation according to claim 1, characterized in that, The solution conditions include the frequency of the excitation source, the percentage error, and the proportion of encrypted subdivision units in each iteration; The frequency range of the excitation source is 2.5~4kHz.

3. A transcranial magnetic stimulation coil design system based on finite element method (FEM) calculation, used to implement the transcranial magnetic stimulation coil design method based on FEM calculation as described in any one of claims 1-2, characterized in that, include: The design parameters preset module (111), the finite element calculation module (112), and the design parameter verification module (113) for the cranial magnetic stimulation coil are included. 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 symptom; The finite element calculation module (112) is used to import the head model, solve it 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 based on the magnetic field and the induced electric field, and to complete the design of the transcranial magnetic stimulation coil.

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