High focusing degree deep transcranial magnetic stimulation coil based on asymmetric topology

Abstract

This invention discloses a high-focusing deep transcranial magnetic stimulation (TMS) coil based on asymmetric topology, comprising at least two mutually coupled coil loops, wherein the parameters of at least one coil loop differ from the others, causing the magnetic induction peak of the TMS coil to deviate from its geometric symmetry center. The parameters of the coil loop include at least one of geometric dimensions, number of winding turns, and shape topology. This invention fundamentally reshapes the spatial distribution of the induced magnetic field, optimizing the directional shift, depth, and focusing performance of the stimulation hotspot without significantly increasing system complexity or introducing new constraints. It achieves better matching for specific nerve fiber pathways, realizing directional and more precise brain stimulation, and reducing the intensity of stimulation in non-target areas. This meets the diverse and individualized treatment needs of different diseases, patients, and brain regions, providing a new technical path for high-precision TMS treatment.

Description

Technical Field

[0001] This invention belongs to the fields of biomedical engineering and power electronics technology, and relates to a series of asymmetric high-focus deep transcranial magnetic stimulation (TMS) coils for non-invasive brain stimulation, particularly a high-focus deep transcranial magnetic stimulation coil based on asymmetric topology. Background Technology

[0002] In the medical field, transcranial magnetic stimulation (TMS), a non-invasive neuromodulation technique that uses time-varying magnetic fields to induce electric fields in the cerebral cortex to regulate neuronal activity, has wide applications in clinical treatment of depression, Parkinson's disease, post-stroke rehabilitation, and brain science research. The core component of this technology is the magnetic stimulation coil, designed to generate a magnetic field or induced electric field with controllable intensity, spatial distribution, and temporal characteristics for non-invasive, targeted electromagnetic stimulation of target areas in biological tissues.

[0003] The geometry of the stimulation coil directly affects the distribution characteristics of the induced electric field, including key parameters such as focusing and stimulation depth. Currently, most mainstream TMS coils have symmetrical structures, primarily categorized as circular coils, figure-eight coils, slinky coils, and cloverleaf coils. While these symmetrical structures achieve focusing to some extent, they have inherent physical limitations, restricting the maximum stimulation point to directly below the coil's geometric center. This means that in clinical treatment, to stimulate a target point a few millimeters off-center, the operator must frequently and significantly move and reposition the entire coil. This is not only time-consuming and dependent on the operator's experience, but also makes it difficult to guarantee positioning accuracy. Even slight patient movements can easily cause target point deviation, severely impacting treatment efficacy and repeatability.

[0004] Furthermore, symmetrical coils face a fundamental contradiction in their design. To stimulate deeper brain tissue, the coil size must be increased to slow down magnetic field attenuation. However, this inevitably leads to dispersion of the stimulation area, reduced focus, and activation of more unnecessary superficial cortical layers, causing side effects such as facial twitching, increasing patient discomfort, and reducing treatment effectiveness. Conversely, pursuing high focus sacrifices stimulation depth.

[0005] To address these shortcomings, existing improvements include employing multi-coil array systems and introducing adjustable mechanical structures. However, these improvements often fail to fundamentally overcome the physical limitations of symmetrical magnetic circuit configurations, instead introducing new complexities and obstacles to clinical application. For example, multi-coil array control systems are complex and costly, with severe electromagnetic coupling interference between units; adjustable mechanical structures have slow dynamic response and insufficient positioning accuracy, making them prone to displacement during treatment.

[0006] Therefore, there is an urgent clinical need for a new coil design method that can fundamentally break through the limitations of symmetrical magnetic circuits in terms of hardware structure, achieve flexible adjustment of stimulation targets, balance depth and focus, and adapt to the complex anatomical orientation of the cerebral cortex. Summary of the Invention

[0007] The purpose of this invention is to provide a high-focusing deep transcranial magnetic stimulation coil based on asymmetric topology. This coil with an asymmetric structure fundamentally reshapes the spatial distribution of the induced magnetic field. Without significantly increasing system complexity or introducing new constraints, it optimizes the directional shift, depth, and focusing performance of the stimulation hotspot, achieving better matching for specific nerve fiber pathways. This enables directional and more precise brain stimulation, reduces the intensity of stimulation in non-target areas, and meets the diverse and individualized treatment needs of different diseases, patients, and brain regions. It provides a new technical path for high-precision TMS treatment and solves the clinical bottlenecks of traditional symmetrical coils, which suffer from fixed stimulation targets, difficulty in balancing stimulation depth and focus, and inability to flexibly adapt to the complex pathways of the cerebral cortex due to structural symmetry.

[0008] To achieve the above objectives, the solution of the present invention is:

[0009] A high-focusing deep transcranial magnetic stimulation coil based on asymmetric topology includes at least two mutually coupled coil loops, wherein the parameters of at least one coil loop are different from those of the other coil loops, causing the magnetic induction peak of the transcranial magnetic stimulation coil to deviate from its geometric symmetry center and reduce the stimulation intensity to non-target areas; wherein the parameters of the coil loop include at least one of geometric dimensions, number of winding turns, and shape topology.

[0010] The coil mentioned above includes a first coil wing and a second coil wing. The first coil wing is elliptical and the second coil wing is circular. The two are connected in series at the point of tangency through a central bridging section. The number of turns of the first coil wing and the second coil wing are different.

[0011] The aforementioned central bridging section is made of copper.

[0012] The aforementioned coil includes a third to a sixth coil wing, which are arranged in a cross shape. The third coil wing is elliptical, while the fourth to sixth coil wings are all circular and have the same number of winding turns. The number of winding turns of the third coil wing is less than the number of winding turns of the fourth to sixth coil wings.

[0013] The third to sixth coil wings mentioned above are located in the same plane, and an insulating bridging structure is provided at the center intersection.

[0014] The third coil wing and the fifth coil wing are arranged opposite each other and are located in the first plane; the fourth coil wing and the sixth coil wing are arranged opposite each other and are located in the second plane; the first plane and the second plane are adjacent to each other vertically.

[0015] The aforementioned coil includes a seventh coil wing and an eighth coil wing. Both the seventh and eighth coil wings are D-shaped and have different geometric dimensions. They are integrally wound with continuous conductors, and the straight-edge conductor portions of the two are parallel to each other and are tightly bonded after being physically isolated by an insulating medium.

[0016] By adopting the above scheme, the present invention can control the shift of the peak value of the induced magnetic field by adjusting asymmetric parameters such as radius ratio, turn density and shape factor, thereby achieving target adjustment in one-dimensional or two-dimensional direction, better matching the complex orientation of the cerebral cortex, and effectively avoiding non-target brain tissue, reducing adverse reactions during stimulation, and meeting the diverse needs for stimulation depth, focus and directionality in different clinical scenarios.

[0017] This invention has at least the following beneficial effects:

[0018] 1. Addressing the limitations of rigid target points in traditional coils, this invention achieves controllable shifting of the magnetic field focus by introducing an asymmetric design in radius, number of turns, and shape. Fine-tuning of the stimulation target point can be achieved by selecting coils with different asymmetric characteristics, avoiding frequent and large-amplitude physical displacement operations, thus improving the convenience and positioning accuracy of treatment and meeting the needs of individualized precision treatment.

[0019] 2. Compared with traditional symmetrical coils that have to be enlarged in order to pursue stimulation depth, the present invention adopts an asymmetrical structure. Based on the synergistic effect principle of "large coil boosting and small coil focusing", while maintaining effective penetration depth, it reduces the magnetic field distribution range and intensity of the epidermal layer, reduces additional stimulation to non-target areas, thereby reducing or avoiding adverse reactions such as headaches and convulsions during treatment, and improving the comfort and tolerance of treatment.

[0020] 3. This invention provides a richer selection of focusing patterns in one-dimensional and two-dimensional dimensions through the figure-eight asymmetric structure and the four-leaf clover asymmetric structure, respectively. It can generate anisotropic electric field distributions with specific directions and can perform directional stimulation according to the complex orientation and crossing relationship of nerve fiber bundles, showing unique technical advantages in fine neuromodulation applications.

[0021] 4. Compared to traditional circular coils where only a single point of current superposition occurs at the center tangent, resulting in low energy utilization, this invention employs a double-D asymmetric structure to achieve a balance between high field strength and low power consumption. This invention utilizes a parallel superposition structure of straight edges to straight edges, significantly improving electromagnetic conversion efficiency while changing the stimulation focus. To generate the same stimulation intensity, the required excitation current is reduced, effectively suppressing coil heat generation and improving the stability and safety of the equipment.

[0022] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention;

[0024] Figure 2 yes Figure 1 Simulation contour plot of magnetic flux density distribution of the structure shown in the XZ plane;

[0025] Figure 3 It is a simulation cloud map of the magnetic induction intensity distribution of the symmetrical figure-eight structure in the XZ plane;

[0026] Figure 4 This is a schematic diagram of the structure of Embodiment 2 of the present invention;

[0027] Figure 5 yes Figure 2 Simulation contour plot of magnetic flux density distribution of the structure shown in the XY plane;

[0028] Figure 6 It is a simulation cloud map of the magnetic induction intensity distribution of a symmetrical four-leaf clover structure in the XY plane;

[0029] Figure 7 This is a schematic diagram of the structure of Embodiment 3 of the present invention;

[0030] Figure 8 This is a simulation cloud map of the magnetic induction intensity distribution of an asymmetric double-D structure in the XZ plane. Detailed Implementation

[0031] This invention provides a high-focus deep transcranial magnetic stimulation coil based on asymmetric topology, comprising at least two mutually coupled coil wings, wherein at least one of the coil wings has a differentiated design in terms of geometry, number of turns of winding, or shape topology, so that it forms an asymmetric magnetic field generating structure with the other coil wings, thereby breaking the symmetry of the magnetic field distribution, achieving controlled shift of the peak value of the induced magnetic field, and reducing the stimulation intensity to non-target areas.

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1:

[0034] Please see Figures 1-3 To address the need for focus offset along a one-dimensional axis, this invention provides a technical solution: an asymmetric figure-eight transcranial magnetic stimulation coil. This embodiment includes a first coil wing and a second coil wing, which are tangent at their geometric center and connected in series via a copper central bridging segment to form an asymmetric figure-eight-like structure.

[0035] In this embodiment, the first and second coil wings are unequal in size, topology, and number of turns. The first coil wing is elliptical, and the second coil wing is circular, with the smaller radius coil wing having a higher turn density. The larger radius coil wing generates a deep background magnetic field with a low attenuation rate, while the smaller radius coil wing with a high turn density generates a high-gradient focusing magnetic field. The superposition of these two elements causes a controlled shift in the peak value of the induced magnetic field, thereby achieving fine-tuning of the target point in one dimension, reducing the magnetic field intensity in non-target areas such as the scalp and skull, and greatly alleviating patient discomfort.

[0036] In an asymmetric figure-eight structure, the total magnetic field Magnetic field generated by the first coil wing The magnetic field generated by the second coil wing It is formed by the superposition of vectors, and its mathematical representation is:

[0037]

[0038] According to the Biot-Savart law in electromagnetism, the magnetic field generated by a current-carrying coil in space is not only proportional to the excitation current but also strictly constrained by the coil's geometric parameters. For a circular coil in space, the magnetic field strength along its z-axis is... With distance The attenuation relationship satisfies the formula:

[0039]

[0040] in the formula The number of turns in the winding. To excite the current, Let be the radius of the coil. From this formula, it can be seen that the radius... The larger the coil, the greater its magnetic field becomes with distance. The slower the decay, the deeper the background magnetic field can be provided. In small-radius coils, the magnetic field decays rapidly with increasing distance, but has an extremely high spatial gradient in the near-field region, which can sharpen the focusing effect. When the magnetic fields of the large and small wings are superimposed, the peak position of the induced electric field is... It will no longer be located at the geometric center, but will satisfy the following offset relationship:

[0041]

[0042] in, This is the geometric center distance between the centers of the first and second coils. The asymmetry parameter ratio is adjusted... This causes the maximum induced electric field to shift in a controlled manner towards the smaller coil. This allows for precise movement of the target, while the slow decay characteristics of the large coil maintain the effective stimulation intensity of deep brain regions.

[0043] contrast Figure 2 and Figure 3 As can be seen, under the same pulse excitation of 800A, the maximum magnetic induction intensity of Example 1, i.e., the area within the red box, is not located directly below the geometric boundary between the two coils, but is significantly shifted laterally to the right side of the smaller radius coil. As shown in the figure, the maximum induction intensity of the asymmetric figure-eight coil is 265.1 mT, while that of the symmetrical figure-eight coil is 269.3 mT, both essentially the same. However, the magnetic field contour lines below the smaller radius coil on the right are denser than those of the symmetrical figure-eight coil, indicating a steeper and more focused magnetic field gradient on that side. Furthermore, comparing the magnetic field intensity of the right coil, i.e., the area within the yellow box (the non-target area), it is clear that the asymmetric figure-eight coil has a smaller magnetic field intensity and a shallower stimulation depth. This indicates that this design can maintain effective stimulation intensity in deep tissues while reducing the superficial stimulation area, thus mitigating therapeutic side effects.

[0044] Example 2:

[0045] Please see Figures 4-6To address the need for focus shift in a two-dimensional plane, this invention provides a technical solution: an asymmetric cloverleaf-shaped transcranial magnetic stimulation coil array. This array comprises four coil wings arranged in a cross shape, corresponding to four different quadrants of the plane. The main coil wing located in a specific quadrant has a larger physical size than the secondary coil wings in the other three quadrants, but fewer turns. Because the larger wing generates a stronger magnetic thrust, the induced electric field converging at the center is no longer a perfect cross, but is pushed diagonally towards a specific quadrant, allowing the stimulation target point to shift within the two-dimensional plane to adapt to the complex sulci and gyri of different quadrants of the cerebral cortex. In terms of arrangement, the four coil wings can be located in the same plane within the four quadrants, with an insulating bridging structure at the central intersection; or adjacent coil wings can be located in adjacent first and second planes to avoid wire interference. This embodiment shows the second arrangement.

[0046] In the superposition of spatial magnetic fields, the overall magnetic field distribution in the central working area is the result of the vector synthesis of the magnetic fields generated by the four blades. Let the magnetic induction intensity components generated by the four blades in the central region be as follows: , , and The resulting magnetic induction intensity It can be represented as:

[0047]

[0048] In a traditional symmetrical four-leaf clover coil, the four magnetic field components are of equal magnitude, and the focal point of the combined magnetic field is strictly located at the geometric center, with a maximum magnetic field strength of 369.7 mT. However, in this embodiment, as... Figure 5 As shown, the large-sized main blade, due to its larger spatial envelope area, generates a magnetic field component that dominates in amplitude, completely disrupting the spatial balance of the composite vector. The large-sized main coil blade produces a stronger spatial magnetic flux thrust, forcing the region of highest magnetic induction intensity converging at the center to undergo a two-dimensional vector displacement along the diagonal direction, with a value of 371.6 mT. Ultimately, this magnetic field shift directly determines the shift of the induced electric field.

[0049] By comparison Figure 4 Asymmetric four-leaf clover magnetic field simulation cloud map and Figure 5The simulated magnetic field cloud diagram of the symmetrical four-leaf clover pattern clearly shows that the magnetic field hotspots of the asymmetrical array exhibit significant directional shifts, and under the same pulse excitation of 800A, the maximum magnetic induction intensity is greater than that of the symmetrical four-leaf clover array. Simultaneously, the magnetic field intensity and stimulation depth of the other three non-target coils are significantly lower than those of the other three coils in the symmetrical four-leaf clover pattern. This demonstrates that this structural characteristic not only increases the maximum magnetic induction intensity and reduces the stimulation intensity on non-target areas, but also allows for more precise positioning of the target point of the induced electric field that ultimately exerts the stimulation effect within a two-dimensional plane, thereby better matching the cerebral cortical sulci and chiasmatic tracts with specific tilt angles.

[0050] Example 3:

[0051] Please see Figures 7-8 To address the need for high-gradient sharpening and focusing, this invention provides a technical solution: an asymmetric double-D-shaped transcranial magnetic stimulation coil. To further improve the conversion efficiency of electromagnetic energy and the focusing gradient in the central region, this embodiment modifies the basic circular coil into a D-shaped topology. The device consists of a first D-shaped coil wing with a larger envelope area and a second D-shaped coil wing with a smaller envelope area. In actual physical entities, the two coil wings are typically integrally wound with continuous conductors, with their straight-edge conductor portions spatially parallel and tightly fitted together after being physically isolated by an insulating medium; in the electromagnetic equivalent model, such as... Figure 7 As shown in the simulation model, this special structure manifests as two D-shaped envelope surfaces with their straight edges tangent. This special structure transforms the point contact of a traditional circular coil at the center into a line contact, thereby forming a straight parallel current band in the central working area. Utilizing the maximum vector superposition characteristic of straight currents, this structure compresses the diffuse induced electric field at the center into a high-intensity, narrow band distribution, reducing the stimulation intensity on surrounding non-target tissues and improving the spatial resolution of the stimulation.

[0052] According to the principle of electromagnetic field vector superposition, the combined magnetic induction intensity generated by a parallel current-carrying straight conductor in the surrounding space is the greatest. The unidirectional excitation currents within this linear parallel current band can achieve maximum overlap of the spatial magnetic fields. Assume the effective length of this parallel straight line segment is... When an electric current is passed through it, the rate of change of magnetic flux passing under this straight segment is extremely compressed, resulting in the maximum induced electric field in the surrounding space. Satisfies the functional relationship:

[0053]

[0054] in the formula This represents the effective magnetic flux passing through the central working region. Due to the introduction of the parallel current band length L, the magnetic field superposition efficiency in the central region increases significantly. According to... Figure 8The simulation results of the magnetic flux density cloud map show that its maximum magnetic flux density is 25237 mT. This asymmetric double-D structure generates an extremely high-intensity strip-shaped magnetic field focusing region directly below the straight edge. Figure 2 Compared to conventional circular structures, the asymmetric double-D structure, even with a smaller number of turns, significantly enhances the absolute peak value of the central magnetic induction intensity under the same 800A pulse excitation. Furthermore, it causes more dramatic edge attenuation in the focal region. This high-gradient, sharp edge corresponds to a highly concentrated induced electric field, effectively reducing false stimulation of surrounding non-target brain tissue.

[0055] In summary, the coil provided by this invention can achieve dual functions when an excitation current is applied: it uses a larger coil wing to generate a wide-coverage deep background magnetic field, and a smaller or specially shaped coil wing to generate a high-gradient focusing magnetic field. Through the vector superposition of the two, the peak of the induced electric field is driven to deviate from the geometric center and shift in a controlled manner toward the high-gradient coil side. This maintains the deep stimulation effect while strictly limiting the superficial stimulation to the periphery of the target area, greatly reducing the risk of adverse reactions to non-target brain regions.

[0056] This invention, through an innovative asymmetric geometry—specifically, differentiated radii, number of turns, and shape configurations—successfully addresses the challenges of traditional symmetrical coil stimulation, such as fixed target points, difficulty in balancing stimulation depth and focus, and inability to flexibly adapt to the complex pathways of the cerebral cortex. This approach utilizes the high gradient of small coils and the deep penetration of large coils to achieve the shifting and reshaping of the magnetic field focus. This structural design, without adding additional mechanical movement devices, achieves precise control of the intracranial stimulation region through the inherent asymmetry of the structure, providing a new hardware foundation for high-precision, deep transcranial magnetic stimulation.

[0057] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0058] For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances. When an element is referred to as being "assembled on," "mounted on," "fixed to," or "set on" another element, it may be directly on the other element or there may be an intermediate element present. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate element present. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible embodiments.

[0059] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0060] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

Claims

1. A high-focusing deep transcranial magnetic stimulation coil based on asymmetric topology, characterized in that: It includes at least two mutually coupled coil loops, wherein the parameters of at least one coil loop are different from those of the other coil loops, such that the magnetic induction peak of the transcranial magnetic stimulation coil deviates from its geometric symmetry center; wherein the parameters of the coil loop include at least one of geometric dimensions, number of winding turns, and shape topology.

2. The coil as described in claim 1, characterized in that: The coil includes a first coil wing and a second coil wing. The first coil wing is elliptical and the second coil wing is circular. The two are connected in series at the point of tangency through a central bridging section. The first coil wing and the second coil wing have different numbers of winding turns.

3. The coil as described in claim 2, characterized in that: The central bridging section is made of copper.

4. The coil as described in claim 1, characterized in that: The coil includes a third to a sixth coil wing, which are arranged in a cross shape. The third coil wing is elliptical, and the fourth to sixth coil wings are all circular and have the same number of winding turns. The number of winding turns of the third coil wing is less than the number of winding turns of the fourth to sixth coil wings.

5. The coil as described in claim 4, characterized in that: The third to sixth coil wings are located in the same plane and have an insulating bridging structure at the center intersection.

6. The coil as described in claim 4, characterized in that: The third coil wing is positioned opposite to the fifth coil wing and is located in the first plane; the fourth coil wing is positioned opposite to the sixth coil wing and is located in the second plane; the first plane and the second plane are vertically adjacent.

7. The coil as claimed in claim 1, characterized in that: The coil includes a seventh coil wing and an eighth coil wing, wherein the seventh coil wing and the eighth coil wing are both D-shaped and have different geometric dimensions, and are integrally wound with continuous conductors. The straight conductor portions of the two are parallel to each other and are tightly bonded after being physically isolated by an insulating medium.

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