Coil array control method and transcranial magnetic stimulation device

Abstract

The invention provides a coil array control method and a transcranial magnetic stimulation device. The method comprises the following steps: firstly, establishing a volume conductor model of the brain of a subject and a spatial position model of a coil array; secondly, calculating a lead field matrix generated by the coil array to the brain of the subject; and finally, setting a target distribution matrix of the induced electric field, establishing a target function of the distribution matrix of the induced electric field, and optimizing the target function through the current derivative of the coil array to obtain specific setting of the coil array under the target distribution matrix of the induced electric field, thereby realizing accurate control of the coil array. In addition, the method has the advantages of simplicity in operation, energy conservation, low consumption, high efficiency and flexibility.

Description

Technical Field

[0001] The present invention relates to the field of biological detection, and in particular to a coil array control method and a transcranial magnetic stimulation device. Background Art

[0002] Transcranial magnetic stimulation (TMS) technology in the field of neuroscience research, especially multi-channel transcranial magnetic stimulation technology, is used to control the coil array used in multi-channel transcranial magnetic stimulation so that it can generate a predetermined induced electric field distribution, which is suitable for transcranial magnetic stimulation treatment and brain function exploration research.

[0003] Transcranial magnetic stimulation (TMS) is a non-invasive, safe and efficient neurostimulation technology. The time-varying magnetic field generated by the TMS coil can pass through the skull almost without loss, generate an induced electric field in the cerebral cortex, and affect brain metabolism and neural electrical activity. Transcranial magnetic stimulation can be used clinically to treat neurological diseases such as depression and sleep disorders. In scientific research, it can be used in conjunction with neuroimaging technologies such as electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) to study brain function.

[0004] Traditional transcranial magnetic stimulation devices use manual or mechanical arms to clamp a single circular or "8"-shaped coil to focus the electric field at a specific position, which has the problems of insufficient positioning accuracy and slow stimulation position conversion speed. Therefore, the prior art has designed a multi-channel transcranial magnetic stimulation device: the device uses an array composed of multiple coils, and achieves electric field focusing at a specific position by superimposing the induced electric fields generated by each coil. The mechanical control of the traditional device is replaced by circuit control, which provides an extremely fast stimulation position conversion speed while maintaining sufficient positioning accuracy. However, multi-channel transcranial magnetic stimulation devices still have the problem of not being able to accurately control each coil to achieve an ideal electric field focusing effect.

[0005] Therefore, how to precisely control each coil to achieve an ideal electric field focusing effect has become one of the problems that technicians in this field need to solve urgently.

[0006] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present invention and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because these solutions are described in the background technology section of the present invention. Summary of the invention

[0007] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a coil array control method and a transcranial magnetic stimulation device, so as to solve the problem that the transcranial magnetic stimulation device and system in the prior art cannot accurately control the coil array.

[0008] To achieve the above-mentioned purpose and other related purposes, the present invention provides a coil array control method, the steps of which include at least: S1: collecting brain information of a subject, and establishing a volume conductor model of the subject's brain based on the brain information of the subject; establishing a spatial position model of the coil array based on the coil array used; S2: calculating the distribution matrix of the lead field of the coil array used; S3: setting a target distribution matrix of the induced electric field, and establishing an objective function about the induced electric field distribution matrix; using the current derivative of the coil array as an independent variable, optimizing the objective function using a regularization parameter and an iterative algorithm, and obtaining a solution set consisting of a set of solution vectors of the objective function; selecting an optimal solution vector from the solution set, and setting the coils to be activated in the coil array according to the characteristics of the optimal solution vector.

[0009] Optionally, in step S1, a three-dimensional coordinate system is established with the center of the subject's brain as the coordinate origin, and a spatial position model of the coil array is established according to the radius, center position and normal direction of each coil in the coil array.

[0010] More optionally, the normal directions of the coils of the coil array are all directed toward one side of the subject's brain, or are all directed toward a side away from the subject's brain.

[0011] Optionally, in step S1, a volume conductor model is established for the subject's brain according to the characteristics of each tissue in the subject's brain, and the volume conductor model is discretized into a three-dimensional grid array to quantitatively describe the electrical characteristics of the subject's brain as a three-dimensional shape in an induced electric field.

[0012] More optionally, in step S2, the distribution matrix of the lead field Where n represents the number of coils in the coil array, L i represents the lead field generated by the i-th coil in the coil array to the volume conductor model, L i =[L i (r1),...,L i (r j ),...,L i (r m )] T , r j represents the position of the jth grid point in the volume conductor model, and m represents the number of grid points in the volume conductor model; wherein, L i The calculation formula for (r) is Among them, e k Represents the unit orthogonal vector in three-dimensional space, Φ i represents the magnetic flux generated by the unit current dipole source at position r in the i-th coil, Q(r) represents the unit current dipole source at position r, Si represents the area enclosed by the i-th coil, B Q represents the magnetic induction intensity generated by the unit current dipole source at position r; B Q The calculation formula is Where μ0 represents the vacuum magnetic permeability, J tot (r) represents the body current induced by a unit current dipole source at position r, and V represents the volume of the subject's brain.

[0013] More optionally, in step S3, a rated induced electric field strength is set at a corresponding position of the target grid point in the distribution matrix of the induced electric field, and the induced electric field strengths of other elements in the distribution matrix of the induced electric field are set to zero, so as to set a target distribution matrix of the induced electric field when the coil array is focused on the target grid point in the subject's brain.

[0014] Optionally, in step S3, the optimization function is in, represents the target distribution matrix of the induced electric field, represents the distribution matrix of the lead field, J represents the distribution vector of the current derivative in the coil array, ||·||2 represents the L2 norm, ||·||1 represents the L1 norm, α and λ represent regularization coefficients, and 0<α<1, λ≥0.

[0015] Optionally, in step S3, the infinite norm of the optimal solution vector is the smallest among the infinite norms of all solution vectors, and the number and positions of the required activated coils in the corresponding setting of the coil array are set according to the number and positions of non-zero elements in the optimal solution vector.

[0016] To achieve the above-mentioned object and other related objects, the present invention provides a transcranial magnetic stimulation device, which includes a coil array, and the coil array is used to implement the coil array control method.

[0017] Optionally, the coil array includes 3n coils, each three coils form a group, and each group of three coils are placed perpendicular to each other; wherein n is a natural number greater than or equal to 1.

[0018] As described above, the coil array control method and transcranial magnetic stimulation device of the present invention have the following beneficial effects:

[0019] 1. The present invention establishes a volume conductor model for the subject's brain and a spatial position model for the coil array, so as to pre-calculate the lead field of the coil array, and efficiently and flexibly calculate the induced electric field generated by the coil array on the subject's brain by the pre-calculated lead field.

[0020] 2. The present invention optimizes the objective function by using the current derivative, which can greatly reduce the complexity of the objective function optimization, improve the convergence speed of the objective function, and finally obtain the solution vector of the objective function.

[0021] 3. The objective function used in the optimization problem of the present invention can reduce the current used under the target induced electric field and reduce the number of activated coils, thereby achieving the purpose of energy saving and low consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Shown is a flow chart of the coil array control method of the present invention.

[0023] Figure 2 Shown is a schematic diagram of a discretized three-dimensional grid array of a subject's brain according to the present invention.

[0024] Figure 3 A schematic diagram of a discretized three-dimensional grid array of the coil array of the present invention is shown.

[0025] Figure 4 A diagram showing a first normal direction arrangement of the coil array of the present invention is shown.

[0026] Figure 5 A diagram showing a second normal direction arrangement of the coil array of the present invention is shown.

[0027] Figure 6 It is a schematic diagram showing the arrangement of the coil array of the present invention under the optimal solution vector.

[0028] Figure 7 Shown is a schematic structural diagram of the transcranial magnetic stimulation device of the present invention.

[0029] Figure 8 Shown is a schematic diagram of the structure of a group of coils in the transcranial magnetic stimulation device of the present invention.

[0030] Component number description

[0031] 1 Coil array

[0032] 1a Coil DETAILED DESCRIPTION

[0033] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0034] See also Figure 1-Figure 8It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0035] Embodiment 1

[0036] like Figure 1 As shown, this embodiment provides a coil array control method, and the steps of the coil array control method include:

[0037] like Figure 1 As shown, in step S1, brain information of the subject is collected, and a volume conductor model of the subject's brain is established based on the brain information of the subject; and a spatial position model of the coil array is established based on the coil array used.

[0038] Specifically, in this embodiment, a magnetic resonance imaging (MRI) is used to scan the subject's head, and after collecting the subject's brain information, a volume conductor model is established for the subject's brain based on the electrochemical parameters, position parameters, and diffusion tensor imaging data of each tissue in the subject's brain, so as to quantitatively describe the electrical characteristics of the subject's brain as a three-dimensional shape in the induced electric field: Figure 2 As shown, the subject's brain is discretized into a three-dimensional grid array according to the required accuracy, and a corresponding conductivity value is assigned to each grid point. Therefore, the higher the required accuracy, the higher the density of the three-dimensional grid array, and the greater the calculation amount of the volume conductor model. As an example, according to the electrochemical parameters, position parameters and diffusion tensor imaging data of the normal brain tissues of the human body, the density of the three-dimensional grid array of the subject's brain is 2.5mm*2.5mm*2.5mm, the conductivity assigned to the subject's scalp is 0.33S / m, the conductivity assigned to the skull is 0.0042S / m, the conductivity assigned to the cerebrospinal fluid is 1.79S / m, the conductivity assigned to the gray matter is 0.33S / m, and the conductivity assigned to the white matter is 0.14S / m, where S / m represents Siemens per meter. In actual applications, the conductivity of each tissue of the subject's brain and the density of the three-dimensional grid array are set according to actual conditions, and are not limited to this embodiment.

[0039] Specifically, in this embodiment, the multi-channel transcranial magnetic stimulation coil array to be used is determined, and in order to quantitatively describe the position of the coil array used in three-dimensional space, a spatial position model of the coil array needs to be established. Further, a three-dimensional coordinate system is established with the center of the subject's brain as the coordinate origin. In this three-dimensional coordinate system, Figure 3As shown in , the spatial position model of the coil array is established according to the radius, center position and normal direction of each coil, and the coil array is discretized into a three-dimensional grid array according to the required accuracy; among them, since there are two options for the normal direction of each coil, Figure 4 As shown, the normal direction of each coil is uniformly toward one side of the subject's brain, and the normal direction of each coil is in a focused state, or, as shown in FIG. Figure 5 As shown, the normal direction of each coil is uniformly directed toward the side away from the subject's brain, and the normal direction of each coil is divergent. In practical applications, the three-dimensional coordinate system can be selected from any one of the Cartesian coordinate system, the spherical coordinate system, or the cylindrical coordinate system, and no specific limitation is made here.

[0040] like Figure 1 As shown, in step S2, the distribution matrix of the lead field of the coil array used is calculated.

[0041] Specifically, in this embodiment, after establishing the volume conductor model of the subject's brain and the spatial position model of the coil array, the lead field generated by the coil array on the subject's brain after being energized can be calculated. The lead field describes the distribution of the induced electric field generated by the coil array at each grid point of the three-dimensional grid point array of the volume conductor model. Further, the lead field is described by the distribution matrix of the lead field. The distribution matrix of the lead field is Where n represents the number of coils in the coil array, L i represents the lead field generated by the i-th coil in the coil array to the volume conductor model, L i =[L i (r1),...,L i (r j ),...,L i (r m )] T , r j represents the position of the jth grid point in the volume conductor model, and m represents the number of grid points in the volume conductor model. i The calculation formula for (r) is Among them, e k Represents the unit orthogonal vector in three-dimensional space, Φ i represents the magnetic flux generated by the unit current dipole source at position r in the i-th coil, Q(r) represents the unit current dipole source at position r, S i represents the area enclosed by the i-th coil, B Q represents the magnetic induction intensity generated by the unit current dipole source at position r. Furthermore, B Q The calculation formula is Where μ0 represents the vacuum magnetic permeability, J tot(r) represents the body current induced by the unit current dipole source at position r, and V represents the volume of the subject's brain. As an example, when calculating the distribution matrix of the lead field, the magnetic induction intensity B generated by the unit current dipole source at position r (the point element abstracted from the volume conductor model) is first calculated. Q ; then calculate the lead field generated by the unit current dipole source of the ith coil at position r; then calculate the lead field generated by the ith coil for all grid points of the entire volume conductor model; finally calculate the distribution matrix of the lead field generated by all coils of the coil array for the volume conductor model. In practical applications, the calculation method of the distribution matrix of the lead field is set as needed, which is not limited to this embodiment.

[0042] It should be noted that the spatial position model established by the coil array used in this embodiment is unchanged, that is, the position of the coil array used in this embodiment is unchanged, so the distribution matrix of the lead field is also unchanged. In actual use, it is only necessary to change the target distribution matrix of the induced electric field according to the target point to be stimulated, and change the distribution vector of the current derivative during the optimization process. Therefore, the calculation of the lead field can be completed in advance, and all subsequent calculations do not need to recalculate the lead field.

[0043] like Figure 1 As shown, in step S3, the target distribution matrix of the induced electric field is set, and the objective function of the induced electric field distribution matrix is ​​established; the current derivative of the coil array is used as an independent variable, and the objective function is optimized using a regularization parameter and an iterative algorithm to obtain a solution set consisting of a set of solution vectors of the objective function; the optimal solution vector is selected from the solution set, and the coils to be activated in the coil array are set according to the characteristics of the optimal solution vector.

[0044] Specifically, in this embodiment, the target distribution matrix of the induced electric field is set according to the target position of the subject's brain to be activated, that is, the target grid point of the three-dimensional grid point array of the subject's brain. Since the volume conductor model is a discretized three-dimensional grid point array, when the induced electric field is focused at the target grid point, the rated induced electric field strength can be set by the corresponding position of the target grid point in the distribution matrix of the induced electric field, and the induced electric field strengths of other elements in the distribution matrix of the induced electric field can be set to zero, so as to set the target distribution matrix of the induced electric field when the coil array is focused on the target grid point in the subject's brain. Furthermore, since the distribution matrix of the guide field and the distribution matrix of the induced electric field have the following relationship: Where J = [J1, .., J i ,..,J n ] T , I irepresents the current passing through the i-th coil. Therefore, the actual distribution matrix E of the induced electric field can be made close to the target distribution matrix of the induced electric field by changing the circuit on-off status of each coil in the coil array.

[0045] Specifically, in this embodiment, by optimizing the objective function (Elastic-net regression), the distribution matrix of the induced electric field actually generated by the coil array is made to continuously approach the target distribution matrix of the induced electric field, so as to achieve cranial brain stimulation at the target grid point by the coil array, wherein the objective function is represents the target distribution matrix of the induced electric field, represents the distribution matrix of the lead field, J represents the distribution vector of the current derivative in the coil array, ||·||2 represents the L2 norm, ||·||1 represents the L1 norm, α and λ represent regularization coefficients, and 0<α<1, λ≥0. Furthermore, since the spatial position model established by the coil array used is unchanged in this embodiment, the distribution matrix of the lead field is also unchanged. In step S3, the objective function can be optimized only by changing the distribution vector J of the current derivative, that is, the distribution vector J of the current derivative is the independent variable of the objective function. Furthermore, using J as an independent variable can greatly reduce the complexity of the objective function and improve the convergence speed of the objective function; and, the one used in the objective function This L2 norm penalty term can limit the value of the independent variable J to achieve the target focusing effect of the electric field with energy saving and low consumption; the L1 norm penalty term of ||J||1 used can introduce sparsity to the independent variable to achieve the selection of activating each coil in the coil array (which can be determined by judging J i Whether it is 0, it is known whether the i-th coil in the coil array needs to be energized, so as to set the coil to be activated in the coil array).

[0046] Specifically, in this embodiment, the solution vector with the smallest infinite norm among all solution vectors is the optimal solution vector, and the number and position of the required activated coils in the corresponding setting of the coil array are set according to the number and position of the non-zero elements in the optimal solution vector. Further, after obtaining the solution set for the objective function, a specific method of selecting the optimal solution vector from the solution set is as follows: first, the infinite norm ||J|| of each solution vector in the solution set is calculated. ∞ =max{|J i |}, where |J i | represents the absolute value of each element in the solution vector; secondly, the optimal solution vector is the solution vector with the smallest infinity norm among all solution vectors; the optimal solution vector can minimize the energy consumption of the coil array. As an example, according to the number and position of non-zero elements of the optimal solution vector in the solution set of the target distribution matrix of the induced electric field, set Figure 6The number and position of the activated coils in the coil array shown in FIG. 1 are as follows. Since the number of non-zero elements of the optimal solution vector is 3, Figure 6 The number of activated coils is also 3. In practical applications, the specific configuration of the coil array is set according to needs, and is not limited to this embodiment.

[0047] It should be further explained that if there are multiple target distribution matrices of the induced electric field (i.e., the electric field needs to be focused at multiple target points), the activation status of the coil array under each target distribution matrix of the induced electric field can be set one by one according to the optimal solution vector under each target distribution matrix of the induced electric field. After the selection is completed, the coils that need to be activated in each specific activation situation are linearly superimposed to obtain the settings required for the coil array when the electric field needs to be focused at multiple target points.

[0048] Embodiment 2

[0049] like Figure 7 As shown, this embodiment provides a transcranial magnetic stimulation device, which includes a coil array.

[0050] Specifically, in this embodiment, the transcranial magnetic stimulation device can provide an induced electric field to the subject's brain by energizing the coil array to generate the stimulation signal required by the subject's brain. Figure 8 As shown, the coil array includes 3n coils, each of which is a group of three coils, and each group of three coils is placed perpendicular to each other, where n is a natural number greater than or equal to 1; when each of the three coils is a group, and as shown Figure 8 When arranged in the manner shown, the mutual inductance between a group of coils can be very small, and the interference between the coils can be minimized. In addition, the induced electric field generated by the coil array can cover the subject's brain as much as possible, so that the subject's stimulation blind area is minimized as much as possible. As an example, three copper Litz wires with an outer diameter of 2mm are wound with a diameter of 50mm and 20 turns of annular elements placed vertically to each other as a group. Each group of coils is arranged at the electrode position of the standard EEG 10-10 system to form a multi-channel coil array. In actual applications, the coil placement position of the coil array is set as needed, not limited to this embodiment.

[0051] It should be noted that the transcranial magnetic stimulation device of this embodiment can be used to implement the coil array control method of embodiment 1, and can also be used to implement other coil array control methods, which are not specifically limited here.

[0052] In summary, the coil array control method and transcranial magnetic stimulation device of the present invention: first, establish a volume conductor model of the subject's brain and a spatial position model of the coil array; second, calculate the lead field matrix generated by the coil array on the subject's brain; finally, set the target distribution matrix of the induced electric field, and establish the objective function of the induced electric field distribution matrix, optimize the objective function through the current derivative of the coil array, and obtain the specific settings required for the coil array under the target distribution matrix of the induced electric field, so as to achieve precise control of the coil array. In addition, the present invention has the advantages of simple operation, energy saving, low consumption, high efficiency and flexibility. In addition, the present invention can effectively exclude coils that do not need to be started, reduce the control burden of the multi-channel transcranial magnetic stimulation system, and has the advantages of simple operation, energy saving, low consumption, high efficiency and flexibility. Therefore, the present invention effectively overcomes the various shortcomings in the prior art and has a high industrial utilization value.

[0053] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A coil array control method, characterized in that: The steps of the coil array control method at least include: S1: collecting brain information of the subject, and establishing a volume conductor model of the subject's brain based on the brain information of the subject; Establishing a spatial position model of the coil array based on the coil array used; S2: Calculate the distribution matrix of the lead field of the coil array used; S3: setting a target distribution matrix of the induced electric field, and establishing an objective function about the induced electric field distribution matrix; taking the current derivative of the coil array as an independent variable, optimizing the objective function using a regularization parameter and an iterative algorithm, and obtaining a solution set consisting of a set of solution vectors of the objective function; selecting an optimal solution vector from the solution set, and setting the coils to be activated in the coil array according to the characteristics of the optimal solution vector.

2. The coil array control method according to claim 1, characterized in that: In step S1, a three-dimensional coordinate system is established with the center of the subject's brain as the coordinate origin, and a spatial position model of the coil array is established according to the radius, center position and normal direction of each coil in the coil array.

3. The coil array control method according to claim 2, characterized in that: The normal directions of the coils of the coil array are uniformly directed toward one side of the subject's brain, or uniformly directed toward a side away from the subject's brain.

4. The coil array control method according to claim 1, characterized in that: In step S1, a volume conductor model is established for the subject's brain according to the characteristics of each tissue in the subject's brain, and the volume conductor model is discretized into a three-dimensional grid array to quantitatively describe the electrical characteristics of the subject's brain as a three-dimensional shape in an induced electric field.

5. The coil array control method according to claim 4, characterized in that: In step S2, the distribution matrix of the lead field Where n represents the number of coils in the coil array, L i represents the lead field generated by the i-th coil in the coil array to the volume conductor model, L i =[L i (r1),...,L i (r j ),...,L i (r m )] T , r j represents the position of the jth grid point in the volume conductor model, and m represents the number of grid points in the volume conductor model; Among them, L i The calculation formula for (r) is Among them, e k Represents the unit orthogonal vector in three-dimensional space, Φ i represents the magnetic flux generated by the unit current dipole source at position r in the i-th coil, Q(r) represents the unit current dipole source at position r, S i represents the area enclosed by the i-th coil, B Q It represents the magnetic induction intensity generated by the unit current dipole source at position r; B Q The calculation formula is Where μ0 represents the vacuum magnetic permeability, J tot (r) represents the body current induced by a unit current dipole source at position r, and V represents the volume of the subject's brain.

6. The coil array control method according to claim 4, characterized in that: In step S3, a rated induced electric field strength is set at a corresponding position of the target grid point in the distribution matrix of the induced electric field, and the induced electric field strengths of other elements in the distribution matrix of the induced electric field are set to zero, so as to set a target distribution matrix of the induced electric field when the coil array is focused on the target grid point in the subject's brain.

7. The coil array control method according to claim 1, characterized in that: In step S3, the optimization function is in, represents the target distribution matrix of the induced electric field, represents the distribution matrix of the lead field, J represents the distribution vector of the current derivative in the coil array, ||·||2 represents the L2 norm, ||·||1 represents the L1 norm, α and λ represent regularization coefficients, and 0<α<1, λ≥0.

8. The coil array control method according to claim 1, characterized in that: In step S3, the infinite norm of the optimal solution vector is the smallest among the infinite norms of all solution vectors, and the number and positions of the required activated coils in the corresponding setting of the coil array are set according to the number and positions of non-zero elements in the optimal solution vector.

9. A transcranial magnetic stimulation device, characterized in that: The transcranial magnetic stimulation device comprises a coil array, and the coil array is used to implement the coil array control method according to any one of claims 1 to 8.

10. The transcranial magnetic stimulation device according to claim 9, characterized in that: The coil array includes 3n coils, each of which is a group of three coils, and each group of three coils is placed perpendicular to each other; wherein n is a natural number greater than or equal to 1.

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