A multi-brain region electrode optimization method for transcranial electrical stimulation

Abstract

The application discloses a multi-brain region electrode optimization method for transcranial electrical stimulation, which comprises the following steps: firstly, constructing a head simulation model, solving the electric field transfer matrix of each electrode by using a finite element method, then selecting a target region which needs to be optimized and one or more target points of brain regions which need to be inhibited, optimizing the electric field of the target region, inhibiting the electric field intensity of the specific brain region near the target region, and restraining the number of electrodes used, the current size of a single electrode and the total electrode current, and finally evaluating the optimization effect by simulating and calculating the electric field intensity of the stimulated brain region and the inhibited brain region. The electrode optimization method can inhibit the electric field intensity of one or more specific brain regions near the target brain region while applying the electric field to the target brain region. Compared with the past stimulation of a brain region, the electrode optimization method can meet the personalized and accurate demand and avoid the unpredictable influence caused by the activation of some brain regions near the target brain region.

Description

Technical Field

[0001] This invention belongs to the field of biomedical engineering technology, specifically relating to a multi-brain region electrode optimization algorithm for transcranial electrical stimulation. Background Technology

[0002] Transcranial electrical stimulation (TCS) is a neuromodulation technique that uses electrodes to deliver weak electrical currents onto the scalp to alter the activity of neurons in the cerebral cortex, thereby regulating brain function. Currently, TCS is widely used to treat epilepsy, depression, stroke, and other diseases. In addition, TCS has been found to improve cognitive abilities, including language and memory. Traditional TCS uses two rectangular electrodes with an area of ​​25-35 cm². However, this stimulation method produces a relatively low electric field intensity in the target brain region, and the electric field distribution introduced intracranially is quite diffuse. It also induces electric fields in non-target brain regions, potentially activating other brain areas and causing adverse consequences.

[0003] To more precisely control the distribution of the electric field and improve the accuracy and effectiveness of stimulation, several electrode optimization methods have been proposed. Electrode optimization induces a specific intracranial electric field distribution by selecting appropriate electrode combinations, including the number of electrodes, electrode locations, and current intensities, to achieve the desired stimulation effect. Electrode optimization methods typically use a large number of smaller electrodes (1-2 cm²) instead of traditional large patch electrodes. Combined with individual differences in brain structure, this can significantly improve the focusing of the electric field. Common electrode optimization methods include the least squares method, the maximum intensity method, and the linearly constrained minimum variance method. The least squares method can obtain relatively concentrated stimulation by minimizing the second-order error term, but the stimulation focusing is lower. The maximum intensity method aims to achieve high-intensity stimulation but sacrifices focusing. The linearly constrained minimum variance method includes a hard constraint, that is, the stimulation electric field intensity in the target brain region must be forced to be equal to the required electric field intensity. Under this premise, the electric field energy in non-target regions is minimized. This method can guarantee the stimulation effect, but requires too many electrodes, making the implementation difficult in practice. Furthermore, with the development of neural circuitry, there is an increasing desire to target stimulation of a specific brain region while minimizing its impact on other specific brain regions, in order to facilitate the study of dose-response relationships in neural regulation. In clinical practice, it is also often necessary to stimulate one brain region while avoiding stimulation or interference with one or more specific surrounding brain regions.

[0004] However, when current electrode optimization methods perform transcranial electrical stimulation on a certain brain region, due to the characteristics of the electric field distribution, the nearby brain regions will also have a certain electric field intensity, and thus will inevitably be affected by the stimulation. Summary of the Invention

[0005] This invention proposes a multi-brain region electrode optimization method targeting two objectives: electric field strength and focusing. This method can achieve targeted stimulation by simultaneously stimulating a target brain region and constraining the electric field strength in specific nearby brain regions.

[0006] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0007] A method for optimizing multi-regional electrodes for transcranial electrical stimulation, comprising the following steps:

[0008] (1) Construct a head simulation model;

[0009] (2) Select the target area that needs to be optimized and the target points of one or more brain regions that need to suppress the electric field intensity, respectively;

[0010] (3) Perform finite element analysis to optimize the electric field of the target area, while suppressing the electric field intensity of specific brain regions nearby, and constraining the number of electrodes used, the magnitude of the current of a single electrode and the total electrode current.

[0011] (4) The optimization effect is evaluated by simulating and calculating the electric field strength of the brain regions that are stimulated and inhibited.

[0012] Preferably, the construction of the head simulation model specifically includes the following steps:

[0013] (1.1) The magnetic resonance imaging data is segmented to divide the individual head model structure into scalp, cerebrospinal fluid, skull, and white and gray matter of the brain;

[0014] (1.2) Place the electrodes by placing virtual electrodes using electrode positioning methods, including the 10-05 system and the 10-10 system;

[0015] (1.3) Perform finite element meshing to generate a three-dimensional mesh and perform structural repair, generating a tetrahedral mesh from the segmented magnetic resonance imaging;

[0016] (1.4) The electric field transfer matrix of each candidate electrode is obtained by finite element calculation.

[0017] Preferably, the coordinates of the corresponding MNI target point are determined based on the location of the target area and the brain region where the inhibitory electric field is located.

[0018] Preferably, the expression for electric field optimization is:

[0019]

[0020] Where s represents the magnitude of the electrode current, λE represents the target electric field distribution in the target area. foc E represents the parameter for focused optimization.inv-target <The magnitude E of the electric field strength in a specific brain region where inhibition is indicated by E0 inv-target should be less than the value constant E0.

[0021] Preferably, the number of electrodes used in the constraint, the magnitude of the current of a single electrode, and the total electrode current include: restricting the number of electrodes used in the optimization result to a specific value. The specific process is as follows: First, perform an optimization without restricting the number of electrodes. Select several electrodes with the largest current from the optimization result as the new solution space. The number of electrodes selected is the same as the number of electrodes finally required, and then perform another optimization to obtain the final electrode optimization result. The constraint conditions also include:

[0022] ① The sum of the absolute values of the currents is not greater than a specific value I total

[0023] ② The absolute value of the current of a single electrode is not greater than a specific value I m

[0024] ③ The magnitude of the input current is equal to the magnitude of the output current.

[0025] Preferably, observe the inhibition effect by calculating the electric field strength of the electric field established by the electrode current in the target region in the optimization result and calculating the electric field strength of the inhibited brain region; visually view the electrode optimization effect according to the electric field distribution diagram on the template.

[0026] Advantages of the present invention:

[0027] (1) The electrode optimization method proposed by the present invention can inhibit the electric field strength of one or several specific brain regions near the target brain region while applying an electric field to the target brain region. Compared with the previous method of stimulating a single brain region, which may cause unpredictable effects due to the activation of some nearby brain regions, it meets the need for personalized precision.

[0028] (2) The present invention restricts the electrodes used in transcranial electrical stimulation to a certain number, thus meeting the actual use conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a flowchart of the method of the present invention;

[0030] Figure 2 is a schematic diagram of segmenting an individual's head model;

[0031] Figure 3 is a schematic diagram of placing electrodes on the head model;

[0032] Figure 4 is a schematic diagram of performing finite element meshing on the head model;

[0033] Figure 5This is a schematic diagram showing the target point coordinates of the selected brain region;

[0034] Figure 6 This is a three-dimensional simulation result of the electric field when the electric field intensity of a target brain region is optimized while suppressing the electric field intensity of a nearby specific brain region (left) and when the electric field intensity of a nearby brain region is not suppressed (right). Detailed Implementation

[0035] To further understand the content of the present invention, the present invention will be described in detail with reference to the embodiments. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0036] This embodiment relates to a multi-brain region electrode optimization method for transcranial electrical stimulation. First, a head simulation model is constructed. Then, the target brain region to be optimized and the target points of the non-target brain region whose electric field intensity needs to be suppressed are selected respectively. Then, the electric field of the target brain region is optimized, while the electric field intensity of specific non-target brain regions is suppressed. The number of electrodes used, the magnitude of the current of a single electrode, and the total electrode current are constrained. Finally, the optimization effect is evaluated by electric field simulation and calculation of the electric field intensity of the stimulated target brain region and the suppressed brain region.

[0037] See Figure 1 This is a simplified implementation flowchart of the multi-brain region electrode optimization for transcranial electrical stimulation in this embodiment. It includes three parts: constructing a head simulation model, selecting the target coordinates of the stimulation and inhibition brain regions, optimizing the electrodes for the target brain regions and the brain regions with the inhibition field strength, and evaluating the optimization effect.

[0038] I. Construction of the head simulation model

[0039] See Figure 2 First, the magnetic resonance imaging (MRI) data was segmented using SPM12 software, dividing the individual head model structure into scalp, cerebrospinal fluid, skull, and cerebral white and gray matter. Further segmentation was performed using MATLAB script functions, including smoothing, cavity filling, and free voxel removal; see [link to relevant documentation]. Figure 3 Then, place the electrodes, selecting the 10-10 system electrode positioning method to place the virtual electrodes; see [reference needed]. Figure 4 Next, finite element meshing was performed using the iso2mesh tool in MATLAB to generate a 3D mesh, and structural repair was performed. The cgalv2m function was used to generate a tetrahedral mesh from the segmented magnetic resonance imaging. Finally, the electric field transfer matrix of each candidate electrode was calculated using finite element methods.

[0040] II. Determine the target coordinates of the target brain region and the inhibitory brain region.

[0041] Open the head template through the MRIcron medical image analysis software, select the positions of the target regions on the template respectively, and then view the corresponding MNI coordinates as the target coordinates. Repeat the same steps for selecting the target points of the inhibitory brain regions as those of the target points.

[0042] III. Electrode Optimization for Stimulating and Inhibiting Brain Regions

[0043] Use the MNI standard brain region template or perform electrode optimization through finite element calculation on the individual head model. The optimization of the electric field for the target region while suppressing the electric field intensity of specific non-target brain regions includes: while optimizing the electric field intensity and focusing of the target region, restricting the magnitude of the electric field in other specific brain regions. The general electrode optimization formula is:

[0044]

[0045] where s represents the current magnitude of the electrode, represents the target electric field distribution of the target region, λE foc represents the parameter for focusing optimization, E inv-target <E0 represents the magnitude of the electric field intensity of the specific brain region to be suppressed E inv-target should be less than the value constant E0.

[0046] The constraints on the number of electrodes used, the current magnitude of a single electrode, and the total electrode current include: restricting the number of electrodes used in the optimization result to a specific value. The specific process is to first perform an optimization without restricting the number of electrodes, select several electrodes with the largest current (the number of electrodes selected is the same as the final required number of electrodes) from the optimization result as the new solution space, and then perform another optimization to obtain the final electrode optimization result. Additionally, the constraint conditions also include:

[0047] ①. The absolute value sum of the currents is not greater than the specific value I total

[0048] ②. The absolute value of the current of a single electrode is not greater than the specific value I m

[0049] ③. The magnitude of the input current is equal to the magnitude of the output current

[0050] IV. Calculate the Electric Field Intensity and Perform Electric Field Simulation Based on the Optimization Result

[0051] The evaluation of the optimization effect through electric field simulation and calculation of the electric field strength in the target brain region and the inhibitory brain region includes calculating the electric field strength established by the electrode current in the target region in the optimization result, and simultaneously calculating the electric field strength in the inhibitory brain region to observe the inhibitory effect. The greater the electric field strength in the target region and the smaller the electric field strength in the inhibitory brain region, the better the optimization effect. After electric field simulation, the effect of electrode optimization can be visually viewed based on the electric field distribution diagram on the template.

[0052] See Figure 5 Using MRIcron software, the target coordinates of the target area are selected. First, the location of the brain region to be transcranial electrical stimulation is determined. Then, a standard brain region template is opened in the MRIcron software, and the brain region slice image is displayed. Figure 2 (left side) or 3D image ( Figure 2 Click on the center point of the template brain region on the right to obtain the corresponding MNI coordinates, which are the target coordinates. Figure 2 The selected brain region was the Superior Parietal Lobe (SPL), and the final target point MNI coordinates were [26, -69, 66]. Then, the coordinates of the supramarginal gyrus (SMG) and angular gyrus (ANG) near the SMG were selected using the same procedure. In this embodiment, the SPL was used as the stimulation brain region, and the SMG and ANG as the inhibition brain regions.

[0053] See Figure 6 This invention optimizes electrodes in the SPL brain region while simultaneously suppressing and not suppressing the electric field intensity in the SMG and ANG brain regions. The color of the brain region template in the figure represents the electric field intensity, indicated by the color bar on the right, which displays the electric field intensity in the range of 0–0.3 V / m. The circles in the figure represent the electrodes used, and their colors correspond to the magnitude of the current flowing into or out of that electrode, indicated by the color bar on the left. In the results on the left, the electric field intensities in the SPL, SMG, and ANG brain regions are 0.1124 V / m, 0.0500 V / m, and 0.0380 V / m, respectively. In the results on the right, the electric field intensities in the SPL, SMG, and ANG brain regions are 0.1439 V / m, 0.1294 V / m, and 0.0863 V / m, respectively. It can be seen that this invention can effectively suppress the electric field intensity in the nearby SMG and ANG brain regions while ensuring the stimulation effect on the SPL brain region.

[0054] Although preferred embodiments of the present invention have been described above in conjunction with examples, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art, under the guidance of the present invention, can make many other modifications without departing from the spirit and scope of the claims, such as considering the randomness of soil parameters, considering the randomness of the necking length, or considering different or more safety parameters. These all fall within the scope of protection of the present invention.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for optimizing multi-regional electrodes for transcranial electrical stimulation, characterized in that, It includes the following steps: (1) Construct a head simulation model; (2) Select the target area that needs to be optimized and the target points of one or more brain regions that need to suppress the electric field intensity, respectively; (3) Perform finite element analysis to optimize the electric field of the target area, while suppressing the electric field intensity of specific brain regions nearby, and constraining the number of electrodes used, the magnitude of the current of a single electrode and the total electrode current. (4) The optimization effect is evaluated by simulating and calculating the electric field strength of the brain regions that are stimulated and inhibited. The expression for electric field optimization is: ; Where s represents the magnitude of the electrode current, This indicates the target electric field distribution in the target area. The parameters representing focus optimization, This indicates the magnitude of the electric field strength in the inhibitory brain region. It should be less than the value constant. ; The constraints on the number of electrodes used, the magnitude of the current of a single electrode, and the total electrode current include: limiting the number of electrodes used in the optimization results to a specific value. The specific process is as follows: first, an optimization without electrode number restrictions is performed, and several electrodes with the largest currents are taken from the optimization results as a new solution space. The number of these electrodes is the same as the final required number of electrodes. Then, another optimization is performed to obtain the final electrode optimization result.

2. The method for optimizing multi-brain region electrodes for transcranial electrical stimulation according to claim 1, characterized in that, The construction of the head simulation model specifically includes the following steps: (1.1) The magnetic resonance imaging data was segmented to divide the individual head model structure into scalp, cerebrospinal fluid, skull and white and gray matter of the brain; (1.2) Place the electrodes by placing virtual electrodes using electrode positioning methods, including the 10-05 system and the 10-10 system; (1.3) Perform finite element meshing to generate a three-dimensional mesh and perform structural repair, generating a tetrahedral mesh from the segmented magnetic resonance imaging; (1.4) The electric field transfer matrix of each candidate electrode is obtained by finite element calculation.

3. The method for optimizing multi-brain region electrodes for transcranial electrical stimulation according to claim 1, characterized in that, The corresponding MNI target coordinates are determined based on the location of the target area and the brain region inhibiting the electric field.

4. The multi-brain region electrode optimization method for transcranial electrical stimulation according to claim 1, further includes the following constraints: ① The sum of the absolute values ​​of the currents shall not exceed a specific value Itotal; ② The absolute value of the current in a single electrode shall not exceed a specific value Im; ③ The magnitude of the input current is equal to the magnitude of the output current.

5. The method for optimizing multi-brain region electrodes for transcranial electrical stimulation according to claim 1, characterized in that, The inhibitory effect is observed by calculating the electric field strength established by the electrode current in the target area and the electric field strength in the inhibited brain region in the optimization results; the effect of electrode optimization is visually observed by referring to the electric field distribution map on the template.

Images