A directional stimulation simulation method for a multi-point deep brain electrode model

Abstract

The present invention relates to a stimulation model for an implantable deep brain stimulation electrode, belonging to the field of medical devices. Due to surgical errors, the deep brain stimulation electrode may cause unpredictable displacement of the electrode, resulting in the effective stimulation area deviating from the designated area. The multi-point deep brain stimulation electrode has the characteristic of high spatial resolution compared with the traditional circular deep brain stimulation electrode; the designed directional stimulation model can be used for the stimulation area regulation of the circumferential multi-point electrode. At the same time, this method can decouple the two position parameters of the effective stimulation area, namely the offset angle θ and the offset distance R, so that the control steps are independent of each other, without the need to readjust according to the result feedback, reducing the control difficulty.

Description

Technical Field

[0001] The present invention belongs to the technical field of medical devices, and particularly relates to a directional stimulation method for a multi-point deep brain stimulation electrode. Background Art

[0002] Brain nervous system diseases such as epilepsy, Parkinson's disease, and chronic pain are all caused by abnormal electrical discharges in specific regions of the brain. Deep brain stimulation (DBS) is a neuroengineering applied to the deep brain developed based on traditional neuroengineering. DBS controls abnormal brain neuron discharges by stimulating specific deep cranial nerve nuclei through implanted electrodes, thereby controlling diseases such as epilepsy and Parkinson's disease at the source. The DBS system mainly consists of three parts: a pulse generator that emits pulse voltage or current, electrical connections such as wires, and an implanted electrode. Among them, the implanted electrode is the most important component in the DBS system. However, the development of DBS electrodes has stagnated in recent years. The traditional ring electrode is no longer competent for the increasingly complex implantation requirements, and the performance of the implanted electrode has become a bottleneck in the development of the DBS system.

[0003] The traditional DBS electrode is a ring electrode, and the stimulation area is single and uncontrollable. The stimulation domain of the omnidirectional electrode used in traditional DBS is a circumferentially uniform stimulation area. However, surgical errors and postoperative displacement will cause the electrode to have unforeseen displacement, resulting in the effective stimulation domain deviating from the designated area. In recent years, some multi-point stimulation electrodes have been gradually applied, but they still cannot solve the problem of arbitrarily regulating the orientation of the effective stimulation domain, and can only improve the angular resolution of the electrode by increasing the circumferential point distribution. Contarino MF, Bour LJ et al. provided a related study on a 32-point deep brain stimulation electrode in 2014 [1] In 2013, a related study on a 32-point deep brain stimulation electrode was provided. However, the decrease in the stimulation point area will lead to a decrease in the stimulation effect of a single electrode. H.C.F. Martens, E. Toader et al. proposed a non-polar stimulation domain regulation method based on a four-point electrode in 2011 [2] In 2011, a non-polar stimulation domain regulation method based on a four-point electrode was proposed, but this method completely decouples the offset angle θ and the offset distance R, and the maximum error of R reaches 1 mm. Existing solutions cannot simultaneously obtain high-precision angles and efficient stimulation effects. Summary of the Invention

[0004] In order to solve the above problems existing in the prior art, the present invention proposes a directional stimulation method for a multi-point deep brain stimulation electrode. The technical problems to be solved by the present invention are realized through the following technical solutions:

[0005] The present invention provides a directional stimulation method for a circumferential multi-point deep brain stimulation electrode, which is characterized by using a multi-point deep brain stimulation electrode to perform electrical signal stimulation with point-by-point control. By superimposing different stimulation signals at each point, directional control of the effective stimulation area can be achieved. The multi-point deep brain stimulation electrode is an array formed by a plurality of electrode units distributed in a cylindrical shape. The electrode units at the same axial position are defined as a group, and the n units of each group of electrodes are evenly distributed on the circumferential surface corresponding to the axial position, where n≥3; as Figure 2 The shown deep brain stimulation electrode has 3 points in the circumferential direction and 4 points in the axial direction, that is, 4 groups, with 3 click units in each group.

[0006] The directional stimulation method of the multi-point deep brain electrode is characterized in that by controlling the input voltage or current values at different points, the superposition of the spatial electric fields is realized, so that the effective stimulation area deviates from the center to obtain an eccentric effective stimulation area at a specified position. The effective stimulation area is measured by the range surrounded by the equipotential lines of the electric potential, and the directional offset of the effective stimulation area is measured by the offset of the centroid of the area surrounded by the equipotential lines of the transverse section of the activated electrode points relative to the center of the electrode. As Figure 3 shown, the effective stimulation area is the area surrounded by a certain defined equipotential line on the plane passing through the center of the circumferential electrode and perpendicular to the electrode axis. When there are more electrode points in the axial direction, this stimulation area can be extended to other electrode planes.

[0007] The directional stimulation method of the multi-point deep brain electrode is characterized in that the electrical signal input to each electrode point is regulated. Since at least two basic vectors are required for the superposition of spatial vectors, but the stimulation points need to completely decouple two parameters of the centroid of the stimulation area, the number of electrode points distributed circumferentially can be any number of three or more.

[0008] The directional stimulation method of the multi-point deep brain electrode is characterized by:

[0009] First, according to the axial position of the electrode corresponding to the target stimulation area, select the corresponding group of electrode units as the working electrode units. In the cross-section perpendicular to the axis of the working electrode group, establish a plane coordinate system, and the center of the DBS electrode is the origin;

[0010] Preset an offset angle θ and an offset amount R of the centroid of the target stimulation area, and calculate the magnitude of the stimulation signal required for each electrode point, where the stimulation signal can be voltage or current.

[0011] Let the target unit vector constructed from the origin to the centroid of the target stimulation area be , and from the origin to the n working electrode units, construct the electrode unit vectors as (i = 1, 2,..., n), then the decomposition value V of the target unit vector i on each electrode unit vector is:

[0012] When the included angle with is less than 90°, then V i > 0, indicating that this electrode unit is a positive electrode;

[0013] When the included angle with is ≥ 90°, then V i < 0, indicating that this electrode unit is a negative electrode.

[0014] By defining the maximum voltage threshold V of a single electrode max , the largest item in the decomposition value V of the positive electrode i is amplified to V max , with an amplification ratio of k. All other positive electrodes are voltage-amplified according to the amplification ratio of k. Similarly, another proportionality coefficient j is set for all negative electrodes, and j can vary from 0 to k. By adjusting the value of j, fine-tuning of the offset distance R can be achieved without changing θ within an acceptable error range.

[0015] The multi-point deep brain electrode stimulation method of the present invention has the following advantages:

[0016] 1) This method can use a smaller number of electrode positions to achieve stepless regulation of the angle and offset of the centroid of the effective stimulation area, thereby reducing the risk of failure of brain electrode implantation, improving the implant error tolerance, and postoperative movement can avoid reoperation by adjusting the stimulation area. 2) The two parameters R and θ of the centroid of the stimulation area of the multi-point stimulation electrode can be completely decoupled. The user can achieve completely independent regulation of any angle and offset of the stimulation area by adjusting the two proportional parameters k and j. When the stimulation signals of two dominant electrodes are fixed, by changing the stimulation signals of other electrodes in equal proportion, R can be changed steplessly between 0 and R max , where R max is the polar coordinate distance R of the centroid of the stimulation area when k is 0. When regulating R, the change amount of the θ value is less than 0.5°. 3) This method has high versatility and is applicable to all multi-point deep brain stimulation electrode physical objects with 3 or more circumferential electrodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a structural block diagram of a directional stimulation method for a multi-point deep brain stimulation electrode proposed by the present invention;

[0018] Figure 2 is a schematic diagram of a circumferential 3-point and axial 4-point electrode applicable to the present invention;

[0019] Figure 3 is a pattern diagram of the Z-axis cross-section of a circumferential four-point electrode applicable to the present invention;

[0020] Figure 4 The relationship between the centroid offset R value and the j value of the position parameter of the effective stimulation region proposed by the present invention;

[0021] Figure 5 The relationship between the centroid offset angle θ value and the j value of the position parameter of the effective stimulation region proposed by the present invention;

[0022] In the figure: 1 is an electrical stimulation generator, 2 is a multi-point deep brain stimulation electrode, 3 is the electrical signals of each stimulation point, 4 is the synthesized effective stimulation region, 5 is the centroid position of the target effective stimulation region, 6 is the 0.2V equipotential line, and the enclosed area is the effective stimulation region. Specific implementation mode

[0023] The following further describes the present invention in detail with reference to specific embodiments, but the implementation mode of the present invention is not limited thereto.

[0024] The present invention proposes a directional stimulation method for a circumferential multi-point deep brain stimulation electrode, which is characterized in that electrical signal stimulation with point-by-point control is performed using a multi-point deep brain stimulation electrode. The directional control of the effective stimulation area can be achieved by superimposing different stimulation signals at each point. The multi-point deep brain stimulation electrode is a circumferentially distributed multi-point electrode, and the number of points in the axial direction of the electrode can be any number greater than or equal to 1. In this example, a simulation is performed on a multi-point deep brain stimulation electrode model with 4 circumferential electrodes and 2 axial electrodes. The layout of each group of electrode units is shown as Figure 3 shown. The diameter of this model is 0.05 inches to conform to the industry-wide common size, and finally the relevant results of this example are obtained.

[0025] The directional stimulation method of the multi-point deep brain electrode realizes the superposition of the spatial electric field by controlling the input voltage or current values of different points, so that the effective stimulation area deviates from the center to obtain an eccentric effective stimulation area at a specified position. The effective stimulation area is measured by the surrounding range of the equipotential line of the electric potential. The directional offset of the effective stimulation area is measured by the offset of the centroid of the cross-sectional equipotential line surrounding area of the activated electrode points relative to the center of the electrode. Therefore, the polar coordinates (R, θ) of the centroid of the effective stimulation area relative to the center of the electrode can be set.

[0026] In this embodiment, the specific steps for performing directional stimulation of the multi-point deep brain stimulation electrode are as follows:

[0027] Step 1, refer to Figure 3 , according to the electrode axial position corresponding to the target stimulation area, select the four electrode units S1, S2, S3, and S4 of the first group as the working electrode units. In the cross-section perpendicular to the axis of the working electrode group, establish a plane coordinate system, and the center of the DBS electrode is the origin;

[0028] Step 2: Preset an offset angle θ and an offset amount R of the centroid of the target stimulation region, and calculate the magnitudes of the stimulation signals required for each electrode position, where the stimulation signal can be voltage or current. In this embodiment, Figure 3 the label 5 in

[0029] gives the centroid position of the target stimulation region, and θ is 56.31°. Let the target unit vector constructed from the origin to the centroid of the target stimulation region be , and the electrode unit vectors are constructed from the origin to the 4 working electrode units as (i = 1, 2, 3, 4). Then the decomposition values V i of the target unit vector on each electrode unit vector are:

[0030] Specifically in this embodiment, V 1 = 2 / , V 2 = -3 / , V 3 = -2 / , V 4 = 3 / . It can be seen that S1 and S4 are positive electrodes, and S2 and S3 are negative electrodes.

[0031] Take the upper limit V max of the single-electrode stimulation voltage as 3V, then the amplification ratio k = . It can be calculated that V 1 = 2V, and j can take values from 0 to . By assigning V 1 = 2V, V 2 = -3j / V, V 3 = -2j / V, V 4 = 3 / V.

[0032] Step 3: Obtain different R values by changing the value of j. When j = 1, R is 0. When j = 0, R reaches the maximum value R max . In this example, a simulation is performed on a multi-point deep brain stimulation electrode model with 4 circumferential electrodes and 1 axial electrode. When V 1 = 2V and V 4 = 3V, the change amount of the θ value is examined by taking j from 0 to 0.8.

[0033] By plotting and analyzing the j-R relationship obtained in Step 3, the j-R trend line is obtained and the relational expression R = f(j) is obtained for applying any other k 1Value. At the same time, it is necessary to analyze the change amount of the centroid offset angle θ during this process. If the change amount requires correction of j, no correction is needed if the change amount is small.

[0034] Figure 4 The results show that the j-R relationship can be approximately fitted to a quadratic function, and its R 2 is greater than 0.99, showing a high goodness of fit. Therefore, in this method, when determining the θ parameter, the relationship between the centroid offset R and the j value can be described as R = A j 2 + B j + C, where A, B, and C are constants to be calibrated.

[0035] Figure 5 It is to verify the relationship between the centroid offset angle θ and the j value when the j value changes. The simulation results show that the change amount of the θ value is small when the j value changes. Especially when j < 0.6, the change amount of the θ value is less than 0.5 degrees. In this method, the j value and θ can be considered to be completely decoupled, so each step can be implemented serially without returning for correction. This greatly simplifies the complexity of the model.

Claims

1. A directional stimulation simulation method for a multi-point deep brain electrode model, where the multi-point deep brain electrode model is an array formed by a number of electrode units distributed in a cylindrical shape. The electrode units at the same axial position are defined as a group, and the n units of each group of electrodes are evenly distributed on the circumferential surface corresponding to the axial position, where n≥3. Characterized in that, This method includes the following steps: Step 1: According to the axial position of the electrodes corresponding to the target stimulation area, select the corresponding electrode unit group as the working electrode unit. In the cross-section perpendicular to the axis of the working electrode group, establish a plane coordinate system with the center of the DBS electrode as the origin. Step 2: Preset an offset angle θ and an offset amount R of the centroid of the target stimulation area, and calculate the magnitude of the stimulation signal required for each electrode point, where the stimulation signal is voltage or current. Let the target unit vector pointing from the origin to the centroid of the target stimulation area be , and the electrode unit vectors are constructed by pointing from the origin to n working electrode units as (i = 1, 2,..., n). Then the decomposition value V of the target unit vector i on each electrode unit vector is: When the included angle is less than 90°, then V i > 0, indicating that the electrode unit is a positive electrode; When the included angle ≥ 90°, then V i < 0, indicating that the electrode unit is a negative electrode; Step 3: By defining the maximum voltage threshold V of a single electrode max , the decomposition value V of the positive electrode i The largest item in is amplified to V max , with an amplification ratio of k. All other positive electrodes are voltage-amplified according to the amplification ratio of k. Similarly, another proportionality coefficient j is set for all negative electrodes, and j can vary from 0 to k. By adjusting the value of j, fine control of the offset distance R can be achieved without changing θ within an acceptable error range.

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