A method for improving image reconstruction quality during the treatment of cerebral edema

Abstract

The present invention discloses a method for improving the quality of image reconstruction during the treatment of cerebral edema. First, by determining the linear relationship between the change in the measured boundary voltage and the degree of dehydration, and then combining with the prior matrix to select the change in the measured boundary voltage caused solely by the scalp corresponding to the degree of dehydration, the image reconstruction of the intracranial dehydration region is achieved by suppressing the influence of scalp dehydration. The method proposed by the present invention can effectively improve the spatial resolution of the reconstructed image, thereby improving the imaging quality, and has a wide range of applicability and great application potential in electrical impedance tomography of the brain.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrical impedance tomography, and particularly relates to a method for improving the quality of image reconstruction during the treatment of cerebral edema. Background Art

[0002] Medical imaging is a key part of the clinical treatment process, which provides the possibility for the diagnosis, monitoring and treatment of human diseases. At present, many medical imaging technologies have been developed. Among these technologies, computed tomography (CT) and magnetic resonance imaging (MRI) are commonly used for clinical diagnosis. However, CT has radiation, while MRI is expensive. In recent years, compared with CT and MRI, an emerging electrical impedance tomography (EIT) has the characteristics of being portable, non-invasive and low-cost, and is more suitable for bedside monitoring of patients, which has attracted considerable research interest from scholars. Due to its significant advantages, EIT shows great potential in medical applications, such as in the fields of lung ventilation, brain imaging and breast cancer detection.

[0003] Cerebral edema is one of the main neurological diseases leading to high morbidity and mortality, accounting for up to 50% of the mortality of victims suffering from traumatic brain injury. In addition, due to the occurrence of swelling, brain hernia and cerebral ischemia may be caused. Therefore, the monitoring of cerebral edema is very important and helps in the timely diagnosis and treatment of patients with such diseases. In order to reduce the mortality of patients and improve the prognosis, accurate imaging examinations are crucial in clinical treatment. As is well known, the change of pathological tissues will lead to the change of conductivity distribution, which provides the possibility for monitoring cerebral ischemia with EIT technology. Cerebral edema often occurs after brain injury, endangering human health. During the dehydration treatment of cerebral edema, the conductivity distribution in this area will change. As a visualization technology, electrical impedance tomography (EIT) is favored because of its ability to reconstruct conductivity distribution, which makes it the preferred method for monitoring the treatment of cerebral edema. However, when treating brain tissue dehydration, the scalp will also dehydrate. The simultaneous dehydration of brain tissue and scalp will greatly affect the quality of image reconstruction. To solve this problem, the present invention proposes a method aimed at reducing the impact of scalp dehydration on intracranial monitoring and thus improving the quality of image reconstruction.

[0004] In existing research, Haoting Li et al. published an article titled "Automatic evaluation of mannitol dehydration treatments on controlling intracranial pressure using electrical impedance tomography" in the 20th volume of the IEEE Sensor Journal, pages 4832 - 4839 in 2022. This literature shows that during the mannitol dehydration treatment for cerebral edema, both the cerebral tissue layer and the scalp layer will dehydrate. The increase in scalp layer impedance further hinders the current injected into the cerebral layer, which will bring difficulties to the accurate monitoring of intracranial dehydration. However, the above method is mainly a classification study on the side effects of improper use of mannitol, and does not involve the research on suppressing the EIT data perturbation caused by scalp dehydration and thus improving the image reconstruction quality.

[0005] In order to improve the spatial resolution of the reconstructed image, especially to enhance the quality of brain imaging, the present invention proposes a method for improving image reconstruction quality to reduce the influence of scalp dehydration during the treatment of cerebral edema. This method uses the change amount of the optimized boundary voltage measurement value for image reconstruction, and can effectively improve the reconstruction quality of the image. Summary of the Invention

[0006] The technical problem solved by the present invention is to propose a method for improving image reconstruction quality during the treatment of cerebral edema. This method determines the degree of dehydration by establishing a linear relationship between the change amount of the boundary voltage measurement value and the degree of dehydration, and then finds the change amount of the boundary voltage measurement value caused by separate scalp dehydration corresponding to the prior matrix according to the degree of dehydration, and then conducts optimization, and finally realizes the reconstruction of intracranial images.

[0007] The present invention adopts the following technical solution to solve the above technical problem. A method for improving image reconstruction quality during the treatment of cerebral edema, characterized in that the specific steps are as follows:

[0008] Step S1, according to the shape information of the skull and brain, and combining the conductivities corresponding to the scalp layer, skull layer, and cerebral tissue layer, construct a standard 2D model of the skull and brain on a computer. This model is a three-layer structure of the scalp, skull, and cerebral tissue, and the conductivities of the scalp layer, skull layer, and cerebral tissue layer are set respectively;

[0009] Step S2: Obtain the boundary voltage measurement value U0 of the 2D cranial model when the brain tissue layer and the scalp layer are not dehydrated, and then obtain the boundary voltage measurement value U and the sensitivity matrix J of the 2D cranial model when the brain tissue layer and the scalp layer are dehydrated by 2% - 10% simultaneously;

[0010] Step S3: Establish a linear relationship between the change in the boundary voltage measurement value and the degree of dehydration. The specific process is as follows:

[0011] Step S301: When the degree of dehydration gradually increases between 2% and 10%, obtain the absolute average value |ΔU| of the change in the boundary voltage measurement value at different degrees of dehydration * , and the calculation process of the absolute average value of the change in the boundary voltage measurement value is as follows: First, take the absolute value of the change ΔU of 192 boundary voltage measurement values; Second, perform feature extraction on the change ΔU of 192 boundary voltage measurement values, that is, take the average value;

[0012] Step S302: Through fitting, the linear relationship expression of |ΔU| * changing with the degree of dehydration can be obtained as |ΔU| * = 1.172×d - 1.454×10 -2 , where the interval step of the degree of dehydration d is 0.5%;

[0013] Step S4: When the degree of dehydration of the single scalp layer changes between 2% and 10%, measure the boundary voltage measurement value U of the model at different degrees of dehydration of the single scalp layer s , U s = {U s2％ , U s2.5％ , U s3％ …U sd％}, the interval step of d is 0.5%, and U sd represents the boundary voltage measurement value of the model when the degree of dehydration of the single scalp is d. Subtract the empty-field boundary voltage measurement value U0 when both the brain tissue layer and the scalp layer are not dehydrated from U sd to obtain the change in the boundary voltage measurement value of the model when the degree of dehydration of the single scalp layer is d, which is ΔU sd = U sd - U0. Set the change in the boundary voltage measurement value of the model at different degrees of dehydration as ΔU s = {ΔU s2％ , ΔU s2.5％ , ΔU s3％ …ΔU sd％};

[0014] Step S5: Establish a prior matrix that one-to-one corresponds to the change in the boundary voltage measurement value of the model of the single scalp layer at different degrees of dehydration and the degree of dehydration ​ The interval step size of the dehydration degree d is set to 0.5%, where, represents the real number field, H represents the number of changes in the measured values of the model boundary voltage, and Y represents the number of dehydration degree data;

[0015] Step S6, measure the actual boundary voltage measurement values U of the brain tissue layer and the scalp layer under dehydration conditions m and the actual boundary voltage measurement values U when neither the brain tissue layer nor the scalp layer is dehydrated i , then U m - U i is approximately the change in the actual boundary voltage measurement value caused solely by dehydration;

[0016] Step S7, first, take the absolute value of the change in the actual boundary voltage measurement value U m - U i caused solely by dehydration, average it, and substitute it into the linear relationship expression in step S302 to determine the current dehydration degree; then, in the prior matrix P T in step S5, select the change in the measured value of the model boundary voltage ΔU sd corresponding to the current dehydration degree d during separate scalp dehydration;

[0017] Step S8, subtract the change in the measured value of the model boundary voltage ΔU m during separate scalp dehydration from the actual boundary voltage measurement value U sd of the scalp and the brain tissue at the dehydration degree d, and then subtract the empty field boundary voltage measurement value U0 when neither the scalp nor the brain tissue is dehydrated to obtain the compensated voltage b', that is, b' = U m - ΔU sd - U0;

[0018] Step S9, regard the electrical capacitance tomography problem as an inverse problem b' ≈ J·g, where g is the change in conductivity. Based on the L1 regularization method, the conductivity distribution is estimated as where λ is the regularization parameter used to balance the fidelity term and the weight between the penalty term ||g||1;

[0019] Step S10, use the alternating direction multiplier method to solve the optimal conductivity distribution in step S9, and reconstruct the image according to the coordinate position information of the obtained optimal conductivity distribution.

[0020] Further specified, the specific process of step S2 is:

[0021] Step S201: Set 16 electrodes of the same size equidistantly outside the field of the 2D cranial model. Adopt the mode of relative current excitation and adjacent voltage measurement, that is, select any pair of relative electrodes as the excitation electrodes, and sequentially measure the boundary voltage measurement values between other adjacent electrodes except the selected excitation electrodes, a total of 12; sequentially cycle through 16 pairs of relative electrodes, and a total of 16×12 = 192 boundary voltage measurement values are collected.

[0022] Step S202: Measure the open-field boundary voltage measurement value U0 when neither the brain tissue layer nor the scalp layer is dehydrated; when both the brain tissue layer and the scalp layer are dehydrated, measure the model boundary voltage measurement values U corresponding to the dehydration degrees from 2% to 10%, where U = {U 2％ , U 2.5％ , U 3％ …U d％}, the subscript d represents the corresponding dehydration degree, and the value range is d = {2%, 2.5%, 3%…10%}, that is, the interval step of d is 0.5%. That is, at a certain dehydration degree, the change amount of the boundary voltage measurement value can be expressed as ΔU = U d - U0.

[0023] Step S203: Based on the open-field boundary voltage measurement value U0 when neither the brain tissue layer nor the scalp layer is dehydrated, and combined with the calculation of the sensitivity theory, obtain the sensitivity matrix J. The calculation formula of the sensitivity theory is:

[0024] In the formula, J mn is the sensitivity coefficient of the nth electrode pair to the mth electrode pair, φ m , φ n are the field potential distributions of the mth electrode pair and the nth electrode pair respectively when the excitation currents are I m , I n ; s R represents the measurement field; ▽ is the gradient operator.

[0025] The beneficial effects of the present invention are as follows: The present invention proposes a method for improving the image reconstruction quality by reducing the influence of scalp dehydration during the treatment of cerebral edema. First, by determining the linear relationship between the change amount of the boundary voltage measurement value and the dehydration degree, and then combining the prior matrix to select the change amount of the boundary voltage measurement value caused solely by the scalp corresponding to the dehydration degree, the image reconstruction of the intracranial dehydration area is realized by suppressing the influence of scalp dehydration. The present invention can effectively improve the spatial resolution of the intracranial reconstructed image, thereby improving the imaging quality, and has great application potential in brain medical imaging. Brief Description of the Drawings

[0026] Figure 1Flow chart of a method for improving image reconstruction quality during the treatment of cerebral edema provided by the present invention;

[0027] Figure 2 Pattern of the 2D model single-section measured field, electrode distribution, excitation current, and measurement voltage of the present invention (taking the rabbit cranium as an example); Figure 2 In the figure: 1 - scalp layer, 2 - skull layer, 3 - brain tissue layer, 4 - cerebral ischemia, 5 - electrode, 6 - measurement voltage, 7 - excitation current;

[0028] Figure 3 Schematic diagrams of the image reconstruction results of four models without compensation and the image reconstruction results of the method proposed by the present invention;

[0029] Figure 4 For the correlation coefficient (CC) and blur radius (BR) of the reconstruction results of four models. Detailed implementation manner

[0030] The method for improving image reconstruction quality during the treatment of cerebral edema provided by the present invention will be described in detail in combination with the accompanying drawings and embodiments.

[0031] A method for improving image reconstruction quality during the treatment of cerebral edema according to the present invention aims to improve the image reconstruction quality during intracranial dehydration. Aiming at problems such as artifacts in the reconstructed image and the inability to present the target object when both the scalp and brain tissue are dehydrated, the compensated and optimized boundary voltage measurement value is used for image reconstruction to improve the spatial resolution of the intracranial reconstructed image and effectively improve the quality of the reconstructed image.

[0032] As Figure 1 shown, it is a flow chart of a method for improving image reconstruction quality during the treatment of cerebral edema provided by the present invention, and the specific steps are as follows:

[0033] Step S1, according to the shape information of the cranium and in combination with the conductivities corresponding to the scalp layer, skull layer, and brain tissue layer, construct a standard 2D model of the cranium on a computer. This model is a three-layer structure of the scalp, skull, and brain tissue, and the conductivities of the scalp layer, skull layer, and brain tissue layer are set to 0.44 S / m, 0.012 S / m, and 0.149 S / m respectively.

[0034] Step S2, obtain the boundary voltage measurement value U0 of the 2D cranium model when the brain tissue layer and the scalp layer are not dehydrated, and then obtain the boundary voltage measurement value U and the sensitivity matrix J of the 2D cranium model when the brain tissue layer and the scalp layer are dehydrated simultaneously by 2% - 10%. Specifically:

[0035] Step S201: Set 16 electrodes of the same size at equal distances outside the field of the 2D cranial model. Adopt the mode of relative current excitation and adjacent voltage measurement, that is, select any pair of relative electrodes as the excitation electrodes, and successively measure the boundary voltage measurement values between other adjacent electrodes except the selected excitation electrodes, a total of 12; cycle through the excitation of 16 pairs of relative electrodes in turn, and a total of 16×12 = 192 boundary voltage measurement values can be collected.

[0036] Step S202: Measure the empty-field boundary voltage measurement value U0 when neither the brain tissue layer nor the scalp layer is dehydrated; when both the brain tissue layer and the scalp layer are dehydrated, measure the model boundary voltage measurement value U corresponding to the dehydration degree of 2% - 10%, where U = {U 2％ , U 2.5％ , U 3％ …U d％}, the subscript d represents the corresponding dehydration degree, and the value range is d = {2%, 2.5%, 3%…10%}, that is, the interval step of d is 0.5%. That is, at a certain dehydration degree, the change amount of the boundary voltage measurement value can be expressed as ΔU = U d - U0.

[0037] Step S203: Based on the empty-field boundary voltage measurement value U0 when neither the brain tissue layer nor the scalp layer is dehydrated, and combined with the calculation of the sensitivity theory, the sensitivity matrix J can be obtained. The calculation formula of the sensitivity theory is: In the formula, J mn is the sensitivity coefficient of the nth electrode pair to the mth electrode pair, φ m , φ n are the field potential distributions of the mth electrode pair and the nth electrode pair respectively when the excitation currents are I m , I n ; s R represents the measurement field; ▽ is the gradient operator.

[0038] Step S3: Establish a linear relationship between the change amount of the boundary voltage measurement value and the dehydration degree, specifically:

[0039] Step S301: When the dehydration degree gradually increases between 2% and 10%, obtain the absolute average value |ΔU| * of the change amount of the boundary voltage measurement value at different dehydration degrees. The calculation process of the absolute average value of the change amount of the boundary voltage measurement value: First, take the absolute value of the change amount ΔU of the 192 boundary voltage measurement values; second, perform feature extraction on the change amount ΔU of the 192 boundary voltage measurement values, that is, take the average value.

[0040] Step S302: Through fitting, the linear relationship expression of |ΔU| * changing with the dehydration degree can be obtained as |ΔU|* =1.172×d-1.454×10 -2 , where the interval step size of the dehydration degree d is 0.5%.

[0041] Step S4, when the dehydration degree of the individual scalp layer varies between 2% and 10%, the model boundary voltage measurement value U of the individual scalp layer at different dehydration degrees is measured. s , U s = {U s2％ , U s2.5％ , U s3％ …U sd％}, the interval step of d is 0.5%, U sd Represents the model boundary voltage measurement value when the scalp dehydration degree is d. sd The difference between the measured value of the boundary voltage of the empty field when the brain tissue layer and the scalp layer are not dehydrated, U0, is used to obtain the change in the measured value of the boundary voltage of the model when the dehydration degree of the scalp layer is d, which is ΔU sd =U sd -U0, the change of the model boundary voltage measurement value under different dehydration degrees is set to ΔU s ={ΔU s2％ , ΔU s2.5％ , ΔU s3％ …ΔU sd％}.

[0042] Step S5, establishing the variation of the model boundary voltage measurement value of the individual scalp layer at different dehydration levels Dehydration One-to-one correspondence prior matrix The interval step size of the dehydration degree d is set to 0.5%. represents the real number domain, H represents the number of changes in the model boundary voltage measurement values, and Y represents the number of dehydration degrees.

[0043] Step S6, respectively measuring the actual boundary voltage measurement values U of the brain tissue layer and the scalp layer under dehydration conditions m The actual boundary voltage measurement value U when the brain tissue layer and the scalp layer are not dehydrated i , then U m -U i Approximately the amount of change in the actual boundary voltage measurement caused by dehydration alone.

[0044] Step S7, first, the change in the actual boundary voltage measurement value caused by dehydration alone, U m -U i After taking the absolute value and averaging it, substitute it into the linear relationship expression in step S302 to determine the current dehydration degree; then, in step S5, the prior matrix P TSelect the change amount ΔU of the model boundary voltage measurement value during single scalp dehydration corresponding to the current dehydration degree d sd 。

[0045] Step S8: Subtract the change amount ΔU of the model boundary voltage measurement value during single scalp dehydration from the actual boundary voltage measurement value U when the scalp and brain tissue are at the dehydration degree d m Then subtract the empty field boundary voltage measurement value U0 when neither the scalp nor the brain tissue is dehydrated to obtain the compensated voltage b', that is, b' = U sd - ΔU m - U0. sd -U0.

[0046] Step S9: Regard the electrical impedance tomography problem as an inverse problem b'≈J·g, where g is the change amount of conductivity. Based on the L1 regularization method, the conductivity distribution is estimated as where λ is the regularization parameter used to balance the weight between the fidelity term and the penalty term ||g||1.

[0047] Step S10: Use the alternating direction multiplier method to solve the optimal conductivity distribution in Step S9. Reconstruct the obtained optimal conductivity distribution according to the coordinate position information.

[0048] As Figure 2 shown, it is the mode of the single cross-section scalp layer 1, skull layer 2, brain tissue layer 3, cerebral ischemia 4, excitation current 7, measurement voltage 6 and the electrode 5 distribution of the 2D rabbit head model. 16 electrodes 5 are evenly distributed outside the field of view.

[0049] Select the cases where the target is located at four different positions in the brain tissue layer as examples. The true distribution of the target in the field of view is as Figure 3 shown in the first row. The second row is the reconstructed image obtained without compensation. It can be seen that there are many artifacts in the background and the size and position of the target cannot be basically reconstructed. In contrast, the third row is the reconstructed image obtained by using the method proposed in the present invention. For the four models A, B, C, and D, the target can be well reconstructed and there are almost no artifacts in the background. The results show that this method can effectively improve the image quality of intracranial imaging, improve the resolution of image reconstruction, and has important guidance for timely determining the condition clinically.

[0050] As Figure 4As shown, the correlation coefficients (CC) and blur radii of the reconstructed results of four models without compensation and the method proposed in the present invention. (a) shows the CC values of the four models, and (b) shows the BR values of the four models. The expression of CC is shown as follows. The larger the correlation coefficient value of the reconstructed image, the better the quality of the reconstructed image.

[0051]

[0052] In the formula, g c is the calculated conductivity, and g a represents the actual conductivity. and respectively represent the conductivity values on the e-th element. and respectively represent the average values of g c and g a .

[0053] The BR expression is shown as follows. The smaller the blur radius value of the reconstructed image, the better the quality of the reconstructed image.

[0054]

[0055] In the formula, A S is the area of the target region, and A0 is the area of the entire field.

[0056] It can be seen that the correlation coefficient of the reconstructed image by the method proposed in the present invention is much larger than that of the reconstructed image before compensation, and the blur radius of the reconstructed image using the method proposed in the present invention is much smaller than that of the reconstructed image before compensation. This further confirms the superiority of the method proposed in the present invention and can effectively improve the quality of the reconstructed image.

[0057] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for improving the quality of image reconstruction during the treatment of cerebral edema, characterized in that The specific steps are as follows: Step S1: Based on the shape information of the skull and brain, and in combination with the conductivity corresponding to the scalp layer, skull layer, and brain tissue layer, construct a standard 2D model of the skull and brain on a computer. This model has a three-layer structure of the scalp, skull, and brain tissue, and the conductivity of the scalp layer, skull layer, and brain tissue layer is set respectively; Step S2: Obtain the boundary voltage measurement value U0 of the 2D skull and brain model when the brain tissue layer and the scalp layer are not dehydrated, and then obtain the boundary voltage measurement value U and the sensitivity matrix J of the 2D skull and brain model when the brain tissue layer and the scalp layer are dehydrated by 2% - 10% at the same time; Step S3: Establish a linear relationship between the change in the boundary voltage measurement value and the degree of dehydration. The specific process is as follows: Step S301, when the dehydration level gradually increases between 2% and 10%, obtain the absolute average value |ΔU| of the change in the boundary voltage measurement value at different dehydration levels * , calculation process of the absolute average value of the change in the boundary voltage measurement value: First, take the absolute value of the change ΔU of 192 boundary voltage measurement values; Second, perform feature extraction on the change ΔU of 192 boundary voltage measurement values, that is, take the average value; Step S302, the linear relationship expression of |ΔU| varying with the dehydration degree can be obtained through fitting. * The linear relationship expression of |ΔU| varying with the dehydration degree is * = 1.172×d - 1.454×10 -2 , where the interval step of the dehydration degree d is 0.5%; Step S4, when the dehydration degree of the single scalp layer varies between 2% and 10%, the measured model boundary voltage measurement values U of the single scalp layer at different dehydration degrees s , U s = {U s2％ , U s2.5％ , U s3％ …U sd％}, the interval step size of d is 0.5%, U sd represents the measured model boundary voltage value at the dehydration degree d of the single scalp, and the difference between U sd and the measured value U0 of the empty field boundary voltage when neither the brain tissue layer nor the scalp layer is dehydrated is obtained, and the change amount of the measured model boundary voltage value of the single scalp layer at the dehydration degree d is obtained as ΔU sd = U sd - U0, and the change amounts of the measured model boundary voltage values at different dehydration degrees are set as ΔU s = {ΔU s2％ , ΔU s2.5％ , ΔU s3％ …ΔU sd％}; Step S5: Establish the variation of the measured boundary voltage of the separate scalp layer under different degrees of dehydration and the degree of dehydration a one-to-one corresponding prior matrix The interval step size of the degree of dehydration d is set to 0.5%, where represents the real number field, H represents the number of variations of the measured boundary voltage of the model, and Y represents the number of degree of dehydration data; Step S6, respectively measure the actual boundary voltage measurement values U of the brain tissue layer and the scalp layer under dehydration conditions m and the actual boundary voltage measurement values U when neither the brain tissue layer nor the scalp layer is dehydrated i , then U m -U i is approximately the change in the actual boundary voltage measurement value caused solely by dehydration; Step S7: First, take the absolute value of the change in the actual boundary voltage measurement value U m -U i caused solely by dehydration, average it, and substitute it into the linear relationship expression in step S302 to determine the current degree of dehydration. Then, select the change in the model boundary voltage measurement value ΔU T corresponding to the current degree of dehydration d during separate scalp dehydration from the prior matrix P sd in step S5; Step S8: Subtract the change in the measured boundary voltage of the model during the dehydration of the scalp alone, ΔU, from the measured boundary voltage U of the actual boundary between the scalp and the brain tissue at the dehydration level d. m Then, subtract the measured boundary voltage U0 of the empty field when neither the scalp nor the brain tissue is dehydrated. The compensated voltage b' is obtained, i.e., b' = U sd - ΔU m - U0; sd ​ Step S9, regarding the electrical tomography problem as an inverse problem \(b' \approx J\cdot g\), where \(g\) is the change in conductivity, and estimating the conductivity distribution based on the L1 regularization method as where \(\lambda\) is the regularization parameter used to balance the weights between the fidelity term and the penalty term \(\|g\|_1\); Step S10: Use the alternating direction method of multipliers to solve the optimal conductivity distribution in Step S9, and reconstruct the image of the obtained optimal conductivity distribution according to the coordinate position information.

2. The method for improving image reconstruction quality during the treatment of brain edema according to claim 1, characterized in that The specific process of Step S2 is as follows: Step S201: Set 16 electrodes of the same size at equal intervals outside the field of the 2D skull and brain model, and adopt the mode of relative current excitation and adjacent voltage measurement, that is, select any pair of relative electrodes as the excitation electrodes, and sequentially measure the boundary voltage measurement values between other adjacent electrodes except the selected excitation electrodes, a total of 12; cycle through the excitation of 16 pairs of relative electrodes in sequence, and a total of 16×12 = 192 boundary voltage measurement values are collected; Step S202, measure the empty-field boundary voltage measurement value U0 when neither the brain tissue layer nor the scalp layer is dehydrated; when the brain tissue layer and the scalp layer are dehydrated simultaneously, measure the model boundary voltage measurement value U corresponding to the dehydration degree of 2% - 10%, where U = {U 2％ , U 2.5％ , U 3％ …U d％}, the subscript d represents the corresponding dehydration degree, and the value range is d = {2%, 2.5%, 3%…10%}, that is, the interval step of d is 0.5%, that is, at a certain dehydration degree, the change amount of the boundary voltage measurement value can be expressed as ΔU = U d - U0; Step S203: Based on the measured value U0 of the empty-field boundary voltage when neither the brain tissue layer nor the scalp layer is dehydrated, and combined with the calculation of the sensitivity theory, a sensitivity matrix J is obtained. The calculation formula of the sensitivity theory is as follows: Where, J mn is the sensitivity coefficient of the nth electrode pair to the mth electrode pair, and φ m , φ n are the potential distributions in the field domain when the excitation currents of the mth electrode pair and the nth electrode pair are I m , I n respectively; s R represents the measurement field domain; is the gradient operator.

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