A method, device, and equipment for removing contact impedance noise in brain impedance measurement

Abstract

The present invention discloses a method, device and equipment for removing contact impedance noise in brain impedance measurement, including the following steps: (1) Collecting brain voltage and brain current with a mixed excitation signal of low-frequency and high-frequency sine waves; (2) Analyzing the voltage and current values of the low-frequency and high-frequency parts by Fourier transform, and calculating the high-frequency segment impedance value Zh and the low-frequency segment impedance value Zl; (3) Obtaining the contact impedance Zc and the high-frequency segment mapping value Zhcs of the extracranial tissue impedance through the high-frequency segment impedance value Zh and the low-frequency segment impedance value Zl; (4) Continuously measuring the brain voltage and brain current multiple times and calculating the high-frequency segment impedance value Zh and the high-frequency segment mapping value Zhcs each time according to the above steps (2) and (3), and obtaining the change Z' of the intracranial tissue impedance between two measurements through the calculated values of the two measurements. The method of the present invention can effectively remove the influence of electrode contact impedance and capture the change of intracranial tissue impedance. It can reduce the signal interference in complex environments such as body movement and electrode-skin contact during measurement.

Description

Technical Field

[0001] The present invention belongs to the field of non-invasive human brain impedance measurement, and particularly relates to a method, device and equipment for removing contact impedance noise in brain impedance measurement. Background Art

[0002] Brain electrical signals and brain impedance are important ways for screening brain diseases. Brain electrical signals are the overall effect of the electrical activities of a large number of brain nerve cells in a highly coherent state on the cerebral cortex, caused by the potential activities of the dendrites of a large number of cerebral cortical neurons. When the brain is stimulated by the outside world, thinking, or the physical state changes, the frequency and amplitude of the brain electrical signals will change. Brain impedance is a method for monitoring the function and blood supply of the blood vessels in the head, and can reflect peripheral resistance, vascular elasticity, and blood supply. Therefore, collecting brain electrical signals and brain impedance information is an important means for monitoring the skull and brain.

[0003] Existing brain impedance measurement technologies mainly use general human tissue impedance measurement methods (such as the four-electrode method), and only obtain the overall brain impedance by exciting with high-frequency current signals. Its disadvantages include: the measured value contains electrode contact impedance noise; during the measurement, the subject needs to remain absolutely quiet, and actions that affect the skin such as speaking and swallowing are very likely to interfere with the measurement results. Summary of the Invention

[0004] The purpose of the present invention is to provide a method, device and equipment for removing contact impedance noise in brain impedance measurement in view of the defects of the existing technology.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: A method for obtaining the impedance change of intracranial tissue in brain impedance measurement, measuring brain impedance by the four-electrode method, wherein a pair of excitation electrodes are respectively placed at the roots of the left and right ears, and a pair of acquisition electrodes are placed at positions adjacent to the excitation electrodes. Specifically, the following steps are adopted:

[0006] (1) Mix and excite a low-frequency signal fl and a high-frequency signal fh to collect brain voltage and brain current;

[0007] (2) Use Fourier transform to analyze the collected signals, obtain the voltage and current values of the low-frequency and high-frequency parts, and calculate the high-frequency segment impedance value Zh and the low-frequency segment impedance value Zl;

[0008] (3) Obtain the intracranial tissue impedance Zn through the high-frequency segment impedance value Zh and the low-frequency segment impedance value Zl;

[0009] (4) Measure the brain voltage and brain current in real time and calculate the intracranial tissue impedance Zn each time according to the above steps (2) and (3), and obtain the intracranial tissue impedance change Z' between two measurements through the two measurement calculation values.

[0010] Further, in step (2), the Fourier transform is used to analyze the collected signals to obtain the complex voltages Vl and Vh of the low-frequency and high-frequency parts, and the complex currents Cl and Ch. The low-frequency impedance Zl and the high-frequency impedance Zh are calculated according to Equations (1) and (2) respectively:

[0011] Zl = Vl / Cl = Zlreal + Zlimage (1)

[0012] Zh = Vh / Ch = Zhreal + Zhimage (2)

[0013] The low-frequency impedance Zl and the high-frequency impedance Zh are complex impedances.

[0014] Further, in step (3), the intracranial tissue impedance Zn is obtained specifically by the following steps:

[0015] 3.1 Calculate the equivalent resistance value Rcs and the equivalent capacitance Ccs of the human head through the impedance value Zl corresponding to the low-frequency signal fl using Equation (3):

[0016] Zl = Zc + Zs = Rcs - 1 / (2πfl*Ccs)j (3)

[0017] Where: Zc is the contact impedance, Zs is the extracranial tissue impedance, Rcs is equal to the real part of Zl, Rcs = Zlreal,

[0018] -1 / (2πflCcs) is equal to the imaginary part of Zl, Ccs = -1 / (Zlimage*2πfl);

[0019] 3.2 Calculate the theoretical mapping value Zhc + Zhs of Zc + Zs when transformed from the low frequency fl to the high frequency fh using Equation (4), denoted as Zhcs:

[0020] Zhcs = Zhc + Zhs = Rcs - 1 / (2πfh*Ccs)j (4)

[0021] 3.3 Calculate the intracranial tissue impedance Zn using Equation (5):

[0022] Zn = Zhs 2 / (Zhcs - Zh) - Zhs (5)

[0023] Where: Zhs is the extracranial tissue impedance at the high frequency fh.

[0024] Further, in step (4), the change Z' in the intracranial tissue impedance is obtained specifically by the following steps: Obtain the brain voltage and brain current in two consecutive measurements and calculate the change value Zn' in the intracranial tissue impedance between the two measurements using Equation (6):

[0025] Zn’ = Zhs22 / (Zhcs2 - Zh2) - Zhs2 -

Zhs12 / (Zhcs1 - Zh1) - Zhs1

[0026] = 1 / (Zhcs2 - Zh2) - 1 / (Zhcs1 - Zh1) (6)

[0027] Among them, the extracranial tissue impedance Zhs can be regarded as a constant 1.

[0028] An electronic device, the electronic device includes: at least one processor; and a memory communicatively connected to the at least one processor; wherein, the memory stores a computer program executable by the at least one processor, and the computer program is executed by the at least one processor so that the at least one processor can execute the above method.

[0029] A computer-readable storage medium stores computer instructions for implementing the above method when executed by a processor.

[0030] The human skull has a relatively high resistance to low-frequency current signals and good penetrability to high-frequency current. Generally, high-frequency current signals are used to excite non-invasive brain impedance measurement, and its measurement results inevitably include electrode contact impedance, extracranial tissue impedance, and intracranial tissue impedance. Among them, the contact impedance has the largest interference noise due to the influence of the electrode and the skin; the extracranial tissue impedance is mostly composed of venous blood vessels, and the change in blood volume is not obvious, and the pulse wave change cannot be observed in the low-frequency signal measurement. For the measurement of the continuous impedance change in the intracranial cavity, the extracranial tissue impedance can be regarded as a constant; the change in intracranial tissue impedance can reflect the change in intracranial blood volume and the development of lesions such as intracranial edema and ischemia, which is the main significance of brain impedance measurement applications.

[0031] The present invention uses a low-high frequency mixed current signal excitation measurement based on the four-electrode method. The low-frequency part of its current cannot penetrate the skull and can be used to measure the contact impedance and extracranial tissue impedance. In this low-frequency band, the brain impedance can be equivalent to a resistor-capacitor series circuit ( Figure 1 ). The high-frequency signal can penetrate the skull to measure the mixed impedance of the three. In this high-frequency band, the intracranial tissue impedance can be equivalent to being in parallel with the extracranial tissue impedance ( Figure 2 ).

[0032] Adopt this equivalent circuit method to map the contact impedance and extracranial tissue impedance collected by the low-frequency signal to the high-frequency band, obtain the theoretical mapped impedance of the contact impedance and extracranial tissue impedance under the high-frequency signal, and finally remove this mapped impedance from the mixed impedance measured under the actual high-frequency signal to obtain a purer intracranial tissue impedance change.

[0033] The advantages of this application are as follows: It can effectively remove the influence of electrode contact impedance and capture the impedance changes of intracranial tissues. It can reduce signal interference in complex environments such as body movement and electrode-skin contact during measurement. Description of the Drawings

[0034] Figure 1 is the equivalent circuit in the low-frequency band in the embodiment.

[0035] Figure 2 is the equivalent circuit in the high-frequency band in the embodiment. Detailed Embodiment

[0036] In order to enable those skilled in the art of this technology to better understand the solution of this application, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of this application.

[0037] It should be noted that the terms "including" and "having" in the description and claims of this application and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products, or devices.

[0038] Measure the brain impedance by the four-electrode method, where a pair of excitation electrodes are placed at the root of the left and right ears, and a pair of acquisition electrodes are placed at positions adjacent to the excitation electrodes. The specific steps are as follows:

[0039] 1. Acquisition of low- and high-frequency mixed excitation signals

[0040] Acquire the brain voltage and current with a mixed excitation signal of low-frequency (below 100 Hz) and high-frequency (20 KHz and above) sine waves.

[0041] 2. Analyze the voltage and current values of the low-frequency and high-frequency parts through Fourier transform, and calculate the impedance values Zl and Zh.

[0042] 3. Calculate the high-frequency segment mapping value Zhcs of the contact impedance and the extracranial tissue impedance.

[0043] 4. Continuously measure and calculate multiple times to obtain Zh and Zhcs.

[0044] 5. Calculate the intracranial tissue impedance change Z' according to Equation ③.

[0045] Based on the four - electrode method, a low - high frequency hybrid current signal is used for excitation measurement. The low - frequency part of the current cannot penetrate the skull and can be used to measure the contact impedance and the impedance of extracranial tissues. In this low - frequency band, the brain impedance can be equivalent to a series circuit of resistance and capacitance ( Figure 1 ). The high - frequency signal can penetrate the skull to measure the mixed impedance of the three. In this high - frequency band, the intracranial tissue impedance can be equivalent to being in parallel with the extracranial tissue impedance ( Figure 2 ).

[0046] Using this equivalent circuit method, the contact impedance and extracranial tissue impedance collected by the low - frequency signal are mapped to the high - frequency band to obtain the theoretical mapped impedance of the contact impedance and extracranial tissue impedance under the high - frequency signal. Finally, in the mixed impedance measured under the actual high - frequency signal, this mapped impedance is removed to obtain a purer change in intracranial tissue impedance.

[0047] Impedance value in the low - frequency band:

[0048] Zl = Zc + Zs = Rcs+1 / (2πfCcs)=Zlreal + Zlimage

[0049] Where Rcs is the equivalent resistance value, Ccs is the equivalent capacitance value, f is the excitation signal frequency. By measuring the real part Zlreal and imaginary part Zlimage of Zl in the low - frequency band, Rcs and Ccs can be calculated. When f changes from low - frequency to high - frequency, the theoretical value Zhcs = Zhc + Zhs of Zc + Zs in the high - frequency band can be obtained through this formula. Then

[0050] Zhc = Zhcs - Zhs ①

[0051] Impedance value in the high - frequency band:

[0052] Zh = Zhc+Zn*Zhs / (Zn + Zhs)

[0053] Transform this formula to get the expression of intracranial impedance:

[0054] Zn=(Zhc*Zhs - Zh*Zhs) / (Zh-(Zhc + Zhs))

[0055] Substitute ① into it to get

[0056] Zn = Zhs 2 / (Zhcs - Zh)-Zhs ②

[0057] Where Zhcs is the mapped impedance, Zh is the measured impedance in the high - frequency band, Zhs is the extracranial tissue impedance in the high - frequency band, and Zhs can be regarded as a constant in continuous measurement.

[0058] For the measurement of the continuously changing signal of intracranial impedance Z’ = Zn2 - Zn1

[0059] Substitute ② into it to get

[0060] Z’ = Zhs 2 (1 / (Zhcs2 - Zh2) - 1 / (Zhcs1 - Zh1))

[0061] For scenarios that only need to apply the trend of intracranial tissue impedance changes (such as EIT, REG, etc.), the constant Zhs can be regarded as 1.

[0062] That is, Z’ = 1 / (Zhcs2 - Zh2) - 1 / (Zhcs1 - Zh1) ③

[0063] The above is a further detailed description of the present invention, and it should not be regarded as a limitation to the specific implementation of the present invention. For those of ordinary skill in the technical field to which the present invention pertains, any simple deduction or substitution without departing from the concept of the present invention falls within the protection scope of the present invention.

Claims

1. A method for obtaining impedance changes of intracranial tissues in brain impedance measurement, characterized in that: Measure the brain impedance by the four - electrode method, where a pair of excitation electrodes are respectively placed at the roots behind the left and right ears, and a pair of acquisition electrodes are placed at positions adjacent to the excitation electrodes. The specific steps are as follows: (1) Mix a low - frequency signal fl and a high - frequency signal fh to excite and collect the brain voltage and brain current; (2) Use Fourier transform to analyze the collected signals, obtain the voltage and current values of the low - frequency and high - frequency parts, and calculate the high - frequency segment impedance value Zh and the low - frequency segment impedance value Zl; (3) Obtain the intracranial tissue impedance Zn through the high - frequency segment impedance value Zh and the low - frequency segment impedance value Zl; (4) Measure the brain voltage and brain current in real - time and calculate the intracranial tissue impedance Zn each time according to steps (2) and (3) above. Obtain the change in intracranial tissue impedance Zn' between two measurements through the calculated values of the two measurements; In step (2), use Fourier transform to analyze the collected signals to obtain the complex voltages Vl, Vh of the low - frequency and high - frequency parts, and the complex currents Cl, Ch. Calculate the low - frequency segment impedance Zl and the high - frequency segment impedance Zh according to equations ① and ② respectively: Zl = Vl / Cl = Zlreal+Zlimage ① Zh = Vh / Ch = Zhreal+Zhimage ② The low - frequency segment impedance Zl and the high - frequency segment impedance Zh are complex impedances; In step (3), the specific steps for obtaining the intracranial tissue impedance Zn are as follows: Step (3.1): Use the impedance value Zl corresponding to the low - frequency signal fl and calculate the equivalent resistance Rcs and equivalent capacitance Ccs of the human head using equation ③: Zl = Zc+Zs = Rcs - 1 / (2πfl*Ccs)j ③ Where: Zc is the contact impedance, Zs is the extracranial tissue impedance, Rcs is equal to the real part of Zl, Rcs = Zlreal, -1 / (2πfl*Ccs) is equal to the imaginary part of Zl, Ccs = -1 / (Zlimage*2πfl); Step (3.2): Use equation ④ to calculate the theoretical mapping value Zhc+Zhs of Zc+Zs when the low - frequency fl is transformed to the high - frequency fh, denoted as Zhcs: Zhcs = Zhc+Zhs = Rcs - 1 / (2πfh*Ccs)j ④ Step (3.3): Calculate the intracranial tissue impedance Zn through equation ⑤: Zn = Zhs² / (Zhcs - Zh)-Zhs ⑤ Where: Zhs is the extracranial tissue impedance at the high - frequency fh; In step (4), the specific steps for obtaining the change in intracranial tissue impedance Zn' are as follows: From equation ④, we get equation ⑥: Zhc = Zhcs - Zhs ⑥ The high - frequency segment impedance value is obtained from equation ⑦: Zh = Zhc+Zn*Zhs / (Zn+Zhs) ⑦ Transform equation ⑦ to get the intracranial impedance expression: Zn=(Zhc*Zhs - Zh*Zhs) / (Zh-(Zhc+Zhs)) ⑧ Substitute ⑥ into ⑧ to get: Zn = Zhs² / (Zhcs - Zh)-Zhs Obtain brain voltage and brain current in two consecutive measurements and calculate the change value Zn' of the intracranial tissue impedance between the two measurements using Equation ⑨: Zn' = Zhs2² / (Zhcs2-Zh2)-Zhs2-【Zhs1² / (Zhcs1-Zh1)-Zhs1】 = 1 / (Zhcs2-Zh2) - 1 / (Zhcs1-Zh1) ⑨ Among them, the extracranial tissue impedance Zhs is a constant value of 1 Ω.

2. An electronic device, characterized in that: The electronic device includes: at least one processor; and a memory communicatively connected to the at least one processor; wherein, the memory stores a computer program executable by the at least one processor, and the computer program is executed by the at least one processor so that the at least one processor can execute the method described in Claim 1.

3. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer instructions, and the computer instructions are used to implement the method described in Claim 1 when executed by a processor.

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