Surface Laplacian potential monitoring system based on tripolar concentric ring active electrode

Abstract

The invention discloses a surface Laplace potential monitoring system based on three-pole concentric ring active electrodes, which relates to measurement for diagnosis purposes and comprises an acquisition system circuit and a plurality of three-pole concentric ring active electrodes connected with the acquisition system circuit. Wherein the three-pole concentric ring active electrode comprises a three-pole concentric ring electrode which adopts a discontinuous circular ring structure, so that three electrodes in the three-pole concentric ring electrode are in conformal contact with a human body; and the electrode front-end circuit is integrated in the tripolar concentric ring active electrode and is used for receiving signals of the three electrodes of the tripolar concentric ring electrode and calculating the surface Laplace potential of the center point of the electrode. The brain physiological electrical signal acquisition quality and spatial resolution can be improved, noise interference can be reduced, scalp electroencephalogram can be accurately acquired, and real-time surface Laplace potential calculation can be carried out.

Description

Technical Field

[0001] The present invention relates to measurements for diagnostic purposes and, more particularly, to a surface Laplace potential monitoring system based on a tripolar concentric ring active electrode. Background Art

[0002] Electroencephalography (EEG) is acclaimed for its high temporal resolution and ease of use, making it a prime candidate for brain-computer interface (BCI) applications. However, the low spatial resolution of EEG complicates the precise mapping of brain activity, and its sensitivity to physiological artifacts limits wider applications. Electrodes, as key sensors in EEG monitoring systems, are responsible for converting ionic currents generated by human cells into electrical signals. In non-invasive EEG monitoring, signals must pass through various media such as the skull, blood, and skin, which are affected by the volume conductor effect. This results in a decrease in the ability to accurately locate the spatial activity of brain neurons and makes EEG signals susceptible to interference from other physiological signals.

[0003] Hiorth was the first to apply the surface Laplace operator to EEG. The Laplace operator is the second-order spatial derivative of the surface potential and can be regarded as a spatial filter. It is more sensitive to signals near the observation position, reduces the influence of the body conductor effect, and improves spatial selectivity. The traditional method of calculating the surface Laplace potential is to use a wet electrode array for calculation and then use a spline algorithm for post-processing. The algorithm is highly complex, the electrode spacing is large, and the calculation accuracy is not high.

[0004] In response to these problems, Besio proposed the concentric ring electrode (CRE), which not only greatly reduced the number of electrodes required, but also made the signals monitored by the electrodes highly concentrated on local physiological activities due to the close distance between the rings, thereby more effectively reducing electrooculogram (EOG) and electromyogram (EMG) artifacts. However, surface Laplace potentials have not been widely used in brain research. First, due to the need to design special electrodes and acquisition circuits, there are currently few commercial devices for surface Laplace potential monitoring. Secondly, due to the small distance between electrode rings, not only is it easy to cause short circuits between adjacent rings, but the signal difference between electrodes is small, and the requirements for signal amplification are more stringent. Currently commercial CREs are rigid and the contact surface is a planar structure, which may lead to mechanical mismatch with the skin and cause fluctuations in the contact interface. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a surface Laplace potential monitoring system based on three-pole concentric ring active electrodes in response to the shortcomings of the existing technology, which can improve the quality and spatial resolution of brain physiological electrical signal acquisition, reduce noise interference, accurately collect scalp EEG, and perform real-time surface Laplace potential calculation.

[0006] The surface Laplace potential monitoring system based on the three-pole concentric ring active electrode of the present invention comprises a collection system circuit and a plurality of three-pole concentric ring active electrodes connected thereto; wherein,

[0007] The three-pole concentric ring active electrode comprises:

[0008] A three-pole concentric circular ring electrode adopts a discontinuous circular ring structure so that the three electrodes in the three-pole concentric circular ring electrode form conformal contact with the human body;

[0009] The electrode front-end circuit is integrated in the three-pole concentric ring active electrode and is used to receive signals from the three electrodes of the three-pole concentric ring electrode and calculate the surface Laplace potential of the center point of the electrode.

[0010] Preferably, the surface Laplace potential is calculated as follows:

[0011]

[0012] Where, L V0 is the surface Laplace potential, r is the distance between the ring electrodes, V i 、V m 、V o are the signal values ​​measured by the central circle electrode, the middle ring electrode and the outer ring electrode, respectively. 4 ) is the fourth-order infinitesimal of r.

[0013] Preferably, the three electrodes of the three-pole concentric circular ring electrode are respectively a central circular electrode, a middle ring electrode and an outer ring electrode; wherein the middle ring electrode and the outer ring electrode are discontinuous circular ring structures, the central circular electrode is a continuous structure, and the areas of the central circular electrode, the middle ring electrode and the outer ring electrode are all the same.

[0014] Preferably, the central circular electrode, the middle ring electrode and the outer ring electrode are all made of a flexible conductive composite material.

[0015] Preferably, the lower surfaces of the central circular electrode, the middle ring electrode and the outer ring electrode are all in an arc-shaped structure, and the lower surfaces of the central circular electrode, the middle ring electrode and the outer ring electrode together form a contact arc surface structure.

[0016] Preferably, the three-pole concentric ring active electrode also includes a shell, in which a conductive layer is provided, one side of the conductive layer is connected to the electrode front end circuit, and the other side surface of the conductive layer is Ag / AgCl material, which is connected to the three-pole concentric ring electrode.

[0017] Preferably, the electrode front-end circuit includes three voltage follower groups, each of which includes three voltage followers; in one voltage follower group, the input ends of the three voltage followers are respectively connected to the three electrodes of the three-pole concentric circular ring electrode in a one-to-one correspondence.

[0018] Preferably, the acquisition system circuit includes an analog front-end amplifier module and a main control module; the input end of the analog front-end amplifier module is connected to the output end of the voltage follower, the data output end of the analog front-end amplifier module is connected to the data input end of the main control module, and the analog front-end amplifier module uses the Laplace nine-point method to measure the EEG signal.

[0019] Preferably, the analog front-end amplifier module includes two ADS1299 chips; the Laplace nine-point method is specifically:

[0020] Two ADS1299 chips are connected in a daisy chain manner, and the eight PGAs of each ADS1299 chip are configured in differential mode. Three terminals on the ADS1299 chip corresponding to the three electrodes of the three-pole concentric ring electrode are selected and recorded as the Inner end, the Middle end and the Outer end respectively. The Inner end is differentiated from the Middle end and the Outer end respectively to obtain two groups of signals V_(IM) and V_(IO); the Inner end is directly differentiated from the reference electrode to form V_(IR).

[0021] Preferably, the surface Laplace potential monitoring system also includes a right leg driving electrode for suppressing common mode signals; the right leg driving electrode is integrated into a clip placed at the left earlobe, and the right leg driving electrode is connected to the analog front-end amplification module through a right leg driving circuit.

[0022] Beneficial Effects

[0023] The advantages of the present invention are:

[0024] 1. The present invention adopts a three-pole concentric ring structure in conjunction with an electrode front-end circuit to achieve wearability of the entire system. At the same time, the signal amplification function can be realized on the electrode front-end circuit, cable noise can be reduced, and real-time surface Laplace potential calculation can be performed, effectively reducing the mutual information of adjacent channels, improving spatial resolution, reducing interference from other physiological electrical activities, and improving the spatial resolution and anti-interference ability of signal acquisition, especially anti-interference of electromyographic physiological electrical signals.

[0025] 2. Design a special discontinuous ring structure, while ensuring that the ring electrodes have the same contact area (that is, the contact impedance tends to be consistent) and have high mechanical strength (while making the flexible electrode less likely to break, the overall electrode size is made as small as possible), which effectively improves the accuracy of Laplace potential calculation.

[0026] 3. The material of the part in contact with the human body is made of flexible conductive composite material, and the overall surface of the electrode in contact is an arc structure that fits the skull, ensuring conformal contact with the human body and reducing noise interference, especially movement noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the architecture of the surface Laplace potential monitoring system of the present invention;

[0028] Figure 2 It is a schematic diagram of the internal structure of the three-pole concentric ring active electrode of the present invention;

[0029] Figure 3 It is a bottom-up structural schematic diagram of the three-pole concentric ring active electrode of the present invention;

[0030] Figure 4 It is a schematic diagram of the structure of the right leg driving circuit of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with the embodiments, but it does not constitute any limitation to the present invention. Any limited number of modifications made by anyone within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0032] See also Figure 1-Figure 4 The surface Laplace potential monitoring system based on the three-pole concentric ring active electrode of the present invention comprises a collection system circuit 1 and three three-pole concentric ring active electrodes 2 connected thereto. Figure 1In the figure, the three three-pole concentric ring active electrodes 2 are E1, E2, and E3 respectively. The three-pole concentric ring active electrode 2 includes a three-pole concentric circular ring electrode 22 and an electrode front-end circuit 21. The three-pole concentric ring active electrode 2 is referred to as ATCRE for short; the three-pole concentric circular ring electrode is referred to as TCRE for short, which serves as an EEG measurement electrode and directly contacts the contact part of the human body. The three-pole concentric circular ring electrode 22 adopts a discontinuous circular ring structure so that the three electrodes in the three-pole concentric circular ring electrode 22 form conformal contact with the human body; the electrode front-end circuit 21, which is integrated in the three-pole concentric ring active electrode 2, is used to receive signals from the three electrodes of the three-pole concentric circular ring electrode 22 and calculate the surface Laplace potential of the center point of the electrode. The design simultaneously realizes the head EEG acquisition and the calculation of the surface Laplace potential at that position. The three-pole concentric ring active electrode 2 is composed of a three-pole concentric ring electrode 22 and an electrode front-end circuit 21. The electrode front-end circuit 21 can suppress noise caused by cable movement, unstable electrode-skin contact interface, etc., to improve the signal-to-noise ratio. A miniaturized scalp Laplace potential acquisition circuit suitable for the ATCRE is developed to form a scalp surface Laplace potential monitoring system based on the three-pole concentric ring active electrode 2. The entire system is wearable, providing a new research equipment option for brain science research.

[0033] The system of the present invention includes three ATCREs, each of which is connected to three independent signal channels for acquisition. Each channel can be regarded as an independent EEG collected by each independent ring electrode. Therefore, the surface Laplace potential of the ATCRE is calculated by the following formula:

[0034]

[0035] Where r is the spacing between the ring electrodes, V i 、V m 、V o are the signal values ​​measured by the central circle electrode, the middle ring electrode and the outer ring electrode, respectively. The signal value is the voltage value. 4 ) is the fourth-order infinitesimal of r, so the formula can actually be shortened to the following without affecting the accuracy:

[0036]

[0037] In the present invention, the design of the three-pole concentric ring active electrode 2 is as follows.

[0038] The ATCRE proposed in the present invention is composed of a shell 23, an electrode front-end circuit 21 and three annular / virtual annular electrodes made of flexible conductive composite materials, and the three electrodes are named as a central circle electrode 221, a middle ring electrode 222 and an outer ring electrode 223. Among them, there is a conductive layer 24 in the shell 23, one side of the conductive layer 24 is welded to the PCB reserved pad of the electrode front-end circuit 21, and the other side surface is Ag / AgCl material, which is connected to the electrode one by one. ATCRE is connected to the matching collection system circuit 1 through an electrical connector 25 for use. The flexible conductive composite material can be a flexible composite conductive material such as a fabric-based, hydrogel-based, and elastomer-based.

[0039] In order to ensure high Laplace potential estimation accuracy and the same input impedance, the concentric ring electrodes usually have multiple rings of the same area, and the size is as small as possible, and the surface area of ​​the concentric ring electrodes with different radii and the part in contact with the human body should be kept the same, to ensure that the contact impedance of a single ring electrode and the human body tends to be consistent. Therefore, the present invention adopts the lower surfaces of the central circle electrode 221, the middle ring electrode 222 and the outer ring electrode 223 are all arc-shaped structures, and the lower surfaces of the central circle electrode 221, the middle ring electrode 222 and the outer ring electrode 223 together form a contact arc surface structure, thereby ensuring that the surface area of ​​the electrode and the part in contact with the human body is basically the same, reducing the contact error.

[0040] In addition, in order to improve the mechanical strength of the sensing materials of the middle ring electrode 222 and the outer ring electrode 223, and the contact areas of the three electrode rings are the same, the parts of the middle ring electrode 222 and the outer ring electrode 223 that are in direct contact with the human body can be designed as discontinuous structures according to the size, while the center disk is a continuous structure, that is, a solid circle.

[0041] For example, in a specific embodiment, Figure 3 As shown, the middle ring electrode 222 and the outer ring electrode 223 both adopt a discontinuous four-circle ring structure, wherein the radius R0 of the central circle electrode 221 is 4.5 mm. Figure 3 R1=7.5mm, R2=9.75mm, R3=12.75mm, and R4=14.25mm.

[0042] like Figure 1 As shown, the design of the electrode front end circuit 21 is as follows.

[0043] The electrode front-end circuit 21 of the present invention is closely connected to the three-pole concentric ring electrode 22 with a row of pins as an interface, and its connection method is similar to the base of the electrode. At the same time, each three-pole concentric ring active electrode 2 has an integrated LMP7704MA / NOPB, i.e., a precision integrated operational amplifier chip, at the front end. The chip contains four operational amplifiers, three of which are designed as voltage followers 211 and are respectively placed at the three input ends of the three-pole concentric ring active electrode 2 for signal buffering and impedance matching.

[0044] like Figure 1 As shown, the design of the acquisition system circuit 1 is as follows.

[0045] The acquisition system circuit 1 is mainly composed of 9 RC low-pass filter circuits 11, analog front-end amplifier module 12, main control module 13, Bluetooth module, right leg drive circuit 15 and other 5 parts. Among them, the analog front-end amplifier module 12 includes 2 ADS1299 chips and peripheral circuits, and the main control module 13 is the MCU and its minimum system. In addition, this system uses a 3.7V, 150mAh lithium battery pack to power the chip, and uses a TP4056 power management chip to charge the battery.

[0046] The following is a detailed introduction to the first four parts of the acquisition system circuit 1:

[0047] Regarding the RC low-pass filter circuit 11, the 9 RC low-pass filter circuits 11 are divided into three groups, and the RC low-pass filter circuits 11 in each group are connected one-to-one with a group of voltage followers 211, that is, the EEG signal obtained through the three-pole concentric ring active electrode 2 flows into the acquisition system circuit 1, and the EEG signal first passes through the RC low-pass filter circuit 11 to process the high-frequency noise in the EEG signal, and its upper cut-off frequency f_L is 100 Hz.

[0048] For the analog front-end amplifier module 12, the ADS1299 chip is used as the core chip for EEG signal acquisition. It has 8 built-in programmable gain amplifiers, which have the advantages of high sensitivity, low noise, low power consumption, etc. It can amplify and filter weak EEG signals for subsequent processing and analysis. The present invention uses the Laplace 9-point method to measure EEG signals, so it is necessary to configure the 8 PGAs of the ADS1299 chip into differential mode, select its Inner end to be differentiated from the Middle end and the Outer end respectively, so as to obtain V_(IM) and V_(IO) two groups of signals. In order to compare the difference between the two groups of signals after the difference and the original EEG signal output by the Inner end, the Inner end is directly differentiated from the reference electrode E5 to form V_(IR). Secondly, since each three-pole concentric ring active electrode 2 needs to occupy three channels of the ADS1299 chip, and a chip has only 8 PGAs, i.e. programmable gain amplifiers, two ADS1299 chips are connected in a daisy chain manner, sharing the same clock source, and using the SPI communication protocol to transmit data with the MCU.

[0049] The main control module 13 uses the STM32F103RCT6 microcontroller as the MCU of this system. The ADS1299 chip is configured through the initialization program, and the sampling frequency of each channel is set to 1kHz and the baud rate is 115200bps. The zero-phase digital filter and Butterworth filter are used as digital filtering methods to filter out the 50Hz power line interference and high-order harmonic noise in the EEG signal. Finally, the digitally processed data is transmitted to the Bluetooth module through the universal asynchronous receiver and transmitter peripheral of the MCU.

[0050] Finally, the Bluetooth module uses the HC-04 Bluetooth module to communicate with the terminal device 14. The module supports the BLE5.0+SPP2.1 protocol, with a transmission rate of up to 60KB / S and a transmission distance of less than 10 meters. At the same time, due to its small package size, the shape is similar to a stamp, with a length, width and height of 27*13*2.7mm, which is easy to integrate into miniaturized and wearable devices, so it is suitable for the application requirements of this system.

[0051] In addition to three three-pole concentric ring active electrodes 2 and one reference electrode E5, this system also has a right leg driving electrode E4 for suppressing common-mode signals, which is integrated on the clip and placed on the left earlobe. Since EEG signals are extremely weak differential-mode signals, their amplitudes are generally between 0.5 and 100 μV, so they are very susceptible to common-mode noise interference. In order to extract high-quality EEG signals, common-mode noise needs to be suppressed. To suppress the interference of common-mode signals, the following method is used: Figure 4The right leg driving circuit 15 is shown. Since the ADS1299 chip has a BIAS Amplifier specifically used for this function, and the positive input terminal, reverse input terminal, and output terminal are packaged on the chip pins, it only needs to be matched with capacitors and resistors to form a peripheral circuit. This circuit is essentially a voltage negative feedback circuit, which amplifies the common mode noise in reverse and then connects it back to the human body to eliminate the common mode noise, thereby improving the common mode rejection ratio.

[0052] The above is only a preferred embodiment of the present invention. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the structure of the present invention, which will not affect the effect of the implementation of the present invention and the practicality of the patent.

Claims

1. A surface Laplace potential monitoring system based on a three-pole concentric ring active electrode, characterized in that: It comprises a collection system circuit (1) and a plurality of three-pole concentric ring active electrodes (2) connected thereto; wherein: The three-pole concentric ring active electrode (2) comprises: A three-pole concentric circular ring electrode (22) adopts a discontinuous circular ring structure so that three electrodes in the three-pole concentric circular ring electrode (22) form conformal contact with the human body; The electrode front-end circuit (21) is integrated in the three-pole concentric ring active electrode (2) and is used to receive signals from the three electrodes of the three-pole concentric ring electrode (22) and calculate the surface Laplace potential of the center point of the electrode.

2. The surface Laplace potential monitoring system based on three-pole concentric ring active electrodes according to claim 1 is characterized in that: The calculation formula of the surface Laplace potential is: Where, L V0 is the surface Laplace potential, r is the distance between the ring electrodes, V i 、V m 、V o are the signal values ​​measured by the central circle electrode, the middle ring electrode and the outer ring electrode, respectively. 4 ) is the fourth-order infinitesimal of r.

3. The surface Laplace potential monitoring system based on three-pole concentric ring active electrodes according to claim 1 or 2, characterized in that: The three electrodes of the three-pole concentric circular ring electrode (22) are respectively a central circular electrode (221), an intermediate circular electrode (222) and an outer circular electrode (223); wherein the intermediate circular electrode (222) and the outer circular electrode (223) are discontinuous circular ring structures, the central circular electrode (221) is a continuous structure, and the areas of the central circular electrode (221), the intermediate circular electrode (222) and the outer circular electrode (223) are all the same.

4. The surface Laplace potential monitoring system based on three-pole concentric ring active electrodes according to claim 3 is characterized in that: The central circular electrode (221), the middle ring electrode (222) and the outer ring electrode (223) are all made of a flexible conductive composite material.

5. The surface Laplace potential monitoring system based on three-pole concentric ring active electrodes according to claim 3 is characterized in that: The lower surfaces of the central circular electrode (221), the middle ring electrode (222) and the outer ring electrode (223) are all in an arc-shaped structure, and the lower surfaces of the central circular electrode (221), the middle ring electrode (222) and the outer ring electrode (223) together form a contact arc surface structure.

6. The surface Laplace potential monitoring system based on three-pole concentric ring active electrodes according to claim 3 is characterized in that: The three-pole concentric ring active electrode (2) further comprises a shell (23), wherein a conductive layer (24) is provided in the shell (23), one side of the conductive layer (24) is connected to the electrode front end circuit (21), and the other side surface of the conductive layer (24) is made of Ag / AgCl material and is connected to the three-pole concentric ring electrode (22).

7. The surface Laplace potential monitoring system based on three-pole concentric ring active electrodes according to claim 1 or 6, characterized in that: The electrode front-end circuit (21) comprises three voltage follower groups, each of which comprises three voltage followers (211); in one voltage follower group, the input ends of the three voltage followers (211) are respectively connected to the three electrodes of the three-pole concentric circular ring electrode (22) in a one-to-one correspondence.

8. The surface Laplace potential monitoring system based on three-pole concentric ring active electrodes according to claim 7 is characterized in that: The acquisition system circuit (1) comprises an analog front-end amplifier module (12) and a main control module (13); the input end of the analog front-end amplifier module (12) is connected to the output end of the voltage follower (211), the data output end of the analog front-end amplifier module (12) is connected to the data input end of the main control module (13), and the analog front-end amplifier module (12) measures EEG signals using the Laplace nine-point method.

9. The surface Laplace potential monitoring system based on three-pole concentric ring active electrodes according to claim 8, characterized in that: The analog front-end amplification module (12) comprises two ADS1299 chips; the Laplace nine-point method is specifically: Two ADS1299 chips are connected in a daisy chain manner, and the eight PGAs of each ADS1299 chip are configured in a differential mode. Three terminals on the ADS1299 chip corresponding to the three electrodes of the three-pole concentric ring electrode (22) are selected and recorded as the Inner end, the Middle end and the Outer end respectively. The Inner end is differentiated from the Middle end and the Outer end respectively to obtain two groups of signals, V_(IM) and V_(IO); and the Inner end is directly differentiated from the reference electrode (E5) to form V_(IR).

10. The surface Laplace potential monitoring system based on three-pole concentric ring active electrodes according to claim 8, characterized in that: The surface Laplace potential monitoring system also includes a right leg driving electrode (E4) for suppressing common mode signals; the right leg driving electrode (E4) is integrated into a clip placed at the left earlobe, and the right leg driving electrode (E4) is connected to the analog front-end amplification module (12) through a right leg driving circuit (15).

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