CN108714027B - Device and method for measuring multi-channel electrode/scalp contact impedance in real time - Google Patents
Device and method for measuring multi-channel electrode/scalp contact impedance in real time Download PDFInfo
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- CN108714027B CN108714027B CN201810254790.4A CN201810254790A CN108714027B CN 108714027 B CN108714027 B CN 108714027B CN 201810254790 A CN201810254790 A CN 201810254790A CN 108714027 B CN108714027 B CN 108714027B
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves
- A61B5/053—Measuring electrical impedance or conductance of a portion of the body
- A61B5/0536—Impedance imaging, e.g. by tomography
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
- A61B5/6801—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
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Abstract
The invention discloses a device and a method for measuring multi-path electrode/scalp contact impedance in real time, and belongs to the field of bioelectrical impedance imaging technology and application. The device comprises an upper computer, a main control unit, an excitation current signal generation unit, a boundary voltage signal measurement unit, an excitation channel, a measurement channel and a contact impedance measurement module. The invention introduces a far-end reference electrode on the basis of the original imaging electrode, and when the contact impedance is measured, a plurality of imaging electrodes are switched into a contact impedance measuring circuit in sequence through an electrode channel control unit, and the boundary voltage data and the contact impedance data can be synchronously measured in real time through the electrode channel control unit. The method can accurately measure and obtain the information of the contact impedance in the following two dimensions: 1. spatial consistency of multipath contact impedance; 2. time stability of the single contact resistance. Compared with the existing measuring method, the method is simple and convenient to operate and can measure in real time.
Description
Technical Field
The invention belongs to the field of bioelectrical impedance imaging, and particularly relates to a device and a method for measuring multi-path electrode/scalp contact impedance in real time.
Background
The craniocerebral electrical impedance imaging technology is a novel craniocerebral functional imaging technology and has the advantages of no wound, no radiation, quick imaging, long-time continuous imaging and the like. The basic principle is as follows: electrodes attached to the surface of the scalp are used for sequentially injecting quantitative and safe alternating current signals into the cranium, response voltage signals on all related electrodes are measured at the same time, and an image capable of reflecting the electrical impedance distribution in the cranium is obtained through reconstruction through a specific image reconstruction algorithm.
The electrical impedance imaging system for craniocerebral includes a plurality of imaging electrodes, typically 16 electrodes or 32 electrodes, and all of the imaging electrodes are multiplexed between the functions of applying current excitation and extracting response voltage signals. Compared with other simple bioelectric signal extraction occasions (such as an electroencephalograph, a brain-computer interface and the like), the craniocerebral electrical impedance imaging is more complicated in influence degree of electrode/scalp contact impedance. In prior laboratory studies, electrodes were typically inserted into the scalp or fixed to the skull of anesthetized animals to effectively suppress the effects of scalp/contact impedance. However, in clinical application, the electrode is attached to the surface of the scalp, and the electrode/scalp contact impedance is larger and far larger than the transmission impedance of the craniocerebral tissue; during long-term continuous imaging, the electrode/scalp contact impedance fluctuates over time as the performance of the conductive paste declines and the patient moves. Relevant studies prove that when large differences exist between contact impedances of a plurality of imaging electrodes, measurement errors are caused by influencing the performance of a signal acquisition system; during long continuous acquisition, imaging errors are introduced during differential imaging when the contact impedance has a large fluctuation over time.
At present, researches on the influence of electrode/scalp contact impedance in craniocerebral electrical impedance imaging mostly stay in a simulation research stage, and means for acquiring spatial consistency and time stability of multi-path contact impedance in real time is temporarily lacked.
Disclosure of Invention
The invention aims to provide a device and a method for measuring multi-path electrode/scalp contact impedance in real time.
The invention is realized by the following technical scheme:
the invention discloses a device for measuring multi-channel electrode/scalp contact impedance in real time, which comprises an upper computer, a main control unit, an excitation current signal generating unit, a boundary voltage signal measuring unit, an excitation channel, a measuring channel and a contact impedance measuring module, wherein the main control unit is connected with the excitation current signal generating unit; the contact impedance measuring module consists of an electrode unit, an electrode channel control unit, a contact impedance signal measuring unit and an exciting current signal measuring unit; wherein:
the electrode unit comprises a group of imaging electrodes and a reference electrode, wherein the imaging electrodes are used for acquiring electrical impedance imaging data, and the reference electrode is used for assisting in measuring the contact impedance of each imaging electrode;
the electrode channel control unit is used for realizing the alternate operation of two modes of boundary voltage measurement and contact impedance measurement by controlling the switching of the excitation channel and the measurement channel, and the time interval of the two modes is within 1 s;
the contact impedance signal measuring unit is used for processing a contact impedance signal (a response voltage signal between the imaging electrode and the reference electrode) and then transmitting the processed contact impedance signal to the main control unit; the processing refers to the processing of filtering, amplifying, signal conditioning and the like, and then A/D conversion is carried out;
the excitation current signal measuring unit is used for processing an excitation current signal (a voltage signal at two ends of the sampling resistor) and then transmitting the processed excitation current signal to the main control unit; the processing refers to the processing of filtering, amplifying, signal conditioning and the like, and then A/D conversion is carried out;
the upper computer is interacted with the main control unit through a data interface and is used for sending a control instruction to the main control unit, and the main control unit uploads the acquired data to the upper computer; the main control unit firstly generates an alternating current sinusoidal current signal by controlling the exciting current signal generating unit, then sets an exciting channel and a measuring channel by the electrode channel control unit, and finally completes data acquisition by controlling the boundary voltage signal measuring unit, the exciting current signal measuring unit and the contact impedance signal measuring unit.
Preferably, the imaging electrode has two functions of current excitation and voltage measurement, is attached to the surface of the scalp to be measured, and is generally uniformly distributed on a certain specific section of the cranium;
preferably, the reference electrode, there are two alternatives: one is a disposable medical single-pole needle electrode, and the needle head adopts an inclined plane small-angle sharpening structure; the other is a self-adhesive surface electrode, the structure is similar to a disposable electrocardioelectrode, but the area of an Ag/AgCl coating is far larger than that of a common electrocardioelectrode, and the self-adhesive surface electrode can be stuck to the top of the cranium; the two electrodes are purchased from the formal medical equipment company, and the safety is guaranteed.
Preferably, the electrode channel control unit includes a plurality of multi-path analog switching devices for controlling switching of the imaging electrode channel and a plurality of single-pole single-throw switching devices for controlling on/off of the reference electrode channel.
Further preferably, four multi-select-1 analog switching devices are adopted to control the plurality of imaging electrodes, a MUX1 and a MUX2 are used to control a positive excitation channel and a negative excitation channel respectively, and a MUX3 and a MUX4 are used to control a positive measurement channel and a negative measurement channel respectively; the reference electrode is controlled by two single-pole single-throw switching devices SPST1 and SPST 2;
in the boundary voltage signal measurement mode, the SPST1 and the SPST2 are disconnected, the enable pins of the MUX1, the MUX2, the MUX3 and the MUX4 are set to be high, and the excitation channel and the measurement channel are set by controlling the gating of the MUX1, the MUX2, the MUX3 and the MUX 4;
in the contact impedance signal measurement mode, SPST1 and SPST2 are turned on, enable pins of MUX1 and MUX3 are set to high, enable pins of MUX2 and MUX4 are set to low, and the excitation channel and the measurement channel are set by controlling gating of MUX1 and MUX 3.
Preferably, the contact impedance signal measuring unit is composed of a filter circuit, a fixed gain signal amplifying circuit, a program control gain signal amplifying circuit and an a/D conversion circuit, and is used for measuring a voltage signal corresponding to a "two-electrode method"; the excitation current signal measuring unit consists of a sampling resistor, a filter circuit, a fixed gain signal amplifying circuit, a program control gain signal amplifying circuit and an A/D (analog/digital) conversion circuit and is used for measuring current signals corresponding to a two-electrode method.
Further preferably, the sampling resistor has the characteristics of high precision and low temperature drift; the filter circuit consists of a second-order active low-pass filter and a second-order active high-pass filter; the fixed gain signal amplifying circuit is a first-stage amplifying circuit and consists of a precision resistor and an operational amplifier; the programmable gain signal amplifying circuit is a second-stage amplifying circuit and consists of a programmable gain amplifying device, and the gain range of the programmable gain signal amplifying circuit can be dynamically adjusted to meet the signal amplification requirement of the amplitude in a wider dynamic range; the A/D conversion circuit is composed of a high-speed high-precision analog-to-digital converter and a peripheral circuit thereof, and is used as a post-stage circuit of the signal measurement unit.
The invention also discloses a measuring method based on the measuring device, which comprises the following steps:
1) arranging electrodes
Placing a group of imaging electrodes according to a conventional method of craniocerebral resistance imaging, fixing the imaging electrodes, and then selecting a position with approximately the same distance with each imaging electrode to place a reference electrode;
2) boundary voltage data acquisition
The reference electrode access is disconnected through the electrode channel control unit, and a plurality of imaging electrodes in a group are sequentially switched to complete the acquisition of a frame of boundary voltage data, wherein the boundary piezoelectric data is used for imaging and is imaging data;
3) contact impedance data and excitation current data acquisition
Acquiring contact impedance data: the reference electrode channel is conducted through the electrode channel control unit, and the imaging electrode channels are sequentially gated in sequence; by using a two-electrode method, an excitation current signal is injected between a reference electrode and a selected imaging electrode, and a voltage signal between the two electrodes is measured and recorded as UiWherein i is 1,2, …, N is the electrode number, and N is the number of imaging electrodes;
excitation current data acquisition: by measuring the voltage signal across the sampling resistor, the excitation current signal is measured indirectly, denoted as USampling；
4) And (4) repeating the step 2) and the step 3), and entering a next frame data acquisition period until the upper computer sends an acquisition termination instruction.
Preferably, when the reference electrode is arranged in the step 1), selecting according to requirements, if a disposable medical monopolar needle electrode is adopted, puncturing the scalp subcutaneous after disinfection treatment and fixing, and if a disposable customized reference electrode is adopted, attaching the reference electrode on the surface of the scalp and fixing;
preferably, in step 3), the actual excitation current when the imaging electrode i is gated is:
Ii＝Usampling/RSampling；
The impedance values measured by the two-electrode method are:
Zi＝Ui/Ii＝Ui/(Usampling/RSampling)＝Ui*RSampling/USampling；
ZiIs essentially the contact impedance Zc of the imaging electrode under testiA transmission impedance Zt between the imaging electrode and the reference electrodeiAnd the contact impedance Zcf of the reference electrode, i.e.:
Zi＝Zci+Zti+Zcf；
definition of Δ Zm,nThe following were used:
wherein m, N ≠ N, 1, 2.; zcm-ZcnThe difference between the contact impedances of the imaging electrode m and the imaging electrode n is denoted as Δ Zcm,n；Ztm-ZtnThe difference between the transmission impedances of the imaging electrode m and the imaging electrode n, respectively, and the reference electrode is denoted as Δ Ztm,n；Zcfm-ZcfnThe fluctuation error of the contact impedance of the reference electrode in the two measurements is recorded as delta Zcfm,n。
Preferably, two reference electrodes selected in the present invention, one of which penetrates under the scalp and one of which has a large effective contact area, ensure Zcf < ZciAnd Δ Zcfm,nThe distance is approximately equal to 0, and the distances between the reference electrode and each imaging electrode are approximately the same, so that each Zt can be ensurediThe difference between the two is small, namely: Δ Ztm,n＜＜ΔZcm,n；
Then there are: Δ Zcm,n＝Zcm-Zcn≈Zm-Zn；
Definition ofΔZi(t1, t2) is:
wherein, i is 1, 2.. times.n; t1, t2 are two moments; zci(t1)-Zci(t2) is the change value of the contact impedance of the ith imaging electrode between t1 and t2, and is recorded as Δ Zci(t1,t2)；Zti(t1)-Zti(t2) is the change value of the contact impedance of the ith imaging electrode between t1 and t2, and is recorded as Δ Zti(t1,t2)；ΔZcfi(t1, t2) is the change value of the contact impedance of the reference electrode between t1 and t 2;
the transmission impedance is influenced by the electrode position and the intracranial impedance variations, the time stability of which is higher compared to the contact impedance, i.e. Δ Zti(t1, t2) ≈ 0; the reference electrode contact impedance is stabilized over time by manual intervention, i.e. Δ Zcfi(t1,t2)≈0。
Therefore, the method can be used for measuring and obtaining contact impedance information of two dimensions, namely the space consistency index Delta Zc of the contact impedance of the multi-path imaging electrodem,nAnd a time stability index Δ Zc of contact impedance of each imaging electrodei(t1,t2)。
Compared with the prior art, the invention has the following beneficial technical effects:
the invention discloses a device for measuring multi-channel electrode/scalp contact impedance in real time, which is provided with a contact impedance measuring module, wherein the module consists of an electrode unit, an electrode channel control unit, a contact impedance signal measuring unit and an exciting current signal measuring unit. Wherein, the electrode unit comprises a group of imaging electrodes and a reference electrode. The invention introduces a far-end reference electrode on the basis of the original imaging electrode, and when the contact impedance is measured, a plurality of imaging electrodes are switched into a contact impedance measuring circuit in sequence through an electrode channel control unit, and the boundary voltage data and the contact impedance data can be synchronously measured in real time through the electrode channel control unit. The contact impedance signal measuring unit, the exciting current signal measuring unit and the boundary voltage signal measuring unit are independent from each other, so that high-precision measurement of signals with different amplitudes and different types is met.
The invention discloses a real-time measuring method for multi-channel electrode/scalp contact impedance in electrical impedance imaging of craniocerebral, which adopts a 'two-electrode method' measuring principle, respectively measures an actual injection current signal and a response voltage signal between each imaging electrode and a reference electrode by utilizing an excitation current signal measuring unit and a contact impedance signal measuring unit, and calculates to obtain an impedance value between each imaging electrode and the reference electrode; thereby analyzing the spatial consistency and time stability information of the multipath contact impedance. The method can accurately measure and obtain the information of the contact impedance in the following two dimensions: 1. spatial consistency of multipath contact impedance; 2. time stability of the single contact resistance. Compared with the existing measuring method, the method is simple and convenient to operate, can measure in real time, has higher accuracy in obtaining the two dimensional information, and lays a foundation for researching the influence of contact impedance on electrical impedance imaging of the cranium and a restraining method thereof.
Drawings
FIG. 1 is a schematic diagram of a measurement mode of electrical impedance craniocerebral imaging data;
FIG. 2 is a schematic diagram of a contact impedance data acquisition method;
FIG. 3 is a schematic view of the attachment and placement of the imaging electrode and the reference electrode;
FIG. 4 is a structural block diagram of a brain electrical impedance imaging hardware system;
FIG. 5 is a schematic structural diagram of an electrode channel control unit;
FIG. 6 shows the results of a 16-way electrode/scalp contact impedance spatial consistency analysis (16-way contact impedance is relatively uniform); wherein (a) is a 16-way contact impedance measurement (Ω); (b) relative difference (%) for 16 contact impedances;
FIG. 7 shows the results of the spatial consistency analysis of 16 electrode/scalp contact impedance (abnormal contact impedance of No. 6 imaging electrode); wherein (a) is a 16-way contact impedance measurement (Ω); (b) relative difference (%) for 16 contact impedances;
FIG. 8 shows the results of 16-way electrode/scalp contact impedance time stability analysis (the contact impedance fluctuation of imaging electrode No. 8 is large); wherein, (a) is the measured value (omega) of the 16-path contact impedance at the time t1 and the time t 2; (b) the relative change (%) of the 16-way contact impedance between the time t1 and the time t 2.
Detailed Description
The present invention will now be described in further detail with reference to specific examples, which are intended to be illustrative, but not limiting, of the invention.
The purpose of this embodiment is to realize the contact impedance of 16 way imaging electrode of real-time measurement. For a 16-electrode craniocerebral electrical impedance imaging system, a data acquisition mode of 'contralateral excitation and proximity measurement' is adopted. The system has 16 excitation electrode pairs, each excitation electrode pair corresponds to 16 measurement electrode pairs, so that one complete data acquisition comprises 256 measurements, namely one frame of data comprises 256 measurement values. Referring to fig. 1, fig. 1 shows: the response voltage signal on the measuring electrode pair is measured 3-4 by injecting an excitation current through the 1-9 excitation electrode pair into the cranium. Due to contact impedance between the imaging electrode and the scalp, i.e. Zc in the figure1、Zc3、Zc4And Zc9. Thus, the excitation signal loop and the measurement signal loop are simultaneously influenced by the contact impedance.
1. Introduction to the measurement principle
The invention provides a real-time measurement method for multi-channel electrode/scalp contact impedance in a craniocerebral electrical impedance imaging system, which has the following principle: the impedance value between each imaging electrode and the reference electrode is measured in real time by adopting a two-electrode method, and the contact impedance information of the multiple imaging electrodes is obtained by analyzing the impedance values, as shown in fig. 2.
The 16 imaging electrodes of the embodiment are attached to the surface of the scalp and are uniformly distributed on a certain specific section of the cranium; the reference electrode was a self-adhesive surface electrode, attached to the top of the cranium, approximately the same distance as the 16 imaging electrodes, as shown in fig. 3.
The structural block diagram of a craniocerebral electrical impedance imaging hardware system formed by the multi-channel electrode/scalp contact impedance real-time measuring module provided by the invention is shown in fig. 4. The system consists of an upper computer, a data interface, a main control unit, an excitation current signal generating unit, a boundary voltage signal measuring unit, a contact impedance signal measuring unit, an excitation current signal measuring unit, an electrode channel control unit and an electrode unit. Wherein, each unit contained in the dashed line frame forms a 16-way electrode/scalp contact impedance measuring module.
The operation principle of the craniocerebral electrical impedance imaging system is as follows: the upper computer sends a control instruction to the main control unit through the data interface. After the main control unit receives a data acquisition instruction, firstly, an alternating current sinusoidal current signal with set frequency and amplitude is generated by controlling the excitation current signal generating unit; then, an excitation channel and a measurement channel are arranged through an electrode channel control unit; and finally, data acquisition is completed by controlling the boundary voltage signal measuring unit, the contact impedance signal measuring unit and the exciting current signal measuring unit. The main control unit uploads the acquired data to the upper computer through the data interface. The boundary voltage signal measuring unit is used for measuring a boundary voltage signal; the contact impedance signal measuring unit and the exciting current signal measuring unit are respectively used for measuring a voltage signal and a current signal corresponding to a two-electrode method, and then a contact impedance value is obtained through calculation.
In this embodiment, the excitation current signal during the contact impedance measurement and the excitation current signal during the boundary voltage signal measurement are generated by the same excitation current signal generation unit. The working principle is as follows: firstly, a digital frequency synthesis technology is adopted, a DAC device generates a sinusoidal alternating current voltage signal with required frequency and amplitude, and the sinusoidal alternating current voltage signal is converted into a sinusoidal alternating current signal by a voltage-controlled current source after filtering and amplifying processing. The current signal has an electrical amplitude range of 10-2500 uA and a frequency range of 1 k-200 kHz. The current amplitude of 1250uA and the frequency of 50kHz are adopted in the embodiment.
In this embodiment, a specific scheme of the electrode channel control unit controlling the excitation channel and the measurement channel is shown in fig. 5. Four 16-to-1 analog switching devices are used to control 16 imaging electrodes, MUX1 and MUX2 control the positive and negative excitation channels, respectively, and MUX3 and MUX4 control the positive and negative measurement channels, respectively. The reference electrode is controlled using two single pole, single throw switching devices (SPST1 and SPST 2). Under a boundary voltage data acquisition mode, the SPST1 and the SPST2 are disconnected, enable pins of the MUX 1-4 are set to be at a high level, and an excitation channel and a measurement channel are set by controlling gating of the MUX 1-4; in the contact impedance measurement mode, SPST1 and SPST2 are turned on, enable pins of MUX1 and MUX3 are set to high, enable pins of MUX2 and MUX4 are set to low, and the excitation channel and the measurement channel are set by controlling gating of MUX1 and MUX 3.
2. Measured contact impedance data analysis
In this embodiment, the impedance value measured by the two-electrode method is:
Zi＝Zci+Zti+Zcf
wherein, i is 1,2iIs the contact impedance of the imaging electrode i, ZtiIs the transmission impedance between the imaging electrode i and the reference electrode, Zcf is the contact impedance of the reference electrode.
(1) Qualitative analysis of 16-way electrode/scalp contact impedance
The reference electrode used in the embodiment is a single-pole needle electrode which can be punctured into the scalp, so that the contact impedance of the reference electrode is far smaller than that of the imaging electrode;
in addition, studies have reported that the transmission impedance of the cranial tissue is much smaller than the contact impedance of the imaging electrode; namely:
Zcf＜＜Zci,Zti＜＜Zci
thus, Z can be utilizedi≈ZciThe contact impedance of the 16 imaging electrodes was qualitatively evaluated.
Referring to fig. 6(a) and 7(a), the measured values of the 16-way contact impedance are presented using the radar chart method. Fig. 6(a) shows that the 16 contact resistances are close to each other, and that the 16 electrodes are close to each other in contact. In fig. 7(a), it can be observed that the 6 th measured value is significantly larger than other values, which indicates that the contact impedance of the No. 6 imaging electrode is abnormally large, and it can be preliminarily concluded that: no. 6 imaging electrode had poor contact.
(2) Spatial consistency analysis of 16-way electrode/scalp contact impedance
Spatial uniformity refers to the difference between the 16 contact impedances at a given time.
First, 16 measurements are compared to find the minimum value, which corresponds to the electrode number a, defining Δ Zi,aThe following were used:
ΔZi,a＝Zi-Za
＝(Zci+Zti+Zcfi)-(Zca+Zta+Zcfa)
＝(Zci-Zca)+(Zti-Zta)+(Zcfi-Zcfa)
wherein, i is 1, 2. Zci-ZcaThe difference between the contact impedances of the imaging electrode i and the imaging electrode a is denoted as Δ Zci,a；Zti-ZtaThe difference between the transmission impedances of the imaging electrode i and the imaging electrode a, respectively, and the reference electrode is denoted as Δ Zti,a；Zcfi-ZcfaThe fluctuation error of the contact impedance of the reference electrode in the two measurements is recorded as delta Zcfi,a。
Due to delta Zcfi,a0 and Δ Zti,a＜＜ΔZci,aThen, the process of the present invention,
ΔZci,a＝Zci-Zca≈Zi-Za
the spatial uniformity coefficient for the 16-way contact impedance can be expressed as:
referring to fig. 6(b) and 7(b), corresponding to fig. 6(a) and 7(a), respectively, the spatial consistency, i.e., relative difference, of the 16-way contact impedance is exhibited. The 16 numbers in FIG. 6(b) are similar, indicating that the 16 electrodes are in close contact; in fig. 7(a), it can be observed that the 6 th value is significantly larger than other values, which indicates that the contact impedance of the No. 6 imaging electrode is abnormally large, and it can also be preliminarily inferred that: no. 6 imaging electrode had poor contact.
(3) Time stability analysis of 16-way electrode/scalp contact impedance
Time stability refers to the relative rate of change of the 16-way contact impedance over time at some two times. First, 16 contact impedance measurements at two times are shown in the same radar chart, as shown in fig. 8 (a). It can be observed that the 8 th value varies the most between the two moments, and it can be concluded that: the time stability of imaging electrode number 8 is significantly worse than the other imaging electrodes.
To quantify the relative change in 16-way contact impedance over time, Δ Z is definedi(t1, t2) is:
ΔZi(t1,t2)＝Zi(t1)-Zi(t2)
＝[Zci(t1)-Zci(t2)]+[Zti(t1)-Zti(t2)]+ΔZcfi(t1,t2)
wherein, i is 1, 2. Zci(t1)-Zci(t2) is the change in contact impedance of the imaging electrode i between t1 and t2, and is denoted as Δ Zci(t1,t2)；Zti(t1)-Zti(t2) is the change in contact impedance of the imaging electrode i between t1 and t2, and is denoted as Δ Zti(t1,t2)；ΔZcfi(t1, t2) is the variation of the contact impedance of the reference electrode between t1 and t 2.
Due to Δ Zti(t1, t2) ≈ 0 and Δ Zcfi(t1, t2) ≈ 0, then,
ΔZci(t1,t2)＝Zci(t1)-Zci(t2)≈Zi(t1)-Zi(t2)。
the time stability factor of the 16-way contact impedance can be expressed as:
referring to fig. 8(b), corresponding to fig. 8(b), the time stability of the 16-way contact impedance is demonstrated, i.e., the relative change between the two times t1 and t 2. The 8 th value is observed to be the largest, and it can be concluded that: the time stability of imaging electrode number 8 is significantly worse than the other imaging electrodes.
Therefore, two-dimensional contact impedance information can be obtained by analyzing data, namely a space consistency index alpha of 16 contact impedance and a time stability index beta of the contact impedance of each imaging electrode.
The embodiments given above are preferable examples for implementing the present invention, and the present invention is not limited to the above-described embodiments. Any non-essential addition, replacement or simple setting and adjustment of the determination threshold value made by a person skilled in the art according to the technical features of the technical solution of the present invention belong to the protection scope of the present invention.
Claims (8)
1. A measurement method based on a device for measuring multi-way electrode/scalp contact impedance in real time, characterized in that,
the measuring method comprises the following steps:
1) arranging electrodes
Placing a group of imaging electrodes according to a conventional method of craniocerebral resistance imaging, fixing the imaging electrodes, and then selecting a position with approximately the same distance with each imaging electrode to place a reference electrode;
2) boundary voltage data acquisition
The reference electrode access is disconnected through the electrode channel control unit, and a plurality of imaging electrodes in a group are sequentially switched to complete the acquisition of a frame of boundary voltage data, wherein the boundary voltage data is used for imaging and is imaging data;
3) contact impedance data and excitation current data acquisition
Acquiring contact impedance data: the reference electrode channel is conducted through the electrode channel control unit, and the imaging electrode channels are sequentially gated in sequence; by using a two-electrode method, an excitation current signal is injected between a reference electrode and a selected imaging electrode, and a voltage signal between the two electrodes is measured and recorded as UiWherein i is 1,2, …, N is the electrode number, and N is the number of imaging electrodes;
excitation current data acquisition: by measuring the voltage signal across the sampling resistor, the excitation current signal is measured indirectly, denoted as USampling；
In step 3), the actual excitation current when the imaging electrode i is gated is:
Ii＝Usampling/RSampling；
The impedance values measured by the two-electrode method are:
Zi＝Ui/Ii＝Ui/(Usampling/RSampling)＝Ui*RSampling/USampling；
ZiIs essentially the contact impedance Zc of the imaging electrode under testiA transmission impedance Zt between the imaging electrode and the reference electrodeiAnd the contact impedance Zcf of the reference electrode, i.e.:
Zi＝Zci+Zti+Zcf；
definition of Δ Zm,nThe following were used:
wherein m, N ≠ N, 1, 2.; zcm-ZcnThe difference between the contact impedances of the imaging electrode m and the imaging electrode n is recorded as; ztm-ZtnThe difference between the transmission impedances of the imaging electrode m and the imaging electrode n, respectively, and the reference electrode is denoted as Δ Ztm,n；Zcfm-ZcfnThe fluctuation error of the contact impedance of the reference electrode in the two measurements is recorded as delta Zcfm,n
4) And (5) repeating the step 2) and the step 3), and entering a next frame data acquisition period until the upper computer sends an acquisition termination instruction.
2. A method of measurement as claimed in claim 1 wherein the effective contact area of the reference electrode is such as to ensure Zcf < ZciAnd Δ Zcfm,nThe distance is approximately equal to 0, and the distances between the reference electrode and each imaging electrode are approximately the same, so that each Zt can be ensurediThe difference between the two is small, namely: Δ Ztm,n＜＜ΔZcm,n；
Then there are: Δ Zcm,n＝Zcm-Zcn≈Zm-Zn；
Definition of Δ Zi(t1, t2) is:
wherein, i is 1, 2.. times.n; t1, t2 are two moments; zci(t1)-Zci(t2) is the change value of the contact impedance of the ith imaging electrode between t1 and t2, and is recorded as Δ Zci(t1,t2)；Zti(t1)-Zti(t2) is the change value of the contact impedance of the ith imaging electrode between t1 and t2, and is recorded as Δ Zti(t1,t2)；ΔZcfi(t1, t2) is the change value of the contact impedance of the reference electrode between t1 and t 2;
the transmission impedance is influenced by the electrode position and the intracranial impedance variations, the time stability of which is higher compared to the contact impedance, i.e. Δ Zti(t1, t2) ≈ 0; the reference electrode contact impedance is stabilized over time by manual intervention, i.e. Δ Zcfi(t1,t2)≈0。
3. The measuring method according to claim 1, wherein the measuring method is implemented based on a device for measuring the multi-way electrode/scalp contact impedance in real time, and the device for measuring the multi-way electrode/scalp contact impedance in real time comprises an upper computer, a main control unit, an excitation current signal generating unit, a boundary voltage signal measuring unit, an excitation channel, a measuring channel and a contact impedance measuring module;
the contact impedance measuring module consists of an electrode unit, an electrode channel control unit, a contact impedance signal measuring unit and an exciting current signal measuring unit; wherein:
the electrode unit comprises a group of imaging electrodes and a reference electrode, wherein the imaging electrodes are used for acquiring electrical impedance imaging data, and the reference electrode is used for assisting in measuring the contact impedance of each imaging electrode;
the electrode channel control unit is used for realizing the alternate operation of two modes of boundary voltage measurement and contact impedance measurement by controlling the switching of the excitation channel and the measurement channel;
the contact impedance signal measuring unit and the exciting current signal measuring unit are respectively used for measuring a voltage signal and a current signal corresponding to the two-electrode method, and then a contact impedance value is obtained through calculation;
the voltage signal processing circuit is used for processing voltage signals at two ends of the sampling resistor and then transmitting the voltage signals to the main control unit;
the upper computer is interacted with the main control unit through a data interface and is used for sending a control instruction to the main control unit, and the main control unit uploads the acquired data to the upper computer; the main control unit firstly generates an alternating current sinusoidal current signal by controlling the exciting current signal generating unit, then sets an exciting channel and a measuring channel by the electrode channel control unit, and finally completes data acquisition by controlling the boundary voltage signal measuring unit, the exciting current signal measuring unit and the contact impedance signal measuring unit;
the imaging electrodes have the current excitation and voltage measurement functions, and one group of imaging electrodes are attached to the surface of the scalp of the person to be measured.
4. The method of claim 1, wherein the reference electrode is selected from a disposable medical monopolar needle electrode or a self-adhesive surface electrode.
5. The measurement method according to claim 1, wherein the electrode channel control unit comprises a plurality of multi-way analog switching devices for controlling the switching of the imaging electrode channel and a plurality of single-pole single-throw switching devices for controlling the on/off of the reference electrode channel.
6. The measurement method according to claim 5, wherein four 1-out-of-multiple analog switching devices are used to control the plurality of imaging electrodes, a MUX1 and a MUX2 are used to control the positive-going excitation channel and the negative-going excitation channel, respectively, and a MUX3 and a MUX4 are used to control the positive-going measurement channel and the negative-going measurement channel, respectively; the reference electrode is controlled by two single-pole single-throw switching devices SPST1 and SPST 2;
in the boundary voltage signal measurement mode, the SPST1 and the SPST2 are disconnected, the enable pins of the MUX1, the MUX2, the MUX3 and the MUX4 are set to be high, and the excitation channel and the measurement channel are set by controlling the gating of the MUX1, the MUX2, the MUX3 and the MUX 4;
in the contact impedance signal measurement mode, SPST1 and SPST2 are turned on, enable pins of MUX1 and MUX3 are set to high, enable pins of MUX2 and MUX4 are set to low, and the excitation channel and the measurement channel are set by controlling gating of MUX1 and MUX 3.
7. The measuring method according to claim 1, wherein the contact impedance signal measuring unit is composed of a filter circuit, a fixed gain signal amplifying circuit, a programmable gain signal amplifying circuit and an A/D conversion circuit, and is used for measuring voltage signals corresponding to a two-electrode method;
the excitation current signal measuring unit consists of a sampling resistor, a filter circuit, a fixed gain signal amplifying circuit, a program control gain signal amplifying circuit and an A/D (analog/digital) conversion circuit and is used for measuring voltage signals corresponding to the two-electrode method.
8. The measurement method according to claim 7, wherein the filter circuit is composed of a second-order active low-pass filter and a second-order active high-pass filter; the fixed gain signal amplifying circuit is a first-stage amplifying circuit and consists of a precision resistor and an operational amplifier; the program control gain signal amplifying circuit is a second-stage amplifying circuit and consists of a programmable gain amplifying device, and the gain range can be dynamically adjusted to meet the signal amplification requirement of the amplitude in a wider dynamic range; the A/D conversion circuit is composed of an analog-to-digital converter and a peripheral circuit thereof and is used as a post-stage circuit of the signal measurement unit.
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| CN109745047B (en) * | 2019-01-22 | 2021-07-02 | 北京航空航天大学 | Electrical impedance imaging system based on piezoresistive electrode |
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