An electrode contact state detection system for EIT imaging equipment

Abstract

The present invention discloses an electrode contact state detection system for an EIT imaging device; the system comprises an electrode detachment detection circuit module; the electrode detachment detection circuit module is used to detect the detachment of electrodes on an electrode belt of the detected EIT imaging device; the electrode detachment detection circuit module comprises electrical components such as a positive and negative dual-current current source, a high-pass filter and IA1, a low-pass filter and IA2, and a switch matrix, so as to detect the electrodes of the EIT imaging device; wherein the current source is used to generate an alternating current source with a constant amplitude and opposite directions to each other, so as to generate an excitation current between the excitation electrodes; the switch matrix is ​​used to realize the switching of the excitation electrodes, so as to enable the current output to be switched to the expected electrodes; the electrodes on the EIT imaging device are used to be directly connected to the skin of a human body, so as to realize the function of the EIT imaging device.

Description

Technical Field

[0001] The present invention relates to the technical field of EIT imaging equipment, and in particular to an electrode contact state detection system for EIT imaging equipment. Background Art

[0002] As we all know, electrical impedance tomography (EIT) is a type of non-invasive medical imaging. The basic principle is to apply a safe excitation current (voltage) signal to the surface of the target tissue to be measured, and simultaneously measure the voltage (current) signal on the surface of the target tissue. The impedance (or impedance change) image distribution in the detected tissue is obtained by using an image reconstruction algorithm based on the measured signal.

[0003] EIT imaging devices apply a small and safe alternating current (or voltage) to the surface of the tissue being tested, generally using multiple electrodes surrounding the target area. Under the action of the excitation current, the current distribution through the tissue will change due to the difference in electrical impedance at different parts of the tissue. These changes will cause different voltage (or current) signals to be generated at different locations on the tissue surface. By measuring these voltage (or current) signals through multiple electrodes, information about the electrical impedance distribution inside the tissue can be obtained. EIT imaging devices measure the impedance distribution from the surface to the inside. First, a conductivity model of the tissue needs to be established, taking into account the electrode position, shape and geometric structure of the tissue. Using various image processing algorithms, the measured voltage (or current) data is converted into a two-dimensional or three-dimensional image of the internal electrical impedance distribution. This process requires processing complex mathematical calculations to improve the resolution and accuracy of the image.

[0004] EIT imaging equipment does not require the use of radiation or invasive equipment, is non-invasive to patients, and is suitable for frequent monitoring and special groups such as infants and young children. At the same time, EIT imaging equipment has a faster data acquisition and processing speed, and can achieve real-time dynamic monitoring. This is particularly important in applications that require observation of changes in physiological parameters (such as lung function monitoring, brain activity monitoring, etc.).

[0005] In this context, further researchers also found the following problems;

[0006] 1. At present, the electrode contact status detection method for EIT imaging equipment often uses the current source required by the EIT itself in the working state as the detection power supply. By measuring the voltage difference between the excitation electrodes, or the potential difference between a single excitation electrode and the ground, it is determined whether the electrode is detached. If the voltage difference between the excitation electrodes is too large and exceeds a certain threshold, or the potential difference between a single excitation electrode and the ground is too large and exceeds a certain threshold, it can be determined that the electrode is detached.

[0007] Solution 1: If the voltage difference between the excitation electrodes is measured, if the voltage difference exceeds a certain threshold, when judging the detachment, it is impossible to accurately determine which of the excitation electrodes has detached, so an accurate judgment cannot be made. Even if a part of the electrodes that may be connected are screened out through software judgment, it is impossible to achieve truly accurate electrode detachment detection. For example: when electrodes 2 and 4 are detached but electrode 3 is in good contact, it will cause electrodes to be measured as detached during 1, 2 excitations, 2, 3 excitations, 3, 4 excitations, and 4, 5 excitations. However, if electrodes 2, 3, and 4 are all detached, it will also be observed that electrodes are measured as detached during 1, 2 excitations, 2, 3 excitations, 3, 4 excitations, and 4, 5 excitations. Therefore, this solution cannot accurately determine whether the electrode has detached.

[0008] Solution 2 measures the potential difference between a single excitation electrode and the ground. If the potential difference exceeds a certain threshold, it is determined to be off. Since the excitation current can often adjust the frequency and amplitude of the current, the first problem encountered is that this determination method has a strong coupling with the excitation current. In addition, since the amplitude of the excitation current is often large, it is also easy to cause errors in the measurement process. Summary of the invention

[0009] The present invention provides an electrode contact state detection system for EIT imaging equipment, which has important practical significance and application value.

[0010] In order to achieve the above technical purpose, the present invention adopts the following technical solution:

[0011] The present invention provides an electrode contact state detection system for an EIT imaging device, comprising: an electrode detachment detection circuit module; the electrode detachment detection circuit module is used to detect the detachment of electrodes on an electrode belt of the EIT imaging device being detected;

[0012] The electrode detachment detection circuit module includes a positive and negative dual current source, a high-pass filter and IA1, a low-pass filter and IA2, and a switch matrix and other electrical components to detect the electrodes of the EIT imaging device;

[0013] Wherein, the current source is used to generate an alternating current source with a constant amplitude and opposite directions to each other, so as to generate an excitation current between the excitation electrodes;

[0014] The positive electrode of the current source is electrically connected to the input end of the high-pass filter, the input end of the low-pass filter and the positive electrode of the switch matrix, the output end of the high-pass filter is electrically connected to the non-inverting input end (+) of the positive electrode of IA1, the inverting input end (-) of the negative electrode of IA1 is grounded, and the output end of IA1 is used to output the amplified signal for subsequent detection to obtain the actual voltage magnitude out1;

[0015] The first output terminal, the second output terminal and the third output terminal of the low-pass filter are respectively electrically connected to the non-inverting input terminal (+) of the positive electrode of the IA2 and the inverting input terminal (-) of the negative electrode of the IA2, the negative electrode of the current source and the negative electrode of the switch matrix; and the output terminal of the IA2 is used to output the amplified signal for subsequent detection to obtain the actual voltage magnitude out2;

[0016] The switch matrix is ​​used to realize the switching of the excitation electrodes so that the current output can be switched to the desired electrodes;

[0017] The electrodes on the EIT imaging device are used to be directly connected to the skin of the human body to realize the function of the EIT imaging device.

[0018] Preferably, as an implementable embodiment, the current source adopts a composite current source design, which is composed of two independent current sources, namely, an electrode detection current source and an EIT excitation current source;

[0019] Wherein, the EIT excitation current source is a current source of the excitation current used in the EIT imaging device;

[0020] Wherein, the electrode detection current source is a dedicated current source for electrode detection.

[0021] Preferably, as an implementable embodiment, the frequency of the electrode detection current source is higher than the frequency of the EIT excitation current source, and the amplitude is lower than the amplitude of the EIT excitation current source.

[0022] Preferably, as an implementable embodiment, the IA1 is used to measure the voltage between the positive pole of the current source and the ground.

[0023] Preferably, as an implementable embodiment, a high-pass filter is added before IA1 to filter out the signal brought by the excitation current source, but retain the signal of the electrode detection current source;

[0024] The low-pass filter added before IA2 is used to filter out the signal from the electrode detection current source, but retain the signal from the excitation current source.

[0025] Preferably, as an implementable embodiment; when the patient is normally connected to the current electrode on the electrode belt on the worn EIT imaging device, the voltage to the ground measured by the IA1 is u=i*R, then it is determined that the current electrode connection is normal; wherein i is the amplitude of the excitation current source; R is the human body impedance;

[0026] When the current + power supply electrode on the electrode belt of the EIT imaging device worn by the patient falls off, the actual voltage measured by the IA1 is u1=the maximum output voltage Umax of the current source, then it is determined that the current + power supply electrode falls off;

[0027] When the patient is in normal contact with the current +power electrode on the electrode belt on the worn EIT imaging device, and the -power electrode is off; the actual voltage measured by the IA1 is u2=i*(R+Rhg), and the measured actual voltage u2 is significantly greater than u=i*R, then it is determined that the current +power electrode is in normal contact, and the -power electrode is off; where Rhg is the impedance between the human body and the earth.

[0028] Preferably, as an implementable embodiment, the IA2 is used to determine whether the electrode detachment occurs in either the positive electrode of the current current source or the negative electrode of the current current source when the signal of the measured actual voltage magnitude out2 increases abnormally.

[0029] Compared with the prior art, the embodiments of the present invention have at least the following technical advantages:

[0030] The electrode contact state detection system for an EIT imaging device provided by the present invention includes an electrode detachment detection circuit module; the electrode detachment detection circuit module is used to detect the detachment of the electrode on the electrode belt of the detected EIT imaging device; the electrode detachment detection circuit module includes a positive and negative dual-electric current source, a high-pass filter and IA1, a low-pass filter and IA2, and a switch matrix and other electrical components to detect the electrodes of the EIT imaging device; wherein the current source is used to generate an alternating current source with a constant amplitude and opposite directions to each other, which is used to generate an excitation current between the excitation electrodes;

[0031] At the same time, in order to adapt to the design of the composite current source, a high-pass filter circuit needs to be added before IA1, so that it can filter out the signal brought by the excitation current source well, but retain the signal of the electrode detection current source. And a low-pass filter circuit needs to be added before IA2, so that it can filter out the signal of the electrode detection current source well, but retain the signal brought by the excitation current source. In this way, after the electrode detachment detection circuit module of the present invention uses a composite dual-electric current source, it can significantly distinguish between three different situations: good contact, + power supply detachment, + power supply contact is good but - power supply detachment. In summary, the electrode detachment detection circuit module of the present invention can effectively monitor and detect the electrode connection status or electrode detachment status in the EIT system through the combination of a high-pass filter and IA1, a low-pass filter and IA2, and the flexible application of the switch matrix. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1A schematic diagram of an adjacent electrode method of an EIT imaging device in the prior art;

[0033] Figure 2 A circuit diagram of an electrode detachment detection circuit module in an electrode contact state detection system for an EIT imaging device;

[0034] Figure 3 A circuit diagram of IA1 when the current electrode is normally connected in an electrode contact state detection system for an EIT imaging device;

[0035] Figure 4 A circuit diagram of IA1 when an electrode connected to a positive electrode of a current source is disconnected in an electrode contact state detection system for an EIT imaging device;

[0036] Figure 5 A circuit diagram of IA1 in an electrode contact state detection system for an EIT imaging device when an electrode connected to a positive electrode of a current source is normally connected but an electrode of a negative electrode of the current source is disconnected;

[0037] Figure 6 A circuit diagram of an improved IA1 for an electrode contact state detection system of an EIT imaging device;

[0038] Figure 7 The present invention is a circuit diagram of a current source used in an electrode contact state detection system of an EIT imaging device. DETAILED DESCRIPTION

[0039] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] The present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0041] Introduction to the basic concept of EIT imaging equipment: The EIT imaging equipment for detecting detachment and detecting performance evaluation involved in the technical solution of the embodiment of the present invention is a 16-electrode EIT imaging equipment as shown in the figure below; when using it, the patient needs to tie an electrode belt. There are 16 electrodes on the electrode belt. When the equipment is working normally, the adjacent injection method is usually used for impedance measurement. Taking the 16-electrode cylindrical conductor as an example, see Figure 1 ,in Figure 1 Schematic diagram of the adjacent electrode method of EIT imaging equipment.

[0042] First, select electrode 1 and electrode 2 as excitation, measure the voltage between electrode 3 and electrode 4, electrode 4 and electrode 5, ..., until electrode 15 and electrode 16, and obtain 13 measurement values. Then, select electrode 2 and electrode 3 as excitation, measure the voltage between electrode 4 and electrode 5, electrode 5 and electrode 6, ..., until electrode 16 and electrode 1, and obtain 13 measurement values. In this way, select electrode 3 and electrode 4, electrode 4 and electrode 5, electrode 5 and electrode 6, until electrode 16 and electrode 1 as excitation, measure the voltage of other adjacent electrode pairs, and obtain 13x 16 = 208 measurement values ​​in total.

[0043] Embodiment 1

[0044] like Figure 2 As shown, an electrode contact state detection system for an EIT imaging device adopted in the first embodiment of the present invention is used, wherein an electrode detachment detection circuit module detects the detachment of electrodes on an electrode belt of the EIT imaging device being detected;

[0045] like Figure 2 As shown, the electrode detachment detection circuit module includes a positive and negative dual-electric current source, a high-pass filter and IA1 (instrument amplifier 1), a low-pass filter and IA2 (instrument amplifier 1), and a switch matrix and other electrical components to detect the electrodes of the EIT imaging device. That is, the electrode detachment detection circuit module is composed of a positive and negative dual-electric current source, a switch matrix, an electrode, an instrument amplifier, and a filter.

[0046] Wherein, the current source is used to generate an alternating current source with a constant amplitude and opposite directions to each other, so as to generate an excitation current between the excitation electrodes;

[0047] The positive electrode of the current source is electrically connected to the input end of the high-pass filter, the input end of the low-pass filter and the positive electrode of the switch matrix, respectively; the output end of the high-pass filter is electrically connected to the non-inverting input end (+) of the positive electrode of the IA1 (instrument amplifier 1); the inverting input end (-) of the negative electrode of the IA1 (instrument amplifier 1) is grounded; and the output end of the IA1 (instrument amplifier 1) is used to output the amplified signal for subsequent detection to obtain the actual voltage magnitude out1;

[0048] The first output terminal, the second output terminal and the third output terminal of the low-pass filter are respectively electrically connected to the non-inverting input terminal (+) of the positive electrode of the IA2 (instrument amplifier 2) and the inverting input terminal (-) of the negative electrode of the IA2 (instrument amplifier 2), the negative electrode of the current source and the negative electrode of the switch matrix; and the output terminal of the IA2 (instrument amplifier 2) is used to output the amplified signal for subsequent detection to obtain the actual voltage magnitude out2;

[0049] The switch matrix is ​​used to realize the switching of the excitation electrodes so that the current output can be switched to the desired electrodes;

[0050] The electrodes on the EIT imaging device are used to be directly connected to the human skin to realize the function of the EIT imaging device; Figure 2 In the embodiment, the instrument amplifiers (IA1 and IA2) are used to measure the voltage between specific working points to realize the functions of the present invention. The electrodes on the EIT imaging device are used to be directly connected to the skin of the human body to realize the functions of the EIT imaging device.

[0051] The following is an explanation of the electrical components in the electrode contact state detection system for an EIT imaging device used in the first embodiment of the present invention:

[0052] 1. High pass filter and IA1;

[0053] High-pass filter: Function: High-pass filter is used to filter out low-frequency signals and only allow high-frequency signals to pass. In EIT systems, this can be used to remove steady-state signals and extract dynamically changing high-frequency components.

[0054] IA1 (Instrumentation Amplifier 1): Function: The instrumentation amplifier is used to amplify the high-frequency signal after high-pass filter processing with high precision. It has high input impedance, low noise and high common mode rejection ratio (CMRR), which is very suitable for processing weak electrical signals. Function: IA1 amplifies the signal after high-pass filtering and enhances the high-frequency characteristic signal generated when the electrode falls off, which is convenient for subsequent detection and analysis.

[0055] 2. Low pass filter and IA2;

[0056] Low-pass filter: Function: Low-pass filter is used to filter out high-frequency signals and allow low-frequency signals to pass. In EIT systems, low-pass filters are usually used to smooth signals, remove high-frequency noise, and retain the main low-frequency components.

[0057] IA2 (Instrumentation Amplifier 2): Function: Similar to IA1, IA2 is used to amplify the low-frequency signal after low-pass filter processing with high precision. Function: IA2 amplifies the signal after low-pass filtering, enhances the low-frequency characteristic signal generated when the electrode falls off, and further assists in the detection and confirmation of electrode fall off.

[0058] See also Figure 2Therefore, in order to adapt to the design of the composite current source in the embodiment of the present invention, a high-pass filter circuit needs to be added before IA1 (instrumentation amplifier 1) so that it can well filter out the signal brought by the excitation current source, but retain the signal of the electrode detection current source. A low-pass filter circuit needs to be added before IA2 (instrumentation amplifier 1) so that it can well filter out the signal of the electrode detection current source, but retain the signal brought by the excitation current source.

[0059] 3. The switch matrix is ​​used to switch and select between multiple electrodes and control the measurement path between different electrode pairs. In the EIT system, since multiple electrode pairs need to be measured cyclically, the switch matrix ensures that each measurement can be accurately connected to the selected electrode pair. Function: In the electrode detachment detection module, the switch matrix is ​​responsible for dynamically selecting different electrode pairs for signal acquisition and detection, thereby monitoring the connection status of each electrode in real time. This helps to quickly identify disconnected or poorly contacted electrodes and ensure the accuracy of EIT imaging.

[0060] Many EIT imaging devices commonly use 16 electrodes, which are usually evenly distributed around the measured area (such as the chest) to form multiple electrode pairs for current excitation and voltage measurement. Arrangement: The 16 electrodes are usually evenly arranged on the surface of the measured object to form a ring structure to ensure full coverage of the measured area and provide sufficient data for image reconstruction.

[0061] Function of electrodes: Each pair of electrodes is used to inject current and measure voltage in EIT measurement. The switch matrix is ​​responsible for selecting different electrode pairs for alternating measurements to obtain comprehensive impedance data. The electrodes in the present invention refer to the 16 electrodes on the EIT imaging device. These electrodes are connected to the composite current source and measurement module through the switch matrix to ensure that each electrode pair can be effectively detected and monitored. Comprehensive description The electrode detachment detection circuit module of the present invention ensures the stability of the electrode connection state of the EIT system in the following ways;

[0062] In summary, the electrode detachment detection circuit module of the present invention can effectively monitor and detect the electrode connection status or electrode detachment status in the EIT system through the combination of a high-pass filter and IA1, a low-pass filter and IA2, and the flexible application of the switch matrix.

[0063] The following is a further introduction to each electrical component:

[0064] In a specific technical solution, the current source adopts a composite current source design, which is composed of two independent current sources, namely, an electrode detection current source and an EIT excitation current source;

[0065] Wherein, the EIT excitation current source is a current source of the excitation current used in the EIT imaging device, and its frequency and amplitude can usually be adjusted according to the needs of clinical use;

[0066] The electrode detection current source is a dedicated current source for electrode detection; and the frequency of the electrode detection current source is higher than the frequency of the EIT excitation current source, and the amplitude is lower than the amplitude of the EIT excitation current source.

[0067] In a specific technical solution, the IA1 (instrument amplifier 1) is used to measure the voltage between the positive electrode of the current source and the ground.

[0068] When the patient is normally connected to the current electrode on the electrode belt of the worn EIT imaging device, the actual voltage out1 measured by the IA1 (instrumentation amplifier 1) is close to the theoretical voltage value u, thereby determining that the current electrode connection is normal;

[0069] When the patient is disconnected from the current electrode on the electrode belt of the worn EIT imaging device, the IA1 (instrumentation amplifier 1) is also used to determine that the electrode connected to the positive pole of the current source is disconnected when the measured actual voltage out1 (i.e., the voltage at the output end of the current source can reach i*Rg under ideal conditions at this time) is much greater than the maximum output voltage Umax of the current source;

[0070] When the current electrode on the electrode belt of the EIT imaging device worn by the patient is normally connected to the positive electrode of the current source, and the negative electrode of the current source is disconnected, the voltage signal measured by the IA1 (instrument amplifier 1) is i*(R+Rhg), where i is the output current of the current source, R is the human body impedance, and Rhg is the resistance between the human body and the earth. However, since i is usually large, i*(R+Rhg) is often greater than the maximum output voltage Umax of the current source. This means that in theory, the above-mentioned different electrode contact conditions can be measured in different states by IA1 (instrument amplifier 1), but due to the limitation of the current source load capacity, it is impossible to make a precise distinction.

[0071] In the electrode detachment detection circuit module of the present invention, the instrument amplifier plays a key role in signal amplification. The instrument amplifier usually has three ports, which are used for input and output signals respectively.

[0072] About the three ports of IA1 (Instrumentation Amplifier 1);

[0073] Non-Inverting Input (usually marked as + or V+); Function: Receives the positive (non-reverse) part of the input signal.

[0074] Connections in this circuit: Usually connected to the signal source after high-pass filter processing, that is, the output from the high-pass filter. This part of the signal contains high-frequency changes or noise caused by electrode shedding.

[0075] Inverting Input (usually marked as - or V-); Function: Receives the inverted portion of the input signal and determines the amplifier gain and output together with the non-inverting input. Connection in this circuit: Usually connected to a reference voltage or connected to the output through a feedback resistor to set the amplifier gain. In some circuit designs, the inverting input may be connected to the negative portion of the signal to achieve a differential amplification effect, thereby improving anti-interference capabilities.

[0076] Output terminal (Output, usually marked as OUT1); Function: Output the amplified signal for subsequent detection circuit unit processing or directly used for signal analysis (i.e., for subsequent detection circuit unit to measure the actual voltage size out1) to further process the amplified high-frequency signal to determine whether the electrode has fallen off.

[0077] There are three different common problems with the detection of IA1 (instrumentation amplifier 1):

[0078] See also Figure 3 , about IA1 (instrumentation amplifier 1); when the device is in use, the setting of IA1 (instrumentation amplifier 1) can be used to measure the voltage between the positive pole of the current source and the ground. When the patient is properly connected to the current electrode on the electrode belt on the EIT imaging device worn by the patient, the effect is Figure 3 As shown:

[0079] At this time, Figure 3 The resistance in represents the equivalent load of the patient. Since the impedance of the human body between the excitation electrodes is normal, the two symmetrical current sources can work normally at this time. When the current source is working normally, it can be known from Ohm's law that the voltage from the output end of the current source to the ground is u=i*R, where i is the output current of the current source, which is a fixed value. R is the size of the human body load, which is a stable value. At this time, when the electrode contact is good, the phenomenon is that the actual voltage out1 measured by IA1 (instrument amplifier 1) is close to the theoretical voltage value u. Therefore, it can be considered that when the measured signal out1 is not significantly greater than the theoretical voltage value u, it can be determined that the electrode connection is normal.

[0080] The actual current source cannot achieve the performance of the ideal current source. When the load is too large, abnormal conditions will occur. It is obvious that the maximum output voltage of the current source is usually a fixed effective value Umax.

[0081] When the electrode connected to the positive pole of the current source is disconnected, the circuit works as follows Figure 4 As shown: At this time, although the electrode is disconnected, due to the influence of parasitic parameters and distributed parameters, the inevitable current source will be connected to the ground, but its equivalent resistance Rg is extremely large. In an ideal situation at this time, the voltage at the output terminal of the current source can reach i*Rg. However, since the value of Rg is usually large and i is not small enough, i*Rg will be much larger than the maximum output voltage Umax of the current source. Therefore, the current source can only output a voltage equal to the maximum output voltage Umax of the current source. This phenomenon is called the saturation state.

[0082] When the electrode connected to the positive pole of the current source is normally connected, but the electrode at the negative pole of the current source is disconnected, the working condition of the circuit is as Figure 5 shown: At this time, R is the human body impedance, which is usually small. Rhg is the impedance between the human body and the ground. Usually, people do not come into contact with the ground directly, but will have indirect contact through various forms. Therefore, due to the existence of various distributed parameters and parasitic parameters, Rhg is large, but it is still much smaller than Rg. Therefore, for this situation at this time, the voltage signal that IA1 (instrumentation amplifier 1) can theoretically measure is i*(R + Rhg), where i is the output current of the current source, R is the human body impedance, and Rhg is the resistance value between the human body and the ground. However, since i is usually large, i*(R + Rhg) is also often greater than Umax. This means that theoretically, different electrode contact situations can be measured in different states by IA1 (instrumentation amplifier 1), but due to the load-carrying capacity limitation of the current source, it is impossible to make a fine distinction.

[0083] Therefore, according to the above analysis, it is not difficult to find that the voltage at the output terminal of the current source is proportional to the size of the load. The larger the load, the larger the voltage at the output terminal. Therefore, the detection range of out1 for determining electrode detachment is: k*i*R < out1 < Umax, where k represents a constant greater than 1 and less than 10, such as 5; i represents the magnitude of the current output by the current source; R represents the typical value of the human body load, which is a unique fixed value. Then k*i*R is the threshold value set in this electrode detachment detection circuit. Umax is the maximum output voltage of the current source, which is also the maximum value. It is not difficult to find that the voltage range within which out1 can judge electrode detachment is related to the current magnitude i, and the larger i is, the higher the lower limit, but the upper limit will not change, which means that its determination range decreases, and thus the measurement accuracy is reduced.

[0084] To solve this problem, the present invention has made innovations in the design of the current source, as detailed in the following description of the current source.

[0085] See Figure 6, about IA2 (instrumentation amplifier 1); for IA2 (instrumentation amplifier 1), it is not difficult to find that if the electrode of either the positive electrode of the current source or the negative electrode of the current source falls off, the signal of out2 will increase abnormally, thereby judging that the electrode has fallen off. Therefore, when only IA2 (instrumentation amplifier 1) is used, it is impossible to accurately judge the electrode shedding state. But its advantage is that when the electrode in the negative electrode of the + current source and the negative electrode of the - current source are in good contact, the quality of the contact can still be quantitatively analyzed by measuring the size of the load. That is, the larger the contact impedance, the larger the equivalent resistance at the rear end, and the larger the resistance value measured by out2.

[0086] See also Figure 2 and Figure 7 , about the design of the current source; As mentioned above, when the EIT imaging device is in use, the excitation current source amplitude i is usually small. Therefore, in order to enable IA1 (instrumentation amplifier 1) and IA2 (instrumentation amplifier 1) to work better, the current source needs to be designed in the following way: Among them, the current source adopts a composite current source design, which is composed of two independent current sources. Among them, the EIT excitation current source is the current source of the excitation current used in the EIT imaging device, and its frequency and amplitude can usually be adjusted according to the needs of clinical use. The electrode detection current source is a special current source for electrode detection. Its characteristics are that the frequency is significantly higher than the excitation current frequency and the amplitude is significantly lower than the excitation current frequency. Therefore, the three different conventional detection situations of IA1 (instrumentation amplifier 1) stated above will be solved;

[0087] Specifically, the current source adopts a composite current source design, which is composed of two independent current sources, namely, an electrode detection current source and an EIT excitation current source;

[0088] In the above three different situations, when the electrodes are in normal contact, the excitation current source amplitude i is significantly reduced (because the electrode detection current source uses a smaller current), so u=i*R will be significantly reduced. Explanation: when the patient is normally connected to the current electrode on the electrode belt on the worn EIT imaging device, the voltage to the ground measured by the IA1 (instrumentation amplifier 1) is u=i*R, and it is determined that the current electrode connection is normal; i is the excitation current source amplitude; R is the human body impedance;

[0089] When the current + power supply electrode (i.e., the positive electrode of the current source) on the electrode belt of the EIT imaging device worn by the patient falls off, the actual voltage measured by the IA1 (instrumentation amplifier 1) is u1=the maximum output voltage Umax of the current source, then it is determined that the current + power supply electrode falls off;

[0090] When the patient is in normal contact with the current + power electrode (i.e., the positive electrode of the current source) on the electrode belt on the worn EIT imaging device, and the - power electrode (i.e., the negative electrode of the current source) is detached; the actual voltage measured by the IA1 (instrument amplifier 1) is u2=i*(R+Rhg), and the measured actual voltage u2 is significantly greater than u=i*R, then it is determined that the current + power electrode (i.e., the positive electrode of the current source) is in normal contact, and the - power electrode (i.e., the negative electrode of the current source) is detached; wherein Rhg is the impedance between the human body and the earth.

[0091] In summary, after using the composite dual-power current source, three different situations can be clearly distinguished: good contact, + power supply is off, and + power supply contact is good but - power supply is off.

[0092] Therefore, in order to adapt to the design of the composite current source, a high-pass filter circuit needs to be added before IA1 (instrumentation amplifier 1) so that it can filter out the signal brought by the excitation current source well, but retain the signal of the electrode detection current source. A low-pass filter circuit needs to be added before IA2 (instrumentation amplifier 1) so that it can filter out the signal of the electrode detection current source well, but retain the signal brought by the excitation current source.

[0093] In summary, the designs adopted in the present invention are: 1. The current sources are all improved into composite current sources, which are used to be compatible with the excitation current of EIT and the special current for shedding detection. The special current source for shedding detection has the characteristics of a frequency significantly greater than the excitation current source and a magnitude significantly smaller than the excitation current source. 2. The current from the + current source end to the ground is measured, and a high-pass filter structure is added before the instrument amplifier to accurately determine whether the electrode connected to the + current source has fallen off, and can distinguish between three different situations: good contact between the two electrodes, good contact at the + end but abnormal contact at the - end, and abnormal contact at the + end. 3. The voltage between the positive and negative current sources is measured to calculate the size of the contact impedance when the electrodes are in good contact. A low-pass filter structure is added before the instrument amplifier to ensure that the impact of the composite current source is reduced.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. A person skilled in the art may modify the technical solutions described in the above embodiments, or replace part or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrode contact state detection system for an EIT imaging device, characterized in that: include: Electrode detachment detection circuit module; The electrode detachment detection circuit module is used to detect the detachment of electrodes on the electrode belt of the EIT imaging device being detected; The electrode detachment detection circuit module includes a positive and negative dual current source, a high-pass filter and IA1, a low-pass filter and IA2, and a switch matrix and other electrical components to detect the electrodes of the EIT imaging device; Wherein, the current source is used to generate an alternating current source with a constant amplitude and opposite directions to each other, so as to generate an excitation current between the excitation electrodes; The positive electrode of the current source is electrically connected to the input end of the high-pass filter, the input end of the low-pass filter and the positive electrode of the switch matrix, the output end of the high-pass filter is electrically connected to the non-inverting input end (+) of the positive electrode of IA1, the inverting input end (-) of the negative electrode of IA1 is grounded, and the output end of IA1 is used to output the amplified signal for subsequent detection to obtain the actual voltage magnitude out1; The first output terminal, the second output terminal and the third output terminal of the low-pass filter are respectively electrically connected to the non-inverting input terminal (+) of the positive electrode of the IA2 and the inverting input terminal (-) of the negative electrode of the IA2, the negative electrode of the current source and the negative electrode of the switch matrix; and the output terminal of the IA2 is used to output the amplified signal for subsequent detection to obtain the actual voltage magnitude out2; The switch matrix is ​​used to realize the switching of the excitation electrodes so that the current output can be switched to the desired electrodes; The electrodes on the EIT imaging device are used to be directly connected to the skin of the human body to realize the function of the EIT imaging device.

2. The electrode contact state detection system for an EIT imaging device according to claim 1, characterized in that: The current source adopts a composite current source design, which is composed of two independent current sources, namely, an electrode detection current source and an EIT excitation current source; Wherein, the EIT excitation current source is a current source of the excitation current used in the EIT imaging device; Wherein, the electrode detection current source is a dedicated current source for electrode detection.

3. The electrode contact state detection system for an EIT imaging device according to claim 2, characterized in that: The frequency of the electrode detection current source is higher than the frequency of the EIT excitation current source, and the amplitude is lower than the amplitude of the EIT excitation current source.

4. The electrode contact state detection system for an EIT imaging device according to claim 1, characterized in that: The IA1 is used to measure the voltage between the positive terminal of the current source and the ground.

5. The electrode contact state detection system for an EIT imaging device according to claim 1, characterized in that: A high-pass filter is added before IA1 to filter out the signal from the excitation current source but retain the signal from the electrode detection current source; The low-pass filter added before IA2 is used to filter out the signal from the electrode detection current source, but retain the signal from the excitation current source.

6. The electrode contact state detection system for an EIT imaging device according to claim 5, characterized in that: When the patient is normally connected to the current electrode on the electrode belt of the worn EIT imaging device, the voltage to the ground measured by the IA1 is u=i*R, and it is determined that the current electrode connection is normal; wherein i is the amplitude of the excitation current source; and R is the human body impedance; When the current + power supply electrode on the electrode belt of the EIT imaging device worn by the patient falls off, the actual voltage measured by the IA1 is u1=the maximum output voltage Umax of the current source, then it is determined that the current + power supply electrode falls off; When the patient is in normal contact with the current +power electrode on the electrode belt on the worn EIT imaging device, and the -power electrode is off; the actual voltage measured by the IA1 is u2=i*(R+Rhg), and the measured actual voltage u2 is significantly greater than u=i*R, then it is determined that the current +power electrode is in normal contact, and the -power electrode is off; wherein Rhg is the impedance between the human body and the earth.

7. The electrode contact state detection system for an EIT imaging device according to claim 1, characterized in that: The IA2 is used to determine that an electrode detachment phenomenon occurs in either the positive electrode of the current current source or the negative electrode of the current current source when the signal of the measured actual voltage magnitude out2 increases abnormally.

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