Electroimpedance Tomograph Symmetry Tuning for Common-Mode Suppression
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Solution Overview
Problem
Electroimpedance tomography faces challenges in suppressing common-mode signals, which interfere with the measurement of impedance distributions, particularly due to asymmetries in the alternating current feed and electrode arrangements, limiting the permissible measuring currents and affecting the accuracy of impedance changes detection.
Innovation Solution
An electroimpedance tomograph with a common-mode signal measuring electrode and a control unit that detunes the symmetrical AC power source to minimize common-mode signals by adjusting the symmetry based on measured common-mode signals, using either active or passive compensation methods, to optimize the AC power source for each electrode pair.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the measuring current is increased to improve signal strength, then the useful signal becomes larger relative to external interferences, but common-mode signals and crosstalk increase proportionally, worsening measurement precision
Solution Approach 1:
The patent measures the common-mode signal using a dedicated measuring electrode and then deliberately superimposes an opposing common-mode signal from the AC power source to cancel out the harmful common-mode interference. This converts the harmful common-mode signal into a beneficial cancellation mechanism, allowing higher measuring currents without proportional increases in interference.
Solution Approach 2:
The system continuously measures the common-mode signal with a dedicated electrode and uses this measurement to adjust the symmetry of the AC power source in real-time. This feedback loop ensures that common-mode signals are minimized dynamically, enabling the use of higher measuring currents while maintaining measurement precision.
2Object-generated harmful factors
If a symmetrical AC power source is used to reduce common-mode signals, then common-mode interference is reduced, but residual asymmetry persists due to cable routing differences and contact resistances, limiting measurement accuracy
Solution Approach 1:
The system performs preliminary measurement of the common-mode signal using a dedicated electrode before the actual impedance measurement. Based on this preliminary measurement, it pre-adjusts the symmetry parameters of the AC power source to minimize common-mode signals, thereby eliminating residual asymmetry effects before they can degrade measurement accuracy.
Solution Approach 2:
The patent dynamically adjusts the symmetry parameters of the AC power source based on measured common-mode signals. By changing parameters such as the center tap position or voltage balance, the system optimizes the power source symmetry for each measurement configuration, compensating for cable routing differences and contact resistance variations.
3Measurement precision
If additional measuring electrodes and control mechanisms are added to detect and compensate common-mode signals, then measurement precision improves, but device complexity increases
Solution Approach 1:
The dedicated common-mode measuring electrode serves multiple functions: it measures common-mode signals for compensation, can be used as a regular measuring electrode when not needed for common-mode measurement, and helps characterize the body's electrical properties. This multi-functionality reduces the need for additional specialized components.
Solution Approach 2:
The system uses the body itself as part of the measurement circuit for common-mode signal detection. The common-mode measuring electrode measures the potential difference between the body and ground, utilizing the body's own electrical characteristics to provide the compensation signal, thereby reducing the need for external complex compensation circuits.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces common-mode signals, enhancing the accuracy of impedance distribution reconstruction and minimizing interference, thereby improving the quality of the impedance tomograms by compensating for asymmetries and optimizing the AC power source for each electrode pair.
Implementation Method 1
a common-mode signal measuring electrode and a control unit that detunes the symmetrical AC power source to minimize common-mode signals by adjusting the symmetry based on measured common-mode signals
Implementation Method 2
a symmetrical AC power source to reduce common-mode signals. The control and evaluating unit is set up, furthermore, to detune the common-mode signal of the alternating current on the body against the ground
Data Source
AI summary
An electroimpedance tomograph with a plurality of electrodes (1) is provided, which can be placed on the body of a patient and are connected via a selector switch (60) with a control and evaluating unit (20). The control and evaluating unit (20) cooperates with the selector switch (60) such that two electrodes each are supplied with an alternating current from an AC power source (22) and the detected analog voltage signals of the other electrodes are processed in order to reconstruct therefrom the impedance distribution of the body in the plane of the electrodes, wherein a symmetrical AC power source is used to reduce common-mode signals. To further suppress interferences due to common-mode signals, provisions are made for the control and evaluating unit (20) to be set up, furthermore, for detuning the common-mode signal of the alternating current on the body against the ground by means of a common-mode signal measuring electrode (4) and, based on this, the symmetry of the symmetrical AC power source such that the common-mode signal on the body is minimized, and the corresponding detuning parameters are stored for each electrode pair.