Tissue Impedance Measurement Electrode Configuration
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Solution Overview
Problem
Impedance measurements of tissues are susceptible to artifacts caused by electrode polarization and front-end loading effects, leading to inaccurate results in diagnosing cancer and other diseases.
Innovation Solution
A system with multiple electrodes and an electronic switch system that compensates for electrode polarization by making redundant measurements at different distances and correcting for amplifier loading effects, using a 4-lead configuration with sensing electrodes positioned close to driving electrodes to reduce leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If impedance measurements are performed using conventional electrode configurations, then the measurement process is simple, but the measurements are susceptible to artifacts caused by electrode polarization and front-end loading effects
Solution Approach 1:
The measurement system is segmented into separate driving electrodes (for current injection) and sensing electrodes (for voltage measurement), allowing independent optimization of each function. This segmentation enables the sensing electrodes to be positioned close to the driving electrodes without being affected by the same polarization artifacts that affect the current path
Solution Approach 2:
The sensing electrodes act as intermediaries that measure the voltage drop across the tissue without directly carrying the measurement current. This intermediary approach allows the system to measure impedance while avoiding the direct polarization effects that would occur if the same electrodes used for current injection were also used for voltage sensing
2Measurement precision
If multiple measurements are taken at different electrode separations to correct for polarization, then measurement accuracy improves, but the measurement time increases
Solution Approach 1:
The system performs preliminary measurements at multiple electrode separations during an initial calibration phase to establish the polarization characteristics of the specific electrode-tissue interface. These preliminary data are used to compute correction factors that can then be applied to subsequent measurements, avoiding the need to repeat the full multi-separation measurement sequence for every new measurement
Solution Approach 2:
The system creates a mathematical model (copy) of the polarization effect based on initial measurements at different separations. This model is then used to predict and correct polarization artifacts in subsequent measurements, eliminating the need to physically repeat the multi-separation measurement process for each new impedance reading
Data Source
AI summary
A device and method for accurately characterizing tissue impedance employs multiple electrodes at a plurality of separation distances to cancel the effects of front end loading leakage currents and electrode polarization to improve the accuracy of sensitive impedance measurements used to identify cancerous tissues. These measurements may be automated over a range of frequencies.