Probe Position Sensing with Dynamic Impedance Compensation
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Solution Overview
Problem
Existing position sensing systems for objects within a living body face challenges in accurately determining the three-dimensional coordinates of probes due to artifacts caused by changing local impedance at the body surface, such as electrode peel-off, skin moisture, and temperature changes, which affect the reliability and accuracy of medical procedures.
Innovation Solution
The system employs a novel electrode design and driving circuit that measures impedance between a probe and body surface electrodes, using a controller to dynamically compensate for impedance variations by alternating between series and parallel circuit configurations, maintaining constant voltage or current, and adjusting impedance characteristics based on local electrical impedance measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If impedance measurements are used to determine probe position, then real-time spatial coordinates can be obtained, but measurement precision deteriorates due to artifacts from changing local impedance at body surface
Solution Approach 1:
The system performs preliminary calibration by measuring impedance between body surface electrodes and a reference point before actual position sensing. These calibration values are stored and used to compensate for local impedance variations during subsequent measurements, eliminating artifacts caused by skin moisture, temperature, and electrode contact variations
Solution Approach 2:
The system continuously monitors impedance measurements and compares them against calibration values. When deviations are detected that indicate changes in local body surface impedance, the system automatically adjusts position calculations using the stored calibration data, providing real-time compensation for environmental factors
2Reliability
If body surface impedance variations are not compensated, then device complexity remains low, but reliability of medical procedures deteriorates
Solution Approach 1:
The system performs preliminary calibration by measuring impedance between body surface electrodes and a reference point before actual position sensing. These calibration values are stored and used to compensate for local impedance variations during subsequent measurements, eliminating artifacts caused by skin moisture, temperature, and electrode contact variations
Solution Approach 2:
The calibration values act as an intermediary reference that mediates between the raw impedance measurements and the final position calculations. By comparing current measurements against the stored calibration data, the system can distinguish between changes caused by probe position versus changes caused by body surface conditions
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 enhances the accuracy of position sensing, improving the precision of medical procedures like cardiac mapping and ablation by effectively mitigating the impact of impedance changes, thereby ensuring reliable real-time positioning of probes within the body.
Implementation Method 1
measuring an impedance between the probe and each of the body surface electrodes
Implementation Method 2
The controller is adapted to maintain a constant voltage between each of the surface locations and the probe electrode, and to measure respective impedance characteristics by measuring currents at the constant voltage
Data Source
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AI summary
Apparatus and methods are provided for determining in near realtime the position of a probe placed within a living body. Electric currents are driven between one or more electrodes on the probe and electrodes placed on the body surface. The impedance between the probe and each of the body surface electrodes is measured, and three-dimensional position coordinates of the probe are determined based on the impedance measurements. Dynamic compensation is provided for changing impedance of the body surface and its interface with the electrodes, resulting from such causes as electrode peel-off and changes in moisture and temperature. The compensation improves the accuracy of, inter alia, medical procedures, such as mapping the heart or performing ablation to treat cardiac arrhythmias.