Physical study of the sensitivity distribution in multi-electrode systems

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Abstract
The basic aim of bio-electrical multi-electrodes systems is to map the distribution of electrical parameters of the interior of the body by means of external measurements. Ideally, a perfect imaging system would be able to explore individually each point of the medium. In practice each recorded value results from the contributions of many points. For example, in classical tomography, each measurement is the integral along the line between source and detector. The reconstruction algorithm then extracts the individual value for each point of the image. The properties of electrical fields result in multi-path current flow in a medium: a given measurement not only involves the points on the line linking the electrodes, but also other points in the medium. The purpose of this work was to study the distribution of sensitivity in a model. The body was simulated by an insulating cylindrical tank of 19 cm diameter filled with water. Sixteen carbon electrodes of 6 mm diameter were placed regularly around the tank in a transverse plane. The frequency used was 20 kHz. The sensitivity at each point of the model was studied by means of a 21 mm diameter sphere of stainless steel plunged into the tank. Qualitatively the results confirmed that the sensitivity is high in the proximity of the electrodes and lower far from them. Furthermore, it is clear that the sensitivity out of the plane containing the electrodes is far from negligible. The data also allowed us to compare different electrode configurations and select those exhibiting the better sensitivity for interior points.(ABSTRACT TRUNCATED AT 250 WORDS)

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