Numerical Sensitivity Analysis of Microelectrodes for Multi-Local Im-pedance Measurements on Needles

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Needle insertion procedures are inevitable in a wide range of current health care practices. Although these interventions are performed frequently, complications due to incorrect needle positioning still occur. Common assistance systems are found to be time-consuming, expensive, or inaccurate. An alternative approach utilizes impedance measurements which can be used to identify various tissue types based on their variance in dielectric properties. To provide localized information about the present tissue type, an array of microelectrodes on a needle is conceivable. In this work, FEM simulation is used to study the sensitivity distributions of electrode configurations. In particular, a method is proposed to treat singularities that might occur when simulating electric fields. In this method, a finer mesh and a coarser mesh compared to the original mesh are created. A geometric line is constructed originating from the singularity and pointing into free space. Sensitivities are evaluated along this line and a minimum distance from the singular point is determined based on an assessment of the influence of the singularity. Sensitivities are limited to the maximum sensitivity found at the minimum distance. The resulting sensitivity distributions can be exported and used for further analysis. The results are validated comparing the total impedance with the impedance in the sensitivity field.