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Information extraction from impedance spectra: Theoretical predictions and in vivo validation for the oral mucosa

The aim of our study was to investigate the relationship between widely used set of impedance indices (MIX, PIX, RIX, IMIX) and macroscopic tissue properties – tissue electrical conductivity σ and permittivity ε . The issues we addressed theoretically and experimentally are: i) are these indices mutually independent, ii) can they distinguish different tissue structure, iii) what is their coefficient of variation, and iv) are they sensitive to probe geometry being used for impedance measurement. For a tissue modeled as an isotropic dispersive monodomain we have shown theoretically that impedance phase does not depend on geometry of the impedance probe being used nor does the phase depend on the size of tissue sample. Therefore, normalization of phase in the form of PIX index is not necessary. We also demonstrated that MIX, PIX, RIX, IMIX do not depend on probe geometry. This was also proved with finite-element models. Preliminary experimental validation was performed for the oral mucosa where impedance magnitude and phase were measured with two intraoral probes of different geometries. The results, as expected, showed considerable difference in impedance magnitude and negligible difference in impedance phase for the same anatomical location.

bioimpedance; impedance spectrometry; oral mucosa; impedance indices; intraoral impedance probes; FEM model; in vivo impedance measurement

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