Name: Pedro Bertemes-Filho

Email: mpp98pb@sheffield.ac.uk

CompanyName: University of Sheffield

Country: United Kingdom

Abstract: Stand-off Electrode (SoE): A New Method for Improving the Sensitivity Distribution of Tetrapolar Probe

P. Bertemes-Filho, B. H. Brown, A. J. Wilson, R. H. Smallwood

Small tetrapolar probes have been widely used
in Electrical Impedance Spectroscopy (EIS) for
tissue characterisation over a wide frequency
range. Measurement and modelling have confirmed
that these probes have negative sensitivity regions
which may lead to misinterpretation of tissue
properties. Although the sensitivity distribution
can be modified by moving drive and receive electrode
pairs closer together, small electrode-spacing
is not always possible. In this paper we describe
the use of a conductive 'spacer' beneath the electrode
to eliminate negative sensitivity regions from the
material of interest. A home-made sheet of hydrogel
5-mm thick is attached to an electrolytic tank
filled with saline solution. Transfer impedances
(Tz) are measured with and without the sheet of
hydrogel for five electrode spacings. These measured
values of Tz are compared with predicted ones obtained
from a model based on Geselowitz's lead field theory.
Good agreement was obtained between the measured value
of Tz and the predicted ones with a maximum error of 1%.
The sensitivity to a change in resistivity was positive
everywhere within the tank when the electrode spacing is
twice the hydrogel thickness. It can therefore be
concluded that the positive sensitivity distribution
can be confined within a biological material of
interest by using a hydrogel layer having a thickness
of half the electrode spacing. This finding may have
implications for improving tissue characterisation
using electrical impedance spectroscopy.

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