title: Stand-off electrode (SoE): a new method for improving the sensitivity distribution of a tetrapolar probe.
abstract: Tetrapolar probes have been widely used for measuring the impedance spectra of tissues. However, the non-uniform sensitivity distribution of these probes limits the ability to identify conductivity changes in tissue. This paper presents a novel method for improving the sensitivity distribution beneath a tetrapolar probe. The method consists of placing a hydrogel layer between the probe and the tissue in order to make the sensitivity positive everywhere within the tissue. Theoretical and measured sensitivity distributions are compared. A good agreement between theoretical and measured data from an electrolytic tank was obtained with a maximum error of 1.3%. In vivo forearm measurements showed that the use of a conductive layer does enable tissue conductivity spectra to be determined. A smaller variation between subjects was obtained when using the stand-off. It was not possible to assess the absolute accuracy of the method due to the absence of a 'gold standard' for the measurement of tissue conductivity spectra.
authors.affiliation: Department of Medical Physics and Clinical Engineering, University of Sheffield, Sheffield S10 2JF, UK. bertemes@ieee.org
authors.forename: Pedro
authors.initials: P
authors.lastname: Bertemes-Filho
authors.forename: Brian H
authors.initials: BH
authors.lastname: Brown
authors.forename: Rod H
authors.initials: RH
authors.lastname: Smallwood
authors.forename: Adrian J
authors.initials: AJ
authors.lastname: Wilson
mesh_terms: D017097:Electric Impedance; D004566:Electrodes; D005542:Forearm; D006801:Humans; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; D008954:Models, Biological; D012680:Sensitivity and Specificity; D013057:Spectrum Analysis / Q000295:instrumentation* / Q000379:methods*
chemical_list: D020136:Hydrogel, Polyethylene Glycol Dimethacrylate