Medical and Biological Engineering and Computing

, Volume 15, Issue 5, pp 519–527 | Cite as

Electrode guarding in electrical impedance measurements of physiological systems—a critique

  • Robert Plonsey
  • Robert Collin
Article

Abstract

The application of the guard ring has been advanced as a method for focusing the applied current in performing electrical-impedance measurements of volume conductors. The objective is to obtain impedance and/or its variation at localised regions of heterogeneous tissue. The paper discusses the capabilities and limitations of both guarded and unguarded measurements and shows that the application of guarding does not, normally, fulfil the capabilities being ascribed to it. A comparison is made of the guarded system under constant-current and constant-voltage constraints with an unguarded electrode system, and it is shown that the guarded system does not have any significant advantages.

Keywords

Electrical impedance Guard ring 

Sommaire

Certains auteurs ont recommandé la méthode de l'anneau de garde pour focaliser le courant appliqué lors de la mesure de l'impédance de volumes conducteurs. L'objectif est de déterminer la valeur et/ou les variations de l'impédance en des régions données d'un tissue hétérogène. Cet article discute des possibilités et limites de mesures avec électrodes gardées et non gardées et montre que les premières n'ont pas les performances qu'on leur accorde généralement. Une comparaison entre le système à électrode protégée sous intensité et voltage constant par rapport à un système à électrode non protégée montre que le système protégé ne présente aucun avantage significatif.

Zusammenfassung

Die Verwendung des Abwehrrings wurde als Methode für das Fokussieren des angelegten Stroms bei der Durchführung von Messungen der elektrischen Impedanz von Volumenleitern vorgeschlagen. Das Ziel ist, Impedanz und/oder ihre Variation in lokalisierten Regionen heterogenen Gewebes zu erhalten. Dieser Aufsatz bespricht die Möglichkeiten und Beschränkungen sowohl abgeschirmter als auch nicht abgeschirmter Messungen und zeigt, daß die Verwendung von Abschirmung normalerweise die ihr zugeschriebenen Möglichkeiten nicht erfüllt. Ein Vergleich wird angestellt zwischen dem abgeschirmten System unter konstanter Strom- und konstanter Spannungseinschränkung und dem nicht abgeschirmten Elektrodensystem, und es wird gezeigt, daß das abgeschirmte System keinerlei wesentliche Vorteile bietet.

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Copyright information

© International Federation for Medical & Biological Engineering 1977

Authors and Affiliations

  • Robert Plonsey
    • 1
  • Robert Collin
    • 2
  1. 1.Department of Biomedical EngineeringCase Western Reserve UniversityClevelandUSA
  2. 2.Department of Electrical Engineering & Applied PhysicsCase Western Reserve UniversityClevelandUSA

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