Geometry dependencies in tetrapolar electrode systems - A finite element analysis on needle electrodes

Abstract

The tetrapolar electrode system is used in a broad range of bioimpedance measurements. The size and placement of the electrodes in a tetrapolar or four electrode system will always be important for the quality of the measurements. This paper shows how different configurations of large and small electrodes will affect the measurement. COMSOL Multiphysics (CM) VER 3.3 was used to build numerical models of different electrode geometries. CM uses the Finite Element Method (FEM). All models could easily be reproduced by the information given in this paper. All models were made and solved on an ordinary PC. Validity of the models was tested by analytical solutions when available, using the reciprocity theorem along with built in tests from CM. Current shunting through the pickup electrodes is a well-known problem in tetrapolar systems. This paper shows that shunting effect can be significantly reduced by changing the geometry of the pickup electrodes or by increasing electrode separation. The quality of bioimpedance measurements with tetrapolar systems may be dependent on the geometry of the test object itself. This paper shows how measured impedance will change with changes in the dimensions of the test object. © Springer-Verlag 2007.