Simultaneous reconstruction of electrode contact impedances and internal electrical properties: I. Theory

Abstract

In electrical impedance tomography (EIT) currents are applied through the electrodes attached on the surface of the object and the resulting voltages are measured using the same or additional electrodes. The internal admittivity distribution is estimated based on the current and voltage data. When the voltages are measured on the current carrying electrodes the contact impedance that exists in the electrode–surface interface causes a voltage drop. In some cases this effect of the electrodes is known. However, this is not always the case and the contact impedance has to be taken into account in the image reconstruction. In this paper we propose an approach for estimating the contact impedance of the electrodes simultaneously with the estimation of the admittivity of the object. The complete electrode model (CEM) is used in the estimation procedure. We compare the proposed approach to a simple method which is based on the well known definition of the sample resistivity. The proposed approach is tested with real measurements by estimating the admittivity of isotonic saline solution in a cylindrical test cell and with simulations in a three-dimensional cylindrical domain. The CEM-based approach is shown to produce results that are similar to the results obtained with the simple approach in the test cell case. The advantage of the CEM-based approach over the simple approach is that the complete electrode model does not have any geometrical constraints, which makes it possible to utilize it in EIT studies. The results show that the CEM-based approach works well and can be used in practical contact impedance estimation with real measurements. This will be further studied in part II of this paper.

Model-aware Newton-type inversion scheme for electrical impedance tomography

“…Note that (3.5) has at most M ≤ L degrees of freedom, so estimating σ 0 and all individual contact impedances z l , l = 1, ... , L, simultaneously is not directly possible, but σ CEM,z 0 and z CEM,z 0 can be useful initial guesses for other estimation techniques; see [21]. However, (3.5) can be easily extended to estimate each single contact impedance in turn, which can be useful for detecting bad contacts of a measurement setup.…”

Solving the complete-electrode direct model of ERT using the boundary element method and the method of fundamental solutions

“…For the first domain Ω 1 , the discretisation of the boundary ∂Ω 1 , is the same as in Section 6.1. Hence, the BEM reduces the Laplace's equation (48) for u 1 to a new linear system of equations similar to (26), namely,…”

“…Electrical impedance tomography (EIT) is a non-intrusive, low-cost and portable technique of imaging the interior of a specimen based on the knowledge of the injected currents and the resulted voltages which are measured on the electrodes, as explained in [25,26]. It has widespread applications in medicine, geophysics and industry.…”

A flexible statistical and efficient computational approach to object location applied to electrical tomography

“…For a detailed theoretical account of contact impedance see, for example, Vilhunen et al (2002). In what follows, for ease of exposition, the contact impedance between the electrode and the vessel are neglected.…”