Electrode models under shape deformation in Electrical Impedance Tomography

Abstract

Abstract. Electrical Impedance Tomography (EIT) applies current and measures the resulting voltage on the surface of a target. In biomedical applications, this current is applied, and voltage is measured through electrodes attached to the surface. Electrode models represent these connections in the reconstruction, but changes in the contact impedance or boundary relative to the electrode area can introduce artifacts. Using difference imaging, the effects of boundary deformation and contact impedance variation were investigated.The Complete Electrode Model (CEM) was found to be affected by conformal deformations. Contact impedance variability was found to be a significant source of artifacts in some cases.In the context of Electrical Impedance Tomography (EIT), the effect of shape deformation on electrode models is considered and it is shown that under certain conditions significant artifacts can occur. The initial proofs of solution existence and uniqueness used a Continuum Model for the electrodes, implying complete knowledge of all boundary data.[1, 2] More recently, models allowing for regular gaps in the boundary data (Gap Model), or more physically realistic models such as the Shunt Electrode Model (SEM) and Complete Electrode Model (CEM) have also been utilized. The CEM adds a complex impedance for each electrode which models the metal electrode, conductive gel and chemical interaction at the skin-electrode interface. [3,4] (Figure 1) The Finite Element Method (FEM), used in the numerical solution of EIT images, requires boundary conditions based on these mathematical models. The simplest FEM boundary condition to implement is the Point Electrode Model (PEM), applying current and measuring voltage at single nodes on the boundary. An alternative electrode model implements the mathematical SEM, forcing all nodes associated with an electrode to the same voltage. The SEM is appropriate when contact impedances are so small that the matrices become ill-conditioned. [5] To reconstruct accurate images from in-vivo data, an implementation of the CEM is generally preferred.[3] In the EIT inverse problem, under homogeneous conductivity conditions, solving for the CEM's contact impedances has been successful. [6,7,8]

A pipeline for the simulation of transcranial direct current stimulation for realistic human head models using SCIRun/BioMesh3D

“…There are several electrode models in the literature (e.g. shunt, complete, [5], [13], [2]) in which different electrical boundary conditions are applied together with certain assumptions about the electrode-surface interaction. In realistic settings, and in this study, the complete electrode model is often used since it also includes realistic contact impedances ([5]).…”

Jointly reconstructing ground motion and resistivity for ERT-based slope stability monitoring

“…An efficient and accurate method for calculating the electrode position Jacobian on a 2.5-D resistivity model was developed. This work is motivated by developments in Boyle & Adler (2010); Boyle (2010) for 2-D electrode movement, and Boyle et al (2014); Boyle (2016); Boyle & Adler (2016) where this data set and preliminary results were presented. A 2-D cross-sectional Finite Element Method (FEM) model of the local slope topology was built, with electrodes modelled using the Complete Electrode Model (CEM) (Somersalo et al 1992;Rücker & Günther 2011).…”

An instrumental electrode model for solving EIT forward problems

“…There are different kinds of BCs used in the EIT forward problems, including the Gap Model (Boyle and Adler 2010), Shunt Electrode Model (Boyle and Adler 2010) and Complete Electrode Model (CEM) (Boyle and Adler 2010, Cheng et al 1989, Somersalo et al 1992, Vauhkonen et al 1999. The CEM constrains the electrical currents flowing on the electrode surfaces and on the boundary of the imaging volume.…”

“…It has been reported that the CEM can match experimental results with a very high precision up to 0.1 % (Somersalo et al 1992). To reconstruct accurate images from in vivo data an accurate electrode model is usually required, and thus, the CEM is generally preferred (Boyle and Adler 2010). The accuracy of CEM solutions depends on accurate measurements or estimations of the contact impedance.…”