Using Distmesh as a mesh generating tool for EIT

Abstract

We present a collection of automatic mesh generation software tools for electrical impedance tomography (EIT) finite element models (FEMs). Creating an image in EIT involves retrieving conductivity distribution from surface electrode measurements. The initial forward problem of this process requires estimates of electric potential according to the current sources. With non-trivial geometries, this task is difficult analytically and demands a numerical method such as FEM. The areas nearest to electrodes have the highest current density and are the most significant measurement points. For our FEM model, these areas should have the greatest mesh density for the purposes of usefulness and accuracy. The research focuses on Distmesh, an open source MATLAB mesh generator, for creating mesh shapes with non-uniform mesh densities for EIT software. The inherent simplicity of the Distmesh code was the rationale for its evaluation. A mesh shape is defined from specifying its signed distance function and its mesh size distribution is defined with an element length function. We created circular meshes with mesh refinement towards endpoints of distributed electrodes. In three dimensions, cylinders were produced with mesh refinement towards rings of points for each electrode. Finally, to accommodate organic shapes, meshes for closed contours were created using elliptic Fourier descriptors. Because Distmesh was not designed for efficiency, the generation of well-defined meshes is fairly slow. For the contours, Distmesh forms reasonable meshes but is unable to improve node locations upon successive iterations. Distmesh is not a suitable mesh generator for EIT software unless its code is optimized for speed.