Recovery of small perturbations of an interface for an elliptic inverse problem via linearization

Electrical impedance tomography (EIT) is used to find the conductivity dist ribution inside a region using electrostatic measurements collected on the boundary of the region. We study a simple version of the general EIT proble m, in which the medium has constant conductivity but might contain a buried object of unknown shape and different, but also constant, conductivity. Our linearization about an approximate shape of the buried object follows K aup and Santosa and has the advantage that it is valid for large contrast i n the conductivity. We present a procedure to reconstruct the object bounda ry in the case where we know the conductivities and the centre and radius o f a good circular approximation of the object boundary, using analytic solu tions to the forward problem for circular objects with known conductivity. Assuming that the unknown object boundary is star-shaped with respect to th e centre of the circle and a small perturbation of the approximating circle , we develop a linearized relation between the output voltage data that res ult from fixed input currents, entering as parameters, and the interface, e ntering as variables. This relation is used to find the Fourier coefficient s of the perturbation of the interface. At least two measurements are needed to determine all coefficients, and mor e can be used for a least-squares fit. The quality of the recovered perturb ation depends on the input frequency and the frequencies of the perturbatio n. Low frequencies work best as input, and are most easily recovered, in th at case even where the amplitude of the perturbation is not very small. Sev eral dipoles, corresponding to very close pairs of electrodes to induce the current, can be used successfully as input as well.