  We consider an inverse problem of location identification of small
conductivity inhomogeneity inside a conductor via boundary measurements which
occurs in the EIT (Electrical Impedance Tomography). For this purpose, we
derive topological derivative by applying the asymptotic formula for steady
state voltage potentials in the existence of conductivity inclusion of small
diameter. Using this derivative, we design only one-step iterative location
search algorithm of small conductivity inhomogeneity completely embedded in the
homogeneous domain by solving an adjoint problem. Numerical experiments
presented for showing the feasibility of proposed algorithm.
