First-Order Systems Least Squares for Electrical Impedance Tomography

Hugh MacMillan

Dept. Applied Mathematics, CB 526, University of Colorado, Boulder, CO 80309-0526


In electrical impedance tomography (EIT), the impedance within an object is estimated from the surface voltage patterns that are induced by a sequence of known current flux patterns. The mathematical formulation of the EIT problem is a set of elliptic equations (one for each boundary pattern) where both the scalar variables (interior voltages) and the coefficient (interior impedance) are unknown, and both Dirichlet (voltage) and Neumann (current) boundary conditions are known. We develop a new first-order systems least squares (FOSLS) formulation to determine a suitable impedance and investigate the sense in which it is suitable. For each set of boundary patterns, the full domain FOSLS formulation is tailored to balance enforcement of the pair of boundary conditions and the interior PDE . The nonlinearity is mild enough (polynomial) to admit a realizable nonlinear multigrid scheme that yields successive approximations to the impedance and to the scaled interior currents for each test.