An inverse problem for a semilinear parabolic equation arising from cardiac electrophysiology

In this paper we develop theoretical analysis and numerical reconstruction techniques for the solution of an inverse boundary value problem dealing with the nonlinear, time-dependent monodomain equation, which models the evolution of the electric potential in the myocardial tissue. The goal is the detection of an inhomogeneity omega(e) (where the coefficients of the equation are altered) located inside a domain Omega starting from observations of the potential on the boundary partial derivative Omega. Such a problem is related to the detection of myocardial ischemic regions, characterized by severely reduced blood perfusion and consequent lack of electric conductivity. In the first part of the paper we provide an asymptotic formula for electric potential perturbations caused by internal conductivity inhomogeneities of low volume fraction in the case of three-dimensional, parabolic problems. In the second part we implement a reconstruction procedure based on the topological gradient of a suitable cost functional. Numerical results obtained on an idealized three- dimensional left ventricle geometry for different measurement settings assess the feasibility and robustness of the algorithm.