E. V. Zakharov

Numerical methods for some inverse problems of heart electrophysiology

We consider numerical methods for solving inverse problems that arise in heart electrophysiology. The first inverse problem is the Cauchy problem for the Laplace equation. Its solution algorithm is based on the Tikhonov regularization method and the method of boundary integral equations. The second inverse problem is the problem of finding the discontinuity surface of the coefficient of conductivity of a medium on the basis of the potential and its normal derivative given on the exterior surface. For its numerical solution, we suggest a method based on the method of boundary integral equations and the assumption on a special representation of the unknown surface.

Numerical solution of 3D problems of electromagnetic wave diffraction on a system of ideally conducting surfaces by the method of hypersingular integral equations

We construct a numerical method for solving problems of electromagnetic wave diffraction on a system of solid and thin objects based on the reduction of the problem to a boundary integral equation treated in the sense of the Hadamard finite value. For the construction of such an equation, we construct a numerical scheme on the basis of the method of piecewise continuous approximations and collocations. Unlike earlier known schemes, by using the below-suggested scheme, we have found approximate analytic expressions for the coefficients of the arising system of linear equations by isolating the leading part of the kernel of the integral operator. We present examples of solution of a number of model problems of the diffraction of electromagnetic waves by the suggested method.

Numerical Solution of an Inverse Electrocardiography Problem for a Medium with Piecewise Constant Electrical Conductivity

A numerical method is proposed for solving an inverse electrocardiography problem for a medium with a piecewise constant electrical conductivity. The method is based on the method of boundary integral equations and Tikhonov regularization.

Numerical solution of the inverse electrocardiography problem with the use of the Tikhonov regularization method

The inverse electrocardiography problem related to medical diagnostics is considered in terms of potentials. Within the framework of the quasi-stationary model of the electric field of the heart, the solution of the problem is reduced to the solution of the Cauchy problem for the Laplace equation in R3. A numerical algorithm based on the Tikhonov regularization method is proposed for the solution of this problem. The Cauchy problem for the Laplace equation is reduced to an operator equation of the first kind, which is solved via minimization of the Tikhonov functional with the regularization parameter chosen according to the discrepancy principle. In addition, an algorithm based on numerical solution of the corresponding Euler equation is proposed for minimization of the Tikhonov functional. The Euler equation is solved using an iteration method that involves solution of mixed boundary value problems for the Laplace equation. An individual mixed problem is solved by means of the method of boundary integral equations of the potential theory. In the study, the inverse electrocardiography problem is solved in region Ω close to the real geometry of the torso and heart.

Method of hypersingular integral equations in a three-dimensional problem of diffraction of electromagnetic waves on a piecewise homogeneous dielectric body

The problem of electromagnetic diffraction in a piecewise homogeneous medium that can consist of domains with different dielectric properties and can contain ideally conducting inclusions in the form of solid objects and screens is reduced to a system of integral equations with hypersingular integrals over surfaces separating the media with different dielectric properties. We prove the equivalence of the resulting system of integral equations and the original boundary value problem. We construct a numerical scheme for the solution of related integral equations based on methods of piecewise constant approximations and collocations; this scheme can be used on surfaces of fairly arbitrary form.

Method of boundary integral equations as applied to the numerical solution of the three-dimensional Dirichlet problem for the laplace equation in a piecewise homogeneous medium

A Dirichlet problem is considered in a three-dimensional domain filled with a piecewise homogeneous medium. The uniqueness of its solution is proved. A system of Fredholm boundary integral equations of the second kind is constructed using the method of surface potentials, and a system of boundary integral equations of the first kind is derived directly from Green’s identity. A technique for the numerical solution of integral equations is proposed, and results of numerical experiments are presented.

On the study of conditions for the continuity of the Lagrange multiplier measure in problems with state constraints

We study several examples on the Pontryagin maximum principle for problems with state constraints. We show that the well-known conditions of controllability of a trajectory relative to the state constraints are insufficient for the continuity of the Lagrange multiplier measure occurring in the maximum principle.

Method for determining the projection of an arrhythmogenic focus on the heart surface, based on solving the inverse electrocardiography problem

The problem of determining the point on the heart surface (projection) nearest to the arrhythmogenic focus, which is located inside the heart, is considered. Localization of this point is crucial for a successful cardiac ablation procedure. The sought projection is calculated on the basis of solving the inverse electrocardiography problem, which is a generalization of the Cauchy problem for the Laplace equation. The inverse electrocardiography problem is solved by the boundary integral equation and Tikhonov regularization methods. Examples of test computations are demonstrated, and the results of processing real electrophysiological data are presented and compared with the medical observation data.

A numerical way of solving the inverse problem for the wave equation in a medium with local inhomogeneity

The inverse problem of determining the boundary of local inhomogeneity for measuring a field in a bounded receivers location domain in a three-dimensional medium is considered for the wave equation. The problem is reduced to a system of integral equations. An iteration approach to solving the inverse problem is proposed, and the results from numerical experiments are presented.

Limits of applicability of a spherical model for solving problems of electroencephalography

Methods are developed for the localization of neuron brain sources with the potential recorded as an electroencephalogram (EEG). A boundary-value problem for a Poisson equation is considered. A boundary Fredholm integral equation of the second kind is deduced. A method for numerically solving an integral equation is proposed, and the results from a number of computing experiments are given.