In this paper, we consider a method of construction of a velocity field based on an optimization approach. A general formulation of the problem is given. It is shown how, under the appropriate assumption, it reduces to known particular case. Two-dimensional case of the velocity field construction is considered in detail under the gradient constancy assumption of the density of the radiopharmaceutical distribution. The problem is reduced to solving a sparse system of large dimension, and the convergence of the iterative algorithm to the solution is considered. This method can be used in the radionuclide data processing.