Local uniqueness for the Dirichlet-to-Neumann map via the two-plane   transform
  We consider the Dirichlet-to-Neumann map associated to the Schr\"odinger equation with a potential in a bounded Lipschitz domain in three or more dimensions. We show that the integral of the potential over a two-plane is determined by the Cauchy data of certain exponentially growing solutions on any neighborhood of the intersection of the two-plane with the boundary. 
Allan Greenleaf and Gunther Uhlmann