1. A method comprising: acquiring diffuse magnetic resonance imaging data relating to a heart; establishing a model relating to the heart based on a generalized helicoid model that expresses a frame field of local fiber directions in a plane tangent to a heart wall; fitting each data point of the data as a local orthogonal frame expressed as (i, j, k) to represent the local fiber directions from the model; and determining connection forms c ijk at each data point to represent a rotation of the local orthogonal frame in a spatial neighborhood of the data point in accordance with the data.