Fig. 1.

Angular quantification of fiber and sheet structures in the LV. The local fiber ($\widehat{f}$) or sheet direction ($\widehat{s}$) can be expressed numerically as rotations about a coordinate system defined by the local circumferential, radial, and longitudinal direction (θ, r, and l, respectively). The fiber orientation is described by the helix α (which takes on negative values on the epicardium) and transverse α′ angles. A similar approach can be used to express sheet orientation (β and β′). The idealized imaging planes (long and short axes) approximately coincide with the longitudinal–radial plane and circumferential–radial plane near the midventricle.