Three-dimensional tagging and optical flow methodology. Images from a technique involving a three-dimensional CMR tagging sequence and an optical flow method to measure three-dimensional LV wall deformation in a single cine acquisition. Panels A to C illustrate the maximum principal strain (ε1) on three representative short axis slices. The colour of the plot and the length of the overlaid line segments correspond to the magnitude of the strain while the direction is indicated by the vector. The images show the minimum ε1 in the septum and the maximum ε1 in the lateral wall. Panel D shows a mid-wall surface colour-coded by with ε1, with superimposed eigenvector direction at four longitudinal levels. Note that ε1 is directed towards the centre of the LV, indicating in-plane radial thickening.