Relationship between strain and tag frequency for harmonic phase-based strain measurements. A)Contraction of a tagged fibre in the middle increases the tagging frequency (density of tag lines), as shown for the top fibre. Stretching causes a reduction in local frequency. (B) Two-dimensional segmentation of the heart and mesh generation (top panel) and regional strain versus time plots over the cardiac cycle; (C) complete regional strain versus time plots over the cardiac cycle for all segments. ECC = circumferential strain. Reproduced with permission from Lardo et al.