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Figure 1 Schematic illustration of how strain rate within a tissue segment (r) is estimated from the tissue velocity (). The dashed line indicates orientation of the ultrasound beam. The distance along the beam is denoted r. The strain rate is calculated by subtracting (r + r) from (r) over the distance (r) between these two points. Size of r is exaggerated for clarity. l= a given length; l = instantaneous change in length.