Ultrasound data processing method. A: Location of sub-ROIs (yellow and orange boxes) used for quantification of lateral tissue motion. B: Plot of lateral tissue displacement over time. Positive displacement in B corresponds to tissue movement toward the right (rostral, red arrows in A). Negative displacement in B corresponds to tissue movement toward the left (caudal, blue arrows in A). Yellow and orange lines in B respectively correspond to deep and superficial sub-ROIs in A. C: Shear strain model and calculation method. P1 and P2 represent the mean tissue displacement in the deep (yellow) and superficial (orange) Sub-ROIs respectively at each time point as shown in B. Shear strain between the sub-ROIs was calculated as the absolute difference in lateral motion between the superficial and deep sub-ROIs divided by the distance between the centers of the two sub-ROIs (2 mm) and expressed as a percentage.