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Figure 2 Examples of selected two-dimensional color Doppler images in the in vitro model. Image for measurement of forward stroke volume with flow coming towards the transducer in a horizontal plane corresponding to the major axis (top). Images for measurement of regurgitant stroke volume with flow going away from the transducer in a horizontal plane (middle) and in a paired orthogonal plane corresponding to the minor axis (bottom). The sampling rectangular box is below (or above) proximal to the flow convergence region for measuring the forward and regurgitant stroke volume. Note that the velocity profile of prestenotic flow is not flat, and the distance of velocity profile for regurgitant flow in the major axis is larger than it is in the minor axis.