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Figure 2 Schema of the principle for calculating actual flow rate (Q = V x S) using Doppler-imaged flow velocity in a region of interest. Note that obliquity decreases velocities by a cosine function but increases areas by the same function. Five parallel velocity interrogations in a region of interest were averaged by the ultrasound system (see text). S = area, SD = Doppler area, V = velocity, VD = Doppler velocity.
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