Angle correction. (a) Color duplex US image obtained with a 30° corrected angle, which is too low, demonstrates a flow velocity of 21.3 cm/sec in the portal vein. This figure represents an underestimation of the true flow velocity. (b) Color duplex US image obtained with a 70° corrected angle, which is too high, demonstrates a flow velocity of 52.8 cm/sec in the portal vein, which represents an overestimation of flow velocity. Note that the measured flow velocity increases as the corrected angle increases.

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