Normal flow direction in duplex

• A. Toward Transducer
• B. Away From Transducer
• C. Perpendicular To Beam
• D. No Flow

Answer: (A)

In duplex ultrasound, the direction of flow is defined relative to the transducer. The Doppler shift is positive when blood cells move toward the probe, and this is how arterial flow is typically interpreted and displayed. When you place the probe on the skin and align your beam with the vessel so that the blood is moving toward the transducer, you get flow toward the transducer as the normal, expected direction. This is also why color Doppler commonly uses red to represent flow toward the transducer and blue for flow away, and why arterial waveforms are described with flow toward the probe.

If the flow were directed away from the transducer in a given view, the Doppler shift would be negative, which would be interpreted as reversed or abnormal in that arterial orientation. Thus, the normal direction in duplex imaging is toward the transducer.