A negative Doppler shift indicates flow away from the transducer.

A negative Doppler shift indicates flow away from the transducer.

• A. False
• B. True
• C. Depends on machine
• D. Cannot be determined

Answer: (B)

The sign of the Doppler frequency shift tells you whether the flow is toward or away from the transducer. When blood moves toward the probe, the reflected sound has a higher frequency, giving a positive Doppler shift. When blood moves away, the reflections come back with a lower frequency, yielding a negative Doppler shift. This follows the relation Δf ∝ v cos θ, where θ is the angle between the flow direction and the beam; flow toward the transducer makes cos θ positive (0–90°), while flow away makes cos θ negative (90–180°). Because of this convention, a negative Doppler shift indicates flow away from the transducer.

The sign of the Doppler frequency shift tells you whether the flow is toward or away from the transducer. When blood moves toward the probe, the reflected sound has a higher frequency, giving a positive Doppler shift. When blood moves away, the reflections come back with a lower frequency, yielding a negative Doppler shift. This follows the relation Δf ∝ v cos θ, where θ is the angle between the flow direction and the beam; flow toward the transducer makes cos θ positive (0–90°), while flow away makes cos θ negative (90–180°). Because of this convention, a negative Doppler shift indicates flow away from the transducer.