← Ultrasound subtopic / Sim: Doppler Angle

Doppler Angle Explorer

Change the insonation angle (θ) between beam and flow. See how cos(θ) scales the measured velocity — and how the measurement diverges from truth as θ approaches 90°.

Beam angle θ (°) 60 True velocity (cm/s) 120 Transducer f₀ (MHz) 5.0

cos(θ)

—

Doppler shift

—

kHz

Measured velocity

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cm/s

Teaching notes

Doppler shift Δf = 2·f₀·v·cos(θ)/c, where c = 1540 m/s. The scanner inverts this to report velocity, but only if you tell it the angle. At θ = 90° the cosine is zero — brisk flow returns no Doppler signal. Errors in angle estimation are magnified when θ approaches 90° because cos(θ) changes rapidly there. That is why ≤ 60° is the guideline for quantitative velocity measurement.