If the transducer frequency doubles from 5 MHz to 10 MHz while other parameters unchanged, what happens to the Doppler frequency shift for the same v and c?

• A. It doubles.
• B. It becomes zero.
• C. It halves.
• D. No change.

Answer: (A)

Doppler frequency shift scales directly with the transmitted frequency. In ultrasound Doppler, fD = (2 f0 v cosθ) / c, so with v, θ, and c fixed, fD is proportional to f0. If the transducer frequency doubles from 5 MHz to 10 MHz, the shift doubles as well, because the only changing factor is f0. The velocity component along the beam and the speed of sound remain the same, so there’s no other change. Hence the Doppler frequency shift becomes twice as large.