If you increase the Doppler transmit frequency, which of the following will result?

If you increase the Doppler transmit frequency, which of the following will result?

• A. The velocity will increase
• B. The Doppler frequency shift will increase
• C. The penetration will increase
• D. The Nyquist limit will increase

Answer: (B)

Doppler frequency shift scales with the transmit frequency. In ultrasound Doppler, the shift f_D is proportional to f0 for a given blood velocity and beam angle, described by f_D = (2 f0 v cos θ)/c. So increasing the transmit frequency, while velocity and angle stay the same, makes the Doppler shift larger. The velocity calculation uses the ratio f_D/f0, so the actual flow speed remains tied to the true motion, not the transmit frequency itself. Higher frequency reduces penetration (more attenuation), so penetration would not increase. The Nyquist limit depends on the pulse repetition frequency, not on the transmit frequency, so that doesn’t automatically rise either. Therefore, the Doppler frequency shift will increase.

Doppler frequency shift scales with the transmit frequency. In ultrasound Doppler, the shift f_D is proportional to f0 for a given blood velocity and beam angle, described by f_D = (2 f0 v cos θ)/c. So increasing the transmit frequency, while velocity and angle stay the same, makes the Doppler shift larger. The velocity calculation uses the ratio f_D/f0, so the actual flow speed remains tied to the true motion, not the transmit frequency itself. Higher frequency reduces penetration (more attenuation), so penetration would not increase. The Nyquist limit depends on the pulse repetition frequency, not on the transmit frequency, so that doesn’t automatically rise either. Therefore, the Doppler frequency shift will increase.