According to the Doppler equation, increasing transmit frequency will increase the Doppler frequency shift for a given velocity. Which option best reflects this?

According to the Doppler equation, increasing transmit frequency will increase the Doppler frequency shift for a given velocity. Which option best reflects this?

• A. Doppler angle
• B. Transmit frequency
• C. Pulse length
• D. Pulse repetition frequency

Answer: (B)

The Doppler frequency shift scales with the transmitted frequency when velocity and angle are held constant. In ultrasound Doppler, the shift is given by Δf = (2 f_t v cos θ) / c, where f_t is the transmitted frequency. This shows a direct, linear relationship: if you increase f_t, the Doppler shift increases proportionally for the same velocity and angle. The cosine term (angle) determines how much of the flow velocity contributes to the shift, but it is independent of changing the transmitted frequency. Pulse repetition frequency and pulse length don’t change the magnitude of the Doppler shift itself; they affect sampling, aliasing, or resolution, not the fundamental shift value. So the factor that best reflects the described relationship is the transmit frequency.

The Doppler frequency shift scales with the transmitted frequency when velocity and angle are held constant. In ultrasound Doppler, the shift is given by Δf = (2 f_t v cos θ) / c, where f_t is the transmitted frequency. This shows a direct, linear relationship: if you increase f_t, the Doppler shift increases proportionally for the same velocity and angle. The cosine term (angle) determines how much of the flow velocity contributes to the shift, but it is independent of changing the transmitted frequency. Pulse repetition frequency and pulse length don’t change the magnitude of the Doppler shift itself; they affect sampling, aliasing, or resolution, not the fundamental shift value. So the factor that best reflects the described relationship is the transmit frequency.