What factor is necessary to obtain velocity information from the Doppler frequency shift?

What factor is necessary to obtain velocity information from the Doppler frequency shift?

• A. Angle of incidence is known
• B. Transmitter frequency is higher
• C. Imaging depth is shallower
• D. Gain is increased

Answer: (A)

To obtain velocity information from the Doppler frequency shift, you must know the angle of incidence—the angle between the direction of flow and the ultrasound beam. The Doppler shift depends on cos of that angle, so solving for velocity uses the relationship Δf = (2 f0 v cos θ) / c. Knowing θ lets you convert the measured frequency shift into true velocity; without it, you only get the component of velocity along the beam. Increasing transmitter frequency, changing imaging depth, or increasing gain do not provide the angle needed to resolve velocity, even though they can affect the size of the shift or image quality.

To obtain velocity information from the Doppler frequency shift, you must know the angle of incidence—the angle between the direction of flow and the ultrasound beam. The Doppler shift depends on cos of that angle, so solving for velocity uses the relationship Δf = (2 f0 v cos θ) / c. Knowing θ lets you convert the measured frequency shift into true velocity; without it, you only get the component of velocity along the beam. Increasing transmitter frequency, changing imaging depth, or increasing gain do not provide the angle needed to resolve velocity, even though they can affect the size of the shift or image quality.