Increasing the Doppler angle ______ the Doppler frequency shift for any given velocity.

Increasing the Doppler angle ______ the Doppler frequency shift for any given velocity.

• A. Reduces
• B. Increases
• C. Keeps the same
• D. Depends on velocity

Answer: (A)

The Doppler frequency shift comes from the component of the blood’s velocity that is along the ultrasound beam. That component is proportional to cos θ, where θ is the angle between the beam and the flow direction. So for a fixed velocity, the shift is proportional to cos θ. As the Doppler angle increases, cos θ decreases, causing the frequency shift to get smaller. At θ = 0°, the shift is largest; at θ approaching 90°, the shift approaches zero. That’s why increasing the angle reduces the Doppler frequency shift.

The Doppler frequency shift comes from the component of the blood’s velocity that is along the ultrasound beam. That component is proportional to cos θ, where θ is the angle between the beam and the flow direction. So for a fixed velocity, the shift is proportional to cos θ. As the Doppler angle increases, cos θ decreases, causing the frequency shift to get smaller. At θ = 0°, the shift is largest; at θ approaching 90°, the shift approaches zero. That’s why increasing the angle reduces the Doppler frequency shift.