The Doppler frequency shift is defined as:

The Doppler frequency shift is defined as:

• A. The difference between the transmitted and received frequencies
• B. The difference between the Doppler frequency and the imaging frequency
• C. The time between the transmitted and received pulses
• D. The rate at which the transducer emits pulses

Answer: (A)

Doppler frequency shift is the difference between the transmitted (emitted) frequency and the frequency of the echo returned from moving targets. When blood cells or other structures move toward or away from the transducer, the reflected wave is slightly higher or lower in frequency than the original beam. The system interprets this frequency difference, which is proportional to the target’s velocity along the beam, to estimate motion. A common approximation is Δf ≈ 2 f0 v cos θ / c, showing how the shift depends on the transmitted frequency, speed of the target, the angle between flow and beam, and the speed of sound in tissue. So the shift is the difference between transmitted and received frequencies. The other ideas describe time delays, pulse repetition, or unrelated frequency comparisons and don’t define the Doppler shift.

Doppler frequency shift is the difference between the transmitted (emitted) frequency and the frequency of the echo returned from moving targets. When blood cells or other structures move toward or away from the transducer, the reflected wave is slightly higher or lower in frequency than the original beam. The system interprets this frequency difference, which is proportional to the target’s velocity along the beam, to estimate motion. A common approximation is Δf ≈ 2 f0 v cos θ / c, showing how the shift depends on the transmitted frequency, speed of the target, the angle between flow and beam, and the speed of sound in tissue. So the shift is the difference between transmitted and received frequencies. The other ideas describe time delays, pulse repetition, or unrelated frequency comparisons and don’t define the Doppler shift.