A Doppler shift occurs when the received frequency is greater than the transmitted frequency. This shift is described as:

A Doppler shift occurs when the received frequency is greater than the transmitted frequency. This shift is described as:

• A. Positive
• B. Negative
• C. Zero
• D. Double

Answer: (A)

A positive Doppler shift. The sign of the Doppler shift depends on the direction of motion relative to the transducer. When the target (such as red blood cells) moves toward the transducer, the received frequency is higher than the transmitted frequency, giving a positive shift. In ultrasound, this shift is described by fD = (2 f0 v cos θ)/c, where a motion toward the transducer (cos θ > 0) produces a positive fD, motion away (cos θ < 0) produces a negative shift, and no motion or motion exactly perpendicular to the beam (cos θ = 0) yields zero shift.

A positive Doppler shift.

The sign of the Doppler shift depends on the direction of motion relative to the transducer. When the target (such as red blood cells) moves toward the transducer, the received frequency is higher than the transmitted frequency, giving a positive shift. In ultrasound, this shift is described by fD = (2 f0 v cos θ)/c, where a motion toward the transducer (cos θ > 0) produces a positive fD, motion away (cos θ < 0) produces a negative shift, and no motion or motion exactly perpendicular to the beam (cos θ = 0) yields zero shift.