What is the most typical Doppler shift measured clinically?

What is the most typical Doppler shift measured clinically?

• A. 3.5 MHz
• B. 3,500,000 Hz
• C. 1,000 kHz
• D. 2 kHz

Answer: (D)

Doppler shift in medical ultrasound is a small change in frequency caused by moving blood reflecting the sound. The shift is given by Δf = (2 f0 v cos θ) / c, where f0 is the transmitted frequency (usually around 2 to 5 MHz in diagnostic exams), v is blood velocity, θ is the angle between the flow and the ultrasound beam, and c is the speed of sound in tissue (about 1540 m/s). With typical blood velocities (roughly 0.5 to 1 m/s) and common beam angles, Δf falls in the kilohertz range. For a 2 MHz probe, these shifts are usually around 1–3 kHz, with 2 kHz being a representative typical value. The other numbers represent the carrier frequency (millions of hertz) or Doppler shifts that are unrealistically large for physiological motion given the usual probe frequencies and tissue sound speed. Thus, 2 kHz is the most typical Doppler shift measured clinically.

Doppler shift in medical ultrasound is a small change in frequency caused by moving blood reflecting the sound. The shift is given by Δf = (2 f0 v cos θ) / c, where f0 is the transmitted frequency (usually around 2 to 5 MHz in diagnostic exams), v is blood velocity, θ is the angle between the flow and the ultrasound beam, and c is the speed of sound in tissue (about 1540 m/s). With typical blood velocities (roughly 0.5 to 1 m/s) and common beam angles, Δf falls in the kilohertz range. For a 2 MHz probe, these shifts are usually around 1–3 kHz, with 2 kHz being a representative typical value.

The other numbers represent the carrier frequency (millions of hertz) or Doppler shifts that are unrealistically large for physiological motion given the usual probe frequencies and tissue sound speed. Thus, 2 kHz is the most typical Doppler shift measured clinically.