What best describes the difference between the ultrasound frequencies used for Doppler and for B-mode imaging with a given transducer?

• A. A The frequency for Doppler is usually lower than for imaging
• B. B The frequency for Doppler is usually higher than for imaging
• C. C the transmit pulse for Doppler has a greater bandwidth compared to the bandwidth for imaging
• D. D the frequency for Doppler and for B-mode imaging must be identical for a given transducer

Answer: (A)

The main idea is how frequency affects penetration versus resolution. For B‑mode imaging you want high spatial detail to clearly visualize anatomy, which comes from using a higher frequency. But higher frequency waves attenuate more quickly, reducing how deep you can image. Doppler studies, especially when assessing flow at depth, benefit from reaching deeper tissues with less attenuation, so a lower center frequency is typically chosen. The Doppler signal still relies on detecting shifts in frequency caused by moving blood cells, and using a lower base frequency helps maintain signal strength at depth without sacrificing the ability to measure velocity. So, with the same transducer, the Doppler frequency is usually lower than the imaging frequency.