Which of the following could be a source of color Doppler signal?

• A. Blood flow
• B. Breathing motion
• C. Cardiac motion
• D. All of the above

Answer: (D)

Color Doppler signals come from motion along the ultrasound beam. Any moving target with velocity toward or away from the transducer can create a Doppler frequency shift that the system colors to show direction and speed. Blood flow is the primary source, but tissue motion can also produce Doppler shifts. The beating heart moves its walls and valves, and breathing causes chest and abdominal structures to shift, both of which can generate color signals under the right imaging settings. When tools are tuned to emphasize flow and suppress clutter, you’ll still be able to detect signals from these motions; if not, they may appear as clutter, but they still originate from motion along the beam. Therefore, all of the above could be sources of color Doppler signal.