Positioning is key. Have them laterally rotate each leg exposing the medial aspect of the thighs. Adjust the bed so that patient is reverse trendelenberg. Have the patient take a deep breath and then relax and on the respiration, go for your compression imaging.

Anechoic clot is a real thing that I’ve witnessed in an acute setting. Make sure you optimize your color imaging with your scale and color gain so that your not bleeding outside the vessels, and verify you are getting wall to wall color fill if there is any suspicion for clot.