Popliteal vein thrombus- Color Doppler ultrasound video clip:

                                                                               This color Doppler video clip shows the thrombus (arrows), clearly, in transverse section of the vessel.

                                                                       And this- a Color Doppler video clip of the same vessel in longitudinal section.

See:  http://www.ultrasound-images.com/vascular.htm (for more on this case). On that page, you should find more color Doppler images of this case and details of how to image the veins of the lower limb. The interesting and indeed intriguing part of this case is the particulate movement within the thrombus- possibly fibrotic strands within it. This suggests that the thrombus is old or chronic, maybe a month or more old.