Ultrasound assessments of the common femoral and popliteal vein (transverse plane) will be done according to a standardized procedure by independent experts unaware of clinical details and of previous ultrasound findings. Vein diameters will be measured during maximal compression, and considered recanalized in case of a diameter < 2.0 millimeters in a single determination, or a diameter < 3.0 millimeters in two consecutive determinations.