Vascular Ultrasound Versus Intravascular Ultrasound for Diagnosing Iliac Vein Obstruction

Inclusion Criteria: * Advanced Chronic Venous Insufficiency (CEAP 3-6) submitted to clinical treatment for at least 1 year with no response. * Subject must be \> 18 and \< 80 years of age * Willing to participate in and able to understand, read and sign the informed consent document before the planned procedure * On duplex ultrasound: patent common femoral vein, and patent deep femoral vein, and/or femoral vein of the study leg Exclusion Criteria: * Subject cannot or will not provide written informed consent * Previous venous stent implantation involving the study leg or inferior vena cava * Previous venovenous bypass surgery involving the study leg * Known reaction or sensitivity to iodinated contrast that cannot be managed with premedication * Subjects who are pregnant (women of childbearing potential must have a negative pregnancy test within 7 days prior to enrollment * Acute deep venous thrombosis involving either leg * Known history of chronic total occlusion of the common femoral vein of the study leg. * Known history of thrombophilia (e.g., protein C or S deficiency, anti-thrombin III deficiency, presence of lupus anticoagulant, etc.) * Venous compression caused by tumor encasement * Venous outflow obstruction caused by tumor thrombus * Life expectancy of less than 6 months * Lower Extremity Arterial Insufficiency * Elevated baseline blood creatinine (value greater than the upper limit of the normal range) * Any concurrent disease or condition that, in the opinion of the Investigator, would make the subject unsuitable for participation in the study; examples include but are not limited to the inability to lie supine for the index procedure (e.g., severe congestive heart failure), thrombocytopenia or other hematological disorders associated with an unacceptable risk of bleeding, implanted orthopedic hardware that precludes proper imaging, etc.