Venogram vs. Intravascular Ultrasound (IVUS) for Diagnosing Iliac Vein Obstruction

Inclusion Criteria: * Subject must be \> 18 and \< 85 years of age * Willing to participate in and able to understand, read and sign the informed consent document before the planned procedure * CEAP clinical classification: C4, C5, or C6 (enrollment of C4 and C5 subjects will be capped at 50, such that at least 50 C6 subjects can be enrolled) * On duplex ultrasound: patent common femoral vein, and patent deep femoral vein, and/or femoral vein of the study leg * Undergoing iliofemoral and inferior vena caval venography with the intent to treat obstructive lesions 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 metal allergy precluding endovascular stent implantation * 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 * Severe, untreated (and readily treatable) superficial venous reflux (great saphenous vein \>7 mm in diameter, and/or small saphenous vein \>4 mm in diameter) * 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 * 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.