Thrombosis refers to the formation of a blood clot (thrombus) inside a blood vessel, which can partially or completely obstruct blood flow. It can occur in veins (venous thrombosis, most commonly deep vein thrombosis in the legs) or arteries (arterial thrombosis). Ultrasound is the primary diagnostic tool for venous thrombosis, using the compression technique — a normal vein collapses completely under transducer pressure, while a thrombosed vein fails to compress. On B-mode imaging, acute thrombus may appear as hypoechoic material expanding the vein, while chronic thrombus tends to be more echogenic and may partially recanalize. Doppler evaluation shows absent or reduced flow in the affected segment. In arterial thrombosis, echogenic material within the artery lumen with absent flow is the primary finding.
Sonography Term