In cooperation with EKOS Corporation, which pioneered the development and the clinical application of ultrasound accelerated thrombolysis, The Vascular Experts are pleased to be conducting this trial, which is designed to assess the efficacy of ultrasound accelerated thrombolysis using the EkoSonic Endovascular System in patients who suffer from a prior leg DVT (deep vein thrombosis or blood clot). Many patients have suffered from a leg DVT or multiple DVTs that have blocked the main veins in their legs. These patients are initially treated with medicines, only to suffer long-term from debilitating leg pain, in the form of heavy, achy, and swollen legs, as well as painful ulcers. Up until recently, there was little therapy that could be offered to these patients. New technologies and devices are becoming available that actually allow physicians to open these blood vessels that have been closed due to DVT for many years. Dr. Gagne is currently enrolling appropriate patients in this trial.