Catheter-directed thrombolysis requires placement of a multi-sidehole infusion catheter within the pulmonary arterial thrombus burden under angiographic guidance. Thrombolytic medications are slowly infused through the catheter, which is left in place for the duration of the treatment. USAT is a modification of this therapy utilizing a proprietary system of local high frequency, low-power ultrasound to dissociate the fibrin matrix of the thrombus, allowing deeper penetration of lytic medication.