The study will compare standard catheter directed thrombolysis to ultrasound accelerated thrombolysis for the treatment of acute submassive pulmonary embolism (PE). The study population will include patients eligible for catheter directed thrombolysis (CDT) for submassive PE. Subjects will be randomized to, either, standard catheter-directed thrombolysis or ultrasound-accelerated thrombolysis (USAT).