A method of delivery ultrasonic energy and a therapeutic compound to a treatment site and an ultrasonic catheter system are disclosed. The method comprises providing a catheter with a plurality of ultrasound radiating members, wherein the plurality of ultrasound radiating members are allocated into electrical groups comprising more than one ultrasound radiating member. The method further comprises independently driving each group of ultrasonic radiating members, and delivering the therapeutic compound through the catheter to the treatment site.