A catheter system for delivering ultrasonic energy to a treatment site within a body lumen, the catheter comprises a tubular body having a proximal end, a distal end and an energy delivery section positioned between the proximal end and the distal end and a plurality of ultrasound radiating members in the energy delivery section. The plurality of ultrasound radiating members are allocated into electrical groups comprising more than one ultrasound radiating member. Members of one electrical group are spatially interdigitated with members of another electrical group.
