Ultrasonic catheter with axial energy field

A catheter system for delivering ultrasonic energy to a treatment site within a body lumen comprises a tubular body. The tubular body has a proximal end, a distal end and an energy delivery section positioned between the proximal end and the distal end. The catheter further comprises an inner core configured for insertion into the tubular body. The inner core comprises a first ultrasound radiating member axially separated from a second ultrasound radiating member by an intermediate flexible joint region. The inner core further comprises an electrically conductive portion configured to allow a voltage difference to be applied to at least one of the ultrasound radiating members. The inner core further comprises a high impedance cap positioned proximal to at least one of the ultrasound radiating members.