An ablation device includes an elongate catheter body having a lumen extending therethrough and a distal region. An ablation element, such as one or more ultrasound transducers, is disposed within the distal region such that it can emit ablative energy outwardly relative to the longitudinal axis of the catheter body. A balloon is positioned about the distal region of the catheter body, typically with the ablation element positioned within the balloon. The balloon is expandable outwardly from an outer surface of the catheter body such that, when the balloon is inflated, an exterior surface of the balloon stably engages an interior wall of a blood vessel without occluding blood flow therethrough. For example, the balloon can be cross-shaped when inflated. To create circumferential lesions without repositioning the catheter, the ablation element can rotate about and/or slide along the longitudinal axis of the catheter body.
