Apparatus is provided, which includes at least one ultrasound transducer. The ultrasound transducer is configured to be positioned within a lumen of a subject and to ablate tissue surrounding a wall of the lumen without ablating the wall of the lumen, by focusing ultrasound energy on a focal zone that is outside of the wall of the lumen. A transluminal delivery tool is configured to position the ultrasound transducer in the lumen, and a control unit is configured to drive the ultrasound transducer. Other embodiments are also described.
