A system for ablating tissue, said system comprising: an elongate shaft having a proximal portion, a distal portion, and a longitudinal axis; a housing adjacent to the distal end of the elongate shaft; an ultrasound transducer coupled to the distal portion of the elongate shaft, and disposed in the housing, wherein the ultrasound transducer is adapted to deliver a beam of ultrasound energy to ablate target tissue; a barrier disposed between a face of the ultrasound transducer and adjacent blood or tissue, wherein the barrier permits the beam of ultrasound energy to ablate the target tissue without contact between the ultrasound transducer and the target tissue, and wherein the barrier comprises a fluid flow past the ultrasound transducer to prevent blood from coagulating thereon; a reflecting element operably coupled with the ultrasound transducer, the reflecting element redirecting the beam of ultrasound energy emitted from the ultrasound transducer to a desired direction or a pattern, wherein the reflecting element is configured to direct the beam of ultrasound energy through a sidewall of the housing so as to form a continuous lesion in the target tissue; a sensor adjacent the ultrasound transducer or the ultrasound transducer as a sensor, wherein the sensor is adapted to detect characteristics of the ablated tissue, of the unablated or target tissue; and a processor configured to control ultrasound energy delivery from the ultrasound transducer based on information received from the sensor and to control the fluid flow of the barrier by increasing or decreasing the fluid flow based on the information received from the sensor. an elongate shaft having a proximal portion, a distal portion, and a longitudinal axis; a housing adjacent to the distal end of the elongate shaft; an ultrasound transducer coupled to the distal portion of the elongate shaft, and disposed in the housing, wherein the ultrasound transducer is adapted to deliver a beam of ultrasound energy to ablate target tissue; a barrier disposed between a face of the ultrasound transducer and adjacent blood or tissue, wherein the barrier permits the beam of ultrasound energy to ablate the target tissue without contact between the ultrasound transducer and the target tissue, and wherein the barrier comprises a fluid flow past the ultrasound transducer to prevent blood from coagulating thereon; a reflecting element operably coupled with the ultrasound transducer, the reflecting element redirecting the beam of ultrasound energy emitted from the ultrasound transducer to a desired direction or a pattern, wherein the reflecting element is configured to direct the beam of ultrasound energy through a sidewall of the housing so as to form a continuous lesion in the target tissue; a sensor adjacent the ultrasound transducer or the ultrasound transducer as a sensor, wherein the sensor is adapted to detect characteristics of the ablated tissue, of the unablated or target tissue; and a processor configured to control ultrasound energy delivery from the ultrasound transducer based on information received from the sensor and to control the fluid flow of the barrier by increasing or decreasing the fluid flow based on the information received from the sensor.