Apparatus and method for delivering increased amounts of energy to localized treatment zones at a target location are provided. In some instances, using gated pulses of ultrasound in a multi-frequency applicator, microbubbles are generated or excited in or near the target location, for example in a patients tissue or blood stream for enhanced delivery of ultrasound energy to the patient. Applications include ablation of diseased tissue, thrombolysis, blood-brain barrier disruption or tissue diagnosis.
