A system (10) for treating tissue within a body is configured to deliver a first level of ultrasound energy to a target tissue region (42) for a first duration resulting in the generation of micro-bubbles (56) in the target tissue region, determine one or more characteristics of the target tissue region in the presence of the micro-bubbles, and deliver a second level of ultrasound energy to the target tissue region for a second duration, wherein one or both of the second energy level and the second duration are based, at least in part, on the determined one or more characteristics of the target tissue region.