A method is provided for site specific delivering therapeutic or diagnostic agents
to a region in a fluid-filled cavity, vessel or tissue using an agent-loaded microbubble
population. The population has controlled fragility characterized by a uniform
wall thickness to diameter ratio which defines the discrete threshold intensity
value of ultrasonic power where microbubble rupture occurs in the population. The
location of the microbubble population may be monitored by ultrasound to determine
its presence at the region prior to application of the ultrasonic power to rupture
to microbubbles.
