text: The most common use of perfluorocarbon emulsions is as ultrasound contrast agents. In this application, microscopic bubbles containing perfluorocarbon gas are injected intravenously and flow through the bloodstream. An ultrasound machine then sends soundwaves through a tissue of interest, and the bubbles reflect the soundwaves to a greater extent than the surrounding tissues, thereby giving the blood greater contrast on ultrasound viewers. This can allow greater visibility of the structure of an organ of interest, or a better indication of the level of blood perfusion or blood volume in an area of interest. The bubbles persist in the blood stream with half-lives of minutes before the perfluorocarbon molecules leave the bubbles and enter the surrounding fluids, before eventually passing through the lungs where they are exhaled.
  Notable ultrasound contrast agents include Definity and Optison which are FDA approved, Sonazoid which is approved in Japan, and EchoGen which was formerly approved in Europe but never marketed.