Ultrasound contrast agents are gas-filled microbubbles that are administered intravenously to the systemic circulation. Microbubbles have a high degree of echogenicity, which produces a unique sonogram with increased contrast. Microbubbles can be used in a wide variety of animal models, for contrast imaging as well as for drug and gene delivery. Microbubbles are compatible with virtually all ultrasound scanners and Doppler ultrasound.