Echogenicity (misspelled sometimes as echogenecity) is the ability to create an echo, i.e. return a signal in ultrasound examinations. Echogenicity could be increased by intravenously administering gas-filled microbubble contrast agent to the systemic circulation. This is because microbubbles have a high degree of echogenicity. When gas bubbles are caught in an ultrasonic frequency field, they compress, oscillate, and reflect a characteristic echo- this generates the strong and unique sonogram in contrast-enhanced ultrasound. Gas cores can be composed of air, or heavy gases like perfluorocarbon, or nitrogen (Lindner, 2004). Heavy gases are less water-soluble so they are less likely to leak out from the microbubble to impair echogenicity (McCulloch et al., 2000). Therefore, microbubbles with heavy gas cores are likely to last longer in circulation.^[1]