<prompt> Contrasts used in USG:UrograffinUltragraffinSonavistConray  <response>: C i.e. Sonavist Ultrasound contrast agents UCAs It consists of microbubbles filled with air or gases, which acts as echo - enhancer by increasing acoustic impedence at the interface bw gas blood. The ideal USCA, should have:no biological effect with repeat doses. low : attenuation, blood gas solubility diffusivity. high : echogenicity ability to pass through pulmonary circulation. 