This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
[{'content': 'Contrasts used in USG: \nSelect and explain. \nA. Urograffin, B. Ultragraffin, C. Sonavist, D. Conray', 'role': 'user'}, {'content': 'Answer: C \nExplanation: 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 b/w 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.', 'role': 'assistant'}]