This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous, Subject name: Surgery
[{'content': 'Contrast media used in ultrasound is \nSelect and explain. \nA. Ultraffin, B. Hexanol, C. Urograffin, D. Echovist', 'role': 'user'}, {'content': 'Answer: D \nExplanation: D. i.e. (Echovist) (39- 42 - Textbook of colour Doppler Imaging S.K. Bhargava)* Iohexol used in Myelography*** Contrast agent (ECHOVIST) have been used to evaluate tubal potency in infertility and ureteric reflux in children with renal tract infectionsContrast agents in Ultrasound* Contrast agents increases shift frequency and echo strength determines the visualization hence act as echoenhancers* Echo- enhancers are microbubbles - levovist, optisan, sonovue* Range of ultrasound frequencies that are used for clinical diagnosis microbubbles at(1 - 7 m diameter) do not diffuse across the endothelium', 'role': 'assistant'}]