<prompt> Contrast agent which are not used for CT scan:WaterCO2Barium compoundsIodinated high-osmolality contrast media  <response>: Ans. B. CO2Ref Sumer Sethi 6th20; Radiology 6 Imaging by Thayalan159; Dahne Radiology Manual 7th1147-48Radiocontrast agents are a type of medical contrast medium used to improve the visibility of internal bodily structures in X-ray-based imaging techniques such as computed tomography CT, radiography fluoroscopy.Radiocontrast agents are typically iodine or barium compounds.When an agent improves visibility of an area, it is called contrast enhancingGadolinium is a key component of the contrast material most often used in magnetic resonance MR exams.Saline salt water and air are also used as contrast materials in imaging exams.Barium sulfate contrast media continue to be the preferred agents for opacification of the gastrointestinal tract for conventional fluoroscopic examinationsThe current use of iodinated water-soluble contrast media is primarily limited to select situationsTwo commercid water-soluble iodinated high-osmolality contrast media HOCMs specifically designed for enteric opacification are in common use. Gastrografin and, Gastroview 