What is it?
The contrast agents used in CT are usually an iodinated molecule. Iodine is very effective at absorbing radiation, this is why it is used in CT scans. Areas where the contrast media collects will produce a light image; this makes possibly dangerous lesions easier to see. Once injected/ingested, the contrast media is distributed throughout the body by the blood vessels and spreads into extracellular space. Only 1-2% of it actually enters the cells and none of it is metabolized, it is excreted unchanged through normal kidney processing.(1)
Image courtesy of the NCI
Procedure involving contrast agent
If your CT exam involves contrast media, you will need to follow some special procedures. You may be asked to follow a certain diet, which may include fasting. The contrast material can be given orally, intravenously, or both. If it is given orally you may be asked to drink it up to 24 hours before the exam and again shortly before the exam, so it is important to be on time for your exam. If the contrast media is given intravenously, a nurse will put an IV in your arm or hand before the exam. An IV injection of contrast material may make you feel flushed, warm, or nauseas and you may notice a metallic taste in your mouth. These are not serious issues and should subside. Serious reactions from the dye can occur, so tell the nurse about any other problems/feelings.(1)