Radiocontrast Agent
Iodine, as a physically dense element with high electron density and high atomic number, is quite radio-opaque (i.e., it absorbs X-rays well). This property can be fully exploited by filtering imaging X-rays so that they are more energetic than iodine's "K-edge" at 33.3 keV, or the energy where the iodine begins to absorb X-rays strongly due to the photoelectric effect from electrons in its K shell. Organic compounds of a certain type (typically iodine-substituted benzene derivatives) are thus used in medicine as X-ray radiocontrast agents for intravenous injection. This is often in conjunction with advanced X-ray techniques such as angiography and CT scanning. At present, all water-soluble radiocontrast agents rely on iodine.
Read more about this topic: Iodine Compounds, Applications
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