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🤔 Why do we use iodine as an intravenous contrast agent?
The answer requires a review of the composition of the human body and a brief tour of one of my favorites, the Periodic Table of Elements.
🤔 Why do we use iodine as an intravenous contrast agent?
The answer requires a review of the composition of the human body and a brief tour of one of my favorites, the Periodic Table of Elements.
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To begin, it's essential to understand which elements make up the human body. Amazingly, just six compose >98% of your weight:
➤Oxygen: 61% (varies based on water composition)
➤Carbon: 23%
➤Hydrogen 10%
➤Nitrogen: 2.6%
➤Calcium: 1.0%
➤Phosphorus: 0.6%
https://buff.ly/3YU4dIY
One thing you'll notice about these six elements is that they are relatively small (i.e., they have low atomic numbers, aka are low-Z elements).
In addition to being the most prevalent elements in the universe, their low atomic number allows them to more readily form stable chemical bonds.
In fact, when examining the top 30 elements in the human body (by mass), you will again notice that most are low-Z (i.e., have a low atomic number).
But there is one element that is both required and relatively heavy...
https://buff.ly/3YOuTLb
IODINE!
The story of how iodine came to be used by vertebrates is fascinating and may be the focus of a future thread. For now, it is enough to note that...
💡 Iodine is the heaviest element required by humans for biological processes.
https://buff.ly/48RcvWE
But how does the atomic weight of iodine relate to its use as an intravenous contrast? It is precisely this property of iodine that makes it a suitable agent for this purpose.
💡 The higher the atomic number of an element, the greater the absorption of X-rays.
https://buff.ly/3Og7vkM
Fat, muscle, and other soft tissues are primarily comprised of carbon, hydrogen, nitrogen, and oxygen. These smaller elements absorb few X-rays.
When injected into a blood vessel, iodine will absorb more X-rays, appear more opaque, and provide "contrast" with surrounding soft tissues.