Doctors use 'glow-in-the-dark' dyes to make your blood vessels visible on medical scans.

Medical imaging relies on contrast agents to visualize the internal structure of the circulatory system. These substances, often containing iodine or gadolinium, have high atomic numbers that effectively block X-rays or alter magnetic signals. This process is known as angiography, a technique first developed shortly after Roentgen's discovery of X-rays in 1895.Iodinated contrast media are the most common agents used in CT scans and X-rays. Because iodine is very dense, it absorbs X-ray photons much more efficiently than the surrounding soft tissue. This creates a sharp 'white' image of the arteries and veins against the darker background of muscles and organs.In Magnetic Resonance Imaging (MRI), doctors use gadolinium-based contrast agents. Gadolinium is a rare-earth metal that shortens the relaxation time of water protons in the blood. This enhancement makes the blood vessels appear much brighter, allowing radiologists to detect aneurysms or stenoses as small as a few millimeters.Modern contrast agents are designed to be non-ionic to reduce the risk of allergic reactions. They are typically filtered out by the kidneys and excreted from the body within 24 hours. These dyes are essential for diagnosing cardiovascular diseases, which remain the leading cause of death globally according to the World Health Organization.