When an MRI is performed with contrast of the brain, a dye helps certain parts of the brain show up distinctly on the images, according to MedlinePlus. The patient typically receives the dye intravenously in the hand or forearm. If the scan is done without contrast, no dye is used.
Gadolinium, a metal ion, is often used for the contrast dye, reports the FDA. However, patients who have severe kidney disorders are not usually given this contrast, because it puts them at risk for developing nephrogenic systemic fibrosis, a serious disease of the skin and connective tissues. Although most people have no negative reaction to the contrast, it is sometimes problematic for patients with asthma, anemia, low blood pressure or sickle cell disease, Johns Hopkins Medicine observes.