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CT scans and MRI scans are high tech imaging studies that give doctors the ability to look at the internal anatomy of the body in great detail. One of the tools used to help in differentiating normal structures from abnormal structures like tumors, aneurysms, infection, is IV contrast dye. The dye used in CT scans is based on low osmolar contrast material and for MRI scans on gadolinium. The dye is injected through an IV catheter placed in a vein (usually in the arm or hand). The contrast highlights different tissue types bringing out vessels, tumors, inflammation, cysts, etc, that might be missed if the dye was not administered for the scan.
Many patients are unaware of the side effects of the dye or misinformed (and uninformed) about the risk of contrast administration. A recent contrast injection study by the Mayo Clinic in Rochester, MN looked back at over 450,000 dye injections. Below is a brief summary of their experience:
CT scan dye side effects were 0.15%
MRI dye side effects were 0.04%
Most common side effects were hives and nausea
19 patients had a severe side effect (requiring medication, treatment)
1 patient died which is a mortality risk of 0.0003%
Clearly there is a risk of a severe reaction to the dye or even death. However, as the Mayo Clinic reports the vast majority of their patients did not have a reaction.
Although reactions to contrast are rare, it is standard practice to inform you of the possibility of dye administration and its potential side effects. However, keep in mind that many imaging facilities will not have a verbal discussion with you regarding IV contrast administration. It's usually in the paperwork you fill out before the test. Make sure you read and understand what you are signing in advance!