A parathyroid MIBI scan is used to look at possible problems involving the parathyroid gland. The parathyroids are four small hormone glands lying close to (back surface of) the thyroid gland, in the front of the neck. The parathyroid scan uses sestamibi (MIBI), which is a very safe liquid radioactive material that is injected into the body and absorbed by the overactive parathyroid, but not by healthy parathyroids.