Diagnostic
Radioactive iodine uptake.
A capsule or ‘cocktail’ containing a measured amount of radioactive iodine is swallowed; iodine is a critical component of thyroid hormones. The iodine accumulates in the thyroid; more accumulates when the gland is overactive, as occurs in Graves’ disease. After a specified amount of time, a probe similar to a Geiger counter is placed over the thyroid and the amount of radioactivity is compared to the amount that was given.
Treatment
The basic idea behind radioactive iodine is that it is attracted to damaged (cancerous) cells and the radiation kills the cells.
The problem is that if you still have a thyroid, that is the first place the iodine will go, and hence destroy the thyroid. For this reason the medical profession will prefer to remove the thyroid completely so damaged cells in the rest of the body are they only ones killed. The major problem with this is that you then need to take artificial thyroxin for the rest of your life, which can have its own set of side effects.