A thyroid scan is a nuclear medicine examination that uses radioactive iodine to check for hyperthyroidism, thyroid cancer, or other thyroid gland growths.

You will be given a pill that contains radioactive iodine, and then you will wait as the iodine collects in the thyroid. The first scan is usually 4 - 6 hours after the iodine pill is taken. Another scan may be taken 24 hours later. Additional or alternative scans may be done using a compound containing technetium.

After the radioactive iodine has been absorbed by the thyroid, you will lie on your back on a movable table with your neck and chest positioned under the scanner. The scanner detects the location and intensity of the rays given off by the radioactive material. During this part of the procedure, you must lie still to let the scanner get a clear image. A computer displays images of the thyroid.

You must sign a consent form. You may be told not to eat after midnight the night before the exam. Consult the health care provider if you are taking any medications that may need to be regulated, such as thyroid medication and anything with iodine in it. Remove jewelry, dentures, or other metals, because they may interfere with the image.

Some patients find remaining still during the test uncomfortable.