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Alternative namesScan - thyroid; Radioactive iodine screening test - thyroid; RAUI; Nuclear scan - thyroid
DefinitionA thyroid scan is a nuclear medicine examination that uses the emissions of gamma rays from radioactive iodine to help determine whether a patient has thyroid problems; including hyperthyroidism , cancer , or other growths.
How the test is performed
You are given radioactive iodine to drink (or in pill form) and then must wait until the iodine collects in the thyroid. The first scan is usually 4 to 6 hours after the iodine has been ingested, and another scan may be taken 24-hours later. Additional or substitute imaging may be performed using a compound containing technetium.
After the radioiactive iodine has been absorbed by the thyroid, you 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 gamma rays emitted. During this part of the procedure, you must lie still to enable the scanner to get a clear image.
How to prepare for the testYou must sign a consent form. Fasting overnight is a usual requirement. 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.
For infants and children:
The preparation you can provide for this test depends on your child's age and previous experience. For specific information regarding how you can prepare your child, see the following topics:
How the test will feelThe iodine mixture may cause slight nausea when you take it.
Some patients find remaining still during the test uncomfortable.
Why the test is performedWhen thyroid cancer or nodules are suspected.
Normal ValuesThe thyroid appears the correct size, shape, and in the proper location. It appears a uniform gray on the computer.
What abnormal results meanIf the thyroid is enlarged or pushed off to one side, this could indicate a tumor . Nodules will absorb more or less iodine and will appear darker or lighter on the scan (usually lighter if tumor). If part of the thyroid appears lighter, it may indicate there is possible thyroid dysfunction.
Additional conditions under which the test may be performed:
What the risks are
All radiation has possible side effects. There is a very small amount of radiation in the radioisotope ingested during this test, but women who are nursing or pregnant should discuss the risks to the fetus or infant with their health care providers before taking this test.
The concerns regarding radiation side effects are taken into consideration when the test is ordered, but the benefits of taking the test usually far outweigh the risks.
Special considerationsThyroid tests are about 80-85% accurate; however, usually two or more tests are required to determine the cause of thyroid dysfunction.
Update Date: 10/17/2003Jeffrey Brown, M.D., Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO. Review provided by VeriMed Healthcare Network.
Last updated: Tue, 06 Jan 2009 00:20:03 GMT