Scan - thyroid

Alternative names
Thyroid scan; Radioactive iodine screening test - thyroid; RAUI; Nuclear scan - thyroid

Definition
A 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.

Next, the information is sent to a computer that displays images of the thyroid and any possible nodules that have absorbed the iodine.

How to prepare for the test
You 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 feel
The iodine mixture may cause slight nausea when you take it.
Some patients find remaining still during the test uncomfortable.

Why the test is performed
When Thyroid cancer or nodules are suspected.

Normal Values

The thyroid appears the correct size, shape, and in the proper location. It appears a uniform gray on the computer.

What abnormal results mean

If 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 considerations

Thyroid tests are about 80-85% accurate; however, usually two or more tests are required to determine the cause of thyroid dysfunction.

Johns Hopkins patient information

Last revised: December 4, 2012
by Janet G. Derge, M.D.

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