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Thyroid scan 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.
After the iodine has been absorbed by the thyroid, you lie on your back on a gantry (movable table) with your neck and chest positioned under the scanner. The scanner detects the location and intensity of the gamma rays emitted by the iodine. 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 a 2-dimensional image of the thyroid and any nodules that have absorbed the iodine. The image is recorded in the computer and can be reproduced on X-ray film or a computer printout.
How to Prepare:
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.
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
How it Feels:
The iodine mixture may cause slight nausea when you take it.
Some patients find remaining still during the test uncomfortable.
Risks:
All radiation has possible side effects. There is a very small amount of radiation in the iodine 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.
Why this 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.
Abnormal Results:
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:
Cost:
The estimated cost is $50 - $120, plus any hospital stay and extra computer costs.
Special Considerations:
Thyroid tests are about 80 to 85% accurate; however, usually 2 or more tests are required to determine the cause of thyroid dysfunction.
This special scan (scintiscan) shows enlargement of the thyroid gland and extension behind the breastbone (retrosternal space). The false color image was generated by a computer during a radioisotope (I-131) thyroid scan.
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