| Subject | Contents |
| Definition | 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. |
| Alternative Names | Scan - thyroid; Radioactive iodine screening test - thyroid; RAUI; Nuclear scan - thyroid |
| 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 radioisotope 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. 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. 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:infant test or procedure preparation (birth to 1 year) toddler test or procedure preparation (1 to 3 years) preschooler test or procedure preparation (3 to 6 years) schoolage test or procedure preparation (6 to 12 years) adolescent test or procedure preparation (12 to 18 years) |
| 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:anaplastic carcinoma of the thyroidcolloid nodular goitergoitermedullary carcinoma of thyroidmultiple endocrine neoplasia (MEN) IIpapillary carcinoma of the thyroidtoxic nodular goiter |
| 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 to 85% accurate; however, usually 2 or more tests may required to determine the cause of thyroid dysfunction. |
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