Thyroid Scan

A thyroid scan uses a radioactive tracer and a special camera to measure how much tracer is absorbed from the bloodstream by the thyroid gland. During a thyroid scan, the camera takes pictures of the thyroid gland from three different angles. The radioactive tracer used in this test is usually iodine or technetium.

A thyroid scan is done to diagnose problems with the thyroid gland. A thyroid scan may be done to evaluate thyroid nodules, or it may be done along with a radioactive iodine uptake test (RAIU) to evaluate thyroid function.

A thyroid scan can show the size, shape, and position of the thyroid gland. It can also detect areas of the thyroid gland that are overactive or underactive.

Another type of thyroid scan, a whole-body thyroid scan, may be done for people who have had thyroid cancer that has been treated.

Why It Is Done

A thyroid scan is done to:

  • Determine whether thyroid nodules are present.

  • Determine the cause of an overactive thyroid gland (hyperthyroidism).

  • Determine whether thyroid cancer has spread beyond the thyroid gland. A whole-body thyroid scan will usually be done for this evaluation.

How To Prepare

Before having a thyroid scan, tell your health professional if you:

  • Have any allergies to medications, including anesthetics.

  • Take any medications regularly. Be sure your health professional knows the names and doses of all your medications. Your health professional will instruct you if and when you need to stop taking any of the following medications that can interfere with the test results.

    • Thyroid hormones

    • Antithyroid medications

    • Medications that contain iodine, such as iodized salt, kelp, cough syrups, multivitamins, or the heart medication amiodarone (Cordarone, Pacerone)

  • Are allergic to iodine. The radioactive tracer used for this test may contain iodine. However, even if you are allergic to iodine, you will probably be able to have this test because the amount that may be used in the radioactive tracer is so small that your risk of an allergic reaction is very low.

  • Have recently (within 4 to 6 weeks) had any tests in which you were given radioactive materials or had X-rays that used iodine dye. Receiving iodine contrast material prior to a thyroid scan can interfere with test results.

  • Are or might be pregnant.

  • Are breast-feeding.

  • Have ever had a serious allergic reaction (anaphylaxis) from any substance, such as the venom from a bee sting or from eating shellfish.

Before a thyroid scan, blood tests may be done to measure the amount of thyroid hormones (TSH, T3, and T4) in your blood.

Do not eat for up to 2 hours before the test.

Before a thyroid scan, you will either swallow a dose of radioactive iodine or be given technetium intravenously. When and how you take the radioactive tracer depends upon the tracer used.

  • Iodine (taken by mouth before the test) may be taken up to 24 hours before the test.

  • Technetium (given by intravenous injection) is usually given 20 to 30 minutes before the test.

  • Radioactive iodine can be taken as a liquid or capsule. The iodine has little or no taste.

Just before the test, you will be asked to remove your dentures (if you have them) and all jewelry or metal objects from around your neck and upper chest area.

How It Is Done

A thyroid scan is done in the nuclear medicine section of the Heart Institute of the Caribbean by nuclear medicine technologist ( a person trained in nuclear medicine).

If you are to receive technetium, an intravenous line will be inserted into your arm. While the technetium is being injected, you may feel warm, flushed, and nauseated. Taking deep breaths while the technetium is injected may reduce these uncomfortable feelings.

For this test, you will lie on your back with your head tipped backward and your neck extended. It is important to remain still for periods of time during this test. During a thyroid scan, a special camera (called a gamma scintillation camera) takes pictures of your thyroid gland from three different angles. This camera is not an X-ray machine and does not expose you to any additional radiation. A thyroid scan takes about 30 minutes.

After a thyroid scan, you can resume your regular activities. However, you will be asked to take special precautions when you urinate. This is because your body gets rid of the radioactive tracer through your urine (usually within 24 hours). It is important to flush the toilet and wash your hands thoroughly after each time you urinate.

How It Feels

There is no pain associated with this test. However, at times during this test you may find it uncomfortable to lie completely still with your head extended backward.

Risks

There is always a slight risk of damage to cells or tissue from being exposed to any radiation, including the low levels of radiation used for this test. However, the risk of damage from the radiation is usually very low compared with the potential benefits of the test.

This test is not done for pregnant women because of the risk of exposing the baby (fetus) to radiation. This test is also not recommended for breast-feeding women or young children.

What Affects the Test

Factors that can interfere with your test and the accuracy of the results include:

  • Taking thyroid medication.

  • Iodine-containing foods, such as shellfish, iodized salt or kelp.

  • Other contrast materials used in tests.