Thyroid Scan: About This Test

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Thyroid gland

What is it?

A thyroid scan uses a radioactive tracer and a special camera. The tracer can be swallowed or can be injected into a vein. It travels through your body, giving off radiation signals. The camera "sees" the signals and can measure how much tracer the thyroid absorbs from the blood.

Why is this test done?

A thyroid scan is done to:

  • Help find problems with the thyroid gland.
  • Check a thyroid nodule.
  • See whether thyroid cancer has spread outside the thyroid gland. A whole-body thyroid scan will usually be done for this evaluation.

How can you prepare for the test?

  • You may need to stop eating for several hours before the test.
  • Tell your doctor if you have had a CT scan with contrast within the last month.
  • Your doctor may have you stop taking thyroid medicines for some time before this test.
  • If the test is being done to check for thyroid cancer, your doctor may ask you to eat a low-iodine diet for several days before the test.

What happens during the test?

  • The tracer used in this test is either radioactive iodine or technetium.You will either swallow a dose of iodine 4 to 24 hours before the scan or be given technetium in a vein (intravenously) in your arm 15 to 30 minutes before the scan.
  • For the scan, you will lie on your back with your head tipped backward and your neck extended.
  • A special camera takes pictures of your thyroid gland from three different angles.
  • For a whole body thyroid cancer scan, the camera will scan your body from head to toes.

What else should you know about the test?

  • There is always a slight chance of damage to cells or tissue from the low levels of radiation used for this test. But the chance of damage from the radiation is usually very low compared with the benefits of the test.

How long does the test take?

  • After you get the tracer, you may have a scan about 30 minutes later. Or you may need to go back up to 24hours later for one or more scans. Each scan takes only a few minutes.

What happens after the test?

  • You can go back to your usual activities right away.
  • 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. This takes about 24 hours. It is important to flush the toilet and wash your hands thoroughly after each time you urinate.

Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor or nurse call line if you are having problems. It's also a good idea to keep a list of the medicines you take. Ask your doctor when you can expect to have your test results.

Where can you learn more?

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