A thyroid scan uses a radioactive tracer and a special camera to measure how much tracer the thyroid gland absorbs from the blood. 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.
A thyroid scan can show the size, shape, and location of the thyroid gland. It can also find areas of the thyroid gland that are overactive or underactive. The camera takes pictures of the thyroid gland from three different angles. The radioactive tracer used in this test is either iodine or technetium.
A radioactive iodine uptake (RAIU) test may also be done to find problems with how the thyroid gland works, such as hyperthyroidism. For more information, see the medical test Radioactive Iodine Uptake Test.
Another type of thyroid scan, a whole-body thyroid scan, may be done for people who have had thyroid cancer that has been treated. The whole-body scan can check to see if cancer has spread to other areas of the body.
Why It Is Done
A thyroid scan is done to:
How To Prepare
Tell your doctor if you:
Before a thyroid scan, blood tests may be done to measure the amount of thyroid hormones (TSH, T3, and T4) in your blood.
To prepare for a thyroid scan:
Your doctor may ask you to eat a low-iodine diet for several days if this test is being done to check for thyroid cancer.
For a thyroid scan, you will either swallow a dose of radioactive iodine or be given technetium in a vein (intravenously) in your arm. When and how you take the radioactive tracer depends on which tracer is used.
Just before the test, you will remove your dentures (if you wear them) and all jewelry or metal objects from around your neck and upper body.
Before a thyroid scan, you need to sign a consent form that says you understand the risks of the thyroid scan and agree to have it done. Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).
How It Is Done
A thyroid scan is done in the nuclear medicine section of a hospital's radiology department by a person trained in nuclear medicine (nuclear medicine technologist).
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 this test, you will lie on your back with your head tipped backward and your neck extended. It is important to lie still during this test. A special camera (called a gamma scintillation camera) takes pictures of your thyroid gland from three different angles. The test takes about 30 minutes.
For a whole body thyroid cancer scan, the camera will scan your body from head to toes.
After a thyroid scan, you can do your regular activities. But 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.
How It Feels
You may find it uncomfortable to lie still with your head tipped backward.
There is always a slight chance of damage to cells or tissue from radiation, including 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.
This test is not done for pregnant women because of the chance of exposing the baby (fetus) to radiation. This test is also not recommended for breast-feeding women or young children.
A thyroid scan uses a radioactive tracer and a special camera to make a picture of the thyroid gland. The radioactive tracer used in this test is usually iodine or technetium. A thyroid scan is done to help find problems with the thyroid gland.
A whole-body scan will show whether iodine is in bone or other tissue (iodine uptake) after the thyroid gland has been removed for cancer. The whole-body scan can check to see if cancer has spread to other areas of the body.
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
What To Think About
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