Thyroid Scan

Test Overview

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.

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:

• 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 To Prepare

To prepare for a thyroid scan:

• You may need to stop eating for several hours before the test.
• You may need to stop taking some medicines or supplements for a while before the test. Tell your doctor about all of the medicines, vitamins, and supplements you are taking.

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.

• Iodine can be taken as a capsule or a fluid 4 to 24 hours before the scan is done. Iodine has little or no taste.
• Technetium is given 5 to 30 minutes before the scan is done.

If you are breastfeeding, you may want to pump enough breast milk before the test to get through 1 to 2 days of feeding. The radioactive tracer used in this test can get into your breast milk and is not good for the baby.

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 5 to 30 minutes before the scan.

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.

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.

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

For a whole-body thyroid cancer scan, the camera will scan your body from head to toes.

How long the test takes

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

How It Feels

You may find it uncomfortable to lie still with your head tipped backward.

Risks

Anytime you're exposed to radiation, there's a small chance of damage to cells or tissue. That's the case even with the low-level radioactive tracer used for this test. But the chance of damage is very low compared with the benefits of the test.

Steps you can take

• Most of the tracer will leave your body through your urine or stool within a day. So be sure to flush the toilet right after you use it, and wash your hands well with soap and water. The amount of radiation in the tracer is very small. This means it isn't a risk for people to be around you after the test.
• The radioactive tracer used in this test can get into your breast milk. Do not breastfeed your baby for 1 or 2 days after this test. During this time, you can give your baby breast milk you stored before the test, or you can give formula. Discard the breast milk you pump in the 1 or 2 days after the test.
• You can go back to your usual activities right away.

Results

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.