Thyroid Scan

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

Thyroid scan

Normal:

A normal thyroid scan shows a small butterfly-shaped thyroid gland about 2 in. (5 cm) long and 2 in. (5 cm) wide with an even spread of radioactive tracer in the gland.

Abnormal:

An abnormal thyroid scan shows a thyroid gland that is smaller or larger than normal. It can also show areas in the thyroid gland where the activity is less than normal (cold nodules) or more than normal (hot nodules). Cold nodules may be related to thyroid cancer.

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.

Credits

Current as of: December 2, 2020

Author: Healthwise Staff
Medical Review:
E. Gregory Thompson MD - Internal Medicine
Kathleen Romito MD - Family Medicine
Adam Husney MD - Family Medicine

Disclaimer: The information contained in this website, and its associated websites, is provided as a benefit to the local community, and the Internet community in general; it does not constitute medical advice. We try to provide quality information, but we make no claims, promises or guarantees about the accuracy, completeness, or adequacy of the information contained in or linked to this website and its associated sites. As medical advice must be tailored to the specific circumstances of each patient and healthcare is constantly changing, nothing provided herein should be used as a substitute for the advice of a competent physician. Furthermore, in providing this service, Adventist HealthCare does not condone or support all of the content covered in this site. As an Adventist health care organization, Adventist HealthCare acts in accordance with the ethical and religious directives for Adventist health care services.

Find a Doctor

Find an Adventist HealthCare affiliated doctor by calling our FREE physician referral service at 800-642-0101 or by searching our online physician directory.

View Doctors

Set Your Location

Setting your location helps us to show you nearby providers and locations based on your healthcare needs.