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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.
A thyroid scan is done to:
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.
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.
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 jewellery 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.
You may find it uncomfortable to lie still with your head tipped backward.
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.
A normal thyroid scan shows a small butterfly-shaped thyroid gland about 5 cm (2 in.) long and 5 cm (2 in.) wide with an even spread of radioactive tracer in the gland.
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.
Current as of: December 2, 2020
Author: Healthwise StaffMedical Review: E. Gregory Thompson MD - Internal MedicineKathleen Romito MD - Family MedicineAdam Husney MD - Family Medicine
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
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