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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.
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
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.
A thyroid scan is done to:
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
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?).
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.
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 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
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.
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
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.
Reasons you may not be able to
have the test or why the results may not be helpful include:
Other Works ConsultedFischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby.
May 31, 2011
E. Gregory Thompson, MD - Internal Medicine & Matthew I. Kim, MD - Endocrinology
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