Patient Education - Endocrine Encyclopedia
Endocrine Surgery Encyclopedia
 Definition:
A thyroid scan is a nuclear medicine examination that uses the emissions of gamma rays from
radioactive iodine to help determine whether a patient has thyroid problems, including hyperthyroidism,
cancer, or other growths.
Alternative Names: Scan - thyroid; Radioactive iodine screening
test - thyroid; RAUI; Nuclear scan - thyroid
How the test is performed:
You will be given a pill that contains radioactive iodine, and then you will wait as the
iodine collects in the thyroid. The first scan is usually 4 - 6 hours after the iodine has
been ingested, and another scan may be taken 24-hours later. Additional or substitute imaging
may be performed using a compound containing technetium.
After the radioiactive iodine has been absorbed by the thyroid, you will lie on your back
on a movable table with your neck and chest positioned under the scanner. The scanner detects
the location and intensity of the gamma rays emitted. During this part of the procedure,
you must lie still to let the scanner get a clear image.
Next, the information is sent to a computer that displays images of the thyroid and any
possible nodules that have absorbed the iodine.
How to prepare for the test:
You must sign a consent form. You may be told not to eat after midnight the night before
the exam. Consult the health care provider if you are taking any medications that may need
to be regulated, such as thyroid medication and anything with iodine in it. Remove jewelry,
dentures, or other metals, because they may interfere with the image.
How the test will feel:
Some patients find remaining still during the test uncomfortable.
Why the test is performed:
When thyroid cancer or nodules are suspected.
Normal Values:
The thyroid appears the correct size, shape, and in the proper location. It appears a uniform
gray on the computer.
What abnormal results mean:
If the thyroid is enlarged or pushed off to one side, this could indicate a tumor. Nodules
will absorb more or less iodine and will appear darker or lighter on the scan (usually lighter
if tumor). If part of the thyroid appears lighter, it may indicate there is possible thyroid
dysfunction.
Additional conditions under which the test may be performed:
- Anaplastic carcinoma of the thyroid
- Colloid nodular goiter
- Goiter
- Medullary carcinoma of thyroid
- Multiple endocrine neoplasia (MEN) II
- Papillary carcinoma of the thyroid
- Toxic nodular goiter
What the risks are:
All radiation has possible side effects. There is a very small amount of radiation in the
radioisotope ingested during this test, but women who are nursing or pregnant should discuss
the risks to the fetus or infant with their health care providers before taking this test.
The concerns regarding radiation side effects are taken into consideration when the test
is ordered, but the benefits of taking the test usually far outweigh the risks.
Special considerations:
Thyroid scans using radinuclides are used with other studies, such as blood tests and ultrasound,
to evaluate the thyroid. Your doctor may send you for more than one type of test.
Review Date: 8/3/2005
Reviewed By: Jonathan Gross, M.D., Department of Radiology, Columbia University Medical Center,
New York, NY. Review provided by VeriMed Healthcare Network.
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