happens when the test is performed?
- A radionuclide is either injected into a vein or given to you
as a pill. Timing of the test then depends on the type of radionuclide
your doctor uses, and whether you will also have an uptake test.
If you are having only a thyroid scan and your doctor prefers
to give a radionuclide by intravenous injection, the scan can
be done within 30-60 minutes. If you are given radioactive iodine
in pill form, you need to wait four to six hours, and possibly
as long as a day, before having the scan. (This gives the radioactive
iodine time to reach your thyroid.) If you're having both a scan
and the uptake test, you are likely to receive radioactive iodine
in pill form. This allows one radionuclide to be used for both
the scan and uptake test, instead of two, and eliminates the
need for an injection.
After you've received the radionuclide and have waited the appropriate
amount of time, a technician places a radioactivity detector-a
camera specially designed to take pictures of radioactive objects
- against your neck and takes several images. The camera itself
doesn't expose you to any radiation. This portion of the test
usually takes about half an hour.
- An uptake test only takes several minutes and is performed
while you are sitting up. Using a device that resembles a Geiger
counter, the doctor or technician places a probe several inches
in front of your neck, where the thyroid gland is located, and
measures the percentage of radioactivity that is retained by
the thyroid gland. You return the next day for follow-up testing
to obtain a second set of uptake readings, which are then compared
with the first set to determine how much hormone has been formed
and secreted in the interim.