What is a radionuclide scan?
A radionuclide is a chemical that is radioactive. Doctors give you a small dose of the radionuclide. The radionuclide gives off radiation that's picked up by a scanner placed over a certain area of your body. The scanner makes a picture of where the radiation is and how strong it is. This helps show doctors what's going on in the tissue they're testing.
Doctors can give you a radionuclide as:
An injection
Something to swallow
A gas to breathe in
Different radionuclides go to different parts of your body. Doctors pick which radionuclide to use depending on what they need a picture of. A radionuclide scan can help doctors find problems in many parts of your body:
Thyroid gland
Liver
Gallbladder
Lungs
Urinary tract
Bones
Brain
Certain blood vessels
Why would I need a radionuclide scan?
Doctors usually use this test to find problems such as:
Blocked blood flow to your heart
Cancer that has spread to your bones or liver
Inflammation (swelling and pain) or infection inside organs
Bleeding, such as in your intestine
Sometimes, doctors will use the test to see how well a part of your body is working. For example, doctors may see how your heart works when it’s pumping hard by doing the test while you walk or run on a treadmill. If you’ve had a heart attack, doctors may do this test to see how well your heart is recovering.
What happens during a radionuclide scan?
Before the test
You may be asked to not eat or drink for several hours before the scan
Doctors usually inject the radionuclide in a vein but sometimes have you swallow or breathe it
You’ll wait a few minutes or up to several hours while the radionuclide travels through your body
During the scan
You’ll lie still on a table while a scanner takes pictures, usually for about 15 minutes
Sometimes you’ll need to get another scan after waiting for some more time, possibly hours later
After the scan
Doctors will have you drink lots of water or other liquids to help flush the radionuclide out of your body.
What are the risks of radionuclide scanning?
Radiation
You'll be exposed to much more radiation than a plain x-ray Plain X-Rays A plain x-ray is an imaging test that takes a picture of the inside of your body. It uses a low dose of x-ray radiation. X-rays show body parts according to how dense (solid) they are. Doctors... read more 
. Doctors try to limit the total amount of radiation you are exposed to over your lifetime. Getting too much radiation can raise your chance of getting cancer.
If you’re pregnant or could be pregnant, tell doctors before you get radionuclide scanning.
Radionuclides stay in your body for a few days. If you plan to fly on an airplane within a few days after getting this test, you may set off radioactivity alarms in the airport. Get a doctor’s note to have at the airport.
Other problems
The test can take a long time, up to several hours
Radionuclide scans aren't as detailed as pictures from other imaging tests, such as x-rays Plain X-Rays A plain x-ray is an imaging test that takes a picture of the inside of your body. It uses a low dose of x-ray radiation. X-rays show body parts according to how dense (solid) they are. Doctors... read more
, CT scans Computed Tomography A CT scan uses a large machine shaped like a large donut to take x-rays from many angles. A computer then takes the x-rays and creates many detailed pictures of the inside of your body. Each... read more 
, or MRIs Magnetic Resonance Imaging (MRI) MRI is a test that uses a machine with a powerful magnet to make pictures of the inside of your body. A computer records changes in the magnetic field around your body. The computer then uses... read more 
