Before your PET-CT scan, you will get an injection of a small amount of a radioactive sugar called fluorodeoxyglucose This substance is sometimes called FGD, radioactive glucose, or a tracer. The cells in your body absorb sugar. Areas that use more energy pick up more of the sugar. Cancer cells tend to use more energy than healthy cells. The PET scan shows where the radioactive tracer is in your body. The CT scan takes x-rays of your body from different angles.
You might get a shot of dye before the x-rays. This helps some of the details show up better. Your doctor gets a detailed 3-D result that shows anything abnormal, including tumors.
PET-CT scans do carry a risk of radiation. This type of scan uses some radiation from x-rays, the substance used in the PET scan, or both. Scanning a smaller body area means less radiation. So does a CT without the dye that helps show details. The benefits of these tests are usually greater than the risks. During these tests, you will be exposed to small amounts of radiation. This low dose of radiation has not been shown to cause harm. For children or for other people who need multiple PET scans, CT scans, and x-rays, there may be a small potential increased risk of cancer in the future.
Doctors can use lower dose scans or limit the areas that need to be scanned. Make sure all of your doctors know how many imaging scans you have had, including the number and type. This information can help them decide which scans to use in the future to help reduce your risk. If you are concerned about your radiation exposure, talk with your doctor, including asking whether you can have another type of test that uses less radiation instead.
After the test is done, a doctor who specializes in looking at the test results will look at your scan. This person is a nuclear medicine specialist or a radiologist.
They will decide what the results mean. Be sure to follow their instructions carefully to avoid affecting your scan results. Talk with the staff about the following topics, and ask questions about any information that is unclear or concerning to you.
What to eat. You may be told to drink only clear liquids after midnight the night before the scan. Depending on what part of your body will be scanned, you may need to stop all eating and drinking 4 hours before the scan. For some scans, you can eat and drink normally. Your medications and health history. Ask whether you should take your usual medications or supplements on the day of the test. The tracer is radiolabeled, meaning it emits gamma rays that are detected by the PET scanner.
The computer collects the information emitted by the tracer and displays it on the CT cross-sections. The radioisotopes used in PET to label tracers are 11C, 13N, , and 18F carbon, nitrogen, oxygen and 18F used as a substitute for hydrogen.
These radioactive forms of natural elements will pass through your body and be detected by the scanner. Various drugs and other chemicals can be labeled with these isotopes.
The type of tracer used depends on what your doctor wants to measure. For example, if your doctor is looking at a tumor, he or she might use radiolabeled glucose FDG and watch how it is metabolized by the tumor. PET can measure blood flow, blood volume, oxygen usage, tissue pH acidity , glucose sugar metabolism, and drug activity. PET is very useful in detecting the activity of cancer. Because malignant cells grow at a fast rate, they metabolize more sugar than normal cells.
This can give your doctor a glimpse into how aggressive a tumor is or how its growth is slowed by therapy. Another common use for PET is for presurgical evaluation of medically uncontrolled seizures Fig. Positron emission tomography During a positron emission tomography PET scan, you lie on a narrow table that slides into a doughnut-shaped hole. PET scan of the heart Open pop-up dialog box Close. PET scan of the heart This PET image shows an area of reduced blood flow from one of the arteries that feeds the heart.
Request an Appointment at Mayo Clinic. Share on: Facebook Twitter. Radiological Society of North America. Accessed April 6, What is PET? Society of Nuclear Medicine and Molecular Imaging. Umterrainer M, et al. Recent advances of PET imaging in clinical radiation oncology.
Radiation Oncology. Adam A, et al. Adrenal imaging. In: Grainger and Allison's Diagnostic Radiology. Elsevier; American College of Radiology. Cervical cancer. You may be given a medicine to help you feel sleepy and less anxious. You are pregnant or think you might be pregnant. You have any allergies to injected dye contrast. How the Test will Feel. You may feel a sharp sting when the needle with the tracer is placed into your vein.
An intercom in the room allows you to speak to someone at any time. There is no recovery time, unless you were given a medicine to relax. Why the Test is Performed. The most common use for a PET scan is for cancer, when it may be done: To see how far cancer has spread. This helps to select the best treatment approach. To check how well your cancer is responding, either during treatment or after treatment is completed. This test can also be used to: Check brain function Identify the source of epilepsy in the brain Show areas in which there is poor blood flow to the heart Determine if a mass in your lung is cancerous or harmless.
What Abnormal Results Mean. Abnormal results depend on the part of the body being studied. Abnormal results may be due to: Cancer Infection Problem with organ function. Alternative Names. Nuclear Scans Read more.
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