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    PET scan

    Positron emission tomography

    A positron emission tomography (PET) scan is an imaging test that uses a radioactive substance called a tracer to look for disease in the body.

    A PET scan shows how organs and tissues are working. This is different thanmagnetic resonance imaging (MRI) and computed tomography (CT), which show the structure of and blood flow to and from organs,

    Related tests include:

    • Brain PET scan
    • Breast PET scan
    • Heart PET scan
    • Lung PET scan

    How the Test is Performed

    A PET scanuses a small amount of radioactive material (tracer). The tracer is given through a vein (IV),most oftenon the inside of your elbow.The tracertravels through your blood and collects in organs and tissues. This helps the radiologist see certain areasof concernmore clearly.

    You will need to wait nearby as the tracer is absorbed by your body. This takes about 1 hour.

    Then, you will lie on a narrow table thatslides into a large tunnel-shaped scanner. The PETpicks updetects signals from the tracer. A computer changes thesignals into 3-D pictures. The images are displayed on a monitor for your doctor to read.

    You must lie still during test. Too much movement can blur images and cause errors.

    How long the test takes depends on what part of the body is being scanned.

    How to Prepare for the Test

    You may be asked not to eat anything for 4 - 6 hours before the scan. You will be able to drink water.

    Tell your health care provider if:

    • You are afraid of close spaces (have claustrophobia). 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).

    Always tell your health care provider about the medicines you are taking, including those bought without a prescription. Sometimes, medications may interfere with the test results.

    How the Test Will Feel

    You may feel a sharp sting when the needlewith the tracer is placed into your vein.

    A PET scan causes no pain. The table may be hard or cold, but you can request a blanket or pillow.

    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

    A PET scan can reveal the size, shape, position, and some function of organs.

    This test can be used to:

    • Check brain function
    • Diagnose cancer, heart problems, and brain disorders
    • See how far cancer has spread
    • Show areas in which there is poor blood flow to the heart

    Several PET scans may be taken over time to check how well you are responding to treatment for cancer or another illness.

    Normal Results

    A normal result means there were no problems seen in the size, shape, or position of an organ. There are no areas in which the tracer has abnormally collected.

    What Abnormal Results Mean

    Abnormal results depend on the part of the body being studied. Abnormal results may be due to:

    • Change in the size, shape, or position of an organ
    • Cancer
    • Infection
    • Problem with organ function


    The amount of radiation used in a PET scan about the same amount as formost CT scans. Short-lived tracers are used so the radiation is gone from your body in about 2-10 hours.

    Tell your doctor before having this test if you are pregnant or breast feeding.Infants and babies developing in the womb are more sensitive to radiation because their organs are still growing.

    Rarely, people may have an allergic reaction to the tracer material. Some people have pain, redness, or swelling at the injection site.


    It is possible to have false results on a PET scan. Blood sugar or insulin levels may affect the test results in people with diabetes.

    Most PET scans are now performed along with a CT scan. This combination scan is called a PET/CT.


    Ettinger DS. Lung cancer and other pulmonary neoplasms. In: Goldman L, Ausiello D, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 197.

    Griggs RC, Jozefowicz RF, Aminoff MJ. Approach to the patient with neurologic disease. In: Goldman L, Ausiello D, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 403.

    Kramer CM, Beller GA. Noninvasive cardiac imaging. In: Goldman L, Ausiello D, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 56.

    Segerman D, Miles KA. Radionuclide imaging: general principles. In: Adam A, Dixon AK, eds. Grainger & Allison's Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 7.


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                Tests for PET scan

                Review Date: 11/9/2012

                Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, Stephanie Slon, and Nissi Wang.

                The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.

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