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

Unlike magnetic resonance imaging (MRI) and computed tomography (CT) scans, which reveal the structure of the lungs, a PET scan shows how well the lungs and their tissues are working.

See also:

• Chest MRI
• Lung cancer
• Lung gallium scan
• Solitary pulmonary nodule
• Thoracic CT

The health care provider will inject a small amount of a radioactive material into one of your veins, usually on the inside of the elbow. The substance travels through the blood and collects in the tissues of the lungs.

You will be asked to wait nearby as the radioactive substance is absorbed by your body. This usually takes about 1 hour.

Then, you will lie down on a table that slides into a tunnel-shaped hole in the center of the PET scanner.

The PET machine detects energy given off by the radioactive substance and changes it into 3-dimensional pictures. The images are sent to a computer, where they are displayed on a monitor for the health care provider to read.

You must lie still during the PET scan so that the machine can produce clear images of your lungs.

The test takes about 90 minutes.

You must sign a consent form before having this test. You will be told not to eat anything for 4 - 6 hours before the PET scan, although you will be able to drink water.

Tell your doctor if you are pregnant or think you might be pregnant.

Also tell your doctor about any prescription and over-the-counter medicines that you are taking, because they may interfere with the test.

Be sure to mention if you have any allergies, or if you’ve had any recent imaging studies using injected dye (contrast). Tell the PET center if you have diabetes and are taking insulin.

During the test, you may need to wear a hospital gown. Take off any jewelry, dentures, and other metal objects because they could affect the scan results.

You will feel a sharp prick when the needle with the radioactive substance is inserted into your vein. You shouldn’t feel anything during the actual PET scan.

Your doctor may order this test:

• To diagnose lung cancer
• To see if lung cancer has spread to other areas of the body. This is called staging. Staging helps guide future treatment and follow-up and gives you some idea of what to expect in the future.
• To determine whether a growth in the lungs seen on a CT scan is cancerous or noncancerous.
• To determine how well you're responding to cancer treatment.

There are no problems detected in the size, shape, or function of the lungs. There are no areas in which the radiotracer has abnormally collected.

Abnormal results may be due to:

• Cancer that has spread
• Lung cancer
• Solitary pulmonary nodule

The amount of radiation used in a PET scan is low. It is about the same amount of radiation as in most CT scans. Also, the radiation doesn’t last for very long in your body.

However, women who are pregnant or are breastfeeding should let their doctor know before having this test. Infants and fetuses are more sensitive to the effects of radiation because their organs are still growing.

It is possible, although very unlikely, to have an allergic reaction to the radioactive tracer. 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.

Other tests that may be done instead of a PET scan include a gallium scan, CT scan, or MRI scan.

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