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Positron emission tomography (PET) is a sophisticated medical imaging technique. It uses a radioactive tracer to pinpoint differences in tissues on the molecular level. A PET scan can detect differences in body functions, such as blood flow, use of oxygen, and uptake of sugar (glucose) molecules. This allows your doctor to see how certain organs are functioning.
A lung PET scan is often combined with a lung CT scan to detect conditions like lung cancer. The computer combines images from the two scans to provide a three-dimensional image, which highlights any areas of especially rapid metabolic activity. This process is known as image fusion. The scans allow your doctor to distinguish between benign (noncancerous) and malignant (cancerous) masses.
If you need a lung PET scan, you’ll be injected with a small amount of a radioactive tracer substance about an hour before the scan. Most often, an isotope of the element fluorine will be used. The needle may sting temporarily, but otherwise the procedure is painless.
Once in the bloodstream, the tracer substance will accumulate in your organs and tissues and begin to give off energy in the form of gamma rays. The PET scanner detects these rays, and detailed images are created from them. The images can help your doctor examine the structure and functioning of the specific organ or area being examined.
During the exam, you’ll be lying down on a narrow table. The table slides inside a tunnel-shaped scanner. You’ll be able to talk to technicians while the scan takes place, but it’s important to lie still while the scan runs. Too much movement could result in blurry images.
The scan takes about 20 to 40 minutes.
Your doctor will ask you not to eat or drink anything besides water for several hours before the scan. It’s very important to follow these instructions. A PET scan often depends on monitoring slight differences in how cells metabolize sugars. Eating a snack or drinking a sugary beverage could interfere with results.
Upon arrival, you may be asked to change into a hospital gown, or you may be allowed to wear your own clothes. You’ll need to remove any metallic objects from your body, including jewelry.
It’s important to tell your doctor if you’re taking medications or supplements. Some medications, such as diabetes medication, can interfere with the results of a PET scan.
If you’re uncomfortable in enclosed spaces, your doctor may give you medication to help you relax. This drug may cause drowsiness.
A PET scan uses a small amount of radiation. The radioactive tracer will become inactive in your body within a few hours or days. It will eventually pass out of your body through urine and stool.
Although radiation exposure is minimal, you should notify your doctor before undergoing any procedure that uses radiation if you’re pregnant or breastfeeding.
A lung PET scan is also used to stage lung cancer. Fast-growing tissues, such as lung cancer tumors, absorb more of the tracer substance than other tissues. These areas stand out on the PET scan. Your doctor can use the three-dimensional images to detect growing tumors.
Cancer is assigned a stage between 1 and 4. Staging refers to how advanced a particular cancer is. For instance, stage 4 cancer is more advanced, has spread farther, and is usually more difficult to treat than stage 2 cancer. Staging is also used to predict outlook. For example, a person with stage 1 lung cancer is more likely to live longer than someone with stage 4 cancer.
Your doctor can use images from the lung PET scan to determine the best course of treatment.
Written by: Dale Kiefer
Medically reviewed on: Dec 16, 2015: Steve Kim, MD
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