A Chest positron emission tomography (PET) scan is an imaging test that uses a radioactive substance (called a tracer) to look for diseases in the lungs such as lung cancer. A PET scan is an effective way to help identify a variety of conditions, including lung cancer, heart disease, inflammatory lung disease, bronchitis, pneumonia, asthma, bronco congestion, and brain disorders. Your doctor can use this information to help diagnose, monitor or treat your condition. PET and PET-CT scans are highly accurate at determining whether a lung mass is cancerous and may even eliminate the need for surgical biopsy.FDG-PET was reported to be 90% to 94% accurate in the characterization of malignant or benign lung nodules, with a sensitivity of 94% to 96% and specificity of 78% to 86%.
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.
How the Test is Performed
A PET scan requires a small amount of tracer. The tracer is given through a vein (IV), usually on the inside of your elbow. It travels through your blood and collects in organs and tissues. The tracer helps the doctor (radiologist) see certain areas or diseases more clearly.
You will need to wait nearby as the tracer is absorbed by your body. This usually takes about 1 hour.
Then, you will lie on a narrow table, which slides into a large tunnel-shaped scanner. The PET scanner detects signals from the tracer. A computer changes the results into 3-D pictures. The images are displayed on a monitor for your doctor to read.
You must lie still during the test. Too much movement can blur images and cause errors.
The test takes about 90 minutes.
Most PET scans are now performed along with a CT scan. This is because the combined information from each scan provides a more complete understanding of the health problem. This combination scan is called a PET/CT.
How to Prepare for the Test
You may be asked not to eat anything for 4 to 6 hours before the scan. You will be able to drink water.
Tell your health care provider if:
- You are afraid of tight spaces (have claustrophobia). You may be given a medicine to help you relax and feel less anxious.
- You are pregnant or think you might be pregnant.
- You have any allergies to injected dye (contrast).
- You take insulin for diabetes. You will need special preparation.
Tell your provider about the medicines you are taking. These include ones bought without a prescription. Some medicines can interfere with the test results.
How the Test will Feel
You may feel a sharp sting when the needle containing 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
This test may be done to:
- Help look for lung cancer, when other imaging tests do not give a clear picture
- See if lung cancer has spread to other areas of the lungs or body when deciding on the best treatment
- Help determine if a growth in the lungs (seen on a CT scan) is cancerous or not
- Determine how well cancer treatment is working
Normal Results
A normal result means the scan did not show any problems in the size, shape, or function of the lungs.
What Abnormal Results Mean
Abnormal results may be due to:
- Lung cancer or cancer of another area of the body that has spread to the lungs
- Infection
- Inflammation of the lungs due to other causes
Blood sugar or insulin level may affect the test results in people with diabetes.
Risks
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 does not last for very long in your body.
Women who are pregnant or are breastfeeding should let their doctor know before having this test. Infants and babies developing in the womb 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 substance. Some people have pain, redness, or swelling at the injection site. This soon goes away.
