PET Scan

Most scans show what the body looks like. A PET scan shows how parts of the body are working. That makes it useful when the question is whether a spot is active cancer, scar tissue or something else.

PET stands for positron emission tomography. A small amount of a radioactive tracer, most often a form of sugar called FDG, is injected into a vein. Cells that are very active, such as many cancer cells and areas of infection or inflammation, take up more of the sugar and light up on the scan. PET is usually combined with a CT scan (PET/CT), and sometimes with MRI.

In brain and spine care, a PET scan may be used to:

• Look for cancer that has spread to the spine or brain, such as metastatic spine disease or metastatic brain tumors, and find where it started
• Check how active a brain tumor such as a glioma is, or tell tumor regrowth apart from changes caused by radiation treatment
• Look for hidden infection or inflammation in some cases
• Help plan surgery, radiation or other treatment

PET scans are often ordered together with your oncology team.

• Do not eat for 4 to 6 hours before the scan. Plain water is usually fine.
• Avoid hard exercise for 24 hours before the test, because active muscles take up the tracer.
• Some centers ask you to eat a low-sugar, low-carbohydrate diet the day before.
• If you have diabetes, ask the center for special instructions about your insulin or diabetes pills and your blood sugar.
• Tell them if you are pregnant or breastfeeding.
• Wear warm, comfortable clothes without metal.

Your blood sugar is checked, and the tracer is injected through an IV. You then rest quietly in a reclining chair for about an hour while it spreads through your body. Try not to talk or move much during this time. The scan itself takes about 20 to 45 minutes while you lie still on a table that moves slowly through the scanner. Plan on two to three hours in all.

You can usually eat and go back to normal activities right away. Drink plenty of fluids to help the tracer leave your body. For the rest of the day, it is a good idea to limit close contact with babies and pregnant women. The doctor who ordered the scan will go over your results with you.

The radiation dose from the tracer is small, and it leaves your body within hours. Allergic reactions to the tracer are extremely rare. PET/CT adds the radiation from the CT portion. PET scans are generally avoided during pregnancy.

What does it mean if something lights up on a PET scan?

A bright area means cells are using more sugar than usual. That can mean cancer, but also infection, inflammation or healing tissue, so results are always compared with your other scans and history.

Why can I not eat before a PET scan?

Food raises your blood sugar, which can keep the tracer from collecting where it should. Fasting helps make the pictures accurate.

Is a PET scan the same as a CT scan?

No. A CT shows structure, while a PET shows activity. They are often done together in one machine so the activity can be matched to the exact location.

If Dr. Grunch has ordered a PET scan for you and you have questions, call 470-293-9800 or contact us. You can also ask general questions any time through our “Ask Us Anything” chat. For questions about scheduling, cost or arrival time for the test itself, call the imaging center where it is booked.

Related: All imaging and diagnostic tests · Metastatic spine disease · Gliomas

This information is for educational purposes only and is not medical advice. It does not replace individualized care from a licensed physician. Please talk to your provider about your symptoms and follow the instructions from your imaging center.