What is a PET scan?
A positron emission tomography (PET) scan is a type of imaging that uses radioactive medications to evaluate organ function or identify cancer. Whereas other types of imaging exams, such as a CT scan or an MRI, evaluate anatomic structures, a PET scan looks at chemical and metabolic activity in cells. This makes PET scans especially useful for diagnosing diseases or change in organ function, before problems would be visible on other imaging scans or on clinical exam.
How a PET scan works
PET scans work by using radiotracers, or radiopharmaceuticals that are injected into the body. Radiotracers are substances that contain a small, safe amount of radioactive material. The radiotracer collects in in cells that are actively dividing, metabolically active or have specific proteins on their surfaces. The radiation energy from these cells is then imaged in a PET scan.
Types of PET scans
You may have a PET scan on its own, but more often we combine a PET scan with a computed tomography (CT) scan called a PET/CT. A CT scan uses X-rays to produce cross-sectional images of structures in your body from many angles. A computer stacks the images to make detailed pictures of bones, organs, blood vessels, and lymph nodes.
We overlay the CT with the PET scan to show two perspectives: structure and function. This way, we can see the exact location of abnormal cellular activity, such as a tumor. One machine does the PET scan and CT scan at the same time, so you don’t need two separate scans.
Other types of PET scans include:
- Cardiac PET: evaluates blood flow to your heart, heart muscle damage, inflammation, and infection
- FDG-PET scan: the most common PET exam for oncology. This uses a radiotracer that acts like glucose (“sugar). Cancer cells that need a lot of energy to divide will be identified with this scan. Common cancers that are evaluated include lymphoma, lung or breast cancer.
- PSMA PET: an exam that uses a radiotracer to identify prostate cancer cells that are present in the body
- FES PET: an exam that uses a radiotracer to identify some types of estrogen receptor positive breast cancer cells
- Dotatate PET: an exam that uses a radiotracer to identify neuroendocrine tumors
- Brain PET: There are several types of PET scans that can be used to identify different types of brain disorders, such as Alzheimer’s disease, seizure disorders, or the presence of amyloid deposits.
Who might need a PET or PET/CT scan?
The most common reason for a PET or PET/CT scan is to diagnose and monitor cancer. We also use it to evaluate certain types of heart conditions and brain diseases. A PET or PET/CT may:
- Assess damage from a heart attack
- Diagnose dementia or Alzheimer’s disease
- Evaluate neurological disorders such as epilepsy (seizure disorder)
- Find out if cancer has spread or returned after treatment
- Plan heart or brain surgery
What to expect during a PET scan
A health-care provider called a PET technologist performs your scan. A radiologist with specialized training in nuclear medicine and molecular imaging interprets the results.
PET and PET/CT scans take place at hospitals and some outpatient imaging facilities. Your care team will give you instructions about how to prepare for the exam.
We may ask you to fast (stop eating or drinking except water) for several hours before the scan. It’s especially important to avoid caffeine, as it can change the way your body absorbs the radiotracer. People with diabetes will get special instructions about eating and drinking.
Be sure to tell your care team if you’re pregnant or breastfeeding. You may need to pump breastmilk before the exam and wait for the radiotracer to leave your system before breastfeeding again.
PET and PET/CT scans are outpatient procedures, so you go home the same day unless you’re hospitalized. The scan typically lasts about 30 minutes, but it may take up to an hour for the radiotracer to move through your system. Prepare for the entire process to take about two hours.
During the exam, here’s what you can expect:
- You remove all clothing and jewelry and put on a gown.
- We give you an injection of a radiotracer and you wait about an hour.
- If you’re getting a PET/CT, you may also get an injection of a contrast dye to help structures in your body show up in more detail.
- You lie down on a comfortable bed attached to the scanner, which is shaped like a large donut.
- Detectors in the machine rotate around your body and take pictures. You may hear clicking sounds.
- You won’t feel anything during the scan, but it’s important to stay very still.
- Your bed moves out of the scanner when the test is complete.
After a PET scan
There’s no downtime after a PET or PET/CT scan. You can return to normal activities right away. You may feel some soreness in the area where you received the radiotracer injection. Tell your care team if you don’t feel well or experience any side effects.
Does a PET scan have risks?
Some people are concerned about the radiation in the radiotracer. The very small amount of radiation used passes out of your body through urine and stool within a few hours or days. Drinking a lot of water after the exam can help flush it out faster. Some people can experience some mild nausea with some of the injected radiotracers.
Precise PET and PET/CT imaging at Penn Medicine
At Penn Medicine, our expertise in nuclear medicine and molecular imaging makes us one of the leading providers of PET and PET/CT scans in the region. We use the latest technology to diagnose even the most complex diseases as early and as quickly as possible.
We offer:
- Recognized expertise: We’re fully accredited in nuclear medicine and positron emission tomography by the American College of Radiology. We voluntarily seek this accreditation to ensure we meet or exceed the highest quality and safety standards.
- Advanced technology: Penn Medicine is often among the first in the country to pioneer new imaging technology that isn’t widely available. We use the latest equipment to gather as much information as possible about your condition, which helps us make the most effective treatment plan.
- Research and innovation: Decades ago, we were the first in the world to obtain an FDG-PET image. In addition, faculty at Penn Medicine helped to develop the first amyloid PET for Alzheimer’s disease. We continue this tradition of innovation with our dedicated PET Center, which focuses on advancing research and educating clinicians about the latest advances in nuclear medicine.
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