PET/CT scan for cancer

The information on this page was reviewed and approved by
Maurie Markman, MD, President, Medicine & Science at CTCA.

This page was updated on September 17, 2021.

What is a PET/CT scan?

This advanced nuclear imaging technique combines a positron emission tomography scan (PET) and computed tomography scan (CT) into one machine. The combination of CT and PET imaging reveals information about both the structure and function of cells and tissues in the body during a single imaging session.

How is a PET/CT scan performed?

During a PET/CT scan, a technologist gives the patient an intravenous injection of glucose (sugar) solution that contains a very small amount of radioactive tracer for most imaging. Other radioactive agents may be used depending on your cancer type. The radioactive material travels through the bloodstream to the areas of the body with unusual metabolic activity, including any organs or tissues with primary cancer or metastasis.

During the nuclear medicine scan, the patient rests on a table and slides into a large, tunnel-shaped scanner. The PET/CT scanner is then able to "see'' damaged or cancerous cells where the glucose/radiotracer mixture is being taken up (cancer cells often use more glucose than normal cells) and the rate at which the tumor is using the glucose (which may help determine the tumor grade in some tumors). This helps stage your tumor by determining which parts of the body have abnormal activity. The outpatient procedure is painless and varies in length, depending on the part of the body being evaluated.

Why is a PET/CT scan used in cancer care?

By combining information about the body's anatomy and metabolic function, a PET/CT scan provides a more detailed picture of cancerous tissues than either test does alone. The PET and CT images appear in a single scan, allowing for a high level of accuracy. Compared to an X-ray or magnetic resonance imaging (MRI scan), this imaging test enables doctors to examine medical conditions and abnormalities at a cellular level. The use of PET/CT scan helps the oncology team develop the optimal cancer treatment plan. Follow-up may involve additional testing and biopsy or treatment protocols, such as radiation therapy and chemotherapy.

Many oncologists perform a CT scan and/or a bone scan prior to ordering a PET/CT scan.

A PET/CT scan may also:

  • Provide information on how well a treatment is working
  • Help plan future radiation therapy
  • Determine the right place in the body to perform a biopsy, if needed
  • Check for new cancer growth, after treatment ends, during follow-up care

How to prepare for a PET/CT scan

Before the scan

  • Find the right facility for you: PET/CT scans are typically performed at a hospital’s radiology or nuclear medicine department, but you may also find appointments at outpatient imaging facilities.
  • Dress accordingly: You may be asked to disrobe for the procedure, so it may be more convenient to wear loose clothing. The facility may provide a wrap or gown to wear. You’ll also likely be asked to remove jewelry, piercings and metal objects such as dentures or hearing aids.
  • Bring medical records: The technologist may ask for your personal and medical history, including past scans and surgeries and a list of current medications you’re taking.
  • Review instructions for food and drink: You may be asked to avoid eating about six hours before the PET/CT scan and to drink only water. This may be case by case, so ask your doctor ahead of the procedure.
  • Ask about exercise: Your doctor may require that you avoid exercise 24 to 48 hours before the PET/CT scan.
  • Allot enough time: To help the scan produce its images, a small amount of a radioactive sugar substance is injected into a vein, which takes about 30 to 90 minutes to travel throughout the body. The scanning procedure takes 30 minutes to one hour.
  • Lean on a friend or family member: If you have anxiety, it may help to bring a loved one for support. Ask the facility whether there are any restrictions on bringing support.

During the scan

  • Be prepared for the placement: You may be asked to lie down on a table that slides into a large scanning machine with a doughnut-shaped hole in the middle. To get clear images, the technologist may ask you to hold your breath at certain times during the scan.
  • Expect an injection: A small amount of a radioactive sugar substance is injected into your body through an intravenous (IV) line. Cancer is attracted to the energy of this substance and absorbs it, which allows the scanner to detect the substance more easily and produce images of the inside of your body.
  • Don’t be afraid to speak up: It’s not uncommon to feel claustrophobic or anxious during a PET/CT scan, so let the technologist know if you’re too uncomfortable.

After the scan

  • Resume activities: Typically, you may resume normal activities right after the scan.
  • Drink water: It’s a good idea to drink plenty of water afterward to flush out the dye or radioactive sugar.

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