Positron emission tomography (PET) scan

A positron emission tomography (PET) scan is an imaging test that helps reveal how your tissues and organs are functioning. A PET scan uses a radioactive drug (tracer) to show this activity.

The tracer may be injected, swallowed or inhaled, depending on which organ or tissue is being studied by the PET scan. The tracer collects in areas of your body that have higher levels of chemical activity, which often correspond to areas of disease. On a PET scan, these areas show up as bright spots.

A PET scan is useful in revealing or evaluating several conditions, including some cancers, heart disease and brain disorders.

Why it's done Risks How you prepare What you can expect Results

A PET scan is an effective way to examine the chemical activity in parts of your body. It may help identify a variety of conditions, including some cancers, heart disease and brain disorders. The pictures from a PET scan provide information different from that uncovered by other types of scans, such as computerized tomography (CT) or magnetic resonance imaging (MRI). A PET scan or a combined CT-PET scan enables your doctor to better diagnose your condition.


Cancer cells show up as bright spots on PET scans because they have a higher metabolic rate than do normal cells. PET scans may be useful in:

  • Detecting cancer
  • Revealing whether your cancer has spread
  • Checking whether a cancer treatment is working
  • Finding a cancer recurrence

PET scans must be interpreted carefully because noncancerous conditions can look like cancer, and many types of cancer do not appear on PET scans. The types of cancer most likely to show up on PET scans include:

  • Brain
  • Breast
  • Cervical
  • Colorectal
  • Esophageal
  • Head and neck
  • Lung
  • Lymphoma
  • Melanoma
  • Pancreatic
  • Prostate
  • Thyroid

Heart disease

PET scans can reveal areas of decreased blood flow in the heart. This information can help you and your doctor decide, for example, whether you might benefit from a procedure to open clogged heart arteries (angioplasty) or coronary artery bypass surgery.

Brain disorders

PET scans can be used to evaluate certain brain disorders, such as:

  • Tumors
  • Alzheimer's disease
  • Seizures

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