Medical Imaging: PET (Positron Emission Tomography)/CT

Positron emission tomography (or PET scan) is a test that combines computed tomography (CT) and nuclear scanning.  During a PET scan, a radioactive substance called a tracer (18F-FDG) is injected into a vein, usually in your arm. The tracer emits tiny, positively charged particles called positrons that produce signals.  A special camera records the tracer's signals as it travels through your body and collects in your organs.  These signals are converted into three-dimensional images of the examined organ and provide a clear view of any abnormality.

The image produced during a PET scan is not as detailed as a CT scan or magnetic resonance imaging (MRI) picture of the organ. Instead, PET scans provide information about how an organ is working. A PET scan is often used to detect or evaluate tumors, evaluate heart function and blood flow, and examine brain function.

Why is it done?

A PET scan is done to:

  • study blood flow and metabolic activity in the brain, which can help identify certain neurologic and central nervous system disorders, including Parkinson's disease, multiple sclerosis, Alzheimer's disease, transient ischemic attack (TIA), amyotrophic lateral sclerosis (ALS), Huntington's disease, epilepsy, stroke, or schizophrenia
  • diagnose certain types of cancer, particularly of the breast, brain, lung, colon, thyroid, and lymphoma. A PET scan is more sensitive than a CT scan or MRI for detecting tumors in early stages. It can also help determine if a tumor is non-cancerous (benign) or cancerous (malignant). If cancer has been diagnosed, a PET scan can help determine how far advanced the cancer is and whether it has spread to another area of the body (metastasized). It is often necessary to do both CT and PET scans to evaluate metastatic cancer.
  • help determine the most effective treatment for cancer
  • detect poor blood flow to the heart, which may indicate coronary artery disease.
  • distinguish between healthy and damaged heart tissue, especially during the early stages of a heart attack.
  • help determine the best course of treatment for heart disease