• Bookmark this Page
  • Print this Page


PET/CT Scan Testing

A combined PET/CT scan (positron emission tomography/computed tomography) is an imaging study that is used to evaluate a variety of conditions, including neurological conditions, heart disease and cancer. The PET portion of the study shows how your organs and tissues are functioning, while the CT portion of the exam details the anatomy or structure of your organs and tissues.

In order to see how your organs and tissues are functioning, a small amount of a radioactive tracer is injected into a vein. The most commonly used tracer is F-18, fluorodeoxyglucose, which is similar to glucose (sugar). This tracer is concentrated in normal tissues and organs and cancers in proportion to glucose metabolism. Because tumors generally have higher metabolic rates than normal tissues, tumors concentrate more of the tracer than normal cells and show up as brighter spots on the scan. The CT portion of the exam allows the tracer to be accurately localized.

Why is a PET/CT scan done?

PET/CT scans are most often used in patients who have cancer, heart disease or brain disorders.


Cancer cells show up as brighter spots on PET scans because they have higher metabolic rates than normal cells. In patients with cancer, PET scans can show:

  1. Extent or spread of the disease
  2. How well the cancer is responding to treatment
  3. If the cancer has recurred

PET scans have been shown to be especially useful for evaluating:

  1. Lung cancer
  2. Lymphoma
  3. Breast cancer
  4. Esophageal cancer
  5. Colon cancer
  6. Melanoma
  7. Cervical cancer

PET scans also have been shown to be useful for characterizing a lung nodule as benign or malignant.

Heart disease

PET scans are used to detect areas of decreased blood flow in the heart. This information can help show which areas of the heart might benefit from angioplasty, stents or coronary artery bypass surgery.

Brain disorders

PET scans can show how your brain is functioning. They are used to evaluate tumors, memory disorders and seizures.


The amount of radiation that you are exposed to during a PET/CT scan is too low to affect the normal processes of your body. However, this radiation might harm the fetus of a pregnant woman or the infant of a woman who is breast-feeding. You and your doctor can discuss the risk to the fetus or infant versus the benefit of having a PET/CT scan performed. Allergic reactions or side effects from the radioactive tracer are extremely rare.


  1. Do not eat or drink anything except water for at least 6 hours prior to your appointment
  2. Minimize exercise beginning the day prior to your scan
  3. Follow a low carbohydrate diet beginning the day prior to your scan; i.e. minimize your intake of breads, pasta, and rice
  4. Wear comfortable clothes for the scan
  5. If you think you might be pregnant, tell your doctor before undergoing the PET/CT scan
  6. If you have diabetes, you will receive specific instructions before your scan

PET/CT Procedure – What to Expect

  1. Your blood sugar will be measured when you present for your scan. Your blood sugar needs to be in the normal range or only mildly elevated (less than 200), otherwise the scan results may not be accurate
  2. An intravenous catheter will be placed in your upper extremity and your height and weight will be measured
  3. The radioactive tracer will be injected through your intravenous catheter
  4. After the tracer is injected, you will rest quietly in a comfortable chair for approximately 1 hour (uptake period). During this time the tracer will be absorbed by your organs and tissues. You will be asked to drink oral contrast material during the uptake period. This contrast material will allow your intestines to be better delineated on the CT portion of the scan
  5. After the uptake period is complete, you will be asked to void and then you will be assisted onto a narrow table that will move through the PET/CT scanner. The scan will last 15-50 minutes, depending on what part of your body is being scanned. The scan is painless, but you must lie still, otherwise the images will be blurred
  6. If you are claustrophobic, you may feel some anxiety while on the scanner. Please tell the nurse or technologist about any discomfort. Medications can be prescribed to help you feel more relaxed
  7. After the scan is complete, you will be asked to void again. This will help to flush the radioactive tracer from your body
  8. You may resume your normal routine without restrictions following the scan. You should try to drink plenty fluids for the remainder of the day to help flush the radioactive tracer from your body