There is an increasing role for Positron Emission Tomography (PET scan) in the diagnostic evaluation of many types of cancer. This noninvasive technique provides additional information not offered by other diagnostic examinations. PET is also being applied in the neurologic evaluation of seizures and Alzheimer's disease. PET can improve the decision-making process before cardiac surgery in selected patients, as well.

What is a PET scan?

Positron Emission Tomography is chiefly used to provide a map of glucose use in the various tissues of the body. Glucose is a simple sugar that is a main energy source for human cells. A modified form of glucose known as flurodeoxyglucose (FDG) contains a positron emitter whose energy can be recorded on a crystal outside the patient. The recorded emissions provide a three-dimensional map of how glucose is used throughout the body. Cancer cells most often use glucose more rapidly than normal cells and can be higlighted as brighter areas on the map.

How is PET unique?

Conventional cross-sectional imaging studies such as CT, MRI and ultrasound scans create images of the body's structure and make pictures of the size and shape of normal and diseased anatomic structures.

The PET scan provides information about cell function, much different from the structural information provided by conventional imaging studies. "The combination of the anatomic and functional information can be very complementary and powerful in a cancer diagnosis," states radiologist Robert M. Schick, M.D., John Muir Health.

How is the PET scan done?

The PET scan requires a fasting, rested individual to receive an injection of the fluorodeoxyglucose into a small vein in the arm. During a period of quiet rest, the injected FDG is permitted to distribute itself within the cells of the body. Patients who are anxious may ask their physician to provide a preprocedure mild and short-acting anxiety-relieving medication. There is no sensation associated with the FDG injection. Following the injection, the patient lies quietly on a table that moves through a doughnut-shaped opening, where the information is detected and recorded. Nothing contacts the patient during this process. The entire experience takes less than an hour.

Is the procedure safe?

Although there are no known harmful effects from the procedure, there is some radiation exposure associated with the test. Therefore, it is not performed on pregnant patients or those who might be pregnant. The radioactive tracer injected for the PET scan has an extremely short life, changing rapidly to a nonradioactive and inert material by the time the patient leaves the scanning facility. As a result, there is no radiation risk for family members and no restrictions on patient activity following the scan.

Who can benefit from a PET scan?

PET scans are helpful in detecting sites of cancer in the lung, especially in situations where a small shadow of unknown cause is discovered. In patients with known cancer, a PET scan can provide more complete information regarding the extent of cancer throughout the body, permitting improved decision making regarding treatment. Physicians already incorporate PET scanning into their assessment strategies for lung cancer, melanoma, colon and rectal cancer, and lymphoma. "PET promises to be the single most important diagnostic test for early assessment of a patient's response to chemotherapy. It will help determine if the chemotherapy is effective or needs to be supplemented or changed," states radiologist Richard M. Sigel, M.D., John Muir Health. There is increasing evidence for the efficacy of PET in evaluating patients with head and neck cancer, esophageal cancer, ovarian cancer and advanced breast cancer. PET can also be a problem-solver for patients with confusing or contradictory results on conventional imaging studies and can help reduce the need for diagnostic surgical procedures.

PET in Neurologic and Cardiac Diagnosis

A PET scan of the brain in patients with dementia can differentiate a typical pattern for Alzheimer's disease from other causes of premature senility. As treatments improve for Alzheimer's disease, this diagnostic capability will become increasingly useful. PET can provide unique information regarding the source of intractable and disabling seizures in selected patients being considered for epilepsy surgery. PET can also assist in the selection of patients for cardiac surgery by most accurately defining the extent of viable heart muscle.

Resource Directory

For the new Spring/Summer resource directory listing information about medical imaging including PET scan services at John Muir Medical Center, Walnut Creek Campus and John Muir Medical Center, Concord Campus, and a variety of other programs and services, call: (925) 947-5384

Physician Referral and Information Services

For a referral to a physician on staff, call John Muir Health Physician Referral Service at (925) 941-2244.