What is a PET scan?
A positron emission tomography (PET) scan is an imaging test that can help reveal how your tissues and organs are functioning. A small amount of radioactive material is necessary to show this activity.
The precise type of radioactive material and its delivery method depend on which organ or tissue is being studied by the PET scan. The radioactive material may be injected into a vein, inhaled or swallowed.
More radioactive material accumulates in areas that have higher levels of chemical activity. This often corresponds to areas of disease and shows up as brighter spots on the PET scan. A PET scan is useful in evaluating a variety of conditions — including neurological problems, heart disease and cancer.
Why is it done?
A PET scan is an effective way to examine the chemical activity in certain parts of your body, which may help detect abnormalities in those areas. PET scans are most often used in people who have cancer, heart disease or brain disorders.
Cancer cells show up as brighter spots on PET scans because they have a higher metabolism rate than do normal cells. PET scans may be useful in determining:
- The extent or spread of certain cancers
- How well the cancer is responding to treatment
- If the cancer has recurred
PET scans must be interpreted carefully because noncancerous conditions can resemble 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:
Doctors use PET scanning to detect areas of decreased blood flow in the heart. This can help show which areas of the heart might benefit from angioplasty or coronary artery bypass surgery.
A PET scan can show which areas of the brain have the most activity during various tasks. This technology also can evaluate specific brain abnormalities, such as:
- Memory disorders
Although a radioactive substance is used during a PET scan, the amount of radiation that you're exposed to is too low to affect the normal processes of your body.
However, this radioactive material might harm the fetus of a pregnant woman. You and your doctor can discuss risk to the fetus or infant versus the reasoning and benefit of having a PET scan
A PET scan can compare brain activity during periods of depression (left) with normal brain activity (right). An increase of blue and green colors, along with decreased white and yellow areas, shows decreased brain activity due to depression.
This PET image shows an area of reduced blood flow from one of the arteries that feed the heart. This information may help doctors decide whether to suggest bypass surgery or angioplasty to restore that blood flow.
Combining a PET scan with an MRI or CT scan can help make the images easier to interpret. At left is a CT scan, while the center image is from a PET scanner. The image on the right is a combined CT-PET scan. The bright spot in the chest is lung cancer.