A positron emission tomography scan is a safe and effective way to measure the amount of physiological activity in different parts of your body. This information can be used to diagnose diseases, such as cancer, heart disease and brain disorders. PET also is used to monitor the progress of treatments for these illnesses.
Unlike other types of medical imaging that display the body’s structure, PET shows metabolism and other physical processes. Metabolism is when your body burns a fuel such as sugar to make energy. A cancerous tissue, for example, needs more energy than normal tissues, and it will appear as a bright spot on the PET scan. Damaged heart tissue, on the other hand, won’t burn any fuel, so it looks darker than normal heart tissue.
For a PET scan, the patient is injected with a substance, often a sugar, that is specially marked or tagged with a radioactive isotope. When this tag gives off energy, it makes a signal that the PET scanner can pick up. Then a computer combines the signals from all over your body to make a picture.
Your PET exam will take about two or three hours. You will be asked not to eat or drink anything for four to 12 hours before coming to the appointment. If you eat, your muscles will burn the energy in the food, and the activity will show up on the PET scan as extra brightness. This can cover up important information on the image. However, you can drink plenty of water. You also may be asked not to smoke for a day before the exam. Normally, you can wear your regular clothing for the scan, but avoid wearing metal, such as jewelry, buckles and metal buttons.
Before your exam, a nuclear medicine technologist — a skilled medical professional who has received specialized education in patient care, radiation protection, radiopharmaceuticals and nuclear medicine techniques — will explain the procedure and answer any questions you might have.
The technologist then will give you a small injection (about a quarter of a teaspoon) of the radioactive tagged solution. The radioactive tag has a very short half-life, meaning that the radiation disappears quickly. The radioactivity will not last more than a few hours, and you’ll receive no more radiation from a PET scan than you would on a plane flight from Denver to Los Angeles.
After the injection, you’ll have a 45-minute to one-hour wait. During that time, you can read, watch TV or relax in a quiet room. This is to minimize the amount of activity in your muscles, so that the PET scan results are easier to see. At some facilities, you may have other imaging exams during this time, such as a computed tomography scan. The results of these tests can be combined with your PET scan to get even more information.
During the Examination
You will lie on the exam table, which will slowly move through the PET scanner. The machine is very open, and most people do not feel confined or uncomfortable. Three sensors rotate around you during the scan, and you might hear a high-pitched whine. You will need to lie very still during the exam. The technologist will be available throughout the procedure.
Information After the exam, your scans will be reviewed by a radiologist or nuclear medicine physician, specialists in interpreting diagnostic medical images, and your personal physician will receive a report of the findings. Your physician then will discuss the results with you and the need for further treatment, if any.
Once the exam is done, you can eat and resume your daily activities. You will pass the tagged solution out of your body in your urine without noticing anything.