Imaging Without Ionizing Radiation
About This Imaging Test
A positron emission tomography (PET) scan is an imaging test that allows your doctor to check for diseases in your body.
The scan uses a special dye that has radioactive tracers. These tracers are injected into a vein in your arm. Your organs and tissues then absorb the tracer. When highlighted under a PET scanner, the tracers help your doctor to see how well your organs and tissues are working. The PET scan can measure blood flow, oxygen use, glucose metabolism (how your body uses sugar), and much more.
How the Test is Performed
Before the scan, you’ll get tracers through a vein in your arm, through a solution you drink, or in a gas you inhale. Your body needs time to absorb the tracers, so you’ll wait about an hour before the scan begins.
Next, you’ll undergo the scan. This involves lying on a narrow table attached to a PET machine, which looks like a giant letter “O.” The table glides slowly into the machine so that the scan can be conducted.
You’ll need to lie still during the scan. The technician will let you know when it is that you need to remain still. You may be asked to hold your breath for short periods. You’ll hear buzzing and clicking noises during the test.
When all the necessary images have been recorded, you will slide out of the machine. The test is then complete.
How to Prepare for the Test
Your doctor will provide you with complete instructions for how to prepare for your PET scan. Tell your doctor about any prescription, over-the-counter, or supplemental medications you’re taking.
You may be instructed not to eat anything for up to eight hours before your procedure. You’ll be able to drink water, however.
If you’re pregnant or believe you could be pregnant, tell your doctor. The test may be unsafe for your baby. You should also tell your doctor about any medical conditions you have. If you have diabetes, you’ll get special instructions for test preparation because fasting beforehand could affect your blood sugar levels.
You may be asked to change into a hospital gown. You’ll also need to remove all of your jewelry and body piercings because metal can interfere with the testing equipment.
How the Test will Feel
You may feel a sharp sting when the needle with the tracer is placed into your vein.
A PET scan causes no pain. The table may be hard or cold, but you can request a blanket or pillow.
An intercom in the room allows you to speak to someone at any time.
There is no recovery time, unless you were given a medicine to relax.
Why the Test is Performed
Your doctor may order a PET scan to inspect the blood flow, oxygen intake, and metabolism of your organs and tissues. PET scans are most commonly used to detect:
- heart problems
- brain disorders
- problems with the central nervous system
Unlike other imaging tests, such as CT or MRI, PET scans show problems at the cellular level. This gives your doctor the best view of complex systemic diseases, such as:
- coronary artery disease
- brain tumors
- memory disorders
When PET is used to detect cancer, it allows your doctor to see how the cancer metabolizes, and whether it has spread, or metastasized, to new areas. PET also shows how the tumor is responding to chemotherapy.
After the Scan
After the test, you can go about your day unless your doctor gives you other instructions. Drink plenty of fluids after the test to help flush the tracers out of your system. Generally, all tracers leave your body after two days.
Meanwhile, a trained specialist will interpret the PET images and share the information with your doctor. Your doctor will go over the results with you at your follow-up appointment.
A normal result means there were no problems seen in the size, shape, or position of an organ. There are no areas in which the tracer has abnormally collected.
What Abnormal Results Mean
Abnormal results depend on the part of the body being studied. Abnormal results may be due to:
- Change in the size, shape, or position of an organ
- Problem with organ function
The PET scan involves radioactive tracers, but the exposure to harmful radiation is minimal. Radiation levels are too low to affect normal processes in your body. The risks of the test are minimal compared with how beneficial the results can be in diagnosing serious medical conditions.
However, radiation is not considered safe for developing fetuses. If you’re pregnant, think you may be pregnant, or you’re breast-feeding, you shouldn’t get a PET scan.
Other risks of the test include discomfort if you’re claustrophobic or uncomfortable with needles. It’s also possible to have an allergic reaction to the tracers. You should tell your doctor if you’ve experienced an allergic reaction during a PET scan before.
It is possible to have false results on a PET scan. Blood sugar or insulin levels may affect the test results in people with diabetes.
Most PET scans are now performed along with a CT scan. This combination scan is called a PET/CT. This helps find the exact location of the tumor.