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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.
A PET scan is typically an outpatient procedure. This means you can go about your day after the test is finished.
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:
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:
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.
The PET scan involves radioactive tracers, but the exposure to harmful radiation is minimal. According to the Mayo Clinic, 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. The tracer is essentially glucose (sugar) with the radioactive component attached. This makes it very easy for your body to eliminate the tracers, even if you have a history of kidney disease or diabetes.
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.
There are times that, in order to get a more thorough image, a PET scan is combined with a CT scan (computerized tomography scan). If additional radioactive tracer is needed for the CT scan, it can be harmful to people who have kidney disease or who have elevated creatinine level from other medications they are already taking
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.
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.
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.
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.
Written by: Brian Krans
Medically reviewed on: Nov 02, 2015: Steven Kim, MD
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