Guide to PET Scans.

What is a PET Scan?

A positron emission tomography scan referred to as PET scan for short is a type of diagnostic imaging scan. A PET scan is a unique medical imaging scan in that it identifies abnormal metabolic activity, which helps your doctor see how tissues and organs are functioning.

A PET scan involves an injection of a glucose solution with a radioactive component, which is referred to as a radiotracer. The radiotracer moves through your body and is absorbed by the tissues and organs and gives off energy. The energy is detected by the machine, and a camera creates 3-d images of organs and tissues in the body. It is often combined with a CT scan to determine exactly where in the body abnormal metabolic activity is occurring.

What to Expect During a PET Scan?

When you arrive for your PET scan, you may be asked to change into a hospital gown. Your blood sugar level will be checked before the procedure. Next, a radioactive tracer is administered. The technician will start an IV line, and a small amount of the tracer will be injected into your body.

The tracer needs to circulate through the body, which takes about 45 to 90 minutes. During this time, you can sit back and relax. After that, you will move to the scanner room, where you lie on a table. The table moves into a large tunnel-like scanner.  The scanner takes pictures from your head to your toes or vice versa.

Usually, the majority of the time your head is out in the open. During the test, you are required to stay as still as possible to get the most accurate images.

How Long Does a PET Scan Take?  

Your appointment for a PET scan takes anywhere from two to three hours. The first hour to an hour and a half involves administration of the tracer and time to allow it to be absorbed. The actual scanning time varies depending on what body part is being scanned. Typically the scan takes between 30 minutes to an hour.   

Why is a PET Scan Done?

A PET scan may be done for a variety of reasons. It’s commonly used for oncology patients. For instance, it may be performed to determine if cancer has spread or to access how effective a treatment plan is.

But a PET scan is also used in other areas of medicine, such as cardiology. For example, it may be performed to check blood flow to the heart and determine the effects of a heart attack. It is also used in the field of neurology to evaluate abnormalities of the brain, such as seizures and Alzheimer’s disease. 

Preparations Required by the Patient

Specific instructions before a PET scan may vary, so it’s essential to follow your doctor’s instructions. Typically, patients are asked to fast for six to eight hours before the test and avoiding drinking beverages with sugar. You are allowed to drink water.

Your doctor may also ask you to avoid exercise for about 24 hours before the exam. Eating certain foods and exercising can both interfere with the way the tracer is absorbed by the body.

There may be additional instructions. For instance, you may be told to limit the amount of sugar or carbohydrates you eat 24 hours before the scan. If you are a diabetic, you may get special instructors from your doctor on when to take your insulin.


Does a PET scan hurt? The only pain associated with a PET scan is from the needle being inserted into your arm so the radiopharmaceutical can be administered. The scan itself is painless.

How long does the radioactive material stay in the body? The radioactive material decays relatively fast. In addition, the radiopharmaceutical is eliminated when you urinate. Usually, within a few hours, the radioactivity is not detectable.

What happens after the procedure? Unless your doctor instructs you otherwise, you can usually eat and drink normally and return to your regular activities after the scan. You will also be encouraged to drink plenty of fluids to help flush the tracer from your body.

Is a PET scan safe? Having radioactive material injected into your body may sound frightening. But the chemicals used are considered safe and leave your body quickly.

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