What is a Positron Emission Tomography exam?

Positron Emission Tomography (PET) is a nuclear medicine procedure that produces pictures of the body’s biological functions. PET is a unique diagnostic imaging modality that is capable of detecting certain diseases before other imaging modalities such as: computed tomography (CT) and magnetic resonance imaging (MRI). PET is able to capture chemical and physiological changes related to metabolism, as opposed to gross anatomy and structure, which is obtained by CT and MRI. This is important since function changes are often present before structural changes in tissues. PET images may therefore demonstrate pathological changes long before they would be evident in CT or MRI.


How do I prepare for a PET scan?

Your physician will advise on eating or drinking prior to your exam, but typically, you will be asked not to eat or drink anything four to six hours before the exam. During the exam itself, you should wear comfortable clothes and take any prescribed medications on the day of the exam unless instructed not to do so by your physician.


May I eat or drink before the PET scan?

This will depend on the type of study, but typically, you will be asked not to eat or drink anything four to six hours before the exam. If you are a diabetic, please notify the individual who is scheduling your PET exam. Special arrangements may need to be made in advance.


What can I expect during the PET scan?

Before the scan, you will be injected with a radioactive tracer. The tracer is a compound such as sugar, labeled with a short-lived radioisotope. Once injected, you will be asked to rest for approximately thirty to forty-five minutes while the radioactive compound distributes throughout your body, and is processed by the organs being evaluated. The radiation exposure associated with PET is safe and much lower than that associated with conventional CT scanning. The technologist will ask you to lie on the scanner table, which will then slowly pass through the PET scanner. The PET scanner detects and records the signals the tracers emit. The signals are then reassembled into actual images through a computer.


What is a radiopharmaceutical?

A radiopharmaceutical is a radioactive drug. The most commonly used PET radiopharmaceutical is FDG, which is a radioactive form of glucose (sugar). Radiopharmaceuticals are produced by physicists and chemists.


What is FDG?

FDG (Fluoro Deoxyglucose is a type of glucose (sugar) and is the most commonly radiopharmaceutical used in PET. To begin the PET procedure a small amount of glucose is injected into a patient's bloodstream. There is no danger to you from this injection. Glucose is a common substance that every cell in your body needs in order to function. Diabetic patients need not worry; it would take 1,000,000 doses of FDG to equal the glucose in 1 teaspoon of sugar.

FDG has a half-life of approximately 110 minutes and is excreted by way of the kidneys, so it is quickly expelled from your body. FDG must pass multiple quality control measures before it is used for any patient injection.


Is PET Safe?

There are no known side effects associated with PET scanning. The injection is made up of radioactive glucose (sugar).

A PET scan provides an approximately equivalent amount of radiation exposure as several chest x-rays. To put this into perspective, the average person typically is exposed to the rough equivalent of 5-6 chest x-rays per year just through normal daily activities.


How long will my PET scan take?

Every PET exam is different, but most patients can expect to be at the hospital or imaging center for at least two hours. This includes the time needed for the injected tracer to distribute throughout your body, as well as the time you actually spend moving through the PET scanner. The exact length of your exam will be determined by the type of study being performed.


What will happen following my PET scan?

After your scan, you will get up from the scanner bed and check out with the receptionist. You should feel fine following your PET scan. There are no known side effects from the injected tracer. You will be notified when your results will be available to your physician.


How do I find out the results of my PET scan?

Your PET scan will be reviewed by a radiologist or nuclear medicine physician. The radiologist or nuclear medicine physician will send a report to your physicians, who will give you the results of the scan.


Are there potential side effects to a PET scan?

No, there are no known side effects to having a PET scan performed. The only pain involved is the needle prick when you receive the radiopharmaceutical injection, which doesn't differ from any other type of injection.


Are there alternatives to PET?

Yes and no. There are some molecular imaging tests nuclear medicine tests, like Gallium 67 (used for Lymphoma imaging) that are used in oncology but there is no other biological imaging test that provides the sensitivity, specificity, accuracy and whole body tomographic surveying capabilities of PET.

CT and MRI, for example, both examine the anatomical (physical) structure. Therefore, they can be useful in determining the size and location of a tumor; however, neither of them can determine the tumor's viability, whereas PET can determine whether a tumor is still active.


What should I do if my physician doesn't know about PET or if he or she doesn't want me to have a PET scan?
If your physician doesn't know about PET, you can direct them to this website for additional information. You can have additional information mailed to your physician by
clicking here and filing out the attached form with their contact information.


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Why is PET not well known? Why have I never heard of PET before?
PET has been used clinically for the last 14 years but Medicare has only recently begun reimbursing for the studies. Because of the reimbursement issues many physicians did not know or fully understand the benefits of a PET scan.


How many PET studies are performed per year?


Approximately 350,000 PET scans will be performed in 2002. The numbers of scans are increasing dramatically, now that PET is no longer only for research purposes.

It is estimated that within the next five years, in excess of 2,000,000 PET scans will be performed per year.