What is Positron Emission Tomography (PET)?

Positron emission tomography (PET) is a technique most commonly used for imaging metabolic activity in the human subject. It is different from CT (x-ray computed tomography) and MRI (magnetic resonance imaging), which mainly image anatomic structure.

PET looks at function, or physiology. Many times physiologic changes occur before anatomical changes, so we may see changes in physiology before they have caused any structural damage, increasing the chance to avert such damage.

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How does it work?

A small amount of a radioactively labeled pharmaceutical (or radiotracer) is injected into the patient, the patient sits quietly while the radiotracer circulates through the body and the patient is then imaged to see where in the body the radiotracer went. The most commonly used radiotracer is FDG, which is a radio-labelled glucose that the body uses as it would any other sugar. This radioactive glucose is taken up in metabolically active areas and a PET scan can show a physician the metabolically active areas.

Why do we do these scans?

The most common use for PET scans is for cancer imaging. Many cancer cells tend to be very metabolically active, much more so than surrounding healthy tissue, so a tumor tends to use more of the injected FDG (radioactive sugar) than surrounding tissue and can be seen by physicians reading the PET images.

Some of the ways PET scans can be used in cancer imaging are: to diagnose new cancers, to determine if and how much cancer has spread, to measure the response to treatment, or to assist in the treatment planning process for radiation oncology.

Other uses of PET scanning include: in cardiac imaging to determine areas of low blood flow or low metabolic activity, or in brain imaging to determine the foci of seizures or the presence of neurodegenerative disease.

How long will the radioactivity stay in my system?

Most PET radioisotopes are very short-lived (two minutes - two hour half-life) and small amounts are injected. In most cases very little or no activity remain in your body 10 minutes to eight hours after injection. For the most commonly used radiotracer, [F-18]FDG, most will be gone from your system eight hours after injection.

What types of scanners do we use?

Currently, there are three PET and PET/CT scanners in use:

  • Philips Allegro
  • Philips Gemini TF
  • Philips Gemini TF BigBore

What is a typical PET scan like?

A typical PET scan will last between 15 and 45 minutes, but can take up to 75 minutes if the entire body needs to be scanned. The patients will be asked to lie on their backs and remain as motionless as possible for the duration of the study. Generally, the patients' arms are raised above their heads for optimal thoracic imaging quality, however, if the entire body needs to be scanned or if a patient is unable to hold his or her arms above his or her head, the arms will be crossed over the adomen.

In the case of a PET/CT study, the patient will receive a low-dose CT for anatomic correlation, followed by the PET scan. The PET scan is acquired as a series of several distinct bed motions, called bed positions (usually 8-10 for a standard body scan). At each bed position, the scanner acquires for a set amount of time (between 1.5 and 3 minutes for body studies), then moves approximately 9 cm and begins acquiring the next bed position. All of these individual frames are then knitted together to form the final image that the phsyicians will interpret.

How do I schedule a PET scan?

Click here for information about ordering PET studies.