Understanding Positron Emission Tomography (PET Scan)
How many times have you heard these terms:
CT, CAT scan, MRI, or PET scan? These types
of radiology tests are routinely ordered during
the diagnosis and treatment of cancer.
To help patients and their families better understand the various
imaging techniques, the Joan Karnell Cancer Center newsletter presents
a new series, Understanding the ABC's of Imaging. This
issue features Positron Emission Tomography.
Emission Tomography (PET) is a scan which provides diagnostic
information unavailable from other imaging
tests, such as computed
tomography (CT) or magnetic
resonance imaging (MRI). An MRI or CT provides images of the
physical structure of the body. A PET scan
provides imaging that shows how the body's organ systems function
and how cells grow.
PET is able to show whether tissue is normal
or abnormal based on cellular metabolism. This
information allows the doctor to assess chemical and physiological
changes related to metabolism. Because metabolic changes appear before
anatomic changes, PET images can show changes long before they are
visible on a CT or MRI.
PET can precisely locate a tumor, tell if it is benign or malignant,
and measure response to chemotherapy and/or radiation. In addition,
it is used to help diagnose many neurological problems, such as Alzheimer's
disease and epilepsy, and to identify certain types of coronary heart
Preparing for a PET Scan
A PET scan is painless and takes approximately
two hours to complete. You should not do any strenuous exercising
for 24 hours prior to the test. In regards to eating, patients must
fast overnight or for at least six hours prior to the test. Diabetic
patients should contact the PET center for more specific instructions.
Everyone should drink plenty of water before and during the fast.
The PET scan procedure begins with a simple injection of flourodeoxyglucose
(FDG). This is a radiopharmaceutical that resembles glucose (sugar)
already in your body. The FDG gives off signals which are picked up
by the scanner. You will be asked to rest quietly while the FDG circulates
throughout your body. You will then be positioned on the scanning
bed. You must remain still as the images of your body are acquired.
The imaging time usually takes 35-45 minutes.
The future for PET is extremely promising. New advances allow the
PET and CT images to be used together to provide doctors with even
more accurate information on the location of tumors. This information
can be used to plan surgery and in radiation treatment. PET/CT fusion
are already available at Pennsylvania Hospital.
For more information, see these answers to frequently asked questions:
How much radiation exposure does a PET scan produce?
Because the radioisotope used in a PET scan is short-lived, the amount
of radiation exposure the patient receives is the same as from two
Do people experience any reactions as a result of a PET scan?
Patients typically do not experience any reactions as a result of the
PET scan because the tracer material is processed by the body naturally.
Therefore, no side effects are expected.
I've only heard about PET scans recently. Are they new?
PET has been used for more than 30 years. However, only a few institutions
had access to this powerful diagnostic tool. As the technology expands,
this diagnostic tool is becoming more widely available.
Will my insurance cover PET?
Coverage of PET is limited. By itself, PET is an expensive test. Contact
your insurance provider to not only learn if PET is covered, but also
to determine which procedures are covered and under what circustances.