Positron emission tomography (PET) is a test
that uses a special type of camera and a
tracer (radioactive substance) to look at organs
body. The tracer usually is a special form of a substance (such as glucose) that
collects in cells that are using a lot of energy, such as cancer cells.
the test, the tracer liquid is put into a vein
IV) in your arm. The tracer moves through your
where much of it collects in the specific organ or tissue. The tracer gives off
tiny positively charged particles (positrons). The camera records the positrons
and turns the recording into pictures on a computer.
Find changes in the brain
that may cause
Evaluate the extent of some
lymphoma or cancers of the head and neck, brain,
or prostate. In its early stages, cancer may show up more clearly on a PET scan
than on a CT scan or an MRI.
Determine whether a growth in an organ or
in tissue is likely to be cancer, such as a growth in lung tissue.
advanced a cancer is and
whether it has spread to another area of the body (metastasized). It is often
necessary to do both CT and PET scans to evaluate cancer.
doctor choose the best treatment for cancer or to see how well treatment is working.
PET scans may also be done to see
whether surgery can be done to remove a tumor.
Help diagnose Alzheimer's disease when the symptoms are not
clear or when a person has dementia symptoms at a young age (usually younger than
65).footnote 1 This is called amyloid
diabetes. If you take
medicine to control diabetes, you may need to take less
than your normal dose. Talk with your doctor about how much
medicine you should take.
You take any medicines, supplements, or herbal
remedies. You may need to
stop taking some medicines or change your dose before this
You are or might be
You are breastfeeding. The radioactive tracer used in this test
can get into your breast milk. Do not breastfeed your baby for 2 days after this test.
During this time, you can give your baby breast milk you stored before the test, or
you can give formula. Discard the breast milk you pump for 2 days after the test.
have a fear of enclosed spaces.
Do not smoke or drink caffeine or
alcohol for 24
hours before this test.
Do not eat or drink (except water) for at least
6 hours before this test.
You may be asked to sign a consent form.
to your doctor about any concerns you have regarding the need for the
test, its risks, how it will be done or what the results mean. To help you
understand the importance of this test, fill out the
medical test information form(What is a
It Is Done
A positron emission tomography (PET)
scan is done in a hospital nuclear medicine department or at a special PET
center by a
nuclear medicine specialist and a technologist.
will lie on a table that is hooked to a large scanner, camera, and
During the test
radioactive tracer is usually given in a vein
(IV). You may need to wait 30 to 60 minutes for the tracer to move through your
body. During this time, you may need to avoid moving and talking.
The PET scanner,
which is shaped like a doughnut, moves
around you. The scanned pictures are sent to a computer screen so your doctor
can see them. Many scans are done to make a series of pictures. It is very
important to lie still while each scan is being done. At some medical centers,
a CT scan will be done at the same time.
For a PET scan of the
brain, you will lie on a bed. You may be asked to read, name letters, or tell
story, depending on whether speech, reasoning, or memory is being tested.
During the scan, you may be given earplugs and a blindfold (if you do not need
to read during the test) to wear for your comfort.
During the test, you will be alone in the scanner room. The
technologist will watch you through a window and you will be able talk to him
or her through a two-way intercom at all times.
The test takes 1
to 3 hours.
After the test
test, drink lots of fluids for the next 24
hours to help flush the tracer out of your body.
How It Feels
will not feel pain during the test.
The table you lie on may be hard and the room may be cool. It may be difficult
to lie still during the test.
You may feel a quick sting or pinch
when the IV is put in your arm. The tracer is unlikely to cause any side effects.
If you don't feel well during or after the test, tell the person who is doing the
You may feel nervous inside the PET
There is always a slight chance of damage to
cells or tissue from radiation, including the low levels of radiation used for
this test. But the chance of damage is usually very low compared with the
benefits of the test.
Most of the tracer will be flushed from your
body within 6 to 24 hours.
Allergic reactions to the tracer are very rare.
rare cases, some soreness or swelling may develop at the IV site where
the radioactive tracer was put in. Apply a moist, warm compress to your
Positron emission tomography (PET) is a
test that uses a special type of camera and a
tracer (radioactive substance) to look at organs
radiologist may discuss preliminary results
of the PET
scan with you right after the test. Complete results are usually available in
to 2 days.
Positron emission tomography (PET)
Blood flow is normal
and organs are working
well. The flow and pattern of the tracer shows normal distribution in the
blood flow and increased
metabolism may show that the blood vessels are
narrowed or blocked. This may mean
coronary artery disease (CAD) is
Decreased blood flow and glucose metabolism may mean that
heart tissue is scarred and damaged, such as from a
Areas of increased glucose
lower oxygen use and blood flow may mean you have
Decreased oxygen use and blood
flow may mean a
stroke has occurred.
Taking medicines, such as
insulin, that change your
Having recently had surgery, a
What To Think About
CT scan and PET scan are often done at the same
Johnson KA, et al. (2013). Appropriate use criteria for amyloid
PET: A report of the Amyloid Imaging Task Force, the Society of Nuclear Medicine and
Molecular Imaging, and the Alzheimer's Association. Alzheimer's and Dementia, 9(1):
Other Works Consulted
FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed.
Philadelphia: Lippincott Williams and Wilkins.
Pagana KD, Pagana TJ (2010).
Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby.
ByHealthwise Staff Primary
Medical ReviewerAdam Husney, MD - Family Medicine E. Gregory Thompson, MD - Internal Medicine Martin
J. Gabica, MD - Family Medicine Kathleen Romito,
MD - Family Medicine Specialist Medical ReviewerHoward Schaff, MD - Diagnostic Radiology
Johnson KA, et al.
(2013). Appropriate use criteria for amyloid PET: A report of the Amyloid Imaging
Task Force, the Society of Nuclear Medicine and Molecular Imaging, and the Alzheimer's
Association. Alzheimer's and Dementia, 9(1): e1-e16.
This information does not replace the advice of a doctor.
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