Positron
Emission Tomography (PET) Scans - How It Works, How do you Prepare?,
Risks, Technology Used
(August 15th, 2008)
 Positron
emission tomography (PET) is a nuclear imaging tool that produces
a 3D map of the functional areas of the body including the lungs,
heart, chest or abdominal area as well as other internal organs.
A PET scan can help the doctor see how the tissues and organs in
your body are functioning. Unlike Magnetic Resonance Imaging (MRI),
Computed Tomography (CT) scans or X-Rays that are designed to show
visuals of the structural details of your organs, a PET scan was
designed to show chemical activities within certain organs and tissues
in your body. This chemical activity occuring in your organs may
indicates areas where tumors reside, and that other imaging techniques
have failed to detect. Thus, a Positron Emission Tomography (PET)
scan is very useful in examining a variety of conditions including
heart disease, body inflammation caused by asbestos fibers, infections
and other neurological diseases.
How Is a PET Scan Conducted?
 A
PET scan measures important body functions such as oxygen use &
transmission, metabolism, blood sugar & blood flow. This helps
doctors distinguish between abnormal & normal functioning organs
and tissues. A glucose that commonly resides in your body for energy
is mixed together with a radioactive substance called radiotracer
and injected into your bloodstream. This enables the PET scanner
detect which areas of your body are consuming more glucose. The
type of radiotracer you will be given depends on the type of organ
being studied. This is because different tissues of the body use
different types of glucose. The radiotracer gives a slight amount
of radiation exposure which is measured by the PET scanner. The
scanner will tally up how much of the radiotracer substance each
organ being studied has consumed, and thus how chemically active
it is. Organs that consume more glucose are more metabolically active
and appear brighter on the PET scan. Data from the PET scanner is
converted to images and chemical activity in your body is marked
via colors of intensity. Areas of more intense colors show high
radioactive substance use (also known as 'hot spots') Areas of low
radioactive substance use are called cold spots.
The PET scanner on which the patient is placed is shaped like a
big doughnut. The patient is given a radiotracer via an injection
that takes about 60 minutes to flow through the body into different
organs and the bloodstream. During this time, you have to stay still
and not talk. You will have no feeling of the radiotracer substance
moving around in your body. After 60 minutes, you will be moved
to the epicenter of the machine where images of your organs are
displayed on a computer on your side. The PET scanner houses several
detector rings that record the emission of energy from the radiotracer
given to the patient. This in turn helps create images of organs
of your body.
What is a PET Scan Used for?
 A
PET scan like described above is a tool to study chemical activities
in organs in your body that other imaging techniques have failed
to detect, and those that could contain malignant tumors or abnormalities.
PET scans are also used for the following:
- Determining how far the cancerous tumors have spread and how
they could possibly respond to treatment
- PET scans help determine how some cancers could respond to chemotherapy
- PET scans help detect areas of the heart where there is decreased
blood flow, and thus detect dead hurt muscles
Note: PET scans only suggest the presence of cancer, the doctors
will need to perform a biopsy on your lungs to confirm any lung
cancer
Above is image of a PET scan done on a patient's chest. Unlike
X-Rays, PET scans can help detect cancer before organ or gland enlargement
occurs, thus spreading the cancer too far (even to the lymph nodes).
The x-ray portrays the lungs & the heart as being just normal
and fine, while the PET scan assesses chemical activities within
the lungs and can help detect the cancer that has spread to nearby
lymph nodes.
Risks of Positron Emission Tomography (PET) Scans
The risks associated with radiation exposure from PET scans is
minimal. The amount of radiation in the radiotracer is not enough
to affect the normal functioning of your internal organs or strong
enough to create cancerous tissues or tumors. Thus, PET scans are
generally a safe procedure. However, pregnant women should NOT undergo
PET scans because the radiotracer may expose radiation to the fetus
of a pregnant woman or to a woman who has just given birth and is
breastfeeding, which in both cases could negatively hurt the baby.
How to Prepare for a PET Scan
- Do not eat or drink anything for 8 hours before this test
- Do not smoke or drink coffee for 24 hours before this test
- Inform your doctor if you have panic attacks or are afraid of
enclosed rooms with hospital equipment
- Inform your doctor if you are pregnant or breastfeeding a newly
born baby
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