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relating to advanced medical imaging.
Introduction to
Positive Emission Tomography (PET)
Positron Emission Tomography (PET) provides physicians with
information about the body's chemistry not available through
any other procedure. Unlike CT or MRI, which look
at anatomy or body form, PET studies metabolic activity
or body function. PET has been used primarily in cardiology,
neurology, and oncology. In particular, it has
been used to assess the benefit of coronary artery bypass
surgery, identify causes of childhood seizures and
adult dementia, and detect and grade tumors.
In
PET the patient receives a short, half-lived radiopharmaceutical
(produced by a cyclotron or a generator). Because the radioisotope
used in a PET scan is short-lived, the amount of radiation
exposure the patient receives is about the same as from two chest
X-rays. The radiopharmaceuticals discharge positrons from wherever
they are used in the body. As the positrons encounter electrons
within the body, a reaction producing gamma rays occurs.
The patient lies on a table that
slides into the middle of the scanner. Within the scanner are
rings of detectors containing special crystals that produce light
when struck by a gamma ray. The scanner's electronics record
these detected gamma rays and map an image of the area where
the radiopharmaceutical is located. Since the radiopharmaceutical
contains a chemical commonly used by the body, PET enables
the physician to see the location of the metabolic process. For
example, glucose (or sugar, which the body uses to produces energy)
combined with a radioisotope will show where glucose is being
used in the brain, the heart muscle, or a growing tumor. |