Positron emission tomography Scan
Positron emission tomography (PET) is a scanning technique used in conjunction with
small amounts of radiolabeled compounds to visualize brain anatomy and function.
General information about a Positron emission tomography Scan
Positron emission tomography was the first scanning method to provide information on
brain function as well as anatomy. This information includes data on blood flow, oxygen
consumption, glucose metabolism, and concentrations of various molecules in brain tissue.
Positron emission tomography has been used to study brain activity in various
neurological diseases and disorders, including stroke; epilepsy; Alzheimer's disease,
Parkinson's disease, and Huntington's disease; and in some psychiatric disorders, such as
schizophrenia, depression, obsessive-compulsive disorder, attention-deficit/hyperactivity
disorder, and Tourette syndrome. Positron emission tomography studies have helped to
identify the brain mechanisms that operate in drug addiction, and to shed light on the
mechanisms by which individual drugs work. Positron emission tomography is also proving to
be more accurate than other methods in the diagnosis of many types of cancer. In the
treatment of cancer, Positron emission tomography can be used to determine more quickly
than conventional tests whether a given therapy is working. Positron emission tomography
scans also give accurate and detailed information on heart disease, particularly in women,
in whom breast tissue can interfere with other types of tests.
Description of Positron emission tomography Scan
A very small amount of a radiolabeled compound is inhaled by or injected into the
patient. The injected or inhaled compound accumulates in the tissue to be studied. As the
radioactive atoms in the compound decay, they release smaller particles called positrons,
which are positively charged. When a positron collides with an electron (negatively
charged), they are both annihilated, and two photons (light particles) are emitted. The
photons move in opposite directions and are picked up by the detector ring of the Positron
emission tomography scanner. A computer uses this information to generate
three-dimensional, cross-sectional images that represent the biological activity where the
radiolabeled compound has accumulated.
A related technique is called single photon emission computed tomography scan (CT scan)
(SPECT). SPECT is similar to Positron emission tomography, but the compounds used contain
heavier, longer-lived radioactive atoms that emit high-energy photons, called gamma rays,
instead of positrons. SPECT is used for many of the same applications as Positron emission
tomography, and is less expensive than Positron emission tomography, but the resulting
picture is usually less sharp than a Positron emission tomography image and reveals less
information about the brain.
Risks of Positron emission tomography Scan
Some of radioactive compounds used for Positron emission tomography or SPECT scanning
can persist for a long time in the body. Even though only a small amount is injected each
time, the long half-lives of these compounds can limit the number of times a patient can
be scanned |