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Emission Computed Tomography (SPECT)
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A medical imaging technique that uses small amounts of radioactive
material (radioisotopes) attached to radiopharmaceuticals to map
brain function
Single Photon
Emission Computed Tomography (SPECT) is a medical imaging technique
used for mapping brain metabolism and function. SPECT is similar
to positron emission tomography in that once the radio-pharmaceutical
is trapped in the brain, radiation is given off as a result of gamma
emission. Various radioactive pharmaceuticals are injected into
the blood and attach to targets in the brain’s gray matter
for several hours. This allows researchers to image up to several
hours after injection, yet study activity at the time of injection.
Special detectors produce pictures of the radioisotopes in the brain,
permitting scientists to distinguish between normal and abnormal
tissue. This
scanning procedure is somewhat the reverse of a traditional x-ray;
instead of the x-rays coming from outside the body, the radiation
source is inside the body.
At UT-Houston,
SPECT technology is used to study:
- Differences
in brain metabolism characteristic of conditions such as attention
deficit/hyperactivity disorder and various organic mood disorders.
- Drug-induced
changes in brain metabolism, caused by intravenous cocaine use
among drug addicts, and use of Diamox in patients who have had
strokes or obstructed blood supply to the brain, or transient
ischemic attacks. Functional significance in stenosis of the carotid
vessels can also be assessed.
- Changes
in the brain as a result of receiving a physical or psychological
stimulus or challenge (these changes can be correlated with MRI
findings).
- Localization
of regions of decreased perfusion/function, which may represent
a focus of seizure activity. Identification of such a focus can
help in surgical therapy.
Across the
country, brain SPECT has been used to study various receptors, or
groups of cells that receive stimuli. Receptors for the brain chemicals
dopamine and serotonin have been studied, as well as receptors for
opiates. Brain SPECT also can be used in identifying the location
of brain tumors and in conjunction with agents that help detect
brain tumors. The Division of Nuclear Medicine at UT-Houston, for
example, uses Thalium-201 to evaluate recurrences of brain tumors
after therapy – a process that can be very difficult with technologies
that provide only images of structures in the body, such as MRI.
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