CT
Scan Radiation May Affect Kids' IQ
Children who suffer a head injury are
often routinely examined by a CT scan. Now, a Swedish team has
found that radiation doses typically delivered by such a scan
during infancy may harm intellectual capacity later in life.
While high doses of radiation to
the developing human brain are known to cause mental retardation,
it was not known if exposure to low doses "has more subtle effects
on cognitive function," Dr. Per Hall from the Karolinska Institute
in Stockholm and colleagues write in this week's British Medical
Journal.
To investigate, they analyzed mental
function and education in roughly 3000 18- to 19-year-old men
who had been given relatively low doses of radiation before the
age of 18 months to treat a type of birthmark called a cutaneous
hemangioma.
Hall's group classified the subjects
into four radiation dose categories, measured in milligrays (mGy):
1-20, 21-100, 101-250, and over 250 mGy.
They discovered that the percentage
of boys who attended high school decreased with radiation doses
greater than 100 mGy compared with the lowest dose of 1-20 mGy.
The proportion of high school attendees decreased from roughly
32 percent among those with no exposure to radiation, to 17 percent
among those who received > 250 mGy.
Radiation of the brain during infancy
also had a negative effect on tests of learning ability and logical
reasoning but not on tests of spatial recognition.
It is estimated that a head CT
scan performed on an infant imparts a radiation dose of about
120 mGy.
"Irradiation of the brain with
dose levels overlapping those imparted by CT can, in at least
some instances, adversely affect intellectual development," Hall
and colleagues write.
Based on their findings, they think
that "the risks and benefits of CT scans in minor head trauma
need re-evaluating."
SOURCE: British Medical Journal,
January 3, 2004.
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