MRI
Improves Acute Stroke Diagnosis
Comparison of two imaging techniques for the emergency diagnosis
of acute stroke shows that magnetic resonance imaging (MRI) can provide a more
sensitive diagnosis than computed tomography (CT) for acute ischemic stroke,
according to a report in The Lancet.
An MRI was better at detecting acute ischemic stroke - the
most common form of stroke, which is caused by a blood clot in the brain.
The study was conducted by physicians at the National
Institute of Neurological Disorders and Stroke (NINDS).
“These NIH research
findings on acute stroke imaging are directly applicable to real-world clinical
practice,” says National Institutes of Health
(NIH) Director Dr. Elias A. Zerhouni. “The patients involved in
this study were the typical cross-section of suspected stroke patients that
come into emergency rooms on a daily basis.”
The study has good news for patients, according to Dr. Walter
J. Koroshetz, NINDS deputy director.
“This study shows that approximately 25 percent of
stroke patients who come to the hospital within three hours of onset, the time
frame for approved clot-busting therapy, have no detectable signs of damage," says
Dr. Koroshetz.
"In other words, brain injury may be completely avoided
in some stroke victims by quick re-opening of the blocked blood vessel," he
says.
The researchers conducted the study to determine whether
MRI was superior to CT for emergency diagnosis of acute ischemic and hemorrhagic
stroke (caused by bleeding into the brain).
Standard CT uses x-rays that are passed through the body
at different angles and processed by a computer as cross-sectional images,
or slices, of the internal structure of the body or organ.
Standard MRI uses computer-generated radio waves and a powerful
magnet to produce detailed slices or three-dimensional images of body structures
and nerves. A contrast dye may be used in both imaging techniques to enhance
visibility of certain areas or tissues.
Study results show immediate non-contrast MRI is about five
times more sensitive than and twice as accurate as immediate non-contrast CT
for diagnosing ischemic stroke.
Non-contrast CT and MRI were equally effective in the diagnosis
of acute intracranial hemorrhage.
Non-contrast CT has been the standard in emergency stroke
treatment, primarily to exclude hemorrhagic stroke, which cannot be treated
with clot-busting therapies.
“Many patients who come to hospitals with a suspected
stroke ultimately have a different diagnosis," says Dr. Steven Warach, director
of the NINDS Stroke Diagnostics and Therapeutic
Section and senior investigator of the study.
"Most possible stroke victims are first evaluated by non-specialists,
who may be reluctant to treat a patient for stroke without greater confidence
in the accuracy of the diagnosis," he says.
"Our results show
that MRI is twice as accurate in distinguishing stroke from non-stroke. Based
on these results, MRI should become the preferred
imaging technique for diagnosing patients with acute stroke.”
Study leaders hope that because of its increased diagnostic
accuracy, MRI may lead to better patient outcomes and ultimately decrease the
cost of stroke care, through increased use of acute treatments and earlier
initiation of secondary prevention.
“Although MRI is remarkably accurate in detecting
early stroke damage, it can’t substitute for a doctor’s clinical
judgment in making a stroke diagnosis and deciding upon treatment,” notes
Dr. Koroshetz.
“Future studies are needed to determine whether advanced
contrast enhanced CT techniques can afford the same level of clinical information
more quickly and with less expense," he says.
Always consult your physician for more information.
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