Medical Imaging News

February 14, 2007

MRI Better at Diagnosing Form of Acute Stroke

When diagnosing acute ischemic stroke, noncontrast MRI should be the immediate choice, according to a recent study conducted by researchers at the National Institute of Neurological Disorders and Stroke (NINDS), a division of the National Institutes of Health (NIH). NINDS is the nation's primary funder of research on the brain and nervous system.

The study, the most comprehensive to-date comparing MRI to CT for the emergency diagnosis of suspected acute stroke, determined that noncontrast MRI is about 5 times more sensitive than and twice as accurate as immediate noncontrast CT for diagnosing ischemic stroke. MRI appears to be a more sensitive test in detecting the most common form of stroke as well as for diagnosing hemorrhagic strokes. MRI and CT were found to be equally effective in detecting acute intracranial hemorrhage, according to the study.

"Our results show that MRI is twice as accurate in distinguishing stroke from nonstroke," said Steven Warach, MD, PhD, director of the NINDS stroke diagnostics and therapeutic section and senior investigator of the study. "Based on these results, MRI should become the preferred imaging technique for diagnosing patients with acute stroke."

For the study, 356 consecutive patients with suspected stroke received emergency clinical assessments, including the NIH Stroke Scale, by stroke specialists. An MRI was performed prior to CT in 304 patients, with no more than 2 hours passing between exams; the median difference was 34 minutes. Resulting images were sorted randomly and independently by two neuroradiologists and two stroke neurologists.

The four readers were unanimous in their agreement on the presence or absence of acute stroke in 80% of patients using MRI compared to 58% using noncontrast CT. No significant difference using the two technologies was seen in the diagnosis of acute intracranial hemorrhage, which is consistent with previous findings.

"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," said NINDS Deputy Director Walter J. Koroshetz, MD. "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."

All participants received treatment at the NIH Stroke Center at Suburban Hospital in Bethesda, Md.

Full results, titled "Magnetic resonance imaging and computed tomography in emergency assessment of patients with suspected acute stroke: a prospective comparison", are published as part of the NIH Findings the January 27 edition of the The Lancet.

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