Study: MRI beats CT in diagnosing common type of acute stroke

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Magnetic resonance imaging (MRI) has proven more effective for emergency diagnosis of suspected acute stroke than computed tomography (CT), according to a study by physicians at the National Institute of Neurological Disorders and Stroke (NINDS), a part of the National Institutes of Health (NIH). The authors attribute the difference between the modalities to MRI’s superiority for detection of acute ischemic stroke — the most common form of stroke, caused by a blood clot.

“These NIH research findings on acute stroke imaging are directly applicable to real-world clinical practice,” said NIH Director Elias A. Zerhouni, MD. “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 researchers conducted the study to determine which modality is more effective for emergency diagnosis of acute ischemic stroke as well as hemorrhagic stroke (caused by bleeding into the brain).

According to the results, 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, according to a release of the results.

The study is very good news for patients, according to Walter J. Koroshetz, MD, 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. In other words, brain injury may be completely avoided in some stroke victims by quick re-opening of the blocked blood vessel,” said Koroshetz.

The authors hope that through these results, diagnostic accuracy will be improved and costs might go down as well because of an increased use of acute treatments and earlier initiation of secondary prevention.

“Many patients who come to hospitals with a suspected stroke ultimately have a different diagnosis. 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. Our results show that MRI is twice as accurate in distinguishing stroke from non-stroke,” 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.”

These findings first appeared in the January 27, 2007 edition of The Lancet.