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MRI more sensitive than CT in diagnosing common form of acute stroke

Results from the most comprehensive study to compare two imaging techniques for the emergency diagnosis of suspected acute stroke show that magnetic resonance imaging (MRI) can provide a more sensitive diagnosis than computed tomography (CT) for acute ischemic stroke.
 
The difference between MRI and CT was attributable to MRI’s superiority for detection of acute ischemic stroke—the most common form of stroke, caused by a blood clot. The study was led by MUSC’s Julio Chalela, M.D., who was at the National Institute of Neurological Disorders and Stroke (NINDS), a part of the National Institutes of Health (NIH). Findings appeared in the Jan. 27 edition of The Lancet.
 
“These NIH research findings on acute stroke imaging are directly applicable to real-world clinical practice,” said NIH director Elias A. Zerhouni, M.D. “The patients involved in this study were the typical cross-section of suspected stroke patients who come into emergency rooms on a daily basis.”
 
Experts at MUSC said that the study confirmed what already was suspected.
 
“The study shows that MRI is better and more accurate than CT for acute brain infarcts, which was somewhat intuitive but not clearly demonstrated in a well-designed study,” said Zoran Rumboldt, M.D., associate professor of Radiology at MUSC.
 
While CT scans still would be used, Rumboldt said that radiology would increase the use of MRI where appropriate.
 
“MUSC is planning to increase the use of MRI over CT in acute cases,” based on a Jan. 30 meeting between the neuroradiology section and stroke neurologists, Rumboldt said. “But that also depends on MRI availability. CT (including CT perfusion and CTA) would still be preferred in patients with contraindications for MRI, such as certain unstable patients.”
 
Meanwhile, the study provides good news for patients, according to Walter J. Koroshetz, M.D., 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,” Koroshetz said.
 
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. 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, M.D., Ph.D., 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.”
 
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.
 
The study included 356 consecutive patients with suspected stroke arriving at the NIH Stroke Center at Suburban Hospital in Bethesda, Md., a primary stroke center that is designed to stabilize and treat acute stroke patients. Stroke specialists conducted emergency clinical assessments with all patients, including the NIH Stroke Scale which is used to measure stroke severity. MRI was performed prior to CT in 304 patients. Scans were initiated within two hours of each other, with a median difference of 34 minutes. Patients were excluded from the analysis if either CT or MRI was not done. The images were sorted randomly and independently by two neuroradiologists and two stroke neurologists.
 
Results of the study show that standard MRI is superior to standard CT in detecting acute stroke and particularly acute ischemic stroke. The four readers were unanimous in their agreement on the presence or absence of acute stroke in 80 percent of patients using MRI compared to 58 percent using non-contrast CT. No significant difference using the two technologies was seen in the diagnosis of acute intracranial hemorrhage, which is consistent with previous findings.
   

Friday, Feb. 23, 2007
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