"MRI images can serve as a surrogate clock to pinpoint stroke onset in patients whose symptoms began during sleep increasing the number of patients eligible for highly effective clotbusting therapy according to a new study. Researchers found that MRI data could accurately determine if patients had experienced stroke symptoms within a threehour period or less which would allow the use of a clotbusting drug that works best if administered within that window of time. Tissue plasminogen activator known as tPA can dramatically reverse stroke symptoms in those whose strokes are caused by blood clots and blockages which account for an estimated  percent of all strokes. Strokes strike about  Americans each year killing  according to the U.S. Centers for Disease Control and Prevention. The condition is a leading cause of serious longterm disability in the United States. A tool that can estimate the age of stroke would be of great value in cases of unknown stroke onset time said lead researcher Dr. Catherine Oppenheim professor of radiology at Universite Paris Descartes in France. This concerns as many as a quarter of all stroke patients who cannot be given tPA because they wake up with stroke symptoms or are unable to say when their stroke began. Under current guidelines patients who awaken with symptoms are arbitrarily excluded from tPA therapy Oppenheim said because the onset is considered to be the last time the patient was symptomfree which might have been the night before. The clotbusting drug is recommended for use only within . hours of stroke onset because it carries a risk of brain hemorrhage a potentially fatal prospect with the risk increasing as more time passes.  The study reported online Nov.  and in the December issue of the journal Radiology reinforces results from similar research Oppenheim said. Her team reviewed MRI images from  patients treated for clotcaused strokes at SainteAnne Hospital in Paris between May  and October . Of those patients whose average age was . years  underwent MRI within three hours of stroke onset and  were imaged between three and  hours afterwards. With the MRI data radiologists could predict with more than  percent accuracy which patients had experienced stroke symptoms for longer than three hours. However the study did not compare patients with unknown stroke onset who received tPA to those who did not Oppenheim said. Providing stroke neurologists with a reliable marker of stroke age will help to ensure that patients . . . are managed as urgently as those with known stroke onset time she said. These results will be useful for centers that offer hour access to acute stroke patients. The main limitation is the limited access to MRI in emergency rooms worldwide. Oppenheim said the next step would be clinical trials to validate whether MRIs serve as a surrogate clock for stroke onset. Several doctors specializing in stroke care were encouraged by Oppenheims study though they cautioned further research would be necessary to determine if the results could be replicated.  Its potentially helpful and I dont know that it would take years to prove that said Dr. Larry B. Goldstein director of the Duke University Stroke Center in Durham N.C. Goldstein noted that about  percent of stroke patients who arrive at his facility within two hours of symptom onset receive tPA. If they dont the major reason . . . is that they get there too late he said. Dr. Wally Ghurabi emergency department director at Santa MonicaUCLA Medical Center said a group of ongoing studies there include a similar focus on MRIs and stroke. Really pinpointing the time of onset is so crucial for us. This will definitely give us that edge Ghurabi said. Ive seen it with my own eyes  a yearold male or female patient comes into the ER and theyre not able to move on one side or speak. A couple of hours later after therapy they can walk and talk. What more could we as doctors want Dr. David F. Kallmes an interventional neuroradiologist at the Mayo Clinic in Rochester Minn. was also optimistic about Oppenheims results.  The MRI is trying to act as a surrogate clock said Kallmes who edited Oppenheims journal article. Like any imaging technique it has a certain accuracy but it wont be perfect. Its certainly an innovative approach for patients with strokelike symptoms. In October  the American Heart Association the American Stroke Association and the European Stroke Association revised their guidelines to recommend that tPA be used up to . hours after the onset of an ischemic clotcaused stroke but the U.S. Food and Drug Administration has not yet revised its approved treatment window of  hours.  A study in The Lancet Neurology also found that a slight increase in deaths and bleeding in an extended treatment group over a threemonth followup period underlined the notion that treatment within  hours  although not required  is still optimal.  More information Review the warning signs of stroke at the American Stroke Association http_UCM__SubHomePage.jsp. SOURCES Catherine Oppenheim M.D. Ph.D. professor of radiology at Universite Paris Descartes France Larry B. Goldstein M.D. director Duke University Stroke Center Durham N.C. Wally Ghurabi D.O. emergency department director Santa MonicaUCLA Medical Center Santa Monica Calif. David F. Kallmes M.D. professor of radiology Mayo Clinic Rochester Minn. December  Radiology"