Of those patients, whose average age was 64.7 years, 63 underwent MRI within three hours of stroke onset and 67 were imaged between three and 12 hours afterwards. With the MRI data, radiologists could predict with more than 90 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 24-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 Oppenheim's study, though they cautioned further research would be necessary to determine if the results could be replicated.
"It's potentially helpful, and I don't 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 40 percent of stroke patients who arrive at his facility within two hours of symptom onset receive tPA. If they don't, "the major reason . . . is that they get there too late," he said.
Dr. Wally Ghurabi, emergency department director at Santa Monica-UCLA 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 giv
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