Many more stroke victims than previously thought can be saved from disability or death if doctors remove blood clots that are choking off circulation to the brain, a new study has shown.

“These striking results will have an immediate impact and save people from lifelong disability or death,” Dr. Walter J. Koroshetz, director of the National Institute of Neurological Disorders and Stroke, said in a statement. “I really cannot overstate the size of this effect.”

The key finding is that there is often more time than doctors realized in which brain cells can still be rescued by a procedure to remove the clot. Traditional guidelines have set a limit of six hours after stroke symptoms begin, and said after that it would be too late to help.

The study showed that the time window could be expanded to 16 hours. However, the findings do not apply to every stroke victim. The researchers used a special type of brain imaging to identify the patients who still had live brain tissue that could be saved if the blood supply was restored. Only about half the patients who were screened qualified for treatment, known as thrombectomy, which uses a mechanical device to pull clots out of a blood vessel.