Some patients who suffer a stroke as a result of a blockage in an artery in the brain may benefit from a clot-busting drug nine or more hours after the onset of symptoms. The findings are published in the online edition of Radiology.

"Stroke is the third leading cause of death in the U.S.," said the study's lead author, William A. Copen, M.D., Director of Advanced Magnetic Resonance Neuroimaging at Massachusetts General Hospital (MGH) in Boston. "Every hour that we can add to the treatment window would allow vastly more stroke patients to be treated with potentially life-saving therapy."

The most common type of stroke is called ischemic stroke. These strokes occur when a blood clot blocks a blood vessel supplying blood to the brain. Some ischemic strokes can be treated with thrombolytic, or clot-busting, therapy using tissue plasminogen activator (t-PA), which helps dissolve the blockage. However, the window of opportunity to safely administer the medication is generally considered to be just three hours. Because few patients get to the hospital to be diagnosed and treated within that time frame, fewer than seven percent of patients receive the drug…