Within five years the advent of CT scanning began to suggest that he might be right. With scanning you could penetrate the vaulted brain and clearly identify the infarct — the tissue killed by loss of blood flow. By the late ‘70s, advances in imaging technology had revealed that not all brain tissue impacted by a stroke died immediately. The area around the infarct — the penumbra — could survive for several hours.
The implications were huge. For the first time it became clear that there was a window of time in which the devastating effects of a stroke could perhaps be averted. The next step was to figure out exactly what that effective intervention might be.