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.