MR and CT have evolved and are both capable of providing important physiologic information for guiding acute stroke therapy. This information could help to alleviate the growing unease concering the low numbers of patients who meet the nonindividualized epidemiologically-derived enrollment criteria for thrombolysis. Physiologic assessment, such as measurement of blood-brain barrier permeability, could lead to individualization of eligibility for thrombolysis with expanded patient enrollment. Cerebrovasuclar reactivity analysis (“brain stress test”) could improve the management of patients who have carotid occlusive disease. Detection of impaired autoregulation would favor surgical or endovascular intervention as opposed to medical management in these patients. The application of physiologic imaging techniques will undoubtedly play a key role in the management of patients who have disorders of cerebral blood flow.