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everal researchers have reported that CT perfusion studies have been helpful in diagnosing and managing acute ischemic stroke in large numbers of patients. Adding CT perfusion to the imaging protocol improves the accuracy of a stroke diagnosis and is successful in most cases. Incorporating perfusion may even potentially reduce inpatient costs through improvements in management. Research has shown the value of CT perfusion studies in predicting infarction volume and growth. Investigators have also shown a close correlation between the information obtained with advanced CT perfusion protocols and MRI evaluations using the diffusion and perfusion mismatch. Large areas of ischemic injury with low blood volumes have generally been correlated with poor outcome, particularly when acute stroke recanalization methods are ineffective. CT perfusion protocols have been adopted for acute stroke clinical trials (the Desmoteplase In Acute Ischemic Stroke [DIAS-2] study, now under way) and are being used to identify thresholds related to the ischemic penumbra for acute thrombolysis guidance. Mounting evidence suggests that perfusion imaging may offer a safer way to triage and treat acute stroke patients than standard noncontrast CT. The only FDA-approved method of treatment for acute ischemic stroke today is a thrombolytic agent, tissue plasminogen activator (TPA), started intravenously within three hours of stroke onset. According to standard TPA protocol, patients are selected for treatment based on a noncontrast head CT used to exclude hemorrhage or extensive edema. Despite the clear clinical benefits of TPA given in this way,