Magnetic resonance assessment of acute and chronic stroke.

This article describes the important role of magnetic resonance imaging (MRI) in noninvasively assessing human focal ischemic stroke. Conventional MRI, diffusion-weighted and/or perfusion-weighted imaging have been used to facilitate both the qualitative and quantitative evaluation of heterogeneity of ischemic brain tissue. Further, by combining 2 or more magnetic resonance parameters, tissue-signature models have been developed that may be used as surrogate markers of tissue histopathology to characterize ischemic tissue as salvageable, necrotic, or tissue in transition to necrosis. Magnetic resonance tissue-signature models and results are presented. Dynamic changes in the evolution of ischemic tissue to infarction are also discussed. Recovery from acute stroke was studied with blood oxygenation level-dependent functional MRI to investigate the neural mechanisms for recovery from aphasia after stroke.