ABSTRACT
Diffusion magnetic resonance imaging (MRI) provides image contrast that is dependent on the molecular motion of water and therefore provides unique information on the state of brain parenchyma as it responds to acute ischemia. The characteristic changes in diffusion that occur in acute infarctions often enable diffusion-weighted images (DWI) to detect lesions that would not be detected by any other imaging technique. Diffusion MRI has therefore assumed an essential role in the detection of acute ischemic brain infarction and in differentiating acute infarction from other disease processes. The chapter deals with a brief review of the biophysical basis for the changes in diffusion associated with acute stroke followed by a description of the appearance of ischemic lesions as they evolve on diffusion MR images. The biophysical basis for the rapid decrease in diffusion coefficients in acutely ischemic brain tissue is complex. The DWI lesion is thought to represent the infarction core, or tissue that is destined to infarct.
