Diffusion-weighted imaging in acute stroke.

In magnetic resonance diffusion-weighted imaging (DWI), regions of the brain are depicted not only on the basis of physical properties, such as T2 relaxation and spin density, which influence image contrast in conventional MR imaging, but also by local characteristics of water molecule diffusion. The diffusion of water molecules is altered in a variety of disease processes, including ischemic stroke. The changes that occur in acute infarction enable DWI to detect very early ischemia. Also, because predictable progression of diffusion findings occurs during the evolution of ischemia, DWI enables more precise estimation of the time of stroke onset than does conventional imaging.