Diffusion-weighted NMR imaging: application to experimental focal cerebral ischemia.

Changes in diffusion NMR imaging are believed to be based on intra/extracellular water homeostasis and will therefore reflect early disturbances of ion and water homeostasis after the onset of an ischemic event. Diffusion-weighted NMR imaging (DWI) thus has the potential to be a sensitive tool for the observation of stroke evolution. The present state of information extracted from diffusion-weighted NMR imaging for the understanding of cerebral focal ischemia in experimental research has been compiled in this review. The emphasis was set on three essential aspects of the technique in relation to focal ischemia. Firstly, the sensitivity of diffusion-weighted imaging for ischemic alterations is described. A comparison with conventional NMR imaging using relaxation time changes is included. Secondly, the comparison of the diffusion-weighted imaging with invasive techniques is discussed. Here, interpretation of the physiological, metabolic and hemodynamic alterations reflected in the observed diffusion changes is presented. The importance of regionally resolved information for a meaningful assignment of DWI changes to pathophysiological alterations is demonstrated for the differentiation between ischemic core and penumbra from DWI and quantitative diffusion coefficient data. The time dependence of correlations with physiological, biochemical and hemodynamic variables as a further important aspect is stressed. Thirdly, the potential of the technique for the assessment of development and effectiveness of new therapeutical strategies against stroke is demonstrated.