Imagerie par résonance magnétique de diffusion de l'encéphale chez l'adulte : technique, résultats normaux et pathologiques

By probing microscopic molecular motions, diffusion-weighted imaging (DWI) is the only method available today that provides noninvasively information on molecular displacements over distances comparable to cell dimensions. Since it measures a parameter different from those assessed by conventional MRI, DWI represents a new imaging technique that goes beyond depiction of neuroanatomy and evaluates function and physiopathology. Image contrast is related to differences in the diffusion rate of water molecules rather than to changes in total tissue water. DWI has proven its high sensitivity in early detection of acute infarction; it is reliable in differentiating acute stroke from other diseases that mimic acute stroke in clinical terms and on conventional MR images. By differentiating lesions with decreased diffusion from those with increased diffusion, DWI is useful in the evaluation of a wide variety of other disease processes including neoplasms, demyelization, traumatic brain injury, intracranial infections. In particular, DWI can distinguish between epidermoid and arachnoid cysts and provides key information for the diagnosis of cerebral abscess. In some clinical situations, DWI data have a prognostic value.