Diffusion- and perfusion-weighted MRI in cerebral ischaemia - Part 1: Results of animal experiments

New MR sequences are an unique tool for the detection of acute and chronic cerebral ischemia and yield information not readily available from other te chniques on the tissue status. The background of the signal changes in diff usion-weighted MRI (DWI) is complex. In general, DWI visualises cytotoxic c ell swelling. Experimental studies on DWI have shown that DWI is sensitive to water shifts from the extracellular into the intracellular space. Water shifts within these compartments can occur with a large variety of pathophy siological events. They can be due to membrane de-polarisations that can be either reversible such as with spreading depression or irreversible as wit h anoxic depolarisations. Perfusion-weighted MRI (PWI) allows for the semiquantitative assessment of tissue perfusion and is a complementary technique to DWI. DWI and PWI have opened new vistas for the evaluation of acute ischaemic in juries under experimental und clinical conditions. The correlation of DWI a nd PWI changes with metabolic, haemodynamic and histological parameters is discussed.