Diffusion- and perfusion-weighted MRI in acute ischemia - Part 2: Clinicalapplications

New magnetic resonance imaging (MRI) techniques can provide information on tissue status and the pathophysiology in acute stroke. Diffusion-weighted M RI (DWI) is sensitive to changes of water mobility and detects cytotoxic ce ll swelling, an early event in the cascade of ischemic tissue change, befor e T-2-weighted MRI shows any abnormality. It provides a higher lesion-to-no ise contrast than conventional MRI facilitating lesion detection in early s tages of stroke and allows differentiation of acute and chronic tissue path ology. The apparent diffusion coefficient (ADC), a quantitative measure of water diffusion, undergoes dynamic changes following the hyperacute and acu te stages of stroke offering an unique opportunity in visualising the patho logy of acute and chronic ischemia. Dynamic contrast enhanced T-2*-weighted MRI, also known as perfusion-weighted MRI (PWI), is a semiquantitative MRI technique of tissue perfusion that provides complementary hemodynamic info rmation in acute stroke. The combination of DWI and PWI enables the identif ication of the tissue at risk to undergo infarction in the penumbral region of acute ischemia. MR angiography provides information on the presence and site of arterial vessel pathology that is of particular value in very earl y stroke cases with negative DWI. DWI and PWI are new tools in stroke resea rch. In a clinical setting they improve diagnostic accuracy in acute neurol ogical disorders. They facilitate lesion localisation, the staging of acute stroke and provide pathophysiological information. DWI and PWI have the po tential to become the main diagnostic neuroimaging procedures in stroke pat ients influencing clinical decision making.