MR Mismatch Is Useful for Patient Selection for Thrombolysis

T he MR perfusion diffusion (PI/DWI) mismatch concept for the selection of patients for intravenous thrombolysis (IVT) was introduced with several smaller case series in the late 1990s and early 2000s, 1 followed by larger series by many international groups over the last 8 years.A potentially salvageable penumbra was operationally defined as a PI/ DWI-(volume) mismatch where PI indicates the hypoperfused tissue and DWI shows the more or less severe ischemic core. 2 A mismatch volume of 20% (PIϾDWI) has been widely accepted as indicator of a penumbral MRI setting.In an ideal world perfusion postprocessing would provide absolute values for cerebral blood flow (CBF).Perfusion maps could then indicate penumbra based on different thresholds for gray and white matter and thus also take sufficient collateral flow into account.However, absolute CBF values cannot be generated from dynamic susceptibility contrast enhanced PI, and no consensus has been established regarding the optimal perfusion algorithm and mismatch volume threshold.Three large observational studies using stroke MRI in an extended time window in clinical practice as well as 2 randomized phase II trials-the DIAS and the DEDAS trial-have been published, all showing a better safety and efficacy profile of MRI based treatment despite of later time windows.Only in the small phase 2 trials DIAS and DE-DAS, 3,4 a randomized placebo controlled design was used; the other series were larger but open and used contemporary 5,6 or historical 7 controls.Other points in favor of stroke MRI are that normal findings in stroke mimics and additional findings, such as early blood brain barrier disruption, microbleeds, leucoaraiosis, and lack of collateral flow may guide treatment decisions leading to further improved patient selection.Further efforts were undertaken to assess the validity of the PI/DWI mismatch concept with 2 multicenter studies, DE-FUSE and EPITHET.8,9 DEFUSE, simply stated, shows that