Assessing response to stroke thrombolysis: validation of 24-hour multimodal magnetic resonance imaging.

BACKGROUND Imaging is used as a surrogate for clinical outcome in early-phase stroke trials. Assessment of infarct growth earlier than the standard 90 days used for clinical end points may be equally accurate and more practical. OBJECTIVE To compare assessment of the effect of reperfusion therapies using 24-hour vs day 90 magnetic resonance imaging. DESIGN Infarct volume was assessed on diffusion-weighted imaging (DWI) at baseline and 24 hours after stroke onset and on fluid-attenuated inversion recovery images at day 90. The DWI and fluid-attenuated inversion recovery lesions were manually outlined by 2 independent raters, and the volumes were averaged. Interrater consistency was assessed using the median difference in lesion volume between raters. SETTING Referral center. Patients  Imaging data were available for 83 patients; 77 of these patients received thrombolysis. MAIN OUTCOME MEASURES Infarct volume at 24 hours and 90 days. RESULTS The 24-hour DWI infarct volume had a strong linear correlation with day 90 fluid-attenuated inversion recovery infarct volume (r = 0.98, 95% confidence interval, 0.97-0.99). Recanalization had a significant effect on infarct evolution between baseline and 24 hours but not between 24 hours and day 90. Infarct growth from baseline was significantly reduced by recanalization, whether assessed at 24 hours or day 90. Infarct volume at either time point predicted functional outcome independent of age and baseline stroke severity. Interrater agreement was better for DWI than fluid-attenuated inversion recovery (1.4 mL [8%] vs 1.8 mL [17%]; P = .002). CONCLUSIONS Assessment of final infarct volume using DWI at 24 hours captures the effect of reperfusion therapies on infarct growth and predicts functional outcome similarly to imaging at day 90. This has the potential to reduce loss to follow-up in trials and may add early prognostic information in clinical practice.