An attempt to estimate onset time using DWI–FLAIR mismatch in acute ischemic stroke

Abstract

  In thrombolytic therapy for an acute ischemic stroke, the time of onset is very important. The purpose of this study was to identify unknown onset times in acute ischemic stroke within 4.5 hours using diffusion weighted image (DWI) and fluid‒attenuated inversion recovery (FLAIR) mismatch (DWI‒FLAIR mismatch). We retrospectively examined 56 cases of anterior circulation acute ischemic stroke with known onset times that occurred between January 2015 and August 2017 (28 males, 28 females; average age, 77.9±10.8 years). We categorized signal intensities on DWI and the FLAIR results of the same region into negative, moderate, or positive. We investigated relationships between the time interval from onset to MR scan and the 3 categories of FLAIR as a qualitative evaluation; and relationships between the signal intensity ratio (SIR) calculated using the stroke area (defined by DWI) and the region of interest (ROI) in the same region on the contralateral side on FLAIR images as a quantitative evaluation. We also calculated the SIR cut‒off based on the receiver operating characteristic (ROC) curve. Based on visual evaluation, there were significantly more negatives than moderates or positives in cases within 4.5 hours after onset (p＜0.01). There were significant differences between SIR and FLAIR in all categories (p＜0.05). In ROC curves, the cut‒off was 1.24 and the area under the curve (AUC) was 0.88 (95% CI 0.80‒0.97); sensitivity was 93.2% (95% CI 86.5‒99.9), specificity was 91.7% (95% CI 84.3‒99.1), the positive predictive value was 95.3% (95% CI 89.6‒100), and the negative predictive value was 84.6% (95% CI 75.0‒84.2). Under our method, we were able to identify by visual evaluation cases with a negative categorization at or below SIR 1.24 within 4.5 hours after onset, and thereby determine the best choice of treatment for acute ischemic stroke with an unknown onset time.