Fluid-Attenuated Inversion Recovery (FLAIR) Signal Intensity Can Identify Stroke Within 6 and 8 Hours

Background Patients with wake-up or unknown time of onset stroke are usually excluded from recanalization. However, a few studies indicate that some magnetic resonance sequences can help predict time from symptom onset (SxO). Our goal was to assess the value of fluid-attenuated inversion recovery (FLAIR) signal intensity ratio (SIR) in identifying patients within 6 and 8 hours of stroke onset. Materials and Methods We studied consecutive acute stroke patients with known time of onset who underwent magnetic resonance imaging (MRI) within 48 hours of SxO. SIR was calculated as the value of the FLAIR signal intensity of the identified area of infarction divided by the signal intensity in the homologous contralateral side of the brain. Results Out of 160 patients included in this study, 72 and 80 patients had MRI within 6 and 8 hours of SxO, respectively. We found a positive correlation between SIR and time from SxO (Pearson coefficient, .63). Receiver operating characteristic curves indicated that SIR ≤ 1.18 could accurately identify patients within 6 hours of SxO (86% sensitivity, 79% specificity) and a SIR ≤ 1.20 can be identified within 8 hours (89% sensitivity, 76% specificity). Among patients with no visible FLAIR hyperintensity, 83% (95% CI, 77%-89%) were within the 6-hour window. Conclusion Quantitative assessment of FLAIR sequence can be used to identify patients within 6 and 8 hours of stroke onset.