Abstract W MP19: Diffusion-Weighted Imaging-Fluid-Attenuated Inversion Recovery Mismatch at 1.5T VS 3T MRI in Acute Ischemic Stroke

Background and purpose: Although the diffusion-weighted imaging (DWI)-fluid-attenuated inversion recovery (FLAIR) mismatch (DFM) can be a surrogate marker of stroke onset time, DFM at 3T MRI may represent different clinical implications from that at 1.5T MRI. We aimed to compare the prevalence of DFM between 1.5T and 3T MRI, and assess factors associated with the FLAIR lesion positivity, and analyze a sensitivity and a specificity of DFM to identify patients ≤ 4.5h of stroke onset. Methods: Consecutive patients with acute ischemic stroke who underwent 3T or 1.5T MRI including DWI and FLAIR ≤ 12h of onset were enrolled. Random allocation regarding the magnetic field strength was performed according to the MRI availability. More than two stroke neurologists judged whether there is DFM. We identified ischemic lesion corresponding to stroke symptom on DWI and then determined whether the FLAIR lesion positivity is negative, subtle (only slightly different from adjacent parenchyma) or evident (a clearly high signal). DFM was defined as the FLAIR negative or subtle corresponding to the DWI lesion. Results: Of 179 patients (women, 39%; 72±11 years) studied, 89 and 90 received 3T and 1.5T MRI, respectively. The median onset to MRI time (OMT) was 2.5h at both 3T and 1.5T MRI. The FLAIR positivity was negative in 51% at 3T vs. 30% at 1.5T, subtle in 22% vs. 27% and evident in 27% vs. 43%, respectively (p=0.015); thus DFM was identified in 73% vs. 57% (p=0.028). On ordinal logistic regression with backward stepwise selection, 3T MRI (OR 0.40, 95%CI 0.22-0.71) and infratentorial infarction (OR 0.29, 95%CI 0.12-0.68) were negatively, and OMT (per 1h, OR 1.18, 95%CI 1.07-1.30) was positively associated with the FLAIR lesion positivity. DFM ≤ 4.5h was more frequently observed at 3T than 1.5T MRI (80% vs. 60%, p=0.015). Using DFM, patients ≤ 4.5h of onset were detected with a sensitivity of 0.80, a specificity of 0.42, a positive predictive value of 0.77 and a negative predictive value of 0.46 at 3T MRI and 0.60, 0.53, 0.82 and 0.26, respectively, at 1.5T MRI. Conclusions: DFM was more frequently observed at 3T than at 1.5T MRI. Because the FLAIR lesion was associated with 1.5T rather than 3T, DFM at 3T may have different implications regarding time after stroke onset from that at 1.5T.