| Summary: | Background: T 2 relaxation-based magnetic resonance imaging (MRI) signals may provide onset time for acute ischemic strokes with an unknown onset. The ability of visual and quantitative MRI-based methods in a cohort of hyperacute ischemic stroke patients was studied. Methods: A total of 35 patients underwent 3T (3 Tesla) MRI (<9-hour symptom onset). Diffusion-weighted (DWI), apparent diffusion coefficient (ADC), T 1 -weighted (T 1 w), T 2 -weighted (T 2 w), and T 2 relaxation time (T 2 ) images were acquired. T 2 -weighted fluid attenuation inversion recovery (FLAIR) images were acquired for 17 of these patients. Image intensity ratios of the average intensities in ischemic and non-ischemic reference regions were calculated for ADC, DWI, T 2 w, T 2 relaxation, and FLAIR images, and optimal image intensity ratio cut-offs were determined. DWI and FLAIR images were assessed visually for DWI/FLAIR mismatch. Results: The T 2 relaxation time image intensity ratio was the only parameter with significant correlation with stroke duration ( r = 0.49, P = .003), an area under the receiver operating characteristic curve (AUC = 0.77, P < .0001), and an optimal cut-off (T 2 ratio = 1.072) that accurately identified patients within the 4.5-hour thrombolysis treatment window with sensitivity of 0.74 and specificity of 0.74. In the patients with the additional FLAIR, areas under the precision-recall-gain curve (AUPRG) and F 1 scores showed that the T 2 relaxation time ratio (AUPRG = 0.60, F 1 = 0.73) performed considerably better than the FLAIR ratio (AUPRG = 0.39, F 1 = 0.57) and the visual DWI/FLAIR mismatch (F 1 = 0.25). Conclusions: Quantitative T 2 relaxation time is the preferred MRI parameter in the assessment of patients with unknown onset for treatment stratification.
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