Increased corticospinal tract fractional anisotropy can discriminate stroke onset within the first 4.5 hours.

BACKGROUND AND PURPOSE: The role of diffusion tensor imaging in determining stroke age remains unclear. We tested the ability of diffusion tensor imaging metrics to discriminate ischemic stroke <4.5 hours of onset. METHODS: We enrolled 60 consecutive patients for multimodal 1.5 T MRI within 12 hours of middle cerebral artery ischemic stroke onset. We measured fractional anisotropy (FA), mean diffusivity (MD), apparent diffusion coefficient (ADC), and T2-weighted signal intensity in affected ipsilateral and unaffected contralateral deep gray matter, cortical gray matter, deep white matter in the corticospinal tract (CST), and subcortical white matter and calculated ipsilateral-to-contralateral ratios (r). Hyperintensity in infarcted tissue was considered fluid-attenuated inversion recovery-positive. RESULTS: We analyzed the 48 patients (17 women; mean age, 68 ± 14 years) with known onset. In 25 (52.1%) patients, onset was ≤ 4.5 hours (mean, 182.3 ± 65.6 minutes). Variables differing significantly between infarcts <4.5 hours and >4.5 hours were rFA CST (P = 0.001), rMD cortical gray matter (P = 0.036), rADC cortical gray matter (P = 0.009), rT2 CST (P = 0.006), and fluid-attenuated inversion recovery (P<0.001). rFA at CST was the most reliable to discriminate infarcts <4.5 hours (Goodman-Kruskal = 0.76). The sensitivity, specificity, and positive and negative predictive values for infarct <4.5 hours of onset by rFA at CST >0.970 were 93.8%, 84.6%, 88.2%, and 91.7%, respectively. CONCLUSIONS: These preliminary results suggest rFA at CST may be a surrogate marker of acute stroke age.