Perfusion-Weighted Imaging–Derived Collateral Flow Index is a Predictor of MCA M1 Recanalization after IV Thrombolysis

Tmax maps used for nCCD quantification and corresponding ADC maps from 2 patients with different recanalization pattern. Upper images: ADC maps with lesion delineated by visual selection of the most appropriate ADC threshold value (the hotter the color, the lower the ADC value). Lower images: Tmax maps (superimposed on FLAIR images) with colored areas corresponding to moderately (yellow area) and severely (red area) hypoperfused parenchyma. A, 75-year-old woman, proximal MCA-M1 occlusion, NIHSS = 11, TTT = 135 minutes, no MCA recanalization at 24 hours. Volume of DWI abnormalities detected on all brain sections = 54.78 mL. nCCD = 105.14. B, 74-year-old woman, distal MCA-M1 occlusion, NIHSS = 15, TTT = 94 minutes, complete MCA recanalization at 24 hours. Volume of DWI abnormalities detected on all brain sections = 2.74 mL. nCCD = 68.16. Calculation method for nCCD: The yellow area corresponds to moderately hypoperfused parenchyma (Tmax values between lower and upper Tmax thresholds). The red area corresponds to severely hypoperfused parenchyma (Tmax exceeding the upper threshold). Lower and upper thresholds were defined as the Tmax mean value of the whole contralateral hemisphere (calculated from a brain section located at the centrum semi ovale level with exclusion of skull and ventricles). The lower threshold is contralateral Tmax mean value +2 seconds and the upper threshold is contralateral Tmax mean value +6 seconds. The volume of ipsilateral and supratentorial, moderately (yellow area) or severely (red area), hypoperfused parenchyma is calculated from all brain sections. nCCD = (red area volume/yellow area volume) × (red area volume + yellow area volume).