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Table 3 ASITN/SIR Collateral flow grading system

From: Imaging predictors of procedural and clinical outcome in endovascular acute stroke therapy

Grade 0 No collaterals visible to the ischemic site
Grade 1 Slow collaterals to the periphery of the ischemic site with persistence of some of the defect
Grade 2 Rapid collaterals to the periphery of ischemic site with persistence of some of the defect and to only a portion of the ischemic territory
Grade 3 Collaterals with slow but complete angiographic blood flow of the ischemic bed by the late venous phase
Grade 4 Complete and rapid collateral blood flow to the vascular bed in the entire ischemic territory by retrograde perfusion