collateral circulation grading system from the American Society of Interventional and Therapeutic Neuroradiology/American Society of Interventional Radiology (ASITN/SIR)
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
Grade of 0-1 indicates poor collateral circulation
Grade 2 indicates moderate collateral circulation
Grades of 3-4 indicate good collateral circulation
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