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 |