Fig. 2From: Predictive value of cerebral collaterals on CT angiography on the outcome of patients with acute anterior ischemic stroke receiving thrombolysis treatmentMaas system. A No vessel opacification. B Opacification less than that on the contralateral side. C Opacification equal to that on the contralateral side is not shown. D More opacification than that on the contralateral sideBack to article page