Background and Purpose - The Alberta Stroke Program Early CT Score (ASPECTS) is a grading system to assess ischemic changes on CT in acute ischemic stroke. CT angiographysource images (CTA- SI) predict final infarct volume. We examined whether the final infarct ASPECTS and clinical outcome were more related to acute CTA- SI ASPECTS than to the acute noncontrast CT (NCCT) ASPECTS. Methods - ASPECTS was assigned by 2 raters on the acute NCCT, CTA- SI, and follow- up imaging. The mean baseline ASPECTS of acute NCCT and CTA- SI was compared with the follow- up ASPECTS. Rate ratios (RRs) were used to quantify the relationship between the dichotomized baseline ASPECTS (categorized as 0 to 7 versus 8 to 10) and favorable patient outcome. Results - Thirty- nine patients were recruited. Proximal occlusion (internal carotid artery or middle cerebral artery) was seen in 62% , M2 occlusion in 18% , and no occlusion was seen in 20% of patients. The median time between symptom onset and imaging was 1.9 (1.2 to 2.5) hours. There was a significantly larger difference of 1.4 between the mean baseline NCCT and CTA- SI ASPECTS in patients who had more ischemic changes (follow up ASPECTS=0 to 3) than a difference of 0.6 in patients who had near- to- normal CT scans (follow- up ASPECTS=8 to 10). The rate of favorable outcome for acute NCCT ASPECTS of 8 to 10 was 51.8% versus 25.0% for 0 to 7 (RR, 2.1, 95% Cl: 0.7 to 5.9, P=0.12). For acute CTA- SI ASPECTS of 8 to 10, the rate of favorable outcome was 58.8% versus 31.8% for 0 to 7 (RR. 1.8, 95% CI: 0.9 to 3.8, P=0.09). Conclusions - CTA- SI ASPECTS provides added information in the prediction of final infarct size. Background and Purpose - The Alberta Stroke Program Early CT Score (ASPECTS) is a grading system to assess ischemic changes on CT in acute ischemic stroke. CT angiographysource images (CTA- SI) predict final infarct volume. We examined whether the final infarct ASPECTS and clinical outcome were more related to acute CTA-SI ASPECTS than to the acute noncontrast CT (NCCT) ASPECTS. Methods - ASPECTS was assigned by 2 raters on the acute NCCT, CTA- SI, and follow-up imaging. The mean baseline ASPECTS of acute NCCT and CTA- SI was compared with the follow-up ASPECTS. Rate ratios (RRs) were used to quantify the relationship between the dichotomized baseline ASPECTS (categorized as 0 to 7 versus 8 to 10) and favorable patient outcome. Results - Thirty Proximal occlusion (internal carotid artery or middle cerebral artery) was seen in 62%, M2 occlusion in 18%, and no occlusion was seen in 20% of patients. The median time between symptom onset and imaging was 1.9 (1.2 to 2.5) hours. There was a significantly larger difference of 1.4 between the mean baseline NCCT and CTA- SI ASPECTS in patients who had more ischemic changes (follow up ASPECTS = 0 to 3) than a difference of 0.6 in patients who had near-to- normal CT scans (follow-up ASPECTS = 8 to 10). The rate of favorable outcome for acute NCCT ASPECTS of 8 to 10 was 51.8% versus 25.0% for 0 to 7 (RR, 2.1, 95% Cl : 0.7 to 5.9, P = 0.12). For acute CTA-SI ASPECTS of 8 to 10, the rate of the favorable outcome was 58.8% versus 31.8% for 0 to 7 (RR. 1.8, 95% CI: 0.9 to 3.8, P = 0.09). Conclusions - CTA- SI ASPECTS provides added information in the prediction of final infarct size.