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Background and purpose: T2 star weighted MR angiography (SWAN) can detect hemodynamic insufficiency as hypointensity areas in the medullary or cortical veins. In this study, we investigate whether SWAN in 1.5T MRI can help to detect ischemic penumbra-like lesions in acute ischemic stroke (AIS) patients.Materials and methods: Patients showing acute major vessel occlusion (ICA and MCA) within 4.5 hours from onset were consecutively analyzed with MRI including SWAN, DWI, and MRA. To evaluate ischemic area in SWAN and DWI, modified ASPECT (mASPECTS) were used. SWAN- and DWI- based mASPECTS was calculated, and correlation between DWI-SWAN mismatch and final infarct lesion or outcome was evaluated.Results: Thirty-five patients were included in this study. Of the 35 patients (mean age: 73.5 ± 13.5 years), cardioembolic stroke was confirmed in 26 patients, atherothrombotic stroke was in 4 patients, and the others had unknown etiology. Overall, recanalization was achieved in 23 patients (65%), showing higher mASPECTS in follow up DWI and lower mRS at 90 days than patients with no recanalization (P=0.037 and P<0.001). Initial SWAN-based mASPECTS and follow-up DWI-based mASPECTS were both significantly higher in atherothrombotic stroke than in cardiogenic stroke (P=0.016 and P=0.042). Of 12 patients showing no recanalization, DWI-SWAN mismatch was significantly correlated with infarct growth (R2=0.6160, P=0.0025). On the other hand, there was no such correlation for patients showing recanalization. Interestingly, initial SWAN-based mASPECTS was significantly correlated with mRS at 90 days (R=-0.38, P=0.037) regardless of recanalization.Conclusions: DWI-SWAN mismatch in 1.5T MRI could show penumbra-like lesions in AIS patients with major vessel occlusion. Low mASPECTS in initial SWAN might predict unfavorable outcome. Assessment of ischemic penumbra from venous side using SWAN can visualize a lesion’s viable tissue and is quite useful without contrast media.