Background and Purpose -In contrast to platelet-rich white thrombi, red thrombi in the heart are rich in fibrin and trapped erythrocytes. The magnetic susceptibility effect of deoxygenated hemoglobin in red thrombi may result in hypointense signals on T2*-weighted gradient echo imaging (GRE). We tested the hypothesis that a GRE susceptibility vessel sign (SVS) is specific for cardioembolic stroke. Methods -This retrospective study examined data from acute ischemic stroke patients who underwent diffusion-weighted imaging, GRE and magnetic resonance angiography (MRA) within 24 hours of stroke onset and who had symptomatic occl usion of large intracranial arteries in the circle of Willis. Hypointense signals within vascular cisterns on GRE corresponding to symptomatic vascular occlusio n were termed “GRE SVS.”Recanalization was assessed on follow-up MRA performe d within 7 days of onset. The relationships between GRE SVS and stroke subtypes and subsequent recanalization were explored. Results -Of the 95 patients who me t the inclusion criteria, GRE SVS was observed in 45 (47.4%). GRE SVS was more commonly associated with cardioembolic stroke patients (31 of 40, 77.5%) than w ith other stroke subtypes (14 of 55, 25.5%; P < 0.001). In 66 patients who unde rwent follow-up MRA, GRE SVS was associated with subsequent recanalization (P < 0.001). Multivariate analysis showed that GRE SVS was an independent predictor of cardioembolic stroke and subsequent recanalization (odds ratio, 10.75 and 4.2 6; 95%CI, 3.68 to 31.47 and 1.12 to 16.30). Conclusions -GRE SVS may predict c ardioembolic stroke and subsequent recanalization. Identifying clot composition may be important in choosing the optimal treatment based on clot characteristics . Background and Purpose-In contrast to platelet-rich white thrombi, red thrombi in the heart are rich in fibrin and trapped erythrocytes. The magnetic susceptibility effect of deoxygenated hemoglobin in red thrombi may result in hypointense signals on T2 * -weighted gradient echo imaging ( We tested the hypothesis that a GRE susceptibility vessel sign (SVS) is specific for cardioembolic stroke. Methods-This retrospective study examined data from acute ischemic stroke patients who underwent diffusion-weighted imaging, GRE and magnetic resonance angiography (MRA) within 24 hours of stroke onset and who had symptomatic occl usion of large intracranial arteries in the circle of Willis. Hypointense signals within vascular cisterns on GRE corresponding to symptomatic vascular occlusio n were termed “GRE SVS.” Recanalization was assessed on follow-up MRA performe d within 7 days of onset. The relationships between GRE SVS and stroke subtypes and subsequent recanalization were explored. GRE SVS was more commonly associated with cardioembolic stroke patients (31 of 40, 77.5%) than w ith other stroke subtypes (14 Multivariate analysis showed that SVS was an independent predictor of cardioembolic stroke and subsequent (P <0.001). In 66 patients who underwent follow-up MRA, GRE SVS was associated with subsequent recanalization Conclusions -GRE SVS may predictCoedioembolic stroke and subsequent recanalization. Identifying clot compositions may be important in choosing the optimal treatment based on clot (odds ratio, 10.75 and 4.2 6; 95% CI, 3.68 to 31.47 and 1.12 to 16.30) characteristics.