Acute ischemic stroke results in ischemic core surrounded by a tissue at risk, named the penumbra, which is potentially salvageable. One way to differentiate the tissues is to measure the hypoxia status. The purpose of the study is to correlate the abnormal brain tissue volume derived from magnetic resonance-based imaging of brain oxygen saturation (StO2-MRI) to the [18F]FMISO positron emission tomography (PET) volume for hypoxia imaging validation, and to analyse the ability of StO2-MRI to depict the different hypoxic tissue types in the acute phase of stroke.In a pertinent model of stroke in the rat, the volume of tissue with decreased StO2-MRI signal and that with increased uptake of [18F]FMISO were equivalent and correlated (r=0.706; p=0.015). The values of StO2 in the tissue at risk were significantly greater than those quantified in the core of the lesion, and less than those of the healthy tissue (52.3±2.0%; 43.3±1.9% and 67.9±1.4%, respectively). A threshold value of StO2 of ≈60% as the cut-off for the identification of the tissue at risk was calculated. Tissue volumes with reduced StO2-MRI correlated with the final lesion (r=0.964, p<0.0001).The findings show that StO2-MRI approach is sensitive for the detection of hypoxia and for the prediction of the final lesion after stroke. Once validated in acute clinical settings, this approach might be used to enhance the stratification of patients for potential therapeutic interventions.