Reliable estimation of cerebral blood flow (CBF) is crucial for a precise diagnosis of acute ischemia. PET using [15O]H2O remains the reference method to assess CBF but it can also be assessed using MRI. Several post-processing algorithms of perfusion MRI can be used to derive MRI-CBF values. CBF was simultaneously assessed with PET and MRI in a Macaca fascicularis model of stroke using a Siemens PET-MRI hybrid scanner. Four MRI post processing algorithms (sSVD, cSVD, oSVD and Bayesian) were compared against PET estimation of CBF. Bayesian algorithm seems to derive the most reliable estimation of CBF.