Flow diverter (FD) has recently been introduced for cerebral aneurysms, especially for the uncoilable sidewall type in the tortuous internal carotid artery (ICA). However, some of treated aneurysms remain patent in clinical practices, probably because of hemodynamic reason. Four-dimensional phase contrast sequences (4D flow MRI) targeting the aneurysm bulge were prospectively performed. The results showed that intense hemodynamic effect at the aneurysmal neck and large ostium might need a longer time for FD induced occlusion. 4D flow MRI before FD procedures has the potential to depict and quantify ostium hemodynamics that could bring new insights in characterizing their treatment responses.