In vivo visualization and assessment of hemodynamics of intracranial arteries using 4D flow imaging

SUI Binbin; GAO Peiyi; LIN Yan; ZHAO Haiqing; JING Lina; SHEN Mi; SONG Ligang; DENG Yiming

doi:10.19300/j.2017.L5731zt

Abstract：Objective The aim of this study were to investigate the hemodynamic status of intracranial artery of healthy subjects and patients with middle cerebral artery(MCA) stenosis using 4D flow MR imaging,and to compare the bilateral hemodynamic parameters of stenosed and normal intracranial arteries.Methods Five healthy volunteers and three patients with MCA stenosis were enrolled in this study.MR images were acquired on a 3 T MR scanner.Three-dimensional TOF MRA and high-resolution 3D T1-weighted SPACE sequences were used to visualize and analyse the structural features of the circle of Willis.The flow data were acquired using 4D MR flow imaging.The hemodynamic status was assessed at the intracranial portion of the internal carotid artery (ICA),the middle cerebral artery (MCA),and the anterior cerebral artery (ACA).The average vessel area,average and maximum flow velocity,and average net flow rate at different phases of the cardiac cycle were calculated.Flow velocity vectors,streamlines,and particle traces maps were generated.The structural features and hemodynamic status of intracranial circle of willis were analyzed.Independent t-test was applied to test the difference in hemodynamic parameters between bilateral sides in healthy subjects and patients with stenosed MCAs.Results Forthe normal volunteers,symmetrical circle of Willis was found in 4 cases,and asymmetric circle of Willis with an unilateral right fetal PCA (fPCA) was found in one case.No statistical difference was found in hemodynamic parameters including average vessel area,average flow velocity,maximum flow velocity,and average net flow rate between the left and right side of the ICA,MCA,and ACA (P＞0.05).Flow velocity vectors,streamlines,and particle traces maps showed flow with high velocity at ICA.The flow velocity was decreased at late systolic and diastolic phases with irregular flow distribution.For one volunteer with an unilateral right fPCA,the bilateral hemodynamic parameters demonstrated asymmetry.It showed that only the maximum flow velocity of right ACA was lower than the contralateral side.Other parameters including average area,average flow velocity,maximum flow velocity,and average net flow rate of the rest cerebral arteries were all higher at the right side than the contralateral side.For the three patients with MCA stenosis,no statistical difference in hemodynamic parameters was found between bilateral ICA,MCA,and ACA (P＞0.05).The local average net flow rate was lower than the contralateral side in all three cases.The local average flow velocity and relative pressure gradient were decreased than the contralateral side in two cases,while increased intensely in one case.Flow velocity vectors,streamlines,and particle traces maps showed the directions of flow velocity vectors obviously diverged from the main axis of the vessel at stenosed site,with obviously irregular flow distribution.Conclusion Four-dimensional flow MRI can provide comprehensive evaluation of complex hemodynamics of intracranial arteries,including quantitative assessment of flow parameters.The structures of the circle of Willis are associated with hemodynamic status of intracranial arteries.