Arterial Spin Labeling Magnetic Resonance Imaging Estimation Of Antegrade And Collateral Flow In Unilateral Middle Cerebral Artery Stenosis

Background and purpose:In patients with hemodynamic impairment due to intracranial atherosclerotic stenosis, the blood perfusion distal to the lesion site incorporates antegrade flow through the stenotic artery and the retrograde flow through pial arteries. Antegrade flow traverses a relatively short vessel segment, while collateral flow passes through relatively longer pathways. Arterial spin labeling (ASL) perfusion is a novel method to evaluate cerebral hemodynamic status. Three-dimensional pseudo-continuous ASL (3D pCASL) with multiple post-labeling delays (PLDs) has been used to assess cerebral blood flow (CBF) at different arterial bolus arrival time. We used this modality to estimate antegrade and collateral flow in patients with unilateral middle cerebral artery (MCA) stenosis.Methods:Consecutive patients with unilateral MCA 50% to 99% stenosis at two centers underwent pCASL with a PLD of 1.5s and 2.5s. Mean CBF of bilateral MCA territory at the PLD 1.5s and 2.5s were measured. Early-arriving flow proportion was defined as [CBF 1.5s at lesion side/CBF 2.5s at normal side] X 100%. Late-arriving retrograde flow proportion was defined as [(CBF 2.5s minus CBF 1.5s) at lesion side minus (CBF 2.5s minus CBF 1.5s) at normal side]/CBF 2.5s at normal side X 100%. Antegrade and collateral scales were evaluated in patients with conventional angiography. Spearman correlation coefficients were calculated between early-arriving flow and late-arriving retrograde flow proportions on ASL and antegrade and collateral scales on conventional angiography, respectively.Results:Forty-one patients (46.0 ± 12.0 years) were enrolled. The mean early-arriving flow proportion was 78.3% ± 14.9%. The mean late-arriving retrograde flow proportion was 16.1% ± 10.2%. In 21 patients with conventional angiography, Spearman correlation coefficient was 0.53 (95%CI 0.11-0.79) between antegrade grade and early-arriving flow proportion (p=0.01) and 0.81 (95%CI 0.56-0.92) between collateral grade and late-arriving retrograde flow proportion (p<0.0001).Conclusion:Three-dimensional pCASL with two-PLD may provide an empirical approach for estimating antegrade and collateral flow in patients with unilateral MCA stenosis.