Assessing cerebral microvascular pulsatility using flow pulsatile-resolved pseudo-continuous arterial spin labeling MRI

Purpose To develop a flow pulsatile-resolved pseudo-continuous arterial spin labeling (FPR-pCASL) technique for noninvasively assessing cerebral microvascular pulsatility. Methods In FPR-pCASL, a pCASL sequence with single-shot three-dimensional gradient and spin echo acquisition was performed while simultaneously recording cardiac pulse signals using a pulse oximeter, and the pCASL images were retrospectively binned into multiple cardiac phases to resolve pulsatile microvascular blood flow. Both numerical simulations and in vivo experiments were performed to investigate the confounding factors of cardiac-induced variations of labeling efficiency and arterial transit time on pCASL signal fluctuations. An in vivo experiment was conducted to examine and optimize the postlabeling delay in FPR-pCASL. A test-retest study and a cross-validation study were performed to evaluate the reproducibility and reliability of FPR-pCASL for microvascular pulsatility index (PI) measurements. An aging study was conducted to investigate the effect of aging on cerebral microvascular PI. Results Numerical simulation showed that cardiac-induced variations in labeling efficiency and arterial transit time contributed to, at most, 3% and 2% of the pCASL signal fluctuations, respectively, which is nearly an order of magnitude smaller than the measured PI. A good test-retest reproducibility in microvascular PI (intraclass correlation coefficient = 0.86, p = 0.002) and strong correlations with macrovascular PIs by phase-contrast MRI (r = 0.72, 0.63, 0.71, and 0.74 for internal carotid artery, vertebral artery, middle cerebral artery M2/3, and M4, respectively; p < 0.05) were obtained. The elderly adults showed higher microvascular PI values than younger adults (p < 0.001). Conclusion This work has demonstrated the feasibility and reliability of the FPR-pCASL technique for directly assessing cerebral microvascular pulsatility.