MVP-VSASL: measuring MicroVascular Pulsatility using Velocity-Selective Arterial Spin Labeling

Purpose: By leveraging the small-vessel specificity of velocity-selective arterial spin labeling (VSASL), we present a novel technique for measuring cerebral MicroVascular Pulsatility named MVP-VSASL. Theory and Methods: We present a theoretical model relating the pulsatile, cerebral blood flow-driven VSASL signal to the microvascular pulsatility index (PI), a widely used metric for quantifying cardiac-dependent fluctuations. The model describes the dependence of PI on bolus duration τ (an adjustable VSASL sequence parameter) and provides guidance for selecting a value of τ that maximizes the SNR of the PI measurement. The model predictions were assessed in humans using data acquired with retrospectively cardiac-gated VSASL sequences over a broad range of τ values. In vivo measurements were also used to demonstrate the feasibility of whole-brain voxel-wise PI mapping, assess intrasession repeatability of the PI measurement, and illustrate the potential of this method to explore an association with age. Results: The theoretical model showed excellent agreement to the empirical data in a gray matter region of interest (average R² value of 0.898 ± 0.107 across six subjects). We further showed excellent intrasession repeatability of the pulsatility measurement (ICC = 0.960, p < 0.001) and the potential to characterize associations with age (r = 0.554, p = 0.021). Conclusion: We have introduced a novel, VSASL-based cerebral microvascular pulsatility technique, which may facilitate investigation of cognitive disorders where damage to the microvasculature has been implicated.