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 ($\mathrm{PI}$), a widely used metric for quantifying cardiac-dependent fluctuations. The model describes the dependence of the $\mathrm{PI}$ of VSASL signal (denoted ${\mathrm{PI}}_{\mathrm{VS}}$) on bolus duration $\tau$ (an adjustable VSASL sequence parameter) and provides guidance for selecting a value of $\tau$ that maximizes the SNR of the ${\mathrm{PI}}_{\mathrm{VS}}$ measurement. The model predictions were assessed in humans using data acquired with retrospectively cardiac-gated VSASL sequences over a broad range of $\tau$ values. In vivo measurements were also used to demonstrate the feasibility of whole-brain voxel-wise pulsatility mapping, assess intrasession repeatability of ${\mathrm{PI}}_{\mathrm{VS}}$, 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 $R^2$ value of 0.898 $\pm$ 0.107 across six subjects). We further showed excellent intrasession repeatability of the pulsatility measurement ($\mathrm{ICC}=0.960$, ) 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.