Measuring arterial and tissue responses to functional challenges using arterial spin labeling.

The measurement of cerebral blood flow (CBF) in functional MRI studies that aim for non-invasive, quantitative and reliable measurements is a challenge. Here, we tested the feasibility of a recently developed, model-free CBF technique to study vascular dynamics upon functional challenges. Multiple inversion time-point signals were measured from arterial and tissue compartments, allowing for the calculation of CBF through a process of deconvolution. Using graded visual stimulation known to produce increasing hemodynamic responses, we recorded significant and graded DeltaCBF and Deltatau(m) (microvascular arrival time change) that were highly comparable to those estimated by a standard 3-parameter fit based on the general kinetic model, though the absolute values had weaker agreement. Estimated arterial blood volumes (excluding substantial arteriolar contribution) did not show significant change with visual stimulation. Bolus arrival times in the microvascular compartment shortened more as compared to the arrival times from the arterial compartment during visual stimulation, suggesting larger involvement of the microvasculature in local neuronal response. While there are limitations, the model-free analysis method has the potential to offer useful vascular information in fMRI studies.