Intracranial pulse wave velocity using 4D flow MRI: method comparison and covariate analysis

Intracranial pulse wave velocity (PWV) offers the potential to enhance neurovascular care when evaluating cerebrovascular disease. Using 4D flow MRI, we measured PWV in the intracranial vasculature stemming from the internal carotids and basilar arteries using three popular techniques: cross-correlation, waveform optimization and time-to-upstroke which have all been used intracranially, but never compared. Near-perfect agreement between cross-correlation and waveform optimization methods was observed, while the time-to-upstroke method estimated a significantly larger PWV and was more prone to non-physiological values in a cohort of 21 healthy individuals aged 48 ± 18 years. We then analysed our cohort PWV using an ensemble approach given the current lack of methodological consensus. This analysis identified two consistent findings. First, internal carotids measure significantly higher PWV than basilar vascular networks (3.64 ± 1.47 versus 2.53 ± 1.39 m s^-1). Second, in our cohort, intracranial PWV was age-independent. We hypothesize that age independence is a healthy physiological trait to minimize microvascular strain, protecting the integrity of the peripheral bed throughout ageing and cardiac pulsatile deformation. The cause for apparent age independence remains unknown. We also identified that previous work on intracranial PWV is likely biased towards the extracranial vasculature, which may explain the study differences in PWV magnitude and the age-dependent nature.