Comparison of Computational Fluid Dynamics with Transcranial Doppler Ultrasound in Response to Physiological Stimuli

Cerebrovascular haemodynamics are sensitive to multiple physiological stimuli that require synergistic response to maintain adequate perfusion. Understanding haemodynamic changes within cerebral arteries is important to inform how the brain regulates perfusion, however methods for direct measurement of cerebral haemodynamics in these environments is challenging. The aim of this study was to assess velocity waveform metrics obtained using transcranial Doppler (TCD) with flow conserving subject-specific three-dimensional (3D) simulations relying on computational fluid dynamics (CFD). Twelve healthy participants underwent head and neck imaging with 3 Tesla magnetic resonance angiography. Velocity waveforms in the middle cerebral (MCA) artery were measured with transcranial Doppler ultrasound (TCD) while diameter and velocity was measured using duplex ultrasound in the internal carotid (ICA) and vertebral (VA) arteries to calculate incoming cerebral flow at rest, during hypercapnia and exercise. CFD simulations were developed for each condition, with velocity waveform metrics extracted in the same insonation region as TCD. Exposure to stimuli induced significant changes in cardiorespiratory measures across all participants. Absolute measured TCD velocities were significantly higher than those calculated from CFD (all P < 0.05), and these data were not correlated across conditions (r range 0.030–0.377, all P > 0.05). However, relative changes in velocity from resting levels exhibited significant positive correlations when the distinct techniques were compared (r range 0.577–0.770, all P < 0.05). Our data indicate that whilst absolute measures of cerebral velocity differ between TCD and 3D CFD simulation, physiological changes from resting levels in time-averaged velocity are significantly correlated between these techniques.