Insights on arterial secondary flow structures and vortex dynamics gained using the MRV technique

The purpose of this study was to gain an understanding of the formation of arterial secondary flow structures due to physiological parameters such as geometry (curvature), pulsatility and harmonics of inflow conditions. The variation of the unsteady pressure gradient, inflow vorticity and wall shear stress, and its concomitant effect on the secondary flow morphology during the pulsatile flow cycle was investigated. In vitro experimental investigation of arterial secondary flow structures was performed using the magnetic resonance velocimetry (MRV) technique in a 180° curved artery model at Stanford University. MRV benefits include its being a tracer- particle-free technique and its ability to resolve a full, three-dimensional flow field. In this paper, we discuss the kinematics of vorticity in the following two regions of a 180° curved artery model; (i) the entrance- (or straight-inlet pipe) and (ii) the 180° curved pipe-region. We applied the Womersley solution in the entrance-region to ascertain the time-dependent pressure drop per unit length, in-plane vorticity and wall shear stress for a pulsatile, carotid artery-based flow rate waveform. We hypothesize that in the 180° curved pipe region, the time rate of change of circulation will discern the propensity of large-scale, deformed Dean-type vortices to separate into two vortices in pulsatile arterial flows.