Blood flow in the human ascending aorta: a combined MRI and CFD study

Blood flow through the ascending aorta of two individuals is studied numerically. Realistic flow simulation is enabled by the combination of MRI and CFD. The aim of this study is the validation of the calculated flow field and, on the other hand, a comparison between flow distal to an artificial heart valve and native flow of a healthy volunteer. Three-dimensional, time-dependent computer models of the human ascending aorta were reconstructed from three-directional data sets acquired by MRI in the subjects studied. MRI velocity measurements downstream of the aortic valve provided the inflow conditions for the computational study. The pulsatile flow is described by the ALE-modified Navier-Stokes equations with respect to the time-varying flow domain. The numerical approach applies our own developed finite-element solver. During systolic acceleration the flow patterns distal to the valves do not show major differences between the two configurations. During flow deceleration, however, a significant influence of the disturbed inflow conditions can be found in the whole segment. Using the methods proposed, simulation of blood flow in the ascending aorta of the two subjects could be successfully performed. There was good qualitative agreement of blood velocities predicted by CFD and velocity data measured by MRI. In conclusion, the approach described herein might offer a new way towards an improved assessment of detailed in vivo flow conditions and alterations of blood flow associated with heart valve prostheses in particular. Combining CFD and MRI potentially extends the quantification of hemodynamic variables in vivo at a scale beyond the resolution limit inherent to MRI.