Ultrasound evaluation of an abdominal aortic fluid-structure interaction model

Ultrasound measurements are used for evaluating biomechanics of the abdominal aorta (AA) predicted by a fluid-structure interaction (FSI) simulation model. FSI simulation models describe the complete arterial physiology by quantifying the mechanical response in the vessel wall caused by the percolating pulsating blood. But the predictability of FSI models needs validation for these to be usable for diagnostic purposes. Ultrasound measurements are suitable for such an evaluation as the wall displacement can be measured in vivo and compared to the wall displacement simulated in the FSI model. Spectral Doppler velocity data from 3 healthy male volunteers were used to construct inlet profiles for the FSI model. Simultaneously, wall movement was tracked and used for comparison to FSI model results. Ultrasound data were acquired using a scanner equipped with a research interface. The wall displacement was estimated by time shift estimation obtained from cross-correlation of signals to a fixed reference. The FSI model was constructed as a 2D axis-symmetric pipe with lumen diameter predicted by B-mode images from each volunteer. Visual comparison of wall displacement over 1 cardiac cycle show agreement except for 1 volunteer (Male, 23 yrs.). The magnitude of the displacement in simulation, u_fsi, and in vivo, u_iv, is within the same order of magnitude for the young (u_iv = 1.48 mm, u_fsi = 1.12 mm) and middle-aged volunteer (u_iv = 0.783 mm, u_fsi = 1.31 mm). For the elderly volunteer the simulated displacement (u_fsi = 0.975 · 10^-3 mm) is much smaller compared to in vivo (u_iv = 0.979 mm). In conclusion, the FSI model predicts a much stiffer AA wall compared to measured displacements for the elderly volunteer. From the visual comparison in vivo wall motion is captured in the FSI model for 2 of the 3 volunteers.