Computational blood flow modeling based on in vivo measurements

Study of the relationship between hemodynamics and atherogenesis requires a ccurate three-dimensional descriptions of in vivo arterial geometries. Comm on methods. for obtaining such geometries include in vivo medical imaging a nd postmortem preparations (vessel casts, pressure-fixed vessels). We sough t to determine the relative accuracy of these methods. The aorto-iliac (A/I ) region of six rabbits was imaged in vivo using contrast-enhanced magnetic resonance imaging (MRI). After sacrifice, the geometry of the A/I region w as preserved via vascular casts in four animals, and ex situ pressure fixat ion (while preserving dimensions) in the remaining two animals. The MR imag es and postmortem preparations were used to build computer representations of the All bifurcations, which were then used as input for computational bl ood how analyses. Substantial differences were seen between MRI-based model s and postmortem preparations. Bifurcation angles were consistently larger in postmortem specimens, and vessel dimensions were consistently smaller in pressure-fixed specimens. In vivo MRI-based models underpredicted aortic d imensions immediately proximal to the bifurcation, causing appreciable vari ation in the aorto-iliac parent/child area ratio. This had an important eff ect on wall shear stress and separation patterns on the "hips" of the bifur cation, with mean wall shear stress differences ranging from 15% to 35%, de pending on the model. The above results, as well as consideration of known and probable sources of error, suggests that in vivo MRI best replicates ov erall vessel geometry (vessel paths and bifurcation angle). However, vascul ar casting seems to better capture detailed vessel cross-sectional dimensio ns and shape. It is important to accurately characterize the local aorto-il iac area ratio when studying in vivo bifurcation hemodynamics. (C) 1999 Bio medical Engineering Society. [S0090-6964(99)00705-5].