Patient-specific flow descriptors and normalised wall index in peripheral artery disease: a preliminary study

Background and aims: MRI-based haemodynamics have been applied to study the relationship between time-averaged wall shear stresses (TAWSS), oscillatory shear index (OSI) and atherosclerotic lesions in the coronary arteries, carotid artery and human aorta. However, the role of TAWSS and OSI is poorly understood in lower extremity arteries. The aim of this work was to investigate the feasibility of haemodynamic assessment of the superficial femoral artery (SFA) in patients with peripheral artery disease (PAD) and we hypothesised that there is an association between TAWSS and OSI, respectively, and atherosclerotic burden expressed as a normalised wall index (NWI). Methods: Six cases of 3D vascular geometries of the SFA and related inlet/outlet flow conditions were extracted from patient-specific MRI data including baseline, 12 and 24 months. Blood flow simulations were performed to compute flow descriptors, including TAWSS and OSI, and NWI. Results: NWI was correlated positively with TAWSS (correlation coefficient: r = 0.592; p < 0.05). NWI was correlated negatively with OSI (correlation coefficient: r = −0.310, p < 0.01). Spatially averaged TAWSS and average NWI increased significantly between baseline and 24 months, whereas OSI decreased over two years. Conclusions: In this pilot study with a limited sample size, TAWSS was positively associated with NWI, a measure of plaque burden, whereas OSI showed an inverse relationship. However, our findings need to be verified in a larger prospective study. MRI-based study of haemodynamics is feasible in the superficial femoral artery.