Fig. 2.

Illustrative diagram of processing frameworks for the velocity-based (Stalder, AF., et al., 2008) and flow-based (Iffrig, E., et al., 2022) methods to quantify the rz-component of the wall shear stress (WSS) vector from 4D flow MRI data. For the velocity-based method (top row), segmented image data are resampled, and a cubic B-spline is fit to phase-contrast MR (PCMR) derived velocity values across the full diameter at varying circumferential positions. WSS values are calculated at 256 circumferential positions and averaged within 12 sectors. The flow-based method (bottom row) quantifies regional through-plane flow waveforms in overlapping areas defined by rays originating at the lumen centroid with a central angle of 90°. The Womersley solution was applied to quantify WSS in 80 overlapping areas around the vessel circumference, and values were averaged within 12 sectors.