Reproducibility of wall shear stress assessment with the paraboloid method in the internal carotid artery with velocity encoded MRI in healthy young individuals.

PURPOSE: To verify whether wall shear stress (WSS) can be assessed in a reproducible manner using automatic model-based segmentation of phase-contrast MR images by determination of flow volume and maximum flow velocity (Vmax) in cross-sections of these vessels.

MATERIALS AND METHODS: The approach is based on fitting a 3D paraboloid to the actual velocity profiles and on determining Vmax. WSS was measured in the internal carotid arteries of two groups of healthy young volunteers. The reproducibility of rescanning and repositioning was studied in the first group. In the second group a 1-week and a 1-month interval was investigated. Reproducibility was calculated by the intraclass correlation (ICC).

RESULTS: The flow volume, Vmax, and WSS averaged over the cardiac cycle were found to be 287.8 +/- 29.7 mL/min, 37.0 +/- 4.6 cm/s, and 1.13 +/- 0.16 Pa, respectively. The diastolic WSS varied between 1.00 +/- 0.21 Pa without averaging to 0.88 +/- 0.16 Pa with temporal and spatial averaging. Systolic WSS was 1.67 +/- 0.33 Pa without averaging and 1.67 +/- 0.25 Pa with averaging. ICC varied between 0.58 and 0.87 without averaging and between 0.75 and 0.90 with averaging for WSS.

CONCLUSION: WSS in MR images of the internal carotid artery can be assessed semiautomatically with good to excellent reproducibility without inter- or intraobserver variability using model-based postprocessing.