Abstract 5766: 3.0 Tesla MRI Carotid Wall Shear Stress Measurements: Reproducibility and Association with Mean Wall Area in Healthy Subjects
Introduction Wall Shear Stress (WSS) is an important determinant of endothelial function and phenotype. Aims of this study were to assess reproducibility of carotid WSS quantification using 3.0 Tesla MRI and to evaluate the association of WSS with carotid Mean Wall Area (MWA) in healthy subjects.
Methods Three 3.0 Tesla MRI scans were performed in the common carotid arteries of 30 healthy volunteers (aged 42, SD 16) on different days. Axial gradient echo Phase-Contrast images were acquired over 60 phases per heartbeat (retrospective gating), using a 5 cm single-element microcoil (Philips). Sequence parameters: slice thickness 3 mm, non-interpolated pixel size 0.6 × 0.6 mm, velocity encoding 150 cm/s. Image analysis for measurements of maximum velocities and diameters was performed in ImageJ. We calculated WSS by using the Poiseuille equation: WSS = 4 * Vmax/D, were Vmax is the maximum velocity and D is the vessel diameter. 3.0 Tesla MRI axial T1-weighted TSE image stacks were acquired at late diastole for MWA measurements. Sequence parameters: slice thickness 3 mm, non-interpolated pixel size 0.25 × 0.25 mm, TE 11 ms and TR according to heart rate, active fat suppression (SPAIR) and a double inversion black blood prepulse.
Results Mean values were: systolic WSS 1.44 (SD 0.30) N/m2, diastolic WSS 0.47 (SD 0.09) N/m2, MWA 13.1 (SD 4.2) mm2. Systolic and diastolic WSS were inversly associated with MWA (Spearman’s rho −0.592 (p=0.001) and −0.400 (p=0.028) respectively), which disappeared after adjustment for age. The per subject paired mean differences of the initial and repeat scans were: systolic WSS 0.02 (SD 0.19) N/m2, diastolic WSS 0.00 (SD 0.07) N/m2. The intraclass correlation coefficients were: systolic WSS 0.75 (95% CI 0.60 to 0.86, p< 0.001), diastolic WSS 0.71 (95% CI 0.55 to 0.84, p<0.001). Based on a two-sided α of 0.05 and a β of 0.2, the sample size calculation for a longitudinal follow-up study would include 30 subjects per treatment arm to detect a 10% difference in WSS.
Conclusion WSS is associated with common carotid MWA in healthy subjects and this effect was observed to be mainly a consequence of aging. 3.0 Tesla MRI carotid WSS is a well reproducible parameter that may require relatively small sample sizes to detect differences in WSS.