The effect of spatial resolution on wall shear stress measurements acquired using radial phase contrast magnetic resonance angiography in the middle cerebral arteries of healthy volunteers: Preliminary results

We have recently implemented radial phase-contrast techniques that allow high resolution angiograms with velocity information to be acquired within clinically-useful imaging times. 10 healthy volunteers were scanned using PC-VIPR and PC-SOS, two high resolution phase-contrast techniques at spatial resolutions of 0.67x0.67x0.67 mm³ and 0.4x0.4x1 mm³ respectively. The velocity measurements from the two acquisitions were imported into a custom Matlab runtime environment that automatically calculated WSS values using Green's Theorem and B-spline interpolation. Time average axial WSS was 1.069 N/m² (95% confidence interval: 0.8628< x < 1.276) in the left and right middle cerebral arteries of the 10 healthy volunteers (n=20) when scanned by PC-VIPR, and 1.670 N/m² when scanned by PC-SOS (95% confidence interval: 1.395 < x < 1.946). This difference in means was statistically significant (p < 0.002). Previous investigators have found that higher spatial resolution results in higher WSS measurements because smaller voxel size results in fewer partial volume effects. This was true in our study as well. In this study, we found that PC-SOS has significantly higher spatial resolution than PC-VIPR and this followed in the WSS measurements. Higher in-plane spatial resolution allows WSS calculations to be performed more accurately because of increased precision near the vessel boundary.