Abstract|Neuroimaging 1| Volume 357, SUPPLEMENT 1, e63, October 15, 2015

Direct assessment of wall shear stress by signal intensity gradient from time-of-flight magnetic resonance angiography

      Arterial wall shear stress (WSS), the stress tangential to the arterial wall, is known to have pathophysiologic roles in endothelial function and arterial thromboembolism. Time-of-flight magnetic resonance angiography (TOF-MRA) is based on a flow enhancement, and its technique to control intraluminal saturation has been evolved and now universally applied to every subject. It means that intraluminal saturation might be variable because of individual characteristics of arterial geometry and flow velocity.
      Objective: To assess patient-specific WSS directly from TOF-MRA, calculating signal intensity gradient near the arterial wall (TOF-MRA SIG).
      Methods: We developed a new method to calculate the TOF-MRA SIG, and performed validation studies. A phantom study for the TOF-MRA SIG as a function of flow rate was performed. A comparison between the TOF-MRA SIG and WSS from computational fluid dynamics (CFD) was made using 3D TOF-MRA of extracranial carotid artery in 5 healthy volunteers.
      Results: The phantom study showed that the TOF-MRA SIG values were significantly higher in the tube with high flow rate than with low flow rate (p < 0.001). The TOF-MRA SIG values were highly correlated with the various flow rates (β = 0.96, p < 0.001). The comparison study showed that the correlation efficient between the CFD WSS and the TOF-MRA SIG at the carotid artery was more than 0.8 in every section (all p values < 0.001).
      Conclusion: The TOF-MRA SIG was dependent on flow rate, and showed highly significant correlations with the CFD WSS. The TOF-MRA SIG might provide a convenient and efficient screening measurement to assess patient-specific WSS for the risk of vascular disease.