Vector-flow imaging visualizes blood flow velocities in all directions and calculates true flow vector and velocity magnitude in each site. Quantitative evaluation of velocity vectors allows more precise measurements of wall shear stress(WSS).
28 patients (20 males,8 females,aged33-87,median-64y.o.) with and without the presence of carotid plaques were included in this study. In total, 55 carotid arteries were analyzed. Resona 7 system(Mindray,China) was used for VFI and WSS measurements. Plaques characteristics such as echogenicity, degree of stenosis were also assessed.
Patients with carotid plaques have significantly smaller WSS values in CCAthan those without atherosclerosis (2,9vs 3,7pa,p=0,033). Direct correlation was observed between WSS and blood flow velocity(R=0,4,p=0,015) and negative correlation between WSS and intima-media thickness(R=-0,31,p=0,045) and between WSS and Pulse Wave Velocity(R=0,48,p=0,015). Significant heterogeneity in WSS values was detected in carotid bifurcations, areas with turbulent, opposite flow have much smaller WSS values in comparison with parts of the carotid wall that come into contact with laminar flow (0,5vs2,7pa,p < 0,001). WSS values on the surface of carotid plaques depend on echogenicity (hyperechogenic plaques have on average smaller WSS than hypoechogenic ones (4,8vs2,2pa,p=0,002). However, the most interesting observation is that hypoechogenic plaques have marked heterogeneity in WSS values between different parts of plaque in comparison with hyperechogenic ones (DIFFERENCE[MAX-MIN] was 6,4vs2,6,p=0,04). This difference was much more pronounced in cases with high degree stenosis. In fact, there was a direct correlation between degree of stenosis and difference in WSS values between parts of plaque(R=0,49,p=0,004). We developed a general regression model that can predict the maximum WSS value of the plaque on the basis of velocity, plaque echogenicity and degree of stenosis.
VFI can provide detailed information about hemodynamic. The difference in WSS value between parts of the plaque (especially pronounced in hypoechogenic plaques with a higher degree of stenosis) may be linked with plaque instability.
Oleg Kerbikov, RVT, RPVI, Federal Research Clinical Center FMBA of Russia