Improved shear-stress evaluation from velocity profiles

Shear-stress in arteries, due to blood flow, is a significant diagnostic parameter for hypertension; it measures the force exerted by blood on vessel walls. It may be evaluated multiplying the blood viscosity by the shear-rate of the blood, i.e. the velocity gradient, near the walls. Whilst the former factor is easily measured by laboratory analysis, the latter requires the careful examination of the blood velocity profile along an artery diameter. Taking advantage of the Flow Rate Profiler (FRP), built by the authors' group using ultrasound techniques, they can try to extract this information. The main difficulties are due to the distortions of the profile in the neighbouring of walls, in turn due to the finite resolution of the ultrasound system (sample volume). This study is focused on the following topics: evaluation of the sample volume, and consequential correction of the blood velocity profile. First results are encouraging.