Simultaneous measurement of blood flow and arterial wall vibrations in radial and axial directions

The arterial wall expands and contracts during one heartbeat. At the beginning of systole, there is a possibility that vibrations on the arterial wall are caused by wall shear stress due to the rapid increase of blood flow. It is well known that crisis of atherosclerosis and rupture of plaque are basically caused by blood pressure and wall shear stress applied to the arterial wall. In the literature, wall shear stress is estimated by computer simulation. However, measurements of arterial wall vibrations in radial and axial directions as well as their relation to blood flow have not been reported yet. In this paper, by steering ultrasonic beams in two directions, the radial and axial components of arterial wall vibrations and blood flow velocity are simultaneously measured along the two directions. The relationship between the arterial wall vibrations and blood flow near the wall is evaluated based on the time-frequency analysis. In in vivo experiments, the method was applied to the carotid artery of a healthy subject. From experimental results, the radial and axial components of the arterial wall vibrations were measured together with the blood flow near the wall. A clear correlation was observed for each direction component of the vibrations and blood flow velocity. Since arterial wall vibration is caused by change in the blood pressure and shear stress applied to the wall due to the blood flow, the above results might be a clue to estimate the shear stress applied to the arterial wall from measurement of both the wall vibrations and blood flow.