Examples of in-vivo blood vector velocity estimation

In this paper examples of in-vivo blood vector velocity images of the carotid artery are presented. The transverse oscillation (TO) method for blood vector velocity estimation has been used to estimate the vector velocities and the method is first evaluated in a circulating flowrig where performance as function of flow angle is found.

At 90 [deg] beam to flow angle the TO method can estimate the transverse velocity with a mean standard deviation of 2.8 % and with a mean absolute bias of 11.8 %. A carotid artery is scanned in-vivo at three different positions by experienced sonographers. The scanning regions are: 1) The common carotid artery at 88 [deg] beam to flow angle, 2) The common carotid artery and the Jugular vein at ~90 [deg] beam to flow angle and 3) The bifurcation of the carotid artery.

The resulting velocity estimates are displayed as vector velocity images where the velocity vector is superimposed on a B-mode image showing the tissue structures. The volume flow is found for case 1) and when compared with MRI from the literature, a bias of approximately ~20% is found. The maximum flow velocities within the carotid artery is found to be 0.8 m/s, which is normal for a healthy person.

In case 3) the estimated vector velocities are compared with numerical simulations. Qualitatively the same flow pattern can be seen in both simulations and in the vector velocity images. Furthermore a vortex is identified in the carotid sinus at the deceleration phase after the peak systole. This vortex is seen in all of the three acquired cardiac cycles.