Combined 2-D vector and tracking Doppler imaging for improved blood velocity quantification

The maximum velocity of blood flow is the primary means for determining the degree of stenosis in the carotid artery. The current standard for estimating the maximum velocity is Pulsed Wave (PW) Doppler with manual angle correction, assuming that the flow is parallel to the vessel wall. This assumption is not always correct, leading to errors in the velocity estimates and potentially in the assessment of the degree of stenosis. In addition, spectral broadening in the velocity spectra lead to overestimation of maximal velocities. In this work, we propose to combine two velocity estimation methods to reduce the bias and variability in maximum velocity measurements. First, the direction of the blood flow is estimated using a least squares vector Doppler technique. Then, tracking Doppler is performed on the same data, using the direction of the vector Doppler estimate as tracking direction. Simulation results show that the method can estimate the maximum velocity with a bias smaller than 5% for beam-to-flow angles between 30° and 85°, and that the primary source of error is inaccuracy in the flow direction estimate from vector Doppler. In vivo results show the feasibility of the method in the common carotid artery of a healthy volunteer, and also indicate that the beam-to-flow angle changes during the cardiac cycle.