An automatic angle tracking procedure for repeatable blood velocity measurements

One of the major limitations of Doppler systems consists in the difficulty of estimating the blood flow direction with respect to the ultrasound (US) beam, as needed to convert the measured Doppler frequency to velocity. The problem can be solved through an original dual-beam method, in which one of the beams is dedicated to estimate the flow direction. This goal is achieved by recognizing the beam orientation which produces symmetrical spectra, as happens uniquely at transverse Doppler angles. Although the technique has been thoroughly validated in vitro, for its practical in vivo application the needed transverse beam-flow angle should be automatically achieved. In this paper, we present an automatic angle tracking method and its implementation in a prototype Doppler/imaging system. In vitro and in vivo examples of application of the method are described showing that accurate and repeatable velocity measurements can be made.