Doppler angle estimation using correlation

Conventional Doppler techniques can only detect the axial component of bloo d flow. To obtain the transverse how component, an approach based on the de pendence of Doppler bandwidth on Doppler angle has been widely investigated . To compute the bandwidth, a full Doppler spectrum is often required. Ther efore, this approach has not been applied to real-time, two-dimensional Dop pler imaging because of the long data acquisition time. To overcome this pr oblem, a correlation-based method is proposed. Specifically, Variance of th e Doppler spectrum is used to approximate the square of the Doppler bandwid th. Because variance is computed efficiently and routinely in correlation-b ased color Doppler imaging systems, implementation of this method is straig htforward. In addition, the two-dimensional velocity Vector can be calculat ed and mapped to different colors using the color mapping function of curre nt systems. Simulations were performed, and experimental data were also col lected using a string phantom with the Doppler angle varying from 23 degree s to 82 degrees. Results indicate that the correlation-based method may pro duce significant errors if only a limited number of flow samples are availa ble. With averaging, however, the Doppler angles estimated by the correlati on-based method can achieve good agreement with the true angles by using on ly four flow samples with proper variance averaging.