In vitro verification of multiple-receiver Doppler ultrasound for velocity estimation improvement

The coherent scattering effect, which introduces noise in Doppler-derived velocity estimates, is caused by constructive and destructive interference of sound waves scattered from multiple particles. Because the phase relationship between signals scattered from different particles depends on the orientation of the receiver, the error in a given velocity estimate depends on the receiver location. To examine this dependence, the velocity of a steady uniform flow was measured simultaneously with a transceiver and three receivers, and the cross-correlation coefficients between velocity estimates for pairs of crystals were calculated. The velocity estimates were nearly independent, with cross-correlation coefficients of approximately 0.2. This result agrees with our previously published numerical simulation studies which demonstrated that the coherent scattering noise in receivers separated by 5 degrees or more was nearly uncorrelated. Consequently, the contribution of coherent scattering noise can be reduced by averaging out noise in signals obtained from multiple receivers.