Flow imaging with pulsed Doppler ultrasound: refraction artefacts and dual mode propagation

Ultrasound may propagate in solid materials as both shear and longitudinal waves, and if such materials are immersed in fluids, this can lead to significant deformation of the beams produced by piezoelectric transducers. The authors have investigated to which extent such deformations may affect velocity measurements performed by Doppler equipment. By using their prototype multigate instrument, the authors found that the velocity profiles detected from flow within a plastic tube are significantly distorted when the ultrasound beam is oriented at angles over a wide range around a critical angle