Flow imaging with pulsed Doppler ultrasound and flow phantoms

摘要

The use of a multigate profiling system with steady laminar flownin plastic tubes revealed spectral artifacts not previously described.nIn particular, a double or split profile was often observed. In thisnpaper, these artifacts are related to the dual mode ultrasoundnpropagation in the plastic tube. The propagation speeds and, therefore,nrefraction angles and propagation paths are different for thenlongitudinal and the shear wave. The power transmission can benextraordinarily sensitive to small variations in the angle of incidence,nand this may combine with the existence of a range of angles ofnincidence within any focused ultrasound beam to produce spectralndistortions. The plastic tube is thus shown equivalent to a selectivenfilter, which diminishes some frequency components in the Dopplernspectrum relative to others. The spectral artifacts are explained innterms of the relative power transmitted by each mode, and the degree ofnbeam defocusing experienced by each. Spectral distortions persist evennwhen the beam-to-flow orientation is well away from the critical angle.nThe results of this study show that it is feasible to understand thenacoustic transmission behavior of a flow phantom, based on a knowledgenof the material properties, and to demonstrate the usefulness of doingnso