ON THE SPECTRAL PROPERTIES OF DOPPLER THREAD PHANTOMS

It is shown that some of the threads used in Doppler phantoms have a r epetitive structure which leads to peaks in the angular distribution o f the backscattered power at beam axis-to-flow angles of theta = 90-de gree and approximately theta = 70-degree. This nonuniform scattering d oes not significantly interfere with modelling the Doppler spectrum pe ak as a function of velocity and beam-to-thread angle, but makes it im possible to model the spectral width as a function of these parameters . A new plaited structure is described which has a periodicity too sma ll to lead to subsidiary reflection peaks, and which has a more unifor m backscattering profile than the other threads studied.