The effect of acoustic velocity on phantom measurements

Urethane rubber ultrasound (US) phantoms have a much lower acoustic velocit y (1430-1450 m/s) than the accepted soft tissue average of 1540 m/s, Two im portant questions arise: can the rod positions in these rubber phantoms be adjusted so that they may be used to test equipment distance measurement ac curacy for all types of multielement transducers, and can they be used to m easure beam focus (using the spread of the rod blur patterns)? These questi ons were addressed for linear-, phased-, convex- and vector-array transduce rs. Theoretical predictions for the different transducers' distance measure ment errors agreed with careful measurements obtained with a specially desi gned array of stainless-steel rods immersed in paraffin oil (1447 m/s), The conclusions of this study are that phantoms with acoustic velocities diffe rent from 1540 mis cannot be used to check distance measurement accuracies of all the types of real-time transducers, nor to predict a transducer's fo cusing performance in clinical scans. (C) 2000 World Federation for Ultraso und in Medicine & Biology.