Sources of error in maximum velocity estimation using linear phased-array Doppler systems with steady flow

Using linear-array Doppler ultrasound (US) transducers, the measured maximu m velocity may be in error and lead to incorrect clinical diagnosis, This s tudy investigates the existence and cause of maximum velocity estimation er rors for steady flow of a blood-mimicking fluid in a tissue-mimicking phant om, A specially designed system was used that enabled fine control of flow rate, transducer positioning and transducer angle relative to the flow phan tom, Doppler machine settings (transducer aperture size, focal depth, beam- steering, gain) were varied to investigate a wide range of clinical applica tions, To estimate the maximum velocity, a new signal-to-noise ratio (SNR) independent method was developed to calculate the maximum frequency from an ensemble averaged Doppler power spectrum, This enabled the impact of each factor on the total Doppler error to be determined. When using the new maxi mum frequency estimator, it was found that the effect of transducer focal d epth, intratransducer, intramachine, intermachine (that was tested) and bea m-steering did not significantly contribute to maximum velocity estimation errors. Instead, it was the dependence of the maximum velocity on the Doppl er angle that made, by far, the greatest contribution to the estimation err or. Because our maximum frequency estimator took into account the effect of intrinsic spectral broadening, the degree of overestimation error was not as great as that previously published. Thus, the effects of Doppler angle a nd intrinsic spectral broadening are the chief sources of Doppler US error and should be the focus of future efforts to improve the accuracy. (E-mail: cobbold@ecf.utoronto.ca) (C) 2001 World Federation for Ultrasound in Medic ine & Biology.