FLOW VELOCITY PROFILE VIA TIME-DOMAIN CORRELATION ERROR ANALYSIS AND COMPUTER-SIMULATION

An ultrasonic flow velocity profile measurement method employing time-domain correlation of consecutive echo pairs has been developed. The time shift between a pair of range gated echoes is estimated by searching for the shift that results in the maximum correlation. This technique is fundamentally different than the autocorrelation techniques that do not search for the maximum correlation. The time shift indicates the distance a group of scatterers has moved from which flow velocity is estimated. The basis for the computer simulations and error analyses of the scheme includes a band passed white Gaussian noise signal model for an echo from a scattering medium, the estimate of flow velocity from both a single scatterer and multiple scatterers, and a derived precision estimation. The error analysis via computer simulation includes an evaluation of errors associated with the correlation method. For a uniform flow velocity profile, beamwidth modulation represents the greatest error source. However, for a nonuniform flow velocity profile, the jitter caused by a small flow velocity gradient can exceed the other error sources. A detailed computer simulation evaluated the interdependencies of window length, beamwidth, vessel diameter and viewing angle on the estimation of flow velocity. One-dimensional (1-D) flow velocity profiles across the vessel can be obtained but there are engineering trade-offs of beamwidth and window length with the physiologic flow velocity gradient across the range cell to achieve the desired precision. The analyses reported herein are specific for the case when the measured component of flow velocity is parallel to the ultrasound beam axis, that is, axial flow velocity. © 1990 IEEE