Estimation of the correlation amplitude of RF signals in small cutaneous vessels

Time domain correlation technique is a widely used method for blood flow ve locity measurement. The time shift between a pair of windowed ultrasonic ec hoes is estimated by searching the temporal position of the maximum of the interpolated normalized correlation function. Between two consecutive echoe s, the acoustical footprint of a group of scatterers, which are transported with the how, moves and is deformed. This implies a decreasing of the ampl itude of the normalized correlation coefficient. In the case of microcircul ation (low how rate, low SNR), the amplitude of the correlation peak can be used to detect the presence of blood flow and to discriminate false and tr ue detections (reliability index). We have numerically evaluated the statis tical performances of the cross-correlation algorithm used as a correlation peak amplitude estimator in severe conditions (short correlation window le ngth, low SNR). These theoretical results have been compared with in vitro experimentation on a 100-mum-diameter microcirculatory phantom and with in vivo experimentation on a 180-mum-diameter vessel of a human leg carrying e rysipelas.