HIGH-FREQUENCY PHENOMENA IN REGURGITANT JETS - INFLUENCE OF FRAME RATE AND LINE DENSITY ON COLOR-FLOW MAPPING

Color Doppler echocardiography is accepted as a useful tool for evalua ting valvular regurgitation. but, so far, it does not allow for a prec ise quantification of the regurgitant volume since it is limited by th e combination of velocity ambiguities, a limited resolution, and a low frame rate. The low frame rate is imposed by the sector angle, the pa cket size, the pulse repetition rate, the Line density, and the sequen tial analysis of the ultrasound emissions. On the other hand, the imag es are supposed to depict pulsatile jets surrounded by high frequency pulsatile vortices. The present study was designed to search for the p resence of high frequency phenomena in turbulent jets and to analyze t he influence of the low frame rate on the jet images. An in vitro stud y using art aliasing-free laser Doppler and a hydraulic model simulati ng intracardiac jets was carried out. An analysis of flow events with a high bandwidth 1500 Hz) was conducted using M-mode color displays of the velocities. It showed: (1) on the centerline, a slow propagation of the front of the jet, and low frequency velocity fluctuations (< 50 Hz); and (2) at the opposite, in the boundary layer of the jet, very rapid fluctuations with frequencies comprised between 50 and 500 Hz. O n two-dimensional color images of laser Doppler data, the size of the central laminar core appeared strongly modified by a decrease in frame rate up to the maximum one commonly used in color Doppler (30 frames/ sec) as well by a decrease in line density. These data demonstrate tha t higher frame rate could improve the accuracy of ultrasound color Dop pler pow mapping.