Impact of orifice geometry on the shape of jets: an in vitro Doppler color flow study. To investigate the influence of orifice geometry on the three-dimensional shape of jets, an in vitro Doppler color flow study was performed. Jets were formed by discharging blood through round orifices and through orifices with major/minor axis ratios of 2:1, 3:1 and 5:1. These were repeated with orifice areas of 0.1, 0.3 and 0.5 cm2. For turbulent and laminar jets formed by these orifices, Doppler color flow images were obtained from two orthogonal scanning planes aligned with the major and minor orifice axes. Jet width was measured at 1 cm intervals from 0 to 5 cm from the orifice and used to calculate jet eccentricity (ratio of major to minor axis widths) and the rate of divergence of the jet walls. Jets were observed to diverge more rapidly along walls aligned with the orifice minor axis rather than along the major axis. This differential spreading led to the development of circular symmetry at a short distance from the orifice. Jet divergence (theta) occurred more rapidly for turbulent jets and for jets formed by larger orifices: theta (zero) = 0.80 + 6.3.A + 7.0.T + 0.47.E-OR (r = 95, p less than 0.0001, n = 48), where A is orifice area (cm2); T is 0 for laminar jets, 1 for turbulent jets and E-OR combines orifice eccentricity and scanning orientation, ranging from -5 for 5:1 orifices imaged along the major axis, 0 for circular orifices to 5 for 5:1 orifices imaged along the minor axis. Within the jet, eccentricity decayed approximately exponentially with distance from the orifice, more rapidly for turbulent jets, more slowly for the larger and more eccentric orifices. 