In this paper we develop a 3D algorithm based on a helical snake (active contour) for the lumen segmentation in intravascular ultrasound images. The helix snake evolves based on the analysis of the statistical properties until it reaches the luminal border. In addition we show the influence of the ring-down artifact for the luminal border detection by adding a preprocessing step. The algorithm was executed on 2190 images from two clinical IVUS sequences of femoral arteries presenting the ring-down artifact. The performance of the algorithm was evaluated with respect to expert manual plots and gave good performances.