Corpus Luteum segmentation goal and contour initialization. (a) Unprocessed ultrasound image containing a corpus luteum; a small irregularly shaped cystic cavity is visualized within the CL. (b) Manual segmentation of the CL by a human expert. (c) A circular initial contour placed within the CL in the image in (a). (d) The surface (ψ) of the initial signed distance function in which the contour is embedded.