1. A system for segmenting a medical image, the system comprising: an input configured to receive medical image data acquired from at least a portion of a subject's anatomy; at least one processor configured to: i) accept a user selection, from the input, for a first point within a target structure identified on the image, and a second and a third point associated with extents of a target biological tissue, the first, second, and third points defining a sector described by the first point, a central angle, and a subtended arc; ii) determine a plurality of arc points along the subtended arc; iii) extend a plurality of linear segments along directions determined by the first point and the plurality of arc points; iv) determine an intensity profile along each linear segment to identify boundaries of the target biological tissue; v) generate a contour of the target biological tissue using the identified boundaries; an output configured to display information related the contour of the target biological image.