1. A method for the interactive segmentation of medical image slice data using a computer, the method comprising: (a) displaying an image slice p of a set of two dimensional medical image slice data on a display of the computer; (b) applying a set of anchor points on the displayed slice p, the slice p anchor points manually placed by a computer user on a boundary of an item of interest of the displayed slice p; (c) interactively constructing slice p contours, using the slice p anchor points, to form an outline of the boundary of the item of interest on the displayed slice p; (d) projecting the slice p anchor points and the slice p contours to an adjacent image slice q, the projection onto slice q being proximal to a boundary of an item of interest on slice q; (e) determining slice q contours using the projection onto the slice q and the boundary of an item of interest on the slice q; (f) extracting midpoints on the slice q contours between slice q anchor points formed by projecting slice p anchor points in said projecting step; (g) setting the midpoints as the new slice q anchor points; (h) determining new slice q contours using the new slice q anchor points; (i) displaying the new slice q contours and the new slice q anchor points superimposed on the image slice q.