1. A method for detecting a boundary between a first tissue and a second tissue in at least a detection region of a two-dimensional image, comprising: (a) assigning a cost to each voxel in the detection region, the cost being indicative of the likelihood that the voxel is not located on the boundary between the first tissue and the second tissue; (b) designating in the detection region at least one initial point of the boundary and at least one end point of the boundary; (c) obtaining a path of voxels in the detection region joining an initial point and an end point of minimal cost from among two or more paths joining an initial point and an end point, the cost of a path being obtained in a calculation based upon the costs assigned to the voxels of the path; and (d) designating the path having minimal cost as the boundary between the first and second tissues.