Before revision:  We first detect finger cores in three-dimensional (3D) scalar fields to capture the central structures of fingers guided by a ridge voxel detection method ; then, we skeletonize finger cores to reveal their overall topological and geometric structures by a Reeb-graph skeletonization method. From the identified finger skeletons, we design a spanning contour tree-based method to capture how fingers branch in 3D space .
After revision:  We first detect finger cores in three-dimensional (3D) scalar fields to capture the central structures of fingers guided by a ridge voxel detection method , we first extract finger cores from three-dimensional (3D) scalar fields. After skeletonizing finger cores into skeletons, we design a spanning contour tree-based method to capture how fingers branch in 3D space .