Method and apparatus for extending regions in two-dimensional (2-D) image space or volumes in three-dimensional (3-D) image space that are generated by a test area-based region growing mechanism. Embodiments of a dilation mechanism may perform post-processing of a region or volume generated by the test area-based region growing mechanism to correct for an edge inset resulting from a radius used to define the test area. The dilation mechanism may perform a morphological dilate to expand the region or volume to the proper edge of the desired object in the image data within the tolerance range of the threshold, and thus corrects for the inset error introduced by the test area radius used by the region growing mechanism. The dilation mechanism may be limited to extending the region or volume to the radius distance from the edge of the original region or volume generated by the region growing mechanism.