Segmentation of aerated lung volume as a surrogate parameter to assess the multifocal tumor spread. Here in control animal no intrapulmonary masses are seen in micro-CT imaging (A). Seed points are placed manually in the aerated lung (B). Segmentation of the aerated lung is performed by applying a region growing algorithm (C). The entire aerated parts of the lung are segmented. No spread of segmentation volume into adjacent structures occurred.