Automated volumetric approach for quantifying bronchial wall remodeling in MDCT

Follow-up studies of bronchial wall remodeling in asthmatics based on multi-detector computed tomography (MDCT) imaging is the emerging modality for therapy assessment. While providing statistically significant quantification of global variation before/after treatment, the employed cross-section-area estimation techniques cannot guarantee the absolute accuracy of point-by-point estimation. Such uncertainty comes from the impossibility to define an accurate cross-sectional plane of a bronchus at locations where the notion of central axis is questionable. In order to overcome such limitation, this paper develops an original automated volumetric approach for bronchial wall quantification involving a successive model-based 3D reconstruction of the inner and outer bronchial wall surfaces. The inner surface is segmented by means of strong 3D morphological filtering and model-fitting. An optimal geometrico-topological model is generated by using a restricted Delaunay triangulation approach. The model is then dynamically deformed in the surface normal direction, under the constraint of local energy minimization acting at each evolving vertex. The energy potentials oppose a mesh-derived elastic component combining topological and geometric features in order to preserve shape regularity, and an expansion potential exploiting image characteristics. The deformation process both adapts the mesh resolution and handles topology changes and auto-collisions. The developed 3D modeling stabilizes the deformation at the level of the outer surface of the bronchial wall and provides robustness with respect to bronchusblood vessel contacts, where image data is irrelevant. The accuracy of the volumetric segmentation approach was evaluated with respect to 3D mathematically-simulated phantoms of bronchial subdivisions. Comparisons with recent 2D techniques, carried out on simulated and real MDCT data showed similar performances in cross-section wall area quantification. The benefit of using volumetric versus cross-section area quantification is finally argued in the context of bronchial reactivity and wall remodeling follow-up.