3D Pharyngeal Airway Modeling from CBCT Scans

The object of this study was a 13-year-old boy who underwent a Cone-Beam CT (CBCT) scan at the Department of Orthodontics (Stomatological hospital, Dalian, China). The scans were retrospectively collected and used to reconstruct a 3D model of the upper airway (3D eXam; KaVo, Biberach an der Riss, Germany). The recorded scanning parameters were 120 kV and 5 mA, with a scanning time of 14.7 s. Voxel size was 0.2 mm, and each layer was scanned at a 0.2 mm interval, with 14-bit pixel depth and 13 × 17 cm field of view. The CBCT scan was exported in digital imaging and communications in medicine format for further analysis. The airway boundary was defined using a grayscale threshold from − 1024 to − 800 (approximately − 1000 Hounsfield units for air region) in Mimics 23.0 (Materialise, Belgium) that acquired a 3D segmented UA surface model, including nasopharynx, velopharynx, and soft palate within uvula, part of the oral cavity, oropharynx, and laryngopharynx (Fig. 7). In this study, the inlets (nasal choana and oral cavity) and outlet (base of the epiglottis) were elongated to 10 mm, 2 mm, and 40 mm, respectively^{29 (link)}. This surface model was filled as a volume model for the fluid domains and a 2 mm thick airway structure for the solid domain^{12 (link)}.Figure 7

Reconstruction procedure of the fluid region and pharyngeal structure with identified boundary regions. (1) Inlet of nasopharynx, (2) uvula, (3) inlet of oral cavity, (4) tonsil surface, (5) surface of the tongue base, (6) structure of nasopharynx, (7) structure of velopharynx, (8) structure of oropharynx (deformable), (9) epiglottis, (10) bottom of pharyngeal airway, (11) extension.