The use of SPHARM-PDM and mean latitude axis to evaluate airway changes

Abstract

Objective: To introduce new 3-D imaging techniques to characterize shape and volume changes of the oropharyngeal space after bilateral sagittal split osteotomy (BSSO) advancement. Materials and Methods: Longitudinal cone-beam computed tomography (CBCT) scans were obtained for 20 patients undergoing BSSO advancement at three time points (T1presurgery, T2 splint removal, and T31 year after surgery). Segmentation of the airway was performed using the following boundaries: hard palate/posterior nasal spine superiorly and lower border of C3 to the base of the epiglottis inferiorly. For shape measurements, point-based correspondent models and mean latitude axis were obtained for all the data using SPHARM-PDM software. All 3-D correspondent models were rigidly registered using Procrustes alignment. Absolute distance maps and corresponding vector maps were calculated to show shape and vector differences between each correspondent point. Mean latitude axis is a new imaging method to calculate minimum crosssectional areas along the long axis of the airway independent of head position/alignment. Results: The airway volume increased (P , .01) after BSSO advancement (2973.9 mm3 6 27882.0) and was stable (439.9 mm3 6 3308.8) 1 year post-op. 3-D color maps and semitransparency overlays showed more lateral than anteroposterior expansion of the airway after BSSO advancement. Mean latitude axis was used to measure minimum cross-sectional area, showing a statistically significant increase (52.7 mm2 6 46.7) (P , .01) after surgery and remained stable (10.3 mm2 6 43.3) 1 year after surgery. Conclusions: SPHARM-PDM and mean latitude axis are useful tools to assess airway shape change. BSSO advancement produces a significant increase in pharyngeal airway volume and minimum cross-sectional area. The airway space increased more transversely than anteroposteriorly.