Region of interest.Ba, basion; N, nasion; (1) the most anterior point of the posterior border of the nasal septum; (2) the most posterior-inferior point of ethmoid sinus; (3) the most posterior point of the anterior nasal nares; Anterior border: the vertical plane passing point 3; Posterior border: the vertical plane passing point 1; Superior border: A spline curve by basion (Ba), point 2, and nasion (N); Inferior border: natural nasal cavity floor.