Purpose To quantify tracheal collapsibility using low-dose four-dimensional (4D) CT and to compare visual and quantitative 4D CT-based assessments with assessments from paired inspiratory-expiratory CT, bronchoscopy, and spirometry. Materials and Methods The authors retrospectively analyzed 4D CT examinations (January 2016-December 2022) during shallow respiration in 52 patients (mean age, 66 years ± 12 [SD]; 27 female, 25 male), including 32 patients with chronic obstructive pulmonary …