Low-Dose Whole-Chest Dynamic CT for the Assessment of Large Airway Collapsibility in Patients with Suspected Tracheobronchial Instability

Abstract

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 disease (mean forced expiratory volume in 1 second percentage predicted [FEV₁%], 50% ± 27), with suspected tracheal collapse. Paired CT data were available for 27 patients and bronchoscopy data for 46 patients. Images were reviewed by two radiologists in consensus, classifying patients into three groups: 50% or greater tracheal collapsibility, less than 50% collapsibility, or fixed stenosis. Changes in minimal tracheal lumen area, tracheal volume, and lung volume from inspiration to expiration were quantified using YACTA software. Tracheal collapsibility between groups was compared employing one-way analysis of variance (ANOVA). For related samples within one group, ANOVA with repeated measures was used. Spearman rank order correlation coefficient was calculated for collapsibility versus pulmonary function tests. Results At 4D CT, 25 of 52 (48%) patients had tracheal collapsibility of 50% or greater, 20 of 52 (38%) less than 50%, and seven of 52 (13%) had fixed stenosis. Visual assessment of 4D CT detected more patients with collapsibility of 50% or greater than paired CT, and concordance was 41% (P < .001). 4D CT helped identify more patients with tracheal collapsibility of 50% or greater than did bronchoscopy, and concordance was 74% (P = .39). Mean collapsibility of tracheal lumen area and volume at 4D CT were higher for 50% or greater visually assessed collapsibility (area: 53% ± 9 and lumen: 52% ± 10) compared with the less than 50% group (27% ± 9 and 26% ± 6, respectively) (P < .001), whereas both tracheal area and volume were stable for the fixed stenosis group (area: 16% ± 12 and lumen: 21% ± 11). Collapsibility of tracheal lumen area and volume did not correlate with FEV₁% (r_s = -0.002 to 0.01, P = .99-.96). Conclusion The study demonstrated that 4D CT is feasible and potentially more sensitive than paired CT for central airway collapse. Expectedly, FEV₁% was not correlated with severity of tracheal collapsibility. Keywords: CT-Quantitative, Tracheobronchial Tree, Chronic Obstructive Pulmonary Disease, Imaging Postprocessing, Thorax Supplemental material is available for this article. © RSNA, 2024.

Keywords: CT-Quantitative; Chronic Obstructive Pulmonary Disease; Imaging Postprocessing; Thorax; Tracheobronchial Tree.

Graphical abstract

Figure 1:

Study flowchart. Patients were grouped as having fixed stenosis or tracheal collapsibility, the latter with a threshold of 50% or greater reduction of minimal lumen area. The most frequent diagnosis was tracheobronchomalacia (TBM), and its most frequent subtype was crescent-type collapse. (E)DAC = (excessive) dynamic airway collapse.

Figure 2:

Quantification of (A) minimal tracheal lumen area, (B) tracheal volume, and (C) lung volume during the respiratory cycle by using four-dimensional (4D) CT. Patients were grouped according to visual degree of collapsibility. Relative changes during free shallow breathing are shown with the respiratory cycle separated into 21 discrete time points equal to 5%-wide steps at 4D CT. Symbols represent group means, and whiskers indicate standard error of the mean; statistical significance is given for maximum inspiration versus end expiration, with * indicating P < .001. Comparisons of tracheal collapsibility between groups along the 21 steps of the respiratory cycle were made by one-way analysis of variance (ANOVA). For related samples within the patient groups, ANOVA with repeated measures was used. P < .05 was accepted as statistically significant, including corrections for multiple comparisons by Bonferroni method.

Figure 3:

Low concordance of paired inspiratory-expiratory CT with four-dimensional (4D) CT. The top row represents paired inspiratory-expiratory CT (noncontrast, lung window) in (A) inspiratory and (B) expiratory breath hold in axial plane in a 77-year-old male patient. The bottom row shows the same patient under shallow breathing at 4D CT (noncontrast, lung window) in (C) maximum inspiration and (D) end expiration in axial plane. Note that the tracheal collapsibility was less than 50% at paired inspiratory-expiratory CT but 50% or greater at 4D CT. The level of strongest collapse varied slightly between paired CT and 4D CT.

Figure 4:

Representative example of circumferential-type tracheobronchomalacia (TBM). (A) Image from four-dimensional (4D) CT (noncontrast, lung window) in a 72-year-old male patient with circumferential-type TBM at the level of maximum observed tracheal collapsibility at representative selected time points of the respiratory cycle. The upper row shows axial view, the lower row sagittal view. The axial view demonstrates the circular collapse of the trachea because of cartilaginous malacia. (B) Graph shows the changes of minimal tracheal lumen area, tracheal volume, and lung volume in the same patient over the respiratory cycle with 21 time points in 5%-wide steps at 4D CT. (C) Image from correlated bronchoscopy.

Figure 5:

Representative example of excessive dynamic airway collapse (EDAC). (A) Images from four-dimensional (4D) CT (noncontrast, lung window) in a 51-year-old female patient with EDAC at the level of maximum observed tracheal collapsibility at representative selected time points of the respiratory cycle. The upper row shows axial view, the lower row sagittal view. The axial view demonstrates the inward bowing of the posterior membrane while the cartilage retains its normal shape. (B) Graph shows the changes of minimal tracheal lumen area, tracheal volume, and lung volume of the same patient over the respiratory cycle with 21 time points in 5%-wide steps at 4D CT. (C) Image from correlated bronchoscopy.

Figure 6:

Representative example of fixed tracheal stenosis. (A) Images from four-dimensional (4D) CT (noncontrast, lung window) in a 53-year-old female patient with fixed tracheal stenosis at the level of maximum observed tracheal narrowing at representative selected time points of the respiratory cycle. The upper row shows axial view, the lower row sagittal view. No dynamic changes were observed. (B) Graph shows the changes of minimal tracheal lumen area, tracheal volume, and lung volume of the same patient over the respiratory cycle with 21 time points in 5%-wide steps at 4D CT. (C) Image from correlated bronchoscopy.