Comparison of endoscopic versus 3D CT derived airway measurements

Abstract

Objectives/hypothesis: To understand: 1) how endoscopic airway measurements compare to three-dimensional (3D) CT derived measurements; 2) where each technique is potentially useful; and 3) where each has limitations.

Study design: Compare airway diameters and cross-sectional areas from endoscopic images and CT derived 3D reconstructions.

Methods: Videobronchoscopy was performed and recorded on an adult-sized commercially available airway mannequin. At various levels, cross-sectional areas were measured from still video frames using a referent placed via the biopsy port. A 3D reconstruction was generated from a high resolution CT of the mannequin; planar sections were cut at similar cross-sectional levels; and cross-sectional areas were obtained.

Results: At three levels of mechanically generated tracheal stricture, the differences between the endoscopic measurement and CT-derived cross-sectional area were 1%, 0%, and 7% (1.8, 0.8, and 14 mm²). At the vocal folds, the difference was 9% (7.8 mm²). The tip of the epiglottis and width of the epiglottis differed by 27% and 10% (18.73 mm², 0.40 mm). The airway measurements at the base of tongue, minimal cross-sectional area of the pharynx, and choana differed by 26%, 36%, and 30% (101.40 mm², 36.67 mm², 122.71 mm²).

Conclusions: Endoscopy is an effective tool for obtaining airway measurements compared with 3D reconstructions derived from CT. Concordance is best in geometrically simple areas where the entire cross-section measured is visible within one field of view (trachea, round; vocal folds, triangular) versus geometrically complex areas that encompass more than one field of view (i.e. pharynx, choana).

Figures

Figure 1

3D reconstruction of high resolution CT scan of the commercial training mannequin using Mimics software.

Figure 2

Levels of interest chosen for cross-sectional measurements.

Figure 3

Third Stricture. A1, A2: Cross-sectional area, endoscopic, 3D CT (177.0 mm2, 199.2 mm2). B1, B2: Vertical midline diameter, endoscopic, 3D CT (15.6 mm, 17.3 mm). C1, C2: Horizontal midline diameter, endoscopic, 3D CT (13.6 mm, 13.6 mm). Fields of view = 1.

Figure 4

Second Stricture. A1, A2: Cross-sectional area, endoscopic, 3D CT (205.7 mm2, 204.9 mm2). B1, B2: Vertical midline diameter, endoscopic, 3D CT (14.8 mm, 14.2 mm). C1, C2: Horizontal midline diameter, endoscopic, 3D CT (15.6 mm, 15.6 mm). Fields of view = 1.

Figure 5

First Stricture. A1, A2: Cross-sectional area, endoscopic, 3D CT (127.8 mm2, 129.6 mm2). B1, B2: Vertical midline diameter, endoscopic, 3D CT (13.3 mm, 13.1 mm). C1, C2: Maximum vertical diameter, endoscopic, 3D CT (14.1 mm, 13.3 mm). D1, D2: Horizontal midline diameter, endoscopic, 3D CT (10.7 mm, 11.3 mm). E1, E2: Maximum horizontal diameter, endoscopic, 3D CT (10.8 mm, 11.6 mm). Fields of view = 1.

Figure 6

True Vocal Folds. A1, A2: Cross-sectional area, endoscopic, 3D CT (82.0 mm2, 89.8 mm2). B1, B2: Vertical midline diameter, endoscopic, 3D CT (18.8 mm, 21.3 mm). C1, C2: Horizontal midline diameter, endoscopic, 3D CT (4.8 mm, 4.6 mm). D1, D2: Maximum horizontal diameter, endoscopic, 3D CT (5.8 mm, 5.5 mm). Fields of view = 2.

Figure 7

Width of Epiglottis. A1, A2: Width of epiglottis, endoscopic, 3D CT (3.5 mm, 3.9 mm). Fields of view = 1.

Figure 8

Created region behind the tip of epiglottis. A1, A2: Cross-sectional area, endoscopic, 3D CT (51.2 mm2, 69.9 mm2). B1, B2: distance from middle of epiglottis tip to posterior hypopharynx, endoscopic, 3D CT (5.6 mm, 5.3 mm). Fields of view = 2.

Figure 9

Base of Tongue. A1, A2: Cross-sectional area, endoscopic, 3D CT (489.1 mm2, 387.7 mm2). B1, B2: Vertical midline diameter, endoscopic, 3D CT (15.8 mm, 15.8 mm). Fields of view = 4.

Figure 10

Minimal Cross-Sectional Area of the Pharynx. A1, A2: Cross-sectional area, endoscopic, 3D CT (414.4 mm2, 291.4 mm2). B1, B2: Vertical midline diameter, endoscopic, 3D CT (16.6 mm, 22.8 mm). C1, C2: Maximum horizontal diameter, endoscopic, 3D CT (28.6 mm, 12.6 mm). Fields of view = 7.

Figure 11

Left Choana. A1, A2: Cross-sectional area, endoscopic, 3D CT (100.9 mm2, 137.6 mm2). B1, B2: Vertical midline diameter, endoscopic, 3D CT (12.9 mm, 15.2 mm). C1, C2: Horizontal midline diameter, endoscopic, 3D CT (10.3 mm, 11.7 mm). Fields of view = 6.