Airway wall thickness assessed using computed tomography and optical coherence tomography

Abstract

Rationale: Computed tomography (CT) has been shown to reliably measure the airway wall dimensions of medium to large airways. Optical coherence tomography (OCT) is a promising new micron-scale resolution imaging technique that can image small airways 2 mm in diameter or less.

Objectives: To correlate OCT measurements of airway dimensions with measurements assessed using CT scans and lung function.

Methods: Forty-four current and former smokers received spirometry, CT scans, and OCT imaging at the time of bronchoscopy. Specific bronchial segments were identified and measured using the OCT images and three-dimensional reconstructions of the bronchial tree using CT.

Measurements and main results: There was a strong correlation between CT and OCT measurements of lumen and wall area (r = 0.84, P < 0.001, and r = 0.89, P < 0.001, respectively). Compared with CT, OCT measurements were lower for both lumen and wall area by 31 and 66%, respectively. The correlation between FEV(1)% predicted and CT and OCT measured wall area (as percentage of the total area) of fifth-generation airways was very strong (r = -0.79, r = -0.75), but the slope of the relationship was much steeper using OCT than using CT (y = -0.33x + 82, y = -0.1x + 78), indicating greater sensitivity of OCT in detecting changes in wall measurements that relate to FEV(1).

Conclusions: OCT can be used to measure airway wall dimensions. OCT may be more sensitive at detecting small airway wall changes that lead to FEV(1) changes in individuals with obstructive airway disease.

Figure 1.

A screen shot of the Pulmonary Workstation 2.0 software (VIDA Diagnostics, Iowa City, IA) showing a multiplanar reformat of the right lateral basal segmental bronchus. The longitudinal section of the reformatted airway is shown in (A), and the cross-section of the airway at right angles to the center line of the airway segment at the location of the yellow dotted line in (A) is shown in (B). (C) The three-dimensional reconstruction of the airway tree, with the path of airway in (A) highlighted in blue. (D) An internal view of the airway at the level of (B). Measurements of the airway dimensions are automatically calculated for each segment of the airway path (between airway branch points) as indicated by the red lines at the level of the inferior lobar bronchus in (A).

Figure 2.

Optical coherence tomography images of a third-generation airway (A) and a fifth-generation airway (B), which were compared with pulmonary function. The internal perimeter (Pi) and outer perimeter (Po) of the airway wall was manually traced using ImageJ software (National Institutes of Health, Bethesda, MD), and the lumen area (Ai) and wall area (Aaw) were calculated using these boundaries.

Figure 3.

The relationship between percentage of airway wall area (WA%) estimated by computed tomography (CT) and that by optical coherence tomography (OCT).

Figure 4.

The relationship between percentage of wall area of a third-generation airway (A) and a fifth-generation airway (B) as estimated by computed tomography (CT) (open circles) and by optical coherence tomography (OCT) (closed diamonds) and FEV₁% predicted. The slope of the regression line for the OCT is different from that of the CT (P < 0.0001).

Figure 5.

Images of fifth-generation airways obtained using computed tomography (CT) (A, B) and optical coherence tomography (OCT) (C, D). The airways in (A) and (C) were obtained from a subject with normal FEV₁ (118% predicted) and in (B) and (D) are obtained from a subject with an FEV₁ of 52% predicted. The percentage of wall area measured using CT is only 5% different (69 vs. 74%) but 29% different (43 vs. 72%) using OCT. The green dotted arrow in the CT images (A, B) represents the orientation of the longitudinal plane of the reformatted airway path from which the cross-sectional image is obtained (see Figure 1).