Assessment of bronchial wall thickness and lumen diameter in human adults using multi-detector computed tomography: comparison with theoretical models

Abstract

A thickened bronchial wall is the morphological substratum of most diseases of the airway. Theoretical and clinical models of bronchial morphometry have so far focused on bronchial lumen diameter, and bronchial length and angles, mainly assessed from bronchial casts. However, these models do not provide information on bronchial wall thickness. This paper reports in vivo values of cross-sectional wall area, lumen area, wall thickness and lumen diameter in ten healthy subjects as assessed by multi-detector computed tomography. A validated dedicated software package was used to measure these morphometric parameters up to the 14th bronchial generation, with respect to Weibel's model of bronchial morphometry, and up to the 12th according to Boyden's classification. Measured lumen diameters and homothety ratios were compared with theoretical values obtained from previously published studies, and no difference was found when considering dichotomic division of the bronchial tree. Mean wall area, lumen area, wall thickness and lumen diameter were then provided according to bronchial generation order, and mean homothety ratios were computed for wall area, lumen area and wall thickness as well as equations giving the mean value of each parameter for a given bronchial generation with respect to its value in generation 0 (trachea). Multi-detector computed tomography measurements of bronchial morphometric parameters may help to improve our knowledge of bronchial anatomy in vivo, our understanding of the pathophysiology of bronchial diseases and the evaluation of pharmacological effects on the bronchial wall.

Fig. 1

SAB-3D software applied to a chest MDCT acquisition. Volumetric data of a thorax examination were used to reconstruct 1-mm thin-section CT images (a), from which a propagation algorithm allows us to obtain a binary volume and subsequently a skeleton of the airway tree (b, frontal view). An error occurred in the skeletonization of the tracheal division, but this was not detrimental to measurements of main bronchi morphometric parameters. Seven contiguous cross-sectional reconstructions of a bronchus perpendicular to its central axis are shown (c). The selected bronchus belonged to the fifth generation and the anterior segment of the right upper lobe; this is shown on the native CT section (a, arrowhead), and the binary volume and skeleton (b, arrow). The thin section on which measurements were performed was chosen with the minimum of contiguity with surrounding vessels (d, open arrowhead shows the selected bronchus). Detection of airway contours by a Laplacian of Gaussian algorithm was then performed (e, empty arrowhead) to provide automated measurements of LA and WA.

Fig. 2

Plots of mean lumen diameter over all subjects on a logarithmic scale (log LD) against bronchial generations according to Weibel's model (left graph) and Boyden's classification (right graph). Black circles: log of measured LD; open circles: log of theoretical LD calculated with the mean measured HR; dashed line: log of theoretical LD calculated using an HR value of 0.79 (Weibel); dotted line: log of theoretical LD calculated using an HR value of 0.85 (Mauroy).

Fig. 3

Plots of mean homothety ratio over subjects (HR) against bronchial generations according to Weibel's model (left graph) and Boyden's classification (right graph). Black circles: measured HR, solid line: linear regression of the latter curve; open circles: mean measured HR; dashed line: HR value of 0.79 (Weibel); dotted line: HR value of 0.85 (Mauroy).

Fig. 4

Plot of mean wall thickness on a logarithmic scale (log WT) against bronchial generations according to Weibel's classification. Black triangles: log of measured WT; open triangles: log of theoretical WT calculated with the mean measured HR.