Geometric features of pig airways using computed tomography

Abstract

Accurate knowledge of the airway geometry is needed when constructing physical models of the airway tree and for numerical modeling of flow or sound propagation in the airways. Human and animal experiments are conducted to validate these models. Many studies documented the geometric details of the human airways. However, information about the geometry of pig airways is scarcer. Earlier studies suggested that the morphology of animal airways can be significantly different from that of humans. The objective of this study is to measure the airway diameter, length and bifurcation angles in domestic pigs using computed tomography. In this study, lungs of six pigs were imaged, then segmentation software tools were used to extract the geometry of the airway lumen. The airway dimensions were measured from the resulting 3-D models for the first 24 airway generations. Results showed that the size and morphology of the airways of the six pigs were similar. The trachea diameters were found to be comparable to the typical human adult, but the diameter, length and branching angles of other airways were noticeably different from that of humans. For example, pig airways consistently had an early branching from the trachea that feeds the top right lung lobe and precedes the main carina. This branch is absent in the human airways. The results suggested that the pig airways geometry may not be accurately approximated by human airways and this approximation may contribute to increasing the errors in computational models of the pig chest.

Keywords: Airway tree; bifurcating plane; generation; image segmentation; transition zone.

Figure 1

Example of airways that were extracted from CT images of two different pigs (A. Pig 2 and B. Pig 3) using automatic and manual segmentation. The airways are viewed from the anterior side. There is an early airway branching that feeds the top right lung lobe, which was consistently seen in the six study subjects but not usually seen in humans. In addition, the two main bronchi tended to have monopodial morphology and continue in the same general direction after several branching.

Figure 2

(A) Semi log graph of airway diameter versus generation. (B) Airway length versus generation. (C) Bifurcation angle for major daughter (angle 1) versus generation. (D) Bifurcation angle for minor daughter (angle 2) versus generation.

Figure 3

Daughter to parent diameter versus generation (A) major daughter (d1/D) ratio and (B) minor daughter ratio (d2/D).

Figure 4

(A, B) Change in bifurcating plane of parent branch of right and left mainstem bronchi. (C) Side view of the Airway Tree.

Figure 5

(A) Radius of edge of flow divider. (B) Percentage of transition zone at different generations.