Advances in Chronic Obstructive Pulmonary Disease Imaging

Abstract

Chest computed tomography (CT) imaging is a useful tool that provides in vivo information regarding lung structure. Imaging has contributed to a better understanding of COPD, allowing for the detection of early structural changes and the quantification of extra-pulmonary structures. Novel CT imaging techniques have provided insight into the progression of the main COPD subtypes, such as emphysema and small airway disease. This article serves as a review of new information relevant to COPD imaging. CT abnormalities, such as emphysema and loss of airways, are present even in smokers who do not meet the criteria for COPD and in those with mild-to-moderate disease. Subjects with mild-to-moderate COPD, with the highest loss of airways, also experience the highest decline in lung function. Extra-pulmonary manifestations of COPD, such as right ventricle enlargement and low muscle mass measured on CT, are associated with increased risk for all-cause mortality. CT longitudinal data has also given insight into the progression of COPD. Mechanically affected areas of lung parenchyma adjacent to emphysematous areas are associated with a greater decline in FEV₁. Subjects with the greatest percentage of small airway disease, as measured on matched inspiratory-expiratory CT scan, also present with the greatest decline in lung function.

Figure 1:

The technique of image registration and two fundamental approaches to extracting clinically relevant information from image registration. Inspiratory and expiratory images are matched voxel-by-voxel. Structural measures can be obtained by performing a voxel-by-voxel anatomic comparison and assessing the corresponding computed tomography (CT) density change from expiration to inspiration, with compensation for lung deformation through image registration. The top right shows a representative axial section with localization of emphysema (red), functional small airways disease (yellow), and normal (green) voxels in a patient with moderate chronic obstructive pulmonary disease (COPD). The bottom right depicts functional changes on the same slice. Here, the amount of lung deformation between inspiration and expiration is used to derive a measure of regional ventilation, termed the Jacobian determinant, a measure of local volume change from full inspiration to end expiration. The Jacobian determinant ranges from 0 to infinity; values greater than 1 indicate local expansion, and values less than 1 indicate local contraction. PRM = parametric response mapping. Reprinted with permission of the American Thoracic Society. Copyright © 2020 American Thoracic Society. Annals of the American Thoracic Society 2018; 15(3): 281–289

Figure 2:

Computed tomography airway count by generation and airway lumen diameter. The three-dimensional reconstruction of the segmented airway tree generated by VIDA Diagnostics Inc. for never-smokers and participants at risk and with Global Initiative for Chronic Obstructive Lung Disease (GOLD) I and GOLD II chronic obstructive pulmonary disease (A). The plot summary data show airway counts for airways color coded by airway generation (B) and by various sizes divided into discrete bins (C). Error bars represent the SD of the airway counts for all participants. *Significantly different from neversmoker. †Significantly different from at-risk. ‡Significantly different from GOLD I. CT = computed tomography. Reprinted with permission of the American Thoracic Society. Copyright © 2020 American Thoracic Society. American Journal of Respiratory and Critical Care Medicine 2018; 197(1): 56–65.

Figure 3:

Pulmonary vasculature and right (blue) and left (red) ventricular reconstructions from computed tomography images for two subjects with approximately 20% emphysema on computed tomography scan. (A, C, and E) Subject 1 with 19% emphysema and relative preservation of the distal arterial vascular volume (arterial volume for vessels less than 5 mm2 in cross-section = 131 ml). (B, D, and F) Subject 2 with 18% emphysema and relative loss of the distal arterial vascular volume (arterial volume for vessels less than 5 mm2 in cross-section = 70.8 ml). (A and B) Axial images of the epicardial surface of the right ventricle (RV), which is outlined in blue and the epicardial surface of the left ventricle, which is outlined in red. Emphysema is depicted in green. (C and D) Frontal view of the arterial (blue) and venous vasculature and the surface model of the epicardial (myocardium and chamber) RV volume (blue) and epicardial (myocardium and chamber) left ventricular volume (red). The epicardial (myocardium and chamber) RV volume of Subject 1 is 58.9 ml and the epicardial (myocardium and chamber) RV volume for Subject 2 is 140 ml. (E and F) Sagittal views of the arterial (blue) and venous (red) vasculature of the left lung demonstrating the relative loss of distal arterial vascular volume. Emphysema is shown in green. Reprinted with permission of the American Thoracic Society. Copyright © 2020 American Thoracic Society. American Journal of Respiratory and Critical Care Medicine 2019; 200(4): 454–461.

Figure 4:

Age-stratified average relative composition of emphysema (Emph), functional small-airway disease (fSAD), normal tissue, and “other” (dark yellow portions) for each trajectory, as assessed by parametric response mapping analysis. Rows correspond to age strata, and columns correspond to trajectories; color-coded arrows clarify the direction of increasing age for each trajectory. Reprinted with permission of the American Thoracic Society. Copyright © 2020 American Thoracic Society. American Journal of Respiratory and Critical Care Medicine 2018; 198(8):1033–1042.