Relationships Between Airflow Obstruction and Quantitative CT Measurements of Emphysema, Air Trapping, and Airways in Subjects With and Without Chronic Obstructive Pulmonary Disease

Abstract

OBJECTIVE This study evaluates the relationships between quantitative CT (QCT) and spirometric measurements of disease severity in cigarette smokers with and without chronic obstructive pulmonary disease (COPD). MATERIALS AND METHODS Inspiratory and expiratory CT scans of 4062 subjects in the Genetic Epidemiology of COPD (COPDGene) Study were evaluated. Measures examined included emphysema, defined as the percentage of low-attenuation areas ≤ −950 HU on inspiratory CT, which we refer to as “LAA-950I”; air trapping, defined as the percentage of low-attenuation areas ≤ −856 HU on expiratory CT, which we refer to as “LAA-856E”; and the inner diameter, inner and outer areas, wall area, airway wall thickness, and square root of the wall area of a hypothetical airway of 10-mm internal perimeter of segmental and subsegmental airways. Correlations were determined between spirometry and several QCT measures using statistics software (SAS, version 9.2). RESULTS QCT measurements of low-attenuation areas correlate strongly and significantly (p < 0.0001) with spirometry. The correlation between LAA-856E and forced expiratory volume in 1 second (FEV1) and the ratio of FEV1 to forced vital capacity (FVC) (r = −0.77 and −0.84, respectively) is stronger than the correlation between LAA-950I and FEV1 and FEV1/FVC (r = −0.67 and r = −0.76). Inspiratory and expiratory volume changes decreased with increasing disease severity, as measured by the Global Initiative for Chronic Obstructive Pulmonary Disease (GOLD) staging system (p < 0.0001). When airway variables were included with low-attenuation area measures in a multiple regression model, the model accounted for a statistically greater proportion of variation in FEV1 and FEV1/FVC (R2 = 0.72 and 0.77, respectively). Airway measurements alone are less correlated with spirometric measures of FEV1 (r = 0.15 to −0.44) and FEV1/FVC (r = 0.19 to −0.34). CONCLUSION QCT measurements are strongly associated with spirometric results showing impairment in smokers. LAA-856E strongly correlates with physiologic measurements of airway obstruction. Airway measurements can be used concurrently with QCT measures of low-attenuation areas to accurately predict lung function.

Progress in Imaging COPD, 2004 - 2014

“…Murphy, et al, in a study of 216 cigarette smokers showed that LAA exp850 provided remarkably high correlations (r=0.85-0.90) with forced expiratory in 1 second to forced vital capacity (FEV 1 /FVC) ratio and with FEV 1 percent predicted. 50 Schroeder, et al, 13 found similar levels of correlation in a study of 4,062 COPDGene® participants with and without COPD. Quantitative CT evaluation of severity of emphysema and expiratory gas trapping provides a simple way to assign individual COPD patients to subgroups characterized by predominant emphysema, mixed emphysema and gas trapping, and predominant gas trapping.…”

“…57 There are modest correlations between airway wall area % and physiologic impairment. 13,58 Additionally, Washko, et al, 58 showed that on multivariate analysis, wall area % and peak airway attenuation appeared to be independent predictors of FEV 1 % predicted.…”

“…However, the effect of these techniques on visual and quantitative evaluation remains unclear. [9][10][11][12] Expiratory CT is increasingly recognized as an important part of the assessment of COPD, 13,14 to facilitate visual and quantitative assessment of the presence and distribution of air trapping. Expiratory images may be obtained at relatively low CT dose.…”

Heterogeneity of Specific Gas Volume Changes

“…According to a recently published study, 19 For each subject, a plot including all the segments connecting the values of SVg (expressed as percentage of SVg,TLC) and of lung volume (expressed as percentage of predicted TLC volume) at TLC and RV for each bronchopulmonary segment was constructed (gray lines in Fig 2 ). In the same plot, the segment relative to the overall lung was included (black line in Fig 2 ).…”

Emphysema: Imaging for Endoscopic Lung Volume Reduction

“…In contrast, a higher dosage is necessary for the analysis of the airways particularly in the case of software-assisted evaluations. For example, the median effective current exposure time product in the COPD Gene Study was 180 mAs [39]. In our scan protocol, tube current was 100 mAs and tube voltage 120 KV.…”