Spirometric assessment of emphysema presence and severity as measured by quantitative CT and CT-based radiomics in COPD.

BACKGROUND: The mechanisms underlying airflow obstruction in COPD cannot be distinguished by standard spirometry. We ascertain whether mathematical modeling of airway biomechanical properties, as assessed from spirometry, could provide estimates of emphysema presence and severity, as quantified by computed tomography (CT) metrics and CT-based radiomics. METHODS: We quantified presence and severity of emphysema by standard CT metrics (VIDA) and co-registration analysis (ImbioLDA) of inspiratory-expiratory CT in 194 COPD patients who underwent pulmonary function testing. According to percentages of low attenuation area below - 950 Hounsfield Units (%LAA-950insp) patients were classified as having no emphysema (NE) with %LAA-950insp < 6, moderate emphysema (ME) with %LAA-950insp ≥ 6 and < 14, and severe emphysema (SE) with %LAA-950insp ≥ 14. We also obtained stratified clusters of emphysema CT features by an automated unsupervised radiomics approach (CALIPER). An emphysema severity index (ESI), derived from mathematical modeling of the maximum expiratory flow-volume curve descending limb, was compared with pulmonary function data and the three CT classifications of emphysema presence and severity as derived from CT metrics and radiomics. RESULTS: ESI mean values and pulmonary function data differed significantly in the subgroups with different emphysema degree classified by VIDA, ImbioLDA and CALIPER (p < 0.001 by ANOVA). ESI differentiated NE from ME/SE CT-classified patients (sensitivity 0.80, specificity 0.85, AUC 0.86) and SE from ME CT-classified patients (sensitivity 0.82, specificity 0.87, AUC 0.88). CONCLUSIONS: Presence and severity of emphysema in patients with COPD, as quantified by CT metrics and radiomics can be estimated by mathematical modeling of airway function as derived from standard spirometry.

Explorative data analysis techniques and unsupervised clustering methods to support clinical assessment of Chronic Obstructive Pulmonary Disease (COPD) phenotypes.

Chronic Obstructive Pulmonary Disease (COPD) is the fourth leading cause of death worldwide and represents one of the major causes of chronic morbidity. Cigarette smoking is the most important risk factor for COPD. In these patients, the airflow limitation is caused by a mixture of small airways disease and parenchyma destruction, the relative contribution of which varies from person to person. The twofold nature of the pathology has been studied in the past and according to some authors each patient should be classified as presenting a predominantly bronchial or emphysematous phenotype. In this study we applied various explorative analysis techniques (PCA, MCA, MDS) and recent unsupervised clustering methods (KHM) to study a large dataset, acquired from 415 COPD patients, to assess the presence of hidden structures in data corresponding to the different COPD phenotypes observed in clinical practice. In order to validate our methods, we compared the results obtained from a training set of 415 patients with lung density data acquired in a test set of 93 patients who underwent HRCT (High Resolution Computerized Tomography).

Whole-lung densitometry versus visual assessment of emphysema.

We compared whole-lung densitometry with visual evaluation of pulmonary emphysema. Thirty patients with chronic obstructive pulmonary disease underwent multi-detector CT (150 mAs and 0.75 collimation) with double reconstruction: thick (5-mm) slices with smooth filter for whole-lung densitometry and thin (1 mm) slices with sharp filter for visual assessment (one of every ten slices). Densitometry and visual assessment were performed by three operators each, and the time required for assessment, the inter-observer agreement and the correlation with the results of the diffusion capacity of carbon monoxide (DL(CO)) in the same patients were computed. The average time for densitometry (8.49 +/- 0.13 min) was significantly longer (p < 0.0001) than that for visual evaluation (5.14 +/- 0.11 min). However, the inter-operator agreement ranged between "moderate" to "almost perfect" for densitometry (kappa range 0.58-0.87) and "slight" for visual (kappa = 0.20) assessment. The correlation coefficients of DL(CO) with relative area at -960 and -970 Hounsfield units (HU) (both r = -0.66) and of the first percentile point of lung density (r = 0.66) were slightly stronger than that of the visual score (r = -0.62). Densitometry should be preferred to visual assessment because it enables a more reproducible evaluation of the extent of pulmonary emphysema, which can be carried out on the entire lung in a reasonable amount of time.