• Mariaelena Occhipinti, Matteo Paoletti, Francesca Bigazzi, Gianna Camiciottoli, Riccardo Inchingolo, LariciAnna RitaARFrom the Section of Respiratory Medicine, Department of Experimental and Clinical Medicine, University of Florence, Careggi University Hospital, Largo A. Brambilla 3, 50134 Florence, Italy (M.O., M. Paoletti, F.B., G.C., M. Pistolesi); an, and Massimo Pistolesi.
• From the Section of Respiratory Medicine, Department of Experimental and Clinical Medicine, University of Florence, Careggi University Hospital, Largo A. Brambilla 3, 50134 Florence, Italy (M.O., M. Paoletti, F.B., G.C., M. Pistolesi); and Departments of Pulmonology (R.I.) and Radiological Sciences (A.R.L.), Gemelli University Hospital, Catholic University of the Sacred Heart, Rome, Italy.
• Radiology. 2018 May 1; 287 (2): 683-692.

AbstractPurpose To identify a prevalent computed tomography (CT) subtype in patients with chronic obstructive pulmonary disease (COPD) by separating emphysematous from nonemphysematous contributions to total gas trapping and to attempt to predict and grade the emphysematous gas trapping by using clinical and functional data. Materials and Methods Two-hundred and two consecutive eligible patients (159 men and 43 women; mean age, 70 years [age range, 41-85 years]) were prospectively studied. Pulmonary function and CT data were acquired by pulmonologists and radiologists. Noncontrast agent-enhanced thoracic CT scans were acquired at full inspiration and expiration, and were quantitatively analyzed by using two software programs. CT parameters were set as follows: 120 kVp; 200 mAs; rotation time, 0.5 second; pitch, 1.1; section thickness, 0.75 mm; and reconstruction kernels, b31f and b70f. Gas trapping obtained by difference of inspiratory and expiratory CT density thresholds (percentage area with CT attenuation values less than -950 HU at inspiration and percentage area with CT attenuation values less than -856 HU at expiration) was compared with that obtained by coregistration analysis. A logistic regression model on the basis of anthropometric and functional data was cross-validated and trained to classify patients with COPD according to the relative contribution of emphysema to total gas trapping, as assessed at CT. Results Gas trapping obtained by difference of inspiratory and expiratory CT density thresholds was highly correlated (r = 0.99) with that obtained by coregistration analysis. Four groups of patients were distinguished according to the prevalent CT subtype: prevalent emphysematous gas trapping, prevalent functional gas trapping, mixed severe, and mixed mild. The predictive model included predicted forced expiratory volume in 1 second/vital capacity, percentage of predicted forced expiratory volume in 1 second, percentage of diffusing capacity for carbon monoxide, and body mass index as emphysema regressors at CT, with 81% overall accuracy in classifying patients according to its extent. Conclusion The relative contribution of emphysematous and nonemphysematous gas trapping obtained by coregistration of inspiratory and expiratory CT scanning can be determined accurately by difference of CT inspiratory and expiratory density thresholds. CT extent of emphysema can be predicted with accuracy suitable for clinical purposes by pulmonary function data and body mass index. © RSNA, 2018 Online supplemental material is available for this article.

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