Quantifying Pectoralis Muscle and Lung Characteristics in COPD

All patients underwent volumetric, thin-section, chest CT at full inspiration and expiration in the supine position. CT images were acuqired using a first-generation, dual-source CT scanner (Somatom Definition; Siemens Healthcare, Forchheim, Germany) in a caudocranial direction using the following parameters: 140 kVp, 100 mA, 0.9–1 beam pitch and slice thickness 0.6 mm and 3 mm. CT data were reconstructed using a soft convolution kernel (B30f). The pectoralis muscle was evaluated using mediastinal window images [width, 400 Hounsfield units (HU); level, 20 HU].
PMA and PMD were measured on a single axial slice of the chest CT scan above the aortic arch at baseline CT (Fig. 2) [12 (link)]. The pectoralis muscle was segmented by drawing a region of interest (ROI) that traced along the edge of the right and left pectoralis major and minor muscles; COPD severity was blinded during the analyses. PMA (in cm²) was evaluated as the sum of the left and right pectoralis major and minor muscles. PMD (in HU) was defined as the mean attenuation within the ROI that segmented the pectoralis muscle.
Fig. 2

Computed tomography (CT) scans were used to assess the pectoralis muscle area and density. a, the CT axial slice above the aortic arch level shows the pectoralis muscle segmentation (red, pectoralis major muscle; blue, pectoralis minor muscle). b and c, differences between pectoralis muscle densities are depicted in CT images

Using in-house software, whole-lung images were automatically extracted from the chest wall, mediastinum and large airways to quantitatively assess emphysema and bronchial wall thickness. Subsequently, the attenuation coefficients of pixels in these images were measured. The emphysema index (EI) was defined as the volume fraction (%) of the lung below − 950 HU at full inspiration [21 (link)]. Airway dimensions, including wall area (WA), lumen area, and WA% [defined as WA/(WA + lumen area) × 100], were measured near the origin of the right apical and left apicoposterior segmental bronchi [22 (link)]. Furthermore, WA% was used to assess airway thicknesses and the mean values of segmental bronchi in the statistical analyses; these CT measurements were performed on each participant at baseline.