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Figure 1 | Respiratory Research

Figure 1

From: Diagnosis of chronic obstructive pulmonary disease in lung cancer screening Computed Tomography scans: independent contribution of emphysema, air trapping and bronchial wall thickening

Figure 1

Illustration of the lung segmentation process and calculation of CT emphysema and CT air trapping. A = Axial inspiratory CT image; B = Axial expiratory CT image; C and D = Overlay showing the lung segmentation of the right (turquoise) and left (green) lung in an axial slice. The trachea and main bronchi are shown in blue; E = Overlay showing the lung segmentation in a coronal inspiratory CT image; F = Graph showing the attenuation histograms of both the inspiratory and expiratory CT. CT emphysema is calculated as the percentage of voxels below −950 HU. CT air trapping is calculated as the ratio of the expiratory to inspiratory mean lung density.

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