a Inspiratory image demonstrates mosaicism as shown in the difference in attenuation and vessel caliber between the regions marked by the blue arrows. The more lucent (black) region denoted by the lower arrow demonstrates vessel caliber attenuation compared to the region of higher attenuation. This regional difference signifies areas of air trapping in the lung due to small airways disease. The cause of mosaicism on inspiratory images can be confirmed on expiratory images. b Expiratory image is notable for marked air trapping in the regions with decreased attenuation denoted by the lower red and blue arrows. Increased attenuation due to normal air clearance is illustrated by the upper arrows.
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