Lung bronchioles. Three-dimensional computed tomo- graphy (CT) scan of dividing bronchioles in the right lung. Bronchioles are the small tubes leading from the trachea and bronchi to the alve- oli (air sacs) in the lungs. CT scans use X-rays to take slice images through the body, which are combined to give this 3-D endoscopic effect. This virtual endoscopy allows a detailed view of inte- rnal structures without using invasive techniques.