Two sequential frames of the pig trachea (a) immediately before and (b) after 200 µm HRI glass-bead MCT marker particle delivery. The tip of the ET tube is visible on the right side of the image, with the particle-delivery tube (and particles) visible inside it. The dense object is a wire that was placed inside the ET tube of the first animal to aid in locating the tip. No particle identification or tracking was performed on these two images, so particles are unmarked. Scale bar: 5 mm.