Imaging extra-thoracic airways and deposited particles in laboratory animals

Laboratory animals are widely used as models for exploring adverse and beneficial health effects caused by inhalation of suspended particles. Mapping particle deposition throughout the airways of laboratory animals is crucial since the location of particle deposition often determines subsequent clearance, transport and the health effects elicited. Such mapping has yet to be performed systematically due to lack of available methods. In this paper, a new method is presented for imaging both the nasal airways of laboratory animals and particles deposited in them. After inhalation of particles, the rat airways are frozen to lock the particles in place and cast at this temperature to color and support the lumen. Once the cast is cured, an imaging cryomicrotome sections and images the airways as well as the deposited fluorescent particles. Computer software reconstructs the airways and particle maps from these serial images. The method was validated by manually placing boluses of fluorescent particles in nasal airways of a rat and then imaging them to ensure that they were displayed in the correct locations. To demonstrate the method, rats inhaled 2.5 μm particles in a nose-only exposure chamber. Images and reconstructions are presented of the nasal passage and deposited particles for one of these rats demonstrating the method’s usefulness for locating inhaled and deposited therapeutic and toxic particles in the extra-thoracic airways of laboratory animals.