Evaluation of allergic lung inflammation by computed tomography in a rat model in vivo

The ability of micro-computed tomography (CT) to noninvasively evaluate allergic pulmonary inflammation in an experimental model was investigated. In addition, two image segmentation methods and the value of respiratory gating were investigated in the context of this model. Brown Norway rats were exposed to one of four doses of house dust mite (HDM) extract (0, 0.15, 15 or 150 microg) delivered intratracheally every 24 h for 10 days. CT scanning was performed at baseline and after several longitudinal HDM exposures. Both thoracic- and lung-segmentation methods yielded similar results when standardisation practices were employed. While tissue histology correlated well with CT images, cell counts from bronchoalveolar lavage depicted greater inflammation than did density measures from CT images. Evidence from representative CT slices and transaxial density distribution indicated that inflammation was primarily associated with major airways and extended into the periphery from these focal points. Respiratory gating demonstrated that images of the inspiratory state provided greater contrast of inflammatory processes. Lastly, decreases in tidal volumes indicated significant mechanical respiratory changes in animals exposed to both 15 and 150 microg. In summary, CT image segmentation can extract pertinent data on in vivo allergic airway/lung inflammation. Furthermore, respiratory gating provides additional contrast and insight into these quantification practices.