Evaluation of Allergic Lung Inflammation by Computed Tomography in a Rat Model in vivo

¹ Dept of Pathology and Molecular Medicine, Division of Respiratory Diseases and Allergy, Centre for Gene Therapeutics, McMaster University, Hamilton, Ontario, Canada
² Dept of Nuclear Medicine, Hamilton Health Sciences, McMaster University
³ Dept of Medicine, Firestone Institute for Respiratory Health, McMaster University

^* To whom correspondence should be addressed. E-mail: jordanam{at}mcmaster.ca.

	Abstract

The ability of micro-computed tomography (CT) to non-invasively evaluate allergic pulmonary inflammation in an experimental model was investigated. In addition, 2 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 extract (HDM) (0, 0.15, 15, or 150µg) delivered intratracheally every 24 hours 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 broncho-alveolar lavage depicted greater inflammation than did density measures from CT images. Evidence from representative CT slices and transaxial density distribution indicate that inflammation is primarily associated with major airways and extends into the periphery from these focal points. Respiratory gating demonstrated that images of the inspiratory state provide greater contrast of inflammatory processes. Lastly, decreases in tidal volumes indicated significant mechanical respiratory changes in both 15 and 150µg exposed animals.

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.