Counter WB, Wang IQ, Farncombe TH, Labiris NR. Airway and pulmonary vascular measurements using contrast-enhanced micro-CT in rodents. Am J Physiol Lung Cell Mol Physiol 304: L831-L843, 2013. First published April 5, 2013 doi:10.1152/ajplung.00281.2012.-Preclinical imaging allows pulmonary researchers to study lung disease and pulmonary drug delivery noninvasively and longitudinally in small animals. However, anatomically localizing a pathology or drug deposition to a particular lung region is not easily done. Thus, a detailed knowledge of the anatomical structure of small animal lungs is necessary for understanding disease progression and in addition would facilitate the analysis of the imaging data, mapping drug deposition and relating function to structure. In this study, contrast-enhanced micro-computed tomography (CT) of the lung produced high-resolution images that allowed for the characterization of the rodent airway and pulmonary vasculature. Contrast-enhanced micro-CT was used to visualize the airways and pulmonary vasculature in Sprague-Dawley rats (200 -225 g) and BALB/c mice (20 -25 g) postmortem. Segmented volumes from these images were processed to yield automated measurements of the airways and pulmonary vasculature. The diameters, lengths, and branching angles of the airway, arterial, and venous trees were measured and analyzed as a function of generation number and vessel diameter to establish rules that could be applied at all levels of tree hierarchy. In the rat, airway, arterial, and venous tress were measured down to the 20th, 16th, and 14th generation, respectively. In the mouse, airway, arterial, and venous trees were measured down to the 16th, 8th, and 7th generation, respectively. This structural information, catalogued in a rodent database, will increase our understanding of lung structure and will aid in future studies of the relationship between structure and function in animal models of disease. computed tomography; contrast agents; pulmonary circulation; airway nomenclature THE LUNG IS A COMPLEX ORGAN that works dynamically and must react to changes in posture, environment, and disease (20). Its major function is gas exchange, bringing oxygen into the body while removing carbon dioxide. To accomplish this task, a well-coordinated interaction between the lung and pulmonary circulation is essential. The rodent lung is comprised of two branching networks: the airways and pulmonary vasculature. With the advent of small animal imaging systems, researchers are able to visualize these networks in situ and noninvasively study the progression of lung disease and assess drug efficacy in animal models of disease. Much of this research involves combining the anatomical data obtained using computed tomography (CT) with the functional data obtained using single photon emission computed tomography (SPECT) or positron emission tomography (PET). A detailed knowledge of the structure of the lung would facilitate the mapping of functional data relative to lung anatomy and thus further our understandi...