Volumetric Micro-Computed Tomographic Imaging of Lung Anatomy

Objectives Accurate organ size control is of great importance during adult tissue homeostasis. We evaluate the feasibility of measuring lung, airway and alveolar volumes using microfocal computed tomography (micro-CT).

Methods Lungs from a 4 month-old C57BL/6J mouse were insufflated using 4% paraformaldehyde and fixed overnight. Lungs were subsequently dehydrated in a graded ethanol series and immersed in hexamethyldisilazane (HMDS). Air-dried lung specimens were mounted on the micro-CT scanner and scanned at an isotropic resolution of 200 microns at 45kVp, 200mAs. Similar scans were obtained of a small section of the distal lung (approximately 2 x 2 x 4mm³) and scanned at an isotropic resolution of 2 microns. 3D volume rendered CT objects were created on AMIRA software and used to visualize and study morphometry of the lung in various orientations, thereby providing a functional view of the anatomy. Ratio of lung airway volume to total lung volume was extracted from the whole lung image volume and the ratio of alveolar volume to lung parenchymal tissue volume was extracted from the distal lung-section image volume.

Results High quality CT images were acquired of the entire airway volume and the alveoli (Figure 1). We report a total lung volume of 0.64 ml, airway volume of 0.11 ml and alveolar volume of 0.42 mL, which is in agreement with ranges reported in the literature for mice from 2 to 9 months of age of 0.44 ml to 1.58 ml, 0.06 to 0. 25 ml and 0.41 ml to 0.62 mL, respectively. Parenchymal tissue volume of this mouse is ~0.11 ml.

Conclusions The HMDS lung preparation technique preserved the original lung structure for micro-CT and high resolution micro-CT scanning. We conclude that micro-CT is a reliable imaging technique for measuring lung volumes at the whole lung and alveolar levels. Development of such techniques is important for quantification of tissue volume relative to airway and alveolar volume in chronic lung diseases such as fibrosis and emphysema.

Research Support No external funding