Reduction of pulmonary compliance found with high-resolution computed tomography in irradiated mice

Purpose: To demonstrate that high-resolution computed tomography (CT) can be used to quantify loss of pulmonary compliance in irradiated mice. Methods and Materials: Computed tomography images of three nonirradiated (controls) and three irradiated mice were obtained 200 days after a single dose of 16-Gy Co (60) thoracic irradiation. While intubated, each animal was imaged at static breath-hold pressures of 2, 10, and 18 cm H₂O. A deformable image registration algorithm was used to calculate changes in air volume between adjacent-pressure CT image pairs (e.g., 2 and 10 cm H₂O), and functional images of pulmonary compliance were generated. The mass-specific compliance was calculated as the change in volume divided by the pressure difference between the 2 image sets and the mass of lung tissue. Results: For the irradiated mice, the lung parenchyma mean CT values ranged from -314 (± 11) Hounsfield units (HU) to -378 (± 11) HU. For the control mice, the mean CT values ranged from -549 (± 11) HU to -633 (± 11) HU. Irradiated mice had a 60% (45, 74%; 95% confidence interval) lower mass-specific compliance than did the controls (0.039 [± 0.0038] vs. 0.106 [± 0.0038] mL air per cm H₂O per g lung) from the 2-cm to 10-cm H₂O CT image pair. The difference in compliance between groups was less pronounced at the higher distending pressures. Conclusion: High-resolution CT was used to quantify a reduction in mass-specific compliance following whole lung irradiation in mice. This small animal radiation injury model and assay may be useful in the study of lung injury.