Methacholine-induced temporal changes in airway geometry and lung density by CT

Purpose: Electron-beam CT (EBCT) was utilized to assess the time course of changes in airways cross-sectional area (CSA) and lung density during metha choline-induced bronchoconstriction. Materials and methods: EBCT scans (200 ms, 3-mm thickness, 2 mm increments) were obtained before (baseline) and 30 s, 2 min, and 4 min after bolus IV injection of methacholine to pigs receiving mechanical ventilation. A total of seven experiments were analyzed using custom-made image analysis softwa re, With each challenge, five different airways and 50 lung regions of inte rest were studied. Results: The time course of lung density changes paralleled the time course for CSA changes, The maximal response to methacholine, measured in terms o f both CSA and lung density changes, occurred 30 s after injection. Lung de nsity changes were unaffected by reconstruction algorithm, normal (standard ) or sharp thigh resolution). Overall, there was increased air content in t he lung during bronchoconstriction. This effect was significantly greater a t the dependent lung regions. Conclusions: EBCT is an effective tool to assess temporal and regional chan ges in the lung during bronchoconstriction, h Measurements of lung density during bronchoconstriction allow for assessment of peripheral changes that are beyond the CT spatial resolution of airways anatomy.