Purpose: Electron-beam CT (EBCT) was utilized to assess
the time course of changes in airways cross-sectional area (CSA) and
lung density during methacholine-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 software. With each challenge, five
different airways and 50 lung regions of interest 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 of both CSA and lung density changes, occurred
30 s after injection. Lung density changes were unaffected by
reconstruction algorithm, normal (standard) or sharp (high resolution).
Overall, there was increased air content in the lung during
bronchoconstriction. This effect was significantly greater at the
dependent lung regions.
Conclusions: EBCT is an
effective tool to assess temporal and regional changes in the lung
during bronchoconstriction. Measurements of lung density during
bronchoconstriction allow for assessment of peripheral changes that are
beyond the CT spatial resolution of airways anatomy.