2.3 Lung Density Index
For each side of the lungs, separated inspiratory and expiratory lung
volumes and densities were measured. We obtained the MLD during
inspiration and expiration, and the ratio of end expiratory to
inspiratory volume (E/I volume) and MLD (E/I MLD) was calculated. To
investigate the threshold of pathologic expiratory airflow limitation,
we examined the relative volume percentage between -850 and - 950 HU
with an interval of 50 HU. Expiratory low attenuation areas (LAA) below
-850 HU to -950 HU threshold (E850, E900, and E950) and high attenuation
areas (HAA) above -600 HU to -650 HU threshold (E600 and E650) were
measured. Figure 1 shows an example of CT results obtained from a
representative subject.