To determine the improvement of emphysema quantification with density correction and to determine the optimal site to use for air density correction on volumetric computed tomography (CT).

METHODS: Seventy-eight CT scans of COPD patients (GOLD II-IV, smoking history 39.2±25.3 pack-years) were obtained from several single-vendor 16-MDCT scanners. After density measurement of aorta, tracheal- and external air, volumetric CT density correction was conducted (two reference values: air, -1000HU/blood, +50HU). Using in-house software, emphysema index (EI) and mean lung density (MLD) were calculated. Differences in air densities, MLD and EI prior to and after density correction were evaluated (paired t-test). Correlation between those parameters and FEV(1) and FEV(1)/FVC were compared (age- and sex adjusted partial correlation analysis).

RESULTS: Measured densities (HU) of tracheal- and external air differed significantly (-990±14, -1016±9, P<0.001). MLD and EI on original CT data, after density correction using tracheal- and external air also differed significantly (MLD: -874.9±27.6 vs. -882.3±24.9 vs. -860.5±26.6; EI: 16.8±13.4 vs. 21.1±14.5 vs. 9.7±10.5, respectively, P<0.001). The correlation coefficients between CT quantification indices and FEV(1), and FEV(1)/FVC increased after density correction. The tracheal air correction showed better results than the external air correction.

CONCLUSION: Density correction of volumetric CT data can improve correlations of emphysema quantification and PFT.