Volumetric assessment of emphysema on low-dose screening CT scans

A study was performed to test whether automated computer analysis of low-dose helical CT scans can accurately estimate the degree of emphysema. We characterized the severity of emphysema on low-dose high-resolution (2.5 mm slice thickness) CT scans into 4 categories (normal, mild, moderate, and severe) as determined by a thoracic radiologist. From our database we chose 80 cases (20 within each category) for analysis. Our analysis system segments the lung parenchyma from surrounding structures and computes an emphysema index as the volumetric percentage of emphysema for the entire lung volume using a dual thresholding technique. One-way analysis of variance was used to assess the emphysema index. For those cases classified as normal, the emphysema index was 11.74 +/- 1.24 (mean +/- sem), for mild it was 15.00 +/- 1.31, for moderate it was 16.91 +/- 1.72, and for severe it was 26.77 +/- 1.73. The differences were statistically significant (p < 0.0001) and showed an increasing score with increasing severity of emphysema. Our system provides a useful index of the degree of emphysema present. Use of the system allows subjects undergoing lung cancer screening studies to have the extent of their emphysema quantified on a year-to-year basis.