Low agreement of visual rating for detailed quantification of pulmonary emphysema in whole-lung CT

Abstract

Background

Multidetector spiral computed tomography (CT) has opened the possibility of quantitative evaluation of emphysema extent in the whole lung. Visual assessment can be used for such a purpose, but its reproducibility has not been established.

Purpose

To assess agreement of detailed assessment of pulmonary emphysema on whole-lung CT using a visual scale.

Material and Methods

Thirty patients with chronic obstructive pulmonary disease underwent whole-lung inspiratory CT. Four chest radiologists rated the same 22 ± 2 thin sections using a visual scale which defines a range of emphysema extent between 0 and 100. Two of them repeated the rating two months later. Inter- and intra-operator agreement was evaluated with the Bland and Altman method. In addition, the percentage of emphysema at –950 Hounsfield units in the whole lung was determined using fully automated commercially available software for 3D densitometry.

Results

In three of six operator pairs and in one of two intra-operator pairs the Kendall τ test showed a significant correlation between the difference and the average magnitude of visual scores. Among different operators the half-width of 95% limits of agreement (95% LoA) was wide ranging between a score of 14.2–27.7 for an average visual score of 20 and between 18.5–36.8 for an average visual score of 80. Within the same operator the half-width of 95% LoA ranged between a score of 10.9–21.0 for an average visual score of 20 and between 25.1–30.1 for an average visual score of 80. The visual scores of the four radiologists were correlated with the results of densitometry (P < 0.001; r = 0.65–0.81).

Conclusion

The inter- and intra-operator agreement of detailed assessment of emphysema in the whole lung using a visual scale is low and decreases with increasing emphysema extent.