Visual quantitation and observer variation of signs of small airways disease at inspiratory and expiratory CT

Areas of decreased pulmonary attenuation representing small airways disease can be identified on computed tomography (CT). The objective was to quanti fy differences between inspiratory and expiratory CT for the detection of s igns of small airways disease by four observers. Observer Variation and the superiority of a fine versus a coarse grading system were also evaluated. Inspiratory and expiratory CT scans of 106 patients with conditions charact erized by small airways disease and 19 healthy individuals were assessed by four observers. The extent of decreased attenuation was scored on a fine s cale to the nearest 5% and also semiquantitatively on a coarser 5-point sca le. Decreased attenuation was more extensive on expiratory CT (median, 6.7% ; 0-76.7%) than on inspiratory CT (median, 3.8%; 0-81.7%). The fine scoring system had unacceptable interobserver variation (coefficient of variation, 80% for inspiratory CT, 70% for expiratory CT). The semiquantitative syste m had acceptable interobserver agreement (inspiratory CT k(w) = 0.64; expir atory CT, k(w) = 0.69) and good intra-observer agreement (inspiratory CT, k (w) = 0.80; expiratory CT, k(w) = 0.64). The major CT sign of small airways disease is more confidently quantified on expiratory CT. A fine scoring sy stem is associated with unacceptable observer variation, and a coarse semiq uantitative system is more suitable for quantitative studies of small airwa ys disease.