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 quantify differences between inspiratory and expiratory CT for the detection of signs 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 characterized by small airways disease and 19 healthy individuals were assessed by four observers. The extent of decreased attenuation was scored on a fine scale to the nearest 5% and also semiquantitatively on a coarser 5-point scale. 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 system had acceptable interobserver agreement (inspiratory CT k(w) = 0.64; expiratory 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 system is associated with unacceptable observer variation, and a coarse semiquantitative system is more suitable for quantitative studies of small airways disease.