Reproducibility of an airway tapering measurement in computed tomography with application to bronchiectasis
Abstract. We propose a pipeline to acquire a scalar tapering measurement from the carina to the most distal point of an individual airway visible on computed tomography (CT). We show the applicability of using tapering measurements on clinically acquired data by quantifying the reproducibility of the tapering measure. We generate a spline from the centerline of an airway to measure the area and arclength at contiguous intervals. The tapering measurement is the gradient of the linear regression between area in log space and arclength. The reproducibility of the measure was assessed by analyzing different radiation doses, voxel sizes, and reconstruction kernel on single timepoint and longitudinal CT scans and by evaluating the effect of airway bifurcations. Using 74 airways from 10 CT scans, we show a statistical difference, p  =  3.4  ×  10  −  4, in tapering between healthy airways (n  =  35) and those affected by bronchiectasis (n  =  39). The difference between the mean of the two populations is 0.011  mm  −  1, and the difference between the medians of the two populations was 0.006  mm  −  1. The tapering measurement retained a 95% confidence interval of ±0.005  mm  −  1 in a simulated 25 mAs scan and retained a 95% confidence of ±0.005  mm  −  1 on simulated CTs up to 1.5 times the original voxel size. We have established an estimate of the precision of the tapering measurement and estimated the effect on precision of the simulated voxel size and CT scan dose. We recommend that the scanner calibration be undertaken with the phantoms as described, on the specific CT scanner, radiation dose, and reconstruction algorithm that are to be used in any quantitative studies.