Reproducibility of automated three-dimensional airway wall thickness measurements in thoracic computed tomography and influence of inspiration depth

M. Schmidt, E. van Rikxoort, O. Mets, P. de Jong, J. Kuhnigk, M. Oudkerk, H. de Koning and B. van Ginneken

Annual Meeting of the Radiological Society of North America 2013.

PURPOSE Pathological changes of the airways are strongly associated with lung function impairment in chronic obstructive pulmonary disease (COPD). We investigate the reproducibility of CT-based airway dimension measurements and their dependence on the level of inspiration. METHOD AND MATERIALS We analyzed 740 pairs of low-dose chest CT scans of male (former) smokers who were recalled for a three month follow up scan in the NELSON lung cancer screening trial. Given the slow progression of COPD, we expect that no significant COPD-related changes in airway dimensions should exist between baseline and three month follow-up. Each scan was analyzed fully automatic using CIRRUS Lung 13.03 and airway wall thickness (Pi10) and lung volume were recorded. Subjects where processing failed for any of the two scans were excluded for analysis (n=32). First, we analyzed the differences in airway wall thickness measurements for all scan pairs. Next, we determined reproducibility in absence of significant changes in inspiration depth by repeating the analysis for the subset of scans where the difference in lung volume between baseline and follow-up was less than 200ml (n=312). Finally, we investigated the correlation between difference in inspiration depth and airway wall thickness measurements, established a linear correction model for the airway measurements and analyzed differences for corrected measurements. RESULTS Average Pi10 measurements for all 708 scan pairs were 2.46A,A+-0.55mm (range 1.09-4.33mm). Median (95th percentile) absolute difference between baseline and follow-up Pi10 measurements in all 708 scan pairs was 0.13mm (0.53mm), median lung volume differences were 230ml (1050ml). In scan pairs with well reproduced depth of inspiration (AZaEUR?Vol < 200ml, n=312), median absolute Pi10 difference was 0.10mm (0.38mm). Relative differences in lung volume and Pi10 measurements were highly correlated (r=-0.64, p<0.001). After correction for lung volume changes, absolute measurement difference was 0.11mm (0.40mm). CONCLUSION Changes in level of inspiration are significantly associated to changes of airway wall thickness and accounted for approximately 25% of the total differences between baseline and follow-up measurements. CLINICAL RELEVANCE/APPLICATION Inspiration depth should be controlled or linear correction should be applied for monitoring of airway wall thickness. This may help to better differentiate COPD subtypes in chest CT scans.